Passage of a Particles through Hydrogen. 243 



in greater number even than for the same activity (7 ray) from 

 an a-ray tube. As an average of several fairly concordant 

 experiments, the following figures were found for the 

 number of H particles per equivalent mgrm. radium element, 

 observed in air at a distance of 8 cm. from the source. The 

 area of the zinc-sulphide screen observed was 1*17 sq. mm. 



Radium 0... 0" 20 per minute. 

 Ra.Em. ( + A + C in a-ray tube) . . . 0*07 „ „ 



It must be remarked, however, that in the case of radium 

 C on nickel, there is not as much absorption of the lower 

 velocity H particles as in the case of an a-ray tube, since 

 there is the extra thickness of glass in the latter case. At 

 low pressure the number of a particles reaching the screen 

 from the same source of radium C would be 3*1 X 10 4 per 

 minute. The comparatively large number of H particles 

 emitted from radium on nickel seems to suggest that 

 occluded hydrogen or water-vapour is not the cause, unless 

 radium C forms some compound with hydrogen involving 

 an increased chance of collision of the a particles with it. 

 Experiments were also made with a quartz a-ray tube, and 

 again the H particles were observed, though slightly less 

 than half as many as from a glass a-ray tube. The numbers 

 are not strictly comparable however, since the quartz a-ray 

 tube had nearly three times the thickness of the glass a-ray 

 tube, and would therefore absorb the slower H particles. 



Thus there seems a strong suspicion that H particles are 

 emitted from the radioactive atoms themselves, though not 

 with uniform velocity. This does not necessarily disagree 

 with the nuclear hypothesis unless it were further assumed 

 that a particles are ejected not only with definite velocities 

 from the radioactive atoms, but also in definite directions 

 relative to the nuclear and electronic arrangements *. 



In conclusion, we desire to thank Sir Ernest Rutherford 

 for his kind, inspiring interest in these experiments and for 

 providing us with the necessary material. 



Wellington, N.Z., 

 May 1915. 



* Cf. Rutherford, Phil. Mag. xxviii. p. 310 (1914). 



R2 



