598 Prof. J. S. Townsend and Mr. V. A. Baile) 



t on 



6. Since the effect o£ a collision of an electron with a 

 molecule depends on the velocity of the electron, it is of 

 interest to compare the effects of collisions in argon, nitro- 

 gen, and hydrogen when the electrons are moving with the 

 same velocity u. From the determinations that have been 

 made the effects obtained in the three gases may be com- 

 pared when the velocity of agitation is between 8*5 x 10 7 

 and 14 x 10 7 cms. per sec. The values of Z/p required to 

 maintain the velocity of agitation u in each gas are given 

 in Table II. with the corresponding values of the velocities W. 









Table 



II. 









lo- 7 - 



A 



Z/p. 



rgon. 



wxio- 5 - 



Nitrogen. 

 Z/p. W x 10~ 5 - 



Hydrogen. 



Z/p. wxio- 



14 



•82 



915 



74 





215 



57-3 



255 



12 



•40 



8-05 



50-5 





172 



324 



128 



10 



•19 



7-05 



32 





124 



19-2 



69 



8-5 



•10 



6*05 



16 





72 



130 



49 



From the numbers given in Table II., the mean free 

 paths I and the proportions of the energy of an electron 

 lost in a collinson A, may be calculated by the preceding 

 formula}. These are given in Table III. 









Table 



III 



• 







;10- 7 - 



Ar 



IpX 100. 



gon. 



xxio 4 . 



m 

 ipxioc 



trog 



en. 



A X 10 4 . 



Hydrogen. 

 Ip X 100. A X 10 4 



14 



10-8 



1-05 



2-85 





580 



4-35 



815 



12 



168 



1-09 



2-86 





505 



3-32 



280 



10 



26-9 



1-19 



271 





380 



2-52 



117 



8-5 



36-3 



1-24 



2-68 





177 



2-25 



82 



These numbers show that the mean free path I of an 

 electron is about ten times as long in argon as in hydrogen 

 or nitrogen at the same pressure when the velocity is 

 10 8 cms. per second. This result is remarkable, especially 

 as the radii a of the molecules as deduced from the viscosity 

 of the gas are not much different, the values of ax 10 8 being 

 1*80 cms. in argon, 1*88 cms. in nitrogen, and 1*34 cms. in 

 hydrogen. Also there is a large increase in the free path I 

 in argon as the velocity u of the electron is reduced. A 

 similar effect was obtained in nitrogen, oxygen, and hydrogen 

 with lower velocities. Thus in nitrogen at one millimetre 



