240 The Data on which we have to depend 
. Ft. In. 
1. Difference between 5 inch of rain over 624 square 
miles and 44 in.over60 sq.m. ... 1 7 
2. i between 500 gallons and 900 gallons ... 
3. 3 between my two estimates and not relied 
on hi S60 1 5h 
4, 35 between 2 and 10 “Shite of dew nee 8 
5 # between 5 feet 6°6 inches of evaporation 
and Q feet ... sae oe ono 3.4 
Total a ae 7 62 
Deduct loss of flood water, and loss from 
absorption... ae eae Act 6 
Balance to supply 191,500 ine ee 7 O28 
This table, then, exhibits the data on which depend all our 
hopes of an adequate supply of water from Yan Yean. 
If Mr. Hodgkinson is right in assuming these data, we 
shall have a very abundant supply, at least for our present 
wants. If, on the other hand, I shall succeed in showing 
that he is wrong, then, assuredly, the Yan Yean scheme will 
prove a failure, and we shall have to look elsewhere for our 
water supply. 
Having been induced, on public grounds, to investigate 
the points upon which Mr. Hodgkinson differs from myself, 
I trust that, in freely expressing my opinions on our points 
of difference, he will give me credit for simply wishing to 
arrive at the truth, and, as the question at issue isa iost 
momentous one for the public interests, both in a pecuniary 
and in a sanitary point of view, I trust that he will see no 
impropriety in my calling in question his opinions on subjects 
which he himself admits require further elucidation. 
1. What reason does Mr. Hodgkinson assign for assuming 
5 inches of the rainfall, instead of 4 inches or 6 inches? 
This is a very important question, as one inch over 625 
square miles will supply 62,500, at 40 gallons per head, 
per day. ° 
The evaporation tables of Mr. Charnock, the Vice-Presi- 
dent of the Meteorological Society, and Mr. Howard, have, 
according to Mr. Hodgkinson, been chiefly relied on of late 
years, in Y estimating the proportion of the rain that is avail- 
able for water supply i in England. 
The available rain, according to Mr. Charnock, is 4°88 
inches out of a rainfall of 24°6 inches, and according to 
Mr. Howard the proportion is 6°53 inches out of 36 inches. 
- Mr. Charnock’s observations have reference to a previous 
