9 
THEORY OF HEAT AND ITS PRACTICAL APPLICATION. 
The application of heat becomes daily of more importance : we can scarcely 
look into a paper or a periodical without meeting with some announcement of a 
new adaptation of the hot- water processes to the heating of horticultural erections. 
The philosophy is the same in all ; for it is a principle of the law of radiation, 
established in practice, that fuel, however applied, can afford but a certain quantum 
of heat. Hence, no one should be deceived, or suffer himself to be misled, either 
by the assurances of others, or by the flattering suggestions of his own hopes, that 
more heat can be radiated than the quantity of combustible elements can yield. 
Whether, therefore, a good brick flue, led all round a house, terminating in a well- 
adapted shaft ; or a series of iron or earthen pipes, or a tank and a tiled channel 
for the flow of hot water, be the media of conduction, the volume of flame, or 
incandescent matter, in the primary furnace, can produce no more or no less 
radiant heat than is equivalent to the quantity of oxygen, hydrogen, carbon, and 
sulphur, consumed, and chemically changed. 
There are, however, modifications of apparatus, which will economise and duly 
distribute the volume of heat produced ; and as economy is of necessity, as well as 
choice, our governing principle in every branch of practical horticulture, as, more- 
over, our circle of observation becomes more and more extended, it will be the aim 
of the present notice to point out some of those modes of appliance, which 
cannot fail to be useful, and to a certain extent consistent with liberal economy. 
In the first place, however, the object to be pursued, and the quality of the heat 
to be produced, should be maturely considered ; for it is anything but wise 
to employ but one species of machinery for every purpose. If the object be the 
growth of successive pine-apples, a hot-water tank, and channels constructed of 
porous materials, must be most propitious, inasmuch as they keep up a degree of 
atmospheric moisture, which extends nearly to saturation, The Pine revels 
in vapour, and so, in floriculture, does the Gardenia, and a great variety of some 
of the most choice and beautiful plants which bear winter forcing. In a house so 
constructed, we now see Gesnera, Gloxinia, Azalea indica, Euphorbia Jacquini- 
flora, Plumbago rosea : the last-named plant has, indeed, bloomed for several 
months, producing two hundred and more blossoms on a single pendulary spike. 
The moisture of such a house produces neither mouldiness nor decay, provided a 
temperature of 60° be maintained ; even, during a season of bitter wind, total 
gloom, and severe frost, like that which was experienced during the whole course 
of December. 
The chief point which ought to be required is the presence of the flue within 
the house, for by this condition the whole of the heat, be the fuel what it may, 
is appropriated. The furnace-boilers, that directly claim consideration, are 
cylindrical, made by a workman, little known, but who has erected a few for 
VOL. XIT. — NO. CXXXIII. C 
