VOL. LXXI.] PHILOSOPHICAL TRANSACTIONS. ]31 



Before making the 2 mixtures necessary for this experiment, the ice was reduced 

 to a powder, and spread out on a paper beside the hoar-frost till both had acquired 

 the same temperature. 



On Monday night, January 22, about 12 o'clock, having occasion to take up 

 a little snow, there was observed a cohesion among its parts rather greater than 

 what might have been expected in a substance, at that time, so much frozen. 

 This circumstance was further examined by the following experiment. A pane 

 of glass was laid on the surface of the snow till it had acquired the temperature 

 of _|_ 3 ) after which, with a bit of parchment equally cold, some snow was 

 scraped from the very surface, and shaken all over the pane, so as to cover it in 

 most parts lightly. On now lifting the pane, and holding it with the snow 

 undermost, the whole of it adhered, and it required some smart raps before the 

 greater part fell away. What remained cleaved to the glass with still a greater 

 adhesion. 



The experiments related above afford further reasons against the opinion of 

 the difference of temperature between the snow or hoar-frost and the air 

 depending on evaporation. It would also appear, that neither does this pheno- 

 menon depend on the deposition of hoar-frost. What renders this the more 

 probable is, that last year there was a much more copious deposition at times 

 when the difference of temperature was not more remarKable. But allowing 

 that a deposition had been found a necessary circumstance, and always in pro- 

 portion to that difference, the experiments on the capacities of hoar-frost and 

 ice seem to show, that the sensible heat which disappears enters not into the 

 composition of the hoar-frost; otherwise the capacity of this substance for heat, 

 compared to that of ice or common snow, should be very different. It must be 

 confessed however, that the abovementioned experiment would have been more 

 applicable to this reasoning, had it been made with hoar-frost given out in colder 

 states of the air. 



If the air, at low temperatures, had any power of acting on the snow or hoar- 

 frost, so as to produce a gradual melting, this circumstance, according to the 

 known laws of heat, might occasion the difference of temperature under con- 

 sideration. And what renders this idea not altogether improbable, is the peculiar 

 cohesion among the parts of the snow above described. Perhaps a gentle 

 melting might take place without much altering the appearance of the snow or 

 hoar-frost at the surface, as the parts, when dissolved, might be gradually 

 sucked downwards, and be afterwards distributed through the whole drier mass. 

 It may also be worthy of an experimental inquiry to determine, how far that 

 sort of concretion, observable all over the surface of snow which has been 

 long frozen, bears any marks of a slow process of this kind. From a hill, a 

 little way to the n. e. of the town, and which was to windward during the frost, 



s 2 



