Thermions emitted by the Alkali Sulphates. 099 



metal, particularly in the case of the elements of higher atomic 



weight. They are, however, in very good agreement with 



1 e X 



the value calculated from the formula u = -. , where u is 



I m v 



the velocity under unit field, e the charge, m the mass, A, the 

 mean free path, and v the mean velocity of agitation of the 

 ions, on the hypothesis that thev have the same structure as 

 those discovered by Sir J. J. Thomson * in the canal rays. 

 Moreover, the ratio of the velocitv of the negative to that of 

 the positive ions in flames at high temperatures is in good 

 agreement with this view. 



Outside of solutions the number of cases oE positive ions 

 of which the structure has been definitely determined is not 

 very large. The only ones which occur to the author are 

 the a particle, which Rutherford showed to be an atom of 

 helium carrying twice the electronic charge, and the canal 

 rays in different gases, for which the mass of the carriers 

 has been investigated by Wien, Stark, and Thomson. With 

 the exception, possibly, of the particles having a high value 

 of e/m, isolated by Thomson from the canal rays, all these 

 researches agree with the results of the present investigation 

 in making the primitive positive ion an atom of some known 

 chemical element which has lost one or more negative 

 electrons. 



In concluding I wu'sh to thank Mr. Irving B. Crandall, 

 A.B., graduate student in physics, and my assistant, Mr. Cor- 

 nelis Bol, for their help in taking the observations. 



Palmer Physical Laboratory, 

 Princeton, N. J. 



CXI. The Positive Thermions emitted by the Salts of the 

 Alkali Metals. By 0. W. Richardson, ALA., D.Sc, 

 Professor of Physics, Princeton University^. 



IN the preceding paper the author has shown that the 

 positive ions emitted by the sulphates of the different 

 alkali metals are atoms of the constituent metal carrying a 

 single electronic charge. The sulphates were used in the 

 investigation because they are readily obtainable in a state of 

 reasonable purity and are comparatively non-volatile. There 

 is no reason to expect that the sulphates are exceptional in 

 regard to the positive ions they emit. We should, therefore, 



* Phil. Mag. [6] vol. xvi. p. 657 (1908). 

 t Communicated bv the Author. 



