j20 Mr, cavekdIsh’s Ob/erv attorn 
mometer {landing at 40" or 41' below nothing. After having- 
been expofed for near an hour to the air, which was then very 
little above the point of freezing quickflver, only a Imall 
quantity of the lurface was become fluid ; the reft formed a 
frozen globe round the ball of the thermometer, refembling 
polifhed filver, and in iy' after this only a fegment of a globe 
of frozen quickfilver, with a concavity on the infide, formed 
by the ball of the thermometer, was obferved, the thermo- 
meter all this while continuing the fame as before, namely, at 
40° or 41 0 below nothing; fo that in this experiment the ball 
of the thermometer was furrounded for more than an hour 
with quickfilver, which was viflbly frozen and flowly melting, 
and during all which time it continued flationary at 40° or 
41 0 below nothing. 
It mufl be obferved, however, that in the firfl and fecond expe- 
riments, which were both tried with this apparatus, the freezing 
point came out exactly — 40°, whereas in this it feemed about 
half a degree lower ; the reafon of which, in all probability, 
is, that the tube of this thermometer was not fo well fitted to 
its fcale but that it had a little play, which would make the 
freezing point appear near half a degree higher or lower, ac- 
cording as the tube was pufhed up or down. 
Though the foregoing experiments leave no reafonable room 
to doubt, that this is the true point at which quickfilver freezes, 
yet Mr. hutchins has, if poffible, made this fiill more evi- 
dent by his two laft experiments; as, in the firfl of them, he 
froze fome quickfilver in a gally-pot immerfed in a freezing 
mixture, fo that the quickfilver was in contadl with, and co- 
vered by, the fnow and fpirit of nitre ; and in the latter in the 
open air, by the natural cold of the weather, and then dipping 
the ball of the thermometer into the unfrozen part, obferved 
7 what 
