ii 4 THE POPULAR SCIENCE MONTHLY 



ter and could be released from the atom by a variety of agencies. This 

 idea was much widened and strengthened by the investigations of Zee- 

 man and Lorentz, who showed that the radiation of light must be 

 mainly ascribed to the movements of electrons of the same small mass 

 within the atom. 



It does not fall within the scope of my address to outline the very 

 important consequences that followed in many directions from this 

 fundamental discovery of the independent existence of the electron and 

 its connection with matter. It was found by Kaufmann that the mass 

 of the electron was not a constant but increased with its speed, and from 

 this result it was deduced that the electron was an atom of disembodied 

 or condensed electricity occupying an exceedingly small volume, whose 

 mass was entirely electrical in origin. 



Unit op Electricity 

 I should mention here one important consequence that has followed 

 from these discoveries. From the laws which control the passage of 

 electricity in conducting solutions, Faraday recognized that there must 

 be a close connection between the atom of matter and its electrical 

 charge. Maxwell and Helmholtz suggested that the results were simply 

 explained by supposing that electricity was atomic in nature. This 

 conclusion is now definitely established, and the positive charge carried 

 by the hydrogen atoms in the electrolysis of water is believed to be the 

 fundamental unit of electrical charge. This charge is equal to and 

 opposite to the charge carried by the electron. Any charge of elec- 

 tricity, however small or large, must be expressed by an integral mul- 

 tiple of this fundamental unit of electricity. The actual value of this 

 unit charge has been measured by a great variety of methods and with 

 concordant results. One of the most detailed and accurate investiga- 

 tions of this important constant has been made by Professor Millikan, 

 of the University of Chicago. 



Objections to the Atomic Theory 

 We have so far implicitly assumed that the great majority of scien- 

 tific men now regard the atomic theory not only as a working hypothe- 

 sis of great value but as affording a correct description of one stage of 

 the sub-division of matter. While this is undoubtedly the case to-day, 

 it is of interest to recall that less than twenty years ago there was a 

 revolt by a limited number of scientific men against the domination of 

 the atomic theory in chemistry. The followers of this school consid- 

 ered that the atomic theory should be regarded as a hypothesis, which 

 was of necessity unverifiable by direct experiment and should, there- 

 fore, not be employed as a basis of explanation of chemistry. This 

 point of view was much strengthened by the recognition of the power 

 of thermodynamics in affording a quantitative explanation of the 



