182 Britain's Heritage of Science 



which appears near the negative electrode. Important 

 results were obtained in these researches. Investigations by 

 other observers which cannot here be described, led to the 

 conclusion that gases, which ordinarily are insulators, could 

 in various ways be made to conduct electricity, and the 

 phenomena suggested that the conductivity was due to the 

 formation of carriers analogous to the ions which normalty 

 exist in liquids. Gases, in fact, could be ionized. The 

 stage was now reached where experiments definitely pointed 

 to the conclusion that electricity, like water, had an atomic 

 constitution. To furnish the proof, it was necessary to 

 show that the atomic charge was the same in all cases. The 

 experiments with liquids gave no direct measure of this 

 charge, but they allowed us to determine its ratio to the 

 mass of the carrier. That carrier in liquids is the chemical 

 atom, and it was natural at first to suppose that the same 

 would be the case in gases ; if so, the matter could be tested, 

 as we know the relative masses of different chemical atoms. 

 The first experiments made in that direction led to no 

 decisive results, though they supplied a method which proved 

 useful. The question was finally solved by Sir Joseph 

 Thomson, who proved that the carrier of negative electricity 

 had a mass much smaller than that of a chemical atom; 

 ultimately it was found that, near the kathode of an electric 

 discharge through gases, it is actually the atom of negative 

 electricity which is set free, and acts as carrier. 



Thomson further determined the charge of the electron, 

 the name given to the atom of electricity by Johnstone 

 Stoney (see p. 139), and found it to agree with that which 

 may indirectly be derived from the electrolysis of liquids. 



There can be no doubt that Sir Joseph Thomson's ex- 

 periments will be looked upon in future as a landmark in 

 the advance of science as great as those that have been 

 described in our first chapter. % 



Thomson's discovery was announced ~ at the British 

 Association meeting of 1899. Since then our ideas have 

 advanced rapidly, and we now consider corpuscles of positive 

 and negative electricity to be the elemental atoms from which 

 all ^matter is built up. In the origination and development 

 of this theory Sir Joseph Larmor has taken an active part. 



