THE 



POPULAR SCIENCE 

 MONTHLY. 



MAY, 1912 



NEW PEOOFS OF THE KINETIC THEORY OF MATTEE AND 

 THE ATOMIC THEORY OF ELECTEICITY 



Bt Peofessor ROBERT ANDREWS MILLIKAN, Ph.D., Sc.D. 



UNIVERSITY OF CHICAGO 



IT is my purpose herein to review the history of two of our most 

 fundamental physical theories and to present some very simple 

 and easily intelligible experiments which demonstrate the correctness 

 of these theories, though they are by no means the only experiments 

 which lead to the same goal. 



If this statement seems too dogmatic and positive to be scientific let 

 me say that I make it advisedly, for I wish vigorously to combat the 

 point of view which I fear too many of those who are not engaged at 

 first hand in scientific inquiry gain, both from the " revolutionary dis- 

 coveries " which are continually being announced by the daily press, 

 and also from the prominence which scientists themselves naturally give 

 to the demolition of time-honored hypotheses in which they do not 

 believe — the point of view that none of the theories of the scientists are 

 after all any more than transient phenomena, that they are all just a 

 part of the continual change and flux of things, that this generation dis- 

 cards wholesale all the hj^potheses which were held adequate in the last 

 and that the next generation will make equally short work of all the 

 theories which hold sway to-day. In opposition to that point of view 

 I wish to assert that there are some things, even in science, which we 

 may safely say that we know, that there are some theories which we 

 may be reasonably certain are going to endure — that in fact we may 

 divide the theories of science into three categories, with broad and 

 indefinite lines of division between them, it is true, but yet with real 

 dividing areas, if not dividing lines. 



In the first category may be placed the theories which we may say 

 that we know are correct, using the word " know " not in the abstract 



VOL. LXXX. — 28. 



