AS DETERMINED BY FIVE PLATINUM-RESISTANCE THERMOMETERS. 241 
or adopting the temperature coefficient, 0‘00024, as determined by Mr. Griffiths, 
R 14 - R, = R, X 0-00024 X (0 - 14°). 
In this expression R fl is the total resistance in the circuit, and since this includes 
the resistance of the “ concealed coil," we require to know approximately the value of 
that coil in the right-hand side of the equation. This is, perhaps, most easily deter¬ 
mined from the observations of the thermometers themselves at 100° C. and 0° C., 
combined with the constant value found by Mr. Griffiths for the ratio of the corre¬ 
sponding resistances R x and R 0 . 
Thus, if X be the value of this coil, r 0 that of the other coils in use and the bridge 
wire when the thermometer is packed in melting ice, and r x that of the coils and 
bridge wire when it is immersed in steam, reduced to mean box units at 14° C., then 
the total resistances in the two cases are, X + i\ and X -f r 0 , and if we take the 
ratio of these resistances to be 1’3872, # as found by Mr. Griffiths for the wire 
used in the construction of this instrument, then —- 1 = 1’3872, and therefore 
X + r 0 
r 1 - l‘3872r 0 
0-3872 
The values of X found in this way from the observations made on October 4, 5, 
and 6, 1898, for the purpose of standardising the thermometers, are as follows :— 
Thermometer. X. 
1 240-65 
2 -65 
3 -77 
4 . *77 
5 -60 
A. -65 
Mean 240"68 
For any arrangement of coils (Y) and any bridge wire reading (R) we have therefore 
the total resistance in the circuit, X + Y + R, and the coefficient of (6 — 14°) in the 
correction for temperature is 
(X -f- Y + R) x 0-00024. 
We thus find the following table for the two different arrangements which have 
been used in the observations :—- 
VOL. CXCV.—A. 
* ‘Nature,’ November 14, 1895, p. 45. 
2 i 
