1829.] 
Experiments on Evaporation. 
289 
Brought forward, .1394 
Tt is obvious, however, that the water of one field would not pass bodily into 
the next, without mixture with that, which by its rapid entry at the same time, 
pushed it forward. The error on this account must be very great, for we have 
sought in two divisions only ( the terraces) the previous contents of 8, which were 
simultaneously open to the passage of water at 1040 and under, which 8 divi- 
sions contained about 70,000 cubic feet of brine, at about 1070 the previous day ; 
so that less than a third had passed into the terraces, and that partially dilut- 
ed ; add therefore, .0265x70 000 
22 000 
and for reduction from 1070 to 1067 .1108 X 5 3 T 
Correction for filtration from Nullah into No. 3 
2 days of evaporation lost in do. 
influence of ground — perhaps, 
.0050 
.2287 
.004 
.002 
.0053 
.0113 
.240 
By tracing back to a low degree of specific gravity, it was evident the large cor- 
rection for mixture of waters would be so reduced, as to become of small moment, 
and perhaps might be disregarded. A similar method of calculation was, therefore, 
tried with the registers of the days undermentioned, comprehending all above 1021, 
the greatest range I could take, without including the 2 outer fields : it gives the fol- 
lowing table of evaporation from 15 divisions of 86,1000 feet surface, averaging 
about 2 inches deep. 
u 
(£3 
r? fl 
.2 «s 
Corrections for 
1 
O 
o« 
Date. 
Surface in 
square fee 
Volume in 
cubic feet, 
No. of div. 
Mean spec 
gravity. 
* .2 
•f! 
II 
o 
> * 
| Mean tim< 
Daily loss 
perp. incl 
j Rain. 
J Leakage. 
Ground. 
Corrected 
daily eva 
ration. 
905 000 
484 000 
14 
1041.5 
cubic ft 
388 000 
(Is 
60 
.091 
.080 
.011 
.011 
.193 
760 000 
772 000 
14 
1031 .4 
319 000 
.075 
.084 
Oil 
.007 
.177 
464 000 
740 000 
11 
1029. 
283 000 
.066 
.120 
010 
.004 
.200 7 
7th Do 
834 000 
1276 000 
15 
1028. 
121 000 
64 
.093 
.109 
.010 
.005 
.217 
.234] 
13th Do. 
974 000 
1348 000 
16 
1028. 
586 000 
70 
.117 
.100 
.010 
.007 
M 
■an of the 5 trials. 
.0884 
.0986 
.01041.0068 
.2043 
In each case allowance has been made for 452 inaunds of salt not included in 
the estimate for the volume of water. The state of the weather between the 31st 
Mav and 3d June, was such that I considered the intervening evaporation might be 
disregarded • but the days which followed have been reckoned in computing the 
5 _ ' ..1 mi ‘ ...... — » : — .. r, in tlin poeiiltsnKtnmOfl nflpt’ fllt> 9fl.lnn/» 
which the ground previously c . ~ 
on that account that the last result (.234) was a more correct appreciation tlwn the 
mean of the 5 experiments, or even of the 3 last. Comparing these of the 4th and /Hi 
June, there would appear an intervening evaporation of .486 per dfeia, and between 
the 7lli and 13tli .338. The former is no doubt much beyond the tenth, owing to the 
cause already assigned; whereas up to the 2d June inclusive, the tHe-gatesconiimied 
open, and there were also several showers, which might have affected the surface 
(lisproportionallv, from whence alone my Hydrometer was supplied. The ground 
influence I have'taken equally at 1 inch. The correction is trifling in this table, but 
I am not sure that it ought to have been introduced at all. 
To sum up the general result of my experiments, 1 think it may be concluded 
from them imperfect as they are, that a greater evaporation occurs in the neigh- 
bourhood of Calcutta, than Mr. Kyd's experiments had led us to suppose ; and that 
the following rate for fresh water and even for sea water, not stronger than the 
ocean, is not too great. In the months of 
