Yan Yean Water Works. 199 
This supply is equal to 1014 gailons per head per day, for 
a population of 100,000 persons. 
In thus laying before you, Mr. President and gentlemen, 
the results of our investigations, as also the several modes by 
which we have arrived at those results, we do so with 
much diffidence, being fully impressed with the difficulty in 
obtaining accurate results, under constantly varying condi- 
tions, resulting from meteorological changes, configuration 
and character of surface, &c. We believe that refined scien- 
tific deductions, relative to surface absorption and evapora- 
tion, however true under certain circumstances, are liable to 
many sources of error, where so many conflicting conditions 
have to be meted out, adjusted, and balanced with each 
other, so that each shall have a consideration consistent with 
scientific facts. We have not, therefore, attempted to solve 
this, the most important part of the problem, by such*means, 
but viewing it more as a practical question due to this parti- 
cular locality, we have, in the absence of local evidence, 
applied the data for surface evaporation of another country 
to this particular case; in the hope that its falsity or truth 
‘would be shown in the results it gave, when checked by 
legitimate deductions, we have shown how those results have 
been confirmed by the mean discharge on the eastern arm, 
and the other deduced therefrom. This result of mean dis- 
charge on the eastern arm was founded on accurate measure- 
ments, and most minute information as to summer and winter 
levels, furnished by a most intelligent farmer, in the imme- 
diate neighbourhood, who told us that the summer level was 
not lower than what we then saw it, and that the ordinary 
winter level was at the place of measurement up to the top 
of the banks, which exactly measured three feet above the 
summer level, and that the floods were over this again. 
In calculating the mean discharge, we have made no allow- 
ance for increase of fall with the increase of volume, but, in 
ignorance of its amount, have taken it upon the known summer 
fall of 8 inches intwo miles. We have also taken the discharge 
at such a point, near the head of the swamp, as to exclude at 
least six square miles of the drainage basin from the calcula- 
tion. ‘Taking all these circumstances into consideration, we 
believe our result of mean discharge is under the actual amount. 
Our deduction of the mean discharge of the western arm 
from that of the eastern must appear ooviously sound, 
when we consider that their conditions are precisely similar, 
their basins being both in the same formation, having the 
same soil and character, and therefore haying the same per 
