Failure of the Yan Yean Reservoir. 153 
I know of no civil engineer who has added anything to our 
knowledge of the watershed of different countries. Original 
experiments and observations on this subject have been prin- 
cipally contributed by medical men. Perhaps Mr. Dempsey 
may be cited as an exception; but I think the less that is said 
about his evaporation tables the better. 
I need scarcely add that it is not to civil engineers, but to 
members of the medical profession that we owe all our know- 
ledge of the impurities of water, and their injurious effects on 
health, as well as the best and most effectual means of remoy- 
ing and counteracting them. And we are especially indebted 
to Dr. Hassall, of London, for his laborious microscopic ex- 
amination of the impurities of all kinds that abound in the 
water that is supplied to the city. 
Dr. Clarke, Professor of Chemistry in the Marischal Col- 
lege, Aberdeen, is acknowledged to be the highest authority 
in England, in all questions connected with the water supply 
of cities; and Dr. Smith, Professor of Chemistry in the Uni- 
versity of Sydney, who for some years conducted all Dr. 
Clarke’s practical investigations, is the highest authority on 
such questions in the Australian Colonies. 
I think it will be admitted, therefore, that the scientific 
subjects considered in this paper come strictly within my own 
province, as a member of the medical profession, and that 
there is no reason why I should be disqualified to discuss 
them in a scientific manner; and I think I have sufficiently 
demonstrated, by legitimate reasoning, that the calculations 
of the Committee are not based on any correct or scientific 
data at all, but purely on speculations and assumptions of their 
own, and that the results to which they lead, when thoroughly 
investigated, are so incredible, as to carry with them their 
own condemnation. 
In my estimate of the water available for the reservoir, I 
consider that ample justice has been done to all the sources of 
supply. : 
I have shown that, at the time of our late visit to Yan 
Yean, the whole discharge above the swamps was 5,790 gal- 
lons per minute, and, that of this amount, 3,253 gallons per 
minute were lost by evaporation in the swamps, or at the rate 
of four feet four inches in the reservoir; and I have taken for 
granted that effectual means will be adopted to prevent this 
loss, which, I have before stated, amounts to two feet five 
inches in the reservoir in twelve months. The total amount of 
supply for the reservoir I have estimated at eleven feet six 
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