304 Mr. cavendish's Obfervations 
below it. The ball of the thermometer was kept conftantly in 
the middle of the fwelled part of the cylinder, without danger 
of ever touching the fides, by means of fome worfted wound 
round the tube. This worded alfo ferved to prevent the accefs 
of the air to the quickfilver in the cylinder, which, if not pre- 
vented, would have made it more difficult to have communi- 
cated a fufficient degree of cold. The diameter of the bulb of 
the thermometer was rather lefs than one-fourth of an inch, 
that of the fwelled part of the cylinder was two-thirds, fo that 
there was no where a much lefs thicknefs of quickfilver be- 
tween the ball and cylinder than one-fixth of an inch. The 
bulb of the thermometer was purpofely made as fmall as it 
conveniently could, in order to leave a fufficient fpace between 
it and the cylinder, without making the fwelled part thereof 
larger than neceffary, which would have caufed more difficulty 
in freezing the quickfilver in it. Two of thefe inflruments 
were fent for fear of accidents. 
O ne of the moil linking circumftances in the experiments 
which have been made for freezing mercury, is the exceffively 
low degree to which the thermometers funk, and which, if it 
had proceeded, as was commonly fuppofed from the freezing 
mixture having actually produced fuch a degree of cold, would 
have been really aftonilhing. The experiments, however, made 
at Peterfburg afforded the utmoff reafon to fuppofe, and Mr, 
Hutchins’s laft experiments have put beyond a poffibility of 
doubt, that quickfilver contrads in the ad of freezing, or in 
other words, that it takes up lefs room in a folid than in a fluid 
ffate ; and that the very low degree to which the thermome- 
ters funk was owing to this contradion, and not to the inten- 
lity of the cold produced : for example, in one of Mr. 
Hutchins’s experiments a mercurial thermometer, placed in 
the 
