A HISTORY OF SCIENCE 



cloud, Professor Thompson was able to find the volume 

 of the drops and thence the number of particles. The 

 number of particles being known, the charge of elec- 

 tricity carried by each could be determined, as already 

 suggested. Experiments were made with air, hydro- 

 gen, and carbonic acid, and it was found that the par- 

 ticles had the same charge in all of these gases. "A 

 strong argument," says Professor Thompson, " in favor 

 of the atomic character of electricity." When we add 

 that the charge in question was found to be the same 

 as the unit charge of an ion in a liquid, it will be seen 

 that the experiment has other points of interest and 

 suggestiveness. 



Even more interesting in some regards were the re- 

 sults of computation as to the actual masses of the 

 charged particles in question. Professor Thompson 

 found that the carrier of a negative charge could 

 have only about one-thousandth part of the mass of a 

 hydrogen atom, which latter had been regarded as the 

 smallest mass able to have an independent existence. 

 Professor Thompson gave the name corpuscle to these 

 units of negative electricity; they are now more 

 generally termed electrons. "These corpuscles," he 

 says, "are the same however the electrification may 

 have risen or wherever they may be found. Negative 

 electricity in a gas at a low pressure has thus a struct- 

 ure analogous to that of a gas, the corpuscles taking 

 the place of the molecules. The 'negative electric 

 fluid,' to use the old notation, resembles the gaseous 

 fluid with a corpuscular instead of a molecular struct- 

 ure." Professor Thompson does not hesitate to de- 

 clare that we now "know more about 'electric fluid' 



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