cv.] 



OF SELBORNE. 



279 



in a most adroit manner, for a purpose that lias been explained 

 already. 1 



On the 3rd of January, Benjamin Martin's thermometer 

 within doors, in a close parlour where there was no fire, fell in 

 the night to 20, and on the 4th to 18, and on the 7th to 17J 

 a degree of cold which the owner never observed in the same 

 situation ; and he regrets much that he was not able at that 

 juncture to attend his instrument abroad. All this time the 

 wind continued north and north-east ; and yet on the 8th roost- 

 cocks, which had been silent, began to sound their clarions, and 

 crow with clamour, as prognostic of milder weather ; moles also 

 began to heave and work, and a manifest thaw took place. 

 From the latter circumstance we rnay conclude that thaws 

 often originate under ground from warm vapours which arise ; 

 else how should subterraneous animals receive such early intima- 

 tions of their approach. Moreover, we have often observed that 

 cold seems to descend from above; for, when a thermometer 

 hangs abroad in a frosty night, the intervention of a cloud 2 

 shall immediately raise the mercury ten degrees : and a clear 

 sky shall again compel it to descend to its former gage. 



And here it may be proper to observe, on what has been said 



1 See Letter LXI. to Mr. Pennant, page 174. 



2 The cloud of vapour indicates increased radiation of heat and consequent 

 evaporation where it occurs ; as the clear sky is indicative of their absence. 

 The following figures represent the temperature in the open air, at one foot 

 and at two feet under ground, the top figures representing the months, those 

 below, the mean average of each during the ten years. 



It thus appears that the temperature at two feet below the surface is 

 2 33' higher than in the air in January ; 1 70' in February ; 77' in March ; 

 25' in August ; 1 57' in September ; 2" 80' in October ; 3 75' in November ; 

 and 3 84' in December. On the other hand, the temperature is higher \>y 

 0-21' in the open air in April ; 0'98' in May ; 1 21' in June; and 1 12' in 

 July. 



