534 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



darker coloring favoring both absorption and emission; (2) 

 the finest material absorbs and emits best ; and (3) the sur- 

 face of moistened materials is warmed much more slowly 

 than when they are dry, because of the loss of heat in evap- 

 oration of the water (loc. cit., i., 379). 



The Influence of the Color of Soil upon its Temperature. 



This has been made the subject of an elaborate investigation 

 by Wollny. Five series of experiments were made with sand, 

 clajr, and peat, in boxes. These materials were in one series left 

 in their natural color; in the other four were colored, in par- 

 allel trials, white with sand, and black with Frankfort-black 

 these materials being spread over their surface. Observa- 

 tions of temperature of air and of soil, at depths of two, 

 four, and nine inches, were made at intervals of two hours, 

 day and night, in the months of June, August, and October. 

 Among the conclusions are: (1) that during the warmer sea- 

 son the soils with dark surface were the warmer; (2) that the 

 daily variations are larger in the darker soils; (3) that the 

 differences in temperature (in 1) are greatest at the maxi- 

 mum, and very slight at the minimum daily temperature ; 



(4) that the darker soils cool faster at night than the lighter; 



(5) that the differences induced by color decrease downwards 

 in the soil and in colder weather, until they disappear; (C) 

 and that the above phenomena are, however, altered by va- 

 rious circumstances, especially by the amount of humus in 

 the soil {loc. cit., i., 43). 



The Influence of Plant- covering- and Shade upon the Temperature 



of the Soil. 



Wollny has also experimented at length upon this subject. 

 He finds that (1) the temperature of the vegetative layer of 

 the soil is materially influenced by a covering of living plants, 

 or remains of plants e. (/., straw, manure, wood, etc.; (2) soil 

 thus covered is cooler in warm seasons, and warmer in cold, 

 than bare soil; (3) the influence of such coverings on the soil 

 temperature depends upon the physical peculiarities and the 

 thickness of the shaded layer; (4) snow tends to decrease va- 

 riations in soil temperature, and thus protects plants against 

 injury; and (5) the variations of temperature in soils cov- 

 ered with plants, straw, manure, wood, and snow are less 



