TRANSACTIONS OF SECTION A. 801 



one or two, for the thirty 3-ears 1866 to 1895, ia five-yearly periods, was as 

 follows : — For the first lustrum, 186G-70, 35-76 inches ; for the second, 1871-75, 

 59-02 inches; for the third, 1876-80, 40-15 inches; for the fourth, 1881-85, 38-25 

 inches ; for the fifth, 1886-90, 33-07 inches ; and for the sixth, 1891-95, 34-84 

 inches. 



The memoir was accompanied by a map shuwing the position of the rainfall 

 stations and their height above mean sea-level. 



MONDAY, SEPTEMBER 12. 



A discussion was held in conjunction with Section B on the Results of the 

 Kecent Solar Eclipse Expeditions. 



The following Report and Papers were read : — 



1. Interim Report on Electrolysis and Electro-chemistry. 

 See Reports, p. 158. 



2. Dilute Solutions. By E. H. Griffiths, F.R.S. 



3. Conductivity of Dilute Solutions. By W. C. D. Whetham. 



4. Velocity of the Electricity in the Electric Wind. 

 By Professor A. P. Cuattock. 



It is shown tliat when an electric wind is produced by discharge in air from a 

 point against an earth-connected metal plate, the momentum imparted to the air 

 is proportional to the distance from point to plate. From this the author concludes, 

 first, that the velocity of the electricity is directly proportional to the electro- 

 static field which moves it, and secondly, that there is no appreciable kick-ofY or 

 reaction at the point. 



Values are given for the velocity of the electricity relatively to the point and 

 plate in unit electrostatic field and in various gases (not specially purified) at nor- 

 mal temperature and pressure — 



AlS it is shown that the velocity of the wind in which the electricity moves is 

 negligible compared with that of the electricity itself, it follows that these values 

 are those of the electricity carriers relatively to the gas through which they pass. 

 Close to a sharp point it is probable that the actual velocity reached by the carriers 

 exceeds 10" cm. per second. 



5. Dalton's Law. By W. N. Shaw, F.RS. 



Disci-epancies between the sum of the partial pressures of air or nitrogen and 

 saturated vapour and the pressure of mixtures of air and saturated vapour indicat- 

 ing, prima facie, a departure from Dalton's law were shown by Regnault ' to exist 

 for water vapour, the extent of the differences being on the average nearly half a 

 millimetre. 



Regnault himself in his classical paper on the pressure of vapours,* sought to 



' Ann. dc C/iim. [3] vol. xv. 2 Mem. de I'lnstitut, vol. xxvi. 



1898. ■ 3 p 



