THE DEVELOPMENT OF MECHANICS 245 



of view, introduced by Gascoigne and Auzout not long after. 

 It was the combination of these which made possible the un- 

 dreamed-of precision attained by Cassini and all his long line 

 of successors. 



Huyghens was not merely an inventor of clocks and a grinder 

 of beautiful lenses ; he was an astronomer and a thinker. With 

 the telescopes of immense length which he constructed, he was 

 able to discover the first satellite of Saturn and likewise clearly 

 to reveal Saturn's rings. The discovery of the latter was like- 

 wise made before he was thirty, and published by him in an 

 elaborate study. He made profound investigations into the 

 nature of light ; he was the founder of the undulatory theory. 

 He had a wonderfully incisive mind, but an unbridled imagi- 

 nation as well. The fantastic Cosmotheoros, wherein he sets 

 down his wild speculations as to the inhabitants of other planets 

 and a hundred other things, reads like Kepler's S omnium 

 Astronomicum. YOU catch a glimpse of the survival of medieval 

 traditions, even to this late day, from his remark when he dis- 

 covers Saturn's satellite. It is his idea that the number of 

 planets and satellites having now reached twelve, and this 

 being the perfect number, no more remained to be discovered. 

 He would be puzzled, no doubt, could he return now to learn 

 of five hundred more found since his day. 



Beyond doubt Huyghens' most noteworthy work was his 

 Oscillatorium Horologium, published in 1673. Therein he de- 

 scribes in full the pendulum clock, and with it a number of 

 important investigations into the theory of the pendulum and 

 the allied problems of the motion of bodies in a curve. It was 

 in this treatise that he announced the law of centrifugal force, 

 obtaining a numerical measure for the tendency of a body 

 moving in a circle to recede from the centre. He worked this 

 out quite independently of any considerations of planetary 

 motion. It was with him a simple problem in mechanics. 

 He seems never to have thought of extending this prin- 

 ciple to the motion of the bodies he had studied so successfully 

 and so well. He was upon the very edge of the discovery 

 of the law of gravitation. He made distinct contributions to 

 the developing science of mechanics ; he had an essentially 

 mechanical mind, and half his life he had spent in the study 

 of planetary motion. But so far was he from realising the 



