the Motion of Electrons in Argon. 599 



pressure I increases from 0'266 mm. to 0455 mm. when the 

 velocity is reduced Jirom 8*85 x 10 7 to 3\15 x 10 7 cm. per sec. 



The values of X for argon are very much less than for 

 the other gases. They can only be considered as approxi- 

 mate values, owing to the large effect of impurities, one 

 part of nitrogen to 10 5 of argon being sufficient to increase 

 the value of X for argon by 3 per cent. The values of X 

 for nitrogen and hydrogen diminish with the velocity u, and 

 in nitrogen when w=4 x 10 7 cms. per sec. X is 5*5 xlO -4 , 

 which is still about five times as great as the value for 

 argon with the velocity u==10 s . 



7. If the argon were absolutely pure, and if there were 

 no loss of energy when an electron collides with a molecule 

 of argon except the small loss corresponding to the momen- 

 tum imparted to the molecule regarded as a perfectly elastic 

 body, the value of X would be about a quarter of the value 

 found experimentally. The question therefore arises as to 

 whether the amount of nitrogen remaining in the argon 

 after the second purification would be sufficient to increase 

 the value of X from about 0'33 x 10 ~ 4 to the observed value 

 1-2 xlO- 4 . 



The following calculations show what amount of nitrogen 

 would be necessary to produce this effect. If the argon 

 contained one molecule of nitrogen to 4000 molecules of 

 argon, an electron would make one collision with a molecule 

 of nitrogen for 400 collisions with molecules of argon, the 

 velocity of the electron being about 10 8 cms. per second. 

 If E be the energy of the electron, the average loss of 

 energy in each collision with a molecule of nitrogen is 

 3'8xlO~ 2 E, and in each collision with a molecule of argon 

 the loss would be about 3x 10~ 4 E, if the argon be supposed 

 to be perfectly elastic. Thus the average loss of energy in 

 a collision would be 



0-3 x 10" 4 E + 3-8 x 10- 2 E/400, 



and the value of X would be 1*25 X 10 -4 , which is near the 

 observed value. 



From the observations made on the contraction of the 

 gas in the process of purification by sparking, we concluded 

 that the proportion of nitrogen to argon remaining in the 

 gas was much less than one part in 4000, but we cannot be 

 certain that other impurities were present in a smaller 

 proportion, so that notwithstanding the experimental results 

 it may be possible that no part of the energy of the electron 

 is transferred to the molecule in the form of internal 



