One of the most remarkable stereoscopes ever produced commercially was the Ives Kromskop (Patent #531,040, Dec 18, 1894). In it, three stereoscopic glass positives made from negatives exposed through red, green, and blue filters are optically superimposed to give a full color image of remarkable quality. It was more than ten years prior to the introduction of relatively crude full color plates such as the Autochrome.

This viewer and a complementary one-shot color camera were inspired by Frederic Eugene Ives (1856–1937), a pioneer in the field of halftone printing where he held many important patents. The reproduction of nature in full color was his other absorbing interest. It occupied so much of his time that he founded a company at 1324 Chestnut Street in Philadelphia that remained in business over forty years even though mass acceptance of any of his ideas never came to pass. A New York showroom was also established at 18W. 33rd St.

Early attempts

In 1861, James Maxwell, the British Physicist, showed that by projecting superimposed red, green, and blue images, a full color image could be produced. Lack of color sensitive (panchromatic) film in those days was a serious drawback, and some thirty years passed before the emulsions existed which Ives used in making his color separations.

Ives’ first color patent #672,573 (July22,1890) described the basic three color (additive)process and the use of three positive images in a special triple lantern to produce a full color image on the screen (Fig. 1). He also covered the use of negatives in the production of printed color images using the halftone process. The printing colors then become cyan, magenta and yellow, the complementary (subtractive) colors for red, green, and blue. Announcement of his achievement led to an invitation to England in 1892 which lasted for two full years as he “captured crowded audiences at a series of lectures:’

He returned to America in April 1894 and set about putting his ideas into commercial form. This led to the invention of a viewing device first known as the Photochromscope. He was back in England little more than a year later both to promote his halftone process and to introduce the perfected viewer now named the Kromskop. In 1896, the British Kromskop Syndicate was formed to exploit this invention, but it was never successful and the project was terminated in 1898 when Ives returned to Philadelphia. His long sojourn and great promotional activity in England and on the Continent help to explain the relative abundance of these rare viewers on the overseas market.

The real challenge was to find a practical way for optically combining six images to produce a color stereo image. The first images were made on a single glass plate, side by side to fit conveniently in the triple lantern projector. The same three images in the original Ives Photochromscope viewer, although only monocular, required seven reflectors, six lenses, plus the three color screens. The stereo Kromskop finally reached the market with only two tinted transparent mirrors, an external reflector for distribution of illumination, two additional color filters, and the viewing lenses.

The problem had been tackled by other inventors without success. In Fig. 2 a simple arrangement dating back at least twenty years is shown, using a mirror C and two plain glass reflectors A and 8. The three separations are placed ahead of the appropriate color filters and the distance from the viewing lens is constant. There are two basic problems. The optical path is too long, making the picture very small. Also, the glass mirrors, which both transmit and reflect, create annoying double images.

Final form

Ives’ ingenious solution is diagramed in Fig. 3. The original mirror C is eliminated to shorten the optical path. A green transmitting reflector is used for the blue image, and blue for the red image. The green reflector also serves as the color filter for that image. When the red or blue images are reflected from these tinted mirrors, the annoying secondary image that normally bounces off the back side of the glass is absorbed by the complementary color in the glass.

Initial alignment of the viewer is accomplished by the angle and squareness of the two transmitting reflectors shown in Fig. 4. The glasses are spring loaded against rotatable triangular stops to allow a small change in inclination. Through this adjustment, the red or blue images can be raised or lowered independently with respect to the green. The base support for the mirrors can be rotated for initial horizontal alignment. These are normally factory adjustments, but they sometimes have been tampered with and it is not easy to bring back proper alignment. In the early versions, these adjustments were crude. Later versions have threaded verniers that are a great help if things are truly out of line.

The block on which the reflectors are mounted fits slidably into the instrument, coming to rest against a small eccentric wheel. Turning a knob on the outside of the viewer moves the assembly back and forth a small amount. This simultaneously raises and lowers the red and blue images to line them up with the green. In a later design, a threaded screw at the right front of the viewer provides the same function in a more positive manner.

Commercial product

The commercial product, (Patent #531,040, Dec. 18, 1894) is illustrated in Fig. 5. It is a precision device of polished mahogany and brass most likely made in England with final assembly and calibration in Philadelphia. When properly aligned and illuminated, the results are quite spectacular. Superimposing six 2″ by 2″ quality images virtually eliminates grain. The three pairs are precision mounted in masks and held loosely together by silk tapes and are fan-folded for storage (Fig. 6). The positive green image slips into a slot at the rear and is non-adjustable. The blue image lies horizontally on the first step in two-point contact with a factory aligned brass plate. Only a very small horizontal adjustment is possible. The red image mounts similarly at the top, with the addition of a vernier screw at the left for precise horizontal adjustment only. The spacer card between the red and blue images bears the title.

A complete Kromogram unfolded on a light box with the left images filtered to show the color which would be provided and combined by a Kromskop viewer. Except for the green, the images are inverted and reversed for viewing in the transmitting reflectors shown in figure 4. Kromogram windows are exactly 2″ wide with a three-sixteenth inch septum and only 55mm center to center. The mounts are 5.25″ wide.

Notes on use

In use, the viewer is always tipped up to improve illumination, to ensure that the red and blue images lie against the stops, and to make the vernier on the reflectors operate properly.

Proper illumination is most important. A daylight diffuser (Fig. 7) was standard equipment, but it is generally missing. It was of opal glass, mahogany edged, and rested on the two pins at the back of the reflector. A chain permits it to be swung to the rear for changing slides. Ground glass is not a suitable substitute. Normal illumination was by skylight. At night the “Kromskop Night Illuminator” was available for $12 (Fig.8). Two Welsbach gas burners were used and the exterior housing was of polished mahogany and brass.

The reflector at the rear of the viewer sends light through the “green” image. In some instruments, the mirror is tinted green, but it can be a more neutral color such as yellow since the true spectral filter is a transparent mirror inside the viewer. By sliding out the block containing the mirrors, the viewer becomes an ordinary stereoscope for viewing specially mounted glass stereograms or for looking at the “green” image as a black and white positive.

The design just described introduces a small error in registration due to the fact that the green image passes through two slanted transparent mirrors which slightly compress the image vertically. The blue image passes through just one. In compensation, a plain glass (double the thickness of the mirrors) is placed at the same angle just below the “red” image (Fig. 3). This brings the important red and green images into correct register, leaving a small error in the blue which in practice is not noticeable.

Taking pictures

The pictures were generally taken on a single glass plate. For still lifes, a multiple back was sold to use vertically split 5″ by 7″ plates (Fig. 9). A stereo version of this back was also produced using the full plate. Positives made by contact printing were reversed right to left unless a reversing mirror of prism was fitted in the lenses. Glass plates, mounting frames and other supplies plus a mounting service were available. The positives are ready for cutting and mounting directly on the Kromogram frames, but nothing is said about the requirement for great accuracy. Register is on the same order as that used today for lap dissolve pairs.

For instantaneous photographs an ingenious “one shot” camera was produced. In the diagram (Fig. 10) the prisms F and G are placed so that their inner front edges partially cover a rectangular aperture in the lens system. The double internal reflection leaves the two images unreversed, and the greater refractive index of the glass compensates for the longer light path. The camera required exposures on the order of five to ten seconds in bright sunlight. It was priced at $75 with the stereo version projected at something less than double that price. In making single views for the lantern Kromskop, the camera was used in the horizontal position. The later stereo version pared the cameras vertically, allowing a “normal” lens separation.

Available picture series

The Kromskop came with eight Kromograms for $50. A large selection of Kromograms was available, the “A” Series priced at $1 ($10 per dozen) and the “B” Series at $1.50 ($15 per dozen). One 12-page price list covers almost 400 subjects.

While perhaps not a major factor in the failure to achieve commercial success, the pictures as a whole are disappointing. Exposure, general print quality, and color rendition are excellent, but the photography was by people with little or no understanding of good stereo composition.

Outdoor scenes were particularly poor. A group of people including Ives visited Paris in 1897–98 proceeding on to Switzerland, and about three dozen views were published as a result. Scarcely one has a foreground object within 100 feet of the camera, and the need for near perfect registration makes them generally disappointing in the viewer. Even more remarkable was the promotion of upwards of 100stereo pictures of paintings from the National Gallery in London! Still lifes were casually set up with little regard for esthetics. Some thought was given to choosing subjects that demonstrated nuances in color. Some of the flower arrangements are very good, primarily because of the excellent color reproduction.

A special set of medical views was produced in the hope that the medical profession would recognize the great benefits of full color 3‑D. Views were offered from Paris, London, Philadelphia, Niagara Falls and Washington DC. A series of still life subjects and a small number of portraits were an important part of the listings. A portrait of Mrs. McKinley in the White House Conservatory was taken at the same time as the widely distributed Underwood and Underwood view card.

Conclusion

In summary – if you own a Kromskop and have some fine examples to show, treat them with care and be chary about acquiring additional ones which may be mediocre examples from the published lists or even poorer amateur efforts.

No information is available on the number of views produced. Design variations suggest that several small production runs were made, with sales of the last units spread out over a number of years.

Proper illumination and register of the views was a serious drawback. The expense and relatively poor quality of the commercial views must have been a factor. Making Kromograms demanded more skill than the average amateur could give to it. It all added up to failure in spite of the enthusiasm of the professional critics.

At least one competitive system appeared briefly around 1900.It was known as the “Kromaz”. A single lens camera using mirrors made two exposures, and the resulting four images, one red, two green and one blue were optically combined in a viewer.

In the meantime, other inventors, notably the Lumière brothers, were working towards direct color transparencies based on the additive color process. In 1907they began marketing Autochrome plates (including stereo sizes), the first commercially successful color process. It wasn’t until 1935that the superior subtractive color process to be known as Kodachrome virtually put an end to efforts using the familiar red, green, and blue filters.

The Kromskop is seldom mentioned today. Relatively few people have had the opportunity to see properly illuminated views in a Kromskop. These reproductions are the first ever done in 3‑D. They are a reminder of the tremendous achievement of this great inventor.

The author wishes to thank George Eastman House and the International Museum of Photography in Rochester, NY for their help with images and information in this article.

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Paul Wing (Hingham, Massachusetts, USA)

Paul Wing was born in Sandwich, Massachusetts on March 9, 1913. Paul was first intrigued with stereocards in the early 1920s and by the time he finished high school during the Great Depression he was making “cha cha,” stereo photographs using side-step with a [2D] Kodak Brownie camera. In the 1940s, Paul met Dr. Philip Batchelder, a stereo collector and a member of the American Branch of the Stereoscopic Society of Great Britain. “It opened a New World,” Paul wrote in the foreword to his book on stereoscopes.
The importance of Paul Wing in contemporary stereography cannot be overstated. Paul was a veteran of more than a half century of stereoscopy and was one of only four Lifetime Members in the Stereoscopic Society of America (SSA). Member number 385 in the SSA, Paul was an internationally recognized master stereographer and the author of “Stereoscopes: The First One Hundred Years,” (Transition Publishing: 1996), the definitive history on the subject and one which will undoubtedly remain so for a long time to come.
He passed away on March 7, 2002 two days before his 89th birthday.

Full text: 3D Legends

Notes by Pascal Martiné: This article was first published 35 years ago. It is thanks to David Starkman’s presentation for the Virtual Stereoscopic Community that this article is now available to a wider audience. Transferring a print layout to a digital medium requires to pay attention to multiple aspects. That’s why I have allowed myself to re-arrange the pictures within the text and to optimize the graphics. Therefore, I replaced some pictures with newly taken digital photos of my own Kromskop, optimized all graphics and gently sharpened the pictures of Paul Wing’s Kromograms (without changing the color appearance). Finally, because it has become common practice with blog posts, I added subheadings.

Der Beitrag The Ives Kromskop erschien zuerst auf the stereosite.

Today, it is commonly known (at least for those interested in stereoscopy) that our vision consists of two images. Our brain fuses these two images into one and lets us perceive a sense of depth caused by slight differences between the two images.

Back in the 19th century the concept of binocular vision had not yet been explored or written about anywhere. It was a scientist in his mid 30s who not only described the phenomenon later called stereopsis but also constructed a device to view two flat images in 3D which he called a stereoscope. This is especially remarkable as photography was not invented until one year later. Charles Wheatstone’s observations were based only on drawings. Most of these drawings are based on horizontal mirroring which is why we call them mirror stereos today.

Wheatstone’s paper, presented to the Royal Society of London on June 21st 1838, is organized in 16 paragraphs and is therefore quite extensive. But even if the improvements by Sir David Brewster replaced Wheatstone’s stereoscope about ten years later, his observations can still be considered as the birth of Stereoscopy. Therefore, I want to give my full recommendation to read this source entirely. Do you remember your first time looking through a stereoscope? Well, put yourself into the mindset that nothing about it is known. After a talk about binocular vision that you followed with more or less interest, you are presented with a strange-looking optical mirror toy and some hand drawings. But looking through it completely blows your mind…

If you got more interested in the theory of stereoscopy afterwards, you might also want to read David Kuntz’ articles about the baseline and the stereo window or my article about hyper stereos. I’ve also created an interactive version of the graphic in paragraph 15 which can be accessed here.

§1 §2 §3 §4 §5 §6 §7 §8 §9 §10 §11 §12 §13 §14 §15 §16

Philosophical Transactions of the Royal Society of London, Vol. 128, pp. 371 — 394

Contributions to the Physiology of Vision. — Part the First.
On some remarkable, and hitherto unobserved, Phenomena of Binocular Vision.

By CHARLES WHEATSTONE, F.R.S., Professor of Experimental Philosophy in King’s College, London.

Received and Read June 21, 1838.

§ 1.

WHEN an object is viewed at so great a distance that the optic axes of both eyes are sensibly parallel when directed towards it, the perspective projections of it, seen by each eye separately, are similar, and the appearance to the two eyes is precisely the same as when the object is seen by one eye only. There is, in such case, no difference between the visual appearance of an object in relief and its perspective projection on a plane surface; and hence pictorial representations of distant objects, when those circumstances which would prevent or disturb the illusion are carefully excluded, may be rendered such perfect resemblances of the objects they are intended to represent as to be mistaken for them; the Diorama is an instance of this. But this similarity no longer exists when the object is placed so near the eyes that to view it the optic axes must converge; under these conditions a different perspective projection of it is seen by each eye, and these perspectives are more dissimilar as the convergence of the optic axes becomes greater. This fact may be easily verified by placing any figure of three dimensions, an outline cube for instance, at a moderate distance before the eyes, and while the head is kept perfectly steady, viewing it with each eye successively while the other is closed. Plate XI. fig. 13. represents the two perspective projections of a cube; b is that seen by the right eye, and a that presented to the left eye; the figure being supposed to be placed about seven inches immediately before the spectator.

