Page:Proceedings of the Royal Society of London Vol 60.djvu/118

Rh Table V. Forenoon and Afternoon Ratios. Series of observations.

A A.M. P.M. A.M. P.M. i i. 0-29 0-28 1 -82 1 -83 in. 0 -24 0 -33 1-75 1-52 IV. 0 -22 0 -23 1-96 1-88 ?*D/A- ___ ?EI A- rp/x. ___________ A__________ A.M. > P.M. r A.M. P.M. r A.M. P.M. 2-24 2*21 2*62 2-57 — — 2-16 1 -87 2-57 2 17 — — — — 2-76 2-87 3-99 4-46
 * C/Ar c '

and afternoon observations—was T37 in series II, 123 in series III, and 1’48 in series IV.

The difference between tbe 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 seines belongs.

§ 8. It is conceivable that under one regular set of climatic conditions 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 have been divided into sets, according to the value of such a ratio as rE/rA. Attention has been confined to series II, III, and IV, as in series I the times of observation 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/rA available in any one instance to be 2 nor 2» + l, the n cases in which the ratio is largest form one set, the n cases in which it is smallest the othei*. For each of these sets the corresponding mean values of certain meteorological elements have been calculated, the data for the individual 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 .Meteorological Office.