July 20, 1900.] 



SCIENCE. 



103 



ally nil : no amount of analytical manipu- 

 lation, however complicated, will add to it 

 one iota. 



In the present condition of our experi- 

 mental knowledge, theoretical discussions of 

 this nature are indeed pure speculation. 

 But we must remember also that scientific 

 speculation has always been one of the most 

 important aids in the advancement of sci- 

 ence. For a visionary enthusiast specula- 

 tion is a plaything, dangerous to himself 

 and annoying to others. But in the hands 

 of the trained and conservative scientist it 



sequences of each, and testing the conclu- 

 sions by experiment. The kathode rays 

 and the Becquerel rays offer the means by 

 which such tests may be applied. 



Although the theoretical results of 

 Thomson and Heaviside are not in com- 

 plete agreement, they both indicate con- 

 siderable deviations from simple laws 

 when the speed approaches that of light. 

 Thomson states his results in convenient 

 form by saj^ing that the effect of a charge 

 is to increase the apparent mass of the 

 moving body. So long as the speed is 



is a valuable tool, without whose aid the 

 progress of knowledge would be slow in- 

 deed. The present case is one to whose 

 study scientific speculation is particularly 

 applicable. The motion of charged bodies 

 at a speed nearly equal to that of light is a 

 subject that we cannot hope to study by 

 direct experiment. If we ever get a knowl- 

 edge of the laws that apply in such cases, 

 it must be by indirect methods. It is 

 therefore simply a question of trying one 

 hypothesis after another, deriving the con- 



small, the increase is inappreciable. But 

 at high speeds it becomes important, and at 

 the velocity of light the apparent mass be- 

 comes infinite. Since the effective mass is 

 a function of the speed, we might therefore 

 expect the ratio ejm to vary with the ve- 

 locity of the kathode rays. But the hope 

 of explaining the observed discrepancies in 

 this way is illusory, as the apparent mass 

 remains practically constant until the 

 speed is nearly equal to that of light. The 

 manner in which the apparent mass varies 



