Electricity at the Kew Observatory. 



125 



22. A discussion might be based on the previous nine tables alone. 

 Partly, however, to satisfy those who prefer a grouping system like 

 that of Exner, I add further tables, in which the observations are 

 arranged in groups, according to the magnitude of some one meteoro- 

 logical element. In dealing with vapour density, barometric pressure 

 and wind velocity, separating lines have been drawn at fixed values 

 of the element considered. In the case of vapour density the limits 

 required to be altered with the season. In the case of barometric 

 pressure and wind velocity it was deemed sufficient to draw only 

 one separating line, which answered, it will be seen, very nearly to 

 the mean value. In dealing with sunshine and temperature,* the 

 division has been into equal, or as nearly equal, groups as possible. 

 After the tables follows a discussion, which embraces Tables IX to 

 XVII as well. 



Table XVIII. 

 Arrangement according to Vapour Density. 



* The n + 1th constituent in the forenoon observation of Series IV is omitted, as 

 it was doubtful whether to group it with the first n or last n. 



