328 Mr. R. T. Beatty on the Production of Cathode 



experiments. Also the ratios of the ionizations becomes 

 constant for such radiations. The value for Sn lies where 

 one might expect it considering the penetrating power of the 

 Sn radiation compared to that of the radiation from a Rontgen 

 bulb with the alternative spark-gaps mentioned. 



Remarks on figs. 4, 5, 6, 7 (PI. V.). 



In each figure the curves described as "ionization in air" 

 and "ionization in H 2 " are those found directly. The curves 

 described as " cathode ionization in air " are obtained by sub- 

 tracting the part due to direct ionization by the exciting- 

 radiation, leaving only that due to cathode particles. The 

 pressure at which this curve rises to half its final value is 

 indicated by a short horizontal line. 



In the H 2 curves for Fe and Zn radiations practically all 

 the ionization is due to the cathode particles, so that the curve 

 found directly also represents the ionization due to cathode 

 particles only. 



If we take that portion of the ordinate which is intercepted 

 between the "cathode ionization in air'" curve and the hori- 

 zontal straight line which that curve ultimately becomes, and 

 if we plot the logarithms of these intercepts against the 

 corresponding pressures, we get the curves in the figures 

 which are described as log curves. , The deviation of these 

 curves from linearity indicates the departure from the 

 exponential law of absorption of the cathode particles. 



However, as the particles are already scattered to a great 

 extent before emerging from the silver leaf, an exponential 

 absorption is hardly to be expected. Such an absorption 

 would require certain relations between the numbers and 

 velocities of particles leaving the leaf at different inclinations 

 to the normal. 



In determining the cathode ionization in H 2 due to Sn 

 radiation a special method had to be adopted, as owing to the 

 high penetrating power of these particles in H 2 complete 

 absorption of them only took place at pressures nearly atmo- 

 spheric. A series of readings was taken at different pressures 

 with and without the silver leaf in the path of the radiation. 

 On subtracting corresponding ordinates cf these curves we 

 obtain curve III. fig. 7 (PL V.) (marked with crosses). The 

 curves referred to as "ionization in air"" and "cathode ioni- 

 zation in air" were obtained in the usual way, and the 

 abscissae of the latter were multiplied by such a number as 

 to make the curve coincide most nearly with the H 2 curve. 

 This number, 7' 7 9, was then taken as the ratio of the pene- 

 trating power of the particles in H 2 to that in air. 



