216 THE ROYAL SOCIETY OF CANADA 



The track in Fig. 11 and its enlargement in Fig. 12 was also ob- 

 tained with hydrogen and water vapour the field applied being 30 

 volts. In this one the crook at the end is brought out very clearly 

 as well as the abrupt bend at the middle. At this bend there is a 

 slight protuberance or thickening on the convex side which looks some- 

 thing like a shortened spur but it is only just noticeable. Although 

 photographs of many alpha tracks showing abrupt bends were taken 

 this one represents practically the maximum indication of a spur which 

 was obtained. This shows that if the "H" particles really do ionise a 

 gas the kind of collision which results in the liberation of such particles 

 is of exceedingly rare occurrence. 



If the reproduction shown in Fig. 12 be closely examined it will 

 be seen that in addition to the abrupt bend near the middle and the 

 crook at the end there is a slight bend of double curvature between 

 these two. Many of 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 

 deflections through considerable angles and not to a cumulative effect 

 due to a very large number of minute deviations. Continued investi- 

 gation, 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 condensation actually took place. In some of the photo- 

 graphs 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 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 characterised 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 ionisation 

 was in hydrogen and the cloud was formed from alcohol vapour. 

 Similar results were also obtained when the clouds were formed from 

 water vapour. 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. 



