timony, which feems to congeal with a lefs degree of cold than
all the others above-mentioned.
That in fome circumftances mercury may be cooled below its
freezing point without loofing its fluidity, even as far as five and
an half degrees, whilft the portion in which the bulb of the thermometer
is plunged becomes folid.
That there appears nothing in thefe experiments to afFedt the
credit of the mercurial thermometer, as an accurate inftrument
for meafuring the degrees of heat from the point of boiling
water down to that of the congelation of mercury j but that no
conclufions can be drawn from its motions below this point, as
they depend on the contradtion of the metal in a folid Rate,
which ought to be carefully diftinguiihed from what takes place
whilft it preferves its fluidity; that therefore the ideas we have
formed of the cold obtaining in the habited countries near the
poles, and the aftoniihing power of animals to refift it, muft be
erroneous *, as they have been taken from the extraordinary defcent
of the mercury in the thermometer, which, we now know, is
derived from the contradtion of the mercury when frozen, and
not from fuch an extraordinary degree of cold, as, if it had taken
place, muft have deftroyed the whole iyftem of organized
bodies.
* D r . Blagden ingenioufly infers from refponds pretty ex a& ly with the ex -
a comparifon o f natural cold, during a treme o f natural cold in the moft rigor-
feries o f years, at Albany F o r t, meafured ous climates, which can well be inhabit-
b y a (p in t thermometer, and o f artificial ed j and does not exceed 4 6 " o f a ftand-
cold produced by freezing mixtures, ard mercurial thermometer o f Fahrenheit,
that the extreme o f artificial cold pro- Phil. Tran fa c , vo l. lx x iii. p. 387.
duced b y fnow and nitrous acid c o r -
That
That we cannot, according to our prefent knowledge of the
fubjedt aflert, that there exifts a much greater degree of cold than
the point of the congelation of mercury, no other inftrument
having been employed to afcertain it than the mercurial thermometer,
which is now proved of no authority below 32 degrees
of Reaumur.
But it appears, that a thermometer filled with highly rectified
fpirits of wine preferves its fluidity in a cold of 3 5 degrees of
Reaumur, or 47 of Fahrenheit, and probably in a greater, fo that
it may be employed in northern climates with more advantage
than one filled with mercury.
The furprifing coincidence in the freezing of mercury congeled
in Siberia by natural cold, with that eifedted by means of artificial
cold, merits attention, as they both fix the freezing point
of mercury at 32 of Reaumur; particularly profeflor Laxman, in
a late paper to the Imperial Academy, declares, that he found
common mercury conftantly become folid at 210 of De Liile (32
of Reaumur) and that in the year 1782, it continued folid for two
months together; and Dr. Pallas,, in the third volume of his
Travels, mentions the fame phaenomenon taking place about the
iame part of the fcale.” .
Thus far Dr. Guthrie.
From a careful review of Mr. Hutchins’s experiments, and a
comparifon of the thermometers which he employed on that oc-
eafion, Mr. Cavendilh * concludes, that the true point at which
* Philof. Trania& ions, vol. lx x iii. p. a, page 32 1.
quickfilver