328 



FRUIT-HOUSES. 



As we advance to the northward, the dif- 

 ference diminishes ; so that in London 

 it is not more than 2° in favour of the 

 earth." 



If we compare these data with the 

 circumstances of vines growing in earth 

 nearly at the freezing point, while their 

 stems are exposed to a temperature of 

 60° or 65°, we will then surely see the 

 advantage, if not the absolute necessity, 

 of warming vine borders by some means 

 or other. 



The plan recommended by Mr Ainger, 

 in his " Essays on the Production, Distri- 

 bution, and Preservation of Heat," &c, 

 published in " The Gardeners' Chronicle," 

 would be well adapted for heating vine 

 borders. He says : " The application of 

 bottom heat to an exposed border is one 

 of the experiments that remain to be 

 tried; and whether or not it shall appear 

 that glass buildings may be to some 

 extent dispensed with, the increasing con- 

 viction of the value of soil heat leads me 

 to suggest the following mode of support- 

 ing the earth over the cavity containing 

 the water-pipes or other source of tempe- 

 rature. Let the annexed fig. (441) re- 



Fig. 441. 



present a bed of earth sustained upon 

 arches springing from low walls or piers, 

 between which are placed the heating- 

 pipes. If these arches be formed of 

 bricks, they would obstruct the passage of 

 the heat to the soil ; but if turned with 

 hollow earthen voussoirs, as occasionally 

 practised for the sake of lightness in 

 ancient and modern vaultings, we should 

 have, perhaps, as perfect and as cheap 

 an arrangement as 

 could be devised. 

 The earthen vous- 

 soirs would be first 

 formed something 

 like a garden pot 

 without a rim, 

 (a in fig. 442,) and with or without 



Fig. 442. 



a hole in the bottom, as might seem best : 

 this vessel should then be flattened on two 

 sides at the top, b, retaining the circu- 

 lar bottom so as to render its sides paral- 

 lel in one direction, and of course in- 

 creasing the 

 Fig- 443. an gi e 0 f the 



sides in the 

 other, fig. 443. 

 These vessels, 

 baked in the 

 usual way, 



and set in a small quantity of cement, 

 would form arches, fig. 444, of great 

 strength : they would offer a large 



Fig. 444. 



quantity of surface to the warm air 

 or vapour rising from below : that warm 

 air or vapour might, indeed, pene- 

 trate the soil through the numerous 

 interstices presented to it, and, by fill- 

 ing the voussoirs with stones and pot- 

 sherds, the drainage of the soil might be 

 commanded in the most perfect manner. 

 The objection made by Sir John Herschel 

 to the ordinary modes of producing soil 

 heat — that it is greatest below, while in 

 warm countries it is greatest near the 

 surface — shows, at least, that we have the 

 highest scientific authority for attending 

 to the most minute points of resemblance 

 to, or departure from, nature. And 

 though this is perhaps an extreme refine- 

 ment, when compared with such prac- 

 tices as purposely heating the air which 

 nature keeps cool, and leaving to chance 

 the soil, which in the tropics sometimes 

 reaches a temperature of 150°, it may be 

 remarked that the arrangement just pro- 

 posed, in which the heat is in some mea- 

 sure imparted to the soil by warm air 

 and vapour insinuating itself through in- 

 numerable interstices, and having a ten- 

 dency to ascend, would probably approach 

 as nearly as is practicable to the required 

 conditions." 



Fig. 445 shows a section of the new 

 vineries at Yester; while fig. 446 gives a 

 section of the chambered or heated bor- 

 ders for the roots of vines, of which 



