﻿On the Absolute Expansion oj Mercury, 679 



be used, since k is inversely proportional to the pressure, and 

 accurate measurements of the value of N . e may be deduced 

 from observations that require a few minutes to collect the 

 charges on the electrodes. 



Mr. Pomeroy does not give the values of the charges 

 acquired by the electrodes in his experiments, and his 

 reasons for neglecting the effect of self-repulsion are un- 

 satisfactory. In some of the experiments the potential of 

 the plate A was raised to 200 volts, and it was concluded 

 that the charge on each ion was equal to one atomic charge. 

 And in others the potential was 100 volts and the charge 

 was in these cases said to be two atomic charges. Apparently 

 the ring and the disk acquired equal charges, in these 

 experiments. 



The theory of the experiments, however, shows that, when 

 the ions have single atomic charges, and the opening of the 

 stream is due to diffusion only, the ring B and disk C acquire 

 equal charges when the potential of A is 10 volts. If 

 Mr. Pomeroy is correct in supposing that the self-repulsion 

 may be neglected, the logical conclusion to which his experi- 

 ments lead is that in some cases the charges on the ions with 

 which he was dealing were one-tenth, and in other cases one- 

 twentieth of the atomic charge on a monovalent atom in a 

 liquid electrolyte. 



Yours truly, 



John S. Townsend. 



LX1V. On the Absolute Expansion of Mercury. Reply to 

 Criticisms by Scheel and Heuse. By H. L. Callendar*. 



IN the March number of this Journal Scheel and Heuse 

 have pointed out that our recent results for the absolute 

 expansion of mercury do not agree quite so closely with 

 previous determinations by indirect methods as the latter 

 agree among themselves, and have drawn the conclusion that 

 the discrepancy must be due to an error in our measurements. 

 They also complain that we have neglected to bring into the 

 discussion the experiments made at the Reich sanst alt in 1895 

 on the expansion of mercury by the weight thermometer 

 method, and that we have omitted to discuss the results in 

 relation to the expansion of water. This omission was not 

 due to any oversight on our part, but to a natural desire to 

 avoid the appearance of going out of our way to criticise the 

 results of old experiments to which the Authors themselves 

 did not seem at the time to attach much importance as a 



* - * Communicated bv the Author. 



