EXPERIMENT STATION BULLETINS. 



503 



seven in the morning till all the thermometers in the different depths or 

 at any particular depth showed a rise in tem])8ra1ure. These different 

 types of soil were contained in adjacent wooden boxes 3x3x3 feet, 

 without top or bottom, and the soils had lain there for about a year 

 so that they were well compacted by the different climatic agents. They 

 were also covered with a thin layer of a sandy soil so that their insola- 

 tion and evaporafion were more or less equalized. These half-hour 

 records were made at different periods of the season dej)ending 

 upon the condition of the ground, namely, after a long drought, im- 

 mediately after a heavy rain, and a few days after the rain. By mak- 

 ing these observations at different times under this variety of condi- 

 tions, an idea was obtained as to the relative heat conductivity of these 

 distinct kinds of soils in their natural state under field conditions. The 

 data thus obtained are included below : 



TABLE 6.— HEAT CONDUCTIVITY OF SOILS UNDER FIELD CONDITIONS. 



Date. 



July 27 



August 5 . . . . 

 August 26 . . . 

 August 27 . . . 

 September 23. 



Depth. 



6 in. 

 12 in. 



6 in. 

 12 in. 



6 in. 

 12 in. 



6 in. 

 12 in. 



6 in. 

 12 in. 



GraveL 



hrs. 

 firs. 



hrs. 

 hrs. 



4.30 hrs. 

 7 hrs. 



hrs. 

 hrs. 



4 hrs. 

 5.30 hrs. 



Sand. 



hrs. 

 hrs. 



hrs. 

 hrs. 



4 . 30 hrs. 

 7 hrs. 



4 

 6 



hrs. 

 hrs. 



4 hrs. 

 5.30 hrs. 



Loam. 



6.30 hrs. 

 9.30 hrs. 



6 hrs. 

 10 hrs. 



7 hrs. 

 10.30 hrs. 



6 hrs. 

 10.30 hrs. 



6 . 30 hrs. 

 9 hrs. 



Clay. 



6 hrs. 

 9 . 30 hrs. 



5.30 hrs. 

 9.30 hrs. 



6 

 10 



hrs. 

 hrs. 



5 . 30 hrs. 

 10.30 hrs. 



6 

 9 



hrs. 

 hrs. 



Peat. 



hrs. 



8.30 hrs. 

 9 hrs. 



9 hrs. 

 9.30 hrs. 



The figures in each case indicate the number of hours required for 

 the heat to reach the two different depths from the time the air tempera- 

 ture began to rise. The commencement of the ascent of the air tempera- 

 ture was recorded by means of an air thermograph, which commence- 

 ment usually took place from about four to six o'clock in the morning. 

 The data show very conclusively that for both the 6 and 12 inch depths 

 at every observation, the gravel and sand exhibit the greatest power of 

 heat conductivity, followed respectively by clay, loam and peat; that 

 the gravel and sand transmit the heat equally well, as do the loam and 

 clay, but that the peat is the poorest heat propagator; also that the 

 differences between the gravel and the sand are nil, between these and 

 the loam and clay quite marked, while the difference between peat and 

 any of the other soils is very great. One of the interesting points to 

 be observed is the fact that the order as well as the magnitude of heat 

 transmission in all these soils, is fairly constant, especially for the six 

 inch depth for all the different observations. 



Attention should be called to the perfect agreement in the order of 

 heat transmission of these soils as measured under the field conditions 

 and in the laboratory in the natural state. This interesting parallelism 

 receives most important confirmation in the table below which con- 

 tains the relative heat conductivity of these soils as determined under 

 the field conditions on the same day that the cores of the respective soils 

 were taken. The state of the material was the same and consequently 

 the heat propagation under the two different conditions can be more 

 truly compared. 



