Upon a REMARKABLE COLD. 149 



make an appeal to experiment as foon as the froft mould afford 

 an opportunity. 



FIRST of all, it did not feem impoflible, that the air, in fuch 

 low temperatures, might impart fome faline ingredient to the 

 fnow, along with the hoar-frofl it fo freely depofited ; and, by 

 that means, produce a conftant liquefaction at the furface, which, 

 though very inconfiderable, might be fufficient to prevent the 

 fnow from acquiring the warmth of the higher air. I was led 

 to this random fufpicion, by having obferved that mow, after 

 lying for fome time on the ground, acquired a certain degree 

 of firmnefs at the furface, as if the parts there had caked toge- 

 ther by the gradual intervention of fome fluid medium ; and 

 this, too, in cafes where fuch an effect feemed not to depend 

 upon the influence of the fun in the day-time. 



IT was imagined alfo, that, in fevere froft, the fnow fpread 

 abroad upon the face of a country might poflefs a power of de- 

 purating the atmofphere from any phlogiflic taint ; and thus, 

 according to fome late difcoveries of my very ingenious friend 

 Dr CRAWFORD, there would be a conftant production of cold, 

 by the air in contact with the fnow, abforbing fenfible heat, as 

 it was gradually fo purified. 



THAT property of ice, mentioned by MAI RAN, of expand- 

 ing in volume whilft expofed to the action of a fharp and in- 

 creafing froft, joined ,to the prefumption from analogy, that bo- 

 dies, when fo expanding, muft become colder by an increafed 

 capacity for heat, feemed alfo, in. fome meafure, applicable to 

 the prefent difficulty. 



ONE other conjecture was, that the hoar-froft, in the act of 

 feparating from the air, and forming upon the fnow, might af- 

 fume fome particular arrangement, favourable to a fudden in- 

 creafe of its capacity for retaining heat, and thereby give rife 

 to a continual abforption of it; and, of courfe, to a cooling 

 procefs. 



THESE, 



