the Congelation of Quickfilver. ^9 
was fhft obfeived at Glafgow, about twenty years ago, by Dr. 
black and Mr. irwin, who endeavoured to determine its 
mod: material circumftances by various experiments. Since 
that time Dr. black has conikntly taught it in his chemical 
lectures; and confldering the heat which difappears as (fill re- 
maining in the fluid or vapour, but deprived for the time of its- 
property of being, communicated to other bodies, and thereby 
becoming fen Able, he calls it latent heat, a term fufficiently 
expreflive of his manner of conceiving the fact. 
In the year 1772, the celebrated Profeflbr wilcke inferted, 
in the Tranfaftions of the Royal Academy of Sciences at 
Stockholm *, a paper profefledly on the fubjedt of the cold pro- 
duced by J now in melting, which being written in the Swedifh 
language is lefs known 111 this country than it deferves. He 
feems not at all acquainted with what Dr. black had done, but 
fpeaks of it as his own difcovery, originating in an accidental, 
attempt to melt away a quantity of fnow by the affuhon of 
hot water ; when he found the procefs go on fo (lowly, and fo 
little efledl produced, that he determined to inveftigate the 
caufe of fo unexpected an event. After a feries of experiments 
with this view, he came to the following concluflon ; that 
fnow, in melting, conflantly abforbs a certain and equal quan- 
tity of heat, which is employed entirely in giving it fluidity. To 
render fuch a property more intelligible, M. wilcke pro- 
pounds a particular theory of an elaftic fluid between the par- 
ticles of bodies ; and he proceeds to various illuftrations and 
dedudtions, all highly ingenious. 
Two principal methods have been adopted to prove this lofs 
of heat; one, by adding ice at the freezing point to a certain 
proportion of water at a known degree of heat, and obferving 
how much the' temperature of the mixture comes out below 
* Kongl. Vetenfkaps Acad< Handliagar vol. XXXIII. p. oy 
