276 ANNUAL OF SCIENTIFIC DISCOVERY. 



we see landscapes to be when we look through a window of painted 

 glass ? Through the red, are objects beheld as if they were blazing in 

 a fiery furnace ; or do they appear as frigid as a snow scene in blue- 

 eyes as through the blue glass ? Some purpose is served by the rela- 

 tion. 



In the solar spectrum, there are rays independent of those of light, 

 which impart a sensation of heat. These calorific rays are most abun- 

 dant a little beyond the red verge of the spectrum, and diminish grad- 

 ually toward the violet. When it was observed, in the Conservatory 

 at Kew, that plants suffered from the scorching influence of the calor- 

 ific rays through the glass covering, a series of experiments were pur- 

 sued to ascertain the possibility of cutting off the heat-imparting rays 

 by means of tinted glass. A glass tinted of a pale yellow-green pre- 

 vented the permeation of the heat rays to the maximum of the calorific 

 action. The pinky hue of the light was modified, and the scorching 

 influence subdued. What they sought to accomplish was effected. 

 They obtained a properly moderated heat. 



White is the simultaneous sensation of all the prismatic colors. By 

 suppressing red, we obtain a bluish-green hue; by suppressing the blue 

 and the green, we obtain an excess of yellow and red. The purest 

 air, or clearest water, gradually extinguishes, by absorption, the rays 

 passing through it. The natural stimulus of the retina is the action 

 of the luminous rays. Modifications are essential where the activity of 

 perception may be allied to the conditions of diseased sight. " Many 

 are the waves and coruscations, the fiery clouds and flaming spectra 

 which haunt the amaurotic when certain morbid complications exist," 

 and when the optic nerve is peculiarly influenced, a compensatory 

 modification of the peculiarity in regard to tint is made by the adoption 

 of colored glasses for the sight. We may presume that what is in ex- 

 cess in the locust is modified by the red pigment of the eye, and what 

 is superabundant in the grasshopper by the yellow and the blue. 



The eyes of insects are what are called facetted eyes. They are cut 

 in hexagonal compartments, and have the appearance and the power 

 of multiplying glasses. The outer coat is composed of a thin plate, 

 resembling horn. It is stiff but flexible, and compact but transparent. 

 Immediately beneath each corneule or hexagonal compartment, that 

 is, beneath the facets of the outer covering of the eye, is a layer of- col- 

 or. It covers the whole of the inner surface of the corneules, except- 

 ing only in the centre of each where a minute aperture is seen, admit- 

 ting light by the iris. Between the iris and the end of the cornea is a 

 space, flattened and convex, filled with an aqueous hunior. Each con- 

 vex lens corresponds with each facet. The rays of light passing through 

 them fall upon a transparent space occupied by a vitreous humor. The 

 choroid in the eyes of insects, like the choroid in the vertebrata, is the 

 proper vascular structure of the organ of vision. The pigment of the 

 choroid is subject to much variety of color in different insects. In 

 some it is nearly black, in others dark blue, violet, green, purple, 

 brown, and yellow, and in some, two or three layers of pigment are of 

 different colors. The usual arrangement of these variegated pigments 

 is, first, a dark-colored portion near the bulb of the optic nerve, then a 

 Lighter color, and lastly, again, a darker near the cornea. 



Puget adjusted the eye of a flea (Pulex irriians) in such a way as to 



