CULTURE OF THE G 7.' A P E. 299 



sists in leading a covered air-drain from the coldest cor- 

 ner of the house down under the furnace, and bringing it 

 up into an air-space which surrounds the furnace, and 

 which opens into the house. The air, becoming heated 

 in the chamber around the furnace, rises, and produces 

 a draught of air in the drain at the cold end, causing a 

 vacuum, which the warm air flows to fill ; thus creating 

 a continued current, which tends to equalize the tempera- 

 ture of different parts of the house. 



There is no doubt of the efficacy of this plan ; and for 

 narrow houses of moderate elevation it works very well 

 indeed, and is a valuable auxiliary to the simple furnace 

 and flue. Yet there is no disputing its inferiority to the 

 hot-water apparatus. My preference is for the upright 

 boiler of Weathered & Cherevoy, over many others which 

 I have seen and tried. Iron pipes four inches in diame- 

 ter are in general use for circulating the water. The 

 slate-tank, as described for the propagating-house, would 

 give a much greater radiating surface for the same cost, 

 and, upon actual trial, works admirably. Steam-pipes have 

 been used to a limited extent ; but by these the fluctua- 

 tions and the liabilities are increased, without securing 

 any decided advantages. A slight pressure upon the 



