52 



Mr. E. M. Wellisch on the Motion of 



determinations of the critical potential V , while the values 



given in the second table were determined by means of the 



« , 7 d 2 n i 



formula k = -^r- • -p — n. 

 V ft— i 



Press, 

 mm. 



V 



volts. 



i. 



i'. 



/• 



Freq. 



*r 



K v 



1-66 



14-3 



418 



•52 



•540 



829-2 



5574 



1-22 



1-64 



143 



2-84 



•34 



•540 



851-1 



568-2 



1-23* 



101 



9-03 



2-20 



•40 



•574 



851-7 



965 



1-28 



•563 



500 



1-73 



•34 



•574 



836-5 



1781 



1-32 



•416 



6-26 



1-506 



•46 



•584 



8621 



1975 



1-08 



•321 



4-17 



1-84 



•60 



•585 



8333 



3090 



1-31 



•151 



1-13 



105 



•155 



•565 



856-0 



7265 



1-44 



•052 



•55 



•298 



•068 



•565 



842-4 



18250 



1-25* 



•052 



1-15 



•333 



•137 



•565 



842-4 



19130 



1-31* 



Mean value of K 1 : 1'27 

 * a=8 volts (v. fig. 2); for the other determinations a=20. 



The mean value obtained for K x at the higher pressures 

 was 1*23, which is in sufficient agreement with the above 

 values to justify the conclusion that the nature of the positive 

 ion is independent of the pressure. 



The mobilities of both the positive and the negative ions in 

 C0 2 and H 2 were determined over a wide range of pressures: 

 there was no evidence in either gas of any systematic alter- 

 ation in the value of pki or pk 2 as the pressure was reduced. 

 It was deemed unnecessary to extend the determination for 

 these gases down to the low pressures employed in the case 

 of air inasmuch as it was apparent that the processes were 

 entirely similar ; for this reason the law pk = const, was only 

 verified down to a pressure of 4 mm. in C0 2 and 12 mm. 

 in H 2 . The mean values of K for air, 00 2 , and H 2 were 

 estimated from the results obtained at the higher pressures, 

 where the observation error is relatively small, although the 

 results at the lower pressures showed good agreement. The- 

 values thus obtained are as follows : — 





■Ky 



K, 



K 2 /K x . 



Air 



1-23 



•73 

 511 



1-93 

 1-07 

 9-67 



1-57 

 1-47 

 1-89 



C0 o 



H 2 



The values of K refer as usual to the dry gas at atmospheric 

 pressures, and are expressed in cm./sec. per volt/cm. 



