The construction of hot-houses, in general, differs little from that of Green-houses ; because the design of both is to receive as much benefit as possible from the genial warmth of the sun, assisted by the heat artificially procured from subterraneous stoves and flues. - We shall, therefore, at present, only give an analysis (from the 1st. vol. of the second series of Recreations in Agriculture, etc.) of the principle on which Dr. Anderson's improved hot-houses are constructed, and for which he has lately obtained a patent.
He first points out the defects in the present method of erecting hot-houses ; in consequence of which the heat of the sun is not employed with that advantage of which it is susceptible. In the prevailing mode of building these houses, the roof glasses are, with very few exceptions, laid into the frames, by folding one frame over the other, and thus leaving an open space between each pane ; through which the air has a free passage, while the front panes are closely covered round with putty. This communication with the open, air at the upper part of the house, is their chief imperfection ; for the power of the morning sun is thus lost for several hours ; and, in the evening, when the warm air within begins to cool and to contract in bulk, the cold air from without rushes in through the top or roof-glasses, cools the whole house in the most expeditious manner, and thus counteracts the influence of the solar rays.
To remedy these inconveniencies, the patentee proposes the following plan of construction, for houses desigued to force vines, or suck plants as require a similar tempera-ture. The house is to be built of the usual dimensions, but with a glass roof perfectly flat; and, as it never requires to be opened, all the seams or junctures between each pane are to be carefully closed with lead and putty. Over this flat ceiling, another sloping roof is to be erected, and covered either with slate, or likewise with glass, which will better answer the purpose. The upper chamber, which will thus serve as a reservoir for the heated air, communicates with the common atmosphere only, at its lower part, that is immediately over the roof of the lower house ; and there is a contrivance for another occasional communication with the latter, by means of a pipe or tube, that extends from the top of the upper chamber, almost to the ground below.
By this construction, as soon as the sun expands the air in the lower house or chamber, a part of that air rises through the tube into the upper chamber ; where it ascends to the top or roof, forcing out the cooler air contained in the upper chamber, which passes off through the openings left above the floor of this chamber, or in the roof of the lower room.
During the whole of this heating process, the vines, which are trained along, beneath the glass roof of the lower chamber, are surrounded with heated air. In the evening, when the influence of the sun is withdrawn, the warm air begins to cool, and consequently to contract its bulk ; thus the external air rushes in, through the aperture immediately over the lower glass roof, into the upper chamber. This cold air being heavier than that within the house, it can only enter as the latter recedes ; the current through both chambers is now exactly reversed : and the lower room receives all the warm air from the reservoir or upper one, before the cold can reach it.
Dr. Anderson is of opinion, that a few hours sun-shine will at any time be sufficient completely to heat the house in which vines are planted; and thus, without any artificial heat from fuel, a permanent warmth may be maintained, which is sufficient to ripen grapes, In favourable weather, as early as in the months of June, July, and August. He farther suggests that the upper chamber may be converted into an hot-house of inferior rank; and that it would be eminently calculated to serve as a substitute for a green-house or conservatory.
Such is the outline of this very ingenious plan, and the inquisitive reader who wishes to acquire more minute information on this subject, will probably resort to the volume already quoted, where it is amply treated, and illustrated with cuts.
Hot-houses are liable to be infested with a variety of insects known under the different appellations of Cocci, Aphides (lice), etc. that harbour in the walls, and among the trellises, which fasten up vines, and other wall-fruit trees, especially during the winter. In order to destroy these vermin, Mr. Speechley recommends the walls to be washed with common soap-suds, early in the spring, while they are in a torpid state : this liquor is to be poured out of a watering-pot from the top of the wall downwards ; and ought, when used, to be considerably warmer tha new milk: thus, if the suds be properly and plentifully applied, the wall will assume a pale red colour, and the insects be effectually destroyed.
Hot-House. A glass-frame for buildings of this description has lately been invented by M. Bernard : it possesses considerable advantages over those in common The lower part consists of a double square of glass-panes set in wood, or in wood and lead. The upper part is composed of panes of glass fixed in wood, and terminates in an oblong six-sided prism : it may be taken off at pleasure, by a ring connected with the top. - The whole of this fabric has the singular advantage of throwing a great body of light on the plants, while it prevents that sickly growth, denominated etiolation; and renders it easy to produce a variety of temperatures, as occasion may require. M. Benard's hot-house is supplied with heat, at a trifling ex-pence, by common oil; the smoke of which is conveyed round the frame, by means of a flue.