956 EXPERIMENT STATION RECORD.' 



specific heat is higher in proportion to the absorptive capacity for -water 

 vapor and to the water capacity, and vice versa. For this reason the 

 specific heat is greatest in humus, less in clay, and least in quartz, when 

 the relative saturation with water is the same. In soyls containing 

 much water the specific heat is greatest when the particles are fine and 

 compactly arranged. The specific heat is also smaller in soils with 

 crumbly structure than in those having separate grain structure, other 

 things being equal. ^ 



The conductivity of the soil for heat. — The temperature of the upper- 

 most layer of the soil is communicated by conduction to the lower layers. 

 The temperatures in the upper and lower layers tend to equalize them- 

 selves, but for this a certain length of time is of course required. This 

 circumstance explains a number of phenomena noticed in studying the 

 thermal conditions of the soil. 



There is both an upward and downward movement of heat, and it is 

 slowest in humus, quickest in quartz sand, and has an intermediate 

 velocity in clay. Carbonate of lime and ferric oxid have a conductivity 

 for heat intermediate between clay and quartz. In one and the same 

 soil in the dry state the conduction of heat generally increases with 

 an increase in the size of the particles and aggregates. Conduction 

 increases with the proportion of stones and with the compactness of 

 arrangement of the particles. The differeuces also increase, as a rule, 

 with the quantity of water in the soil. Water increases the conduc- 

 tivity of a soil very considerably, and in proportion to the quantity 

 present, other things being equal.^ 



The soil temperature observed under any given circumstances de- 

 pends, in as far as it is affected by the mechanical structure of the 

 soil, on the resultant action of all the factors just described. The 

 causes attributable to the soil itself bear such a varied relationship to 

 one another that no satisfactory explanation can be arrived at from 

 average figures for observations covering long periods of time as to 

 the individual factors in different soils. Only the variations in differ- 

 ent periods with varying external temperature can be decided. This 

 might be inferred from the fact that, under the same external circum- 

 stances, different kinds of soil, in spite of their very different behavior 

 toward variations in heat, show the same yearly average, or differ- 

 ences of only a few tenths of a degree. This is explicable when we 

 bear in mind that differeuces occurring in separate periods are of such 



1 W. Schumacher, Physik des Bodens, p. 242. L. Pflandler, Poggendorff 's Annalen, 

 129, p. 102. H. Platter, Annalen der Landwirthschaft in Prenssen, Mouatshlatt, 1870, 

 No. 52, p. 52. A. von Liebeuberg, Untersuchungen iiber die Bodenwiirme, Habiiita- 

 tiousschrift, Halle, 1875. C. Lang, Forsch. Geb. agr. Phys., 1, p. 109. R. Ulrich, 

 Ibid., 8, p. 1. 



2 F. Haberlandt, Wissenschaftlich-praktische Untersuchungen auf dem Gebiete des 

 Pflanzenbaues, 1, 1875. A. von Littrow, Sitznngsberichte der kaiserl. Akademie 

 der Wissenechaften in Wien, 1875, 61, pt. 2. E. Pott, Laudw. Vers. Stat., 22. F. 

 Wagner, Forsch. Geb. agr Phys., 6, p. L 



