Wheeloch — Nature of Ionization Produced hy a Rays. 249 



On the liyjDOthesis of ionization in columns, it would be 

 expected, since the density of ionization is greater when the 

 polonium is 2"6'^"' fron the chamber, that recombination would 

 be greater. Experiment shows greater recombination with the 

 ionizing source at 2"6'"' than at l-G*^'", but less recombination 

 than when it is at S'S*^"'. However, when the source is 3'5'^'" 

 from the ionization chamber, some of the a particles (those 

 sent off at angles of from 23'2° to 26*6° with the vertical) do 

 not enter the chambei" at all, and most of the ions in the cham- 

 ber are formed by the a particles which are sent off, making- 

 very small angles with the vertical. The columns thus made 

 would be very little broken up by the component of the elec- 

 tric force at right angles to the path of a particles, since this 

 component would be small. 



When the source is 2-6'^" or 1-9'='" from the middle of the 

 chamber all of the a particles cross the ionization chamber, and 

 the perpendicular component of the electric force might have 

 an appreciable effect upon the recombination of ions, since the 

 columns would be more or less broken up.* 



Data obtained icith the perpendicular field. 



, 3-2"" > , 3-6°"» V , 2-3>:"' V 



Voltb/cm. Current % lack Current % lack Current % lack 



2 S-15 55-3 11-98 59-0 ll'l 58-9 



4 11-19 42-8 15-95 45-4 15-23 43-7 



10 14-1 28-5 20-76 29-3 19-65 27-3 



20 16-05 18-0 23-8 18-5 22-43 17-1 



40 17-87 87 26-4 9-6 24-6 9-05 



80 18-6 4-96 27-85 4-6 25-93 4-1 



120 19-1 2-4 28-65 1-9 26-6 1-7 



200 19-5 0-36 29-08 0-41 26-95 0*37 



1000 19-57 0-0 29-2 0*0 27*05 0-0 



For curves see fig. 8. 

 Mean value of % lack of saturation from several curves. 



ts/cm 



Dist. 8-2<="» 



Dist. B^e^™ 



Dist. 2-3^" 



2 



55-6 



59-6 



58-3 



4 



43-3 



45-9 



44-0 



10 



28-0 



30-0 



27-9 



40 



9-1 



10-3 



8-8 



80 



4-8 



5-1 



4-0 



By comparing the lack of saturation at the distances given 

 in the above table, it will be seen that more recombination 



* A better test would have been possible if a particles of longer range 

 than those from polonium had been u.sed, but the thorium I had was too 

 weak and Ra. C decays too rapidly for saturation measurements, which take 

 considerable time. 



Am. Jour. Sci. — Fourth Series, Vol. XXX, No. 178. — October, 1910. 

 17 



