FORCING-PITS OR GREENHOUSES. 85 



the cost of these would not be more than ten per cent, of 

 the whole. A new method of constructing flues (or rather 

 a revived method, for it originated in 1822,) has been in 

 use for the past few years, which has such manifest ad- 

 vantages that many now use it who would no doubt other- 

 wise have used hot water heating. Its peculiarity consists 

 in running the flue back to the furnace from which it 

 starts and into the chimney, which is built on the top of 

 the furnace. As soon as the fire is lighted in the furnace, 

 the brick-work forming the arch gets heated, and at once 

 starts an upward draft, driving out the cold air from the 

 chimney, which puts the smoke flue into immediate action 

 and maintains it ; hence chere is never any trouble about 

 the draft, as in ordinary flues which have the chimney at 

 the most distant point from the furnace. 



By this plan, we not only get rid of the violent heat 

 given out by the furnace, but at the same time it insures 

 a complete draft, so that the heated air from the furnace 

 is so rapidly carried through the entire length of the flue 

 that it is nearly as hot when it enters the chimney as 

 when it left the furnace. This perfect draft also does 

 away with all danger of the escape of gas from the flues 

 into the greenhouse, which often happens when the draft 

 is not active. Although no system of heating by smoke 

 flues is so satisfactory as by hot water, yet there are hun- 

 dreds who have neither the means nor the inclination to 

 go to the greater expense of hot water heating, and to 

 such this revived method is one that will, to a great ex- 

 tent, simplify and cheapen the erection of greenhouses. 

 Many old-established florists, who have had the old plan 

 of flues in use, have changed them to the one here de- 

 scribed, and with great satisfaction. The wonder is that 

 such an important fact has been so long overlooked, for 

 at the time it was discovered, heating greenhouses by flues 

 was almost the only method in use. 



Figure 12 (scale, one-eighth of an inch to the foot), 



