220 



HEATING AS APPLIED IN HORTICULTURE. 



tural Society," vol. ii. p. 57. " The outer 

 line of the ground-plan," fig. 298, "re- 



Fig. 298 



presents the walls of a hothouse. The 

 openings c are external ventilators, for 

 the purpose of admitting fresh air. These 

 are exactly such as might be employed 

 for any other system 

 of heating; they have 

 no necessary connec- 

 tion with Polmaise, 

 and the heating ^ 

 principle acts, whe- 

 ther they are closed 

 or whether they are 

 open. It is evident that, when open, 

 they admit fresh air into the house ; and 

 however cold the weather, any air ad- 

 mitted by them, instead of cutting the 

 plants, as is the case when side sashes are 

 open, will immediately, from its great 

 specific gravity, descend at once into the 

 cold-air drain, and become warm before 

 coming in contact with the vegetation 

 within the house. The number left 

 open will, of course, be dependent on 

 external circumstances; and when they 

 are all closed, the hothouse resembles 

 any other hothouse that is closed ; and 

 thus heating and ventilation are kept 

 apart, the requirements of the two 

 necessarily being different. Within the 

 external walls is a walk round three 

 sides of the house, in which are open- 

 ings, e, leading into drains ; — these drains 

 converging into a main drain, as shown 

 by the arrows. These drains are formed 

 of brick on edge sides, and duchess 

 slates for roof, the soil forming their 

 floor. The main drain is 4 feet wide 

 and 1 foot deep, so that by laying a 

 brick flat and four courses high in the 



centre, and bricks on edge at the sides, 

 two common duchess slates reach to form 

 the roof, and on these is spread some 

 sifted soil to make 

 the drain air-tight. 

 The centre brick- 

 work forms a sup- 

 port on which, in 

 several places, to 

 build up single brick 

 piers to support the 

 iron rafters which 

 carry the slates on 

 which rests the 

 plunging - bed, as 

 shown in longitudinal 

 section," fig. 299. 



" This main drain, 

 which should be slightly on the descent 

 towards the chamber, pierces the end wall 

 of the hothouse, the foundation being left 

 out at that point— the end wall of the house 



Fig. 299, 



being there carried by York flagging, with 

 a centre support — and thus the means are 

 provided for allowing the cold air to travel 

 from the house to the chamber. The 

 openings at e," fig. 298, in Mr Meek's 

 house, "are regulated by sliding lids 

 made of slate, for the purpose of experi- 

 ment. This, for practical purposes, is un- 

 necessary; and in many cases it will be 

 found very convenient to make the cold- 

 air openings in the centre of the house 

 concealed by some ornamental stage, the 

 floor of the walk forming the roof of the 

 cold-air main drain ; or handsome venti- 

 lators may be inserted at once in the roof 

 of the main drain, to take down the cold 

 air." These are points of minor detail, 

 "the great and essential point being to 

 provide a means for the cold air at the 

 extreme end of the house to pass to the 

 hot chamber. The outer wall of the hot 

 chamber is 4|-inch work, — is air-tight as 

 far as regards the external air, having 

 two openings on the side next the house 

 on different levels, the lower one to admit 

 the cold air, the upper one to allow its 

 return when heated. The stove occupies 



