490 METEOROLOGICAL OBSERVATIONS. 



THAW. 



THAWS are sometimes surprisingly quick, considering 

 the small quantity of rain. Does not the warmth at 

 such times come from below ? The cold in still, severe 

 seasons seems to come down from above : for the 

 coming over of a cloud in severe nights raises the ther- 

 mometer abroad at once full ten degrees. The first 

 notices of thaws often seem to appear in vaults, cel- 

 lars, &c. 



If a frost happens, even when the ground is con- 

 siderably dry, as soon as a thaw takes place, the paths 

 and fields are all in a batter. Country people say that 

 the frost draws moisture. But the true philosophy is, 

 that the steam and vapours continually ascending from 

 the earth, are bound in by the frost, and not suffered to 

 escape till released by the thaw. No wonder then that 

 the surface is all in a float ; since the quantity of 

 moisture by evaporation that arises daily from every 

 acre of ground is astonishing 8 . 



8 In the neighbourhood of Spofforlh, when a very sudden and mild 

 thaw takes place with perfect calm after a severe frost of some duration, 

 I am able to prognosticate that a most violent gale of wind will come on 

 in about twenty-four hours. Numbers of times have I prophesied this, 

 and I do not remember having been once wrong. So invariably have I 

 found this to occur that I have acted upon it; and I remember, particu- 

 larly, surprising my groom on a very still and mild day after a frost, by 

 telling him that I would not ride the horse he proposed to have ready for 

 me the next morning on account of its being very skittish in a gale of 

 wind, and the next day it blew a hurricane as I had expected. I appre- 

 hend that it is occasioned by the volume of cold air from Craven and the 

 moors which rushes down upon our lower regions, when the temperature 

 is suddenly raised, and becomes unusually warm. W. H. 



The disappearance of frost and the melting of the snows, accompanied 

 with copious rains, are intended by nature to loosen the soil for the 

 expansion of the roots of plants, and at the same time to supply the fluids 

 which are to form the sap. Where chalk, limestone, or marble abounds 

 either in rock masses, or diffused through the soil in the form of sand or 

 gravel, the thaws of the season tend to disintegrate the more compact 

 portions and set free their carbonic acid, which, being washed down to 

 the roots of plants by rain, constitutes an important portion of their nutri- 

 ment, or at least serves as a stimulant to excite the absorbent orifices of 

 the fibrillae to imbibe nutritive juices. RENNIE. 



