240 
PE. A. A. RAMBAUT ON UNDERGROUND TEMPERATURE AT OXFORD 
ment of coils in use, in. which the corrections have each been diminished by 20 simply 
for the convenience of having the nominal readings of the box apjDroximately equal 
to the temperature of the thermometers :— 
Table I.- —Correction for Coils. 
Plugs in 
Correction. 
Coils in Circuit. 
A, B, C 
- 20-000 
None 
B, C 
- 0-137 
A 
A, C 
+ 19-979 
B 
C 
+ 39-842 
A, B 
A, B 
+ 60-158 
C 
B 
+ 80-021 
A, C 
A 
+ 100-137 
B, C 
None 
- 
+ 120-000 
A, B, C 
The correction to the bridge wire scale is also deduced from the following table, the 
correction being always of the same sign as the reading of the scale 
Table II.—Bridge Wire Table. 
R. 
Corr. 
R. 
Corr. 
R. 
Corr. 
0 
o-ooo 
6 
0-080 
12 
0T61 
1 
•013 
7 
•094 
13 
T74 
2 
■027 
8 
•107 
14 
T88 
3 
•040 
9 
•121 
15 
•201 
4 
•054 
10 
•134 
16 
•214 
5 
•067 
11 
•147 
17 
•228 
6 
•080 
12 
•161 
18 
•241 
We have next to correct for the temperature of the coils and bridge wire. This 
temperature is read from a mercury thermometer which stands in the oil in which 
the coils are immersed, its stem protruding through the marble slab which forms the 
top of the box. The oil in the box was stirred before each series of readings by 
means of a small electric motor. When the observations were prolonged for any 
considerable time, as in the process of standardising, the oil was stirred at frequent 
intervals. 
All observations have been reduced to a standard temperature of 14° C., as being 
about the mean temperature of the observing room throughout the year. 
If R 0 denotes the observed resistance at any temperature 0 , and R u the corre¬ 
sponding resistance for a temperature of the coils of 14° C., they are connected by the 
relation, 
R w — R<n r l + — 14°)}. 
