Failure of the Yan Yean Reservoir. 133 
Total - - - - : 11 ft. 6% in. 
Deduct evaporation - - - - 9 0 
Balance - - - - - 2 64 
Required for present wants - - - 3 8 
Balance deficiency - - - - 1 14 
This is indeed an unfortunate result of the gigantic opera~ 
tions and large expenditure already incurred at Yan Yean. 
And it seems not a little extraordinary that such unlimited 
confidence should have been placed in the abundant supply 
of water; and it is no less extraordinary that Mr. Blackburn, 
with a knowledge of the immense loss sustained from evapor- 
ation in the marshes, should have urged the necessity of 
rescuing the river from this slough of despond only to plunge 
it into an abyss of greater magnitude, where it would be 
scattered, contaminated and rapidly dissipated. 
But it will probably be said, that as 1 have only shown a 
deficiency of one foot and one and a half inches, which is 
rather less than one third of the amount required, I may be 
in error in my estimate, and perhaps the winter rains may 
furnish the amount. Now, I shall admit that in some seasons 
even double this amount may possibly be added to the reser- 
voir from this source, but I do not think that this need be 
regarded as a subject of congratulation. With a stream of 
pure water, encircling this city like a horse shoe, the inhabi- 
tants will not willingly pay £650,000 to be subjected to the 
chances of the seasons, to be dependent on the casualities of 
rain for the first necessary of existence; and, if we must 
speculate on chances, how often do we have summers remark- 
able for droughts, and the prevalence of hot winds? And, 
what we gain by casualties of rain, we shall certainly lose by 
the casualties of evaporation. An inch a day, for hot winds, 
which as we have seen is a small allowance for a temperature 
of 96°, would make short work with two feet in the reser- 
voir, and this is the greatest addition which could reasonably 
be expected from the ordinary rainfall of the winter months. 
It will be readily admitted that in estimating the available 
discharge of a river for the supply of a large city, it is 
necessary to take a low average, instead of the mean for a 
number of years, because it is essential to know what amount 
can really be depended upon for each year, as the water supply 
of a city should be placed beyond the reach of casualties. 
The late Mr. Blackburn was fully impressed with the 
importance of this principle, hence he assumed his measure- 
