300 CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 
where f' and f= observed and corrected readings, 
i and t~ observed and standard temperature, 
change of magnetic moment of the bar for 1° of Fahr. 
li—a . cot V, given above. 
Coefficient of Temperature. — Determination of the lvalue of q. 
The value of q was determined directly at all the principal stations by heat being 
gradually applied to the box at the time the instrument was in adjustment; bf 
adopting this method before sunrise, the thermometer being at the lowest tempera- 
ture, and the changes of force very trifling, I could ascertain at once the changes in 
the readings of the scale corresponding to the changes of the thermometer, and from 
thence the coefficient of temperature in terms of the force; a piece of cotton steeped 
in spirits of wine, ignited and applied carefully to the bottom of the box, gradually 
raised the interior temperature as indicated by the inclosed thermometer. 
The following are the results at the commencement of August 1847 at Batavia; 
the results of the experiments at that station and at the Cocos are alone given, the 
results at all the other stations being precisely similar. 
Coefficient of Temperature at Batavia. 
Thermometer. 
Differences. 
Scale divisions. 
Differences. 
77’Q 
82-6 
85-0 
88- 5 
89- 5 
5-0 
2- 4 
3- 5 
1-0 
76‘8 
103- 1 
104- 0 
107- 2 
108- 1 
6*3 
0-9 
3-2 
0-9 
Sum 
11-9 
11-3 
or one degree of temperature Fahr. for one scale division very nearly : this result 
agrees exactly with similar observations made at other stations. 
Coefficient of Temperature at the Cocos. 
To determine q or the coefficient of temperature the morning that the instrument 
was taken down, a piece of cotton dipped in spirit and ignited, was carefully applied to 
the bottom of the box, between 5 and 6 a.m., when the thermometer was at the mini- 
mum temperature and the changes of force but small, with the following results : — 
Bifilar. 
Thermometer. 
Scale. 
Differences. 
Fahr. 
Differences. 
86-1 
90-8 
96-5 
98-5 
101-7 
4- 7 
5- 7 
2-0 
3-2 
7^9 
79-2 
89- 9 
90- 6 
90-6 
3-9 
10-7 
0-7 
0-0 
Sum 
15-6 
15-3 
