682 Ionization Tracks of Alpha Rays in Hydrogen. 



middle and the crook at the end, there is a slight bend of 

 double curvature between these two. Many o£ the tracks 

 photographed showed this gradual change in curvature, and 

 it was thought at first that they constituted evidence opposed 

 to the view advanced by Rutherford, that the scattering of 

 alpha particles of large amount is the result of single de- 

 flexions through considerable angles, and not to a cumulative 

 effect due to a very large number of minute deviations. 

 Continued investigation, however, showed that the bending 

 mentioned above was mechanical in its origin, and was due 

 to a distortion impressed upon the track of ions in the gas by 

 the irregular movement of the gas in the course of expansion 

 after the alpha-ray particle had passed, but before the con- 

 densation actually took place. In some of the photographs, 

 the distortion of the alpha-ray tracks was very considerable, 

 and an enlargement of one of a number which exhibited this 

 in a very marked way is shown in fig. 13. Here it will be seen 

 that the curvature commences practically at the beginning 

 of the tracks and extends for a considerable distance over 

 their length. 



In this photograph the tracks were in hydrogen, but the 

 cloud was formed from the condensation of alcohol vapour. 

 The field applied was 30 volts. 



Fig. 14 exhibits another feature which characterized a 

 number of the photographs. In this one it will be seen that 

 a considerable space intervenes between the polonium plate 

 and the commencement of the alpha-ray tracks. In this 

 particular photograph, the ionization was in hydrogen and 

 the cloud was formed from alcohol vapour. Similar results 

 were also obtained when the clouds were formed from water 

 v r apour. This absence of condensation at the beginning of 

 the tracks was taken to mean that, owing to the proximity 

 of the copper plate carrying the polonium, the gas in this 

 region was kept sufficiently warm during the expansion to 

 prevent condensation of the vapour. 



IV. Summary of Results. 



1. It has been shown that although alpha-ray tracks in 

 hydrogen are of greater length than those in air, they exhibit 

 similar characteristics to those obtained in air. 



2. It has been shown that alpha-ray ionization tracks can 

 be exhibited by the condensation of alcohol vapour equally 

 as well as with the condensation of water vapour. 



3. The photographs obtained confirm the observation of 

 C. T. R. Wilson, and support the contention of Rutherford, 



