18 



SCIENCE 



[N. S. Vol. XXXIX. No. 992 



pictures thus obtained the inventors, Herr 

 Friedmann and Herr Reiffenatein, have devised 

 another means of making each eye see only 

 one, and that one its own particular image. 

 This consists of the application of the fact that 

 when placed against a white background the 

 image on a positive transparency is visible 

 and that when seen against a black back- 

 ground it becomes invisible, while should the 

 image be bleached the contrary is the case. 

 From the negatives which have been obtained 

 in the ordinary way with the stereoscopic 

 camera are made, therefore, from one, an ordi- 

 nary transparent positive, and, from the 

 other, a negative which is afterwards 

 bleached. Let it be assumed that from the 

 negative corresponding to the image seen 

 with the right eye the ordinary positive is 

 made and that the left eye's picture becomes 

 the bleached negative. If these two trans- 

 parencies were super-imposed one upon the 

 other and laid upon a white background only 

 the right-eye picture would be visible. On the 

 other hand, if placed upon a black background 

 only the left-eye picture would be seen. It is, 

 however, necessary that both eyes should see 

 their respective pictures simultaneously. 

 For this a background is required which to 

 the right eye appears white and to the left 

 eye black. This is provided by a sheet of 

 glass, the back surface of which is prepared 

 in a special manner, while the front surface is 

 ribbed convexly, whereby the rays of light 

 falling upon this surface are broken in such 

 a way as to make it appear black or white ac- 

 cording as looked at from one side or the 

 other. The problem is, therefore, solved. 

 The two transparencies are placed one upon 

 the other , and then both upon this back- 

 ground. The right eye sees only its proper 

 image and the left eye likewise. These com- 

 bine automatically, as is the ease when a 

 stereoscope is used, and the result is a true 

 plastic picture. 



The inventors exhibit five or six specimens 

 of such photographs to which they have given 

 the name of " stereographs." Three of these 

 appeared to the writer of this article to be 

 Almost faultless. One of them represented a 



lump of quartz in which even the shimmer 

 on the surface was reproduced; another, a 

 spray of orchids in a vase, and the third, the 

 skeleton of a gorilla. In the other specimens 

 the two images did not seem to combine 

 easily. The inventors are making arrange- 

 ments for the manufacture in cheap and 

 handy form of " backgrounds " which they 

 hope before long to have brought to such a 

 state of perfection that the process will be 

 generally employed. With such " back- 

 grounds " the inventors state that pictures 

 can be looked at like any other photograph. 

 In the case of the stereographs now being ex- 

 hibited the effect of the black-and-white back- 

 ground is, however, obtained by a different 

 method, which necessitates their being viewed 

 by transmitted light. 



SCIENTIFIC NOTES AND NEWS 



The sixty-fifth meeting of the American 

 Association for the Advancement of Science 

 opened at Atlanta on Monday, Dr. Edmund B. 

 Wilson, of Columbia University, being intro- 

 duced as president, and Professor Edward 0. 

 Pickering, of Harvard University, giving the 

 address of the retiring president on " The 

 Study of the Stars," printed in this issue of 

 Science. Subsequent issues will contain other 

 addresses and reports of the meetings at At- 

 lanta and of the meetings held simultaneouslj 

 at Philadelphia, Princeton, New York and 

 New Haven. 



M. Jean Perrin, professor of physical 

 chemistry of the University of Paris, has been 

 given the degree of doctor of science by Co- 

 lumbia University, to which he is this year 

 visiting professor. 



Sir Philip Watts, K.C.B., F.E.S., has re- 

 ceived the Order of the Eising Sun (second 

 class) from the Emperor of Japan. 



Dr. Charles DeGaemo, since 1898 professor 

 of the science and art of education at Cornell 

 University, will retire at the close of the next 

 summer session. 



The Senate of the University of St. An- 

 drews has invited Professor J. Arthur Thorn- 



