Failure of the Yan Yean Reservoir. 



153 



I know of no civil engineer who has added anything to our 

 knowledge of the watershed of diiferent 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 remov- 

 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 Marlschal 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 mannei*; 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 