The appearances, which are by this simple experiment rendered so obvious, may be easily inferred from the established laws of perspective; for the same object in relief is, when viewed by a different eye, seen from two points of sight at a distance from each other equal to the line joining the two eyes. Yet they seem to have escaped the attention of every philosopher and artist who has treated of the subjects of vision and perspective. I can ascribe this inattention to a phenomenon leading to the important and curious consequences, which will form the subject of the present communication, only to this circumstance; that the results being contrary to a principle which was very generally maintained by optical writers, viz. that objects can be seen single only when their images fall on corresponding points of the two retinæ, an hypothesis which will be hereafter discussed, if the consideration ever arose in their minds, it was hastily discarded under the conviction, that if the pictures presented to the two eyes are under certain circumstances dissimilar, their differences must be so small that they need not be taken into account.

It will now be obvious why it is impossible for the artist to give a faithful representation of any near solid object, that is, to produce a painting which shall not be distinguished in the mind from the object itself. When the painting and the object are seen with both eyes, in the case of the painting two similar pictures are projected on the retinæ, in the case of the solid object the pictures are dissimilar; there is therefore an essential difference between the impressions on the organs of sensation in the two cases, and consequently between the perceptions formed in the mind; the painting therefore cannot be confounded with the solid object.

After looking over the works of many authors who might be expected to have made some remarks relating to this subject, I have been able to find but one, which is in the Trattato della Pittura of LEONARDO DA VINCI¹. This great artist and ingenious philosopher observes, “that a painting, though conducted with the greatest art and finished to the last perfection, both with regard to its contours, its lights, its shadows and its colours, can never show a relievo equal to that of the natural objects, unless these be viewed at a distance and with a single eye. For,” says he, “if an object C (Plate X. fig. 1.) be viewed by a single eye at A, all objects in the space behind it, included as it were in a shadow E C F cast by a candle at A, are invisible to the eye at A; but when the other eye at B is opened, part of these objects become visible to it; those only being hid from both eyes that are included, as it were, in the double shadow C D, cast by two lights at A and B, and terminated in D, the angular space E D G beyond D being always visible to both eyes. And the hidden space C D is so much the shorter, as the object C is smaller and nearer to the eyes. Thus the object C seen with both eyes becomes, as it were, transparent, according to the usual definition of a transparent thing; namely, that which hides nothing beyond it. But this cannot happen when an object, whose breadth is bigger than that of the pupil, is viewed by a single eye. The truth of this observation is therefore evident, because a painted figure intercepts all the space behind its apparent place, so as to preclude the eyes from the sight of every part of the imaginary ground behind it.”

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§ 2.

It being thus established that the mind perceives an object of three dimensions by means of the two dissimilar pictures projected by it on the two retinæ, the following question occurs: What would be the visual effect of simultaneously presenting to each eye, instead of the object itself, its projection on a plane surface as it appears to that eye? To pursue this inquiry it is necessary that means should be contrived to make the two pictures, which must necessarily occupy different places, fall on similar parts of both retinæ. Under the ordinary circumstances of vision the object is seen at the concourse of the optic axes, and its images consequently are projected on similar parts of the two retinæ; but it is also evident that two exactly similar objects may be made to fall on similar parts of the two retinæ, if they are placed one in the direction of each optic axis, at equal distances before or beyond their intersection.

Fig. 2. represents the usual situation of an object at the intersection of the optic axes. In fig. 3. the similar objects are placed in the direction of the optic axes before their intersection, and in fig. 4. beyond it. In all these three cases the mind perceives but a single object, and refers it to the place where the optic axes meet. It will be observed, that when the eyes converge beyond the objects, as in fig. 3., the right hand object is seen by the right eye, and the left hand object by the left eye; while when the axes converge nearer than the Objects, the right hand object is seen by the left eye, and conversely. As both of these modes of vision are forced and unnatural, eyes unaccustomed to such experiments require some artificial assistance.

If the eyes are to converge beyond the objects, this may be afforded by a pair of tubes (fig. 5.) capable of being inclined towards each other at various angles, so as to correspond with the different convergences of the optic axes. If the eyes are to converge at a nearer distance than that at which the objects are placed, a box (fig. 6.) may be conveniently employed; the objects a a’ are placed distant from each other, on a stand capable of being moved nearer the eyes if required, and the optic axes being directed towards them will cross at c, the aperture b b’ allowing the visual rays front the right hand object to reach the left eye, and those from the left hand object to fall on the right eye; the coincidence of the images may be facilitated by placing the point of a needle at the point of intersection of the optic axes c, and fixing the eyes upon it. In both these instruments (figs. 5. and 6.) the lateral images are hidden from view, and much less difficulty occurs in making the images unite than when the naked eyes are employed.

Now if, instead of placing two exactly similar objects to be viewed by the eyes in either of the modes above described, the two perspective projections of the same solid object be so disposed, the mind will still perceive the object to be single, but instead of a representation on a plane surface, as each drawing appears to be when separately viewed by that eye which is directed towards it, the observer will perceive a figure of three dimensions, the exact counterpart of the object from which the drawings were made. To make this matter clear I will mention one or two of the most simple cases.

If two vertical lines near each other, but at different distances from the spectator, be regarded first with one eye and then with the other, the distance between them when referred to the same plane will appear different; if the left hand line be nearer to the eyes the distance as seen by the left eye will be less than the distance as seen by the right eye; fig. 7. will render this evident; a a’ are vertical sections of the two original lines, and b b’ the plane to which their projections are referred. Now if the two lines be drawn on two pieces of card, at the respective distances at which they appear to each eye, and these cards be afterwards viewed by either of the means above directed, the observer will no longer see two lines on a plane surface, as each card separately shows ; but two lines will appear, one nearer to him than the other, precisely as the original vertical lines themselves. Again, if a straight wire be held before the eyes in such a position that one of its ends shall be nearer to the observer than the other is, each eye separately referring it to a plane perpendicular to the common axis, will see a line differently inclined ; and then if lines having the same apparent inclinations be drawn on two pieces of card. and be presented to the eyes as before directed, the real position of the original line will be correctly perceived by the mind.

In the same manner the most complex figures of three dimensions may be accurately represented to the mind, by presenting their two perspective projections to the two retinæ. But I shall defer these more perfect experiments until I describe an instrument which will enable any person to observe all the phenomena in question with the greatest ease and certainty.

In the instruments above described the optic axes converge to some point in a plane before or beyond that in which the objects to be seen are situated. The adaptation of the eye, which enables us to see distinctly at different distances, and which habitually accompanies every different degree of convergence of the optic axes, does not immediately adjust itself to tIme new and unusual condition ; and to persons not accustomed to experiments of this kind, the pictures will either not readily unite, or will appear dim and confused. Besides this, no object can be viewed according to either mode when the drawings exceed in breadth the distance of the two points of the optic axes in which their centres are placed.

These inconveniences are removed by the instrument I am about to describe; the two pictures (or rather their reflected images) are placed in it at the true concourse of the optic axes, the focal adaptation of the eye preserves its usual adjustment, the appearance of lateral images is entirely avoided, and a large field of view for each eye is obtained. The frequent reference I shall have occasion to make to this instrument, will render it convenient to give it a specific name, I therefore propose that it be called a stereoscope, to indicate its property of representing solid figures.

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§ 3.

The stereoscope is represented by figs. 8. and 9; the former being a front view, and the latter a plan of the instrument. A A’ are two plane mirrors, about four inches square, inserted in frames, and so adjusted that their backs form an angle of 90° with each other; these mirrors are fixed by their common edge against an upright B, or which was less easy to represent in the drawing, against the middle line of a vertical board, cut away in such manner as to allow the eyes to be placed before the two mirrors. C C’ are two sliding boards, to which are attached the upright boards D D’, which may thus be removed to different distances from the mirrors. In most of the experiments hereafter to be detailed, it is necessary that each upright board shall be at the same distance from the mirror which is opposite to it. To facilitate this double adjustment, I employ a right and a left-handed wooden screw, r l; the two ends of this compound screw pass through the nuts e e’, which are fixed to the lower parts of the upright boards D D’, so that by turning the screw pin p one way the two boards will approach, and by turning it the other they will recede from each other, one always preserving the same distance as the other from the middle line f. E E’ are pannels, to which the pictures are fixed in such manner that their corresponding horizontal lines shall be on the same level: these pannels are capable of sliding backwards and forwards in grooves on the upright boards D D’. The apparatus having been described, it flow remains to explain the manner of using it. The observer must place his eyes as near as possible to the mirrors, the right eye before the right hand mirror, and the left eye before the left hand mirror, and he must move the sliding pannels E E’ to or from him until the two reflected images coincide at the intersection of the optic axes, and form an image of the same apparent magnitude as each of the component pictures. The pictures will indeed coincide when the sliding pannels are in a variety of different positions, and consequently when viewed under different inclinations of the optic axes; but there is only one position in which the binocular image will be immediately seen single, of its proper magnitude, and without fatigue to the eyes, because in this position only the ordinary relations between the magnitude of the pictures on the retina, the inclination of the optic axes, and the adaptation of the eye to distinct vision at different distances are preserved. The alteration in the apparent magnitude of the binocular images, when these usual relations are disturbed, will be discussed in another paper of this series, with a variety of remarkable phenomena depending thereon. In all the experiments detailed in the present memoir I shall suppose these relations to remain undisturbed, and the optic axes to converge about six or eight inches before the eyes.

If the pictures are all drawn to be seen with the same inclination of the optic axes, the apparatus may be simplified by omitting the screw r 1 and fixing the upright boards D D’ at the proper distances. The sliding pannels may also be dispensed with, and the drawings themselves be made to slide in the grooves.

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§ 4.

A few of outline figures, calculated to give rise to the perception of objects of three dimensions when placed in the stereoscope in the manner described, are represented from figs. 10. to 20. They are one half the linear size of the figures actually employed. As the drawings are reversed by reflection in the mirrors, I will suppose these figures to be the reflected images to which the eyes are directed in the apparatus; those marked b being seen by the right eye, and those marked a by the left eye. The drawings, it has been already explained, are two different projections of the same object seen from two points of sight, the distance between which is equal to the interval between the eyes of the observer; this interval is generally about 2½ inches.

a and b, fig. 10. will, when viewed in the stereoscope, present to the mind a line in the vertical plane, with its lower end inclined towards the observer. If the two component lines be caused to turn round their centres equally in opposite directions, the resultant line will, while it appears to assume every degree of inclination to the referent plane, still seem to remain in the same vertical plane.

Fig. 11. A series of points all in the same horizontal plane, but each towards the right hand successively nearer the observer.

Fig. 12. A curved line intersecting the referent plane, and having its convexity towards the observer.

Fig. 13. A cube.

Fig. 14. A cone, having its axis perpendicular to the referent plane, and its vertex towards the observer.

Fig. 15. The frustum of a square pyramid; its axis perpendicular to the referent plane, and its base furthest from the eye.

Fig. 16. Two circles at different distances from the eyes, their centres in the same perpendicular, forming the outline of the frustum of a cone.

The other figures require no observation.

For the purposes of illustration I have employed only outline figures, for had either shading or colouring been introduced it might be supposed that the effect was wholly or in part due to these circumstances, whereas by leaving them out of consideration no room is left to doubt that the entire effect of relief is owing to the simultaneous perception of the two monocular projections, one on each retina. But if it be required to obtain the most faithful resemblances of real objects, shadowing and colouring may properly be employed to heighten the effects. Careful attention would enable an artist to draw and paint the two component pictures, so as to present to the mind of the observer, in the resultant perception, perfect identity with the object represented. Flowers, crystals, busts, vases, instruments of various kinds, &c., might thus be represented so as not to be distinguished by sight from the real objects themselves.

It is worthy of remark, that the process by which we thus become acquainted with the real forms of solid objects, is precisely that which is employed in descriptive geometry, an important science we owe to the genius of MONGE, but which is little studied or known in this country. In this science, the position of a point, a right line or a curve, and consequently of any figure whatever, is completely determined by assigning its projections on two fixed planes, the situations of which are known, and which are not parallel to each other. In the problems of descriptive geometry the two referent planes are generally assumed to be at right angles to each other, but in binocular vision the inclination of these planes is less according as the angle made at the concourse of the optic axes is less ; thus the same solid object is represented to the mind by different pairs of monocular pictures, according as they are placed at a different distance before the eyes, and the perception of these differences (though we seem to be unconscious of them) may assist in suggesting to the mind the distance of the object. The more inclined to each other the referent planes are, with the greater accuracy are the various points of the projections referred to their proper places; and it appears to be a useful provision that the real forms of those objects which are nearest to us are thus more determinately apprehended than those which are more distant.

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§ 5.

A very singular effect is produced when the drawing originally intended to be seen by the right eye is placed at the left hand sidle of the stereoscope, and that designed to be seen by the left eye is placed on its right hand side. A figure of three dimensions, as bold in relief as before, is perceived, but it has a different form from that which is seen when the drawings are in their proper places. There is a certain relation between the proper figure and this, which I shall call its converse figure. Those points which are nearest the observer in the proper figure are the most remote from him in the converse figure, and vice versâ, so that the figure is, as it were, inverted; but it is not an exact inversion, for the near parts of the converse figure appear smaller, and the remote parts larger than the same parts before the inversion. Hence the drawings which, properly placed, occasion a cube to be perceived, when changed in the manner described, represent the frustum of a square pyramid with its base remote from the eye: the cause of this is easy to understand.

This conversion of relief may be shown by all the pairs of drawings from fig. 10. to 19. In the case of simple figures like these the converse figure is as readily apprehended as the original one, because it is generally a figure of as frequent occurrence; hut in the vase of a more complicated figure, an architectural design, for instance, the mind, unaccustomed to perceive its converse, because it never occurs in nature, can find no meaning in it.

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§ 6.

The same image is depicted on the retina by an object of three dimensions as by its projection on a plane surface, provided the point of sight remain in both cases the same. There should be, therefore, no difference in the binocular appearance of two drawings, one presented to each eye, and of two real objects so presented to the two eyes that their projections on the retina shall be the same as those arising from the drawings. The following experiments will prove the justness of this inference.

