50 Suggestions for a System of 



the only means of cleansing the smaller drains was by open- 

 ing, and, in fact, partially reconstructing them. For the 

 larger sewers there was no alternative hut sending men to 

 remove the filthy deposit. The many manifest objections tothis 

 mode of keeping a clear way, led to a trial of cleansing the 

 large drains and tributaries by other means. The first that 

 suggested itself was by " flushing." This plan was not found 

 to be in all cases practicable ; and, moreover, where it could 

 be applied, the great size of many of the sewers, and the 

 rapid accumulation of deposit in them, required a supply of 

 water not always attainable. From these difficulties arose 

 the trials which more immediately led to the introduction of 

 the tubular system which now prevails so extensively. 



These investigations resulted in the discovery that the force 

 of a given body of water passing down a stated incline was 

 in an almost inverse ratio to the surface presented for it to 

 travel over, a fact which has been illustrated as follows : — 

 " A stream four feet wide and one inch deep, with a fall of 1 

 in 150 is sluggish] the same water if passed through a pipe 

 of twelve inches diameter, having the same rate of fall, would 

 be, comparatively, a rapid stream. The one would deposit 

 silt or sand, the other would certainly remove both." A 

 sewer presenting the sectional shape of an egg was suggested 

 as the most efficient for general purposes where considerable 

 size was necessary, from combining in conformity with the 

 above rule the greatest possible strength with the least 

 obstruction to the passage of water. It was further shown, 

 that while smoothness of surface and exactness of shape were 

 essential, as presenting nothing for sullage to lay hold of, the 

 preservation of or near approach to the circular shape was 

 equally so, as admitting of a nearly equal pressure of fluid at 

 all points. The delivering value of pipes of perfect outline 

 and smooth surface was found to be at least 25 per cent, over 

 slovenly made and irregular tubes, or, in other words, the 

 flow of water through them was one-fourth faster. These 

 experiments further showed that a pipe of three inches 

 diameter, fifty feet long, and laid at a fall of 1 in 120, dis- 

 charged one hundred gallons of water in three minutes, the 

 water not being higher at its inlet than the head of the pipe ; 

 whilst a fifty feet length of pipe, six inches diameter, laid at 

 an inclination of 1 in 100, discharged the same quantity of 

 water in fifteen seconds. Other experiments on tubes of 

 larger size gave correlative results. 



The next point was comparison of tubular drains with the 



