For our Water Supply, 



237 



and contradictory, it rather proves that both the premises 

 and the conclusions are ahke 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 preferino- 

 his own of five and a lialf feet. ° 



I 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 wiU 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, since 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 altoo-ether 

 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 

 ramfall of the rest of the basin, which is thus rendered no 



