Tracks of Alpha Rays in Hydrogen. 681 



" H " particles. In taking the photograph shown in fig. 4 a 

 field of 70 volts was applied in the cloud-chamber, and a 

 Zeiss planar lens F 4'5, 5 cm. focus, was used. The photo- 

 graph was taken on an Ilford Monarch plate. 



The reproduction shown in fig. 7 also shows a sharp bend 

 in one of the tracks, but there is no indication of any spur at 

 the bend. It was obtained with hydrogen and condensed 

 water vapour. The field applied to the cloud-chamber was 

 8 volts. 



Figs. 8, 9, and 10 are reproductions of enlargements of 

 the ends of some alpha-ray tracks in hydrogen, the clouds 

 of which were formed from water vapour. The field applied 

 to the cloud-chamber when they were taken was 8 volts. 

 The interest in these photographs lies in the fact that the 

 ends of the tracks and the curves they exhibit are somewhat 

 more extended than those obtained by Wilson with air. In 

 some cases it will be seen they resemble the curve at the end 

 of a hockey stick, while in others the bends are more like 

 the ends of a shepherd's crook. 



Some oE the tracks shown in fig. 8, as will be seen, appear 

 to be double, while others again are single and very distinct. 

 The double tracks are clearly out of focus and more or less 

 indistinct. From their general appearance the doubling would 

 appear to be entirely an optical effect, but it is just possible 

 that it represents an electrical separation of the ions in those 

 tracks which were produced a short time before the more dis- 

 tinct ones. Against this latter view, however, there is the fact 

 that the separation shown on the photograph appears to be 

 lateral, while if it had been produced by the electrical field 

 the displacement in all probability would have been in a 

 vertical plane or very close to it. 



The track in fig. 11 and its enlargement in fig. 12 was 

 also obtained 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 something 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 ionize 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 



Phil Mag. S. 6. Vol. 30. No. 179. Nov. 1915. 2 Y 



