52 Economising of Surfaces under Glass^ 



adjustment of the two principles above noticed, namely, the 

 chamber mode of heating pits with boarded surfaces, and the 

 mass-of-material mode of heating, as tan, dung, or leaves may 

 be called, would probably be the best way of obtaining a steady, 

 safe, economical, and genial temperature. With this view, a 

 chamber was prepared beneath for the hot-water pipes, and 

 cemented in the bottom, for the purpose of retaining, when it 

 might be requisite, a thin sheet of water. This chamber is 

 made sufficiently capacious to admit a man by a small door or 

 hatch at either end, for the purpose of repairs and the application 

 of water, or a thermometer, when required. It is roofed over 

 with kyanised timber, 3 in. wide, by 2 in. thick, and 1 in. apart. 

 Over this are laid about 8 in. of heat-absorbing materials, as 

 brickbats and stones, the smallest on the top ; next, a thin firm 

 sod, with the grass side down ; and, over all, about 2 ft. of half- 

 decayed leaves. Thus, it will easily be conceived that this mass 

 of materials will not only be capable of retaining the heat 

 derived from the pipes below, but also be conducive to the pro- 

 motion of the heat from the decomposition and slight natural 

 fermentation of the shallow bed of nutritive vegetable matter, 

 the medium for plunging in. On the first heating of the 

 pipes, it took three or four days ere the pit attained its max- 

 imum temperature of ] 00°, when it was ready for the immediate 

 I'eception of the plants, the heat being under complete control. 

 It also turns out that instead of the constant application of the 

 heat from the pipes within the chamber, that the same steady 

 temperature can be kept up during summer, with only one 

 night's application of their action during the week. The pipes 

 are so arranged that either the pit or atmospheric heat of the 

 house can be worked separately or together, as may be required. 

 Another advantage attending these arrangements is, the having 

 a magazine, as it were, of moist heated air, which, without ma- 

 terially deducting from the bottom heat above the chamber, 

 retained by the materials alluded to, can on any emergency of 

 severe weather be added to the surface heat of the house, by 

 simply opening the two small doors at either end of the chamber. 

 Moreover, it is found, that the heat is so regularly diffused over 

 the surface-bed of the pit, that within 2 in. of the kerbs it is 

 always in steady useful action. I calculate that the pots being 

 plunged over the brims as they now are in this bed of leaves, 

 the plants will thereby be allowed to root over it with much 

 advantage to their fruit and suckers, and this too without the 

 smallest risk ; for, in fact, burning the roots, as it is called, can 

 never happen ; the maximum point of bottom heat being within 

 the line of safety. Such a pit, for various purposes of plant- 

 growing, will be found invaluable. Thus, all unseasonable 

 moving of plants or materials is done away with, and a heat 



