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CHAPTER 2.
Methods and instruments,
In the course of the experimental research some delicate
questions, requiring great accuracy in the determination of
temperature, arose. I therefore think it advisable, first to give
an exposition of the
A. Measurements of temperatures and determinations of
the coefficient of apparent dilatation of mercury.
The temperature was observed by means of 3 normal
mercury thermometers, manufactured expressly for these
purposes by Dr. Geissler in Bonn and his successor, Mr. Franz
Müller. In the following these instruments will be denoted
by Oj, Gn & GIU
Gj indicates temperatures from — 1° C to + 26° C
Gj & Gn were made in 1875, Gm in 1880, consequently the
correction for zero at present ought to be constant. It is
however liable to little perturbations. Especially in Gr the
final state of equilibrium of the molecules seems not to have
been attained yet.
By a great number of observations it was ascertained,
that the indications of the different thermometers above zero
corresponded with each other within the limits of 0°.oi or
0°.015 of a centigrade degree. Below zero the correspondence
could not be observed so closely, on account of the difficulty
of maintaining the temperature steady for a long time. It
must also be observed, that during the volumetric experiments
the dilatometer and the thermometer were immersed in a
mercury vessel of wrought iron. The pressure of the mercury
caused a rise of O^.oa C in the indication of temperature. This
is a constant error, to which due reference has been made.
The correspondence of the different instruments being
ascertained to be satisfactory, another question arose of equal
»
»
— 12° C >» + 5° C
22° C
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