MODERN CONCEPTS IN PHYSICS — LuVNOMUIIi 221 



prove the existance of atoms or molecules. He therefore urged that 

 chemists avoid as far as possible the use of sucii hypotiieses. Per- 

 haps tlie cliief result of this altitude was to lead physical chemists 

 to neglect those parts of chemistry where the atomic theory would 

 have been most iielpful and to devote themselves more specially to 

 the fiehls in which energy relationships and thermodynamics were 

 directly applicable. 



Physicists in general did not doubt the existence of atoms and mole- 

 cules, but had by means of this theory developed the kinetic theory 

 of gases which had led to many new quantitative laws, verified by 

 experiment. However, the physicists in general had little to do with 

 atoms and molecules but were more concerned with the ether, in 

 which they believed unreservedly, although direct knowledge of the 

 ether was far harder to obtain than knowledge of atoms and 

 molecules. 



Perhaps one of the main reasons why the physicists were so sure 

 of the ether and the chemists so doubtful of the atoms and molecules 

 was an unconscious belief in the respectable old adage '* Natura non 

 facit saltum," Nature makes no jumps. Certainly in those fields 

 of physics and chemistry in which rigorous quantitative laws had 

 been found applicable no discontinuities or jumps such as those 

 implied by the atomic theory had been found. 



The discovery of X rays by Roentgen, in 1905, marked the be- 

 ginning of an extraordinary revolution which is today still in prog- 

 ress. This sensational event revealed to the physicist that great and 

 fundamental discoveries were still possible even in the field of radia- 

 tion where physics had had such complete success. It immediately 

 caused great numbers of physicists to study the phenomena of electric 

 discharges and to look for other sources of radiation. The discovery 

 of radium and radioactivity by Becquerel and the Curies soon 

 showed the importance of these new forms of radiation to the 

 chemist as well as to the physicist. 



Although Stoney in 1874 had seen that Faraday's laws of electro- 

 lysis together with the atomic theory required that electricity should 

 also have an atomic structure, and although in 1891 he proposed the 

 name electron for these atoms of electricity, J. J. Tiiomson should 

 be regarded as the discoverer of the electron. He was able to show 

 that electrons were contained in all forms of matter and found that 

 the electron nmst weigh only about Visoo as much as a hydrogen 

 atom. 



The studies of radioactivity, largely by Kutherford and his stu- 

 dents, showed that radium spontaneously disintegrated to form 

 helium and proved to the chemist that atoms were not indestructible 

 and even that transmutation of elements was possible. 



