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’
PHIPPS S JOURNAL, 575
The following is Mr. Cavendifh’s account of the corrections to be made for Lord
Charles Cavendifh’s thermometer :
** The thermometer ufed in thefe experiments is fully defcribed in the Philofophical
Tranfactions, Vol. L. p. 308 ; fo that limagine it is unneceflary to mention it here. But
fince the publication of that volume, the late Mr. Canton difcovered that fpirits of wine
and other fluids are compreflible ; which muft make the thermometer appear to have
been colder than it really was, and renders a correction neceflary on that account.
There is another {maller correction neceflary, owing to the expanfion of f{pirits of wine
by any given number of degrees of Fahrenheit’s thermometer being greater in the higher
degrees than the lower. As the method of computing thefe two corrections is not ex-
plained in that paper, it may be proper juft to mention the rule which was made ule of
in doing it.
‘© In adjufting the degrees on the fcale of this thermometer, the tube was entirely full
of mercury, or the mercurv ftood at no degrees on the feale, when its real heat was 65°
of Fahrenheit. Let the bulk of the mercury contained at that time in the cylinder be
called M, and that of the fpirits S ; let the expanfion of {pirits of wine by 1° of Fahren-
heit, about the heat of 65°, be to its whole bulk at that heat, as s to 1; and let its ex-
panfion by one degree at any other heat, as 65°—wx, be to its bulk at 65°,as 5 x1—d-x
to1; let the expanfion of mercury by one degree of heat be to its bulk at 05°, as m to1;
and let pt ue be called Gs let the compreffion of fpirits of wine by the preflure of
s
an hundred fathom of fea-water, when the heat of the fpirits is nearly the fame as that
of the fea at the depth te which the thermometer was let down, be to its bulk at 65°, as
C to1; the compreflion of the mercury is fo fmall that it may be neglected ; let the
thermometer be let down N hundred fathom, and when brought up and put into water
of 65°—F degrees of heat let the mercury in the tube ftand at E degrees; confequently
the heat, as fhewn by the thermometer, is 65°—-F—E: and let the real heat of the fea
at the depth to which it was funk be 65—wx degrees; then 65°—wx=65°—F—E+
CN_EdxE+P+= , CNdxFisx
3G 2G Ore ais Ge
panfion of the fpirits ufed in making it by 1° at the heat of 65°, was found to be
. In this thermometer $=1160; M=c7; the ex-
I ; : k Ei leat i :
7786 of their bulk at that heat ; that is s— no) = Tasos? therefore “G “= 1,013.
From M. De Luc’s experiments * it appears, that the expanfion of fpirits of wine by
1° at any degree of heat, as 65°—x, is to its expanfion by 1° at 65’, nearly as 1 —
2 Raila aH ve s
me to 1: therefore, d= es The compreflibility of the fpirits ufed for this thermo-
3
meter at the heat of 58°, was found to be exaétly the fame as Mr. Canton determines
it to be at that heat; and therefore its compreffibility at all other degrees of heat is
fuppofed to be the fame as he makes it. According to his experimentst, the compref-
fion of fpirits of wine by the preflure of 29} inches of mercury at the heat of 32°, id ¢/,
nearly the heat of the fea in thefe experiments, is 593 millionth parts of its bulk at that
ExE4+F4+x
heat 5 therefore =ngand 65 —x = 6s—F—E4Nx1, 9— a +x
NX1,9 Xb + 2% 59>
Fay eye :
* Modifications de Atmofphere, Vol. I. page 252.
+ Philofophical Tranfattions, Vol. LIV. page 261.
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