Failure of the Yan Yean Reservoir. 137 
The latter writes to the Society, “ that although precluded, 
from want of time, from affording his assistance in the calcu- 
lations of the Committee, yet, if he could have agreed with 
the conclusions arrived at by them, he would have appended 
his name to their report, but he differed very materially from 
some of their views.” 
It is much to be regretted, that the Committee thus lost 
the co-operation. of two of the members, and especially on 
the grounds above stated, as it is evident, that they, as ori- 
ginally constituted, would have arrived at very different 
conclusions, and although I entertain the highest opinion of 
the professional abilities of Messrs. Christy and Acheson, I 
have to state, on public grounds, that however competent 
they may be to draw up a report on the watershed of Eng- 
lish rivers, with the aid of English tables, they cannot be 
supposed to have much practical knowledge of the rivers of 
this country, from their comparatively short colonial expe- 
rience, and they have never actually seen the river Plenty 
in the winter months, although their calculations show that 
they expect nine-tenths of the whole supply from the winter 
rains. The report, therefore, has lost much of that practical 
value that would otherwise have attached to any document 
emanating from a Committee of the Philosophical Society. 
Finding such an enormous difference between my esti- 
mate of the watershed of the Plenty basin, and that ar- 
rived at by the Committee, Mr. Hodgkinson was induced to 
read a very interesting and valuable paper on the subject be- 
fore the Society ; and the result at which he has arrived 
strongly corroborates all my calculations and conclusions 
with respect to the watershed, which is the fulerum upon 
which the sufficiency of the supply for a rapidly increasing 
population will depend. At forty gallons, per head, per day, 
Mr. Hodgkinson calculates that there will be water for 
190,000, so long as there is no drought like that of 1837-38 ; 
as eae a contingency he thinks the supply of water would 
Ta A 
But, it is to be noticed, that this estimate for 190,000 is 
based on a very important consideration, about which there 
_ is at present some difference of opinion. He has taken mea- 
surements of the evaporation from a pond which supplies his 
house, and calculates that it does not amount to more than 
five feet six inches in the year. Dr. Davy, on the other 
hand, who is our highest meteorological authority, regards 
ten feet as the probable evaporation. Now, at forty gallons 
P 
