1829.] 
Experiments on Evaporation. 
287 
Month. 
Sum of 
days. 
Number. | 
Spaces of 
trial, extent 
in square, 
feet. 
Mean 
depth. 
| Mean spe- 
cific gravity. 
Method. 
Evaporation 
per diem. 
Remarks. 
January, ~~~~ 
7 
i 
150,000 
inch. 
4. 
1007.5 
Sp. Gr. 
inches. 
.18 
Towards the end 
of the months and 
February, ~~~ 
42 
5 
500,000 
3. 
1015.5 
.1625 
not satisfactory. 
March, 
190 
ii 
850,000 
4. 
1024. 
.232 
Added 25 P. Ct. 
75 
s 
540,000 
3.4 
1052. 
Wr. Mk. 
.23 
for ground influ- 
May, 
79 
7 
443,000 
4.5 
1066. 
.304 
ence to .1859. 
Mean 
393 
7 
497,000 
3.8 
1037. 
.2226 
excluding Jan. 
386 
7 
583,000 
3.7 
1039.4 
.232 
In forming this tabic, I have rejected all observations which gave manifestly false 
results. The double test of depth and specific gravity was a good means of detec- 
tion, and it did sometimes happen that leakage occurred when there was consider- 
able difference of level between contignous enclosures. By considerable, I mean 
three inches and upwards. Errors of small amount may have arisen from inaccu- 
rate estimate of the rain, which, falling in showers of partial influence, could not be 
correctly estimated by a raiti-guage, stationed in Calcutta, there being none at Bal- 
lyaghat. In most cases however, and those the most important, the showers were 
computed next morning by the water marks of the factory. One enclosure (No. 5 
E. of 36000 square feet) so situated as to lose nothing by soakage, remained 
shut from the 10th to the 28th May, during which time its depth of water was reduced 
from inches 6. 9 to 2.4, notwithstanding 4 showers, computed at 1. 2. The daily 
evaporation therefore in that interval, appears to have exceeded 3. (three tenths of 
an inch) from sea water of average condensation 1072, and ranging between 1056 
and 1120. This far exceeds the fresh water evaporation from Mr. Kyd’s wooden 
cistern of 100 square feet and nine inches mean depth, which served for his experi- 
ments at Kidderpore in 1821 and 1822. Indeed, nil the above results are much in 
excess of his, except as to the month of April ; and I must remark, that the season was 
not a particularly hot or dry one, certainly not in May, which had 11 days of rain 
this year. I have often suspected that the locality of Kidderpore, and the circum- 
stance of the cistern not having been kept full (the sides averaged about three inches 
above the water) might have been unfavourable to evaporation to the extent or even 
20 per cent, or more, 1 believe also it would have been somewhat greater it the 
depth of water had been less. ... , , 
I exnected to find a higher ratio of evaporation on the two large tiled terraces con- 
structed ft condensing the salt at Ballyigbat, each 35000 feet area as the depth of 
water uoon them in most parts did not exceed an inch to an inch and a half, its tem- 
^ture P , undeTth" action of the sun, ranged from 100 to 110 of Fahrenheit and 
sometimes higher. In this I was disappointed, which I attribute to their low level, 
havinv traced* lateral and underground pressure m turn or three places. But the 
passage of water from outside, and from one part of the terraces to another, was so 
frequent, that little faith can be placed in calculations founded on my registered 
notes, as far as they are concerned. Rejecting a large proportion of them manifestly 
unfit for our present purpose, I find the following results. 
Month. 
Days. 
Spaces. | 
Depth. 
Sp. Gravity. 
Method. 
Daily eva- 
poration. 
Remarks. 
March, 
April, 
May, 
24 
iy 
.13 
7f 
2 
2 
10 
5 
2.5 
1.5 
1 . 
1017 
1085 
1144 
Specific Gravity. 
.144 
.150 
.189 
The platforms (or terrace 
divisions) were usually cover- 
ed to the width of 10 or 11 
feet each, leaving 3 or 4 feet 
dry between them. 
Mean of day, 
1.7 
1092 
.161 
