THE WAVE THEORY OF LIGHT. 99 



.standpoint the third book of Optics is no longer only an impartial 

 discussion of opposite systems; it appears as the painting- of the suf- 

 fering of a mighty genius, worried by doubt, now led awa}' by the 

 seductive suggestions of his imagination, now recalled by the impe- 

 rious requirements of logic. It is a drama: the everlasting struggle 

 between love and duty; and duty won. 



Such, I take it, is the inner genesis of the theor}^ of fits — a strange 

 mingling of two opposite systems. It was much admired, presented, 



having too kindly expounded the resources of the Cartesian theory, based on the 

 plenum; he makes an apology as follows: 



"Query 27: Are not all hypotheses erroneous which have hitherto been invented 

 for explaining the phenomena of light by new modifications of the rays? * * * 



"Query 28: Are not all the hypotheses erroneous in which light is supposed to 

 consist in pression or motion, propagated through a fluid medium? * * * and if 

 it (light) consisted in pression or motion, propagated either in an instant or in time, 

 it would bend into shadow. For pression or motion can not be propagated in a fluid 

 in right lines beyond an obstacle which stops part of the motion, but will bend and 

 spread every way into the quiescent medium which lies beyond the obstacle. * * * 

 For a bell or a cannon may be heard beyond a hill which intercept the light of sound- 

 ing body, and sounds are propagated as readily through crooked pipes as through 

 straight ones. But light is never known to follow crooked passages nor to bend into 

 the shadow. * * *" 



Stopping before this objection Newton is forced to come back to the corpuscular 

 theory. 



"Query 29: Are not the rays of light very small bodies emitted from shining sub- 

 stances? * * * 



"Query 30: Are not gross bodies and light convertible into one another * * *? 

 The changing of bodies into light and light into bodies is very conformable to the 

 course of nature, which seems delighted with transmutations. * * *" 



Logic urges him to go on with the old hypothesis of the vacuum and atoms, and 

 even to invoke the axithority of the Greek and Phcenician philosophers in this mat- 

 ter (query 28, p. 343), therefore it is not surprising to see his perplexity expressed 

 l)y the following words: 



"Query 31, and the last: Have not the small particles of Ijodies certain powers, 

 virtues, or forces, bj^ which they act at a distance, not only upon the rays of light for 

 reflecting, refracting, and inflecting them, but also ujion one another for producing 

 a great part of the phenomena of nature? * * *" 



But he perceives that he is going rather far and compromising himself, therefore 

 his secret tendency, developed in the foremost cjueries, reappear a little while: 



<<* * * How these attractions may be performed I do not here consider. What 

 I call attraction may be performed T)y impulse or by some other means mikiiown to 

 me. * * *" 



INIany other curious remarks could l)e made on tlie state of mind of the great 

 physicist, goemeter, and philosopher, whit;h is artlessly revealed in those "(jueries." 

 The preceding short extracts are sufficient, I believe, to justify the conclusion which 

 I get from the study of the third book, namely, that Newton had not at all on the 

 mechanism of light the definite ideas which have been attributed to him as founder 

 of the emission theory. Really, he is hesitating between the two opposite systems, 

 perceiving clearly their insufiiciency; and in this discussion he is endeavoring to go 

 away as little as possible from the facts. That is the reason for which he has stated 

 no dogmatic theory. It would be, therefore, unjust to make Newton resi)onsihIe 

 for every consequence which the emission partisans haveshelted under his authority. 



