142 



HEATING AS APPLIED IN HORTICULTURE. 



carried through a chamber, the sides, 

 bottom, and top of which should be 

 clear of the flue at least 3 inches, and 

 not more than 6. The small quantity 

 of air thus surrounding them would soon 



Fig. 136. 



4 to 6 feet asunder. By such an arrange- 

 ment the fire might be kindled in the 

 evening upon the appearance of frost, 

 and these ventilators opened, in case of 

 need, to their full or half capacity. The 

 heated air, if not required, could be 

 allowed to escape by a small tube built 

 into the extreme end of the chamber, 

 and communicating with the external air, 

 and regulated by a similar ventilator. 

 But this will seldom be required. A 

 similar ventilator should be built in the 

 wall of the chamber near the fireplace, 

 by which a fresh supply of air would be 

 admitted, and propel the heated air in the 

 chamber through the ventilators in the 

 pavement into the house. All underground 

 flues, however, lose much of their heat 

 by its being absorbed by the walls, &c, 

 which surround them, and they can only 

 be recommended when it becomes abso- 

 lutely necessary that they be placed out 

 of sight. Flues, tanks, and the supports 

 of hot-water pipes, should be built upon 

 a solid foundation, to prevent fractures 

 and settlements. Those in plant-houses, 

 where the ground may be supposed to be 

 undisturbed, may be safely placed on a 

 foundation made of two courses of brick 

 laid in cement or grout ; such as are in- 

 tended for peach and grape houses, where 

 the borders may extend under them for 

 the range of the roots, should be always 

 built on arches or piers, linteled over with 

 stone, according to local circumstances. 

 — (Vide Garden Walls, figs. 37, 38.) 



become heated, and should be admitted 

 into the house through neat brass venti- 

 lators, either circular, as figs. 136 and 

 137, or longitudinal, placed in the floor 

 immediately over the flue, and from 



Fig. 137. 



It is always dangerous to build flues on 

 wood, although we have seen examples 

 of this. Flues and hot-water pipes 

 should if possible be carried round the 

 front and ends of the house, not only 

 because these are the coldest parts, but 

 because the heat ascending from those 

 points naturally rises and floats towards 

 the highest parts, completely cutting off 

 the entrance of cold from without. 



Such is the view hitherto taken by 

 most practical men of the operation of 

 heat as respects hothouses. This, how- 

 ever, is perhaps not the most philosophi- 

 cal mode of diffusing heat equally through- 

 Fig. 138. out an y struc " 



ture, as may 

 be seen by a 

 glance at fig. 

 139, by the 

 direction of 

 the arrows. 

 That portion 

 of the house, 

 indeed, shown 

 at the bottom 

 of the back 

 wall without arrows, is usually occupied 

 with the footpath in forcing-houses, and 

 in ordinary greenhouses is seldom used 

 for plants ; and, so far as ordinary prac- 

 tice goes, all is well enough. We should 

 also here observe that the atmosphere of 

 all glass houses is coldest nearest the roof, 

 on account of the loss of heat by radia- 

 tion, which is, at common temperature, 



