PLANTS, WITH GLASS ROOFS. 165 



plan has been successfully carried out by C. W. Martin, Esq., at Leeds 

 Castle, Kent, to heat a range of glass-houses through the floor, as well as 

 a large piece of ground in the kitchen garden. The vault was of the 

 same length and breadth as the floor, with the chimney at one end ; or 

 it occupied a smaller space in the centre of the floor, with a stack of 

 flues rising over it, and forming a mass of heated material in the body 

 of the house. The fire was of wood and made on the floor ; or of 

 charcoal or coal, and made in an open, portable iron cage, like that 

 used by plumbers when soldering joints in the open air, with a plate 

 of iron over it to act as a reverberator, and prevent the heat from 

 rising directly to the roof. The flue by which the smoke escaped had 

 its lower orifice on a level with the floor of the vault, so that the air 

 and smoke did not enter it until they had parted with most of their heat. 

 These modes are capable of great improvement, and in various cases 

 would perhaps be found more eligible and economical than any other, 

 by a gardener who is aware of the importance of connecting with them 

 an efficient means of supplying atmospheric moisture : by placing 

 cisterns of water over the hottest part of the floor, or by having drip- 

 ping fountains formed on the siphon principle, by inserting the ends of 

 strips of woollen cloth in open vessels of water, and placing these in 

 different parts of the house. The danger, however, from the escape 

 of gas into the house is very great, and such modes of heating are 

 but seldom resorted to for the growth of early vegetables, &c. One 

 of the houses was devoted to pine-growing, and the heat was sufficient to 

 maintain them in perfect health, planted out in a bed of soil on the floor. 

 Fives. As the mode of heating by vaults could only be adopted 

 when the plants were to be grown in pots or boxes, as soon as the 

 practice of forcing fruit-trees trained against walls, and having their 

 roots in the border or floor of the house, was introduced, flues in the 

 wall against which the trees were trained, and afterwards detached 

 flues along the front of the house, became necessary ; and when these 

 last are properly constructed, and the dry heat which they produce is 

 rendered moist by placing water over them, they form a convenient and 

 economical mode of heating. The flue is always most efficient when 

 carried along the front and ends of the house, because the air imme- 

 diately within these is more liable to be cooled by the external air than 

 that next the back of the house, the back being generally a wall of 

 brick or stone. Where the house is glass on every side, as well as on 

 the roof, the flues will be most efficient if carried round it, for obvious 

 reasons ; while the air immediately under the roof, in every case, will 

 be kept sufficiently warm by the natural ascent of the heated air from 

 the flue, in whatever part it may be placed ; though when the flues are 

 placed in the lower part of the house there will be a greater circulation 

 than when they are elevated; and this arises from the greater number 

 of particles which must be put in motion by the ascent of warm and 

 the descent of cold air. The quantity of flue requisite for heating a 

 house to any required temperature has not been determined. One fire 

 with a flue in front, and a return in the back, is generally found suffi- 

 cient for a greenhouse of thirty feet or forty feet in length, and from 



