ANIMAL MECHANISM. 1127 



of making vexation, gives strength or greater vividness, 

 as the images are on surfaces of the same structure, 

 transmitting, through the two optic nerves, the same 

 idea, or that indescribable something that creates an idea. 

 The optic axes, spoken of in the books, by this explana- 

 tion, will be understood. If one eye is distorted, 

 pushed by the finger one side, when we are in the act of 

 contemplating an object, it will appear double, but less 

 distinct in the one so distorted. The rationale is this; 

 viz. the visual surface on which the image is made, so 

 exactly alike in both eyes, as to call up but one idea, be- 

 ing forced out of the optic axis, the rays still make the 

 picture, but on a surface, less highly organized, that 

 does not correspond with the surface on that retina which 

 has not been disturbed. The two images have now dif- 

 ferent localities. No course of experiments are more 

 within the reach of those who have the desire to experi- 

 ment, than these.* 



* Generally the eyes of insects are of two kinds ; viz. simple and 

 compound, having the appearance of two crescents, making the larg- 

 est part of the head, and containing an infinite number of little hex- 

 agonal protuberances, convex, and placed in lines. The number of 

 lenses in one eye, vary in different insects. Hooke computed those 

 in the eye of the tabanns or horse-fly, to amount to nearly 7000. 

 Loewenhoek found in that of the libelltda, (dragon-fly) 12,544 ; and 

 17,325 have been counted in a common butterfly ; the picture of an 

 object, impinged on their retinas, must be millions and millions of 

 times smaller than in the human eye. Some insects have a still 

 more curious apparatus of vision ; three small spherical protube- 

 rances rise from the top of the head, and are eyes, in addition to the or- 

 dinary ones on the side of the head. They are solely for seeing distant 

 objects; the first, for near ones. Loewenhoek looked through the 

 eye of a dragon-fly with a microscope, as a telescope, and viewed 

 the steeple of a church, which was 299 feet high and 750 feet dis- 

 tant. He plainly saw the steeple, though it did not appear larger 

 than the point of a very fine needle. He also viewed a house and 

 could distinguish the front, discern the doors and windows, and 

 moreover, perceive whether they were open or shut. The writer 

 has recently seen the light strongly reflected from the eye of the 

 bee-moth, which precisely resembled the ground faces of a stone 

 in a Cratch seal. This, therefore, was a multiplying eye. Several 

 insects present the same structure, hut nature's object is not under- 

 stood by entomologists. 



