340 PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 



deposited on the dust in the atmosphere, he determined the num- 

 ber of particles in a given volume of air, and so the charge and 

 mass of each particle. These results, especially the value of the 

 ratio, m/e, were confirmed in a variety of ways. The most direct 

 and probably the most accurate, determination of the electric 

 charge was that of Millikan, who in 191 1 succeeded in catch- 

 ing electrons on minute drops of oil floating in the air, and in 

 observing with a microscope their behavior in a strong electric 

 field. The charge on each oil-drop was found to be always of 

 a given value or an exact multiple of this value, the amount 

 agreeing in general with the results obtained by Thomson and 

 others. It was evident that electricity was not a continuous fluid, 

 or an ether strain, but existed in discrete separated particles. 

 An atom of electricity became as definite an idea as an atom 

 of matter. 



The mass of the particles which in the cathode rays act as 

 carriers for the electric charges could now be determined. It 

 turned out to be always the same, whatever the nature of the 

 cathode from which it was expelled, not- a particle or atom of 

 any known element, but a thing sui generis, nearly two thousand 

 times smaller than an atom of hydrogen, the lightest atom known. 

 With regard to this particle a new c^uestion now arose. Sir 

 Joseph Thomson had shown years before that the addition of 

 an electric charge tO' a moving body had the effect of increasing 

 the apparent mass of the body, by an amount dependent on the 

 added charge and the speed of the motion. Since these quan- 

 tities — charge, mass, velocity, — are all known with regard to 

 the cathode-ray particles (or electrons, as they were, now 

 called). Thomson's theory could be experimentally tested. Kauf- 

 mann, and afterward Bucherer made the experiments, showing 

 conclusively that the mass of an electron varies with its speed, 

 in a manner exactly concordant with the supposition that the 

 mass is entirely due to the moving electric charge, that is, that 

 the electron is not material at all, but is a free atom of electricity. 

 Since the electrons are obtained, not by means of the cathode 

 rays alone, but by many processes of ionisation, they must be 

 constituent parts of all atoms, which are thus shown to be com- 



