252 ON THE CONSTRUCTION AND HEATING OF HOT-HOUSES. 
combustion of the smoke in passing over the fire, and through the heated passage 
W. The boiler should he placed within the house, either under the plant stage or 
Fig. 3. 
in a pit sunk below the level of the floor ; the end only being built into an opening 
in the wall, for the purpose of supplying the fire with fuel from the back sheds. 
Mr. Cruikshanks seems confident that on this principle a much greater pro- 
portion of the heat generated by the combustion of the fuel may be communicated 
to the atmosphere of the house, and that with less loss of time than by any of the 
methods now in use. The flue or flues surrounded with water may, doubtless, be 
constructed in such a manner that the heated air and vapours passing through 
them may be so far deprived of their caloric as to enter the chimney at a tempera- 
ture little above that of the water ; and beyond this point the economy of fuel 
cannot possibly be carried. 
Fig. 4. 
To limit the loss of heat by the chimney is of course a desideratum in any 
mode of warming buildings ; but it appears to be overlooked in many of the plans 