I procured several pairs of skeleton figures, i. e. outline figures of three dimensions, formed either of iron wire or of ebony beading about one tenth of an inch in thickness. The pair I most frequently employed consisted of two cubes, whose sides were three inches in length. When I placed these skeleton figures on stands before the two mirrors of the stereoscope, the following effects were produced, according as their relative positions were changed. 1st. When they were so placed that the pictures which their reflected images projected on the two retinæ were precisely the same as those which would have been projected by a cube placed at the concourse of the optic axes, a cube in relief appeared before the eyes. 2ndly. When they were so placed that their reflected images projected exactly similar pictures on the two retinæ, all effect of relief was destroyed, and the compound appearance was that of an outline representation on a plane surface. 3rdly. When the cubes were so placed that the reflected image of one projected on the left retina the same picture as in the first case was projected on the right retina, and conversely, the converse figure in relief appeared.

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§7.

If a symmetrical object, that is one whose right and left sides are exactly similar to each other but inverted, be placed so that any point in the plane which divides it into these two halves is equally distant from the two eyes, its two monocular projections are, it is easy to see, inverted facsimiles of each other. Thus fig. 15, a and b are symmetrical monocular projections of the frustum of a four-sided pyramid, and figs. 13. 14. 16. are corresponding projections of other symmetrical objects. This being kept in view, I will describe an experiment which, had it been casually observed previous to the knowledge of the principles developed in this paper, would have appeared an inexplicable optical illusion.

M and M’ (fig. 21.) are two mirrors, inclined so that their faces form an angle of 90° with each other. Between them in the bisecting plane is placed a plane outline figure, such as fig. 15 a, made of card all parts but the lines being cut away, or of wire. A reflected image of this outline, placed at A, will appear behind each mirror at B and B’, and one of these images will be the inversion of the other. If the eyes be made to converge at C, it is obvious that these two reflected images will fall on corresponding parts of the two retinæ, and a figure of three dimensions will be perceived; if the outline placed in the bisecting plane be reversed, the converse skeleton form will appear; in both these experiments we have the singular phenomenon of the conversion of a single plane outline into a figure of three dimensions. To render the binocular object more distinct, concave lenses may be applied to the eyes; and to prevent the two lateral images from being seen, screens may be placed at D and D’.

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§ 8.

An effect of binocular perspective may be remarked in a plate of metal, the surface of which has been made smooth by turning it in a lathe. When a single candle is brought near such a plate, a line of light appears standing out from it, one half being above, and the other half below the surface; the position and inclination of this line chances with the situation of the light and of the observer, but it always passes through the centre of the plate. On closing the left eye the relief disappears, and the luminous line coincides with one of the diameters of the plate; on closing the right eye the line appears equally in the plane of the surface, but coincides with another diameter; on opening both eyes it instantly starts into relief². The case here is exactly analogous to the vision of two inclined lines (fig. 10.) when each is presented to a different eye in the stereoscope. It is curious, that an effect like this, which it must have been seen thousands of times, should never have attracted sufficient attention to have been made the subject of philosophic observation. It was one of the earliest facts which drew my attention to the subject I am now treating.

Dr. SMITH³ was very much puzzled by an effect of binocular perspective which he observed, but was unable to explain. He opened a pair of compasses, and while he held the joint in his hand, and the points outwards and equidistant from his eyes, and somewhat higher than the joint, he looked at a more distant point ; the compasses appeared double. He then compressed the legs until the two inner points coincided; having done this the two inner legs also entirely coincided, and bisected the angle formed by the outward ones, appearing longer and thicker than they did, and reaching from the hand to the remotest object in view. The explanation offered by Dr. SMITH accounts only for the coincidence of the points of the compasses, not for that of the entire leg. The effect in question is best seen by employing a pair of straight wires, about a foot in length. A similar observation, made with two flat rulers, and afterwards with silk threads, induced Dr. WELLS to propose a new theory of visible direction in order to explain it, so inexplicable did it seem to him by any of the received theories.

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§ 9.

The preceding experiments render it evident that there is an essential difference in the appearance of objects when seen with two eyes, and when only one eye is employed, and that the most vivid belief of the solidity of an object of three dimensions arises from two different perspective projections of it being simultaneously presented to the mind. How happens it then, it may be asked, that persons who see with only one eye form correct notions of solid objects, and never mistake them for pictures? and how happens it also, that a person having the perfect use of both eyes, perceives no difference in objects around him when he shuts one of them? To explain these apparent difficulties, it must be kept in mind, that although the simultaneous vision of two dissimilar pictures suggests the relief of objects in the most vivid manner, yet there are other signs which suggest the same ideas to the mind, which, though more ambiguous than the former, become less liable to lead the judgment astray in proportion to the extent of our previous experience. The vividness of relief arising from the projection of two dissimilar pictures, one on each retina, becomes less and less as the object is seen at a greater distance before the eyes, and entirely ceases when it is so distant that the optic axes are parallel while regarding it. We see with both eyes all objects beyond this distance precisely as we see near objects with a single eye; for the pictures on the two retinæ are then exactly similar, and the mind appreciates no difference whether two identical pictures fall on corresponding parts of the two retinæ, or whether one eye is impressed with only one of these pictures. A person deprived of the sight of one eye sees therefore all external objects, near and remote, as a person with both eyes sees remote objects only, but that vivid effect arising from the binocular vision of near objects is not perceived by the former; to supply this deficiency he has recourse unconsciously to other means of acquiring more accurate information. The motion of the head is the principal means he employs. That the required knowledge may be thus obtained will be evident from the following considerations. The mind associates with the idea of a solid object every different projection of it which experience has hitherto afforded; a single projection may be ambiguous, from its being also one of the projections of a picture, or of a different solid object; but when different projections of the same object are successively presented, they cannot all belong to another object, and the form to which they belong is completely characterized. While the object remains fixed, at every movement of the head it is viewed from a different point of sight, and the picture on the retina consequently continually changes.

Every one must be aware how greatly the perspective effect of a picture is enhanced by looking at it with only one eye, especially when a tube is employed to exclude the vision of adjacent objects, whose presence might disturb the illusion. Seen under such circumstances from the proper point of sight, the picture projects the same lines, shades and colours on the retina, as the more distant scene which it represents would do were it substituted for it. The appearance which would make us certain that it is a picture is excluded from the sight, and the imagination has room to be active. Several of the older writers erroneously attributed this apparent superiority of monocular vision to the concentration of the visual power in a single eye⁴.

There is a well-known and very striking illusion of perspective which deserves a passing remark, because the reason of the effect does not appear to be generally understood. When a perspective of a building is projected on a horizontal plane, so that the point of sight is in a line greatly inclined towards the plane, the building appears to a single eye placed at the point of sight to be in bold relief, and the illusion is almost as perfect as in the binocular experiments described in §§ 2, 3, 4. This effect wholly arises from the unusual projection, which suggests to the mind more readily the object itself than the drawing of it; for we are accustomed to see real objects in almost every point of view, but perspective representations being generally made in a vertical plane with the point of sight in a line perpendicular to the plane of projection, we are less familiar with the appearance of other projections. Any other unusual projection will produce the same effect.

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§ 10.

If we look with a single eye at the drawing of a solid geometrical figure, it may be imagined to be the representation of either of two dissimilar solid figures, the figure intended to be represented, or its converse figure (§ 5.). If the former is a very usual, and the latter a very unusual figure, the imagination will fix itself on the original without wandering to the converse figure; but if both are of ordinary occurrence, which is generally the case with regard to simple forms, a singular phenomenon takes place; it is perceived at one time distinctly as one of these figures, at another time as the other, and while one figure continues it is not in the power of the will to change it immediately.

The same phenomenon takes place, though less decidedly, when the drawing is seen with both eyes. Many of my readers will call to mind the puzzling effect of some of the diagrams annexed to the problems of the eleventh book of Euclid; which, when they were attentively looked at, changed in an arbitrary manner from one solid figure to another, and would obstinately continue to present the converse figures when the real figures alone were wanted. This perplexing illusion must be of coimmon occurrence, but I have only found one recorded observation relating to the subject. It is by Professor NECKER of Geneva, and I shall quote it in his own words from the Philosophical Magazine, Third Series, vol. i. p. 337.

“The object I have now to call your attention to is an observation which has often occurred to me while examining figures and engraved plates of crystalline forms; I mean a sudden and involuntary change in the apparent position of a crystal or solid represented in an engraved figure. What I mean will be more easily understood from the figure annexed (fig. 22.). The rhomboid A X is drawn so that the solid angle A should be seen the nearest to the spectator, and the solid angle X the farthest from him, and that the face A C D B should be the foremost, while the face X D C is behind. But in looking repeatedly at the same figure, you will perceive that at times the apparent position of the rhomboid is so changed that the solid angle X will appear the nearest, and the solid angle A the farthest; and that the face A C D B will recede behind the face X D C, which will come forward, which effect gives to the whole solid a quite contrary apparent inclination.”

Professor NECKER attributes this alteration of appearance, not to a mental operation, but to an involuntary change in the adjustment of the eye for obtaining distinct vision. He supposed that whenever the point of distinct vision on the retina is directed on the angle A, for instance, this angle seen more distinctly than the others is naturally supposed to be nearer and foremost, while the other angles seen indistinctly are supposed to be farther and behind, and that the reverse takes place when the point of distinct vision is brought to bear on the angle X.

That this is not the true explanation, is evident from three circumstances: in the first place, the two points A and X being both at the same distance from the eyes, the same alteration of adjustment which would make one of them indistinct would make the other so ; secondly, the figure will undergo the same changes whether the focal distance of the eye be adjusted to a point before or beyond the plane in which the figure is drawn; and thirdly, the change of figure frequently occurs while the eye continues to look at the same angle. The effect seems entirely to depend on our mental contemplation of the figure intended to be represented, or of its converse. By following the lines with the eye with a clear idea of the solid figure we are describing, it may be fixed for any length of time; but it requires practice to do this or to change the figure at will. As I have before observed, these effects are far more obvious when the figures are regarded with one eye only.

No illusion of this kind can take place when an object of three dimensions is seen with both eyes while the optic axes make a sensible angle with each other, because the appearance of the two dissimilar images, one to each eye, prevents the possibility of mistake. But if we regard an object at such a distance that its two projections are sensibly identical, and if this projection be capable of a double interpretation, the illusion may occur. Thus a placard on a pole carried in the streets, with one of its sides inclined towards the observer, will, when he is distant from it, frequently appear inclined in a contrary direction. Many analogous instances might be adduced, but this will suffice to call others to mind ; it must however be observed, that when shadows, or other means capable of determining the judgement are present, these fallacies do not arise.

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§ 11.

The same indetermination of judgement which causes a drawing to be perceived by the mind at different times as two different figures, frequently gives rise to a false perception when objects in relief are regarded with a single eye. The apparent conversion of a cameo into an intaglio, and of an intaglio into a cameo, is a well-known instance of this fallacy in vision; but the fact does not appear to me to have been correctly explained, nor the conditions under which it occurs to have been properly stated.

This curious illusion, which has been the subject of much attention, was first observed at one of the early meetings of the Royal Society⁵. Several of the members looking through a compound microscope of a new construction at a guinea, some of them imagined the image to be depressed, while others thought it to be embossed, as it really was. Professor GMELIN, of Wurtemburg, published a paper on the same subject in the Philosophical Transactions for 1745 ; his experiments were made with telescopes and compound microscopes which inverted the images; and he observed that the conversion of relief appeared in some cases and not in others, at some times and not at others, and to some eyes also and not to others. He endeavoured to ascertain some of the conditions of the two appearances; “but why these things should so happen,” says he, “I do not pretend to determine.”

Sir DAVID BREWSTER accounts for the fallacy in the following manner:⁶ — “A hollow seal being illuminated by a window or a candle, its shaded side is of course on the same side with the light. If we now invert the seal with one or more lenses, so that it may look in the opposite direction, it will appear to the eye with the shaded side furthest from the window. But as we know that the window is still on our left hand, and as every body with its shaded side furthest from the light must necessarily be convex or protuberant, we immediately believe that the hollow seal is now a cameo or bas-relief. The proof which the eye thus receives of the seal being raised, overcomes the evidence of its being hollow, derived from our actual knowledge and from the sense of touch. In this experiment the deception takes place from our knowing the real direction of the light which falls on the seal ; for if the place of the window, with respect to the seal, had been inverted as well as the seal itself, the illusion could not have taken place. The illusion, therefore, under our consideration is the result of an operation of our own minds, whereby we judge of the forms of bodies by the knowledge we have acquired of light and shadow. Hence the illusion depends on the accuracy and extent of our knowledge on this subject; and while some persons are under its influence, others are entirely insensible to it.”

These considerations do not fully explain the phenomenon, for they suppose that the image must be inverted, and that the light must fall in a particular direction but the conversion of relief will still take place when the object is viewed through an open tube without any lenses to invert it, and also when it is equally illuminated in all parts. The true explanation I believe to be the following. If we suppose a cameo and an intaglio of the same object, the elevations of the one corresponding exactly to the depressions of the other; it is easy to show that the projection of either on the retina is sensibly the same. When the cameo or the intaglio is seen with both eyes, it is impossible to mistake an elevation for a depression, for reasons which have been already amply explained; but when either is seen with one eye only, the most certain guide of our judgement, viz. the presentation of a different picture to each eye, is wanting; the imagination therefore supplies the deficiency, and we conceive the object to be raised or depressed according to the dictates of this faculty. No doubt in such cases our judgement is in a great degree influenced by accessory circumstances, and the intaglio or the relief may sometimes present itself according to our previous knowledge of the direction in which the shadows ought to appear; but the real cause of the phenomenon is to be found in the indetermination of the judgement arising from our more perfect means of judging being absent.

Observers with the microscope must be particularly on their guard against illusions of this kind. RASPAIL observes⁷ that the hollow pyramidal arrangement of the crystals of muriate of soda appears, when seen through a microscope, like a striated pyramid in relief. He recommends two modes of correcting the illusion. The first is to bring successively to the focus of the instrument the different parts of the crystal; if the pyramid be in relief, the point will arrive at the focus sooner than the base will; if the pyramid be hollow, the contrary will take place. The second mode is to project a strong light on the pyramid in the field of view of the microscope, and to observe which sides of the crystal are illuminated, taking however the inversion of the image into consideration if a compound microscope be employed.

The inversion of relief is very striking when a skeleton cube is looked at with one eye, and the following singular results may in this case be observed. So long as the mind perceives the cube, however the figure be turned about, its various appearances will be but different representations of the same object, and the same primitive form will be suggested to the mind by all of them: but it is not so if the converse figure fixes the attention; the series of successive projections cannot then be referred to any figure to which they are all common, and the skeleton figure will appear to be continually undergoing a change of shape.

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§ 12.

I have given ample proof that objects whose pictures do not fall on corresponding points of the two retinæ may still appear single. I will now adduce an experiment which proves that similar pictures falling on corresponding points of the two retinæ may appear double and in different places.

