186 BIOGKAPHIES OF SCIENTIFIC MEN 



was not more than twenty million years old, and would 

 not probably sustain life more than ten million years 

 longer ; for in that time the sun would be cool, and 

 therefore organic life on this planet would be impossible. 



In conjunction with the late Professor P. G. Tait, 

 he, in 1867, produced a classical work on Natural 

 Philosophy. He devoted a vast amount of time in 

 studying the constitution of matter the sizes of atoms 

 and molecules, and the force which holds them together. 

 Thomson came to the conclusion from examining the 

 thickness of the wall of a soap bubble, the electrical 

 action of small copper and zinc discs, the refraction of 

 light, and the dynamical theory of gases, that the 

 molecules of air are about large enough to put twenty- 

 five millions of them in a row an inch long. " Imagine 

 a globe of water six inches in diameter magnified to the 

 size of the earth, and its molecules in the same pro- 

 portion ; then, when the drop had become a world, the 

 individual particle would be about the size of small shot, 

 certainly not larger than a football." These calculations 

 were before the discovery of the corpuscular radiations of 

 radium, polonium, actinum, etc., which the experimental 

 researches of Professor J. J. Thomson, of the Cavendish 

 Laboratory, Cambridge, proved to be at least a thousand 

 times smaller than the chemical atom ; although the 

 calculations of Lord Kelvin concerning the atom still 

 remain true. He did not care for the latter-day work 



