1919-20.] Effect of Weather Changes on Soil Temperatures. 77 
snow is lying have, as we have already seen, little effect on soil temperature, 
owing to the great protection given by the snow. 
In fig. 1 I have plotted the deviation from the mean date of 
flowering of Coltsfoot, at Hodsock Priory, against the deviation from the 
mean of the number of frosts when deep snow was not lying during the 
two months previous to the plant flowering. It will be seen that there 
is a remarkable agreement between the two curves, and in fact the average 
error over twenty-six years in predicting the date of first flowering of 
Coltsfoot from the frost curve is only four days. Coltsfoot was chosen for 
the purpose as it is a plant which flowers before its leaves appear, and its 
date of flowering would appear to be entirely dependent on the under- 
ground temperature down to the depth of its roots. 
The zeros of the two curves do not coincide. This was to be expected, 
as the average number of days’ snow in January and February is 10, and 
on some of these frost was bound to occur when deep snow was lying. 
The curves are plotted from the observations of Mr Henry Mellish, Hodsock 
Priory, who kindly provided me with the requisite data.* 
Section X. — Weather Changes of Long Period. 
Daily temperature changes are in the main periodic, the early morning 
minimum and afternoon maximum occurring with great regularity in 
spite of weather changes. But there have been several occasions during 
1919— associated with the passage north of these islands of deep cyclonic 
depressions — when a strong warm west wind has blown for some days 
and the intervals between the minimum and maximum temperatures have 
been as much as 54 hours. From the mathematical theory of conduc- 
tion we should expect that such a state of affairs would produce large 
R 
values of with a consequent considerable rise in underground tempera- 
ture ; of course the passage of such depressions is often accompanied by 
B 
rain, which, we have already seen, causes large values for but the 
K 0 
values have been large even when no rain has fallen, as will be seen from 
Table XIY. 
On November 22, 1919, the surface minimum was 0*0° C., and the 
4-inch depth minimum 0'4° C. ; 34 hours later the surface temperature 
had risen to a maximum of 9*8° C., and the 4-inch depth temperature 
stood at 7T° C. 
Such weather in spring is obviously of the greatest possible assistance 
* The Weather at Hodsock Priory , Henry Mellish. 
