Hot-Wall is a hollow wall, the interior air being so heated by flues or hot water, as to keep the bricks of which its faces are composed so warm as to promote the ripening of the wood and fruit trained against them.

Mr. Loudon observes, that "the flued wall or hot wall is generally built of brick, though where stone is abundant and more economical, the back or north side may be of that material. A flued wall may be termed a hollow wall, in which the vacuity is thrown into compartments to faciliate the circulation of smoke and heat from the base or surface of the ground to within one or two feet of the coping. They are generally arranged with hooks inserted under the coping to admit of fastening some description of protecting covers, and sometimes for temporary glass frames. A length of forty feet, and from ten to fifteen feet high, may be heated by one fire, the furnace of which, being placed one or two feet below the surface of the ground, the first course or flue will commence one foot above it, and be two feet six or three feet high, and the second, third, and fourth courses narrower as they ascend. The thickness of that side of the flue next the south or preferable side, should, for the first course, be four inches, or brick and bed; and for the other courses it were desirable to have bricks cast in a smaller mould; say for the second course, three inches; for the third, two and three quarter inches; and for the fourth, two and a half inches in breadth.

This will give an opportunity of leveling the wall, and the bricks being all of the same thickness though of different widths, the external appearance will be everywhere the same." - Enc. Card.

Hot walls are generally overheated opposite the first turn of the flue, and not heated enough at a distance from the fire. Mr. Hay has obviated this, by having a hollow in the interior of the wall, serving as a general heat-chamber for diffusing and retaining warm air, and also smoke-flues for conveying heat throughout. - Hort. Trans.; Gard. Mag.

The Rev. J. A. H. Grubbe, of Stanton St. Bernard, Wiltshire, has taken out a patent for a Transmitting-heat wall. The intention is to erect this partition in gardens, as a substitute for walls, against which fruit trees may be trained, and through which the warmth of the sun may, by reason of their thinness, be transmitted, which will greatly promote the ripening of the fruit, and improve its flavour. The material proposed to be employed for constructing these walls or partitions, is slate of the ordinary quality, in slabs, of the kind usually applied to the roofing of houses. Iron frames are proposed to be prepared for the reception of the slates, like the frames of windows, (with holes in both sides for inserting wires to serve as a trellis,) and the slates being cut to proper shapes and dimensions, may be secured in the rebates of the frame by putty, in the same way as glass. These frames are to be from six to eight feet wide, and of a suitable height, and may be joined together side by side, by rebates or flanges, and held fast by screws, bolts, pins or staples: or in any way that may be found desirable to secure them firmly.

Temporary blocks of stone may be placed along the ground to support the partitions, with cross pieces to receive standards or slight buttresses to keep the wall or partition perpendicular, and against the face of the wall, trellis work of wood or other fit material may be placed for the support of the branches of the trees. Walls or partitions for gardens formed in this way will transmit the heat of the sun through them, and hence fruit which may be growing against these walls having a northern aspect, will receive the benefit of the sun's warmth transmitted through the slates. In the construction of these transmitting walls, the patentee does not confine himself to slate, but considers that plates of iron, applied in the same way, might answer the purpose nearly as well, provided that their surfaces were blackened, which would cause them to absorb more of the solar rays. Even frames of glass might answer the purpose applied in the same manner, and perhaps some other materials might do; but it is desirable that the frames should be light enough to admit of their being removed without dilliculty, in order that these partitions may be shifted from place to place, (put under cover during winter,) and set up in different parts of the garden, as convenience may dictate. - Nicholson's Journ.; Gard. Mag. See Wall.