288 
Experiments on Evaporation. 
[Octr. 
which compared with the previous table in the corresponding months (.255) shews 
a difference not to be accounted for, hy an excess of .015 in the saltness of the water. 
Several observations of May give .2 in | ds. brine, and one of them .22 in water, at 
1110. A better criterion of the evaporation which really takes place under such cir- 
cumstances is the fact, that at the salt works at Gangs Sugar on the 13th May, 19 
niaunds of salt were obtained from three platforms of similar construction covered with 
brine of an inch to an inch and a half deep on a surface of 1900 feet each ; and on 
the 25th, 50 maunds were collected from 7J platforms flooded t > the depth of |th of 
an inch over a space of 1800 feet each. In the former case the evaporation seems 
to have been about . 17 , and in the latter above .18 from actual brine, in a situation 
more humid and of lower temperature than Ballyaghat. 
It occurred to me that I might obtain a proximate ratio of the aggregate evapora- 
tion from these brine fields by comparing the volume of water .in them at different 
periods. Excluding the two larger outer divisions, liable to be affected by pressure 
through the bunds and under ground as the tides rose or fell, even when the gates 
were shut, I find that in 12 days from the 8th to the 20tl» May the mass of water on 
a space of 800000 square feet, was reduced from 377500 to 189750 cubic feet, to 
which adding 1500 for 65 maunds of salt, reduced into brine of S. G. 1035, we have 
a perpendicular loss of inches 2.64 
Add raiu on 12, th 14th and 17th, .9 
3.54-f-12 = .295 per diem. 
Again, rejecting the largest of the divisions above included (No. 2 W) the mean 
depth of which it was most difficult to compute, we have on a surface of 660000 
square feet, a reduction of volume from 277500 to 156417 cubic feet, which with 
1500 for the salt as before, gives a perpendicular decrease of in. 2.23 
Add rain, .... .... .... . . .9 
3.13 In. 
and 3.13— fl2 gives per diem, .261 
To this however, must be added a correction for pressure from 
No. 2, W. through the bunds of the contiguous enclosure No. 3, 4, 
and a W, which in the whole term was certainly not less than one 
inch, say 149000 
1 X 12= .019 
660000 
the minimum result being .28 
A comparison of specific gravities applied to the whole space of 860000 
square feet during the same period gives per diem, .... .. .117 
Add rain, .... .... .... .... . . .075 
.192 
and ground influence, inches 1.6 — ) .064 
.256 
But here the causes of error are more complicated, as the experiment includes 
large shallow spaces of unequal specific gravity. An addition of .002 to the mean 
difference, would raise the apparent evaporation to .3 per diem. 
This last method of comparison I have applied to the deeper masses accumulated 
when the tide gates were opened at the close of the season, to let in water in reserve 
for the next. 
On the 31st May, X found on the 2 terrace s a volume of 64000 cubic feet at 1067 
surrounded by water, then every where reduced below 1050. In condensation from 
1050 it must have lost about 22000 feet, besides about 2000 in the production of 150 
maunds of salt, since tile dates to which we have buck to ascertain when water ex- 
ceeding 1050 began to appear in other divisions. The evaporation of these 24000 
cubic feet of water appears to have occurred in 1 1 enclosures of the aggregate ex- 
tent of 5300.10 feet, during a mean term of rather more than 20 days (the sum of 
days X the spaces being 10847000,) 
which gives per diem, .... .... .... .. .0265 
Add rain computed for each division, .... .... .. .1129 
1394 
