SOIL HEAT 309 



which may or may not lend themselves to modification 

 in the field. From the fact that type is of primary im- 

 portance in choosing a soil, texture in its relation to con- 

 ductivity might be considered first. From the work of 

 Wagner ! and Potts 2 it is clearly established that the 

 coarser the texture of a soil, the faster the rate of conduc- 

 tion of heat will be, other factors remaining constant. 

 Data quoted from the findings of Bouyoucos 3 substantiate- 

 these results : — 



Conductivity of Various Soils as Measured by the Time 

 Required for a Thermometer 7 Inches from the Source 

 of Heat to Show a Rise in Temperature 



Q ., Relative Rate of 



bo11 Conductivity 



Sand 1.00 



Loam 1.81 



Clay 1.77 



Peat 4.61 



Such results as these are only comparative and qualita- 

 tive. The difficulties of quantitative determinations are 

 so beset by error that only one investigator has as yet 

 made any consistent attempt along this line. Patten, 4 

 who has prosecuted such an investigation, finds that such 

 work may be vitiated by thermometer spacing, size of 

 thermometer, error in readings, moisture control, and 



1 Wagner, F. Untersuchungen iiber das Relative Warme- 

 leitungsvermogen Verschiedner Bodenarten. Forsch. a. d. 

 Geb. d. Agri.-Physik, Band VI, Seite 1-51. 1885. 



2 Potts, E. Untersuchungen Betreffend die Fortpflan- 

 zung der Warme in Boden durch Leitung. Landw. Ver. Stat., 

 Band XX, Seite 273-355. 1877. 



3 Bouyoucos, G. J. An Investigation of Soil Temperature. 

 Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 20. 1913. 



4 Patten, H. E. Heat Transfer in Soils. U. S. D. A., Bur. 

 Soils, Bui. 59. 1909. 



