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XXIII. Possible Magnetic Polarity of Free Electrons. 

 By Arthur H. Compton, Ph.D.* 



l\/rY attention has recently been called by Mr. Shimizu 

 ItX to the fact observed by Mr. C. T. K. Wilson that 

 the paths o£ beta and secondary cathode rays excited by 

 X-rays in air usually terminate in converging helices. The 

 comparatively uniform character of these curves shows itself 

 clearly in certain of Mr. Wilson's beautiful stereoscopic 

 photographs which have not been published but which he has 

 very kindly allowed me to examine. For example, one 

 photograph, which shows the complete tracks of 66 secondary 

 cathode particles, reveals 52 tracks of helical form, only two 

 or three tracks showing no general curvature of this type, the 

 remaining 12 rays having paths too irregular to detect with 

 certainty any helical curvature that may exist. These paths 

 may have the form of either a right- or left-handed helix, 

 and the axes of the different helices have a nearly random 

 orientation. A detailed examination of a large number of 

 tracks to prove that the observed curvature of the paths is not 

 a random one, w T ill necessarily involve much time and labour. 

 In default, however, of a complete proof, it is of interest to 

 see whether an explanation can be offered of the apparent 

 tendency of the beta particles to move in a type of spiral 

 orbit. 



Though the spiral form of the paths would suggest a motion 

 of the particles in a magnetic field, the chance orientation 

 of the axes of the different helices shows that these axes are 

 not determined by any external magnetic field, but are rather 

 characteristic of the individual beta rays. More specifically, 

 the axis of the helix must be parallel with some polarity of 

 the beta particle which is relatively permanent in direction. 

 It is apparent that a simple electric charge can possess no 

 polarity whose orientation will remain constant in spite of 

 numerous collisions with other charges unless it is in rapid 

 rotation. Mr. Shimizu accordingly suggested that Mr. Wil- 

 son's photographs may be explicable on the assumption that 

 the electron has a definite magnetic polarity which on 

 account of gyroscopic action does not change rapidly in 

 direction. 



It is clear that a magnetic field whose direction is deter- 

 mined by the electron passing through it, is capable oi' 

 producing the type of spiral track that is observed. Bui a 

 beta particle which acts as a magnetic doublet as well as an 

 electric charge is capable of producing such a magnetic field 

 * Communicated by Professor Sir E. Rutherford, F.R.S. 



