Lives of the electricians

by William T. Jeans

As indicating the relations that continued to exist between him and Sir David Brewster on the subject of vision, it is worthy of remark that in 1844 Professor Wheatstone brought before the British Association some singular effects produced by certain colours in juxtaposition. Observing that a carpet of small pattern in green and red appeared in the gas-light as if all the parts of the pattern were in motion, he had several patterns worked in various contrasted colours in order to verify and study the phenomena. Both he and Sir David Brewster brought to York separate communications on this subject, and specimens of coloured rugwork to illustrate it; but on seeing Professor Wheatstone’s specimens, Sir David withheld both his paper and his illustrations, and simply made a few remarks on Wheatstone’s paper, stating that when he came to York he did not know that the phenomena were produced by any other colours but red and green, and that he was indebted to Professor Wheatstone for showing him that red and blue had the same effect. The Professor accounted for it by saying that the eye retained its sensibility for various colours during various lengths of time.

In the stereoscope designed by Professor Wheatstone mirrors were used instead of lenses; and though the effect produced by mirrors was similar to that which we now see by means of lenses, its startling novelty did not excite popular interest. Indeed it was only used by two or three Professors to illustrate optical phenomena; and with that exception it might be said to have been unhonoured and unused for several years. It was Sir David Brewster who proposed to use lenses instead of mirrors, and thus gave to it the form in which it eventually became popular; but even then its popularity might be described as of foreign origin. In addressing the British Association in 1848 on the theory of vision, Sir David Brewster said that the solution of some problems that had long baffled opticians was greatly facilitated by that beautiful instrument, the stereoscope of Professor Wheatstone. Next year Sir David exhibited his new form of the stereoscope before the British Association at Birmingham, and in 1850 he exhibited it at Paris, and explained it to M. Duboscq Soleil, an optician of that city, who was so impressed with its advantages that he began to manufacture it, and to call public attention to its powers. One was also exhibited before the French Academy of Sciences, who appointed a committee to examine it.

In 1849 Sir David Brewster offered his improvement in the stereoscope gratuitously to opticians in Birmingham and London; but they did not accept it; and it was only after it became an object of wonder in France that it began to be appreciated in England. At the Great Exhibition of 1851 M. Duboscq Soleil showed a beautiful instrument together with a fine set of binocular daguerreotypes; and another instrument by the same maker was presented by Sir David Brewster to the Queen. In the same year some were exhibited at one of the soirées of Lord Rosse, where they excited much interest. The attention of English photographers being then directed to it, photographic pictures and portraits began to be executed for it in abundance. The stereoscope soon came to be in demand; it was manufactured by English as well as French makers; and thus became a favourite ornament or scientific curiosity. During the next five years 500,000 stereoscopes were sold.

While Sir David Brewster did so much to make the stereoscope popular, Professor Wheatstone was generally accredited with the original invention. In 1849 the eminent French philosophers, MM. L. Foucault and J. Regnault, stated in the Comptes Rendus that “in a beautiful investigation on the vision of objects of three dimensions, Professor Wheatstone states that when two visual fields, or the corresponding elements of the two retinæ, simultaneously receive impressions from rays of different refrangibility, no perception of mixed colours is produced. The assertion of this able philosopher being opposed to the opinion of the majority of those who have attended to the same subject, we have thought it useful to repeat, modify, and extend these experiments; and the stereoscope of Professor Wheatstone offered a simple means of disentangling these delicate observations of all complication capable of injuriously affecting the accuracy of the physiological results.”

In an account of it published in London in 1851 it was truly stated that the phenomena of vision had engaged the attention of the most acute philosophers; and that the researches of Professor Wheatstone had done more than those of any other man to explain the result of single vision with a pair of eyes while under the influence of two impressions; for in his stereoscope two images drawn perspectively upon plane surfaces, when viewed at the angle of reflection appear to be converted into a solid body, and to convey to the mind an impression of length, breadth, and thickness. At the same time it was explained that Sir David Brewster modified the instrument and imitated the mechanical conditions of the eye by cutting a lens into halves, and placing each half so as to represent an eye with a distance of two and a half inches between them. Although it was this use of lenses that made the stereoscope fashionable, Professor Wheatstone continued to recommend his original reflecting instrument as the most efficient form, not only for investigating the phenomena of binocular vision, but also for exhibiting the greatest variety of stereoscopic effects, “as it admits of every required adjustment, and pictures of any size may be placed in it.”

