-i £ Mr. cavendish’s Obfervations 
for if it was, the thermometer could not have remained fo long 
flationary at that point, while furrounded with freezing quick- 
filver ; and it cannot be higher, as the thermometer could not 
fink below the freezing point, while much of the quickfilver* 
with which it was furrounded, remained unfrozen. 
To thofe who have attended to the former part of this paper 
it is needlefs faying, that the reafon why the wooden thermo- 
meter continued finking fo long after the ivory thermometer 
became flationary is, that as the former was placed in the freez- 
ing mixture, the quicklilver in its ball froze, and therefore it 
continued defcending during the greatefl part of that half hour, 
by the continual freezing of frefh portions of quickfilver in its 
ball, and the contraction occafioned thereby ; whereas the latter, 
which was placed only in freezing quickfilver, did not freeze. 
There is a circumfiance, however, in this experiment, the 
reafon of which does not fo readily appear ; namely, on put- 
ting back the apparatus into the freezing mixture, after it was 
taken out to be examined, the thermometer funk to - 42 0 ; but 
in about tour cr five minutes returned back to - 40°. The like 
happened on removing the apparatus into a frefh freezing mix- 
ture, and it then remained about ten minutes before it returned 
to -40°. It Teems probable from this, that the quickfilver in 
the cylinder became intirely frozen about the time that it was 
firfl taken out to be examined, and that it then grew 2 0 colder 
than the freezing point ; and that this degree of cold was not 
fufficient to make the quickfilver in the inclofed thermometer 
freeze, fince mercury, as was before faid, will bear being 
cooled a little below its freezing point without f eezing. What 
confirms this explanation is, that the fpirit thermometers fhew 
that the cold of the mixture was a&ually much the fame as 
that fhewn by the ivory thermometer. 
Ill 
