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 fl-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 hut 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 Eanges, 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 animalculse. 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 



