For our Water Supply. 243 
is relied on as correct for the average surface of England, 
and Mr. Charnock’s tables, which are alone applicable to 
previous well-drained lands, give only 6:11 inches as the 
proportion of available rain for the Upper Plenty District, 
and 6°11 inches, if duly corrected in the manner described 
by Mr. Hodgkinson, would give considerably less than four 
inches. I am at a loss, therefore, to discover by what 
method he has arrived at his conclusion that five inches of 
available rain represent the watershed of the Plenty basin. 
There is nothing in his reasoning to show why he should not 
rather have adopted four inches, but the reverse. 
If he has adopted Mr. Charnock’s proportion of 6:11 
inches, then he has allowed 1°11 inches for all the contingen- 
cies to which he refers, and he has given no reasons why he 
should not rather have adopted Mr. Howard’s proportion, 
which gives, without any correction for temperature, only 4°73 
inches, for the rainfall of the Upper Plenty. And, as it 
appears to me, Mr. Howard’s proportion for England, with 
adequate correction for difference of climate, is the only safe 
proportion from which to deduce the watershed of the Plenty 
basin. 
I have not had an opportunity of correcting either Mr. 
Charnock’s or Mr. Howard’s tables of evaporation, for differ- 
ence of temperature, but I have in the following tables 
corrected Dr. Dalton’s precisely in the manner explained by 
Mr. Hodgkinson, and Dr. Dalton’s estimate of available 
rain for England, which is 8°41 inches, when thus corrected 
gives exactly 4°54 inches as the proportion of available rain 
for our climate, without any correction for our very dry 
atmosphere, for which half an inch in addition may be very 
safely allowed. Thus the conclusion is inevitable that the 
tables of Mr. Charnock, and Mr. Howard, if similarly cor- 
rected would give a still less result. 
Admitting, theréfore, that Mr. Hodgkinson is right in 
assuming Mr. Charnock’s proportion of the available rain as 
applicable to the Upper Plenty district, I do not think that 
he has advanced any good reasons to show that the differ- 
ence in the evaporation of the two countries is so small, as 
to warrant the very small allowance he makes for the differ- 
ences of climate, in adopting five inches. a 
In my former paper I expressed a very decided opinion 
that no confidence could be placed in theoretical estimates 
of the watershed of the Plenty basin, deduced from English 
‘data, at the same time, as a subject of scientific interest, 
rather than of any practical value, I assumed Dr. Dalton’s 
