Proceedings of the Polytechnic Association. 811 



pavement by the machine and hand-brooms in Broadway. 2. A strong 

 shower washes the pavement clean, excepting where there are holes, 

 in which water remains and sediment falls. 3. In wet weather the 

 streets are not swept, bnt mud accumulates for days and weeks ; and 

 the mud holds water like a sponge, and keeps the streets wef for 

 days after the sidewalks would be dry, were the mud not tracked 

 upon them, 4. The best time to wash a street is while it is wet ; 

 the washing engine would then use less water. 5. As soon as rtiin 

 is over, the washing engines would do their work,*and blow the dirty 

 water out of the holes, and leave the pavement nearly dry, so that 

 in half an hour it would be completely dry ; thus saving the muddi- 

 ness, which now lasts from two to six days before the contractor 

 sweeps. 6. The cost of washing by hose-jet in Sheffield was less 

 than half the cost of sweeping and cartage ; proper washing engines 

 would further reduce the cost. The washing would make less dust 

 thaii sweej^ing. 



Considering the mud avoided, and the little if any dust, the wash- 

 ing system would give more than double cleanliness, probably at half 

 the cost of the present inefficient system. 



The washing engines would be efficient fire engines, and would 

 always be ready to leave their street work instantly wlien fires occur : 

 their cost would therefore be little beyond what is now incurred for 

 engines and men, w-ho do but few hours' work in a year. 



Floating fire engines could dredge the docks by jet, while the tide 

 runs outward, and thus clear the docks from the street dirt, and at 

 the same time serve as fire engines better than if kept inactive, 

 without steam up and their fires strong. 



Some of our sewer engineers say that the sewer gullies are not made 

 to pass street dirt, but to catch it; and that, therefore, alterations 

 would be required to make this proposed system practicable. Others 

 say that much of the street dirt does go through the sewers. I am 

 convinced, by evidence published in England, that the system is 

 practicable with the present gullies, and that the gully traps are 

 needed to catch the gravel that is often found in streets, and that 

 might do harm in the sewers. Mr. McElroy's paper is good pro- 

 fessional evidence against the hasty surmises of engineers who have 

 not studied the subject. 



An improvement in city engineering is needed. There should be 

 a chief engineer, under whom the engineers in charge of the aqueduct, 

 sewers, docks, fire department, etc., should serve. The chief should 



