22 An Essay on the Reflection) Refraction, and Inflection 



in an exhausted receiver full as much as it does after the air H 

 let in ; and consequently, as light is reflected in the absence* of 

 the air, and after it has passed through glass, the reflection of 

 light, at least in this case, cannot be owing to either of these 

 bodies, but must be produced by some other substance which is 

 independent of both. 



There is evidently then a fluid adhering to the surface of glass— 

 and by analogy we may suppose to every other medium producing 

 the same eflfect — that, whatever connexion it might originally 

 have had with the air, is so far independent of air that it remains 

 attached to the surface of glass in a receiver where the air is ex- 

 hausted, and it possesses the property of reflecting light, which 

 does not belong to the air in general. 



That it is this fluid that reflects light inwardly from the further 

 surface of the medium, is a position that cannot, after these proofs, 

 be disputed with any show of reason ; and although we can get 

 at no positive proof of the fact, there is every presumption that 

 it is this fluid also, and not the glass, that reflects light outwardly 

 from the first surface ; because, as I before observed, all the par- 

 ticles of glass possess the same nature; and if the particles on the 

 surface of glass reflected the rays of light, those rays that pass 

 through would be reflected by the particles in every succeeding 

 stratum ; which is evidently contrary to fact : for it is< only by 

 supposing that the reflection of light is confined to the surface of 

 glass that we can account for the image being so distinct. AU 

 this difficulty is removed by supposing that it is the substance 

 adhering to glass that produces this effect ; and surely no fair 

 reason can be assigned why it should not reflect light one way, 

 when it can be proved by positive fact that it does the other 

 way ; and that it does do so, is confirmed by the third class of 

 argument I was to adduce in the phaenomenon of Saturn's ring. 



3. This luminous ring has excited the attention of the philo- 

 sopher ever since it was first discovered, and various hypotheses 

 have been formed in order to account for its appearance. For^ 

 innately for my principle, it at once serves to explain and is con- 

 firmed by the phjenomenon. The only philosophical way to ac- 

 count for phaenomena which are out of our reach, is to prove by 

 analogy that such phaenomena may be produced by the cause we 

 have assigned ; that is, that the same causes do actually produce 

 similar effects in instances that are within the reach of our ex- 

 periments. Now I have already proved that there is a fluid ad- 



* The air cannot be entirely exhausted in a receiver, but it may be niad^ 

 ten thousand times rarer than it was before ; and consequently the power 

 of reflecting light, if it belonged to the air, should be ten thousand times 

 less than it was before, and the image reflected by it ten thousand times 

 fiointcr. 



Uering 



