q^6 Influence of Snozv and Rain 



The explanation of the influence of fnow by the continual 

 humidity it fupplies to plants, is the refult of obferva.i 

 which cannot have efcaped intelligent fanners in all ages ; 

 but a knowledge of the influence it has by being a bad eon- . 

 duftor of heat, is the eovifequence of experiments recently 

 made on caloric. The ancients had neither a feries of fafts 

 nor inffruments proper for fuch refearches. They obferved, 

 that the atmofphere ru'ted metals in the fame manner as 

 acids ; from which they concluded, that the air contained an 

 acid. They remarked, that nitre was formed fpontaneoufly 

 on calcareous mafles ; from which they concluded, that the 

 acid of the atmofphere was a nitre : and this conclufion was 

 not far from the truth, fince the latelt experiments, and moft 

 remarkable difcoveries which have contributed in the higheft 

 degree to the vapid progrefs of phyfics, have proved that the 

 tiir is formed of two elements, which enter into the compo- 

 sition of the nitric acid, viz. oxygen and azot. Let us ac- 

 knowledge, therefore, that the philosophers who preceded 

 us pollened no little acutenefs and fagacity to be able to dis- 

 cover, fo long ago, by the accumulation of feveral indirect 

 experiments,- what the moft accurate analyfis demonftrates 

 at prclent. • 



If fnow poflefied only the property of preferving vege- 

 tables, and of preventing them from perifhrng by the icverity 

 of the cold, it is not at all probable that the ancient philofo- 

 phers would have confidered it as depofiting on the earth 

 nitrous falts, as they might have afcertained, by a very Ample 

 experiment, that it contains none of that fait; for they did 

 not afcribe the fame property to rain-water, but they re- 

 marked that fnow burnt the fkin in the manner of acids, as 

 well as other bodies immerfed in it. Being induced to con- 

 clude that there was nitre in the air, it was natural that they 

 fhoukl afcribe to this nitre the burning qualities of fnow, and 

 confcqucnily its influence on vegetation. 



C. Guyton having engaged me to examine the caufe of 

 the difference of the cffecTts of fnow and rain-water on va- 

 rious 



