312 FORCING GARDEN. 



tions of this apparatus ; but it may be proper to direct the 

 attention of the reader to the close boiler represented in 

 Fig. 32, in which is shown how the circulation may be 

 conducted over a door or other obstacle. In this case the 

 upper pipe must not ascend and descend twice : air-tubes 

 ought also to be placed in the boiler, and on the highest 

 part of the pipes ; and the whole must be made consider- 

 ably stronger than on common occasions. The annexed 

 figure will give an idea of an isometrical elevation of a 



Fig. 33. 



hot-water apparatus for a'vinery thirty feet long by eleven 

 wide. A is the boiler, as in the figure on p. 308 ; B the 

 upper or delivering pipe ; C the principal part of the upper 

 pipe, of a flat form, presenting a greater radiating surface, 

 in proportion to the quantity of heat ; D the descending 

 limb; E the returning pipe, of a cylindrical form. 



Mr. Fowler has employed the siphon as a part of the 

 hot-water apparatus ; and in his tract on the Thermo- 

 siphon, as he calls it, has shown how its various modifica- 

 tions may be employed in warming hot walls, as well as in 

 heating glazed houses. The following statement of the 

 principle is given in the Gardener's Magazine, vol. V: 

 " Any one may prove that hot water will circulate in a 



