224 ANNUiiL, REPORT SMITHSONIAN INSTITUTION, 193 5 



According to the idea that has prevailed for 2 centuries, positive 

 and negative electricity should be merely reflected images of each 

 other, their properties being equal and opposite. The behavior of 

 the negative electron and the proton shows nothing inconsistent with 

 this concept as far as electrical properties go. On the discovery of 

 the positive electron it was at first thought that it was shorter lived, 

 or, as a chemist might say, more reactive than its negative counter- 

 part, but this has not been borne out by subsequent investigation.^^ 

 The mass associated with the positive charge in this case has been 

 investigated by several persons. The latest work is that of 

 E. Kupp ^^, who finds that the mass is within 5 percent of that of 

 the negative electron. Eupp appears to have found one point of 

 difference between the two which, if confirmed, will be of impor- 

 tance. 



It has been found that the passage of negative electrons through 

 thin films of metal is accompanied by a diffraction effect, photo- 

 graphs of the electron beam after transmission showing a series of 

 concentric rings. Rupp passed negative and positive electrons 

 through the same films of gold and aluminum, and found that while 

 the negative particles gave the usual rings the positive particles 

 showed a continuous scattering. We will return to the interpretation 

 of this later. 



As to the neutron, it is still uncertain whether it is a proton which 

 has acquired a negative electron or whether it is to be regarded as 

 an independent entity without electric charge. The latter, as we 

 shall see later, would be in serious conflict with present accepted 

 electrical theory. 



There was a time, not so very long ago, when the atom of matter 

 was considered to be its ultimate structural unit. The discovery of 

 the proton and the electron gave meaning to the term subatomic. 

 With this in mind, the question naturally arises as to a possible 

 further subdivision of the electron. Several observers have claimed 

 to have found evidence of smaller charges than that carried by the 

 electron, but Millikan,^^ after an exhaustive discussion of the sub- 

 ject, came to the conclusion that up to 1924 there had been adduced 

 no satisfactory evidence of this smaller charge. 



In the early years of the present century there was some discus- 

 sion as to whether the electron was to be regarded in shape as a 

 rigid sphere (Abraham) or as contractile. The latter hypothesis 

 was advanced by Lorentz to explain the negative result of the 

 Michelson-Morley experiment. Lorentz supposed the electron, by 



" Allowing for relative abundance. 



^ Eupp, Phys. Zeit., vol. 35, p. 999, 1934. But in Zeit. Phys., vol. 93, p. 278, 1935, Rupi 

 has withdrawn his earlier article for further veriflcation. 

 "The Electron, chap. 8. 



