THE FORCING GARDEN. 



531 



flush with the outside of the flues, but slioukl never project 

 over them. If they be an inch, or even two inches, narrower 

 than the full breadth of the flue, so as to allow of a little mor- 

 tar being drawn in to fill up the angle, they will present a 

 lighter appearance. Where only one course of flue can be 

 admitted, the broader it is, the more heat will be given out as 

 it proceeds, and consequently one extremity of the space to be 

 heated will be hotter than the other ; a return, or double course 

 of a narrow flue, is, therefore, almost always preferable to one 

 course of a broad flue. 



Flues vary in size, from six inches in width, and twelve 

 inches in height, to ten inches wide, and eighteen inches 

 high; this should, in a great measure, be regulated by the 

 purposes for which they are intended. The intermediate size 

 between these may, generally, be employed in most forcing- 

 houses; some, however, build their flues much larger, and, 

 instead of laying the bricks on edge, lay them flat, from an 

 idea that the greater the body heated, the longer will it be 

 in cooling, and, consequently, continue to give out its heat for 

 a greater length of time. This is indeed true, but then it 

 requires an equally greater length of time, and a gi'eater force 

 of fire to heat them thoroughly, so that what is gained on one 

 hand is lost on the other; and if ever the temperature be 

 allowed to fall below what is required, flues of such dimen- 

 sions will not heat the house so rapidly, as those of less size, 

 and will likewise require a greater quantity of fuel. 



Much has been said upon the subject of hot air-flues, but 

 they are now almost very justly exploded, as being worse than 

 useless. Nicol was at some pains to prove their inutility, and 

 he proved it in the following manner : The idea," he says, 

 " of collecting the heated air from a furnace, and conducting 

 it to the cold end of the house is just and natural enough ; but 

 if this cannot be done without conducting the tube or flue, 

 which conveys it, upon the fire-flue, to the evident loss of its 

 surfice, and of its best part, I would ask, what is gained by 

 the experiment, or rather, what is lost by it ? Evidently a 

 great deal : all the expense, and double the quantity of heat, 

 that can be thus conveyed. The fact is, there is no heat comes 

 to the far end of the house, hut just what is col.ccted from the 



