THE SUCCESSORS OF GALILEO 



course, came to nothing, but go to show the fertile 

 imagination of the man, and his tireless energy. He 

 experimented with electricity and made some novel 

 suggestions upon the difference between the electric 

 spark and the glow, although on the whole his con- 

 tributions in this field are unimportant. He also first 

 pointed out that the motions of the heavenly bodies 

 must be looked upon as a mechanical problem, and was 

 almost within grasping distance of the exact theory of 

 gravitation, himself originating the idea of making use 

 of the pendulum in measuring gravity. Likewise, he 

 first proposed the wave theory of light ; although it was 

 Huygens who established it on its present foundation. 



Hooke published, among other things, a book of 

 plates and descriptions of his Microscopical Observa- 

 tions, which gives an idea of the advance that had 

 already been made in microscopy in his time. Two 

 of these plates are given here, which, even in this age 

 of microscopy, are both interesting and instructive. 

 These plates are made from prints of Hooke' s original 

 copper plates, and show that excellent lenses were 

 made even at that time. They illustrate, also, how 

 much might have been accomplished in the field of 

 medicine if more attention had been given to micros- 

 copy by physicians. Even a century later, had 

 physicians made better use of their microscopes, they 

 could hardly have overlooked such an easily found 

 parasite as the itch mite, which is quite as easily de- 

 tected as the cheese mite, pictured in Hooke' s book. 



In justice to Hooke, and in extenuation of his other- 

 wise inexcusable peculiarities of mind, it should be 

 remembered that for many years he suffered from a 



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