COSMIC RADIATION" — JOHNSON 



201 



of the ray to the magnetic bending force. This property, which we 

 may call the magnetic rigidity or, for brevity, the rigidity, depends 

 upon the product of mass and velocity of the ray divided by the 

 amount of its charge. 



In the case of the cosmic radiation a magnetic analysis hag been 

 carried out, using the method of cloud-track photography, by Ander- 

 son in California, Kunze in Germany, and Blackett in England. A 

 typical photograph of Anderson's is represented in plate 2, figure 1. 

 A magnetic field of 12,000 gauss was applied to the cloud chamber 

 and the ray was bent into a circular arc. The direction of bending 

 show3 that the ray is negative. From the radius of curvature it is 

 found that the rigidity of this ray corresponds to a particle of 

 the mass and charge of the electron and with a velocity such as 

 would be gained by a fall through a difference of potential of 18 

 million volts. The expression " corresponds to " is used because 

 other values of mass, charge, and velocity could give the same rigid- 

 ity. That the ray is really an electron may be inferred from the 

 fact that the track is a thin one, A proton of greater mass but of 

 the game rigidity would have been moving more slowly. With more 

 time to act upon the atoms along its path the track would have been 

 denser. If the charge were greater, as in the case of the alpha parti- 

 cle represented in plate 2, figure 2, the track would have been very 

 much denser. From all of the evidence it is possible to distinguish 

 between the various kinds of rays, for the number of possibilities is 

 small. In fact the different kinds of rays believed to exist are limited 

 to those with small integral values (0, 1, 2, etc.) of both mass and 

 charge, the respective units being the masg and charge of the proton. 

 All of the combinations known to exist are contained in table 1. 

 Those designated by (?) are anticipated but not known to exist. 

 The table extends along the diagonal to the lower right, including 

 the nuclei of the stable atoms. 



