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The table shows us we cannot at all seasons rely on the superior temperature of the sewers for ventilation.
The last part of my subject presents fewer difficulties, I think, than the sewers.
No description of the way in which underground railways are now ventilated need be entered into.
We are all acquainted with the stifling atmosphere underground, and the choking, burning-matches odor which pervades the stations and streets near them. The insertion of iron grids in the roofs of the tunnels and the discharge of the noxious vapor and steam into the streets can hardly be considered a satisfactory solution of the question.
I believe we must here call mechanical ventilation to our aid. But first, let us consider the condition of the structure we are going to treat.
Taking one of the metropolitan railways as a type, we see it consists of a series of tunnels, and open or semi-open stations. The foul air is generated chiefly during the passage of trains through the tunnels, and
a certain quantity of this foul air is thrust into the station by the train as it enters the further end of the tunnel. This foul air, being heated, slowly ascends, filling the streets and neighboring houses.
The stations are nothing more than dwarf ventilating shafts in which the passengers are partially stifled previous to the completion of the process in the tunnel.
Having stated the conditions of the structure, let us consider what is required to be done.
First, we have a certain quantity of foul air to get rid of without harm or annoyance to the public. Secondly, the stations must be kept so clear as to allow of passengers using them with comfort. And thirdly, circulation of air should be maintained in the tunnels, wbich should be kept as sweet as possible, not only for the sake of the passengers, but for the workmen also, and for .the greater security of the public against accidents.
It seems to me that these objects will be best accomplished by reversing the present system, turning the stations into downcast
shafts, and drawing the foul air away at the middle of the tunnels.
A little consideration will show how a series of tunnels might be connected together by what might be called air sewers, and the foul gases led to one or more pumping stations, there to be forced up high chimneys.
The pumps might be either air pumps, such as are I believe used in some Belgian collieries, or machinery similar to Nixon's ventilator, or one of the many kinds of fan.
Some of these machines are very powerful. At the navigation pit, near Aberdare, Mr. Smyth gives the theoretical quantity of air expelled per minute, by one of Nixon's machines, at 166,000 cubic ft. In Belgium many fans of enormous power are at work ventilating coal mines.
Thc chief difficulty is the expense, but I submit this ought not reasonably to stand in the way.
I believe, however, that a plan could be found, which would accomplish the object at no very extravagant outlay.
I have said nothing about ventilating
ordinary railway stations--first, because it is difficult, if not impossible, to apply any system to a building which sometimes consists of but one wall, and a part of a roof; and secondly, when the station is of greater pretention, it is almost always open at both ends, and has usually a great deal too much air in it already.
Free escape for steam must be provided, and I think a good example of roof for this purpose was shown, to those of the members who visited the Great Eastern Railway extension works, on Friday last, at the low level station at Shoreditch.
In conclusion, I would again insist on the deep importance of the subject especially to Engineers and Architects. The limits of my space, not to mention other causes, have, I am well aware, prevented justice being done to it; but the object of a paper like this, is more to put forward sound principles and throw out ideas, which may when opportunity requires be worked out to good purpose, than to lay down schemes to meet every or any particular case,