428 An Essay on the Reflection, Refraction, and Infleciion . 



grounded on analogy, or on any acknowledged principle in the 

 laws of nature ; it is in fact nothing more than an opinion sup- 

 porting an opinion, and conseqijentlv affords no proof of the truth 

 of the position. Stones falling upon vv;iter certainly do cause 

 undulations in the water; hut there is no instance of a stone be- 

 ing lifted up bv these undulations, and therefore this is no proof 

 that light may be reflected by the undulations of a medium. It 

 is moreover contrary to every principle in nature, to suppose that 

 a medium which suffers one ray to pass through it, should be 

 able to turn the next back, merely because the substance of 

 which it is composed is put iu motion by the admission of the 

 first rav, — a circumstance which implies weakness rather than 

 strength, — for the rarer any substance is, the more easily it is put 

 in motion. It is contrary also to every principle, to suppose that 

 the returning vibrations should be so exactly proportioned to the 

 velocity of light, as to cause the rays to turn back in angles that are 

 always equal to the angles of incidence, — a j)hacnomenon which 

 can only be explained by supposing the substance to be stationary 

 that produces the reflection. Neither can any reason be assigned 

 why vibrntions, which are excited in the medium by the percus- 

 sion of the rays of light, should be able to overtake the ray after 

 it has passed through, and increase its velocity; for there is no 

 iijstance of a stone being overtaken in the water by the vibrations 

 occasioned by its percussion, and the velocity of light is infinitely 

 greater than any thing with which vve are acquainted. No rea- 

 son, again, can be assigned why the reflection of light should be 

 always on the two surfaces, and never happen in the interior oF 

 the medium let the medium be of what thickness it may; and 

 not only are all these arguments unsupported by any principle, but 

 the fact itself, even if the principle were true, is mis-stated. 



Sir Isaac Newton calls his fits of easy reflection and refraction 

 alternate ; says, " this action or disposition intermits and returns 

 bv equal intervals," and has given a scale of alternate numbers, 

 13 5 7 9 — 2 4 () 8 10, to show at what distances the ray is 

 disposed to be reflected or transmitted. Now if we look through 

 a pane of glass at any object, the glass hardly intercepts any 

 light at all, at least we do not discover any diminution or faint- 

 ness in the colours ; but the images of objects reflected from glass 

 arc always very faint, so much so, that we are obliged to silver 

 OLsr looking-glasses, in order to make thenj throw out a greater 

 body of light. From this it is evident that at least twenty 

 of the rays must pass through for one that is reflected; and it is 

 surely begging the question, and not argument, to su|)pose that 

 these vibrations will suffer nineteen of the ravs to pass on, and 

 then dispose the twentieth to be easily reflected. 



Newton, in all probability, conceived that every part of a inc- 



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