Trans. N. VY. Ac. Scz. 116 Feb. 13, 
Fournal of Science. (Mr. STEVENS here read an extract from the 
original paper, published by Professor HIMES, in the Amerzcan Journal 
of Photography for September 1, 1862.) Shortly before the appear- 
ance of this paper, two Germans, ROLLET and BECKER,” published 
a method of securing binocular fusion of similar images with optic 
divergence, the possibility of such fusion having been already mentioned 
by BURCKHARDT. Professor HIMES’ experiments were doubtless con- 
temporaneous with those of the Germans just named, and were wholly 
independent of them. 
‘‘My own discovery of the possibility of stereoscopic vision by optic 
divergence was likewise independent. I subsequently learned of the 
previous experiments on this subject by ROLLET, BECKER, and HELM- 
HOLTZ, and duly credited them in my paper before this Academy on 
the 6th of last June. Professor HIMES’ papers were sent me after mine 
had been published in the Amerzcan Journal of Sczence for last Novem- 
ber. He deserves the credit of being the first in the country to secure 
stereoscopic vision with conscious optic divergence. My own claim is 
based rather upon the analysis than the discovery of this mode of 
stereoscopy. For years past, oculists have subjected their patients to 
the use of prisms for the purpose of testing the strength of the external 
rectus muscles of the eyeballs, in diverging the visual lines while the 
eyes receive, from an object in front, rays of light that are refracted by 
transmission through the glasses. In view of this fact, it is remarkable 
that BREWSTER’S geometric theory of stereoscopic vision should still 
hold its place in our text-books of physics. His theory of color has 
been abandoned, and his theory of binocular perspective is awaiting the 
same fate. 
‘In regard to the phenomenon of the apparent enlargement of the 
moon when seen at the horizon, Professor HIMES’ stereograph gives 
an excellent illustration, superior to that of BREWSTER,’ because the 
two parts, which are to be contrasted in the external projection of the 
binocular image, are more nearly aligned, and no motion of the stereo- 
graph is necessary.. While the angular diameter of the moon remains 
nearly constant, being slightly greater when near the zenith, because the 
observer’s true distance is diminished by nearly the earth’s semi-diame- 
ter, its apparent magnitude varies with its estimated distance, and it 
appears much smaller when near the zenith, instead of larger. The 
cause of this illusion of distance, producing an illusion in regard to size, 
which is well illustrated by the present stereograph, has been the sub- 
ject ofmuch discussion. In so late a book as LOCKYER’s Astronomy,‘ 
2. Helmholtz, Optique Physiologique, pp. 827, 828. 
3. The Stereoscope. London, 1855, p. 201 ef seg. 
, Elements of Astronomy, Appleton & Co., N. Y., 1873, p. 116. 
