ON THE QUANTITIES OF RAIN AT YORK. 173 
conditions, viz., the vertical measure of the tract of air interven¬ 
ing between the stations, and the temperature of the season of 
the year; the former determining the ratio of the differences of 
quantity of rain at different elevations above the ground, the 
latter influencing the amount of these differences. The depen¬ 
dence of this amount upon the temperature inversely, and con¬ 
sequently upon the humidity of the season directly, led to an 
attempt at a simple explanation of the phenomenon, not ma¬ 
terially different from that proposed (as M. Arago has informed 
me) without experimental proof by M. Boisgiraud. 
The second series of observations confirmed very completely 
the conclusion previously adopted, of the dependence of the 
amount of the difference of rain between a station on the ground 
and others at some height above it, upon the temperature in¬ 
versely. But the ratio of the differences at different elevations, 
which had been formerly supposed constant, was found to vary, 
and also to exhibit some characteristic variations in different 
seasons of the year. This suggested the hope of determining, 
by a third series, the limits of the variation of the ratio, not only 
in different years, but in different seasons of the year, and of 
thus advancing a considerable step toward a satisfactory solu¬ 
tion of the whole problem. 
We may first consider the amount of the differences between 
the quantity of rain at the upper stations and that on the ground; 
this being exactly proportional to the coefficient m in the discus¬ 
sion of the first series. 
Table of the Quantities of Rain and Ratios of the Quantities 
at the Three Stations , for Three Years , in different Seasons 
of the Year. 
Minster. 
Museum. 
Ground. 
Ratios. 
3 summer months.... 
Inches. 
13-473 
Inches. 
17-430 
Inches. 
20-306 
66-35 
85-83 
100 
5 warmer months .... 
20-012 
26-126 
30-916 
64-82 
84-50 
100 
7 warmer months .... 
24-834 
32-320 
38-551 
64-42 
83-84 
100 
7 colder months. 
18-220 
25-100 
33-999 
53-58 
73-82 
100 
5 colder months. 
14-130 
19-789 
26-879 
52-60 
73-62 
100 
3 winter months .... 
14-138 
12-170 
17-320 
49-94 
70-26 
100 
General ratio derived from the sums of the quantities 
59-15 
79-14 
100 