Present, in the stereoscope, to the right eye a vertical line, and to the left eye a line inclined some degrees from the perpendicular (fig. 23.); the observer will then perceive, as formerly explained, a line, the extremities of which appear at different distances before the eyes. Draw on the left hand figure a faint vertical line exactly corresponding in position and length to that presented to the right eye; and let the two lines of this left hand figure intersect each other at their centres. Looking now at these two drawings in the stereoscope, the two strong lines, each seen by a different eye, will coincide, and the resultant perspective line will appear to occupy the same place as before; but the faint line which now falls on a line of the left retina, which corresponds with the line of the might retina on which one of the coinciding strong lines, viz. the vertical one, falls, appears in a different place. The place this faint line apparently occupies is the intersection of that plane of visual direction of the left eye in which it is situated, with the plane of visual direction of the right eye, which contains the strong vertical line.

This experiment affords another proof that there is no necessary physiological connection between the corresponding points of the two retinæ,—a doctrine which has been maintained by so many authors.

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§ 13. 

Binocular Vision of Images of different Magnitudes.

We will now inquire what effect results from presenting similar images, differing only in magnitude, to analogous parts of the two retinæ. For this purpose two squares or circles, differing obviously but not extravagantly in size, may be drawn on two separate pieces of paper, and placed in the stereoscope so that the reflected image of each shall he equally distant from the eye by which it is regarded. It will then be seen that, notwithstanding this difference, they coalesce and occasion a single resultant perception. The limit of the difference of size within which the single appearance subsists may be ascertained by employing two images of equal magnitude, and causing one of them to recede from the eye while the other remains at a constant distance ; this is effected merely by pulling out the sliding board C (fig. 8.) while the other C’ remains fixed, the screw having previously been removed.

Though the single appearance of two images of different size is by this experiment demonstrated, the observer is unable to perceive what difference exists between the apparent magnitude of the binocular image and that of the two monocular images to determine this point the stereoscope must be dispensed with, and the experiment so arranged that all three shall be simultaneously seen ; which may be done in the following manner:—The two drawings being placed side by side on a plane before the eyes, the optic axes must be made to converge to a nearer point as at fig. 4., or to a more distant one as at fig. 3., until the three images are seen at the same time, the binocular image in the middle, and the monocular images at each side. It will thus be seen that the binocular image is apparently intermediate in size between the two monocular ones.

If the pictures be too unequal in magnitude, the binocular coincidence does not take place. It appears that if the inequality of the pictures be greater than the difference which exists between the two projections of the same object when seen in the most oblique position of the eyes (i. e. both turned to the extreme right or to the extreme left), ordinarily employed, they do not coalesce. Were it not for the binocular coincidence of two images of different magnitude, objects would appear single only when the optic axes converge immediately forwards; for it is only when the converging visual lines form equal angles with the visual base (the line joining the centres of the two eyes) as at fig. 2., that the two pictures can be of equal magnitude; but when they form different angles with it, as at fig. 24., the distance from the object to each eye is different, and consequently the picture projected on each retina has a different magnitude. If a piece of money be held in the position a, (fig. 24.) while the optic axes converge to a nearer point c, it will appear double, and that seen by the left eye will be evidently smaller than the other.

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§ 14. 

Phenomena which are observed when objects of different forms are simultaneously presented to corresponding parts of the two retinæ.

If we regard a picture with the right eye alone for a considerable length of time it will be constantly perceived; if we look at another and dissimilar picture with the left eye alone its effect will be equally permanent; it might therefore be expected, that if each of these pictures were presented to its corresponding eye at the same time the two would appear permanently superposed on each other. This, however, contrary to expectation, is not the case.

If a and b (fig. 25.) are each presented at the same time to a different eye, the common border will remain constant, while the letter within it will change alternately from that which would be perceived by the right eye alone to that which would be perceived by the left eye alone. At the moment of change the letter which has just been seen breaks into fragments, while fragments of the letter which is about to appear mingle with them, and are immediately after replaced by the entire letter. It does not appear to be in the power of the will to determine the appearance of either of the letters, but the duration of the appearance seems to depend on causes which are under our control: thus if the two pictures be equally illuminated, the alternations appear in general of equal duration; but if one picture be in ore illuminated than the other, that which is less so will be perceived during a shorter time. I have generally made this experiment with the apparatus, fig. 6. When complex pictures are employed in the stereoscope, various parts of them alternate differently.

There are some facts intimately connected with the subject of the present article which have already been frequently observed. I allude to the experiments, first made by DU TOUR, in which two different colours are presented to corresponding parts of the two retinæ. If a blue disc be presented to the right eye and a yellow disc to the corresponding part of the left eye, instead of a green disc which would appear if these two colours had mingled before their arrival at a single eye, the mind will perceive the two colours distinctly one or the other alternately predominating either partially or wholly over the disc. In the same manner the mind perceives no trace of violet when red is presented to one eye and blue to the other, nor any vestige of orange when red and yellow are separately presented in a similar manner. These experiments may be conveniently repeated by placing the coloured discs in the stereoscope, but they have been most usually made by looking at a white object through differently coloured glasses, one applied to each eye.

In some authors we find it stated, contrary to fact, that if similar objects of different colour be presented one to each eye, the appearance will be that compounded of the two colours. Dr. REID⁸ and JANIN are among the writers who have fallen into this inconsiderate error, which arose no doubt from their deciding according to previous notions, instead of ascertaining by experiment what actually does happen.

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§ 15.

No question relating to vision has been so much debated as the cause of the single appearance of objects seen by both eyes. I shall in the present section give a slight review of the various theories which have been advanced by philosophers to account for this phenomenon, in order that the remarks I have to make in the succeeding section may be properly understood.

The law of visible direction for monocular vision has been variously stated by different optical writers. Some have maintained with Dr’s. REID and PORTERFIELD, that every external point is seen in the direction of a line passing from its picture on the retina through the centre of the eye; while others have supposed with Dr. SMITH that the visible direction of an object coincides with the visual ray, or the principal ray of the pencil which flows from it to the eye. D’ALEMBERT, furnished with imperfect data respecting the refractive densities of the humours of the eye, calculated that the apparent magnitudes of objects would differ widely on the two suppositions, and concluded that the visible point of an object was not seen in either of these directions, but sensibly in the direction of a line joining the point itself and its image on the retina; but he acknowledged that he could assign no reason for this law. Sir DAVID BREWSTER, provided with more accurate data, has shown that these three lines so nearly coincide with each other, that “at an inclination of 30°, a line perpendicular to the point of impression on the retina passes through the common centre, and does not deviate from the real line of visible direction more than half a degree, a quantity too small to interfere with the purposes of vision.” We may, therefore, assume in all our future reasonings the truth of the following definition given by this eminent philosopher :—“ As the interior eye-ball is as nearly as possible a perfect sphere, lines perpendicular to the surface of the retina must all pass through one single point, namely the centre of its spherical surface. This one point may be called the centre of visible direction, because every point of a visible object will be seen in the direction of a line drawn from this centre to the visible point.”

It is obvious, that the result of any attempt to explain the single appearance of objects to both eyes, or, in other words, the law of visible direction for binocular vision, ought to contain nothing inconsistent with the law of visible direction for monocular vision.

It was the opinion of AGUILONIUS, that all objects seen at the same glance with both eyes appear to be in the plane of the horopter. The horopter he defines to be a line drawn through the point of intersection of the optic axes, and parallel to the line joining the centres of the two eyes; the plane of the horopter to be a plane passing through this line at right angles to that of the optic axes. All objects which are in this plane, must, according to him, appear single because the lines of direction in which any point of an object is seen coincide only in this plane and nowhere else; and as these lines can meet each other only in one point, it follows from the hypothesis, that all objects not in the plane of the horopter must appear double, because their lines of direction intersect each other, either before or after they pass through it. This opinion was also maintained by DECHALES and PORTERFIELD. That it is erroneous, I have given, I think, sufficient proof, in showing that, when the optic axes converge to any point, objects before or beyond the plane of the horopter are under certain circumstances equally seen single as those in that plane.

Dr. WELLS’S “new theory of visible direction” was a modification of the preceding hypothesis. This acute writer held with AGUILONIUS, that objects are seen single only when they are in the plane of the horopter, and consequently that they appear double when they are either before or beyond it; but he attempted to make this single appearance of objects only in the plane of the horopter to depend on other principles, from which he deduced, contrary to AGUILONIUS, that the objects which are doubled do not appear in the plane of the horopter, but in other places which are determined by these principles. Dr. WELLS was led to his new theory by a fact which he accidentally observed, and which he could not reconcile with any existing theory of visible direction ; this fact had, though he was unaware of it, been previously noticed by Dr. SMITH; it is already mentioned in § 8., and is the only instance of binocular vision of relief which I have found recorded previous to my own investigations. So little does Dr. WELLS’S theory appear to have been understood, that no subsequent writer has attempted either to confirm or disprove his opinions. It would be useless here to discuss the principles of this theory, which was framed to account for an anomalous individual fact, since it is inconsistent with the general rules on which that fact has been now shown to depend. Notwithstanding these erroneous views, the “essay upon single vision with two eyes” contains many valuable experiments and remarks, the truth of which are independent of the theory they were intended to illustrate.

The theory which has obtained greatest currency is that which assumes that an object is seen single because its pictures fall on corresponding points of the two retinæ, that is on points which are similarly situated with respect to the two centres both in distance and position. This theory supposes that the pictures projected on the retinæ are exactly similar to each other, corresponding points of the two pictures falling on corresponding points of the two retinæ. Authors who agree with regard to this property, differ widely in explaining why objects are seen in the same place, or single, according to this law. Dr. SMITH makes it to depend entirely on custom, and explains why the eyes are habitually directed towards an object so that its pictures fall on corresponding parts in the following manner:—“ When we view an object steadily, we have acquired a habit of directing the optic axes to the point in view; because its pictures falling upon the middle points of the retinas, are then distincter than if they fell upon any other places; and since the pictures of the whole object are equal to one another, and are both inverted with respect to the optic axes, it follows that the pictures of any collateral point are painted upon corresponding points of the retinas.”

Dr. REID, after a long dissertation on the subject, concludes, “that by an original property of human eyes, objects painted upon the centres of the two retinæ, or upon points similarly situated with regard to the centres, appear in the same visible place; that the most plausible attempts to account for this property of the eyes have been unsuccessful ; and therefore, that it must be either a primary law of our constitution, or the consequence of some more general law which is not yet discovered.”

Other writers who have admitted this principle have regarded it as arising from anatomical structure and dependent on connexion of nervous fibres; among these stand the names of GALEN, Dr. BRIGGS, Sir ISAAC NEWTON, ROHAULT, Dr. HARTLEY, Dr. WOLLASTON and Professor MÜLLER.

Many of the supporters of the theory of corresponding points have thought, or rather have admitted, without thinking, that it was not inconsistent with the law of AGUILONIUS; but very little reflection will show that both cannot be maintained together; for corresponding lines of visible direction, that is, lines terminating in corresponding points of the two retinæ, cannot meet in the plane of the horopter unless the optic axes be parallel, and the plane be at an infinite distance before the eyes. Some of the modern German writers⁹ have inquired what is the curve in which objects appear single while the optic axes are directed to a given point, on the hypothesis that objects are seen single only when they fall on corresponding points of the two retinæ. An elegant proposition has resulted from their investigations, which I shall need no apology for introducing in this place, since it has not yet been mentioned in any English work.

R and L (fig. 26.) are the two eyes; C A, C’ A the optic axes converging to the point A; and C A B C’ is a circle drawn through the point of convergence A and the centres of visible direction C C’. If any point be taken in the circumference of this circle, and lines be drawn from it through the centres of the two eyes C C’, these lines will fall on corresponding points of the two retinæ D D’; for the angles A C B, A C’ B being equal, the angles D C E, D C’ E are also equal; therefore any point placed in the circumference of the circle C A B C’ will, according to the hypothesis, appear single while the optic axes are directed to A, or any other part in it.

I will mention two other properties of this binocular circle: 1st. The arc subtended by two points on its circumference contains double the number of degrees of the arc subtended by the pictures of these points on either retina, so that objects which occupy 180° of the supposed circle of single vision are painted on a portion of the retina extended over 90° only; for the angle D C E or D C’ E being at the centre, and the angle B C A or B C’ A at the circumference of a circle, this consequence follows. 2ndly. To whatever point of the circumference of the circle the optic axes be made to converge, they will form the same angle with each other; for the angles C A C’, C B C are equal.

In the eye itself, the centre of visible direction, or the point at which the principal rays cross each other, is, according to Dr. YOUNG and other eminent optical writers, at the same time the centre of the spherical surface of the retina, and that of the lesser spherical surface of the cornea; in the diagram (fig. 26.), to simplify the consideration of the problem, R and L represent only the circle of curvature of the bottom of the retina, but the reasoning is equally true in both cases.

The same reasons, founded on the experiments in this memoir, which disprove the theory of AGUILONIUS, induce me to reject the law of corresponding points as an accurate expression of the phenomena of single vision. According to the former, objects can appear single only in the plane of the horopter; according to the latter, only when they are in the circle of single vision; both positions are inconsistent with the binocular vision of objects in relief, the points of which they consist appearing single though they are at different distances before the eyes. I have already proved that the assumption made by all the maintainers of the theory of corresponding points, namely that the two pictures projected by any object in the retinæ are exactly similar, is quite contrary to fact in every case except that in which the optic axes are parallel.

GASSENDUS, PORTA, TACQUET and GALL maintained, that we see with only one eye at a time though both remain open, one according to them being relaxed and inattentive to objects while the other is upon the stretch. It is a sufficient refutation of this hypothesis, that we see an object double when one of the optic axes is displaced either by squinting or by pressure on the eye-ball with the finger; if we saw with only one eye, one object only should under such circumstances be seen. Again, in many cases which I have already explained, the simultaneous affection of the two retinæ excites a different idea in the mind to that consequent on either of the single impressions, the latter giving rise to the idea of a representation on a plane surface, the former to that of an object in relief; these things could not occur did we see with only one eye at a time.

Du TOUR¹⁰ held that though we might occasionally see at the same time with both eyes, yet the mind cannot be affected simultaneously by two corresponding points of the two images. He was led to this opinion by the curious facts alluded to in § 14. It would be difficult to disprove this conjecture by experiment; but all that the experiments adduced in its favour, and others relating to the disappearance of objects to one eye really proves, is, that the mind is inattentive to impressions made on one retina when it cannot combine the impressions on the two retinæ together so as to resemble the perception of some external objects; but they afford no ground whatever for supposing that the mind cannot under any circumstances attend to impressions made simultaneously on points of the two retinæ, when they harmonize with each other in suggesting to the mind the same idea.

