1882. 115 Trans. N. VY. Ac. Sct, 
substitute one more in accordance with the theory of rapid successive 
convergency of the optic axes in the estimation of distance. The 
effect was a decided surprise in its illustration of the phenomenon, but 
even more so as a corroboration of the theory. It consisted simply of 
two concentric circles, respectively 15g inch and % inch in diameter 
as the left-eye picture, and a circle 15g inch in diameter, enclosing two 
circles % inch in diameter each, with their centres respectively I-10 
inch to the right and left of the centre of the large circle, as the right- 
eye picture, the centres of the large circles being about 25g inches 
apart. The expectation was, that the successive combination, so to 
speak, of the small circles of the right-hand figure, could at least be 
made so rapidly that a comparison of the sizes could be made at the 
varying apparent distances. The apparent szweultaneousness of the 
appearance of the near and remote circles, with the expected differ- 
ence in apparent size, constituted the surprise, which has been ex- 
perienced by every one upon examining such a slide for the first time. 
Attention was called to the diagram in a published discussion of some 
of Sir DAVID BREWSTER’S views of the theory of the stereoscope in 
1864, in the Brztzsh Journal of Photography ; and subsequently a 
dealer in stereographs placed it among his slides; but it is more than 
possible that even those interested in this subject may not have met 
with it, and I have therefore presumed to call attention to it in connec- 
tion with the very interesting articles upon the subject before alluded to. 
CARLISLE, Pa., January 30, 1882. 
Mr. STEVENS exhibited the stereograph described by Professor 
Himes, and by large diagrams on paper explained the difference 
between this and Brewster’s method of illustrating the phenomena of 
the horizontal moon. In addition, he remarked substantially as 
follows : 
“It gives me much pleasure to present this paper by Professor HIMES, 
and to call attention to his careful observations on the nature of binocu- 
lar vision, which were made twenty years ago, and have not received 
the full notice to which they were properly entitled. The great name 
of Sir DAVID BREWSTER carried with it a degree of authority which 
caused the general acceptance of the geometric theory of binocular 
vision. Professor W. B. ROGERS,! in this country, bad also written 
a series of very able papers, in which he calculated what must be the 
form of the externally projected binocular image, assuming each point 
of this to be determined by intersection of visual lines. Professor 
HIMES discovered that such intersection is not necessary; but, unfor- 
tunately, his paper on this subject was not published in the dmerzcan 
1, Am. Jour. Science, vols, XX. and XXI., 1855 and 1856. 
