26 



MODE OF HEATING 



over the slate keeps all tight. The heat is regulated not by 

 expensive cocks or valves, which contract the flow, and are 

 liable to get out of order, but by series of cast-iron cisterns 



M'hich supply the place of elbows, and being cast with one, two, 

 or three sockets of the same bore as the pipes, may be plugged off 

 with a conuuon piece of wood, with a little cloth wrapped round 

 it, so as to clieck or entirely cut oft" the supply from any part 

 which may not need it. 



But the most perfect system of heating would be vain without 

 good ventilation night and day. If my theory is correct, the 

 air of plant houses of this description should be in direct pro- 

 portion to the light, the moisture, and to the heat. This is best 

 attained (where the quantity is easily controlled) in a small 

 house, for the temperature must not be lowered too much by 

 the admission of external air, while, on the other hand, it must 

 not be dried by artificial heat. To obviate this difficulty, you 

 will observe an air chamber between the two buildings, wliich 

 has its opening at a lower level, near the ash pit ; from this 

 chamber several small drains open into the pits, &c. 6 inches 

 above the floor, with gratings of (about 6 inches square) per- 

 forated zinc. From these a constant supply of fresh air in 

 small and broken quantities arises, so that no strong draught is 

 created ; and this, passing over the surface of the pipes, under 

 which it enters, loses its chill, while the open troughs supply it 

 Mith moisture ; these are constantly open, but may be closed 

 if necessary. Tliere are also ventilators in the front and back 

 walls, and at the top of the orchid house. It will be perceived 

 that the ridge piece is raised above R. the roof, the south side of 

 which carries a roller for sun-blinds, while the north side has a 

 row of luft'er boards, which are opened and shut at pleasure, 

 by balance weights within. The front of tlie orchid house is 

 fitted with Plartley's patent rough plate-glass, which answers 

 admirably without diminishing tlie light ; indeed, a blind is still 

 needed for tlie orchids in very bright weather. One word as to 

 drip — by adopting the pattern of sash-bar given by Mr. Lyons 

 in his work on Orchids, this is entirely avoided, even when the 

 house is saturated with moisture, and a cold Mind blowing 

 without. 



