34 Britain's Heritage of Science 



average. Through mutual collisions or otherwise, each 

 particle constantly changes its velocity both in magnitude 

 and direction, and it becomes important to determine the 

 law regulating the distribution of velocities. Maxwell's 

 classical investigation of this difficult problem has since 

 been modified in detail and extended, but the manner in 

 which he attacked it introduced an entirely novel method of 

 applying mathematical reasoning to physical phenomena. 

 Its results were decisive, and led to the discovery of new 

 experimental facts connected with the internal friction of 

 gases. When a metal disc is suspended from a wire passing 

 through its centre so that the plane of the disc is horizontal, 

 a twist imposed on the wire will cause the disc to perform 

 oscillations in its own plane, which diminish in magnitude 

 and gradually disappear owing to the internal friction of 

 the gas surrounding it. Maxwell's calculations Jed to the 

 unexpected result that this retarding effect should be the 

 same whatever the pressure of the gas, so that air at a 

 pressure of a few millimetres should diminish the motion of 

 the disc as rapidly as when it is at atmospheric pressure. 

 This surprising result was tested experimentally and found 

 to be correct. 



We are naturally interested in the personal history of 

 those who have initiated new departures in science, and it 

 is more especially instructive to record the character of their 

 early education and the conditions under which they accom- 

 plished their work. Without entering into biographical 

 details, we may briefly state, so far as they have not already 

 been given, the essential facts in the lives of the great men 

 whose achievements have formed the subject of this chapter. 



Isaac Newton, the posthumous son of a small freehold 

 farmer in Lincolnshire, is reported to have been like Kepler 

 a seven months' child. While attending school at Grantham, 

 he showed little disposition towards book learning, but 

 great aptitude for mechanical contrivances, and he amused 

 himself with the construction of windmills, water clocks, and 

 kites. Not being considered fit to be a farmer, he was 

 sent to the University of Cambridge in 1661, on the recom- 

 mendation oi an uncle who was a graduate of Trinity College. 

 He does not seem to have received much inspiration from 



