3o5 Mr. cavendish’s Obfervation* 
be done without a lofs of cold ; and what Is dill worfe, if be- 
fore the experiment was completed the cold of the mixture 
was fo much abated as to become lefs than that of congealing 
mercury, the frozen quickfilver would begin to melt, and the 
operator would have no way of detecting it, but by finding 
that great part of his labour was undone. For this reafon two 
other mercurial thermometers were fent called A and B by Mr. 
hutchins, the feales of which were of wood, for which 
reafon I (hall call them, for (hortnefs, the wooden thermo- 
meters, as I (hall call the two others the ivory ones, their feales 
being of that material ; they were graduated to about 6oo° be- 
low nothing, and their balls were nearly equal in diameter to 
the fwelled part of the cylinders, in order that the quickfilver 
in both (hould cool equally faff ; and it was recommended to 
Mr. hutchins to put one of thefe into the freezing mixture 
along with the apparatus : for then, if the cold of the mixture 
was fufficient, both thermometers would link faff till the 
quickfilver in the cylinder began to freeze, when the ivory 
thermometer would become dationary, but the wooden one 
would (Fill continue to (ink, on account of the contra&ion of 
the quickfilver in its ball by freezing ; but if this lad thermo- 
ter, after having continued to fink for fome time after the 
ivory one had become dationary, ceafed at lad to defeend, it 
would (hew, that the mixture was no longer cold enough to 
freeze mercury ; for as long as that was the cafe, the wooden 
thermometer would continue to defeend by the freezing of 
-fre(h portions of quickfilver in its ball, but would ceafe to do 
fo as focn as the cold was at all lefs than that. As I was afraid, 
however, that the quickfilver might poffibly freeze and dick 
tight in the tube of this thermometer, and prevent its (inking, 
which would make the cold of the mixture appear too fmaH 
when 
