﻿122 Mr. Clinton J. Davisson on the Positive 



emission, and the nature of the particles carrying the charge *. 

 Experiments with the first of these ends in view have been 

 productive of several more or less general empirical la v\s. 

 Attempts to determine the nature of the ions have, however, 

 been less uniformly successful if one may judge by the 

 variety of answers the query has received. This lack of 

 unanimity has arisen, it appears, from the impossibility of 

 inferring the nature of the ions from data that can yield 

 with certainty only the laws of emission. The small value 

 of such data as a means of identifying the ions has been 

 often recognized, and it has been frequently suggested that 

 their true nature would not be known with any degree of 

 certainty until reliable determinations of their specific charge 

 had been made. 



Of the experiments which have been made to determine 

 the value of e/m for these ions, those of Richardson (/. c.) 

 alone seem sufficiently reliable and extensive to serve as a 

 basis for legitimate inference f. Richardson made deter- 

 minations of e/m for the positive thermions from various salts 

 of the alkali metals, and found that they admit of classi- 

 fication under two heads : 1st those which agree with the 

 value of e/m for sodium or for potassium in electrolysis ; 

 and 2nd, those which agree with the electrolytic value of 

 e/m for the metallic ions of the salt nnder test. From these 

 results he has inferred that the ions which are emitted by 

 such salts when heated are single atoms of the metal minus 

 single electronic charges. The values of e/m corresponding 

 to ions of sodium and potassium are taken to indicate the 

 presence of these elements as impurities in the specimens of 

 the salts examined. 



Object. 



The present investigation was undertaken for the purpose 

 of making similar tests upon a large number of salts other 



* Beattie, Phil. Mag. April 1901. Garrett & Willows, Phil. Mag- 

 Oct. 1904. Garrett, Phil. Mag. June 1907. Thomson, Camb. Phil. 

 Soc. Proc. 1906-1908, p. 105. Thomson, Camb. Phil. Soc. Proc. vol. xv. 

 Feb. 1909. Horton, Camb. Phil. Soc. Proc. 1909, p. 329. Garrett, Phil. 

 Mag. Oct. 1910. Richardson, Phil. Mag. Dec. 1910. p. 981. Richardson, 

 Phil. Mag. Dec. 1910, p. 999. Horton, Proc. Roy. Soc, A. vol. lxxxiv. 

 no. 572, Dec. 1910. Horton, Camb. Phil. Soc. Proc. vol. xvi. pt. i. Feb. 

 1911. 



t Reliable determinations of e/m for positive ions from heated anodes 

 coated with salts in discharge-tubes have been made by Gehrcke & 

 Reichenheim {Phys. Zeit. viii. p. 724, Oct. 1907). There are good reasons 

 for thinking, however, that such emissions in high-tension tubes are not 

 closely related to the more strictly thermal phenomena dealt with in the 

 present investigation. 