A perfectly original theory has been recently advanced by M. LEHOT¹¹, who has endeavoured to prove, that instead of pictures on the retinæ, images of three dimensions are formed in the vitreous humour which we perceive by means of nervous filaments extended thence from the retina. This theory would account for the single appearance to both eyes of objects in relief, but it would be quite insufficient to explain why we perceive an object of three dimensions when two pictures of it are presented to the eyes; according to it, also, no difference should be perceived in the relief of objects when seen by one or both eyes, which is contrary to what really happens. The proofs, besides, that we perceive external objects by means of pictures on the retinæ are so numerous and convincing, that a contrary conjecture cannot be entertained for a moment. On this account it will suffice merely to mention two other theories which place the seat of vision in the vitreous humour. VALLEE¹², without denying the existence of pictures on the retina, has advocated that we see the relief of objects by means of anterior foci on the hyaloid membrane; and RASPAIL¹³ has developed at considerable length the strange hypothesis, that images are neither formed in the vitreous humour nor painted on the retina, but are immediately perceived at the focus of the lenticular system of which the eye is formed.

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§ 16.

It now remains to examine why two dissimilar pictures projected on the two retinaæ give rise to the perception of an object in relief. I will not attempt at present to give the complete solution of this question, which is far from being so easy as at a first glance it may appear to be, and is indeed one of great complexity. I shall in this place merely consider the most obvious explanations which might be offered, and show their insufficiency to explain the whole of the phenomena.

It may be supposed that we see but one point of an object distinctly at the same instant, the one namely to which the optic axes are directed, while all other points are seen so indistinctly, that the mind does not recognize them to be either single or double, and that the figure is appreciated by successively directing the point of convergence of the optic axes successively to a sufficient number of its points to enable us to judge accurately of its form.

That there is a degree of indistinctness in those parts of the field of view to which the eyes are not immediately directed, and which increases with the distance from that point, cannot be doubted, and it is also true that the objects thus obscurely seen are frequently doubled. It may be said, this indistinctness and duplicity is not attended to, because the eyes shifting continually from point to point, every part of the object is successively rendered distinct; and the perception of the object is not the consequence of a single glance, during which only a small part of it is seen distinctly, but is formed from a comparison of all the pictures successively seen while the eyes are changing from one point of the object to another.

All this is in some degree true; but were it entirely so, no appearance of relief should present itself when the eyes remain intently fixed on one point of a binocular image in the stereoscope. But on performing the experiment carefully, it will be found, provided the pictures do not extend too far beyond the centres of distinct vision, that the image is still seen single and in relief when this condition is fulfilled. Were the theory of corresponding points true, the appearance should be that of the superposition of the two drawings, to which, however, it has not the slightest similitude. The following experiment is equally decisive against this theory.

Draw two lines inclined towards each other, as in Plate XIX. fig. 10, on a sheet of paper, and having caused them to coincide by converging the optic axes to a point nearer than the paper; look intently on the upper end of the resultant line, without allowing the eyes to wander from it for a moment. The entire line will appear single and in its proper relief, and a pin or a piece of straight wire may without the least difficulty be made to coincide exactly in position with it; or, if while the optic axes continue to be directed to the upper and nearer end, the point of a pin be made to coincide with the lower and further end or with any intermediate point of the resultant line, the coincidence will remain exactly the same when the optic axes are moved and meet there. The eyes sometimes become fatigued, which causes the line to appear double at those parts to which the optic axes are not fixed, but in such case all appearance of relief vanishes.. The same experiment may be tried with more complex figures, but the pictures should not extend too far beyond the centres of the retinæ.

Another and a beautiful proof that the appearance of relief in binocular vision is an effect independent of the motions of the eyes, may be obtained by impressing on the retinal ocular spectra of the component figures. For this purpose the drawings should be formed of broad coloured lines on a ground of the complementary colour, for instance red lines on a green ground, and be viewed either in the stereoscope or in the apparatus, fig. 6, as the ordinary figures are, taking care, however, to fix the eyes only to a single point of the compound figure; the drawings must be strongly illuminated, and after a sufficient time has elapsed to impress the spectra on the retinæ, the eyes must be carefully covered to exclude all external light. A spectrum of the object in relief will then appear before the closed eyes. It is well known that a spectrum impressed on a single eye and seen in the dark, frequently alternately appears and disappears: these alternations do not correspond in the spectra impressed on the two retinæ, and hence a curious effect arises; sometimes the right-eye spectrum will be seen alone, sometimes that of the left eye, and at those moments when the two appear together, the binocular spectrum will present itself in bold relief. As in this case the pictures cannot shift their places on the retina in whatever manner the eyes be moved about, the optic axes can during the experiment only correspond with a single point of each.

When an object, or a part of an object, thus appears in relief while the optic axes are directed to a single binocular point, it is easy to see that each point of the figure that appears single is seen at the intersection of the two lines of visible direction in which it is seen by each eye separately, whether these lines of visible direction terminate at corresponding points of the two retinæ or not.

But if we were to infer the converse of this, viz. that every point of an object in relief is seen by a single glance at the intersection of the lines of visible direction in which it is seen by each eye singly, we should be in error. On this supposition, objects before or beyond the intersection of the optic axes should never appear double, and we have abundant evidence that they do. The determination of the points which shall appear single seems to depend in no small degree on previous knowledge of the form we are regarding. No doubt, some law or rule of vision may be discovered which shall include all the circumstances under which single vision by means of non-corresponding points occurs and is limited. I have made numerous experiments for the purpose of attaining this end, and have ascertained some of the conditions on which single and double vision depend, the consideration of which, however, must at present be deferred.

Sufficient, however, has been shown to prove that the laws of binocular visible position hitherto laid down are too restricted to be true. The law of Aguilonius assumes that objects in the plane of the horopter are alone seen single; and the law of corresponding points carried to its necessary consequences, though these consequences were unforeseen by its first advocates, many of whom thought that it was consistent with the law of Aguilonius, leads to the conclusion that no object appears single unless it is seen in a circle passing through the centres of visible direction in each eye and the point of convergence of the optic axes. Both of these are inconsistent with the single vision of objects whose points lie out of the plane in one case and the circle in the other; and that objects do appear single under circumstances that cannot be explained by these laws, has, I think, been placed beyond doubt by the experiments I have brought forward. Should it be hereafter proved, that all points in the plane or in the circle above mentioned are seen single, and from the great indistinctness of lateral images it will be difficult to give this proof, the law must be qualified by the admission that points out of them do not always appear double.   

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1. See also a Treatise of Painting, p. 178. London, 1721; and Dr. SMITH’S Complete System of Optics, vol. ii. r. 244, where the passage is quoted. ↑
2. The luminous line seen by a single eye arises from the reflection of the light from each of the concentric circles produced in the operation of turning; when the plate is not large the arrangement of these successive reflections does not differ from a straight line. ↑
3. System of Optics, vol. ii. p. 388. and r. 526. ↑
4. “We see more exquisitely with one eye shut than with both, because the vital spirits thus unite themselves the more, and become the stronger: for we may find by looking in a glass whilst we shut one eye, that the pupil of the other dilates.” — Lord BACON’S Works, Sylva Sylvarum, art. Vision. ↑
5. BIRCH’S History, vol. ii. p. 348. ↑
6. Natural Magic, p. 100. ↑
7. Nouveau Système de Chimie Organique, 2me edit. t. 1. p. 333. ↑
8. Enquiry, Sect. xiii. ↑
9. Tortual, die Sinne des Menschen. Münster, 1827. Bartels, Beitrage zur Physiologie der Gesichtssinnes. Berlin, 1834. ↑
10. Act. Par. 1743. M. p. 334. ↑
11. Nouvelle Théorie de la Vision, Par. 1823. ↑
12. Traité de la Science du Dessein, Par. 1821, p. 270. ↑
13. Nouveau Système de Chimie Organique, t. 2. p. 329. ↑

Der Beitrag The birth of Stereoscopy: Wheatstone on Binocular Vision 1838, original source erschien zuerst auf the stereosite.

One essential part of becoming a serious collector is frequent research from different online sources such as eBay, platforms of traditional auctioneers, etc. For further information, I recommend the article Collecting Stereoscopes by André Ruiter. Most often, you only find particular items or previous collections, but you never know where a specific viewer originally came from.

Thus said, there are some fortunate exceptions. One is the so called vide de grenier in France which means ‘emptying of the attic’. This can simply happen like a traditional flea market with items from one single household. Such sales are typically done by heirs after a bereavement. But the heirs could also hire a professional and the vide de grenier becomes a professional auction held on site — and nowadays sometimes streamed online.

That way, you will get a glimpse of the individual history of your treasure and know where it was stored, wether it was looked after or long forgotten, if the owner was well situated or not, etc. For me, these stories are invaluable and add a more personal aspect to a collectible. This counts even more because those stereoscopes will usually contain photos that tell even more about their past.

As a passionate restorer, I especially appreciate viewers that have remained untouched since their last use. I carefully remove the dust of decades to reveal the original beauty of a stereoscope. Being the first one to do so feels almost like getting in touch with those who bought it a century ago. I want to take you to one of those journeys.

A vide de grenier took place on September 30, 2021 in Abbeville in the north-west of France near the coast. As usually, you could take a look at the location online a few weeks in advance. Between furniture, knickknacks and rubbish — all tagged on with a little number — I spotted a tabletop stereoscope carelessly placed in a closet:

The large black knob on the site of the device identifies it as a revolving stereoscope (for additional information on this type see the article A Multiview Stereoscope Comparison). Furthermore, the little keyhole and the and the indistinct horizontal line above tell that you can flip back the top to replace the whole chain. Indeed, on the left of the viewer you can see a second chain including stereo photos. I easily recalled the model. This type of viewer was only manufactured by Mattey both for the 8.5x17 and the 6x13 format. If you used card board frames it was also suitable for the 45x107 format introduced by Jules Richard in 1893 (for background information see the article Le Taxiphote). Once again, André Ruiter has written an interesting article about exactly this type, the Mattey Revolving Stereoscope. While he has one of the rare deluxe models, this one is the more common mahogany standard version. Nonetheless, the exchangeable chain makes it one of the more advanced viewers of that time.

So, I subscribed to the auction and logged in live at September 30. As you may have already guessed, I won it for a good price, and after the normal process I received the stereoscope a few weeks later.

According to my request, they had removed the chain to prevent unwanted movement during the transport. So I was not able to tell which series of stereo photos was inside the viewer most recently. One consisted of family and travel photos, one of a mix of professional and amateur slides depicting the first World War. What I could tell was that the latter was used a lot more frequently — the black paint on the right turning knob was almost completely worn down. Also, this one is the original chain that came with the viewer. Both bear the serial number 1213. The additional chain has the number 1220. So I can assume that it was bought at the same time or only slightly later.

Mattey produced this viewer model for quite a long time without any remarkable changes. So how can I tell if my viewer is an early model from shortly before 1900 or a late model from around 1920? As far as I know there is no reference to the serial numbers and a low four digit number is neither definitely earlier nor later.

Luckily, restoration always requires a really close look. The smaller turning knobs that let you adjust the oculars are made of wood and have a narrow notch. Actually, that notch is the reason why I am familiar with this kind of knob: it’s terribly annoying to clean it perfectly. It seems that most manufacturers, despite all competition, used the same focusing knobs. That’s why I’ve come across this type many times. But only on early viewers! They all seem to have changed to bakelite knobs at some point. More precisely, Richard already started to use bakelite knobs with the introduction of the Stéréo-Classeur in 1900, while the chain-operated predecessor still used these wooden knobs.

Another piece of evidence is that my similar 8.5x17 Mattey viewer has also wooden knobs and bears the serial number 891 which is only a little earlier than 1213. On the other hand, two later Mattey models have also changed to bakelite knobs but it seems that Mattey discontinued using serial numbers so this reference is unavailable. Nevertheless, it seems reasonable for me to conclude that I got an early model from around 1900.

After this little digression about dating the viewer, let’s return and take a closer look. Did I say that I enjoy removing dust from an untouched viewer? I have to clarify that I was talking about gently blowing or wiping it of. This time it would be hard work.

This viewer was extraordinary dirty and made me doubt if I could reach a satisfying result. There was some sort of grey powder everywhere, even on the inside and on every single stereo photo. So I did a cleaning of the outside with a damp sponge before I tried to disassemble as much parts as possible.

I then applied a water based liquid including abrasives that sanded off the remaining dirt and smoothed the shellac. For a more detailed description see my article about Restoring Stereoscopic Antiques. I had already seen that there was a flaw in the top trim, but with the dirt gone I discovered even more scratches especially on the top, but also here and there on the base. Fortunately, front, back and the sides were not affected at all. Still, before I could do the finishing I would have to do an additional step.

Whether you use shellac, oil or wax, each will change the color of the wood in different ways. For that reason, you may indeed apply different layers one after another, but you have to build up the surface the same way on every part. In this case, a thin layer of linseed oil varnish would bring back the typical shine on polished shellac. But if there’s a scratch down to the wood oil will penetrate through it and this part of the wood would become much darker than the surrounding areas. I like visible scratches as a part of the patina, but they don’t need to be highlighted. To prevent that from happening, I would need to retouch the scratches with shellac first. I only dabbed a little bit of shellac into the scratches with a cotton swab and repeated the treatment with the polishing liquid. I finished the wood working with a layer of shellac on the trims because these parts are generally worn and I wanted to bring back an overall shiny effect.

Even though I think that the handles were originally burnished and not brass colored I had to grind them off with steel wool to remove all signs of corrosion and make them shine again. By leaving out the deeper lying areas I still achieved a nice antique effect.

I also used my polishing liquid for the black painted metal oculars and steel wool for screw heads, etc. Finally, I put on a thin layer of linseed oil varnish on all wooden or painted parts and penetrating oil on metal parts to protect them from further corrosion. I also cleaned the inside and the chain with a soft brush and applied only a little linseed oil varnish to increase the saturation of the black paint. A little oil on all moving parts and that’s it.

I think it was good that the stereoscope was hidden in a closet and the sun could not bleach the wood. Though, if you have a stereoscope that looks pale on the side that stood towards a window for years, this is not always problem. For example, if you have a waxed surface you can simply wash it off. After you applied oil to the wood the color will mostly come back. But this is always a problem with shellac. Oil can not penetrate the wood through it and you don’t want to remove the original shellac because you will always be able to distinguish between old and new shellac. But that’s another story.

