. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. 856 PHYSIOLOGY OF THE DOMESTIC ANIMALS. equal refracting power. Of the one a double convex lens is made, of the other a double concave, and the two combined. They must be of dif- ferent dispersive power, or the degree of concavity which would correct the chromatic aberration would also destroy the converging power of the convex lens. In crown glass and flint glass we have such media. The flint glass has greater dispersive power, hence the degree of concavity necessary to correct the chromatic aberration wi
. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. 856 PHYSIOLOGY OF THE DOMESTIC ANIMALS. equal refracting power. Of the one a double convex lens is made, of the other a double concave, and the two combined. They must be of dif- ferent dispersive power, or the degree of concavity which would correct the chromatic aberration would also destroy the converging power of the convex lens. In crown glass and flint glass we have such media. The flint glass has greater dispersive power, hence the degree of concavity necessary to correct the chromatic aberration will be attained before the degree of concavity will be reached which would destroy the converging power of the convex lens of crown glass. In the different refractive media of the eye such combinations are to a certain extent represented, and serve, together with the action of the pupil in shutting off the circumferential rays, to correct chromatic aberration. The eye as an optical instrument is analogous to the camera obscura, and forms, in a manner to be described directly, an inverted image in. Fig. 377.—Diagram illustrating the Decomposition, in Passing Through a Prism, of White Light into the Seven Colors op the Spectrum. (Bbclard.) r, red ; o, orange; j, yellow; v, green; b, blue; i, indigo ; vi, violet. reduced size of objects before it. Instead of a single lens, as in the camera, the eye is composed of a number of different refractive media placed behind eacli other—the cornea, the aqueous humor, and the lens. The field of projection, or the point on which the image is focused, is the retina, and from changes which have recently been discovered to take place in the retina in which the visual purple becomes bleached the analogy to the process of photograph}* is very striking. As is well known, by means of a convex lens an image of any object may be formed upon a screen; thus, if a convex lens be held before a window, and a piece of paper placed behind it as a screen,
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