98 THE WAVE THEORY OF LIGHT. 



nomona of thin plates prove that the luminous ray is put alternatively 

 in a certain state or tit of easy reflexion and of easy transmission. He 

 adds, however, that if an explanation of these alternative states is 

 required they can be attributed to the vibrations excited by the shock 

 of the corpuscles, and propagated under the form of a wave in ether. ^ 

 After all, notwithstanding his desire to remain on the firm ground 

 of facts, Newton can not help trying a rational explanation. He has 

 too carefully read the writings of Descartes not to be heartily, as 

 Huygens, a partisan of the universal mechanism and not to wish 

 sccretlv to find in the pure undulations the explanation of the beauti- 

 ful phenomena he has reduced to such simple laws. But his third 

 book on optics more especially proves his Cartesian aspirations, and, 

 above all, his perplexity. His famous Queries expose so forcibly his 

 argument in favor of the wave theory of light that Thomas Young will 

 later cite them as proof of the final conversion of Newton to the wave 

 theory. Newton would certainh" have yielded to this secret inclination 

 had the inflexible logic of his mind allowed him to do so; but when 

 after enumerating the arguments the wave theory of light offers in 

 explanation of the intimate nature of light, when he arrived at the 

 last "queries" he stops, as if seized by a sudden remorse, and throws 

 it away. And the sole argument is that he does not see the possi])ility 

 of explaining the rectilinear transmission of light.^ Viewed from this 



' Sir Ii?aac Newton, Opticks: or a Treatise of the Reflections, Refractions, Inflexions, 

 and Colors of Light. London, 1718. Second edition, with additions, p. 299. 



Tirst, here is an extract from the Queries which prove the leaning of Newton's 

 views toward the imdulatory theory and the Cartesian ideas. 



"Query 12: Do not the rays of light in falling upon the bottom of the eye excite 

 vibrations in the Tunica Retina? Whicji vibrations, being propagated along the 

 solid fibers of the optic nerves into the brain, cause the sense of seeing. * * * 



"Query 13: Do not several sorts of rays make vibrations of several l)igne.sses, 

 which, according to their bignesses, excite sensations of several colors, nmch after 

 the manner that the vibrations of the air, according to their several bignesses, excite 

 sensation of several sounds? And particularly do not the most refrangible rays excite 

 the shortest vibrations for making a sensation of deep violet, the least refrangible 

 the largest for making a sensation of deep red, etc.? * * * 



"Query 18: * * * Is not the heat of the warm room conveyed through the 

 vacuiun by the vilirations of a much subtiler medium than the air, which, after tlie 

 air was drawn out remained in the vacuum [etlier], and is not this medium the same 

 with that medium bj- which light is refracted and reflected, and by whose vibrations 

 light commmiicates heat to bodies, and is put into fits of easy reflection and easy 

 transmission? * * * And is not this medium exceedingly more rare and subtile 

 than the air, and exceedingly more elastic and active, and doth it not readily pervade 

 all bodies, and is it not (by its elastic force) expanded through all the heavens? 



Newton, afterwards, considers the possible connection of this medium (ether) with 

 the gravitation and the transmission of the sensations and motion in living creatures 

 (queries 19 to 2-4) . 



The dissymmetrical properties of the two rays propagated in the Iceland spar, draw 

 equally his attention (query 25 to 26) . 



Here appears this sudden and unexjiected going back, this sort of remorse from 



i 



