MEASUREMENT OF TEMPERATURE. 
199 
for the purpose of interpolation. The close agreement of the values of the ratio r, 
obtained from different resistances and at considerable intervals, shows the accuracy of 
the resistance-boxes and the reliability of the method. Observations taken at lower 
temperatures were even more concordant. The porcelain tube was enclosed in an iron 
tube to render the temperature more uniform and steady. 
Table IX. 
Time, 
May 25. 
Quantity observed. 
Resistance from 
box. 
Galvanometer 
throws. 
Deduced 
value. 
Remarks. 
h. m. 
r 
R 
E 14-38 
Balance 
14-380 E 
Iron tube full red hot. 
4 15 1 
r= (lT 1000 ) 
M 640 
15 left 
l 64026 — 
J * 
l 
\R ) 
641 
43 right 
Temperature nearly steady. 
640 
15 left 
4 21 
R 
E 14-39 
Balance 
14-390 E 
Temperature of air inside box E, 
18°'5 C., constant throughout 
this hour. 
(I' 14 ' 39 ) 
M 921 
11 left 
l 19-2138 M 
Ratio deduced, "64029 
922 
18 right 
J 
E 
Resistance f 2 
150 right 
1 
of ^3 
105 left 
> -0259 E 
connexions f2 
Insulation re-1 
sistance / 
-4^2250 
148 right 
J 
225000 E 
4 33 
R 
E 14-43 
Balance 
14-430 E 
(?• 1443) 
M 924 
Balance 
9-240 M 
Ratio deduced, ’64033 
hi 
VR J 
The following Table X. shows the reduction of some of the observations. The first 
pair of observed resistances are reduced from the observations recorded in the previous 
Table. The difference of reduced resistances is found by the simplest possible reduc¬ 
tion from the corrected ratio by means of the formula 
* *A = !n_ 
R 0 
The value of R/R 0 is only approximate, and the difference of the mean coefficients 
/ li \ 
(a —a') is found by dividing ( ——, j by the approximate value of the temperature. 
\K 0 -U 0 j 
The mean coefficient of the standard wire is assumed to be constant, and the relative 
variations of the other tabulated; the column of temperatures is calculated by 
assuming for each wire a constant coefficient equal to the mean value between 0° and 
100°; the difference column shows how very closely the two platinum wires agree : 
although their temperature coefficients differ about 3 per cent., yet the temperatures 
deduced by using either wire agree to nearly 1 in 1000. Several other observations 
were taken at different times with the same comparison coils ; they all agree within 
the limits of error of the resistance-boxes. No zero variation of either wire could be 
■with certainty detected ; and observations taken with the temperature varying at the 
rate of 10° per minute agree to 1 in 5000 with the best. 
