2131. Heating the atmosphere of conservatories, hothouses, &c. Figs. 625, 626, and 627. represent a mode of heating water in pipes by the agency of steam. It is well known, that, by the common hot-water apparatus, the heating of an extensive and unconnected establishment of houses by one fire is impracticable in most cases; but, in the mode here represented, the extent of application is in a manner unlimited, whatever be the number or situation of the houses requiring heat. It likewise combines all the advantages of steam as a conductor of heat, with that of a bulk of water as a retainer. The first adoption of this mode was in a forcing-house, belonging to Mr. Sturge, near Bath. The water-pipes were 8 in. in diameter, and about 28 ft. long. The steam-pipe of 1 in. in diameter, entering at the centre of one end, and proceeding in rather an inclined direction to the other, is then returned, still inclining, and passed out at the bottom of the bore immediately under the place where it entered; it is then formed into a siphon (b) about 3 ft. deep, whence the condensed water is conveyed away. A smaller pipe is also connected with the top of the large one, to receive the increase of water by expansion when heated, which, as the large pipe cools, returns into it again. Fig. 627. shows the arrangement of the front pipes under the floor. The air being admitted from the air chamber underneath, through an opening extending the whole length of the pipes, and passing through the upper chamber on each side of the pipes, is discharged through the grating into the house. The arrangement of the back pipes is similar. Shallow cisterns are connected with the upper part of the pipes, about 18 ft. from each other, by means of hollow screws, which admit the water to pass to and fro reciprocally; the capacity of the cistern is more than sufficient to receive the increased bulk of the water, which expands when heated, and returns again into the pipes as the water cools. The external diameter of the front pipes in this instance is 13 in., and of the back pipes 10.5 in.; each set of pipes is divided in the middle of their length, except that the nearest division of the front pipes returns about half-way round, the end being in length rather more than 60 ft. These water-pipes have 1.25 in. steam-pipes, extending in them their whole length, and returning again, preserving a regular inclination throughout. The back pipes have steam-pipes of 1 in. in diameter, passing through them in a similar way, and the feeding-pipes are so arranged that either division of the pipes may be heated separately, or in conjunction with the rest. Another advantage attending this mode of applying heat is, that as no returning pipes are necessary as in the common hot-water apparatus, the bulk of water is doubled, with the same extent of heating surface, and the retaining power of the apparatus is doubled accordingly. The cisterns are farther serviceable for regulating the humidity of the house, which can be done with the greatest accuracy by attending to the covers.