Electricity at the Kew Observatory. 



Table V. 

 Forenoon and Afternoon Ratios. 



103 



and afternoon observations was T37 in series II, T23 in series IU, 

 and 1*48 in series IV. 



The difference between the mean potentials at the two hours on 

 the specified days being so large, we may reasonably suppose that if 

 any two other hours had been selected results would have been 

 obtained showing a degree of accordance similar to that in Table V. 

 The degree of accordance in the case of series II is truly remarkable, 

 and in series IV, considering the smaller number of observations, it is 

 but little inferior. If series III stood alone, we might suspect that in 

 the afternoon the potential fell off more at the higher stations than at 

 the lower, and this may of course be a true phenomenon of the season, 

 midsummer, to which that series belongs. 



Possible Dependence of Ratios on the Weather. 



8. It is conceivable that under one regular set of climatic condi- 

 tions the potentials at the higher stations might relatively to the 

 lower be either abnormally high or abnormally low. To test this 

 point, the observations in each series Kave been divided into sets, 

 according to the value of such a ratio as r E /r A . Attention has been 

 confined to series II, ill, and IV, as in series I the times of observa- 

 tion were less regular ; but the forenoon and afternoon observations 

 in series II and III have been considered separately. 



Supposing the number of measures of, say, r E /r A available in any 

 one instance to be 2n or 2n + l, the n cases in which the ratio is 

 largest form one set, the n cases in which it is smallest the other. 

 For each of these sets the corresponding mean values of certain 

 meteorological elements have been calculated, the data for the indi- 

 vidual times of observation being derived from the self-recording 

 instruments employed in the Observatory. The figures as to aqueous 

 vapour and humidity have been deduced from, the thermograms, with 

 the aid of a modification of Glaisher's table, compiled by the Meteoro- 

 logical Office. 



