56 



Proceedings of the Royal Irish Academe/. 



XII. — Just as we have found ( Section VI) in respect to the casual 

 method, so with the " charge " method ; the quotient of the potential by the 

 " step " voltage, or that of the total charge by the average step " rise," each 

 give the same number. "We have already identified this number ■svith the 

 number of electron charges on the nuclei. It is difficult to suggest any 

 reason why groups of two or more electrons should attach themselves at 

 once ; in fact, thi'oughout many thousands of observations of an analogous 

 case, Millikan found only one doubtful ease where more than a single 

 electron charge was taken up at one time. "We, therefore, feel particularly 

 confident in attributing the '"' steps " to successive electrons, and that we 

 may thus determine the charges on the nuclei under any given field. 



l^olrs(fter2.'}c«)IO 



XIII. — This, however, leads to a serious difficulty. In experiments 

 of the Millikan type, fields of thousands of volts per centimetre are used, 

 and the resulting velocity attained by the charged drops is only of the order 

 of a millimetre per second at most. In oui- work, although a measurement 

 of the velocity was difficult, it was certainly, at least, a centimetre per 

 second, and the field was only forty volts per centimetre. Thus, with charges 

 of about the same magnitude the moMlity in our case is about mie thousand 

 times that of one of Millikan's drops. 



