30 GARDEN MxVNAGEilENT. 



by the power of man, unless at a ruinous expenditure of labour and money. 

 Hence the importance of choosing a chalky, rocky, or gravelly subsoil, as the 

 best site for building or gardening purposes, and of rejecting a green sand or 

 heavy clay as the worst. Where the fall is ample, the worst oi clays may to 

 some extent be dried by efficient drainage ; but the percolation of water 

 through them is exceedingly slow, and is sometimes almost counteracted by 

 the rapid conduction of water to the surface by the process oi capillary 

 attraction. It is this power that conducts the moisture up walls and through 

 v/alks made on such soils. The same cause also imparts that peculiarly un- 

 healthy musty odour characteristic oi houses and gardens in damp situations. 

 Papers on the walls are moulded, carpets rotted, fm-niture ruined : the roots 

 of fruit-trees and other plants and shrubs literally starved by having their 

 tender spongioles thrust into and kept in a perpetual cold bath, by the ex- 

 cessively active capillary power possessed by heavy soils, which originate 

 sterUity, stunted growth, disease, and death, among them ; producing, also, 

 the greatest of all miseries in a garden,— a wet adhesive soil and hai*d-baked 

 surface. All, therefore, who value health, or wish to possess a garden as a 

 means of contributing to their happiness, must choose a dry site, if they would 

 enjoy it. 



82. WarmtJi. — The second condition of a healthy situation is warmth, 

 using the word comparatively, and with a special application to our own 

 climate. It is well known that localities within a few miles ot each other vary 

 considerably in temperature. Other conditions being favourable, then, the 

 warmer any given spot is, the better is it adapted for a garden site. A dry 

 situation is much warmer than a wet one, because moist air is a rapid, and 

 diy air a slow conductor of heat ! and not a drop of water can be raised or 

 evaporated from the surface of any body vmtil it has been rendered buoyant 

 by the absoi-ption of heat from that body or the surrounding air ; consequently, 

 the greater the evaporation of water from the earth's surface, the colder, of ne- 

 cessity, that sm-face must become. The air is not sensibly heated by the direct 

 communication of warmth by the sun's rays, but by its contact with the warm 

 surface of the earth ; whatever cools that sm-face, must, in the same proportion, 

 lower the temperature of the air, Watei', in fact, is the passenger to be 

 conveyed ; heat is the carriage that conveys it. Each passenger requires a 

 separate carriage ; consequently, the more drops requiring removal, the greater 

 the absorption of heat, and, of necessity, the colder the earth and air in con- 

 tact with it become. Every drop of water that passes through a porous soil, 

 while it raises its temperature by communicating its own heat, also prevents the 

 surface fi'om being cooled by its own removal ; the air is thus maintained in a 

 dry state. The free percolation of water through the soil assists in warming 

 the earth, and has thus a threefold influence in increasing its temperature. 

 It not only, as we have just shown, adds to and prevents the destruction of 

 the heat, but it envelops the earth in a stratum of dry air, which is one of the 

 most efficient obstacles to the conduction or withdi-awal of heat. Shelter is 

 also a most efficient means of husbanding and preserving heat, and should 



