Septemder 10, 1909] 



SCIENCE 



343 



doscopic relief was obtainable at will from a 

 pair of exactly similar drawings by varying 

 the conditions of geometric perspective with 

 regard to two eyes. So far as the experiment 

 is concerned, priority must now be assigned to 

 Tourtual. In Helmlioltz's standard work on 

 physiological optics Tourtual's name is sev- 

 eral times mentioned in connection with other 

 subjects, but, until recently, his experiments 

 on the subject now under discussion seem to 

 have been completely forgotten. 



Wheatstone's most persistent and malignant 

 critic was Sir David Brewster, whose lenticu- 

 lar stereoscope was brought out in 1849. 

 There have been few quarrels in connection 

 with scientific discovery more bitter than this, 

 at least on one side. That Brewster was both 

 ■wrong and unreasonable seems to have been 

 conceded quite generally. A partial excuse 

 was found in his advanced age, eighty-six 

 years at the time of his death in 1868. . 



During the decade from 1850 to 1860 the 

 interest in stereoscopy, both on the part of 

 students of science and by the general public 

 was at its height; as great perhaps as the 

 popular enthusiasm about X-rays during the 

 first year or two after Roentgen's discovery in 

 1895. The possibility of its application to the 

 microscope was soon recognized, and the first 

 binocular microscope was devised and de- 

 scribed by Dr. Riddell, of New Orleans, in 

 1852. It was greatly improved subsequently, 

 especially by Wenham in England, whose con- 

 tributions on this subject extend from 1853 to 

 1878. There was a large field for activity in 

 the application of photography to the prepara- 

 tion of double pictures for use with the stereo- 

 scope. This was first done by Wheatstone; 

 and the first binocular camera was devised by 

 Brewster in 1849. Dr. F. A. P. Barnard, for 

 nearly a quarter of a century president of 

 Columbia College, published in 1853 a method 

 of taking daguerreotype pictures for the stereo- 

 scope, by suitable adjustment of mirrors in 

 conjunction with an ordinary camera. Pro- 

 fessor Rood, in 1861, published a method of 

 producing stereographs by hand, and an article 

 on the practical application of photography to 

 the microscope. Among others in America 



who were active during this period was Pro- 

 fessor W. B. Rogers, founder of the Massa- 

 chusetts Institute of Technology, who in 1855 

 and 1856 published several notable articles on 

 binocular vision in what was then known as 

 SilKman's Journal. Professor Edward Emer- 

 son, who has but lately passed away, was first 

 stimulated by his colleague, Rood, and pub- 

 lished papers on this subject in 1863 and 1864, 

 his second paper being a vigorous blow against 

 Brewster in the unhappy strife already men- 

 tioned. In 1861 Dr. Oliver Wendell Holmes 

 devised what became currently known as the 

 American stereoscope, the only form exten- 

 sively used in this country since that time. 

 He declined to patent what would certainly 

 have been a fertile source of revenue. Such 

 was the popular demand that according to 

 Brewster's estimate more than a half million 

 of his stereoscopes were made during the first 

 six years after his invention was put on the 

 market by Duboscq, the head of a well-known 

 firm of French opticians. On both sides of 

 the Atlantic the market became overstocked, 

 and after the first dozen years both scientific 

 and popular interest in stereoscopy steadily de- 

 clined. This decline, in the opinion of von 

 Rohr, reached its lowest point during the de- 

 cade from 1880 to 1890. The public had been 

 sated, amateur workers found little more to 

 seek, and investigators like Dove and Helm- 

 holtz, though still faithful, were turning their 

 attention into other directions. 



Accepting these facts it was perhaps nat- 

 ural for von Rohr to assume that in America, 

 the home of practical men, it was useless to 

 look for further work in physiological optics. 

 He has no references to work published in any 

 American scientific journal since 1865. The 

 present writer is indebted to him for some 

 very appreciative words about a form of re- 

 versible stereoscope designed for special pur- 

 poses in 1882, but von Rohr's knowledge of 

 the instrument was obtained from the patent 

 office records, and not from the American 

 or English scientific journals. It was rather 

 unwillingly patented with full knowledge 

 that it had little or no commercial value. 

 But the most important oversight has been 



