354 OBSERVATIONS ON 



are at such times partial fogs about ; where the fog obtains, little 

 or no frost appears : but where the air is clear, there it freezes 

 hard. So the frost takes place either on hill or in dale, wherever 

 the air happens to be clearest and freest from vapour. 



THAW.i 



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 thermometer abroad at once full ten degrees. The first notices 

 of thaws often seem to appear in vaults, cellars, &c. 



If a frost happens, even when the ground is considerably 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. 



FROZEN SLEET. 



January 20. Mr. H's man says that he caught this day, in 

 a lane near Hackwood park, many rooks, which, attempting to fly, 

 fell from the trees, with their wings frozen together by the sleet, 

 that froze as it fell. There were, he affirms, many dozen so 

 disabled. 



MIST, CALLED LONDON SMOKE. 



This is a blue mist which has somewhat the smell of coal- 

 smoke, and as it always comes to us with a N. E. wind, is 

 supposed to come from London. It has a strong smell, and is 

 supposed to occasion blights. When such mists appear they are 

 usually followed by dry weather. 



^See Letter LXI. to Harrington.] 



