ELECTRIC DISCHARGE IN GASES 113 



Maxwell, Clausius, and Willard Gibbs belong to more recent 

 times. And the sum of their work is the principle of the Con- 

 servation of Energy which, with the Conservation of Matter, lies 

 at the foundation of all physical science, including chemistry. 

 These two fundamental propositions are now regarded as practi- 

 cally axiomatic, and are not likely to undergo serious modifica- 

 tion or correction as the result of further research. On the other 

 hand, conceptions relating to the Atomic Theory, the pro- 

 cess of electrolysis, and the nature of chemical action have 

 undergone very important developments within the present 

 generation, and the general nature of present views will be 

 explained in the following chapters. 



CHAPTER V 

 ELECTRIC DISCHARGE IN GASES-ELECTRONS 



THE smallest part of any substance capable of independent 

 existence is called a molecule, and according to Avogadro's 

 law already quoted the number of molecules in a given volume 

 of any gas, under like conditions, is the same, and is independent 

 of the composition of the gas. It requires a little thought to 

 realise how tiny are these particles and how many there are 

 crowded together in any small portion of a gas. In gases also 

 they are much further apart than in a liquid or solid. As to 

 their size no better idea can be conveyed than in the words of 

 Lord Kelvin in a lecture at the Royal Institution in 1883. He 

 says : " To form some conception of the degree of coarse-grained- 

 ness indicated imagine a globe of water or glass, as large as a 

 football (or say a globe 16 centimetres diameter) to be magnified 

 up to the size of the earth, each constituent molecule being 

 magnified in the same proportion. The magnified structure 

 would be more coarse-grained than a heap of small shot, 

 but probably less coarse-grained than a heap of foot- 

 balls." 



To express their number in any visible portion of matter is 

 even more difficult. But as the result of the application of a 

 considerable number of different methods it may be stated that 

 it has been estimated that I cubic centimetre of air. under 



