328 METEOROLOGICAL OBSERVATIONS 



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. Thaws are sometimes surprisingly quick, consider- 

 ing 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 mois- 

 ture. 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 north-east 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.* 



* Fogs happen every where, caused by the upper regions of the 

 atmosphere being colder than the lower, by which the ascent of aqueous 

 vapour is checked, and kept arrested near the surface of the earth. But 

 fogs are more dense about London, and probably all other great cities, 

 than elsewhere : the reason is, because the vast quantity of fuliginous 

 matter floating over such places mingles with the vapour, and renders the 

 whole so thick, that darkness is sometimes produced at noonday, rendering 

 candles and gas lights necessary for the transaction of ordinary business 

 in the shops and public offices. Such circumstances happen frequently 

 during winter ; but on some occasions, (as about two o'clock p. M. on the 

 27th December, 1881, ) this foggy daikness is truly awful. This extraordi- 

 nary appearance is, however, caused by a very ordinary accident, namely, 

 a change of wind. The west wind carries the smoke of the city to the 

 westward in a long train, extending to the distance of twenty or thirty 

 miles, as may be seen in a clear day by any person on an eminence five 

 or six miles from the city. , ED. 