So, overall I’m really happy how it turned out and I hope you enjoyed this time travel back to the original look of this stereoscope as much as I did during the process. Yes, this is really the same viewer.

After this resurrection, it was, of course, not difficult to find a nice place on my shelf, where it is surrounded by comrades made by Richard, Bize, Zeiss and others.

Der Beitrag A Restorer’s Journey erschien zuerst auf the stereosite.

Jules Richard and the Verascope

Jules Richard took over his father’s precision instrument company in the late 19th century and patented a stereo camera called the Verascope in 1893. The name is derived from the antique Goddess of truth Veritas and the Greek word σκοπός (watcher). This neologism refers to the separation of the camera lenses, which is just about the average human eye spacing. 

The camera itself was also a high precision instrument. It was entirely made of metal to prevent humidity and temperature from affecting its operation. But most important, it used a new image format, 45x107mm, which was much smaller than the two common stereo formats of that time – and so was the camera, too.

Despite a widespread interest in stereoscopy, the smaller size was probably the required spark that ignited the boom in amateur stereo photography.

In addition to handheld viewers, Richard also manufactured revolving stereoscopes for glass slides in the new format. These viewers were all simply labeled Stéréoscope, vues prises avec le Verascope (Stereoscope for views taken with the Verascope). Verascope became a synonym for amateur stereo cameras.

Even today, stereo cameras and stereoscopes in the French local advertisements are still titled Verascope and Taxiphote sometimes, even if they were made by other manufacturers.

The revolving stereoscope had one large drawback: changing the slides is extremely annoying and so you would only have access to a limited selection of your photos in the end. And while the Verascope is a high precision device, flipping the glass slide through your field of vision is rather simple and the viewing experience is not as good as with a handheld viewer.

Stéréo-Classeur

But in 1899 Richard and his technician Louis Colardeau patented a new system that allowed the use of bakelite magazines containing 25 slides each. The dimensions of that stereoscope were the same as the common tabletop viewers, but instead of 50 views, it could hold up to 300 views in drawers underneath the mechanism.

They simply called it Stéréo-Classeur (stereo cabinet), and it was offered in their catalogue in 1900, unspectacularly besides the various revolving stereoscopes. This would change soon after.

Le Taxiphote

I believe that the Stéréo-Classeur was planned as a test run. The viewer was renamed to Taxiphote one or two years later – without any changes of the mechanism. From then on there would be an update or extension of the Taxiphote family every year, widely promoted through advertisements.

If you thought the Taxiphote has anything to do with the vehicle, you’re wrong. The name is again derived from ancient Greek: the first part comes from τᾰ́ξῐς (arrangement/ordering) and the second from φῶς (light). In fact, this is quite close to the former name Stéréo-Classeur.

It’s time to take a closer look.

In most cases, the standard Taxiphote, later called Taxiphote foyer moyen (long focus), consists of a storage base and an upper part housing the mechanism, just like the Stéréo-Classeur before. After placing the magazine on a carrier, a lever on the right operates two metal arms below the carrier that push the individual slides to the ocular level for viewing. These two metal arms need to move very precisely to prevent scratching the neighboring slides. When the slide is brought back into the magazine the carrier is moved backwards so that the metal arms access the next slide. This horizontal movement is connected to a counter on the left side of the Taxiphote. If you hold down the main operating lever you can turn the knob on the counter and navigate directly to a specific slide in the magazine.

The new Verascope slides all had some blank space in between the two single images. This area was commonly used to record information about the stereo photo, like place and date. Another lever on the left of the Taxiphote tilts down an additional lens and mirror system that enables viewing that space with your right eye.

Finally, like all better stereo viewers, the Taxiphote also has adjustable focus.

In addition to viewing photos, a 1902 advertisement tells us about a lantern attachment that could be used for projection over distances of up to 4m. The combination of lantern attachment and Taxiphote resulted in a huge apparatus that allowed only monoscopic, and not stereo, projection. In 1923, the projection unit was substantially reduced in size, and in 1927, anaglyph 3D projection was introduced.

In 1903, an employee of the Richard company wrote to a photography reseller that the Taxiphote would also be available for the 6x13 and 8,5x17 formats. One year later, Richard introduced another new format upon suggestion of the members of the Stéréoclub Français. This 7x13 format was said to be the most rational stereo format for several reasons.

These four formats were continuously produced even though the storage space in the base varied. In most catalogues the names are as follows:

• Taxiphote normal / foyer ordinaire / foyer moyen for 45x107
• Taxiphote no. 1 for 7x13
• Taxiphote no. 1bis for 6x13
• Taxiphote no. 2 for 8,5x17

Also in 1904, Richard patented a new feature for all models. From now on, the two oculars were placed on two wooden plates that allowed interocular adjustment to suit the eye spacing of the individual person.

If the label on your device already bears the Taxiphote name but the interocular distance can’t be changed, then your unit was presumably made between 1900 and 1903.

Le Taxiphote court foyer

It goes without saying that the distance between the lenses and the slide has to be at least the width of a magazine, which is almost 10cm. This is no problem for the larger formats, but when viewing Verascope slides, it feels like you were standing in a dark room with a small window, because large areas of your field of vision are just black space. 

This seems to have bothered Richard several years. In my opinion, this was possibly the most challenging task in the development of the Taxiphote. It would take five patented attempts finally resulting in two different solutions.

Modèle mécanique

There were several handheld Richard viewers that had less distance between the slide and the lenses. This court foyer (short focus) provided a superior viewing experience, whereas 45x107 slides still looked just like 6x13. Richard wanted to make that possible for the Taxiphote as well. In 1905, two patents show mechanisms that carried the individual slide both vertically from the magazine to the ocular level, and afterwards also horizontally towards the lenses. A catalogue proves that this so called modèle mécanique was sold in 1909, but it is rarely seen. Probably the mechanism was not perfected yet – this would take a few more years.

Modèle optique

The more commonly used method was the so called modèle optique, which took a completely different approach. Instead of a horizontal movement, it used additional block lenses to magnify the photo.

These lenses could be either permanently lowered in front of the oculars or manually by another lever on the left. Using lenses for that purpose leads to some distortion at the edge of the image, but overall, the viewing experience is quite satisfying, especially if you were annoyed by the black space around the image. On the other hand, you had to pay quite a high price, because the stereo photo was cropped. Not much, but sometimes you were going to miss details in the corners.

Modèle simplifié

Starting at 250 francs the average price for a Taxiphote would be around 300 francs. In 1908 Richard introduced a new version only for the Verascope format at a price of 148 francs. The so called Modèle simplifié (simplified model) had a crank operated mechanism instead of a lever, and is very comfortable to use. In fact, you can easily move back and forwards just by turning the crank the other way around. 

There was still a counter on the left with another extremely clever improvement. While you need to hold down the lever of the other Taxiphote models to freely navigate through the inserted magazine, you now just needed to push the knob before turning. The crank operating system was probably the key for the further development of the modèle mécanique.

Still, this model was cheap overall. No storage base, no profiled corners, poor construction for reading slide titles, etc. In the cheapest version, the adjustable interocular distance was also missing. The simplified product line was continuously produced though. A 6x13 version appeared in 1926, and in 1931 the wooden body was enlarged for a more comfortable viewing height and a storage base was added.

Meanwhile, an electric lamp attachment clair soleil was patented in 1909 for all formats and the wooden ocular plates were replaced by adjustable eyepieces entirely made of metal, patented in 1911. The latter are a good hint for dating Taxiphotes, because the serial numbers hardly provide reliable information.

Taxiphote court foyer, modèle mécanique – Part 2

Even though the modèle mécanique was already available, it seems likely that Richard changed the mechanism. This is extraordinary especially because the mechanism wasn’t changed in any of the other models, except the addition of new features.

But in 1911, there are two more patents on the modèle mécanique. It seems to me that this new mechanism was introduced another two years later in 1913 because the price suddenly jumped, while the prices for the other models remained the same. Indeed, it’s worth it!

The mechanism is now driven by a crank, just like the modèle simplifié. One turn to lift the slide and another turn to move it towards the oculars. No cropping of the image, no distortion. The viewing experience is fantastic. In my opinion this is really the best Taxiphote ever produced.

It takes also advantage of the push-and-turn mechanism of the simplified model to navigate through the slides. The lens and mirror system for reading the slide title is now lowered by pulling a chain on the left. I think this looks a little weird and unstable compared to the former lever mechanism but it works very well.

Autochromes and the Taxiphote

Because of the success of color photography achieved with Autochrome slides, many manufacturers like Gaumont, Plocq or Hemdé offered special magazines to handle Autochrome slides. This was necessary because Autochromes were developed as direct positives and there was no possibility for inverting the left and right images, except by cutting the glass and switching the positions. Therefore, a second glass was typically added for stabilization and protection because autochromes were extremely prone to humidity. So, the slides were twice as thick as normal slides. This is the reason why different magazines were required.

Richard went a more sophisticated way. Instead of cutting Autochromes he recommended turning the slides upside down (because this switches the left and right images as well!) and then attaching prisms on the oculars to invert the image. These so called Redresseurs became available 1913 as well.

Because Autochromes were expensive and difficult to develop, a stereo photo collection would typically consist of mostly black and white photos, with just a few color images. Switching the Taxiphote from viewing black and white to color thus meant manually exchanging the oculars from time to time. Unfortunately, this would take a few moments each time.

This leads to the last addition for the Taxiphote modèle mécanique: A quick exchange mechanism for the entire eyepiece assembly together with two additional sets in a high-quality leather case. One set for Autochrome lenses, and one set to change the short focus back to the long focus– for whatever reason.

Further developments

In 1923, additional magnifying lenses were available also for the 6x13 and 7x13 Taxiphotes. These had the same short focus effect as the modèle optique.

As mentioned above there was a smaller design for the projection lantern in 1923 as well as an extension and a redesign of the simplified model in 1926 and 1931. Also, in 1927 anaglyph projection units became available. The 8,5x17 model disappeared in 1930.

But, we can conclude that all important developments were finished by 1915 and all models were in continuous production until the 30’s. With the introduction of the Verascope F40, the era of the multi-slide-viewers ended.

Deluxe versions and furniture

To arouse interest there were also specially designed deluxe versions of the Taxiphote that were not always available according to catalogues.

For those who had larger photo collections, there were storage cabinets especially designed for the Taxiphote and produced by Richard. You could also buy just the drawers and incorporate them into other pieces of furniture to suit your purpose.

Conclusion

The Verascope and the Taxiphote are two halves of an unbelievable stereo development effort that went on for 40 years essentially without any changes. The Taxiphote was exported to and patented in many countries. All this serves as an example of how attractive stereoscopy was at that time, and also confirms the quality of the Taxiphotes as a technical device. We can only guess at the prestige of having a Taxiphote at that time. 

But what would better illustrate the meaning of the Taxiphote to its owners than the Autochrome stereo photo Thomas Asch found in one of his devices?

If not otherwise stated all pictures show pieces of my personal collection. I’m thankful that Sébastien Lemagnen from antiq-photo.com provided me with some photos as well as Thomas Asch and Paul Burford.

Der Beitrag Le Taxiphote — the most famous French stereo viewer erschien zuerst auf the stereosite.

3D filmstrip viewers are a family of stereo viewers that gained prominence in the early 20th century. In fact, it was a small filmstrip viewer called Tru-Vue that re-introduced 3D viewing as a mid-century pastime, made it more affordable than earlier stereoscope sets, and paved the way in the hearts and minds of consumers for the popular 3D reel & card viewers that would come later. For this reason,  Tru-Vue has often been called “the missing link” in stereoscopy. Although Tru-Vue was the most commercially successful filmstrip stereo viewer in the United States, maybe even worldwide, it wasn’t the first. Here, in chronological order, I present some of the most interesting mid-century filmstrip viewers, including those that came before Tru-Vue, co-existed and competed with Tru-Vue and those that followed much later. The scope of this article doesn’t include 3D viewers like Stéréo Alain, Celde, Pendoplast and Stereo-foto that use stereo transparencies in a roll format.

Homéos, 1910’s

Dating to around 1914, this 3D filmstrip viewer is an accessory to the Homéos stereo camera (which is said to be the world’s first 35mm stereo camera) and was created by the French industrialist Jules Richard who helped spread stereo photography to the masses with the popular Vérascope line. The Homéos viewer is a small wooden viewer that can be found with different variations on the design. One has film canisters on the side to hold the film, a long handle underneath that rotates the film and a lever to adjust the lenses. Another can be found without those features and still another can be found where the eyepieces are shaped differently. 

Hollywood Filmoscope, 1920’s

In 1929, an ad in the L.A. Times advertised the first showing of the Hollywood Filmoscope, “a new device that moves a series of views on motion picture film before your eyes in plastic relief.” It sold for $2.50 with extra films going for 50 cents. All 15 films available for it were Hollywood-related. Although this small metal viewer says Hollywood on it, an article in the Santa Ana Register dated March 15, 1929 stated that a Laguna Beach, CA company called Craftsman Studios signed a contract to produce 200,000 Filmoscope devices. According to that article, the device should say “Made in Laguna Beach, California” on it but I’ve not seen any with that wording. Patent was applied for in 1928 by Andre Barlaiter and granted in 1931. The device is rare and the films are extremely rare.

Colleen Moore Magic Theatre

Colleen Moore was a famous silent movie star with a passion for building doll houses. In the late ’20s, she spent today’s equivalent of $7M to build an elaborate dollhouse. In the 1930’s, the Magic Theatre viewer and its accompanying film served as an advertising piece for the dollhouse. The cardboard version consists of 2 separate pieces — one piece is inserted completely inside the other. The wood version, which may be an early prototype, is one piece. A complete set with intact viewer, film, and brochure, all in good condition, is rare.

DeVry, 1930’s

This viewer has ties to today’s DeVry University and at least one of its films has ties to the Olympic swimmer Jam Handy. The DeVry stereo viewer out of Chicago was created by the movie projection company DeVry Corp which was founded by Herman DeVry. It competed with Chicago-based Tru-Vue by also selling films of the 1933 Century of Progress World’s Fair. In addition to the 6 films for the world’s fair, DeVry partnered with the Jam Handy Picture Service (also out of Chicago) to produce a 56-frame commercial film for Goodyear. Besides being an Olympic swimmer, Jam Handy’s company was well-known for producing tons of training films for the military and auto companies. As for the tie to DeVry University, in 1931 the same Herman DeVry founded DeForest Training School (named after his friend), it was renamed DeVry Technical Institute in 1953, then renamed DeVry Institute of Technology in 1968, then came partnerships, stock, acquisitions and a DeVry Inc came to be, then a DeVry Education Group and somewhere in the mix DeVry University was born. 

