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This table shows, that the apparent dilatation of the
mercury in the dilatometer was equal [= 27.. . millimetres =
0.006242 cc] for every centigrade degree observed on the scales
of the Geissler thermometers Gn & Gm. The variations [0.3
unto 0.7 millimetre] are due to the difficulty of maintaining a
steady temperature in the mercury vessel for a sufficiently
long time. I estimate the unavoidable oscillation of
temperature at about 0’.o2 C for temperatures above —10° C. For
lower temperatures (as for example — 16° to — 17° C) the error
is somewhat greater.
This speaks strongly in favor of the Geissler
thermometers. They are in fact excellently graduated after the
principle of the mercury thermometers. I therefore, upon reflection,
thought it advisable, to apply this principle exclusively to all
measurements of temperature given in this paper. The
numbers therefore refer to the indications of correctly calibrated
mercury thermometers. Besides, all measurements of
temperatures of ice or water, hitherto published in hydrographic
researches, are made with mercury thermometers, and the
following results would be incapable of comparison with those
of my predecessors, if I were to apply another standard of
temperature. Still I think it to be a serious inconvenience,
that science nominally proclaims one standard of temperature
[the dilatation of dry air] but practically applies another [the
dilatation of mercury].
The preceding experiment also serves another purpose.
For the following determinations it was necessary to know
the coefficient of absolute dilatation of the glass reservoir of
the dilatometer. This number is easily calculated from the
last column of the table 1 series a & b. If
q denotes the coefficient of absolute dilatation of mercury,
» » » » apparent
g » » » » cubic dilatation of glass,
then
g = q — ¡1
ft being a constant (see last column of table 1, a & b), the
value of g depends upon wdiat number is substituted for q.
Here another great inconvenience arises from the uncertainty
of the absolute coefficient of expansion of mercury at 0° and
lower temperatures. According to Regnault’s determinations
q = 0.00017905 at 0°.
According to Wiillner’s recalculation of Regnault’s
experiments, it ought to be
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