Page:Proceedings of the Royal Society of London Vol 60.djvu/140

Rh § 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, iu which the observations are arranged in groups, according to the magnitude of some one meteorological 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 tempei-ature,* 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. Electricity at the Observatory. 125 Arrangement according to Vapour Density. 1 • * Forenoon. A Afternoon. _a ___ Series V apour Number Mean X Mean Number Mean Mean J of observations. grams per metre. of observations. vapour density. potential at A. of observations. vapour density. potential at A. T r > 6 7 7-71 191 4 6-61 141 1 1 < 6 11 5*27 147 3 5-13 143 f > 7 8 8*12 185 6 8-35 140 11 \ 7 to 6 8 6-39 170 6 6-45 168 1 <6 8 5-40 333 8 5-46 219 f > 1 0 4 12-30 104 6 11-11 92 n i l 10 to 9 4 9-39 117 5 9-66 122 L < 9, 8 8-12 93 3 7-92 96 >6 6 7-58 266 4 7-38 286 IV 1 !_______ < 6 7 4 83 279 6 5-37 171

it was doubtful whether to group it with the first n or last n.
 * The n + 1th constituent in the forenoon observation of Series TV is omitted, as