26 PHYSICS 



temporarily imparted by friction or other process, is a fundamental 

 property of matter. According to this newer conception of matter, 

 the fruit of the ionic theory, the ultimate parts of matter are elec- 

 trically charged particles. In the language of Rutherford: * 



"It must then be supposed that the process of ionization in gases 

 consists in a removal of a negative corpuscle or electron from the 

 molecule of gas. At atmospheric pressure this corpuscle immediately 

 becomes the centre of an aggregation of molecules which moves 

 with it and is the negative ion. After removal of the negative ion 

 the molecule retains a positive charge and probably also becomes 

 the centre of a cluster of new molecules. 



"The electron or corpuscle is the body of smallest mass yet known 

 to science. It carries a negative charge of 3.4 X 10~~ 10 electrostatic 

 units. Its presence has only been detected when in rapid motion, 

 when it has for speeds up to about 10 10 cms. a second, an apparent 

 mass m given by c/m 1.86X10 7 electromagnetic units. This 

 apparent mass increases with the speed as the velocity of light is 

 approached." 



At low pressures the electron appears to lose its load of cluster- 

 ing molecules, so that finally the negative ion becomes identical 

 with the electron or corpuscle, and has a mass, according to the 

 estimates of J. J. Thomson, about one thousandth of that of the 

 hydrogen atom. The positive ion is, however, supposed to remain 

 of atomic size even at low pressures. 



The ionic theory and the related hypothesis of electrolytic dis- 

 sociation afford a key to numerous phenomena concerning which 

 no adequate or plausible theories had hitherto been formed. By 

 means of them explanations have been found, for example, of such 

 widely divergent matters as the positive electric charge known to 

 exist in the upper atmosphere, and the perplexing phenomena of 

 fluorescence. 



The evidence obtained by J. J. Thomson and other students of 

 ionization, that electrons from different substances are identical, 

 has greatly strengthened the conviction which for a long time has 

 been in process of formation in the minds of physicists, that all 

 matter is in its ultimate nature identical. This conception, neces- 

 sarily speculative, has been held in abeyance by the facts, regarded 

 as established, and lying at the foundation of the accepted system 

 of chemistry, of the conservation of matter and the intransmut- 

 ability of the elements. The phenomena observed in recent investi- 

 gations of radioactive substances have, however, begun to shake our 

 faith in this principle. 



If matter is to be regarded as a product of certain operations 

 performed upon the ether, there is no theoretical difficulty about 



1 Rutherford, Radioactivity, p. 53. 1904. 



