RECENT DEVELOPMENTS IN ELECTROMAGNETISM. 



By Eugene Block, 

 Professor at the Lyc6e Saint Louis. 



The domain of electromagnetism is to-day so broad and so com- 

 plex that in a few pages we can not hope to show all its frontiers. 

 For the present, therefore, we will limit ourselves to reviewing cer- 

 tain problems which particularly attract our attention, either by the 

 number or the importance of the investigations which they have 

 produced. We will start with the theoretical developments and end 

 with the results gained in the laboratory.^ 



I. THE DYNAMICS OF THE ELECTRON AND ELECTROMAGNETIC MASS. 



The electromagnetic theory of matter and the ether in the per- 

 fected form due to H. A. Lorentz is really a theory of electrons. 

 Matter in all its forms is by it considered as made up of complex 

 groups of which an essential element is the negative electron either 

 free or bound to an atom. This element is defined by its charge e 

 (4.5X10~^° electrostatic units) and its mass, which is invariably at 

 small velocities (e/m=1.76XlO^ electromagnetic units). This result 

 was the logical consequence of a long and brilliant series of discov- 

 eries which marked the end of the last and the beginning of the 

 present century (cathode rays, X rays, gaseous ions, Zeeman effect, 

 radioactivity, etc.). 



A fundamental problem of this theory is evidently the study of 

 the motion of an isolated electron and the electromagnetic perturba- 

 tions which accompany it. This problem gains in interest as experi- 

 mental demonstration becomes possible. Cathode rays from all 

 sources (rays from Crookes's tubes, from the photoelectric effect, the 

 ^ rays from radium) are, indeed, fluxes of electrons projected at 

 great velocities from matter. Let us, therefore, review first the 

 important results of the theory which was developed by Heaviside 



» Translated by permission from Revue g^nerale des Sciences pures et appliquees, Paris, 

 24th year, No. 8, Apr. 30, 1913. 



2 It will be out of the question, for instance, in this review to consider the recent 

 researches on the larger ions, X-rays, radioactivity, vacuum tubes, and the phenomena 

 connected with them (positive rays, etc.), or atmospheric electricity. 



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