150 JOHN M. SMAIL. 
Board of Water Supply and Sewerage, in connection with this. 
matter. Observations were made at two points on a line of sewer, 
viz., one at a shaft ten feet deep and another fifty feet deep. The 
observations were taken a depth of ten and forty feet respectively. 
It was found during the months of June, July, August, September 
and October the current set steadily from the low to the higher 
shaft, the hourly discharge at the latter being 14,000 cubic feet— 
the air being drawn in at two low points. This action was. 
reversed during the warm weather, the low points discharging, and 
the deep shaft acting as an induct. The diagram attached shews. 
the results of the temperature of sewers at ten and forty feet deep,. 
mean external temperature and mean humidity of open air. 
Barometic changes also affect the amount of foul air in the 
sewers. The diminution in barometic pressure leads to the escape 
of gases which are stored in the interstices of the sewage and 
favour decomposition. An increase of barometric pressure enables. 
sewer air to carry a large amount of the vapour of water and the 
sewage to retain a larger volume of the offensive gases due to. 
decomposition or absorption, without parting with them. 
The next force which affects the air of sewers is wind. The 
observations made by officers of the Sewerage Department shew 
that the action of the wind had great effect upon the currents in 
the sewers. On quick grades the current was in direction of the 
flow, if the force of the wind was small; on easier grades the 
current was reversed, so that in a line of sewer might be found 
currents setting in different directions according to circumstances. 
Observations have been made in Wimbledon, England, by Mr. 
Santo Crimp, A.M.1.c.E., with like results, the conclusion arrived 
at by that gentleman after a series of tests, being that the wind was 
the principal agent in controlling the air currents in a sewer— 
these observations were made, as in the case of the Sewerage 
Department, on sewers properly laid and ventilated by manholes. 
Old system of sewers.—The old system of Sewerage of this City 
was initiated by the old City Commissioners in 1853. The sewers 
were constructed on the then known principles as regards form, 
