3 1 8 - Mr. cavendish’s Obfervatiom 
- 72°, and Toon after remained fixed at - 79 . While it Was 
at - 79 0 , the apparatus was twice examined, and the quickiilver 
found fluid ; but being again examined after having been re- 
moved into a frefh mixture, it was found folid. 
It feems likely from hence, that the quickiilver, in the cylin- 
der was quickly cooled fo much below the freezing point as to 
make that in the inclofed thermometer freeze, though it did 
not freeze itfelf. If fo, it accounts for the appearances per- 
fedlly well ; nor does there feem any thing improbable in the 
explanation, except that it is contrary to what happened in the 
three firfl experiments ; hut the degree to which fluids will 
bear being cooled below the freezing point without freezing 
feems to depend on fuch minute circumftances, that, I think, 
this forms no objection. It mu ft be obferved, that the cold of 
the mixture appeared by the fpirit thermometer to be five or fix 
degrees below the freezing point ; fo that if the quickiilver in 
the cylinder was as cold as the mixture, and I have no reafon 
to think it was not, it is not at all extraordinary that the ther- 
mometer fhould have froze ; the only thing extraordinary is, 
that the quickfilver in the cylinder fhould have borne that cold 
without freezing. 
The fame phenomenon occurred in the fixth and feventh 
experiments, on putting the fame apparatus into the freezing 
mixture. 
In the fourth experiment the ivory thermometer funk quickly 
to -42°; but foon after rofe half a degree, probably from the 
cold of the mixture diminifhing ; it then, after having re- 
mained fix or feven minutes at thofe two points, funk very 
quick to - 77 0 . It does not appear, at what time the quick- 
filver in the cylinder began to freeze, as it was not examined 
till long after the thermometer had funk to — 77 0 , when it was 
2 found 
