a ee a ee 
Surron—Study of Evaporation from Water-Surfaces. 161 
Here we see that as 6 increases the temperature 7’ of the water 
increases, the relative humidity A of the air decreases, and the 
evaporation £ increases, while the velocity W of the wind is of 
uncertain influence, as before. ‘Thus, so far as Table 16 goes, the 
rate of evaporation may depend either upon 6, or 7, or H, either 
or all. Now it is known that an increased water-temperature will 
increase the rate of evaporation, although it is possible that the 
effect has been somewhat overestimated. In any case it will not 
be necessary to discuss this particular point at present. 
Tf we arrange the details from which Table 16 is derived into 
groups of given vapour-tension differences, in which the relative 
humidity is greater or less than its median value, we get the 
following averages :— 
Taste 17.—Open Cup. (1.) 5 to 8 p.m. 
Wivverence H > Median | H < Median 
of Vapour- 
Tension | No. T | W | EB |\ No. T W E 
inch ° ° 
*150—-249 9 65°3 3°4 lbgr. 9 52°7 One l6gr. 
*250-—-299 8 65:5 2°9 17 9 56°6 2°4 18 
*300-—"349 10 67:0 2°6 20 12 62°7 3°8 25 
*350—"399 9 72°9 4°4 31 6 66°3 3°2 27 
*400-—"449 6 73°38 2. 30 6 69°0 ord 30 
*450—-349 10 (art 2-4 39 9 72°4 5°0 51 
*550-"599 3 76°9 2°0 38 + 76°) 3 jo7/ 50 
ovale. 55 70:2 3°0 PAT | 55 63°7 3°9 30 
100-149 | 7 | 66-1 oes || 7 | cape 2-9 9 
150-199 | 12 | 61-1 3°5 i | 13 | 50-0 3°8 13 
200-249 | 15 | 641 3° 14 || 15 | 55-6 3°3 4 
-250--299 7 68°4 1:9 oe pee o 63:2 6:1 26 
300-399 | 8 | 700 | 3:0 | 23 || 8 | 656 | 41 | 27 
Total, . | 49 | 65-1 3-0 13 | 52 | 55-7 | 9399 17 
