CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 301 
Descending^ Scale. 
97*0 
92*0 
89*6 
87*3 
4*7 
5-0 
2-4 
2-3 
83-6 
79*6 
77*6 
76-6 
o o o o 
Sum 
14-4 
Sum 
14*0 
Although the partial differences do not agree exactly, yet at the two extremes there 
is but little difference either in the ascending or descending scales of temperature. 
In the former, for an increase of 15°'3 of temperature the scale reading increased 15*6 
divisions, and then fell back 14*4 scale divisions with a decrease of 14°; q therefore 
=*0002402 of the force. As these results are strictly in accordance with similar 
observations made at other stations, viz. at Sarawak, Padang, &c., I have not had 
the least hesitation in assuming the value of q equivalent to one scale division : 
increasing scale readings denote an increase of temperature or decrease of force. 
Oscillation or Variation of the Bifilar. 
From page xlviii to Iv inclusive, are given the oscillation, or more properly, the 
range of the horizontal intensity, given in detail in Table B ; first, the mean oscil- 
lation of the horizontal intensity at all the stations comprised in the Survey ; and at 
those stations where observations have been taken for more than a month, as at 
Batavia, Sarawak, and Padang, the mean oscillation has been found from the monthly 
oscillations. At pages 1 and li are given the comparison of the observatory with the 
portable bifilar ; but these are in scale divisions, and their values in terms of the force 
are different. The maximum range in the one case is 3*91 X '000240=*0014, and 
in the other case 8*23 X ■000197='0016 of the force; and the mean range is, of the 
portable bifilar, 2*48 X *000240=*000595, and of the observatory bifilar 2*87 X *000197 
=*000565 of the force*. 
Singapore a Station for Comparison. 
In order to have a fixed station where the hours of maxima and minima and ex- 
treme range may be known, the oscillation of the observatory bifilar is given in scale 
divisions at pages lii and liii for each of the seasons, for each of the months, and 
finally, the mean of each year. 
* It is evident that the great difference between the portable and observatory bifilar magnetometers takes 
place in the morning, or when the atmosphere is most saturated with moisture. The observatory bifilar mag- 
net being well protected, and suspended by silver wire, would not be affected by humidity. The portable 
bifilar, on the other hand, being more exposed, and the magnet suspended by filaments of silk, it is to be pre- 
sumed that the thread would be somewhat affected by damp. It may here be observed, that the same silk 
threads for the bifilar suspension were in use during nearly the whole period of the Survey ; the suspension 
thread was formed by placing three filaments of silk together, their torsion having been previously taken out, 
and after running them through a very weak solution of gum and water, wiping them quite dry ; the threads 
thus treated lasted for more than three years. 
