THE SUCCESSORS OF GALILEO 



thus formed edged with a fringe of color and indistinct. 

 Bui, fortunately for the early telescope makers, the 

 degree of this aberration is independent of the focal 

 length of the lens; so that, by increasing this focal 

 length and using the appropriate eye-piece, the image 

 can be greatly magnified, while the fringe of colors re- 

 mains about the same as when a less powerful lens is 

 used. Hence the advantage of Huygens's long tele- 

 scope. He did not confine his efforts to simply length- 

 ening the focal length of his telescopes, however, but 

 also added to their efficiency by inventing an almost 

 perfect achromatic eye-piece. 



In 1663 he was elected a fellow of the Royal Society 

 of London, and in 1669 he gave to that body a concise 

 statement of the laws governing the collision of elastic 

 bodies. Although the same views had been given by 

 Wallis and Wren a few weeks earlier, there is no doubt 

 that Huygens's views were reached independently; 

 and it is probable that he had arrived at his con- 

 clusions several years before. In the Philosophical 

 Transactions for 1669 it is recorded that the society, 

 being interested in the laws of the principles of motion, 

 a request was made that M. Huygens, Dr. Wallis, and 

 Sir Christopher Wren submit their views on the sub- 

 ject. Wallis submitted his paper first, November 15, 

 1668. A month later, December iyth, Wren imparted 

 to the society his laws as to the nature of the collision 

 of bodies. And a few days later, January 5, 1669, 

 Huygens sent in his " Rules Concerning the Motion of 

 Bodies after Mutual Impulse." Although Huygens's 

 report was received last, he was anticipated by such a 

 brief space of time, and his vews are so clearly stated 



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