Novelview, 1930’s

An ad in the Dayton Daily News dated February 26, 1939 announced “the amazing ‘Novel-viewer’ as “a new scientific marvel” that could be obtained, along with the Treasure Island film, for 10 cents plus one seal from a 1 lb can of Cocomalt. Like DeVry, Novelview (also known as a Moviescope) was yet another competitor to Tru-Vue and was produced by the Novelart Company in New York. There are approximately 65 unique film titles, the rarest and most valuable being a series of baseball films. There are 2 versions of the viewer — one with a silver faceplate that slides in and out to advance the film and one a brown faceplate and a knob to advance the film. The silver version can usually be found as part of a radio promotion package advertising Jack Armstrong’s Jungle Adventure. The film, featuring Jack Armstrong in Africa, was a promo sponsored by Wheaties on the Jack Armstrong radio show. A complete version of that package with viewer (not rusted), intact film, brochure, and box is hard to find. 

Tru-Vue, 1930’s

The Tru-Vue filmstrip stereo viewer was produced by Rock Island Bridge & Iron Works in Rock Island, Illinois, United States. As mentioned earlier, Tru-Vue ushered in a whole new generation of 3d viewing. I could spend 10 pages going through its history, marketing, and the evolution of its viewers in the decades before and alongside View-Master. However, in the interest of space in this article, I’ll just highlight a few things and then write a separate article just on Tru-Vue. Joshua H. Bennett invented the first Tru-Vue stereoscope after experimenting with the concept for many years and brought the idea with him when he came to work for Rock Island Bridge & Iron Works in 1933. Originally, the device was used to document and showcase the dam being built over the Mississippi river but the opening of the 1933 Century of Progress World’s Fair in Chicago presented a whole new marketing opportunity that they took advantage of. Tru-Vue would go on to create numerous styles of viewers, over 400 consumer films and many commercial films. They would eventually lose business to Sawyer’s View-Master and become acquired by them. 

True-View, 1950’s

The elephant in the room: almost an exact copy of the 1940’s Tru-Vue stereo viewer is the differently spelled “True-View” filmstrip viewer from S.E.L. (Signalling Equipment, Ltd) out of England. There are a couple of different theories as to how they came to produce exact replicas of Tru-Vue’s viewer, packaging, instruction sheet — everything! — without suffering harsh consequences from Tru-Vue. I discovered a new clue in a 1949 article where Tru-Vue’s chief sales rep Fred B. Ingram stated, “England is out at the moment, because of the pound devaluation. Previously, London was one of our big foreign markets.” Given that particular insight, it makes sense that a “different” version would suddenly appear in that market and quickly capitalize on the absence of the original Tru-Vue by visually duplicating Tru-Vue’s assets. Their films are different though — a set of 30 filmstrips focusing on London scenery, the Betram Mills’ Silver Jubilee circus, British railways and other England-related subjects.

Verascope F40, 1940’s

Out of France in the late 40s & early 50’s, this beautiful filmstrip viewer was a companion to the F40 camera. It takes in light from a diffuser on its top and has a reversing prism behind each lens so you can view image pairs in 3D directly from the camera, without having to cut, flip and mount the images. The first version was mahogany & chrome. A later version was made from black bakelite and was designed to completely contain the filmstrip inside the unit. Both could be mounted on a stand which is extremely hard to find today.

Sightseer, 1950’s

This small bakelite stereo filmstrip viewer from API, Ltd in England is fairly hard to find, as are the films. The viewer came in at least 3 colors that I’ve seen and there are about 204 Sightseer films ranging in topics from city scenics (Oxford, London, Canterbury, Edinburgh, etc.) to Locomotives, Madame Tussaud and a Dog Show.

Pan-Pet, 1970’s

Jumping a couple of decades ahead to the ‘70s, Japan hosted its first world fair in Osaka in 1970 called Expo ’70 — the theme was Progress and Harmony for Mankind. Thanks to Gakken in Japan producing this plastic panoramic filmstrip viewer, we can see panoramic views of the fair in 3D! In addition to 5 series of films from the Expo, Pan-Pet produced films on golf, trains and nudes.

3Discover, 1990’s

Lastly, we’ll again take a 2‑decade jump to the 90’s to take a look at this the battery-operated, cartridge-based, panoramic stereo filmstrip viewer 3Discover by 3D Vision in Canada. You can advance the film in either direction using the buttons on top of the viewer and it makes a cool, and oddly satisfying, whirring sound as the picture changes. There are over 20 cartridges available, covering subjects from travel to the solar system to insects to Celine Dion and the quality of the color images is superb.

Der Beitrag Mid-Century 35 mm Filmstrip Stereo Viewers erschien zuerst auf the stereosite.

Why Restore? Guiding Principles

A lover of antiques also loves the stories they come with and the traces those stories have left – something which we call ‘patina’. We must thus ask the question of why one would even consider restoration, a process which will surely alter an object.

Water stains, cracks, even the loss of parts — are these flaws worthy of restoration? Don’t we have to preserve the artifact as it is, with its history intact? This is certainly a valid arena for debate. For me personally, there are some very good arguments for restoration. However, one should always err on the side of caution. These are applicable to antiques in general, but are particularly relevant when considering stereoscopic antiques:

Firstly, it is usually a goal of mine to restore the functionality of stereoscopes and stereo cameras to a point where they are still usable as intended. This also includes conservation, ensuring that functionality will not be lost in the coming decades.

Secondly, things like dirt or water damage might prevent us from understanding how an object may have looked originally, or how comfortable it may have been to use; in short, how the object would have appeared to its contemporaries. This, in my opinion, is also part of historical research on a particular object.

Inevitably, antiques are only ever available in limited quantities. Their current owners might not always consider them to be worth preserving, although the Internet now makes it easy to get background information and estimate the demand for objects. Nevertheless, a stereoscope or stereo camera that is in poor condition is less likely to find a buyer, and might therefore permanently disappear. In addition to a measureable increase in value, a restoration is often the last resort in saving an object that has already survived destruction for a century or more.

I have already mentioned that the patina of an antique is a considerable attraction, and it is desirable in any case that the age of an antique remains obvious to the observer. When I restore a stereoscope or stereo camera, I am not trying to give the impression that it is a modern product. It is also not my intent to improve its performance from how it was originally constructed, even if later models from the same manufacturer did exactly that.

When considering restoration, I always ask myself one very simple question: What would this stereoscope look like today if it had never disappeared from its owner’s living room, but had been cherished and cared for continuously for over 100 years?

Disassembly and Reassembly

Looking at an old stereoscope, it is easy to see that the moving parts are worn, and that freely accessible surfaces show abrasion. This is usually the result of normal use and superficial cleaning. Stubborn dirt is mainly found in corners and cracks, or behind levers, cranks, knobs, or the oculars. Normal use mainly leaves behind dust and bodily fluids, such as sweat, which has hardened from decades of storage in damp and poorly ventilated rooms.

Whether you want to perform a relatively superficial cleaning or a full restoration, it is important to disassemble the stereoscope as much as possible! There are four main reasons for this:

First, there are some areas that you simply cannot reach at all, e.g., the inside of the openings through which the eyepieces are moved when focusing. But it is precisely in these places that further abrasion tends to happen when the stereoscope is in use.

Second, different materials require different cleaning techniques. Cleaning wood with liquids damages metal parts and, conversely, polishing metal makes neighbouring shellacked wood parts look dull and scratched. Without completely disassembling an object, there is no way of completely cleaning the areas of transition from one material to the other.

Third, cleaning sometimes requires the application of some mechanical force to the object. Not to mention clamping parts that need to be re-glued, using a hammer to fit in missing parts, or replacing lost nails. If everything is still assembled, you may loosen, bend, or break intact connections in doing so.

Finally, this is also about the philosophy of restoration. We want to work conservatively throughout the entire process and, if possible, even reverse processes of decay. However, if you were to clean an object without dismantling it first, you may actually accelerate the process of decay. This is because wear will inevitably continue on the freely accessible areas by your cleaning activity, while dirt in cracks and crevices has not ever been reached. This might lead to a situation where you have to apply new paint because you rubbed the worn old paint off the already worn wooden surface even though you really only wanted to get to the back of a Bakelite knob.

Tools

A small standard toolbox is ideal for dismantling, since it usually contains screwdrivers in various sizes as well as flat-nose pliers and side cutters.

If you want to fix, grip or pull something with the flat-nose pliers, remember to use a piece of fabric or cork to prevent the pliers from scratching your surface. You can use the side cutter to loosen (not to cut off!) small nails. This is especially useful for removing things like manufacturer’s labels.

The most important tool, however, is the screwdriver. Stereoscopic antiques typically utilize slotted screws exclusively (not Phillps head or Allen head). For the smaller screws, you may have to resort to watchmaker’s tool sets, but standard screwdrivers can usually be used successfully here. However, especially the larger screws used in antique stereoscopes tend to have much narrower slots than modern screws of the same size. So, a modern screwdriver of the proper blade width won’t fit in the slot, while a watchmaker’s screwdriver which is thin enough to go in the screw slot won’t be wide enough to apply the mechanical force necessary to turn the screw. My recommendation: Buy a large screwdriver with a comfortable handle and a blade about 4 mm (i.e. 1/8 in) wide and grind the blade down to be much thinner — as flat as a butter knife.

If with the right tools, many screws will still refuse to loosen straight away. If the shanks are metal, carefully spray the head with some penetrating oil, e.g. spray-on WD-40, and leave it to do its job. Sometimes you will have to do this multiple times before unscrewing is possible.

If the screw head is recessed deep into the wood, it helps to carefully scrape the head free with a knife.

If the screws are dirty, you can scrape out the slot in the screw with the corner of the screwdriver head. It might also help to loosen the screw by trying to turn it back and forth a little at first. If it gets difficult and you have to use more force, hold the neck of the screwdriver to keep it from slipping and scratching the surface.

Procedure

I have come across different makes and models of stereoscopic antiques time and again over the past few years and it is impossible to give a complete explanation. Still, there are a few things in common.

For example, eyepieces or lenses can usually be unscrewed and disassembled by hand. Beware of too much pressure! If you grip them too tightly, you may break or bend the eyepiece mounts or the threaded rings! It’s best to place your palm flat against the entire ring and then twist. If your hand keeps slipping, try putting on rubber gloves.

Levers that do not have a screw can sometimes be amazingly easy to pull out. Often, however, nipped nails also serve as pins for holding them in place. If this is the case, these levers are generally impossible to detach.

If prismatic lenses or glass panes are held in place with pieces of wood glued inside the device, see if you can gently break off these pieces of wood with your bare hands. You can also use a knife or a screwdriver as a lever. Make sure that any damage you may cause will not be visible from the outside and consider whether it is worth dismantling this part of your object for the restoration.

Depending on the order in which you do things, you won’t have to dismantle everything at once. For example, it is advisable to keep eyepieces assembled when you are not working on them so that you don’t have too many small parts out at a time. A type case or a magnetic tray is ideal for storing the smallest parts.

The mechanisms inside larger table stereoscopes can usually be taken out of their casings and cleaned without further dismantling is necessary.

When reassembling the device after cleaning, you will notice that screws or nails may no longer grip because the hole has gotten too large. To fix this, spread some wood glue on the tip of a toothpick, insert it into the hole in the wood, and then break it off. To prevent the screw from changing its position, you can use a small nail to prepare a hole in the screw’s original position by hand.

Expect having to replace rusty screws and not be able to reuse small nails. It’s important to check your local hardware store for suitable replacements before dismantling.

Cleaning and Finishing

The majority of my restoration process consists of very thorough cleaning.

Lacquered Surfaces with Glossy Finish and Bakelite

I use the same cleaning fluid for shellac-polished wood, lacquered metal with a glossy finish, and Bakelite parts. There used to be a product from the German company Clou for polishing shellac – a water-based suspension that contained a little soap and pumice powder as an abrasive. The liquid soap was ideal for loosening encrusted dirt, and the abrasives smoothed the surface without leaving any visible marks. The fluid was applied with a ball of cloth and, after drying, polished with a clean cloth until it was shiny. Unfortunately, this product was discontinued.

Two years ago, I finally came across an alternative that is easy to make at home. There are many different polishing pastes for car paint that contain abrasives. Look for a water-based product and above all, make sure it does not contain any wax or silicone. Dilute the product with water until it has reached the consistency of milk.

The application is then exactly as described above – there will probably be some light clouding on the surface after the product has dried (likely due to the abrasive), but it can easily be wiped off with a damp cloth. Afterwards, you should dry the surface quickly with a fresh, clean cloth and polish it until it is shiny.

A final treatment is optional after cleaning. Bakelite gets a nice, even shine if you treat it with colourless wax. Usually there are specific products for the care of antique wooden furniture. After rubbing the wax in, let it dry completely and polish it briefly, and thoroughly, with a dry cloth until it shines.

The same treatment is also useful for wood with a shellac surface; isolated scratches or blunt spots can be concealed well this way. However, be careful to apply very little wax and avoid unnecessary contact with the surface for several days after polishing. The wax takes a long time to dry completely because it cannot be absorbed into the wood. Don’t worry about overdoing it. You can completely remove excess wax with a soft cloth. I strongly advise against treatment with standard liquid oily standard furniture polish! The oil penetrates even the smallest cracks in the paint and pulls into the wood underneath. This results in dark spots, that will be irreversible or at least visible for a long time.

Caution: Repairs to wood, metal and Bakelite parts must be made before the final treatment of the surface!

Waxed Wood

I generally try to change the original surface as little as possible. An exception is waxed wood, as there are water stains under the wax layer and new wax that is applied to the surface combines seamlessly with existing wax residues (in contrast to lacquer).

If the dirt is just superficial, I resort to the same method I explained in the previous section. In the case of water stains, heavily bleached wood, or partial loss of the wax layer, I remove the old wax layer or loosen it. To do this, I rub the wood thoroughly with a bale of the finest steel wool (grade 0000), which I regularly soak in cleaning gasoline. This process washes off the old wax and at the same time smooths the surface. The result always looks terrifying. Surfaces appear spotty and extremely clouded, like a badly wiped school blackboard.

Do not try to repeat the process until the wood looks even, as this would mean that you’ve sanded off the entire top layer of the wood. This is neither desired nor necessary, and would only distort the original colour. You can always check how the surface will look later as long as the cleaning gasoline has not evaporated and the wood is still damp.

