CONDUCTIVITY OF SOIL CONSTITUENTS 169 



of temperature in the subsoil. Looking at the soil and subsoil 

 together, a greater conduction of heat (other conditions being 

 equal) will be attended with a higher summer temperature, 

 and a lower winter temperature. 



E. Pott (Landw. Versiichs-Stationen, xx. 288) has compared 

 the power of conducting heat possessed by the principal con- 

 stituents of soil, and has studied the influence of various 

 conditions on their conductivity. The soil to be studied was 

 placed in a cylindrical vessel, about one foot in length, lying 

 on its side, the bulbs of six thermometers being sunk at equal 

 distances along its axis. The cylinder was surrounded by 

 a non-conducting material. One end of the cylinder consisted 

 of a copper plate ; this during the experiment was in contact 

 with the flat surface of a vessel containing hot water. The 

 temperature of the water at starting was in every case 35 C. 

 above that of the soil. The temperature of the water was 

 maintained without alteration during the whole experiment, 

 which lasted in every case twelve hours. The mean rise in 

 temperature of the five thermometers furthest from the source 

 of heat was taken as the figure for comparison. The sub- 

 stances experimented on were quartz powder, and quartz 

 sand of different degrees of fineness; kaolin and potter's 

 clay ; levigated chalk (whiting) ; peat powder. The average 

 results of Pott's experiments are shown in the following state- 

 ment : 



Relative Conductivity for Heat 

 i. In air-dry condition 



Lightly shaken together. 



Quartz Powder ......... 100-0 ...... 106-7 



Peat ......... 90-7 ... 98-1 



Kaolin ... ...... 90-7 ... 96-4 



Chalk 85-2 92-6 



