Vapour Density.
§ 23. In Tables XVII and XVIII the forenoon observations of series IV, and both forenoon and afternoon observations of series II, support Exner’s theory to a certain extent, inasmuch as they decidedly, on the whole, associate higher potential with lower vapour density. The forenoon observations, however, of series I lead in both tables to exactly the opposite result. Also in Table XVII, in five cases out of eight, the higher potential is associated with the higher vapour density. In some instances, e.y., the afternoon observations of series III and IV, Tables XVII and XVIII lead to diametrically opposite conclusions. The following are instances of corresponding means of vapour density and potential, culled from the several tables. In Table XVIII, 8T2 occurs with both 185 and 93 ; in Table XI, 6-64 with 229; in Table XII, 6’62 with 180 ; in Table XVII, 6'57 with 204, 6'35’with 342, and 6’31 with 237; in Table XVIII, 6*61 with 141, 6’45 with 168, and 6-39 with 170. Again, in Tables XV and XVI we find6T0 associated with 273, and 6T7 with 217. Lastly, in Table XVIII we have the following combinations, 5'46 with 219, 5-40 with 333, 5’37 with 171, and 5‘27 with 147.
In tbe face of such results, it seems difficult to believe in any intimate and uniform connexion whatsoever between potential gradient and vapour density.
Relative Humidity.
§ 24. No special table is devoted to this. In Table XVII no less than six sub-cases out of eight associate higher relative humidity with higher potential. It will be noticed, however, that in three out of the six sub-cases referred to the differences between the mean humidities answering to the two groups are smaller than in either of the two sub-cases which associate higher relative humidity with lower potential. With the exception of the forenoon observations of series I, and the afternoon observations of series III, the differences between the mean relative humidities in the two groups are very small. Thus, on the whole, the evidence in favour of any distinct association of higher relative humidity and higher potential is insufficient.
Sunshine.
§ 25. There is in both the Tables XVII and XIX a balance of evidence in favour of a connexion of low potential with long previous sunshine. Out of eight sub-cases in each table, five favour this connexion in Table XVII, and six in Table XIX. The only sub-case in which the tables agree in associating higher potential with longer previous sunshine is the afternoon observations of series I, and, for