From here there are several options:

a) Deep scratches, breakouts, or other areas where the original surface has been completely removed and which therefore emerged brightly before removing the wax layer can be re-coloured with wood stain (water-based without any wax components) in the appropriate colour.

b) If the wood in general, or in larger areas, looked very pale and colourless, you can rub the entire wood with linseed oil varnish. Let the varnish take effect briefly, rub off any excess liquid with a cloth and let it dry sufficiently!

c) If, by and large, the wood looked even and had a nice colour before removing the layer of wax, skip both of the above steps and apply a new layer of wax straightaway. Use a colourless wax made for wooden furniture. There are often special products for antiques. Distribute the wax with a piece of cloth. Too much wax won’t harm your surface, but it will cause you to have to polish more. For starters, the surface should feel like your hands after putting on hand cream. Let the wax dry long enough and rub it off briefly and vigorously, creating a satin gloss. Rubbing for too long will heat up the wax, causing you to merely smear it around. If in doubt, let it dry again. Cracks and ridges are easily polished with a brush. If at the end you still see rubbing patterns, you have probably used too little wax, or the wood has soaked up too much of it. In this case, just repeat the process.

Caution: repairs to the wood must be made before oil and wax are applied!

Metal

Cleaning metal parts that have not been painted or tempered is generally very easy, but might require patience and focus. For stereoscopic antiques, you’ll mostly encounter brass, and possibly nickel-plated brass. Rub off any dirt or stains with the finest steel wool (grade 0000) without applying too much pressure. Not all stains can be completely removed, and you always have to consider when to stop. There are limits to cleaning, especially with nickel-plated brass.

Tempered metal can sometimes be cleaned at least a little with penetrating oil and a cloth. But be very careful: even a little too much pressure will cause the colour to come off.

The cleaning of the mechanical work of table stereo viewers is mostly done by simply removing dust, dried-on oil, or graphite. I use a toothbrush on which I put penetrating oil, for example spray-on WD-40. I rub larger areas clean with an oil-soaked cloth. Oil the moving parts, but otherwise rub off all of the oil afterwards. Do not use sandpaper or steel wool. Unfortunately, I speak from experience when I say that these leave permanent traces.

Leather

I use Vaseline or modern coloured shoe polish to care for leather. I make sure not to use any products with grease, as it tends to react with the leather in the long term, making it brittle. Further information can be found within the book restoration community if needed.

Repairing and replacing

In comparison to possible serious damage, everything that has been said so far is relatively manageable. If a stereoscope or stereo camera is not only heavily soiled, but has parts that are broken off, permanently stuck together or have even disappeared completely, you must always decide on a case-by-case basis. Still, there are a few common methods that I would like to address briefly:

Gluing

Bone glue was most frequently used in antiques, and we cannot produce it today without great effort. That is why I myself use modern glue for my restorations. I make sure, however, that it doesn’t contain any solvents, because I don’t know to what extent those solvents might attack the materials.

Usually wood glue takes some time to dry, making it is essential to hold the parts together with clamps. Don’t forget to put wood or cardboard underneath the clamps to avoid scratching the surface. I also use white bookbinding glue for leather or textile. Bookbinding glue retains some elasticity and dries clear.

White glue that spills out from cracks when gluing things can be easily scraped off with a fingernail once it has hardened a bit. Any leftovers can then be wiped off with a damp paper towel.

Superglue is useful for broken Bakelite parts and two-part resin epoxy is suitable for metal parts that are subject to stress.

Bending

Bent metal parts are very common. Mostly they are not cast metal parts, but rather wires, stamped sheet metal or the like. If you are careful and think carefully about where to start, most parts can easily be bent back into shape. I mostly use flat-nose pliers for this. Don’t forget to put a piece of fabric between the pliers and the metal part! I usually only use only one pair of pliers while I hold the part with my bare hand. I like to think that that gives me a better sense of how much strain the metal is under when bending.

Coloured Wax Putty

It is not uncommon for antiques to be infested with household pests, e.g. woodworm. After dismantling, it makes sense to treat the infested parts either with a pesticide, or put in the oven. The tell-tale holes in the wood can usually be hidden well with coloured wax. Coloured wax is also good for filling in small cracks or imperfections, both in wood and in Bakelite.

Felt

Even after a number of restored stereoscopes, you can still discover new things! Many stereoscopes have two metal rings in their wooden casings, through which the tubes of the eyepieces move when we adjust the focus. Felt or velvet was always used inside these rings. However, one can often no longer find the slightest trace of it. If you look closely, you might at least see the glue residue. I definitely recommend putting a thin layer of felt back on. This prevents the metal tubes from being scratched and, above all, stabilizes the guide when setting the focus, which often remains a bit wobbly without felt.

Spare Parts

Although I said at the outset that restoration is sometimes the last chance to save an antique from destruction, there are also those that are too damaged to save. Keep an eye out for these objects. Sometimes they can serve as a source of replacement parts. In particular, the eyepiece frames and Bakelite parts were made by large manufacturers, and are the same for most stereoscopes. The same thing is true for screws. Even if you ever need to replace a piece of wood, it is certainly preferable to use a vintage piece of wood that might allow you to keep the original shellac surface.

Conclusion

I would like to return to my guiding question: “What would this stereoscope look like today?” Restoring always brings me closer to a possible answer even though this remains always just an approximation. Another picture that I used in my article was to reverse a process of decay. This means, restoration is always like a journey into the past and even if you restore regularly, you will never know where it leads you. Another aspect is becoming kind of intimately familiar with the object you are working on, examining it closely, deciding wether to do a step of restoration or not and still being excited. Turning an old and forgotten stereoscope into a truly personal object is invaluable. It’s more than just finding it. In some way it’s also recreating it and literally becoming involved in its history.

Der Beitrag Restoring Stereoscopic Antiques erschien zuerst auf the stereosite.

In my previous post I shared some tips about collecting stereoviews on online auction sites. This time I will talk about collecting antique stereoscopes for glass stereoviews from the period 1850 to 1930. Some tips from my previous post can also be applied to stereoscopes, so I recommend to read this post first. However, collecting stereoscopes comes with some additional challenges that I will address now.

Stereoscope types

There are two types of stereoscopes: handheld stereoscopes and table stereoscopes. Within these main groups there are many variations and I will not cover all of them. The handheld stereoscopes are generally simple devices to view stereoviews one by one. A table stereoscope offers more functionality and this group also includes the sophisticated multi-view devices. In this post I will focus on a number of viewers that are readily available.

Define your goal

First, you have to determine your goal before acquiring a stereoscope. Do you want to use it for viewing your collection or is it primarily intended as a decorative item in your showcase? The first viewers from the period 1850 – 1870 are beautiful, but they don’t offer the best optical quality. You’re better off with a later model from around 1910 – 1930 to view your collection. I have a beautiful early Brewster style handheld stereoscope from around 1860. It looks nice in my cabinet, but to enjoy my glass slides I prefer the Zeiss Ikon viewers from the late 1920s.

Different formats

The most common glass stereoview formats are 45 x 107mm, 6 x 13cm and 8.5 x 17cm. Most stereoscopes only support one format. I’ve noticed that the supported format is not always mentioned by the seller or an incorrect format is listed. Keep this in mind and contact the seller if in doubt.

Handheld stereoscopes

A wooden closed box viewer is a good start to view your collection. Finding such a viewer is quite easy because they’re widely available. Not much can go wrong with these viewers and if the seller has made a series of good photos, the choice can be made quickly. Make sure the lenses are clear and free of fungus and the eyepiece holders are not rusty. Scratches on the woodwork are not your biggest problem when your intention is to use it for viewing your collection.

Table stereoscopes – slide tray

The showpiece in your collection should be (in my humble opinion) a beautiful slide tray multiviewer. These devices are easy to use, decorative and provide a good viewing experience. The disadvantage is that they are expensive and there is a greater risk that the advance mechanism is not in optimal condition. They often use gears and springs to position the stereoviews and to transport the slide tray over a rail. These are precision instruments and a small deviation can cause the glass slides to jam.

The most ideal situation is to test the device before buying. If this is not possible, the advice is to contact the seller and ask for detailed information. Keep in mind that not every buyer is aware of what they are selling. The stereoscope may be inherited and the seller may have little knowledge of the device and how it works. This will become clear from the answers you’ll get. If the seller has no clue, just move on or take the risk. If the seller has some knowledge about the the viewer, ask if it can show all images one by one, without getting jammed. If this is the case, you’re probably good to go.

After receiving your stereoscope, I recommend you test it with some uninteresting glass stereoviews from your collection. You don’t want to destroy your precious stereoviews because of a jamming viewer.

About auction houses

Sometimes stereoscopes are offered by an auction house. They auction large numbers of objects at the same time and are not necessarily specialized in stereoscopy. You can ask if the device is in good condition, but often they simply do not know and don’t have the skills or time to perform a test.

Slide tray included please…

If you want to use your desired stereoscope with slide trays, it’s good to ask if at least one tray is included. When buying a Taxiphote or Métascope, this is less important because these slide trays are reasonably available. Finding a slide tray for a Polyphote or Multiphote can be a big challenge.

Table stereoscopes – chain type

An alternative to the slide tray device is the chain type revolving stereoscope. These are the most simple multi-view devices and they often support both glass stereoviews and paper stereocards. They pop up on auction sites regularly for reasonable prices. Because of their simple mechanism they are often in good working order, but the viewing experience of these devices is generally not very good and replacing stereoviews is cumbersome. I have some chain type viewers as I like their appearance, but I don’t use them often for viewing my collection.

How is it presented?

Pay attention to how the stereoscope is presented on the online auction site. Some sellers ask $1000 for a table viewer, but all you can see are some blurry images and a description “good condition”. I cannot recommend these sellers. I prefer sellers who take the trouble to show a series of good photos with an extensive description. It’s no guarantee for a satisfying acquisition, but at least it’s a good start.

Don’t hesitate to ask for extra images when in doubt. If the price is high, you should expect a seller to help you. It’s also a good way to get a feel for the seller. How quickly does the seller respond? Do you get comprehensive answers? It can all help you to purchase with confidence.

What’s a good price?

In my experience, sellers generally ask too much for a stereoscope or have a high starting bid. This applies to both handheld stereoscopes and the table models. Handheld stereoscopes are easily offered between $200 and $500, but a price between $100 and $250 for a device in good condition is more realistic. If it’s in mint condition or rare you can pay more. For a table stereoscope with slide trays in good condition you should think between $500 and $1,000. I bought my Taxiphote for $800, which is a good price as it’s in excellent condition. However, this same Taxiphote type is easily offered for $1,500. My price estimates are based on the European market. I’ve understood that the prices of stereoscopes in the United States are much higher.

Der Beitrag Collecting Stereoscopes erschien zuerst auf the stereosite.

I have been collecting stereoscopy antiques for some years now. My most cherished pieces in my collection are the multiview stereoscopes. I thought it would be interesting to compare these stereoscopes based on their mechanism which is used to position the stereo views in front of the lenses.

Multiview stereoscopes are table stereoscopes that are capable of showing multiple images in one viewing session. These viewers use a slide tray or chain in which the stereoviews are placed. By turning a crank or pushing down a lever, the images are displayed one by one. The multiviewers with slide trays are only suitable for glass stereoviews. The chain viewers are also available for paper stereocards and sometimes they support both glass and paper stereoviews.

To compare the multiviewers, I use four categories: Chain, Lifting, Pick-Up and Gravity. I came up with these categories myself so they’re not commonly used classifications among enthusiasts.

Chain stereoscopes

The revolving chain types are the oldest multiview stereoscopes. They were produced from 1860 and are based on a patent of Alexander Beckers from New York. They are therefore also called American or Beckers stereoscope. 

This type of mechanism includes a chain and holders. The chain is made of wood and iron or completely iron for viewers that support heavier glass slides. A stereoview is placed in each holder. By turning a knob, the stereoview is placed in a vertical position in front of the lenses. Turning the chain further will display the next stereoview. A chain can usually have 50 stereoviews, but there are also tall floor standing models that are suitable for 100 or 200 images. The viewing experience isn’t great with these viewers and replacing the stereoviews can be cumbersome. Some models allow removing the entire chain with holders from the device, which will make replacing the stereoviews easier. Most English and France manufacturers from 1860 to 1930 had a revolving chain type stereoscope in their product range.

Lifting stereoscopes

These are the most sophisticated stereoscopes. They use a bakelite or wooden slide tray to place the glass slides. A slide tray has room for around 25 slides. Depending on the model, special trays for the thicker Autochrome slides are also available.

The lifting stereoscopes use an advanced mechanism, often with gears and springs to display the stereoviews. The tray with glass slides is placed in the device. By turning a crank or pressing down a lever, a stereoview is pushed up from the tray by a metal pin and is placed in front of the lenses. Rotating further lowers the stereoview and places it back in the tray. Within the same movement, the tray is moved forward over a rail so the next slide can be lifted.

The lifting stereoscopes are user friendly and offer a good viewing experience. They require that the mechanism is in good working condition because a slight misalignment will cause jamming and can break your glass slides. Some examples of lifting stereoscopes are the Taxiphote of Jules Richard, Unis France Métascope, Gaumont Stéréodrome, Ernemann Magazin and the table stereoscopes of Hemdé.

Pick-Up stereoscopes

This is a variation on the lifting stereoscopes. It was an invention of Alexander Plocq from Paris and his Planox Stéréoscope Magnétique are the only models that work this way. The mechanism works roughly the same as the lifting stereoscopes, but instead of lifting the slides they are picked up by a magnet. Each slide has to be provided with a metal strip at the top to make the slides magnetic.

The mechanism works well in practice, but I don’t see any real advantages compared to the lifting devices. A disadvantage is that you have to provide every slide with a metal strip. Once attached, you should leave it because removing them can damage the glass and the emulsion.

Gravity stereoscopes

This type of stereoscope excels because of its simple mechanism. It uses gravity to place the slides by a “falling motion”. The lack of a sophisticated mechanism allows a compact design. The first example is the Multiphote, designed by Lucien Bize.

The Multiphote tray with 24 slides is placed on the top section of the device. By removing a metal slide at the bottom of the tray, the slides fall into position. The empty tray is now placed in the bottom part of the device to catch the slides.

By turning the knobs, the viewer part with the lenses moves outward and the rearmost slide falls down and is placed in viewing position. By turning the knobs a little bit further, the slide drops into the slot of the slide tray. This procedure is repeated for every slide. After viewing all the slides, the tray can be removed from the bottom part to reload the device. 

The second example is the ICA Stereospekt from Germany. The slides of the Stereospekt are mounted in a metal harmonica belt with frames. The belt can contain up to 12 slides. The slides are firmly clamped in frames, which indicates that the slides should remain permanently in the belt. By depressing a small lever on the right side, the slides are released and “fall” in front of the lenses.

Der Beitrag A Multiview Stereoscope Comparison erschien zuerst auf the stereosite.