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XII. Magnetic Survey of the Eastern Archipelago. By Captain C. M. Elliot, of the 
Madras Engineers. Communicated by Lieut. -Col. Sabine, V.P. Treas. R.S.Sfc. 
Received January 15, — Read January 16, 1851. 
In accordance with instructions received from the Honourable the Court of 
Directors of the East India Company, and at the recommendation of the Royal 
Society, I commenced, in the month of January 1846, the Magnetic Survey of the 
Eastern Archipelago. 
As, in the prosecution of this work, I was left entirely to my own discretion, I may 
be permitted to state, that the principal object of the Survey appeared to me to consist 
in determining the position of certain magnetic lines which were included within the 
space I had to traverse ; such, for instance, as the line of no dip, and of the maximum 
horizontal component of the force ; from these, to determine the line of minimum in- 
tensity ; and finally, the line of no variation and its direction. The determination of 
these lines I considered to be the principal object ; but in addition, I was anxious to 
take hourly observations of the elements of the earth’s magnetism, in order to ascertain 
whether the changes of declination and of magnetic intensity were uniformly similar 
over so large an area. The fixed stations for this latter purpose were sixteen in 
number, and the time employed at each station varied from a few days to several 
months. The fixed stations were spread over an area of 28° of latitude and of 45° of 
longitude, viz. from 16° latitude north to 12° latitude south, and from 80° to 125° 
longitude east. With reference to the line of no dip, which in this part of the globe 
coincides very nearly with the line of minimum intensity, I may state, that of the 
sixteen stations, nine were to the south, three to the north, and four in its immediate 
vicinity. With reference to geographical position, four were in the islands adjacent 
to Singapore ; one in Borneo ; one in the island of Java ; two in Sumatra ; one in the 
island of Mindanao ; one in Celebes ; one at the Cocos or Keeling Islands, which 
was the most southern station to which I could venture ; one at Penang, and one in 
its immediate vicinity ; one at Nicobar, in the bay of Bengal ; one at Moulmein, which 
was my most northern ; and, finally, one at Madras, which was my most western 
station. The Survey is however incomplete, as it would have been desirable to extend 
it considerably more to the eastward, in order to lay down with greater certainty the 
continuation, of the line of no dip and of the line of minimum intensity ; and likewise 
I should have wished to proceed more to the northward, to ascertain with greater 
exactitude, at what distance north of the line of minimum intensity, the magnetic 
declination changes those periods of extreme easterly and extreme westerly variation, 
by which it is characterized in the southern magnetic hemisphere. 
In January 1846 I started from Singapore, and after visiting some islands in the vici- 
