THE PROGRESS OF SCIENCE AS EXEMPLIFIED IN THE 

 ART OF WEIGHING xVND MEASURING.* 



By Prof. William Haiikxess, U. *'. Xaval Olmrvatorij. 



Two centuries ago the work! was juist begiuning- to awaken from an 

 intellectual lethargy which had lasted a thousand years. During all 

 that time the children had lived as their parents before them, the 

 mechanical arts had been at a standstill, and the dicta of Aristotle had 

 been the highest authority in science. But now the night of mediteval- 

 ism was approaching its end, and the dawn of modern i^rogress was at 

 hand. Galileo had laid the foundation for accurate clocks, by discover- 

 ing the isochronism of the simple pendulum; had proved that under the 

 action of gravity, light bodies fall as rapidly as heav y ones; had invented 

 the telescope and with it discovered the spots on the sun, the moun- 

 tains on the moon, the satellites of Jupiter, and the so-called triple 

 character of Saturn ; and, after rendering himself immortal by his advo- 

 cacy of the Copernican system, had gone to his grave, aged, blind, and 

 full of sorrows. His contemporary, Kepler, had discovered the laws — 

 which while history endures, will associate his name with the theory 

 of planetary motion ; and he also had passed away. The tirst Cassiui 

 was still a young man, his sou was a little child, and his grandson and 

 great-grandson, all of whom were destined to be directors of the Paris 

 Observatory, were yet unborn. The illustrious Huyghens, the discov- 

 erer of Saturn's rings, and the father of the undulatory theory of light, 

 was in the zenith of his powers. The ingenious Hooke was a little 

 younger, and Newton, towering above them all, had recently invented 

 fluxions, and on the 28th of April, 1686, had presented his Priucipia 

 to the Royal Society of London and given the theory of gravitation to 

 the world. Bradley, who discovered nutation and the aberration of 

 light; Franklin, the statesman and philosopher, who first drew the 

 lightning from the clouds; DoUond, the inventor of the achromatic tol- 

 escoj)e; Euler, the nuithenuitician who was destined to acicomplish so 

 much in perfecting algebra, the calculus, and the lunar theory; Laplace, 

 the author of the Mecanique Celeste; Rnmford, who laid the founda- 



*Presideutial address delivered before the Philosophical Society of Washiugtou, 

 December 10, 1887. (Bulletin Phil. Soc., vol. x, pp. xxxix-lxxxvi.) 



r)97 



