ON THE AERIAL SYSTEM OF FORCING. 
157 
To be a little more particular, let us suppose the case of an amateur devoted to 
horticulture, but whose position demands the exercise of thorough economy; he 
intends to build on a principle that shall secure the consumption of the lowest grade 
of fuel, cinders, breeze, screenings of coke, &c, and convey the heat developed, void 
of all the sulphurous and other noxious gases, usually produced by exposed heated 
surfaces, intermixed and diluted with pure atmospheric air and aqueous vapour, so 
as to fill the entire area of the erection. 
Let the erection be from 24 to 30 feet long, and 16 to 20 feet wide in the clear 
of the external walls, within which a walk of convenient width to allow of a 2-feet- 
wide shelf passes on three of the sides ; the inner space will, form an oblong chamber 
or pit, built of 4£in. brickwork, and made perfectly air-tight, excepting in parts where 
air openings are left for especial purposes. This pit will perform all the offices of 
the dung, tan, or leaf-bed of the old stoves, or of the brick water- tank of modern 
erections ; and houses so furnished are qualified to act as Pine or plant stoves, or 
for the purposes of propagation. If the chambered pit be omitted, greenhouse 
culture can be followed out to perfection by a modification of the furnace and 
channels of heated air suited to the particular objects of the party. 
The furnace must be placed either at one end, or at the center of the back 
wall of the house, according to the construction and aspect of the latter. It is to 
be so arranged as to deliver the whole of its radiated heat into the area of a 
chamber rendered completely air-tight on the sides and at the roof, and to convey 
the hot air into the pit by propulsion from a concentrated stream of cold air that 
shall pass below the floor of the pit, through openings left for the express purpose. 
Thus, by what the learned style vis a tergo (a force from behind), a column of dense 
cold air will propel forward the warm air of the fire-chamber, attenuated and 
rendered more specifically light by the expansive power of a broad heated surface ; 
and being so pushed onward by a perpetually moving power from below and 
behind, it will naturally find its way through six or more orifices left in the walls 
of the pit at half their height above the floor, and in places remote from the 
furnace. 
Persons will be apt to exclaim — this is the Polmaise to all intents and purposes. 
We meet the objection, if such it be, by observing that we repudiate the term, 
because it implies the original superfluity or rather deformity of the blanket 
appendage ; and again, because it fosters a feeling of prejudice which is always 
inimical to improvement. 
We have witnessed, and can vouch for the reality of steady advances in horti- 
cultural architecture ; we have felt and paid for the defects of flues, and of water 
channels ; we know that there must exist causes of loss in fuel : but comparing 
results, and judging from analogy, we are satisfied that from the first brick laid to 
the completion of a greenhouse, warm-pit, or enlarged stove, and thence onward 
throughout the progressive operations of simple protection to those of the most 
exalted power of forcing, economy in the best sense of the word does and will 
