WheelocTc — Nature of Ionization Produced ly a Hays. 235 



On the hypothesis of " Initial Recombination" it wonld be 

 expected that recombination would be less in the part of the 

 range where the velocity of the a particle is greater, since the 

 electron would probably be ejected with greater velocity and 

 thus have more cliance to escape the remaining positive ion. 



The a particle is a more efficient ionizing agent near the end 

 of its path, but since it is moving slovver here than when the 

 source is nearer the chamber, more recombination would take 

 place. This would also be the case if the lack of saturation 

 were due to columnar ionization, because of the greater density 

 of ions within the cohunns. 



The purpose of the experiments here described is : — 



I. {a) To compare the saturation curve obtained when an 

 electric field is applied parallel to the path of the a particle 

 with that obtained when the field is perpendicular to the path ; 

 (b) To compare the a ray curves with those obtained when /3 

 and 7 rays are used as ionizing agents. 



II. To test for the existence of columnar ionization. 



III. To get a mathematical expression for the saturation 

 curve, on the hypothesis of ionization in columns, and to com- 

 pare the calculated curves with those experimentally obtained 

 when the field is applied parallel to the path of the a particle. 



IV. To show that the lack of agreement between the calcu- 

 lated and experimental curves is not due to an inclination of 

 the columns in the ionization chamber used. 



Y. To compare the curves obtained with the source at dif- 

 ferent distances from the ionization chamber, for both parallel 

 and perpendicular fields. 



VI. To compare the curves obtained at different pressures 

 in both chambers. 



Description of Apparatus, 



For the field parallel to the path of the a particle, the appa- 

 ratus used (fig. 1) was similar to that of Bragg and Ivleeman. 



The ionization chamber, 7"5''" in diameter and 4"" in depth, 

 was formed of a wire gauze N, insulated from the siipporting 

 ring by small pieces of amber, and a brass plate A, insulated 

 from the top, E, of the containing vessel by means of an ebonite 

 plug. A second wire gauze, D, grounded through the top of 

 the containing vessel, formed with N a second ionization cham- 

 ber, which prevented stray ions fi'om entering the i(4pization 

 chamber proper. t^ 



The plate A was connected to one pair of quadrants of a 

 Dolezalek electrometer, the second pair of quadrants being 

 earthed. The gauze N was connected with a battery and 

 could be charged to any desired potential. The high potential 

 wire C was carefully screened to prevent stray ions from being 



