﻿518 



Prof. J. A. Pollock on the 



Table I.* contains the observed values of the reciprocals 

 of the mobilities, reduced to standard atmospheric pressure, 

 together with the temperature and vapour-pressure at the 

 time the observations were made. 



Table L 



l/«. 



t. Pi. pt. 



*r | 





Cent. mm. mm. 



mm. 





Grouped results. 





1253 



18-3 



15-62 | 0-60 



067 



1802 



18-8 



1612 545 



5-87 



3077 



16-3 



13-77 11-81 



14-90 



3155 



23-2 21-11 18-86 



15-51 



3226 



15-9 13-42 12-41 



1605 





Single observations. 





2310 



15-3 



12-95 



6-60 



8-85 



2570 



20-9 



18-04 



10-64 



10-24 



2640 



201 



1722 



U-02 



11-11 



2725 



235 



20-94 



14-24 



11-80 



Values of the reciprocals of the mobilities of the large ions reduced 

 to standard atmospheric pressure, aud the temperature and water-vapour 

 pressure at the time the observations were made, together with the 

 vapour pressure reduced to 20° C. 



The single observations are those depending on one day's 

 measures only, natural air being used. For these determi- 

 nations the humidity was calculated from the wet and dry 

 bulb readings; whereas in the case of the grouped measures 

 where the moisture in the air was artificially controlled, the 

 humidity was found by absorbing the water vapour and 

 weighing. The estimations of the humidity by the wet and 

 dry bulb readings now appear to be low, though from a com- 

 parison of the two methods of determining the humidity, 

 made at an early stage of the investigation, no constant 

 difference was apparent. 



When the humidity changes, the ions do not at once reach 

 a stage of equilibrium with the new vapour-pressure con- 

 ditions, and in the determinations, when a change of humidity 

 occurred, 13 minutes were allowed to elapse before the 

 measurements for mobility were made. In reviewing the 

 observations, I think it is possible that this interval may not 

 have been long enough in the case represented by the first 



* For details see Journ. and Proc. Roy. Soc. N. S. Wales, xliii. pp. 61 

 and 198 (1909). A single observation, given in one of the tables pre- 

 viously published, has been omitted, as on looking up the original 

 records the result is found to be unreliable. 



