430 An Eisayon the Re/lection, Refraction, and Iiijlect'wn 



one of which reflects light, and the other refracts it, all the phae- 

 noniena of light in passing through a medium are explained, and 

 every difficulty vanishes. The rays of light that strike against 

 the reflecting substance are turned back from it, while those that 

 strike upon the refracting substance pass on to the other side, 

 where, according as ihey strike upon either substance, they are 

 reflected back into the medium or pass out altogether, being sub- 

 ject however at both surfaces to the law of efraction. I have 

 proved that this substance does exist, by showing that it can be 

 removed, and I have anticipated and answered every objection 

 that I can conceive can be brought against it. If anv other hy- 

 pothesis can be produced that will explain these phaenomena as 

 satisfactorily as mine has, I am jcadv to withdrav/ my preten- 

 sions : but if no such hypothesis can be produced, I exiect in 

 common justice that mine will be received as the true cause of 

 the reflection and refraction of light. 



Having now proved what the substance is that produces the 

 'reflection and refraction of light, it may be worth while, before I 

 quit this subject altogether, to make a \gv/ observations concern- 

 ing the nature of these phaenomena, or the manner in which they 

 act ; premising however, that if what I iiave to say should not 

 be satisfactory, it cannot aflfect the truth of my hypothesis, be- 

 cause every other system is equally obnoxious to the same ob- 

 jection, if it is to be considered in that light. The reader will 

 perhaps have observed that tlie substance in a medium that re- 

 flects light, reflects both ways, inwardly as well as outwardly, 

 but that the refracting substance refracts onlv on the outside; 

 for if it was otherwise, one refraction woidd counteract the other, 

 and the direction of the rav would not be at all altered. The 

 only way I can account for this, is by supposing that the power 

 of retracting light is not in the substance itself, but in an efflu- 

 vium that CKudes from it, and which always proceeds one way, 

 that is, outside into the air, not inwards towards the glass. This 

 opinion, while it is sufficieut to account for the phanouicnon, is 

 b_\' no means iniproliable, for the thagnet attracts only at one end, 

 and therefore this substance may do the same. Admitting this, 

 it cannot at all aifcct my system whether attraction be an eflflu- 

 vium or i;ot; but there is good reason to believe that it is, be- 

 cause it is only in this way that we can account for bodies feeling 

 the influence of attraction when thev are at a distance from the 

 attracting body. Refraction then in all probability is caused 

 by an eflfiuvium issuing from the refracting substance, that attracts 

 the rays of light the moment they arc within reach of its power, 

 which however barely extends beyond the surface of the refract- 

 ing substance. Reflection, on the contrary, i» best explained 

 without supposing any such effluvium ; most likely it is passive 



and 