But in 1856 the chorus of unanimity as to the original invention of the stereoscope was broken. Detraction then began. A book, which was published in that year, not only disputed the scientific accuracy of the principles of vision enunciated by Professor Wheatstone, but endeavoured to divest him of all credit in connection with the invention of the stereoscope. Who ever could have written such a book? Sir David Brewster! Nor did a book suffice. In 1860 he read a paper before the Photographic Society of Scotland “respecting the invention of the stereoscope in the sixteenth century and of binocular drawings by Jacopo da Empoli, a Florentine artist.” He stated that inquiry into the history of the stereoscope showed that its fundamental principle was known even to Euclid; that it was distinctly described by Galen 1500 years ago; and that Baptista Porta had, in 1599, given such a complete drawing of the two separate pictures as seen by each eye, and of the combined picture placed between them, that in it might be recognised not only the principle, but the construction of the stereoscope.

It is noteworthy that Sir David Brewster first gave Professor Wheatstone the credit of being the inventor of the telegraph, and afterwards ridiculed his claims.

As to the principle of the stereoscope, it was at the meeting of the British Association in 1848 that Sir David Brewster definitely disputed the theory of vision which ascribes to experience instead of intuition the correct perception of objects and of distances with two eyes as well as with one. He observed that an infant obtained his first glances of the external world by opening on it both eyes which evidently conveyed single vision to the mind; and in like manner he contended that young animals saw distances correctly almost at the instant of their birth. The duckling ran to the water almost as soon as it broke the shell; the young boa constrictor would involve and bite an object presented to it; and on the other hand no person ever saw a child use such motions as proved it to perceive objects at its eye, to grasp at the sun or moon or other inaccessible objects, but quite the contrary. Dr. Whewell entirely dissented from the views of Sir David Brewster, which were not new; and in confirmation of Dr. Whewell’s contention that experience was a necessary guide in the use of the senses, a Bristol oculist gave several instances of persons who on being restored to sight from total blindness could not at first form any idea of the distances, or directions, or shapes of bodies; in one instance the patient, for a length of time, was in the habit of shutting her eyes entirely and feeling the objects, in order to get rid of the confusion which vision gave rise to; and it was only as her experience grew more perfect that she saw with increasing correctness and pleasure, until at length her sight became perfect. The controversy on this subject has engaged the attention of many philosophers and has not yet been settled. In later years Helmholtz, who preferred the mirror stereoscope of Wheatstone to the lenticular one of Brewster on the ground that the former gave more sharply-defined effects, stated that the hypotheses successively formed by the various supporters of the intuitive theories of vision were quite unnecessary, as no fact had been discovered inconsistent with the empirical theory, which supposes nothing more than the well-known association between the impressions we receive and the conclusions we draw from them, according to the fundamental laws of daily experience.

In 1851 Professor Wheatstone invented the pseudoscope, an instrument which conveys to the mind false perceptions of all external objects, called conversions of relief, because the illusive appearance had the same relation to that of the real object as a cast to a mould or a mould to a cast. Thus a china vase ornamented with flowers in relief showed in the pseudoscope a vertical section of the interior with painted hollow impressions of the flowers. In like manner a bust became a deep hollow mask. When two objects at different distances were viewed through it, the most remote object appeared the nearest, while the nearest became the most remote. A flowering shrub in front of a hedge appeared in the pseudoscope as behind the hedge, and a tree standing outside a window was transferred to the inside of the room.

This instrument has been useful in illustrating mental phenomena according to the impressions it produces on observers. It is found that with most persons the inverted appearance that an object presents when seen through the instrument is alone seen at first; but after the real form of the object becomes known, their visual perception is so much under the control of their matter-of-fact experience that they are unable again to see the inversion of the object. With other observers the real appearance of the object lasts a shorter or longer time, after which their visual impressions predominate to such an extent that it again appears inverted.