254 On Constructing Hot-house Flues. 



effectually than the one for which it had been substituted ; 

 and it was not found that the house cooled, when the fire 

 declined, more rapidly than it used to do. As long as 

 any fire remains, the thin parts permit the heat to pass 

 through, and the brick-work is altogether massive enough 

 to be slow in cooling. A similar result has been attained 

 in Scotland, by the use of can fines, or flues made of 

 earthen cylinders joined longitudinally: these are very 

 good, but more difficult to make and troublesome to 

 repair, and their rounded surface renders it impossible to 

 place a pot upon them. It may here be as well to remark, that 

 in the arrangement of flues I have found great advantage 

 result from attending to a hint communicated to me by that 

 most zealous and successful horticulturist, the Hon. and Rev. 

 William Herbert, who instructed me to carry the end of 

 the flue on into the chimney directly over the fire-place, so 

 that the chimney might be powerfully heated by the fire. A 

 considerable rarefaction of the air is thus produced at the far- 

 ther end of the flue, and as a constant equable draught is thus 

 maintained, the flue becomes regularly heated all round, 

 which never happens in the common way, where the circula- 

 tion of the heated air along the horizontal flue, depending 

 wholly upon the impulse given it by the fire, soon stagnates, 

 and loses its elasticity, the heat being absorbed in the first half 

 of its course, and the further part of the flue is only slightly 

 warmed. The flues in Lord Carnarvon's and Mr. Her- 

 bert's hot-houses, which have been built upon this princi- 

 ple, keep regularly warm throughout, and there is scarcely a 

 difference of temperature between the two extremities of the 

 houses. 



