486 Dr. C. Chree : Results obtained at Kew Observatory with 



association, the whole year round, of high values of a + and 

 a_ with low values of P, but this association according to 

 Table III. is decidedly less marked in summer than in winter 

 or equinox. There is, however, room for doubt whether the 

 apparent difference between summer and the other seasons 

 is real. It is due almost entirely to the one summer 1907. 

 In all four months of that season, the group of days of 

 largest P had the higher mean value of a_, and in two cases 

 out of four the higher mean value of a + . 



Tables VII. and VIII. both suggest that a_/a + has a 

 slight tendency to be large when P is high, but the 

 numerical differences for q and q' in Table III. are too small 

 to rely on and tend to differ in sign. 



Tables IV., VIP, and VIII. agree in associating large values 

 of both a + and a_ with high temperature, but the apparent 

 closeness of the association is widely different at the different 

 seasons. It is conspicuous in winter, but tends to disappear 

 in summer. In fact, when the three years are combined, 

 the two hottest months July and August associate high 

 values of a + and a_, not with the higher but with the lower 

 temperature group of days. Of the 24 individual months in 

 Table VII. which associate high values of a + with high 

 temperature, no less than 11 are contributed by winter, so 

 that the two other seasons only contribute 13 out of a 

 possible of 24. The association of high values of a_/a + with 

 high temperature is, according to Table IV., pronounced in 

 equinox but not in the other seasons. 



The relationship between temperature and potential pre- 

 sents closely similar features in its annual variation. It is 

 marked in winter in Table IV., high temperature going with 

 low potential, but not in equinox or summer. As Table VII. 

 shows, high temperature was associated with low potential 

 in 22^- of the 36 months, but no less than 11 of these were 

 winter months, and an actual majority of summer months 

 associated high temperature and high potential. 



The apparent relation between dissipation and barometric 

 pressure is in several respects the exact opposite of that 

 with temperature. According to Table V., high pressure is 

 at all seasons associated with low values of a + and a_, but 

 the association is much less apparent in winter than in 

 summer. This fact is all the more striking because the 

 mean pressure difference between the groups of days of high 

 and low barometer was conspicuously large in winter. As 

 shown in Table VII., the number of individual months which 

 associate high values of a + and a_ with high pressure is 

 appreciable, but winter is responsible for 6 out of 10 in the 



