136 THE LIMITATIONS OF SCIENCE 



assume that the electrical charge on matter is a quan- 

 tity varying with the velocity of a body. 



So great a revolution in thought as to consider 

 inertia a variable quantity and to substitute electricity 

 for matter as the substance of the universe, would only 

 have been undertaken from a fancied necessity. A 

 mere matter of convenience would scarcely warrant 

 the labor of revising the work of the past and of dis- 

 carding what has been considered, until lately, as 

 definitely established. The need for some such radical 

 change in theory is based on the experimental facts dis- 

 covered in connection with the passage of electricity 

 through highly rarefied gases, and with radio-activity. 



We may consider it established that the phenomena 

 noted, when electricity is discharged in a high vacuum, 

 are most readily explained by supposing the current 

 due to a stream of electrified particles moving with a 

 velocity comparable to light. The experiments of Sir 

 J. J. Thomson and C. T. R. Wilson go to show that 

 the masses of these projectiles, when charged nega- 

 tively, are about the one-thousandth part of the mass 

 of a hydrogen atom, provided the charge on each is 

 assumed to be the same and equal to that of the hydro- 

 gen atom. Those charged positively are comparable to 

 the various chemical atoms. 



Radio-activity, on the whole, is best explained by the 

 projection of positive and negative electrons from a 

 certain class of bodies. 



