PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 475 



The question of the best system of sewerag'e for cities and towns is very 

 urgent, and at no period has it ever been of greater importance than at the 

 present time. The healthy existence of cities and towns must ever be 

 influenced by. their sanitary condition. 



Disease.s are natural to man when thickly congregated, whether in cities, 

 towns or armies, but their ravages are greatly aggravated by the physical 

 impurities of the atmosphere. 



It is impossible, unless at great expense, to construct a culvert (or 

 sewer) on the old method, through quicksands and springs, so as to pre- 

 vent the water from working through the lower arch and thereby washing 

 the sand through the joints into the sewer from behind the brickwork, 

 causing the brick to press out and undermine the upper arch when there is 

 an internal pressure from a great flow of sewerage, thereby causing fre- 

 quent repairs, or facilitates their acting like sieves by allowing the filth 

 to percolate between the cracks, leaving the soiid parts of the sewerage- 

 matter to settle, deposit and become a nuisance for want of sufficient water 

 to carry it ofiF in suspension. The ground around the sewer becomes filthy, 

 which causes the oftensive odor and poisonous gases to arise, so frequently 

 complained of in cities, from the long retention of matter putrifying in 

 and around the sewers. 



The advantages of the improved suspension culvert (or sewer) may be 

 stated as follows: 



1st. The iron counter will obviate all the difficulties in constructing 

 sewers thrttugh swamps, quicksajid, springs &c., and it will prevent any 

 of the liquid within from percolating the street, and with the smoothest 

 possible surface for the passage of the water, will keep the sewerage 

 matter in suspension until carried off by the ordinary flow of water. 



2d. It is simple in its construction. While it is durable, less expensive, 

 and can be built with more correctness and regularity, the accuracy of the 

 form and the exactness with which it can be laid to a true inclination is of 

 a great practical importance, by keeping the flow in motion and preventing 

 the sewerage-matter from settling. 



3d. The expense and trotible of putting in the cradling, coffer dams, &c., 

 and the dangers that are connected with the breaking of these, are avoided. 



4th. The filth and dirt which are often gathered in those places through 

 •which culverts are required to be built, can remain and need not be dis- 

 turbed in order to put in the suspension arch. 



5th. The filling-in can be carried on while the workmen are putting the 

 bottom counter to its place, and the water can pass through it while the 

 masons are building the top arch. 



6th. The stringers and flanges can be used as a railway to convey the 

 materials to the workmen. 



Ith. It can be constructed with perfect safety at any season of the j'car, 

 and only a portion of the piles necessary in the old method are required. 



8th The culverts can be carried out to the ends of piers, so that the 

 filth wir be emptied into the current and carried away, by which arrange- 

 ment the docks -vill bo kept clear, and all causes of disease arising from 

 malaria in such places "ill be avoided. 



9 th. When laid iu quick:=!ands the top arch can be cast of iron and bolted 



