436 Prof. E. M. Wellisch : Experiments on 



particles of radium. These experiments cover in many 

 respects the same ground as those here described ; this fact 

 was not recognized till the present series was completed. 

 Eckinann's work may be, for convenience, summarised under 

 the following heads : — 



(1) Distribution of the deposit in electric fields ; 



(2) Investigation with regard to aggregates ; 



(3) Determination of the coefficient of diffusion (D). 



With regard to (1) he comes to the conclusion that about 

 98 per cent, of the particles are positively charged, the 

 remainder being negatively charged. This is of course 

 opposed to the results of the present investigation. Eckmann 

 assumes that the total deposit is the sum of the deposits 

 obtained on a central electrode when it is first raised to a 

 high positive and then to a high negative potential. The 

 present experiments show that this assumption is incorrect, 

 the 2 per cent, which is obtained in the latter instance being- 

 due to the diffusion to the central electrode of a small 

 fraction of the neutral particles. Eckmann ascribes the 

 deposit on the anode to negatively charged particles, and 

 accordingly neglects a considerable amount of deposit which 

 settles on the case of his vessel. 



Eckmann's work with regard to aggregates anticipates to 

 a large extent that described in the present paper. He- 

 shows that they are charged, and is undoubtedly correct in 

 his assumption that they owe their charge to the ions present 

 in the gas. He shows also that the anomalous results 

 obtained by Debierne * in a series of experiments with 

 regard to the diffusion of radium active deposit can be 

 explained by taking into consideration the formation of 

 aggregates. The present experiments bring out several new 

 points of interest, but on the whole serve merely to confirm 

 the results of Eckmann in this connexion. 



With regard to the determination of D, Eckmann collected 

 the total amount of gas deposit on a piece of gauze ; he 

 found, for the particular vessel which he employed, that this 

 deposit was equivalent to a formation for "6 minute ; in 



other words, S = If (with the notation of Section 6). He 



then employed the formula Gr = "/fy - (Section 3) in order to 



estimate D, which came out as *06 ; this formula, however, 

 neglects the diffusion to top and bottom, which was impor- 

 tant for the cylinder which he used. It is of interest to 



* Debierne, Le Radium, vi. p. 27 (1909). 



