of Light ; and a new Theory of Vision. 423 



hering to the surfaces of glass and water that has the property- 

 of reflecting light, and consequently there can be nothing unrea- 

 sonable in supposing that the luminous appearance of Saturn's 

 ring is produced by a similar fluid resting on his atmosphere : 

 and this opinion is the more probable, because it coincides in 

 every respect with the known laws of nature ; for we observe in 

 our own atmosphere that heavy bodies sink downwards towards 

 the earth, while light ones are lifted up by it ; and therefore to 

 suppose that this ring is produced by the reflection of any solid 

 body in that situation, and not by such a light substance as I have 

 imagined, is to suppose what is contrary to all analogy, and what 

 moreover is wholly uimecessary, as it can be proved that a fluid 

 is capable of producing the effect, while no such proof can be 

 adduced in favour of glass or crystal. 



If this hypothesis of the cause of the phaenoraenon of Saturn's 

 ring be admitted — and it is the only one analogy will warrant— 

 the phaenomenon confirms all I wish to establish concerning my 

 principle of reflection. Whatever may be the substance that reflects 

 this light, it proves that atmospheric air does not reflect light, be- 

 cause in that case the whole of Saturn's atmosphere would re- 

 flect light as well as this substance that reflects his ring ; and a$ 

 the light of the ring is reflected both ways, outwardly as well as 

 inwardly, if this substance be such a fluid as I have supposed, 

 the fluid adhering to the surface of glass may do so also ; and 

 then there can be no necessity for the agency of glass or water in 

 the reflection of light, any further than as these bodies attach to 

 themselves the fluid that does reflect light, and all the inconve- 

 niences attending that opinion are consequently avoided*. 



Having now fully proved that there is a fluid adhering to glass 

 and other mediums that has the proj)erty of reflecting light, it 

 may be worth while, before I commence my inquiries concerning; 

 the refraction of light, to endeavour to ascertain the cause of its 

 existence. The reader will however miderstand that what ! have 

 to pro))Ose is merely conjectural ; and if I should be mistaken iu 

 my opinion concerning the cause of the existence of this fluid, 

 my mistake cannot in any wise invalidate the principle that such 

 a fluid does exist, because the existence of it has been proved, 

 jiot upon the mere plea of a probable supposition, but by the 



• If the ring of Saliirn should be as I have supposed a fluid, and not a 

 fixture, we arc provided by it witl) a means of ascertaining the depth of 

 hui atmosphere ; for as all bodie-s with which we are acquainted are subject 

 to tiic laws of ;;ravity, this fluid could not remain where it i.-, unless there 

 was some substance imuiediatLly below it that ])revcntod its descent, and 

 that subxtance can be no otlicr than the atmosphere of Saturn. So that bj 

 drductinj^ the diameter of Saturn's bulk from the diameter of his ring, and 

 dividing the reinaiiid(;r, the gunj remaining will be th? amount of the depth 

 Cf )i;» atmospherf. 



evident 



