STATE AGRICULTURAL SOCIETY. 121 



wetness or dryness, whether they be an impervious sub-soil, or 

 springs coming to the surface, or the amount and frequency of 

 rain-falls, taken with other meteorological 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 establish a 

 system of rivers and streams. This is not the place to enter into 

 a discussion of the causes that may determine or modify climate, 

 but to illustrate the effect that may be produced by means within 

 human control, it may be stated that previous 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 ofP a forest, 

 and in consequence the streams dried up, and the productiveness 

 of the country was seriously diminished. 



4. The angle at which the sun's rays strike a soil is of great influ- 

 ence 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 soulliern 

 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 pt-rpetual snow lies on their northern inclinations.* 



• Malaglti and DcnocnER have made some observations on the temperature of soils 

 which have come to my knowledge since the ulove was written. They found that the temp, 

 of a garden Foil, just below the surface, was on the avernge 6° Fahr. higher thim that of iho 

 air, but that thin higher temperature diminished at a greater depth. A thermometer buried 

 four inches indicated a mean temperature only 3° above that of (he atmos| here. Besides the 

 garden earth ju: t Uientioned, whicli had a dark gray color and wns a mixture of sand and 

 gravel containing but little ciny, with about five jk r cent, humus, the thern;ometric churac- 

 ien of the following soils were observed, viz: a gray i.>-h -white quartr. snnd, a grayi.-h-l n wn 

 granite (and, a fine light-gray clay, (pipe clay) a yellow fandy clay, and finally four lime 

 soils of different physical qualities 



The influence of a wall or other reflecting surface upf)n the warmth of a soil lying to the 

 south of it, was observed in the case of the garden soil. The highest teuipora'ure indicated 

 by a therniometer placed in this mil ot a dif^tunce of 6 inches from tl.e wall, during a series of 

 observatins lasting seven days, (Ajril lSi2) wos 32*^ Fahr. higher at the surface, and 16° 

 hiphrr at a de| th of f»ur iichcs than in the f^ame soil on the north side of the wall. The 

 ave rage ti m^arature of the former during this time was 8^' higher than that of the latter. 



