610 Dr. N. Bohr on the Decrease of 



in hydrogen A w = l'15.10 3 . The value given by (34) is 

 5*9 A w . The first value is 4 times smaller than the ioniza- 

 tion observed. The latter value is of the right order of 

 magnitude, but is a little larger than the experimental 

 value. 



For helium W is nearly twice as great as for hydrogen. 

 From (31) and (34) we should therefore expect a value for 

 the ionization only half of that in hydrogen. Taylor, how- 

 ever, found the same ionization in hydrogen as in helium. 

 Since in this case the value observed is greater than that 

 calculated from (34), the disagreement is difficult to explain, 

 unless the high value observed by Taylor possibly may be 

 due to the presence of a small amount of impurities in the 

 helium used. This seems to be supported by experiments of 

 W. Kossel* on the ionization produced by cathode rays. 

 This author found that the ionization in helium was only 

 half as large as that in hydrogen — in agreement with the 

 theory. The cathode rays used had a velocity of 1*88 . 10 9 , 

 corresponding to a fall of potential of 1000 volts, and the 

 number of ions produced in passing through 1 cm. of 

 hydrogen at a pressure of 1 mm. Hg was equal to 0*882. 

 This corresponds to 670 pairs of ions at atmospheric pressure. 

 Putting Y= 1*88 . 10 9 and E = e, and using the same values 

 for W, e, ??i, N, and n as above, we get from (31) A w = 300. 

 From (34) we get T = 4*5 A w . 



If we consider a substance such as air, which contains a 

 greater number of electrons in the atoms, we do not know 

 the value of W for the different electrons. A sufficiently 

 close approximation may, however, be obtained, if in the 

 logarithmic term of (35) we put W = hv, where h is Planck's 

 constant. This gives, if we at the same time introduce the 

 value for Q from (32), 



T 27r<? 2 E 2 NA^i / 2V 2 ?»M 2 \ /Q .. 



If now in this formula we introduce the values for n and 

 -Xlogy used in section 4 in calculating the absorption of 



a. rays in air, and put W 1 = 1'25 . 10" 11 , we get 1 = 3*6 . 10 4 . 

 This is the same order of magnitude as the value 2*25 . 10* 

 observed by Geiger, but somewhat larger ; this would be 

 expected from the nature of the calculation. The value to 

 be expected from the formula (33) cannot be stated accurately 

 on account of the uncertainty as to the magnitude of the W's, 

 * Ann. d. Physik, xxxvii. p. 393 (1912). 



