NEWTON AND COMPOSITION OF LIGHT 



I observed that by turning it a little about its axis to 

 and fro, so as to vary its obliquity to the light more 

 than an angle of 4 or 5, the colors were not thereby 

 sensibly translated from their place on the wall, and 

 consequently by that variation of incidence the 

 quantity of refraction was not sensibly varied. By 

 this experiment, therefore, as well as by the former 

 computation, it was evident that the difference of 

 the incidence of rays flowing from divers parts of the 

 sun could not make them after decussation diverge 

 at a sensibly greater angle than that at which they 

 before converged; which being, at most, but about 

 31 'or 32', there still remained some other cause to be 

 found out, from whence it could be 2 49'." 

 . All this caused Newton to suspect that the rays, after 

 their trajection through the prism, moved in curved 

 rather than in straight lines, thus tending to be cast 

 upon the wall at different places according to the 

 amount of this curve. His suspicions were increased, 

 also, by happening to recall that a tennis-ball some- 

 times describes such a curve when "cut" by a tennis- 

 racket striking the ball obliquely. 



" For a circular as well as a progressive motion 

 being communicated to it by the stroke," he says, 

 "its parts on that side where the motions conspire 

 must press and beat the contiguous air more violently 

 than on the other, and there excite a reluctancy and 

 reaction of the air proportionately greater. And for 

 the same reason, if the rays of light should possibly 

 be globular bodies, and by their oblique passage out of 

 one medium into another acquire a circulating motion, 

 they ought to feel the greater resistance from the 



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