CONSTRUCTION OF GARDEN WALLS. 



91 



in the right direction, in doing away 

 with the antiquated, expensive, and 

 labour- wasting details of ponderous rafters 

 and framed sashes. 



The following description will explain 

 our fig. 79 of the section, while fig. 80 is 

 a section of the astragal. The width of 



Fig. 79. 



the structure at the bottom is 8 feet, 

 tapering to 18 inches at the top. The 

 ends of the house face the south and 

 north. The astragals are of iron, and 

 fixed into a top and bottom rail : they 

 are formed flat at top, and on them the 

 glass is laid, and kept in its place by a 

 bead, which is screwed down, having a 

 thin strip of Indian rubber between it 

 and the glass, both to keep the glass 

 steady and also to prevent its being 

 broken by pressure or concussion. We 

 would have placed a similar piece under 

 the glass also, for a like purpose. No 

 putty is used. The astragals are made 

 to take out of their fittings, and when 

 the beads are unscrewed the glass is 

 readily removed, and packed by until 

 again required. The coping at the top, 

 and the ventilators at the bottom, are of 

 zinc or galvanised iron. The glass is 18 

 inches in width : e e are the ventilators ; 

 d d astragals ; a a trellis for training the 

 trees on; cc 

 Flg - 80 - border; b foot 



passage along 

 the centre. On 

 fig. 80, e is the 

 screw; dbead; 

 c Indian rub- 

 ber, placed be- 

 tween the glass 

 and astragal ; b b glass ; a astragal. 



The operations of culture, as will be 

 seen, are carried on from within ; and 

 from the general construction, many 

 plants may be protected in these walls 

 during winter. With a hot-water pipe 

 placed at each side, between the trellis 

 and the glass, and a simple mechanical ap- 

 pliance, to effect simultaneous ventilation 

 both at the bottom and the top, we would 

 have in such a structure all that is re- 

 quired for ripening wall fruits in very 

 great perfection, and at comparatively 

 little cost — indeed, much about that re- 

 quired to erect a common brick wall. 

 Neither Mr Spencer nor Mr Ewing hold 

 out their respective inventions as com- 

 pletely adapted to very early forcing, but 

 as accelerators and protectors only ; and 

 so far as this goes, both are entitled to 

 our fullest approval. 



Wooden walls have the property of 

 affording shelter from the winds ; but 

 their non-conducting nature unfits them 

 for attracting or reflecting solar heat, at 

 least to such an extent as to be of much 

 utility to trees trained upon them. They 

 may indeed, by being covered with coal 

 tar, asphalte, or perhaps other mineral 

 matter, particularly of a black colour, be 

 somewhat improved. Wooden walls are 

 colder in winter and spring than brick 

 ones ; but this circumstance is often an 

 advantage, by retarding the blossoming 

 of the trees, and lessening the risk of 

 their being injured by spring frosts. It 

 has been suggested to construct wooden 

 walls hollow, and to fill the space between 

 the boarding with pounded charcoal, coke, 

 or clinkers, as means of absorbing heat 

 during the day, and giving it out during 

 the night. The heat that would pass 

 through an inch-and-half board would be 

 so trifling that it could never be calcu- 

 lated upon to be of the least practical 

 utility; besides, such walls would be 

 much more expensive than those with a 

 single surface of boarding. Many authors 

 have advocated their use ; and amongst 

 them Nicol, who says that he has " con- 

 structed many hundred lineal feet of 

 wooden walls." In one particular that 

 authority differs from most others, inas- 

 much as he places them out of the perpen- 

 dicular by inclining them "considerably 

 towards the north — fig. 81 — presenting 

 a surface at a better angle," as he thought, 

 " with the sun, than if they were upright. 



