un heat, yet the case is different;
the sun's rays have then much greater power, and it is found that their
influence is sufficient, without at all times admitting them directly on
the plants growing in these artificial atmospheres.

[Illustration]

The position of the Cucumber house, with reference to the ground line,
must be determined by local circumstances; if the situation and sub-soil
be dry, it may be carried below the surface in the manner represented in
the annexed engraving, of which (_a_) is the ground line, (_b_) the
pathway, and (_c_) the lowest point excavated: the same course may be
adopted if the soil, though not naturally so dry as this, can be rendered
so by thorough drainage; but when the ground does not admit of perfect
drainage, the structure must be sufficiently elevated to avoid the risk of
injury from the dampness of the locality.

The angle of elevation is not, as it is sometimes asserted to be, a point
of indifference, though mathematical accuracy is certainly by no means
required: in the annexed engraving, the angle of the roof is about 55 deg.,
this provides for the admission of the sun's rays in the winter months,
when his position is comparatively low in the horizon, to a much greater
extent than could take place if a more ordinary slope were adopted. A
still more elevated pitch would doubtless effect this object in a still
more perfect manner; but would not be equally applicable to the
requirements from a permanent structure, which would be wanted for summer
as well as winter use.

A reference to the sketch, will at once shew the general nature of the
internal arrangements. There should be a tank (_d_) supported by brick
piers (_p_) in which a circulation of heated water would supply a genial
warmth to the soil above, and to the roots of the plants growing in the
soil; this tank should be heated by a small boiler, conveniently placed
with reference to adjacent arrangements; a series of iron pipes (_e_)
attached to the same boiler, would supply the requisite heat to the
atmosphere. It may perhaps be thought that the application of the gutter
system of heating would in this case be preferable; but as there would be
a perfect command of moisture, as will be explained further on, it is
desirable to have dry heat also, under controul, and this can be better
effected by means of the pipes than by adopting the gutter plan of
heating. I cannot in this place forbear protesting against the li