684 



THE SOUTHERN PLANTER. 



ing and retaining warmth. The vast quan- 

 tity of heat needful to gratify the demand 

 of the vapor that is constantly forming, 

 explains this. From this cause the differ- 

 ence in temperature between dry and wet 

 soil may often amount to 10° to 18°. Ac- 

 cording to the observation of Dickinson 

 made at Abbot's Hill, Herts, and continued 

 through eight years 90 per cent, of the 

 water falling between April 1st and Octo- 

 ber 1st, evaporates from the surface of the 

 soil ; only 10 per cent, finding its way into 

 drains laid three and four feet deep. The 

 total quantity of water that fell during 

 this time, amounted to about 2,900,000 

 lbs. per acre ; of this more than 2,600,000 

 evaporated from the surface. It has been 

 calculated that to evaporate artificially, 

 this enormous mass of water, more than 

 seventy-five tons of coal must be consum- 

 ed. 



Thorough draining, by loosening the soil 

 and causing a rapid removal from below, 

 of the surplus water, has a most decided 

 influence, especially in spring time, in 

 warming the soil, and bringing it into a 

 suitable condition for the support of vege- 

 tation. 



It is plain then that even if we knew 

 with accuracy what are the physical char- 

 acters of a surface soil, and if we were 

 able to estimate correctly the influence of 

 these characters on its fertility, still we 

 must investigate those circumstances 

 which affect its wetness or dryness, whe- 

 ther they be an impervious sub-soil, or 

 springs coming to the surface, or the 

 amount and frequency of rain-falls, taken 

 with other meterological causes. We 

 cannot decide that a clay is too wet or a 

 sand too dry, until we know its situation 

 and the climate it is subjected to. 



The great deserts of the globe do not 

 owe their barrenness to necessary poverty 

 of soil, but to meteorological influences — 

 to the continued prevalence of parching 

 "winds, and the absence of mountains to 

 condense the atmospheric water, and es- 

 tablish a system of rivers and streams. — 

 This is not the place to enter into a dis- 

 cussion of the causes that may determine 

 or modify climate, but to illustrate the ef- 

 fect that may be produced by means within 

 human control, it may be stated that pre- 

 vious to the year 1821, the French district 

 Provence was a fertile and well watered 

 region. In 1822, the olive trees which 



were largely cultivated there were injured 

 by frost, and the inhabitants began to cut 

 them up root and branch. This amounted | 

 to clearing off a forest, and in consequence 

 the streams dried up, and the productive- 

 ness of the country was seriously dimin- 

 ished. 



4. The angle at which the sun's rays 

 strike a soil is of great influence on its 

 temperature. The more this approaches 

 a right angle the greater the heating effect. 

 In the latitude of England the sun's heat 

 acts most powerfully on surfaces having a 

 southern exposure, and which are inclined 

 at an angle of 25° and 30°. The best 

 vineyards of the Rhine and Neckar, are 

 also on hill-sides, so situated. In Lapland 

 and Spitzbergen the southern side of hills 

 are often seen covered with vegetation, 

 while lasting or even perpeLiid snow lies 

 on their northern inclinations.* 



* Malaguti and Durocher have made some 

 observations on the temperature of soils w^hich 

 have come to my knowledge since the above 

 was written. They found that the temperature 

 of a garden soil, just below the surface, was on 

 the average 6° Fahr. high-^r than that of the air, 

 but that this higher temperature diminished at a 

 greater depth. A thejmoaieter buried four in- 

 ches indicated a mean temperature only 3° 

 above that of the atn:osphere. Besides the gar- 

 den earth just mentioneJ, which had a dark gray 

 color and was a mixture of sand and gravel con- 

 taining but little c'a/, with about five per cent, 

 humus, the thermometric character of the follow- 

 ing soils were observed, riz : a grayish-white 

 quartz sand, a grayish brown granite sand, a fine 

 light-gray clay (pipe clay) a yellow sandy clay, 

 and finally foui lime soils of difterent physical 

 qualities. 



The influ .oce of a wall or other reflecting 

 surface upon the warmth of a soil lying to the 

 south of it, was observed in the case of the gar- 

 den soil. The highest temperature indicated by 

 a thermometer placed in this soil at a distance 

 of 6 inches from the wall, during a series of 

 observations lasting seven days, (April 1852) 

 was 32° Fahr. high-r at the surface, and 18° 

 higher at a depth >f four inches than in the 

 same soil on the north side of the wall. The 

 average temperature of the former during this 

 time was 8° higher than that of the latter. 



In another trial in March, the difference in 

 average temperature between the southern and 

 northern exposures was nearly double this 

 amount in favor of the former. Among the soils 

 experimented on it was found that when the ex- 

 posure was alike, the dark-gray granite sand be- 

 came the warmest, and next to this the grayish- 

 white quartz sand. The latter, notwithstanding 

 its lighter color, often acquired a^iigher tempe- 

 rature when at a depth of four inches than the 

 former, a fact to be ascribed to its better con- 



