136 Britain's Heritage of Science 



From purely theoretical considerations, James Thomson was 

 able to predict that the freezing point of water must be 

 lowered by pressure. His starting point was that water 

 increases in volume on being converted into ice, and the 

 reasoning depends on an application of the second law of 

 thermodynamics. The fact itself was verified soon afterwards 

 by Lord Kelvin, and though the change in the freezing point 

 only amounts to three quarters of a degree Centigrade for 

 100 atmospheres, it yet plays an important part in the 

 behaviour of glaciers, for it explains the plasticity of ice 

 discovered by Forbes. The binding together of snow by 

 the pressure of the hand is also a consequence of the partial 

 melting by pressure, and solidification when the pressure is 

 removed. 



Scotland claims also Sir William Rowan Hamilton (1805- 

 1868) as one of its great men, though his life was spent in 

 Dublin, where his father a solicitor had settled as a 

 young man. The genius of men possessing exceptional 

 mathematical powers frequently shows itself at a very early 

 age, and Hamilton was no exception to this rule. But 

 even before he had an opportunity of discovering his own 

 powers in that direction, he showed a wonderful facility of 

 acquiring foreign languages. At the age of thirteen he 

 is reported to have learned Persian, Arabic, Sanskrit, and 

 Malay, besides the classical and modern European languages. 

 At the age of sixteen he had mastered Newton's " Principia " 

 and the " Differential Calculus," and soon after began a 

 systematic study of Laplace's " Mecanique Celeste." When 

 he was eighteen years old Dr. John Brinkley, the Astronomer 

 Royal for Ireland, is said to have remarked : " This young 

 man, I do not say will be, but is the first mathematician of 

 his age." He entered Trinity College, Dublin, but before he 

 had taken his degree, his career as a student was cut short 

 by his appointment to the Professorship of Astronomy at the 

 Dublin University, and he established himself at the Dunsink 

 Observatory. To all students of Mathematics and Physics, 

 " Hamilton's Principle " is known as one of the fundamental 

 instruments of dynamics, which may be applied to nearly all 

 natural phenomena. 



Hamilton's first investigation on " Systems of Rays " 



