Inclement Weather, Diseases, Etc. 261 



be disturbed in the valley between. In cases when cold vis- 

 its us in this way, the earth itself, and all the stratum of air 

 lying between it and the rolling volume are warmer than the 

 wind above. We know this because the thermometer rises as 

 soon as the gale has stopped, but the highest points coming 

 in immediate contact, lose more latent heat, and suffer most 

 with cold. 



" On the other hand, when intense cold is brought about 

 by radiation, it is the crust of the earth, and low grounds 

 which are coldest, and the air in contact with the earth parts 

 with its heat, only by conduction, to restore in part that 

 which the ground has lost by radiation. The hill-tops grow 

 cold also, and rob the air above them of its heat ; but, as the 

 air on the hill-tops parts with its heat, it becomes heavier 

 than the horieontal stratum of air pressing against it at the 

 margin of the hill, and displacing the lighter air, it rolls down 

 the hill-side, continually forming lakes or ponds of cold be- 

 low, while warmer air takes its place upon the hills."] 



It has also been observed that bodies in motion are 

 less liable to freeze than those which are perfectly still. 

 For this reason it is that the wine-growers of Auvergne, 

 who preserve a long shoot on their plants for fructifica- 

 tion, fasten it to the stakes only after the period of the 

 late frosts. These long shoots, put in motion by the 

 slightest breath of air, freeze less easily than those 

 which are fastened immediately after the pruning. 



The action of frosts is more pernicious to plants in 

 proportion as the thawing is more sudden. It would 

 seem that this sudden transition, from a frozen state to 

 a higher temperature, makes a great impression on the 

 tissues. It is for this reason that vineyards situated on 

 hill-sides exposed to the rising sun, suffer more from 

 frost than those exposed to the setting sun. 



