CHAPTER IX. 



FURTHER DETAILS CONCERNING ELECTRONS AND 



IONS. 



Confirmatory Measurements of Charge. 



A CONFIRMATORY measure of the charge e, can be 

 made by first observing the rate of fall of a cloud 

 condensed round the ions acting as nuclei a 

 measurement which gives the weight w of each 

 drop, and, then applying to the cloud a vertical 

 electric field and adjusting its strength until it is just 

 able to check the fall and hang the drops in air like 

 Mahomet's coffin. For under these conditions of 

 course w = Ee, and since everything except e has been 

 measured, e is at once known. This ingenious pro- 

 cess was devised by Mr. H. A. Wilson, and is 

 described by him in the Philosophical Magazine for 

 April, 1903. In practice the above would be slightly 

 modified and a simple differential method employed. 

 The numerical result at which he arrived was that 

 the value of e = 3'I x 10 ~ 10 . The result also had the 

 effect of confirming the applicability of Stokes' law, 

 in the cases where fall had been permitted. 



This seems to be the value obtained for the electric 

 charge associated with every kind of monad ion, both 

 positive and negative, as well as for the separate 



