Page:The library a magazine of bibliography and library literature, Volume 6.djvu/109

 Ventilating and Heating System of Aberdeen Public Library. 97 below its level is an apartment, open on one side to the external atmosphere, the size of the opening being 6 feet 6 inches by 5 feet 6 inches. It is through this opening that all the air sup- plied to the building comes. To ensure its proper distribution there in all conditions of atmosphere, the air is drawn in by means of a Blackman fan, 5 feet in diameter, which is propelled by means of an Otto gas engine of 3 h.p., at such speed as may be thought necessary. The fan is placed at the entrance of a large duct, from which other ducts branch off to the several floors. In order that this incoming current of air may be as clear as possible, before it is propelled through the various channels, it is drawn through a screen of manilla hemp, which is kept moistened by an occa- sional automatic flush of water, thus effectually excluding all dust, soot, &c. In the winter time, when the outside temperature is lower than is desirable, the incoming current of air, after passing through this screen, traverses a large coil of high pressure hot-water pipes, heated by a patent slow combustion furnace, by means of which it is suitably warmed prior to distribution. Now having seen the beginning of the strong current of fresh air (cool in summer, warm in winter), let us enter one of the large rooms and see what is taking place there. At various points along the wall are oblong openings at a height of six feet from the floor. These are the inlets for the fresh air. As outlets we have several grated openings 20 inches high and of various lengths, and placed at intervals on the walls, but quite close to the floor. These latter openings lead into various shafts, which find their final outlet in one large central shaft at the roof of the building. But to return to the fresh air in the room. This air we have seen is forced into it at various openings overhead, and circulates through the room before it finds an outlet on the level of the floor. The result is that the entire air of the room may be renewed from four to nine times per hour, according to the speed at which the propelling engine is worked. And yet while this thorough change is going on, there is none of that perceptible current which, under the name of draught is, or is fancied to be, so often hurtful. If you place your hand, or a lighted taper, over any of the inlets, the strength of the incoming current is sufficiently felt. So if you spread your handkerchief over any of the gratings at which the spent air is being forced out of the room, or apply the lighted taper, you are no less sensible of the change that is going on, and yet, so equally is the force of