On tlie Botany Waterslied. 79 



engineering, are of opinion that from 75 to 84 per cent, of the 

 rainfall can be available in such towns as Manchester and 

 Paisley ; surely with such a highly favourable watershed as that 

 of Botany, we may reckon upon an available quantity of at 

 least SO per cent, of the entire rainfall, even with reservoirs and 

 ponds uncovered ; and, if covered, we may reckon upon nearly 

 the whole. However, regardless of all this, the Commissioner 

 deputed by the Water Commission to inquire into the Botany 

 supply, in making his calculations (page 108) of the proportion 

 of flow to rainfall, reduces it to one-fourth. Then he says, 

 ''^ This xvoulcl he rather a small proportion.'''' Why, I would ask ? 

 If his elaborate calculations and deductions are worth the paper 

 they are written upon, why cast them aside and say, without 

 reference to any calculation at all, " this would be rather a 

 small proportion ?" I perfectly agree with that Commissioner 

 that one-fourth would, in fact, be too preposterously low to be 

 believed by any one, even the most credulou?!. It would seem 

 that some one had suggested this, for he says immediately 

 afterwards, and again without reference to any calculations or 

 deductions, " It is considered that one-third of the rainfall may 

 reasonably be relied upon, even in the driest season.'" Now", 

 although this is but a mere guess, it is an advance from one- 

 fourth to one-third ; and while he was about it, he might as well 

 have extended it to two-thirds. It would have accorded more 

 with the results of practice, and would have been more con- 

 sistent in every respect. In the next page (110) in continuing 

 his calculation, he puts aside two-thirds of the entire rainfall 

 as an absolute loss, and then immediately afterwards makes 

 another reduction for loss by evaporation from reservoirs at the 

 rate of 6 feet per annum, when the evaportion at the Tan Yean 

 in the report of the Water Commission, as before stated, is given 

 at two feet only. If the evaporation at the Tan Tean is 

 believed not to exceed 2 feet per annum, why does the Commission 

 state that 4 or 6 feet for Sydney is " as near an approximation 

 as our present knowledge will justify." The report further 

 states that in India and other tropical countries the rate for 

 evaporation generally allowed is 6 or 8 feet per annum— the 

 report does not tell us by whom this allowance is made. They 

 are no better informed in India on this subject than we are 

 here. They have their Observatory instruments, from which 

 they tell us that the rate of evaporation at Bombay is 8 feet, 

 and at Calcutta, where there is but little sensible difference in 

 climate or atmosphere, they tell us it is 15 feet. This shows 

 that the results obtained at different observatories with regard 

 to evaporation are themselves so anomalous that they cannot 

 be depended upon as even relatively correct, and consequently 

 the results derived from the instruments by which they profess 



