146 Failure of the Yan Yean Reservoir. 
of importance in this inquiry, it may be asked why the Com- 
mittee allow no watershed for the four summer months; 
their own reason is, that they think there is none; this ad- 
mission, therefore, is not to be regarded.as a set-off for their 
assuming 10°69 inches as the watershed of the eight 
months. 
According to Mr. Dempsey’s tables, the proportion of the 
rain that reaches the rivers in the four summer months in 
England is equal only to one-fifth ofan inch. Now, without 
any correction for the higher mean temperature here, one- 
fifth of an inch for our four summer months is too trifling to 
be noticed. 
This extraordinary error of the Committee in their mis- 
application of Mr. Dempsey’s tables, leads, as might be ex- 
pected, to very extraordinary results, and it is necessary to 
follow out their reasoning to its legitimate conclusion. 
Above Yan Yean, in January, the river gave three feet 
four inches in the reservoir in twelve months, and one foot 
one and a third inches in four months, or two feet two and 
two-third inches in eight months. The whole rainfall for 
twelve months, at thirty-one inches, is 68-2 feet in the re- 
servoir. Deduct the rain for the four summer months, 
which is equal to 5:77 inches, or twelve feet six inches in 
the reservoir, and we have fifty-five feet eight inches as the 
rainfall of eight winter months. Take 42-4 per cent. of 
this which gives twenty-three and a half feet in the reser- 
voir as the watershed of the Plenty in eight winter months, 
according to the calculations of the Committee. Add to this 
one foot two inches, or one-third of three feet four inches, 
to represent the discharge of the river for four summer 
months, and we have twenty-four feet eight inches as the 
total amount that comes down the river. 
Of this enormous amount of water, they generously pro- 
pose to bestow one-half on the district, which will be suffi- 
cient, as we shall presently see, to flood the river during 
the whole year, and may therefore prove a source of great 
inconvenience to the inhabitants. And it is their intention 
to appropriate the other half for the reservoir. 
Their calculations may be represented as follows :— 
i Ft. In. 
From the river during eight months - 23 6 
Do. four summer months - 1 2 
Total - - - 24 8 
