PRESIDENTIAL ADDRESS SECTION A. 35 



these have to take the risk of heresy. We know that in New- 

 ton's case this binding down of posterity was against all his 

 instincts. He claimed to confine himself exclusively to " actual 

 facts " ; he disliked and avoided " hypotheses " : yet in " Corol- 

 laries to the great laws,'' on which have l^een built all our 

 Exact Sciences, he dropped into unguarded statements on 

 " absolute time '" and " space " and " motion," which have, per- 

 haps, hitherto ke])t us out of the very middle of the current of 

 truth. 



The Science of Mechanics is founded on the following 

 events: Copernicus, a. quiet monk from East Prussia (147310 

 1545), published arguments which very gradually convinced the 

 thinking world that the Earth was a planet and moved round 

 the Sun. 



Kepler, of Wurtemberg (1571 to 1630), after a lifetime of 

 guessing in twilight at the laws of motion of the planets, dis- 

 covered that (contrary to all the accepted Aristotelian theories) 

 the planets moved in ellipses with the Sun at one focus (not in 

 circles) and obeyed two other laws. 



Galileo (1564-1642), Professor of Mathematics at Pisa 

 and Padua, in 1609 invented the telescope, and later the micro- 

 scope. He had to face the Inf|uisition for his " heretical '' views 

 on the Earth's motion. (He was a devout Catholic: the heresy 

 was not against Christianity, but against the ])revailing Aristote- 

 lian philosophy). He had to retract; and, broken in health and 

 later blind, he retired to Arcetri and worked out the laws of 

 motion. He had used the famous leaning tower of Pisa to 

 denionstrate that all l)odies fall at the same rate, the resistance 

 of the air explaining apparent anomalies ; but the end of his 

 life he devoted to the scientific formulation of the laws accord- 

 ing to which motion takes place. It seems strange that such a 

 task should be found undone at such a late date in civilization; 

 hut we must remember that printing only dates from 1455, that 

 the Arabic notations in arithmetic was not established in Europe 

 before 1300. and symbolical algebra not before 1600. (Galileo's; 

 greatest feat consisted in grasping and enunciating the law of 

 inertia — that the normal state of a free body is permanent 

 motion in a straight line with tmiform velocity. This was the 

 generalized result of his proof by means of inclined planes that 

 the velocity of a falling body is proportional to its time of falling, 

 and that in conseciuence the distance fallen is proportional to 

 the square of the time. He obtained this law with the help of 

 an informal axiom that a body canot be made, by moving down 

 and up inclined planes, to rise higher than its starting point. 



Nezvton (not improbably "the finest intellect in history") 

 was lx)rn in the year of (ialileo's death (1642) ; he completed the 

 work begun by (jalileo by establishing the laws of motion in the 

 form in which we know them to-day. and bv them deduced 

 from Kei^ler's astronomical data the true motion of the solar 

 system and the law- of gravitation. But between Galileo and him 

 come two men to whom the Science of Mechanics owes much — 



