[CALLBNDAR & m'lbod] OBSERVATIONS OF SOIL TEMPERATURES 111 



A ciu've giving the variations of daily mean temperature of the air 

 above the ground, at the rate of one millimetre to 1° F., is also shown on 

 the diagram, as well as the depth of snow lying (1 mm. to 1 inch), and 

 the rainfall (1 cm. to 1 inch)/ 



Following the very warm Aveather of Ma}^ 6th to 11th of last year, 

 there was a cold period extending to May 22nd, with rain on the 11th 

 and 12th, which reversed the direction of the isotherms down to a depth 

 of 40 inches, and retarded the penetration at lower depths. From May 

 22nd onwards, the temperature at all depths increased rapidly, the 10 

 inch thermometer reaching its maximum for the year of 70-6°F., on July 

 9th, and the 20 inch that of 66-6°F, on the same day. At greater depths 

 the maxima were considerably retarded. The 40 inch thermometer 

 reached a maximum of 61-0°F. on July 26th, the 66 inch 57-3°F on .Sept. 

 16th, and the 108 inch 52 8°F. on Sept. 30th. 



The onset of winter is marked by the rapid and steady fall of the 

 isotherms from I^ov. 22nd onwards. The isotherm of 32°F. becomes 

 established about the beginning of December, but the ground was not 

 thoroughly frozen until the beginning of January, The remarkable 

 absence of snow till Jan. 24th allowed the isotherm of 32°F. to penetrate 

 to a depth of nearl}^ 20 inches, but after that date the temperature of the 

 surface soil rose considerably in spite of the very cold spell of Feb. 16th. 

 The winter was remarkable for the lateness of the heavy snowfall, and 

 for the rapidity of its disappearance. The snow had disajjpeared by 

 Api'il 17th, and the ground had thawed through at a depth of 10 inches 

 on April 20th, the same date as last year. The rapidity of the thawing 

 of the ground and of the disappearance of the isotherm of 40°F., which 

 took place in 11 days from the iinal melting of the snow as compared 

 with 30 days last year, is probably to be accounted for by the greater 

 dryness of the soil and the smaller quantity of ice in the surface layers. 



Effect of Eainfall. 



The very rapid lowering of the temperature of the soil by rain, 

 Avithout material decrease in the air temperature, was exhibited several 

 times during the summer. On July 30th, a rainfall of 1-2 inches lowered 

 the average dail}' temperature of the 4 inch thermometer from 65-o to 

 60-8°F. in 24 hours, and the 10 inch thermometer from 65-6° to 61 4°F. 

 in 48 hours. Similar and even more extensive changes occurred after 

 the heavy rainfalls of Aug. 17th and 18th, and Sept. 11th. The rains ot 

 Sept. 29th and 30th, followed by the colder autumn weather, produced a 

 rapid decrease in the temperature of the soil down to the 66 inch line, 

 and man}^ of the higher isotherms did not again reach the 10 inch ther- 



» For convenience of reproduction, the figures have been reduced to about half 

 the scale of the originals. 



