670 ON THE RELATION OF NATURAL SCIENCE TO ART. 
of our northern home, above all in closed rooms, they are somewhat 
out of place. 
In another direction Wheatstone has added valuable information to 
the knowledge of painters and designers with his stereoscope. It dem- 
onstrates the fundamental difference which distinguishes binocular 
vision of near objects from monocular vision, as well as from binocular 
vision of objects so far removed that the distance between the eyes 
vanishes as compared with their distance. An impression of solidity 
can only be obtained by each eye getting a different view of an object, 
the two images being fused into one, so as to appear solid. A painter 
can therefore only express depth by shading and aérial perspective; he 
will never be able to produce the impression of actual solidity on his 
canvas. While Wheatstone’s pseudoscope exhibits the unheard-of spec- 
tacle of a concave human face, Helmholtz’s tele-stereoscope magnifies, 
as it were, the space between the eyes, and resolves a far-off range of 
woods or hills without aérial perspective into its different distances. 
Finally, Halske’s stereoscope, with movable pictures, confirms old Dr. 
Robert Smith’s explanation of the much-debated circumstance that the 
sun and moon on the horizon appear larger by almost a fifth of their 
diameter than when seen in the zenith, and reduces the problem to the 
other question: why the vault of the sky appears to us flattened in- 
stead of hemispherical. 
However, the almost contemporary invention of photography was des- 
tined to be of vastly greater importance to the fine arts. It had always 
been the dream of artists as well as physicists to fix Della Porta’s 
charming pictures—a dream the realization of which did not seem quite 
impossible since the discovery of chloride of silver. One must have 
witnessed Daguerre’s invention, and Arago’s report of it in the Chamber 
of Deputies, to conceive the universal enthusiasm with which it was 
welcomed. Daguerre’s method, being complicated and of restricted 
application, was soon cast into the shade by the one still essentially 
practiced at the present day. However, it is worth recording that, 
when the first specimens, imperfect as they were, reached us from Eng- 
land, no one foresaw the immense success in store for Talbotypes; on 
the contrary, the change from silver-coated plates to paper impregnated 
with the silver salt was received with doubt and considered a retro- 
gression. 
Thus photography entered on its marvellously victorious career. 
With respect to art, it promptly fulfilled what Arago had promised in 
its name. It not only facilitated the designing of architecture, interi- 
ors, and landscapes, and rendered the camera clara unnecessary even 
fer panoramas, but also furnished many valuable hints with regard to 
light and shade, reflection and chiaroscuro, and the general means of 
reproducing as closely as possible on a level surface the raised appear- 
ance of solid forms. A competent, judge of both arts might find it 
an interesting task to ascertain what share photography has had in 
