Electricity at the Kew Observatory. 131 



traced in 25 to 28 between low potential and long previous sun- 

 shine, high temperature, low barometric pressure, and high wind 

 velocity constitute the normal state of matters at every station, 

 irrespective of the hour or the season. Provisionally 1 should 

 prefer to regard these associations as possibly accidental, even at 

 Kew, but believe they indicate the lines on which more exhaustive 

 inquiries might profitably proceed. 



Another possibility indicated by these associations, viz., that the 

 potential tends to be higher during anticyclonic than during cyclonic 

 weather seems also worthy of attention. An attempt was indeed 

 made in the present instance to check this conclusion directly by 

 reference to the weather reports of the Meteorological Office. The 

 published data relate, however, to 8 A.M. and 6 P.M. ; so that, on a 

 considerable number of occasions the nature of the isobars at the 

 hours of the observations was uncertain. Taking the remaining 

 instances, I calculated the mean potential for the cyclonic and anti- 

 cyclonic conditions separately for each one of the four series, treating 

 the forenoon and afternoon observations apart, except in the case of 

 the first series. In live cases out of the seven thus presented, the 

 mean potential for the anticyclonic group exceeded that for the 

 cyclonic. There is thus something to be said for the hypothesis. It 

 should be mentioned, however, that individual occurrences of high 

 potential in cyclonic weather and of low potential in anticyclonic 

 weather were not infrequent. 



30. The results of the present inquiry are, I believe, irreconcile- 

 able with Exner's theory, in so far as it connects simultaneous 

 individual values of potential and vapour density. The question 

 remains open whether the annual variations of potential and vapour 

 density may not be related through a formula of Exner's type 



where A and B are constants for a given station, dV/dn and q 

 representing monthly means of potential gradient and vapour density 

 near the ground. 



Whilst the data available are far too limited for drawing a final 

 conclusion, I think it worth while to add in Table XXIII a compari- 

 son of the results at station A regarded as 60 inches above the 

 ground with those deduced from Elster and Geitel's special form of 

 the equation 



dV/dn = 



The figures are the arithmetic means of the values for the forenoon 

 and the afternoon hours of observation. 



