286 A SHORT HISTORY OF SCIENCE 



Highness than to my small efforts, since I should only have been able 

 to boast of having conceived it, while it owes its birth absolutely to 

 the honor of your commands. The length and difficulty of the ordi- 

 nary means in use have made me think on some help more prompt and 

 easy to relieve me in the great calculations with which I have been 

 occupied for several years in certain affairs which depend on the 

 occupations with which it has pleased you to honor my father for the 

 service of his Majesty in Normandy. I employed for this investi- 

 gation all the knowledge which my inclination and the labor of my first 

 studies in mathematics have gained for me, and after profound re- 

 flection, I recognized that this aid was not impossible to find. 



MECHANICS AND OPTICS : HUYGENS. Most notable among 

 the successors of Galileo in mechanics before we reach Newton 

 was Huygens of Holland (1629-1695) who combined mathematical 

 power with exceptional practical ingenuity. He first (in 1655) 

 explained as a ring the excrescences of Saturn which had been 

 misunderstood by Galileo and others, publishing his discovery in 

 the occult form a 7 c 5 d l e 5 g l h l i 7 l 4 m 2 n g o 4 p 2 q l r 2 s l t 5 u 5 . (Annulo cingitur 

 tenui, piano, nusquam coh&rente ad eclipticam inclinato.) He also 

 discovered Saturn's largest moon. About the same time he made 

 his great invention of the pendulum, clock. Accepting a call to 

 Paris by Colbert at the founding of the French Academy, he 

 remained there from 1666 to 1681. 



In optics he developed and maintained even in opposition to 

 the authority of Newton the undulatory or wave theory which 

 only found general acceptance a century later. The velocity of 

 light Galileo had failed to measure by means of signal lanterns, 

 and Descartes had likewise been unable to ascertain it by compar- 

 ing the observed and computed instants of a lunar eclipse. 

 Huygens points out that even this latter test does not prove in- 

 stantaneous transmission. Romer's conclusive report on observa- 

 tions of a satellite of Jupiter dates from 1675. On this basis 

 Huygens estimated the velocity of light at 600,000 times that of 

 sound, a result about one-third too small. 



The medium in which light waves travel Huygens named the 

 ether, attributing to its particles three properties in comparison 



