[1] The values for nickel and bismuth given in the table are much
higher than later values obtained with pure electrolytic nickel and
bismuth.
[2] The value here given, namely 12.885, for the electric
mass-resistivity of liquid mercury as determined by Matthiessen is
now known to be too high by nearly 1%. The value at present accepted
is 12.789 ohms per metre-gramme at 0 deg. C.
[3] The value (1630) here given for hard-drawn copper is about 1/4%
higher than the value now adopted, namely, 1626. The difference is
due to the fact that either Jenkin or Matthiessen did not employ
precisely the value at present employed for the density of hard-drawn
and annealed copper in calculating the volume-resistivities from the
mass-resistivities.
[4] Matthiessen's value for nickel is much greater than that obtained
in more recent researches. (See Matthiessen and Vogt, _Phil. Trans._,
1863, and J. A. Fleming, _Proc. Roy. Soc._, December 1899.)
[5] Matthiessen's value for mercury is nearly 1% greater than the
value adopted at present as the mean of the best results, namely
94,070.
[6] The samples of silver, copper and nickel employed for these tests
were prepared electrolytically by Sir J. W. Swan, and were
exceedingly pure and soft. The value for volume-resistivity of nickel
as given in the above table (from experiments by J. A. Fleming,
_Proc. Roy. Soc._, December 1899) is much less (nearly 40%) than the
value given by Matthiessen's researches.
[7] The electrolytic bismuth here used was prepared by Hartmann and
Braun, and the resistivity taken by J. A. Fleming. The value is
nearly 20% less than that given by Matthiessen.
[8] In 1899 a committee was formed of representatives from eight of
the leading manufacturers of insulated copper cables with delegates
from the Post Office and Institution of Electrical Engineers, to
consider the question of the values to be assigned to the resistivity
of hard-drawn and annealed copper. The sittings of the committee were
held in London, the secretary being A. H. Howard. The values given in
the above paragraphs are in accordance with the decision of this
committee, and its recommendations have been accepted by the General
Post Office and the leading manufacturers of insulated copper wire
and cables.
[9] Platinoid is an alloy introduced by Martino, said to be similar
in composition to German silver, but with a little tungsten added. It
varies a good deal in composition according to manufacture, and the
resistivity of different specimens is not identical. Its electric
properties were first made known by J. T. Bottomley, in a paper read
at the Royal Society, May 5, 1885.
[10] An equivalent gramme molecule is a weight in grammes equal
numerically to the chemical equivalent of the salt. For instance, one
equivalent gramme molecule of sodium chloride is a mass of 58.5
grammes. NaCl = 58.5.
[11] F. Kohlrausch and L. Holborn, _Das Leitvermogen der Elektrolyte_
(Leipzig, 1898).
[12] It should be noticed that the velocities calculated in
Kohlrausch's theory and observed experimentally are the average
velocities, and involve both the factors mentioned above; they
include the time wasted by the ions in combination with each other,
and, except at great dilution, are less than the velocity with which
the ions move when free from each other.