142 Failure of the Yan Yean Reservoir. 
to check this result, they consult Mr. Dempsey’s tables, and 
find that exactly 57-6 per cent. of the ram in England is 
evaporated, and 42-4 per cent. goes to the rivers; and, for- 
getting that this colony is not England, and that our 
temperature is much higher, and that the evaporation from 
the surface of our uncultivated lands is vastly greater, they 
regard this coincidence as a proof of the correctness of their 
theory, and forthwith apply Mr. Dempsey’s English evapora- 
tion to determine the discharge of the Plenty river in the 
winter months. 
This extraordinary coincidence between their calculations 
and Mr. Dempsey’s tables, even to a decimal fraction, might 
at first sight, be supposed to prove the mathematical accuracy 
of both, but a mere coincidence is not to be regarded as a 
proof of the correctness of either, it is necessary that one or 
other should first be established on a firm scientific basis before 
such a coincidence could prove anything at all. I shall not 
attempt to explain this singular coincidence, though, doubtless, 
it would form an interesting subject in an essay on probabilities. 
I have already shown that Mr. Dempsey’s tables give three 
times the amount of watershed that Dr. Thomson calculated 
for Great Britain, and I am prepared to show that they give 
a very erroneous and incorrect result of the proportion of the 
rain that is evaporated here, for, when corrected for the 
difference of temperature, they give only one-fourth of the 
watershed calculated by the Committee, and therefore the 
data upon which they rely to check their own calculations 
will prove that they are altogether unworthy of confidence, 
and must be divided by four to give a truthful result. 
It appears, from the report, that the Committee chiefly 
rely on the eastern arm of the Plenty, for the supply of the 
reservoir. 
Taking their own measurements in January, as the summer 
discharge, although, in consequence of rain, it considerably 
exceeded Mr. Blackburn’s measurement in December, with a 
velocity of one and one-third mile per hour, it only gives 
4,450 gallons per minute, which for the six summer months 
is equal to three feet in the reservoir; their whole discharge 
for the Plenty they calculate at twenty-four feet eight inches 
in the reservoir, therefore the winter discharge for six months 
wil be eight times the amount of the summer discharge; but 
the section of the river will only contain three times the 
volume, supposing the stream to be level with the banks, with 
the same velocity, and they do not calculate for an increased 
