(c.) They are also affected by the fluctuations of the flow of sewage in the sewer, or by barometric changes in the atmosphere.
(d.) The situation of the open grids in the street is sometimes somewhat awkward for traffic, and horses will frequently shy at them, they also admit solid road detritus into the sewer unless they are protected by a catch plate of some description.
(e.) They are tempting places for children to play over, with what results may be imagined.
(2.) Open shafts are carried up the sides (gable ends if possible) of buildings in the neighbourhood of the sewer; these shafts may be either open at the top, or be furnished with exhaust cowls. This system is sometimes employed in conjunction with inlet shafts at the sides of the street, in the manner shown by the drawing which follows:
This method has the advantage over the first system I have mentioned of carrying the smells further from our reach, but it also has the following disadvantages:
(a.) The distance and the number of bends and elbows the gases have to traverse before reaching the external air.
(b.) The difficulty of fixing them just at the points where they are most required with reference to the gradients of the sewer, especially if they are to be constructed of such an internal diameter as will ensure their efficiency.
(c.) The great objection raised by occupiers and owners of premises against having them fixed on their premises, both on sanitary and legal grounds.
(d.) Their great expense.