The first binocular microscope was invented by the previously mentioned Father Chérubin, whose instrument consisted of two inverting systems, and consequently gave a totally wrong impression of depth, i.e. depressions appeared as elevations, Microscope. and vice versa, or, as we must say after Charles Wheatstone, it presented a pseudoscopic impression; this quality, however, was not recognized by the microscopists of the time. The instrument subsequently fell into complete neglect for nearly two centuries, to be revived in 1852 by Charles Wheatstone, who has stated that he had previously studied the problem; the publication of his views in his second great paper “On Binocular Vision,”[2] in the Phil. Trans. for 1852, undoubtedly stimulated the investigation of this instrument, which was carried on with zeal and success more especially in England and the United States. In 1853 the American J.L. Riddell (1807-1867) devised his binocular microscope, which contained the essentials of Wheatstone’s pseudoscope. F.H. Wenham, another constructor, did not at first succeed in avoiding the pseudoscopic effect, but, by the application of refracting dividing prisms, he subsequently arrived at orthoscopic representations and continued the development of the different methods for producing micro-photographic stereograms; this was effected in the first case by placing a diaphragm over one half of the objective for each exposure, and in the second case by a suitable direction of the illuminating pencil (fig. 6). Of greater benefit, however, for stimulating interest in binocular microscopes, was his invention of reflecting dividing prisms (fig. 7). Other experiments, begun by Powell and Lealand, and developed with greater skill by Wenham, were concerned with the binocular vision of identical images. Such an impression could not possibly be stereoscopic, and these experiments led to the construction of a non-stereoscopic binocular microscope. Of the other workers in this field mention may be made of Alfred Nachet, who in 1853, and subsequently in 1863, brought forward two forms of binocular microscope.
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The earliest stages of the development of the binocular microscope had been always confined to those instruments with one objective, in the immediate neighbourhood of which the systems for dividing the pencil were placed. At a later date attempts were made to separate the two halves of the objective by modifying the eye-piece; this led to the construction of stereoscopic eye-pieces, initiated by R.B. Tolles, E. Abbe and A. Prazmowski. Of special importance is the work of Abbe; although, as he himself has stated, his methods accidentally led to the Wenham system, he certainly was far above his predecessors in his theoretical treatment of the problem, and in the perspicuity and clearness of his explanation. To him is also due the re-establishment of the instruments, which Wenham had abandoned by reason of too great technical difficulties (fig. 8). The newest form of the binocular microscope is very similar to the oldest form in which two completely separated tubes were employed. The inventor, H.S. Greenough, employs two systems for setting up the image, in order to avoid the pseudoscopic effect. After experiments in the Zeiss works, the erecting of Porro’s prisms simultaneously permitted a convenient adaptation to the eye-distance of the observer.
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| Fig. 6. | Fig. 7. | Fig. 8. |
| Fig. 9. |
The first binocular magnifying glass or simple microscope (German, Lupe) was devised by J.L. Riddell in 1853; in this instrument (fig. 9) the pencil of light is transmitted to the eyes by means of two pairs of parallel mirrors. Simple microscope. Of the many different improvements mention may be made of A. Nachet’s. H. Westien made use of two Chevalier-Brücke’s simple microscopes with their long working distances in order to form an instrument in which the curvature of the image was not entirely avoided. Mention may also be made of the binoculars of K. Fritzsch (formerly Prokesch) and E. Berger.
Binocular Instruments for Range-finding.—For measuring purposes binocular telescopes with parallel axes are the only types employed. The measurement is effected by adjoining to the space or interval to be measured some means of measurement defined; for example, by a fixed scale which extends into the space, or by a movable point (Wandermarke). This instrument shows a transition to the stereoscope, inasmuch as the scale or means of measurement is not directly observed, but to each eye a plane representation is offered, just as in the stereoscope; the space to be measured, on the other hand, is portrayed in exactly the same way as in the double telescope. The method for superposing the two spaces on one another was deduced by Sir David Brewster in 1856, but he does not appear to have dealt with the problem of range-finding. The problem was attacked in 1861 by A. Rollet; later, in 1866, E. Mach published a promising idea, and finally—independently of the researches of his predecessors—Hektor de Grousilliers, in partnership with the Zeiss firm (E. Abbe and C. Pulfrich), constructed the first stereoscopic range-finder suitable for practical use.
(O. Hr.)
[1] The term binocular (from the Lat. bini, two at a time, and oculi, eyes) was originally an adjective used to describe things adapted for the simultaneous use of both eyes, as in “binocular vision,” “a binocular telescope or microscope”; now “a binocular” is used as a noun, meaning a binocular microscope, a field-glass, &c.