BOOK III. 



FIXED STRUCTURES. 



305 



visable unless the wall is kept constantly covered with glass, in which case, without 

 this precaution, constant fires might injure, by occasioning the partial growth of the 

 trees, or even burning those parts of them immediately opposite the furnace. To 

 prevent accidents of this kind, the furnace must always be placed at some distance, 

 say from eighteen inches to three feet from the back of the wall. 



1561. The cettidar wall (fig. 238.) is a recent invention (Hort. Trans, vol. iv.), the 

 essential part of the construction of which is, that the wall is built hollow, or at least 

 with communicating vacuities, equally distributed from the surface of the ground to the 

 coping. If the height does not exceed 10 or 12 feet, these walls maybe formed 

 of bricks set on edge, each course or layer consisting of an alternate series of two bricks 

 set edgeways, and one set across, forming a thickness of nine inches, and a series of cells, 

 nine inches in the length of the wall, by three inches broad. The second course being 

 laid in the same way, but the bricks alternating or breaking joint with the first. The 

 advantages of this wall are obviously considerable in the saving of material, and in the 

 simple and efficacious mode of heating ; but the bricks and mortar must be of the best 

 quality. This wall has been tried in several places near Chichester ; and at Twickenham, 

 by F. G. Charmichael, and found to succeed perfectly as a hot- wall, and at 10 feet high 

 to be sufficiently strong as a common garden-wall, with a saving of one brick in three. 

 As a whole, indeed, it is stronger than a solid nine-inch wall, on the same principle that a 

 hollow tube is less flexible than a solid one. It is evident, that the same general plan 

 might be adopted in forming cellular walls of greater height, by increasing their width. 

 A very high wall might have two systems of cells divided vertically, one or both of 

 which might be heated at pleasure. The same idea may be advantageously applied to 

 flues, for heating hot-houses by steam, and for other purposes. Piers may be formed 

 either on both sides of the wall (a), or on one side by bricks on edge (6), so as to bond 

 in with the rest of the work. 



m 



1562. Hollow walls may also be formed by using English instead of Flemish bond : 

 that is, laying one course of bricks along each face of the wall on edge, and then bonding 

 them by a course laid across and flat. Such a mode has been practised and described by 

 Dearne, an architect in Kent. 



1563. Where wall-fruit is an object of consideration, the whole of the walls should be flued 

 or cellular, in order that in any wet or cold autumn, the fruit and wood may be ripened 

 by the application of gentle fires, night and day, in the month of September. It is an 

 error to light the fires of hot- walls only in the evenings, the effect of heat in the process 

 of maturitiou being much greater when accompanied by light. In all hot-walls one 

 precaution must not be neglected, the building in, on the inferior or outer side, small 

 cast-iron doors, or framed stones, which may be opened at pleasure, in order to withdraw 

 the soot. They must be made perfectly air-tight, which is readily accomplished by 

 having double cast-iron doors, in what is called Count Rumford's manner. 



1564. T/ie mud or earth-wall (Jig. 239.) is formed of clay, or better of brick earth in a 

 state between moist and dry, compactly rammed and pressed together between two 

 moveable boarded sides (a, a), retained in their position by a frame of timber (b, 6), 

 which form, between them the section of the wall (c, c) : these boarded sides are placed, 

 inclining to each other, so as to form the wall tapering as it ascends ; one layer of 

 the length of twelve or twenty feet being completed, another layer is formed on that, 



