64 POPULAR SCIENCE MONTHLY. 



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 e/m = 1.86 X 10 7 electromag- 

 netic 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 clustering 

 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 dissocia- 

 tion afford a key to numerous phenomena concerning which no ade- 

 quate or plausible theories had hitherto been formed. By means of 

 them explanations have been found, for example, of such widely diver- 

 gent 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, necessarily specu- 

 lative, 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 intransmutability of the elements. 

 The phenomena observed in recent investigations of radioactive sub- 

 stances have, however, begun to shake our faith in this principle. 



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

 formed upon the ether there is no theoretical difficulty about transmu- 

 tation of elements, variation of mass or even the complete disappear- 

 ance or creation of matter. The absence of such phenomena in our 

 experience has been the real difficulty, and if the views of students of 

 radioactivity concerning the transformations undergone by uranium, 

 thorium and radium are substantiated, the doctrines of the conserva- 

 tion of mass and matter which lie at the foundation of the science of 

 chemistry will have to be modified. There has been talk of late of 

 violations of the principle of the conservation of energy in connection 

 with the phenomena of radio-activity, but the conservation of matter is 

 far more likely to lose its place among our fundamental conceptions. 



The development of physics on the speculative side has led, then, 

 to the idea, gradually become more definite and fixed, of a universal 

 medium, the existence of which is a matter of inference. To this 

 medium properties have been assigned which are such as to enable 

 us to form an intelligible, consistent conception of the mechanism by 

 means of which phenomena, the mechanics of which is not capable of 

 direct observation, may be logically considered to be produced. The 



