are often covered with a plate having a correspond ing opening or terminated by a more or less ornamental extension of sheet metal, as in Figure 9 G61. 2), and are carried above the ridge of the roof to such a height as will assure the carrying off of the smoke. Further to assist this process, and particularly to nullify the effect of unfavorable winds, chimney tops are frequently set on. They are either movable or sta tionary. Figure 2 (pl. ro) exhibits a movable one, consistino- of a metal pipe the width of the chimney fastened in such a manner.that it can revolve and ending in a funnel opening sideways. It also carries a vane made as large as possible. As the wind blows, the vane causes the tou to turn so that the mouth of the funnel is directed al.vay from the wind. A rarefaction of the air thus occurs directly in front of the opening-, suction is induced, and the draught upon the smoke is increased. The only defect in this construction is that a sudden change in the direction of the wind may affect the mouth of the funnel and interfere with the outlet of the smoke. The chimney top also requires careful attention, that it may always be in condition to move freely. In this respect, the stationary tops are more reliable. Figures 3 and 4 exhibit examples of the latter. The object in this case is to break the direction of the wind so that it is deflected toward the top, inducing suction. In the example shown in Figure 3, a conical screen of metal is combined with a cylindrical metal pipe which is placed either in or upon the top of the chimney.
4 shows the patent cap, or top, invented by Wind bansen and 13iissing of Brunswick, and called the "deflector." The screen, as shown in the cut, is more sloped, and is surrounded by a pecu liarly shaped case with openings on the lower edge for the admission of air; the upper part stands out in such a manner as to allow the wind to enter and assist in getting rid of the smoke. The other parts of the appa ratus, such as the flat cover in Figure 3 and the funnel hung in the casing and furnished with small pipes as in Figure 4, serve to hinder the entrance of rain, and also to prevent the chilling- of the air within the chimney.
Factory Chimneys are built either square, octagonal, or circular on both the outside and the inside, or occasionally with an octagonal form on the outside while circular on the inside. As great height is required, not only to induce the necessary draught, but also to prevent annoyance from the smoke, they generally tower above the surrounding buildings, and are built tapering, in order to insure greater stability.
The taper usually extends through about one-twentieth of the full height of the chimney, and on both the outside and the inside. Thus a chimney 98 feet high with an upper wall 9.8 inches thick will have a lower wall of from 19.7 to 21.7 inches in thickness. As a rule, when the chimney is circular, requiring- wedge-shaped bricks, the wall may be thin ner than the other forms. The thickness of the lower wall of the chimney need not bear any special proportion to the pediment, which is almost always seen in factories, and is generally square in cross-section with thicker walls. The tapering on the inside is clone either at certain sec tions or continuously, but care must be taken that the upper diameter on the clear is not too small to permit the free passage of the smoke.
It is impossible here to consider in any way the proportions of the quan tity and pressure of steam or the number and capacity of boilers in relation to the height of chimneys. Being generally built of brick, factory chim neys are readily ornamented at the top. Figure 5 (pt. ro) exhibits one with an octagonal cross-section; Figure 6 shows one of a circular cross section with the corresponding arrangement of its pediment. As the illus trations indicate, pleasing effects are obtained by the introduction of spe cially shaped and tinted bricks. Some of these structures are notable for their great height. The loftiest chimney (454 feet high) in the world, and one of the highest masonry structures, was built at Port Dundas, Glasgow, Scotland, in 1857-1859. There are only two church-steeples in Europe that exceed it—namely, the Cologne Cathedral (5ro feet) and that of Stras burg (468 feet); and but one loftier structure in America—namelv, the Washington Monument (55o feet). A few of the most prominent factory chimneys, arranged in the order of their height, are named in the following table: Heating and Uentilating Afifiaraters.—The direct object of all heatincr apparatns is the production of warmth, but the different uses to which this product is applied necessitate great variations in the mechanical details. The methods by which heat is utilized for the transformation or combina tion of diverse materials in different industries will not here be considered, as they belong more directly to mechanical or chemical science; the pres ent examination will, therefore, be restricted to the appliance of heat to the particular requirements of the rooms of buildings and for culinary pur poses. The apparatus for heating rooms is of necessity intimately con nected with the methods for securing ventilation or with the arrangements by which a free circulation and change of air are maintained in closed apartments.
Object of Heating first object in beating is to raise the air contained in the apartment to a given temperature, and afterward to maintain it at that point against the loss of heat from the entrance of cold air through windows and doors, and also from the effect of the con ducting surfaces of walls, ceilings, floors, and especially glass. The gen eration of the heat is accomplished frequently in a suitable apparatus con tained in the room, the heat being transmitted directly from the walls of the apparatus or from the hearth itself to the air of the apartment. By another arrangement, means are provided for conducting the heat from apparatus outside the room, and this is done by air, water, or steam. The warming of the air of a room is produced by circulation when no change of air is required, and this circulation, or movement, is maintained by the rising of the particles of air near the source of the heat as they become rarefied, while the particles coming- in contact with the walls and windows, being cooled, become specifically heavier and sink in a corresponding degree.