THMPERATUEB OF SAND. 95 



Quartz sand, pure yellowish grey in colour, 37 '2 

 Pure clay, yellowish grey, 

 Humid acid, brownish black, 

 Field earth, grey, 

 Garden earth, blackish grey, 

 This table shows, first, that the power of becoming heated 

 possessed by pure sand may be appreciably increased by an admix- 

 ture of humus, apparently in consequence of the dark colour of this 

 substance. The dry sand becomes heated some 21°, and the wet 

 13° E., 79° and 61° Fahr. above the temperature of the atmosphere; 

 and while the sand is a bad conductor of heat, the heat, does not 

 penetrate to a great depth ; much more is communicated by conduc- 

 tion and radiation to the superincumbent stratum of air. Kerner 

 found on still warmer days than these on which Schuebler experi- 

 mented that the temperature of drift-sand at Pesth half an inch 

 below the superficial stratum was only 40° odds, and at three inches 

 deep only 25° odds. 



The faculty of retaining heat, or, in other words, the rapidity with 

 which it is discharged, is something different from the capability of 

 absorbing it, and the result of experiment by Schuebler, shows that 

 representing the time required for cooling by lime as 100, the time 

 required by other substances compared with it was as follows : 

 Quartz sand, ... ... .... 96 



Pure clay, ... ... ... ... 67 



Fine carbonate of lime, ... ... 61 



Humid acid,... ... ... ... 49 



Field earth, ... ... ... ... 70 



Garden earth, ... ... ... 65 



After sunset the temperature of the superficial layers of the drift 

 sand sinks very rapidly. Kerner saw on a broiling day in June, on 

 the drift sand at Pesth, a thermometer sunk half an inch deep, which 

 at sunshine showed 35|°, within three hours had sunk to 16°, 

 from 112° to 68° Fahr. 



The most superficial layer of the Hungarian drift sand shows 

 the extraordinary great variation of temperature of from 40° to 45° E., 

 122° to 133° Fahr. But at the depth of only three inches the 

 variation is only 25°, or 88° Fahr., and at four inches, at which 

 depth the temperature in winter does not sink below the freezing 

 point, the variation of temperature does not exceed 20°, 77° Fahr. 

 But at the depth of three fathoms the annual variation does not 



