22 



THE PRACTICAL GARDENER. 



return to the boiler by a pipe immediately below it, which will 

 enter the boiler near its bottom. The water in this lower pipe 

 will travel with more rapidity by forming an inclined plane 

 from the extremity to the boiler ; the top pipe may be per- 

 fectly level. Thus the water will continue to circulate in the 

 pipes long after the fire is extinguished, or, indeed, as long as 

 any heat remains in the boiler or brick work round it. It 

 has been ascertained that water heated by this means will tra- 

 vel at the rate of forty feet per minute, with an ordinary fire, 

 but this rate may be much increased. The distribution of heat 

 by this mode is so equal, that the pipes will be found as warm 

 fifty or sixty feet from the boiler, as they are where they are 

 connected to it. This is never the case with smoke flues ; from 

 which arises the many complaints that hot walls are burnt up 

 in one part, and little affected by the heat in others. (For a 

 more full account of this mode of heating, see the Forcing 

 Garden). 



Sunk walls, or such as are built under the general surface 

 of the ground, or nearly so, and are known by the names of 

 haha's, or sunk fences, have not been often adopted for general 

 purposes. Instances occui', however, of the adoption of these 

 walls, where it has become necessary to conceal them fi:om the 

 sight. These walls have many advantages, and might be much 

 more generally adopted than they are ; they, however, possess 

 this disadvantage, that they present only one surface for the 

 purpose of planting trees against; but, to balance this defect, 

 they are much stronger, are not liable to be blown down, and 

 from the rays of heat being reflected from them to the opposite 

 bank, and again reflected upon the wall, together with theii 

 being completely sheltered fi'om cutting winds, renders then 

 extremely well calculated for the production of early fruits ; i,i 

 addition to which, a garden enclosed with sunken walls may 

 be rendered more picturesque than one with lofty walls, which, 

 in confined places, are often difficult to hide. In our practice, 

 we once had a sufficient proof of their superiority as regard? 

 the production of early crops. In the management of sucl 

 walls, the trees may either be planted in the bank and ben* 

 into the wall, or, in many cases, they may, with greater pro- 

 priety, be planted behind and trained downward The ex- 



