Page:Proceedings of the Royal Society of London Vol 60.djvu/144

Rh reasons already mentioned, this is not an important exception. There is thus a certain amount of general support to Elster and Geitel’s theory. An examination, however, of numerical details does not seem favourable to any such intimate connexion between sunshine and potential, as the formula suggested by them would imply.

Taking, for instance, Table XIX, we notice in series III that, in the afternoon, a mean potential of 106, answering to a mean of 3‘6 hours’ sunshine, falls only to 101 when the hours of sunshine rise to 9-5. Again, in the forenoon observations of the same series, the mean hours of previous sunshine increase fully six times, while the potential falls only from 111 to 93.

The afternoon observations of series II are a striking illustration of the diverse conclusions to which the different methods adopted in Tables XYII and XIX may lead.

§ 26. The forenoon observations of series IV, and both forenoon and afternoon observations of series II associate high potential with low temperature in both Tables XVII and XX ; and the balance of evidence is unquestionably in this direction. The only sub-case in which the two tables agree in associating higher potential with higher temperature is the afternoon observations of series I, which, as already explained, is the least important of the eight instances. On the whole, the evidence in favour of a connexion of high potential with low temperature is just about as strong as that in favour of a connexion of high potential with little previous sunshine.

§ 27. Higher potential is associated with higher pressure in the forenoon observations of each of the four series both in Tables XVII and XXI. In the afternoon observations, however, the higherpotential is associated with the lower pressure in three cases out of four in Table XVII, and in two cases out of four in Table XXI. The phenomenon, in short, is an apparently clear association of high potential and high barometric pressure in the forenoon, and an apparent absence of any connexion in the afternoon.

§ 28. A somewhat striking similarity exists here to the phenomena observed in the case of barometric pressure. In both the Tables XVII and XXII there is in the forenoon results a conspicuous association of high potential with low wind velocity. In Table XXII, it is true, series I observations form an exception,.