on Vegetation. 235 



Capable of fupporting different degrees of it, there will perifli 

 in that feries a greater number in proportion as the cold has 

 been greater ; but if, by means of" a covering, v. c intercept 

 the cold, and prevent the plants from being expofed to a di- 

 minution of heat as great as that which exifls without, fe- 

 veral plants which would otherwife have periflied will be 

 preferved ; feveral of thole which would have been difeafed 

 will be healthy and vigorous, and their number will be 

 greater in proportion as the covering has intercepted a greater 

 degree of cold. 



The earth has a heat accumulated in its interior parts : 

 this heat is perceived in all fubterranean places of fufficient 

 depth to prevent the external cold or heat from penetrating 

 thither. This temperature is equal to 13 on the decimal 

 fcale of the mercurial thermometer (55 "4 Fahr.). Snow is 

 a bad conductor of heat; cold penetrates it with difficulty, 

 and its temperature when it melts is zero. When the fur- 

 face of the earth is covered to a confiderable depth with 

 mow, the cold of the atmofphere, in contact with it, tends 

 to cool its mafs; and the internal heat of the earth tends to 

 warm it. Through the mafs of mow there is then a con- 

 teft of heat and cold, the ufual rcfult of which is to melt a 

 portion of the fnow, and to carry to zero the temperature of 

 the middle, in which the plants are fituated. 



Thus fnow has the property of keeping the plants which 

 it covers at the temperature of melting ice; of preferving 

 them from the influence of a greater cold ; of fupplying 

 them with continual moifturc; of preventing a great num- 

 ber from pcrifhing, and ftill more from languifhing; and, 

 confequently, of giving more ftrength and vigour to vege- 

 tables than they would have obtained had they not been 

 covered with fnow. It appears then that we may explain a 

 part of the influence which fnow has upon vegetation, with- 

 out havintr recourfe to the falts or nitre which it is laid to 



D 



contain, and which analyfis and experiments have proved 

 do not exift, 



7 The 



