For our Water Supply. 237 
and contradictory, it rather proves that both the premises 
and the conclusions are alike unworthy of confidence. 
I could readily understand how Messrs. Acheson and 
Christy might be right and Mr. Hodgkinson wrong, or 
vice versa, but I cannot imagine how both could be right. 
If Mr. Hodgkinson is correct in assuming five inches as the 
highest reliable amount of the available rainfall in the 
Plenty basin, then most assuredly Messrs. Acheson and 
Christy are egregiously wrong in assuming 10°69 inches, or 
more than double that amount; and if they are right in 
relying on Dr. Davey’s experiments and observations on 
evaporation, then, in like manner, Mr. Hodgkinson is wrong 
in rejecting Dr. Davey’s estimate of nine feet, and prefering 
his own of five and a half feet. 
IT have thought it necessary to notice this supposed coinci- 
dence, because it is very probable that many persons may 
be deceived by it. Most people are satisfied with merely 
looking to the results in any inquiry, without examining the 
data or calculations on which they are founded, and, in this 
instance, being so positively assured of a very abundant 
supply of water in two different ways, they will regard the 
supply as all the more certain on that account, and will be 
contented to have it either way. 
It is far more correct, therefore, to infer that both are 
wrong than that either is right, smce each denies and con- 
troverts the premises of the other; and it is altogether a 
fallacy to suppose that the similarity of their results will be 
of any avail in securing a more certain or abundant supply of 
water. 
And I trust to be able to show in this paper that no con- 
fidence whatever is to be placed either in theoretical esti- 
mates of the available rainfall of the Plenty basin, or in 
experiments on ‘evaporation conducted on ponds and water- 
holes, but that’ actual measurements of the river, and Dr. 
Davey’s estimate of the evaporation are alone to be depended 
on in deciding the important question whether the Yan Yean 
Reservoir scheme ought to be proceeded with, or altogether . 
abandoned. 
This leads me to notice the confusion that seems to arise 
from the use of the term “ available rainfall.” As applied to 
the Plenty basin it has no intelligible meaning, because many 
thousand acres, according to Mr. Hodgkinson, are so swampy 
that there is not only no available rainfall from them, but 
they evaporate and absorb a large proportion of the available 
rainfall of the rest of the basin, which is thus rendered no 
