of Light ; and a new Theory of Vision. 429 



«iium, instead of only a certain portion of it, possesses this dispr- 

 sition ; and if it was as he supposed, my hypothesis could not ac- 

 count for the reflcctTon and refraction of liglit; and his, faulty a$ 

 it is, would Ije the best that has yet been imagined. It is necessary 

 tlien for nie to explain why the whole of the surface of glass is co- 

 vered by the image of the reflected object, when only parts of it 

 reflect the rays of light; and fortunately for me this is very easy 

 to be done. 



Whenever the table of a camera-obscura is removed further 

 from the lens through wliich the light is admitted, the images 

 of the olijects represented upon it grow larger and become fainter, 

 that is, the ra\s of light from these objects are more scattered, 

 and occupy a larger space. Still however the ravs, scattered as 

 they are, are in contact with each other; for we can discover no 

 break in the picture ; and the images, except that they are fainter, 

 are as perfect as before. 



The cause of this phasnomenon is as apparent as the fact is 

 ♦'fident. The particles of light are evidently compressible, because 

 they may be compressed by a burning-glass into a space much 

 smaller than what they usually occupy; and it is only in this way 

 that we can account for the rays of light crossing each other, as 

 they are con>tantIv doing, without meeting any impediment. 

 Now, u|)on this principle, when the rays enter the eye in great 

 numbers; that is, when they are reflected from a body like quick- 

 S'ilver, that reflects ligiit from every part of its surface, they must 

 necessarily be comjiressed into a smaller space, and in propor- 

 tion to their numbers give out a greater body of light; but when 

 they are reflected from glass, whose surface but partially reflects 

 light, a great part of this pressure is consequently taken off, and 

 they expand themselves accordingly, in the same maimer as tie 

 air does in a receiver when a portion of it is drawn off; so that 

 the retina, as before, is still entirely covered witli the particle* 

 of light, no breaks are made in the picture, but the images are 

 fainter in proportion to the paucity of the rays. 



To suppose that the same sitbstance has the power of reflect- 

 ing and refracting light, is to suppose what cannot be proved 

 upon the old principle of alternate reflection and refraction, or 

 in any other way, and what moreover is contrary to all analogy, 

 and is founded ujjon no principle whatever; whereas, it can be 

 no objection to my hypothesis that it supposes that the rays of 

 light are not reflected from every part of the surface of a mediiun, 

 because it is very evident that thev hare the power of expanding 

 them«elves whenever they are not confined l)y tlie pressure of 

 other rays, and there is no other o!»jection with whicii I am ac- 

 quainted that can be brought against it. By supposing a fluid 

 adhering to the surface of a medium consistipg of two substances, 



one 



