Emanation and Active Deposit produced by it. 375 



Again, it' q be the rate at which the emanation is leaving the 

 salt per sq. cm., we have 



q — -K 1T - when x = 0; 

 2 dx 



and since dP /a<i -^ ~ ^^ ,x 



dP _ Ai_ 



P * 



^a/K^Pq, or p o^^7g^-, 



q - V^ . x 

 * x/KiXi 



If, now, we assume that the same law governs the diffusion 

 of the emanation which holds for a small quantity of one 

 gas diffusing into a second we may take 



K — ^ 



where p is the pressure of the gas in which the diffusion 

 takes place and Aj is a constant. 

 We have then 



r = q . i_— e Al . 



In order to find the pressure corresponding to a maximum 

 deposit for a selected value of x it suffices to apply the 

 condition 



dp 

 This gives 1 /\ 



or p=£fr, , , , , , . (1) 



i. e. the pressure corresponding to the maximum deposit at 

 a point at a distance x from the salt should, with the as- 

 sumptions made above, be inversely proportional to the 

 square of the distance of the point under observation from 

 the surface of the salt. This result, it will be seen, is dis- 

 tinctly at variance with the law of distribution discovered by 

 Kennedy. 



If, however, we assume that K, the coefficient of diffusion 



2C2 



