64 The Drainage of Melbourne. 



the existing population of 200,000 would be about £10,000, 

 instead of £900 only, the sum provided in the essay. If it 

 be urged that the sum of £900 is, as stated in the essay, for 

 pumping only, not one of the numerous other items just 

 mentioned is provided for. 



11. The next point that may be considered is the engine- 

 power allowed for pumping. The work to be done by the three 

 pumps is to raise 18,300 gallons — equal to 183,000 lbs. — per 

 minute to a height of 15 feet, or 2,745,000 foot-pounds per 

 minute. One effective horse-power being represented by 

 33,000 foot-pounds per minute, it is clear that the effective 

 power required is that of over 83 horses. Adding one- 

 fourth to cover loss by friction, &c., the result is that 104 

 horse-power engines ought to be provided, instead of 79 

 only. Professor Rankine's rule* gives the same result. The 

 point is, perhaps, chiefly a question of the definition of 

 terms ; one manufacturer asserting that his engines are 

 capable of doing more work than that expressed by their 

 nominal horse-power. Whatever pump-makers may, how- 

 ever, promise on behalf of their machinery, it would be only 

 prudent to make a considerable extra allowance for safety. 

 In any case, the question could be settled by adding to the 

 amount of the estimate. 



12. A very important point in any drainage scheme is 

 how the sewage is to be finally disposed of. The locality 

 selected in the essay for Melbourne is a portion of the 

 Sandridge Flat. It is little more than two miles from the 

 heart of the city in a south-west direction; and it is due 

 west of Sandridge and Emerald Hill, close to the former and 

 about a mile and a half from the latter place. As the wind 

 blows from one or the other of these two points for nearly a 

 quarter of the year in an average season, it is most impor- 

 tant that there should be no doubt as to the area being suffi- 

 cient and suitable for purifying the sewage at all times, 

 without the risk of being offensive in any way. Yet it is* 

 scarcely possible to inquire into the provision made in the 

 essay for this part of the scheme without serious mis- 

 givings. 



13. The area said to be at present required is 120 acres, 

 formed into three divisions of 40 acres each ; one division to 

 be in use for four months or longer, while the other two 

 divisions are being cultivated. It is suggested that irrigation 



* Eankine's Civil Engineering, p. 734. 



