THE SIZE OF ATOMS. 163 



article which was published thirteen years ago 

 in Nature}- 



" Now let a second plate of zinc be brought 

 by a similar process to the other side of the plate 

 of copper ; a second plate of copper to the remote 

 side of this second plate of zinc, and so on till a 

 pile is formed consisting of 50,001 plates of zinc 

 and 50,000 plates of copper, separated by 100,000 

 spaces, each plate and each space i/ioo,oooth of 

 a centimetre thick. The whole work done by 

 electric attraction in the formation of this pile 

 is two centimetre-grammes. 



" The whole mass of metal is eight grammes. 

 Hence the amount of work is a quarter of a centi- 

 metre-gramme per gramme of metal. Now, 4030 

 centimetre-grammes of work, according to Joule's 

 dynamical equivalent of heat, is the amount re- 

 quired to warm a gramme of zinc or copper by 

 one degree Centigrade. Hence the work done 

 by the electric attraction could warm the substance 

 by only i/i6,i2Oth of a degree. But now let the 



1 See article " On the Size of Atoms," published in Nature, 

 vol. i. p. 551 ; printed in Thomson and Tail's Natural Philosophy, 

 Second Edition, 1883, vol. i. part II, Appendix F. 



M 2 



