of some Gas Molecules for Electrons. 231 



factors. In general it was observed that for a set of curves 

 taken at different pressures and frequencies, the values of n 

 were uniformly greater the lower the pressure. However, 

 the parts of the curves from which n was taken under these 

 conditions also lay at progressively lower values of the 

 voltage as the values of n increased. It was therefore 

 a priori difficult to determine which of the variables, if 

 either, was responsible for the changes in n As has been 

 pointed out before, this variation in n does not necessarily 

 invalidate the theory of electron attachment which assumes 

 n to be a constant; for the change in n may be only 

 apparent. A real change in K' of the equation (1) (about 

 whose behaviour little is known) could be the real cause of 

 the variation. 



In the hope of gaining some insight into this situation, the 

 values of n were determined for mixtures of oxygen and 

 nitrogen. It was found that as the nitrogen became very 

 pure the value of K, the mobility of the carriers, became 

 quite large. In pure nitrogen, values of K were obtained of 

 the order of 1100 cm./sec. It was further found that the 

 variation in n due to pressure observed when the quantities 

 of oxygen were small, was greater than with air or pure 

 oxygen. For example, it was found that in order to change 

 n from 1 x 10 5 to 9 x 10 5 in air the pressure-change required 

 was from 150 mm. down to 20 mm. In a mixture of 1 mm. 

 oxygen to 745 mm. nitrogen it required a change from 

 508 mm. to 222 mm. to cause a change in n (computed back 

 to air) of from 1*0 X 10 5 to 1*5 X 10 6 . The change of n with 

 the voltage was about the same in the two cases. The effect 

 is then obviously not produced by a variation in the pressure 

 alone, and is perhaps influenced by the value of the field 

 strength. 



An investigation of the electronic mobilities became im- 

 perative, in view of the fact that measurements had revealed 

 negative carriers in pure nitrogen whose mobility was five 

 times as great as those assumed for K', from the work of 

 earlier observers *. The mobilities of electrons in pure 

 nitrogen gas were determined, using high-frequency oscilla- 

 tions from an audion oscillator These results are being 

 published elsewhere f. The measurements showed that the 

 mobility of the electron in nitrogen was far higher than 

 had been anticipated. It was further found that K' was not 



* J. Franclc, Verh. d. Beut. Phys. Ges. xii. p. 613 (1913) ; W. B. Haines, 

 Phil. Mag. (6) xxx. p. 503 (1915) ; E. M. Wellisch, Am. Journ. Sci. July 

 1917, p. 11. 



f To appear in the Physical Review, 1921 . 



