128 DESCRIPTION OF HOTHOUSES., 



horizontal form, should be so constructed that 

 the heat may be conveyed to all parts of the 

 house ; and it is of great advantage to have them 

 detached from the walls two or three inches or 

 more, that they may give the heat from both 

 sides. It is highly requisite to carry one flue 

 along the front, and both ends of the house, con- 

 tinued to that behind, being of considerable 

 utility in resisting the severity of the frost, cold 

 damps, &c. ; and the back flues should be ar- 

 ranged in two or three returns, one over the 

 .other, the uppermost terminating with a chimney 

 for carrying off the smoke, after having passed 

 through all the flues. Generally the walls of the 

 flues should be made of brick on edge only, that 

 they may impart the heat early and with more 

 effect, six or nine* inches in width, by twelve deep 

 in the clear. Good mortar should be used to the 

 brick- work, and made very close at the joints, to 

 prevent any smoke oozing out into the house > 

 The insides may be thinly plastered, and each 

 range, and the returns, covered with paving tiles r 

 also closely cemented. 



When the hothouse is of very wide dimensions, 



