Surron—Study of Evaporation from Water-Surfaces. 157 
If now we arrange the details from which Table 12 was made 
into subordinate groups in which, for each 5 per cent. of relative 
humidity, 6 is greater or less than its median value, we get the 
following averages :— 
TasLe 13.—Open Cup. (1.) 5 to 8 p.m. 
5 < Median 53> Median 
Relative 
BE eo. (a | W | B No | 2 | v E 
apeig | ae Ge wl feeal |) een se) agen) oe) eee. 
35-39% | 11 | 639 | 3:3 27 10 | 75:5 | 27 42 
40-44 2 s | 57-3 | 3:5 20 9 | m8 | 21 31 
454927 | 13 | 589 | 3:4 18 | Gey i een 27 
Total, 40 | 61:9 | 39 26 41 | 73:0 | 926 35 
(2.) 8 to 11 p.m. 
40-44 2 7 | 55:7 | 62 20 7 | 70-4 | 3:4 27 
45-49 x 8 | 50:0 | 3 13 g | 69-7 | 4-6 28 
50-54 2 9 | 50-1 || 3-3 12 s | 61-9 | 3-4 15 
55-59 2 g | 547 | 3:6 7 7 | 65-2 | 35 18 
Total, 32 | 52:5 | 3:8 14 30 | 66:7 | 3-7 29 
Table 13 gives us the following further particulars:—For each 
given humidity group the evaporation is greater or less according 
as the difference of vapour-tensions is greater or less. But it also 
happens that the temperature of the water is greater or less under 
the same circumstances. Wherefore, so far as Table 13 can help 
us, the rate of evaporation might depend upon either the differences 
6 or the temperatures 7’, or both. 
Tables 14 and 15 give corresponding information to that of 
Tables 12 and 13; but for the one-foot pipe. 
