Page:Proceedings of the Royal Society of London Vol 60.djvu/146

Rh traced in §§ 25 to 28 betw een low potential and long previous sunshine, high tem perature, low barom etric pressure, and high wind velocity constitute the norm al state of m atters a t every station, irrespective of the hour or th e season. Provisionally I should prefer to regard these associations as possibly accidental, even a t Kew, but believe they indicate th e lines on which m ore exhaustive inquiries m ight profitably proceed.

Another possibility indicated by these associations, viz,, th at th e potential tends to be higher du rin g anticyclonic th an during cyclonic w eather seems also w orthy of attention. An attem p t was indeed made in th e present instance to check this conclusion directly by reference to the w eather reports of the M eteorological Office. The published data relate, however, to 8 a.m. and 6 p. m. ; so th at, on a considerable num ber of occasions the nature of the isobars a t the hours of the observations was uncertain. T aking th e rem aining instances, I calculated the mean potential for the cyclonic and anticyclonic conditions separately for each one of the four series, treatin g the forenoon and afternoon observations apart, except in the case of the first series. In five cases out of the seven thus presented, the m ean potential for the anticyclonic group exceeded th at for the cyclonic. There is thus som ething to be said for the hypothesis. I t should be m entioned, however, th a t individual occurrences of high potential in cyclonic w eather and. of low potential in anticyclonic w eather were not infrequent.

§ 30. The results of the present inquiry are, I believe, irreconcileable w ith E x n er’s theory, in so far as it connects sim ultaneous individual values of potential and vapour density. The question rem ains open w hether the annual variations of potential and vapour density may not be related through a formula of E xner’s ty p e— dV/dn = A /(1 + B 2o),

where A and B are constants for a given station, dV/dn and ,> representing m onthly means of potential gradient and vapour density near the ground.

Whilst the data available are far too lim ited for draw ing a final conclusion, I think it w orth while to add in Table X X III a com parison of the results at station A—regarded as 60 inches above th e ground—with those deduced from E lster and G eitel’s special form of the equation dV/dn = 1410/(1 + ri52o)-

The figures are the arithm etic means of the values for the forenoon and the afternoon hours of observation.