of Radioactive. Products present in the Atmosphere. 83^7 

 for Q becomes approximately 



X E N E * . , ■ - , , \ E X E 



Q = 47ryct/t* — : — — instead of Q = 47r/it/..' 



^a + ^ Xa + \/a . ^ 



The calculated value of N E can be brought into agreement 

 with those directly found at the places already referred to 

 by taking \ about I'd times the value of \a, or, in other 

 words, if the half-value period of radium A in its initial 

 state be taken about 14 seconds. Of course the value of \ 

 here given only indicates the order of magnitude. 



(18) If the last view is correct, the relative amount of the 

 radium and thorium emanations is to be calculated approxi- 

 mately from the following equation 



I_ _ 7c X E ^ E , ^e _ I_ \ F / 7b / + 7c / 



1' ~" 7b+ 7c' A.e'Nk' N f / "" 1' Xk 7c 



From the average values given in (a) and (d), Art. 3, 



—^,=47,000 for the upper wire, i. e. in the vicinity 

 E of the height of 6'5 metres above the 



ground, and 



AT 



24 ; 000 for the lower wire, i. e. in the vicinity 



T ' 



E of the height of 1*5 metres. 



(19) By making use of a similar formula, W. Wilson f 

 found the relative amount of the two emanations at Man- 

 chester to be 37,000. It may be mentioned that the formula 

 used by him had been deduced from Dadourian's assumption* 

 that, when the radioactive equilibrium is established on the 

 wire, the number of atoms of the deposit breaking up per 

 second is equal to that of the emanation in that vicinity, 

 which is X E N E according to our notation. Thus there is a 

 fundamental difference between our arguments and those 

 of the latter. It would be evident that X E N E is the number 

 of atoms of the emanation breaking up or that of radium A 

 producing per c.c. of air, but not the number of atoms of the 

 radium A deposited on the wire or that of the radium C 

 breaking up per sec. per cm. of the wire in equilibrium. 



(20) Whatever may be the nature of the change in 



* It may be recalled that, in the case of ordinary gaseous ions in the 

 atmosphere, while there are 40 to 50 times as many heavy ions as the 

 small ones, the mobility of the former is only a fraction of one-thousandth 

 of that of the latter. It follows, therefore, that the product of the 

 number present and tbe mobility for the heavy ions is negligibly small 

 compared with that for the small ones. 



t W. Wilson, I. c. X Dadouriau, /. c. 



Phil. J fac. S. 6. Vol. 22. No. 132. Dec 1911. 3 K 



