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these bombardments no protons at all, or at least none surely due to 

 disintegration of nuclei. Yet Bothe and Franz had observed protons 

 issuing from magnesium, as one of the curves in Fig. 8 gives witness. 

 There remains the third method for detecting transmutation, the 

 most beautiful and spectacular of all — the Wilson method, the one in 

 which the trails of small charged particles are made visible by water 

 condensing in droplets on the ions which the particles leave behind 

 them as they tear through the gas. This seems a very inefficient 



Fig. 11— Transmutation of a nitrogen atom attended by capture of the impinging 

 alpha-particle (\V. D. Harkins and A. E. Schuh). 



scheme, considering how often one must photograph the trails of 

 alpha-particles which do not effect a transmutation, before having the 

 good fortune of finding on one's plate the record of one of the very rare 

 alpha-particles which do. Inefficient it certainly is; nevertheless, by 

 setting up apparatus which automatically repeats the experiment over 

 and over and over again and automatically takes a new photograph at 

 each repetition, one is able to assemble data enough to provide evi- 

 dence of transmutation. Patience and perseverance are required, for 

 there is one part of the process which cannot be delegated to a machine: 



