Proceedings. xi 
the question of the probable amount of the water-shed of the Plenty, 
which he estimated, according to Dr. Thomson’s method, at one- 
ninth (1-9) part of the rain ; and showed that the evaporation in 
this country was so enormous that if the whole water-shed of the 
Plenty could be secured for the reservoir it would be nearly all 
evaporated in twelve months. 
After the reading of the paper the Chairman called on the 
members to offer their remarks upon its contents. 
Mr. Acheson stated on the part of the committee the result of 
their calculations. 
Mr.Christy observed that about the same quantity of water reached 
the river here as in England. 
Dr. Wilkie said he was exceedingly sorry that the members of 
the commission had not brought up their report- He was also 
much surprised to find that, instead of availing themselves of the 
actual measurements, and from them deducing the supply for the 
reservoir, they had merely given some theoretical views with respect 
to the probable amount, and which were founded upon the deduc- 
tions of Mr. Dempsey, whose name he had never heard. The late 
Mr. Blackburn had, in his evidence before theSelect Committee, given 
5,000 gallons per minute as the average discharge of both branches 
of the river above the swamps, and he, Dr. Wilkie, had founded all 
his calculations upon that estimate, although, before the river reaches 
Yan Yean, one half was lost by evaporation in the swamps. He had, 
however, allowed an increase of one-third in the volume of the 
river for the six winter months, independent of floods; and now 
argued that, as the climate of Australia was exceedingly dry, and 
there were very few rivers, and those had but a small quantity of 
water in them, a much less proportion of rain reached the rivers 
here than in England. It was utterly impossible, he considered, 
that out of an inch of rain three-fourths could reach the river from 
every part of the drainage area; but his opinion was, that from the 
geological formation of the Plenty Ranges, a very large proportion 
of the rain was absorbed, and that it was because the ranges retained 
the winter rain and gave it out during the summer, that the stream 
was permanent. 
Dr. Iffla directed the attention of the meeting to the importance 
of the purity of water to the health of the inhabitants; for when 
filled with a great quantity of vegetable matter it was likely to be 
contaminated by a large quantity of animalcule. This was the 
more likely to take place in a reservoir, where the water could not 
freely flow, and where it was constantly under the action of the 
solar rays. 
The President of the Society who in the mean time arrived, 
said that the thanks of the public were due to Dr. Wilkie, for having 
directed public attention to this most important subject in a paper 
written with so much care. The meeting could not come to any 
