144 



CASSELL'S POPULAE GARDEXIXG. 



sun and air, this method of remo^'ing• it becomes also 

 a means of hardening the surface into a state of in- 

 tractable sterility- for the time being. The extra 

 moisture in well-drained lands when it is most needed 

 — i.e.,- during long spells of drought — is not only 

 matter of common observation, but the extra produce 

 resulting from the di^ainage is almost entirely owing 

 to this indirect or side influence of drainage. Un- 

 dimned gardens and fields have no storehouse for 

 sui'plus water, unless on the surface, where it is 

 wasted by any vdnd. that blows, or drunk up by every 

 thirsty sunbeam. The storing-cisterns of drained 

 land are deep and wide as the area of its tilths, and 

 hence the provision of water enough and to spare for 

 every cultm-al and climatic emergency. 



Drainage also Makes Land Warm. — Of 



coiu-se primarily the sun is the gTcat source of solar 

 heat, and it has been so admirably arranged that the 

 earth must be warmed before the air, which only gets 

 its heat second-hand from the earth. Hence it fol- 

 lows that the warmer the earth the warmer the aii', 

 and also, as we experience in these temperate climes, 

 the hotter the climate. It follows fi-om this that 

 the temperature of the earth becomes a matter of 

 the most ^dtal concern, not only to the plants that 

 gTOw in it, but also to all that live on its surface. 

 At first sight, on recognising the full force, unerring- 

 exactness, and stupendous powers of the great forces 

 and laws that control all the arrangements for water- 

 ing and warming the world, it seems jDresumptuous to 

 suppose that any power of man can alter their cha- 

 racter or modify their force. Every one, however, 

 that di-ains a field or garden does so to a far greater 

 extent than might be supposed. True, the absolute 

 heat of the sun may be very much (not quite, how- 

 ever) the same, but the same amoimt of heat, which 

 is always and ever^^where equivalent to force, may 

 be directed to different objects and, in fact, for dif- 

 ferent purposes. In this case the heat may be made 

 a lifting power or a warming force, and what is ex- 

 pended on the former sj)ecies of work cannot be also 

 employed on the other. On undrained land much of 

 the heat of the sun must necessarily be expended in 

 lifting the excess of sm-face water from the earth. 

 It has no choice of work ; while that remains its re- 

 moval must precede the warming of the ground. This 

 lifting of the water causes an enormous expenditure 

 of heat. Exact calculations would only puzzle the 

 general reader, to whom we wT.sh to be at once 

 interesting, instructive, and attractive. Comiparing 

 the sun's force, then, to a steam-engine of 500 

 horse-power, it is no exaggeration to say that the 

 strength of 400 horses would be expended in lifting 

 the water from the surface, while that of only 100 is 

 left to warm the earth. 



Xor does that comparison by any means fairly 

 represent the loss of heat resulting from the lack of 

 ch-ainage ; for not only is all this heat wasted in 

 lifting the water, but the lifting by evaporation — 

 the only possible method in this case — is one of the 

 most potent cooling j)rocesses known in nature. 

 Even drinks and water can be cooled thus into ice 

 in the tropics ; and the same tendency and results, 

 though not carried to the same extent simply 

 because the evaporation is not so intensely active, 

 is manifested at all times and in all places when 

 water is lifted from the surface of the earth by evapo- 

 ration. Using the simplest and broadest figures for 

 the sake of illustration, it may be broadly asserted 

 that if it takes three or four units of heat to lift 

 a given weight of water, thi'ee or four units are 

 lost to the earth as the water leaves its surface. 

 Nor is this all the loss of caloric that water-logged 

 land suft'ers. The earth is warmed by warm showers 

 of rain as well as by the direct action of the sun on 

 its surface ; but these are prevented from penetrating 

 and adding their warmth to undrained gardens. 

 The water already in possession refuses to quit for 

 the new-comer, and hence the warm rains are kept 

 lying on the surface till lifted up again, to the 

 further cooling of the earth. 



But how is it that the rain-water cannot enter 

 undrained land? The answer is of vital impor- 

 tance, and f m-nishes the most powerful of all possible 

 arguments that can be advanced in favour of the 

 thorough draining of gardens and fields. It is this : 

 Water is heavier at a temperature of forty degrees 

 than it is at any other temx^erature. Cold increases 

 the weight or sj)ecific gravity of most substances 

 and fluids in a regular ratio at all tempera- 

 tm-es. AVater forms a grand exception to this 

 general law, the exception and its results being 

 among the most marvellous provisions found in 

 nature for the conservation of the heat of the earth. 

 Though hardly germane to our subject, it may be 

 briefly added in a sentence here, that had water 

 increased in weight till it became solid ice, it would 

 sink so soon as formed, and all rivers and seas in 

 cold climes become solid instead of liquid. Such a 

 result would have rendered the earth unfit for culti- 

 vation or the abode of man ; for water, once cooled, 

 can hardly be warmed from above. The experi- 

 ment has been tried again and again of pouring- 

 boiling water on a mixture of soil and water. The 

 heat cannot be passed downwards more than six 

 inches or a foot, while in a vessel two or three feet 

 deep the temperature at the bottom remains the 

 same. 



But place a stop-cock in the bottom of the vessel, 

 and turn that as the water is added at top, and the 

 entire mass is quickly heated to the same tempera- 



