AGRICULTURE AND RURAL ECONOMY. 533 



meter (39.4 inches) square and 30 centimeters (11.8 inches) 

 deep, without bottoms, were set into the ground and filled 

 with soil of four different kinds. In parallel trials one soil 

 of each kind was left to settle itself, while the other was com- 

 pressed by pounding so as to reduce the volume by -- to yV. 

 Observations of temperature were made with corrected ther- 

 mometers, graduated to tenths of a degree centigrade, in the 

 soils, at a depth of 10 centimeters, and in air, in the shade, 1 

 meter above the soil. The experiments were made in Au- 

 gust, 1875 ; June, 1876; June, 1877 ; and from April to Octo- 

 ber, 1877. In short periods in June they were made every 

 two hours during the twenty-four. In the series from April 

 to October they were made daily at 7 A.M., 12 M.,and 5 30 

 P.M. Over 12,000 observations were made. In general, the 

 compact soils were warmer by day and in warm weather, 

 and colder bv night and in cold weather, than the loose 

 soils. The differences in temperature were, however, very 

 slio-ht, averaging from 0.1 to 0.9 C. The variations of 

 temperature were greater in the compact than in the loose 

 soils. Wollny shows that these phenomena cannot be due 

 to differences in thermal capacity, radiation, permeability 

 to air, or content of water, and must be ascribed to the 

 superior conductivity of the compact soils. The heat, hav- 

 ing less distance to pass from particle to particle, and 

 less air to impede it, in the compact soil, would natu- 

 rally leave and return to it more readily ; and hence the 

 compact soil would be the more susceptible to changes 

 of temperature outside (Forschungen auf dem Gebiete der 

 Agrikidturpliysik, i., 133). 



The Absorption and Emission of Heat by Soils 



have also been studied by Lange, in several series of exper- 

 iments. The absorption experiments were made with mate- 

 rials in cylinders so arranged as to prevent absorption or 

 emission as far as possible, except from the surface, where 

 the changes in temperature were determined by a ther- 

 mometer. The emission experiments were made by aid 

 of a thermopile. Quartz, sand, kaolin, marble, humus, and 

 peat were used, in their natural condition and covered with 

 lamp-black. Lange concludes that (1) the influence of 

 color on the thermal economy of the soil is very great, the 



