CONTEMPORARY ADVANCES IN PHYSICS 173 



that out of them he estimated the enormous values of 7 and 15 niilHons 

 of equivalent volts for the energy of the two particles. As for those 

 of which the tracks were not sensibly curved by the field, the enerj^^y 

 of some at least (assuming them to be electrons!) must have exceeded 

 15.10^ equivalent volts. (Of the rest, the paths were so unfavorably 

 placed that absence of sensible curvature might have been compatible 

 with energy- values as low as, but no lower than, 3.10^.) 



This method has also been adopted by Millikan's collaborator, 

 C. D. Anderson, who has a magnetic field of great extent, pervading 

 a large expansion-chamber so oriented that particles coming along 

 or near the vertical (we shall see evidence that near sea-level, the 

 particles do favor that direction) are subjected over a long distance to 

 its deflecting power, and electrons with energy values amounting to 

 scores of millions of equivalent volts are sensibly deflectible. On some 

 of his plates there are trails curved in the right sense for electrons com- 

 ing downward from above, with energy amounting to 70 millions. On 

 some there are trails curved in the opposite sense; if they were made by 

 electrons, these must have been travelling from the earth upwards; 

 if they were made by descending particles, as seems more plausible, 

 these must have been positively-charged. On one there appear three 

 paths, two apparently springing from a common origin near the wall 

 of the chamber; one is curved in the proper sense for an electron, one 

 in the opposite sense — if it is the track of a proton, this must have had 

 energy of 120 millions — the third is sensibly straight. ^^ Skobelzyn too 

 had got plates on which two or three tracks appeared, coming probably 

 from a common point of departure. 



It appears from these pictures that the immediate agents of the 

 ionization ascribed to "cosmic rays" are able to produce long trains 

 of ions closely crowded together (the number of ions per centimetre is 

 probably of the order of one hundred) " which is so far as our experience 

 runs, a distinctive feature of electrified material particles such as 

 electrons and protons; that some are deflected in practicable magnetic 

 fields; that from the deflections it probably follows that the charge is 

 sometimes negative and sometimes positive (the uncertainty being due 

 to the fact that from the curvature one cannot tell the sign of the 

 charge unless one knows in which sense the particle is going along the 

 path) ; that the ones which are known to be charged have enormous 



'^ I am much indebted to Dr. Millikan for showing and interpreting these plates to 

 me. They have been shown in scientific meetings and mentioned in the press; the 

 pubUcation of the pictures and the work in the scientific journals will be eagerly 

 awaited. 



'■* The values most highly esteemed are obtained not by counting droplets, but by 

 using the third method to determine the number of ionizing particles, the first to 

 determine the total ionization; Kolhorster and Tuwim give 135 zb 10%. 



