INSTRUMENTS OF PRECISION 



have been given the credit of the invention at dif- 

 ferent times. It would seem from certain papers, now 

 in the library of the University of Ley den, and in- 

 cluded in Huygens's papers, that Lippershey was 

 probably the first to invent a telescope and to describe 

 his invention. The story is told that Lippershey, who 

 was a spectacle-maker, stumbled by accident upon the 

 discovery that when two lenses are held at a certain 

 distance apart, objects at a distance appear nearer 

 and larger. Having made this discovery, he fitted 

 two lenses with a tube so as to maintain them at 

 the proper distance, and thus constructed the first 

 telescope. 



It was Galileo, however, as referred to in a preced- 

 ing chapter, who first constructed a telescope based on 

 his knowledge of the laws of refraction. In 1609, hav- 

 ing heard that an instrument had been invented, con- 

 sisting of two lenses fixed in a tube, whereby objects 

 were made to appear larger and nearer, he set about 

 constructing such an instrument that should follow 

 out the known effects of refraction. His first tele- 

 scope, made of two lenses fixed in a lead pipe, 

 was soon followed by others of improved types, 

 Galileo devoting much time and labor to perfecting 

 lenses and correcting errors. In fact, his work in 

 developing the instrument was so important that the 

 telescope came gradually to be known as the " Galilean 

 telescope." 



In the construction of his telescope Galileo made 

 use of a convex and a concave lens; but shortly after 

 this Kepler invented an instrument in which both 

 the lenses used were convex. This telescope gave a 



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