On the specific resistance op mercury. 
185 
Date. 
No. of 
tube. 
Mean temperature 
of water in the 
trough. 
Resistance in 
water. 
Resistance 
at 0°. 
Difference for 
l°-eiesistance 
at 0°. 
Mean of the 
four values in the 
last column. 
March 13 . 
III. 
O 
127 
1-00814 
•99720 
•000863 
„ 14 . . . 
III. 
13-25 
1-00874 
•99725 
•000870 
„ 28 . . . 
III. 
12-8 
1-00810 
■99720 
•000854 
UUUoOJL^ 
«> 24 . . . 
IY. 
12 5 
•51318 
•50774 
•000857 
The above determined mean coincides with the value found by Schroder van der 
Kolk,! whose observations, however, related to a much greater range of temperature. 
An observation by Werner Siemens J between the temperature 18°*5 and 0° gives for 
the coefficient ‘00090. 
The difference between the coefficients '00074 and '00086, as applied to the reduc¬ 
tion from 1 8°'7 (the mean temperature of the tubes in Dr. Matthiessen’s observations) 
to 0°, would account for about one quarter of the difference between his results and 
our own. 
The remainder of the discrepancy may possibly be connected with the manner in 
which Dr. Matthiessen’s tubes were calibrated. Although in the description of the 
process a small column of mercury is spoken of (Reprint, p. 128), it is distinctly stated 
on the preceding page that the lengths of the columns of mercury were 383, 291, 245 
millims. respectively, i.e., nearly half the lengths of the tubes. It is possible that this 
may be a mistake ; but if such lengths were really used, the correction for conicality 
would have been much underestimated, so that the specific resistance of mercury would 
come out too high. In the case of uniform conicality the true correction would be four 
times as great as that obtained by applying the formula applicable to short threads, to 
cases where the length is about half that of the tube. 
[January , 1883.—The measuring rod and the weights used in the above investiga¬ 
tion have been compared with standards verified by the Board of Trade, and the errors 
have been found to be negligible. But since the value of p employed relates to weigh¬ 
ings in vacuo, a corresponding correction is called for here. On this account the final 
number, "95418, should be reduced to 
•95412.1 
* It should be noticed that the resistances here compared are those of the contents of a certain glass 
tube at various temperatures, so that the accompanying temperature variations of length and section are 
determined by the properties of glass and not by the properties of mercury. The results are therefore 
not quite comparable with those obtained in similar experiments with solid metallic wires, which are free 
to determine for themselves their length and section. 
t Pogg. Ann., cx., 1860. 
1 Ibid., cxiii., 1861. 
MDCCCLXXXIII, 2 B 
