For our Water Supply. 257 
from English tables, the rate of evaporation being doubled 
with every increase of 20° of Fahr. 
But Dr. Davey has also shown that the mean dew-point of 
our hottest months is 50°, thus showing a dryness of 19°, or 
in the proportion of two and one-fourth to one compared 
with London. 
Now, according to the formule of Dr. Dalton, and Dr. 
Ure, 9°73 inches corrected for our dryness, would. give 16°22 
inches for each month, or 48°66 for three months. 
The above table shows that the English evaporation for the 
other nine months, corrected for temperature alone, is 47°85 
inches. 
As there are no correct data to show our relative dryness 
for these months, this correction must be omitted, but, even 
without this, the rate of evaporation deduced from English 
tables, in the manner described by Mr. Hodgkinson, amounts 
to eight feet 0°51 inches. 
Thus, if we make some additional corrections for our greater 
dryness for the nine months, and for the more “ intense action” 
of our dry winds, I do not see how Mr. Hodgkinson can 
escape from the conclusion, even according to his own method 
of calculation, that the evaporation from the surface of water 
in this colony is little short of nine feet. 
In my former paper I stated, on the authority of the Year 
Book of Facts for 1854, that Mr. Glaisher had estimated the 
evaporation at Greenwich at five feet; I have now ascertained 
from his Hygrometric Tables, that his estimate is four feet 
two inches, so that Mr. Hodgkinson’s estimate of five feet 6°6 
inches for Melbourne, is very little more that Mr. Glaisher’s 
for Greenwich, and the Greenwich evaporation when corrected 
f or our higher temperature, would give six feet three inches 
without any corrections for dryness and winds. 
But why does he resort at all to English data in order to 
deduce our evaporation in a troublesome and unsatisfactory 
manner? Had Dr. Dalton any peculiar method of determin- 
ing the evaporation at Manchester different from that adopted 
by Dr. Davey in Melbourne? [If it is correct to deduce our 
evaporation from Dr. Dalton’s evaporation for the nine months, 
why is it incorrect to depend on Dr. Davey’s evaporation for 
the three months? 
Both these gentlemen have adopted precisely the same 
method of experimenting in determining their respective rates 
of evaporation. 
Dr. Dayey’s experiments, which were conducted daily 
during the period referred to, are in every respect similar to 
GG 
