370 Taylor — Retardation of Alpha Bays by Metals. 



gies consumed in air and hydrogen respectively is in agreement 

 also with the decrease in the hydrogen-equivalent of the 

 celloidin film. 



Still making use of our hypothesis, the ratio of the energy, 

 consumed in the 9th and 10th centimeters of air at reduced 

 pressure, to that consumed in the same centimeters of hydrogen 



312 

 at normal pressure, is expressed by the fraction . The 



77 

 same ratio for the 13th and 14th centimeters is — . These 



83 - 



ratios were obtained by measuring with a planimeter the areas 

 in figure 2. The former ratio divided by the latter gives 1*10. 

 Since the hydrogen equivalent of the celloidin film is but 

 slightly more than two centimeters, the ratio of its values at 9 

 and 13 cms respectively from the polonium should be the same 

 as the above ratio. The hydrogen equivalents of the film in 

 the two positions (see figure 1) are 2*320 and 2*120 cms respect- 

 ively, and the ratio of the former to the latter is 1*09, which 

 differs little from the calculated ratio 1*10 given above. 

 Hence it is seen that the differences between the curves of 

 figure 2 are sufficient to account for the change in the 

 hydrogen-equivalent of the celloidin film and consequently for 

 the increase in the air-equivalents of the hydrogen sheets when 

 moved away from the source of rays. This agreement between 

 the relative ionizations and the relative losses of energy of the 

 particle in the two gases gives a considerable degree of 

 probability to our hypothesis connecting the relation of the 

 ionization produced to the energy consumed. 



The experimental results show that the air-equivalents of the 

 metal sheets decrease with the speed of the alpha particle, and 

 hence the ratio of the energy of the alpha particle, consumed 

 by its passage through a sheet of metal, to the energy that 

 would be consumed by one centimeter of air at the same 

 point in the path of the particle, decreases as the range of the 

 alpha particle decreases. The behavior of the metal sheets 

 relative to the air is entirely analogous to the behavior of the 

 air, or celloidin relative to hydrogen. Consequently if it were 

 possible to measure the ionization produced by the alpha 

 particle at different points in the path of the rays in the 

 metals, and if the ionization curves were plotted on the same 

 scale as those shown for air and hydrogen, figure 2, it is prob- 

 able that the curves for the metals would all present some 

 such differences from the air curve as those existing between 

 the air and hydrogen curves. Moreover these differences might 

 be expected to be such as to agree with the different rates at 

 which the air-equivalents of the different metal sheets change. 



