354 Sir E. Rutherford, Prof. Barnes, and Mr. Richardson : 



The following table shows how closely the frequencies up 

 to the maximum as given by this empirical relation agree 

 with the observed values. 



Table II. 



Volts in 



Calculated 



Observed 



thousands. 



frequency. 



frequency. 



13-2 



3-07 XlO 18 



2-94 XlO 18 



20 



4-54 „ 



4-41 „ 



30 



6-55 „ 



6-44 „ 



40 



8-39 „ 



8-34 „ 



50 



10-06 „ 



10-1 „ 



60 



11-56 „ 



11-6 „ 



70 



12-88 ., 



J 30 „ 



80 



14-04 „ 



14-1 „ 



90 



15-02 „ 



15-3 „ 



100 



15-83 „ 



16-0 „ 



110 



16-47 „ 



16-5 „ 



125 



171 „ 



16-9 „ 



142-5 



17-4 „ 



174 ., 



With the exception of the values for low voltages, where 

 the frequency is difficult to determine accurately, the agree- 

 ment between the calculated and observed values is remark- 

 ably good and within experimental error. 



Absorption in Lead, 



Several experiments were made to find the absorption jn 

 lead of the radiation excited by the higher voltages. Pre- 

 liminary experiments showed that the " end " radiation 

 was absorbed nearly exponentially in that substance as in 

 aluminium. The values of the absorption coefficient /jl for 

 lead were found to be 36, 29, 23, 23, 23 for the end radiation 

 excited by 96,000, 110,000, 125,000, 155,000, 175,000 volts 

 respectively. Since the absorption coefficient for lead on 

 the average decreases rapidly with increased frequency 

 over the range considered, it was thought that the small 

 change of frequency observed by measuring the absorption 

 of the radiation in aluminium would show up more promi- 

 nently when lead was the absorber. No certain difference 

 in the absorption was, however, observed from 125,000 to 

 175,000 volts. 



The final measurement of the end radiation was made 

 after the rays had passed through 2*49 mm. of lead. The 

 ionization observable through 3 mm. of lead is certainly less 

 than 1/10000 of the initial value. Even with very intense 



