PAPERS ON CHEMISTRY AND PHYSICS 331 



THE EFFECT OF SHORT ELECTROMAGNETIC 

 WAVES ON A BEAM OF CATHODE RAYS 



C. J. Lapp, University of Illinois 



SYNOPSIS 



Much has been written concerning discontinuous wave 

 fronts of electromagnetic radiation. Sir J. J. Thomson 

 and A. Einstein have definitely developed such theories. 

 As an experimental test, apparatus^ was devised by 

 means of which electrons were projected through a com- 

 pact beam of radiation, such as ultra violet light or X- 

 Rays. In order to magnify any possible eifect the elec- 

 tron beam was twisted into a long spiral of about 3 cm. 

 pitch and 1.5 cm. mean diameter, by means of a strong 

 magnetic field. The helical beam thus formed was about 

 70 cm. long, and the path of each individual electron much 

 longer. If the electron beam was permitted to fall on a 

 photographic plate, traces made on the plate when the 

 radiation was turned off should be different from those 

 made when the radiation was present if any effect oc- 

 curred. The results recorded photographically may be 

 summarized as follows : 



1. When a strong beam of radiation of wave lengths 

 from 8000 to 1300 Angstrom units fell across a stream 

 of rapidly moving electrons, there were indications of a 

 slight decrease in the velocity of the electrons. This 

 eft'ect, however, was smaller than the errors of measure- 

 ment. 



2. With the above radiation wave lengths the evidence 

 is very strong that there Avas a scattering of the electrons 

 in the beam. 



3. When hard X-rays were used instead of the radia- 

 tion given in 1, there was a distinct decrease in the ve- 

 locity of the moving electrons, as is shown by the decrease 

 in the diameter of the electron trace. 



4. It was also found that X-rays caused a decided 

 scattering of the electrons in the beam. 



1. J. J. Thomson, "Electricity and Matter", Ch. 3, pp. 53-70 ; Phil. Mag. 

 V. 335, Feb. (IBIO). 



