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Proceedings of the Royal Society of Edinburgh. [Sess. 
II. — The Cooling of the Soil at Night, with Special Reference 
to Late Spring Frosts (II). By Captain T. Bedford 
Franklin, B.A. (Cantab.). Communicated by The General 
Secretary. 
(MS. received September 26, 1919. Read November 3, 1919.) 
SUMMARY. 
SECTION 
I. Introduction ......... 
R 
II. The Values of ^ in Soil of Varying Degrees of Wetness — 
R 0 
{a) Wet just after rain ....... 
(6) Drying after a number of fine days . . ... 
(c) Dry ......... 
R 
III. Values of the Lag corresponding to Various Values of ^ . 
K 0 
R 
IV. Connection between the Relative Humidity, and the Number of 
Degrees Centigrade ( e ) which the Surface can fall below the 
Temperature of the 4-in. Depth before the Upward Conduction 
BALANCES THE RADIATION ....... 
V. Differences between the Air Minimum over Open-Soil and Surface- 
Soil Minimum on Clear Nights ..... 
VI. The Forecast Equation . . . . 
VII. A Comparison of the Forecasted and Observed Minimum Tempera- 
tures of Open Soil on Clear Nights . . . . 
VIII. Conclusions . . 
I. Introduction.* 
In my previous paper to the Society on the same subject I came to the 
conclusion that the temperature of the surface of open cultivated soil 
fell rapidly at the beginning of a calm clear night until it was such a 
number of degrees below the temperature at the 4-in. depth as to make 
the upward conduction from that depth to the surface balance the 
radiation. After this stage was reached the surface and 4-in. temperatures 
fell at the same rate. 
If, therefore, the temperatures of the surface and 4-in. depth and 
the conductivity of the layer of soil between the 4-in. depth and the 
surface were known from readings of electrical resistance thermometers, 
* The temperatures throughout this paper are in degrees centigrade. 
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