tical fact established beyond question, another consideration arises
as to the best means of producing it, and of regulating its application.
Various substances and materials have been submitted to a process of
fermentation, and so employed to effect it: stable manure, tanner's bark,
and the leaves of trees, are among the principal of these materials, and
either of them will supply just what the plants require, as truly as these
wants can be supplied by any other means; but from their very nature, they
are violent, and fluctuating, and ephemeral in their action, and setting
aside the labour which the employment of them necessarily involves, we
have in these particulars, the special points in which the tank system of
applying bottom heat far excels them: it is uniform, and constant, in its
action; there need be no apprehension of the soil becoming overheated, for
the source whence it derives its warmth ought never to boil; neither need
there be any fear of its decline, or of a want of power, for when once
thoroughly heated, a body of water will part with it in such a manner,
that a very little attention to the fire, and a very little expenditure of
fuel, will maintain its temperature for an almost incredible length of
time; and as to power, it never should for a moment form a question,
because a powerful degree of bottom heat ought never to be applied: a
close attention for one or two hours during the twenty four which form a
day, will maintain any apparatus in an effective state of action, if it is
properly erected. How different is this, to what has been in days now
past! when in rigorous weather, with the heat of his dung bed declining,
the cultivator knew that at the peril of his crop, he scarcely dared to
attempt to revive it, without involving a more serious because an
accelerated evil; at any rate, if at an immense sacrifice of labour, his
dung casings were replenished piece by piece, he knew too well, that often
many days would elapse, before their action would be efficient and
satisfactory, unless indeed an unlimited supply of materials, were in a
constant state of preparation. By means of the tank, a fire could be
lighted up, and the required effect produced in as many hours, as days
would have been formerly required.

What has been already advanced, tends to the conclusion, that small
forcing houses are preferable, and in the end more economical than pits
and dung beds; and that the tank as a means of supplying