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IX. Contributions to Terrestrial Magnetism. — No. IV. 
By Lieut. -Colonel Edward Sabine, R.A., F.R.S. 
Received May 5, — Read May 18, 1843. 
§ 7- Second Series of Magnetic Determinations, by Captain Sir Edward Belcher, R.N. 
In the present number of these Contributions, I resume the consideration of Captain 
Sir Edward Belcher’s magnetic observations, of which the first portion, viz. that of 
the stations on the north-west coast of America and adjacent islands, was discussed 
in No. II. The return to England of Her Majesty’s ship Sulphur by the route of the 
Pacific Ocean, and her detention for some months in the China Seas, have enabled 
Sir Edward Belcher to add magnetic determinations at thirty-two stations to those 
at the twenty-nine stations previously recorded. 
In the notice of the earlier observations, a provisional coefficient was employed in 
the formula for the temperature corrections of the results with the intensity needles, 
as no experiments had then been made for the determination of their individual co- 
efficients. As soon therefore as Sir Edward Belcher had completed the observation 
of the times of vibration of those needles at Woolwich, as the concluding station of 
the series made with them, Lieut. Riddell, R.A. undertook the determination of 
their several coefficients, which was performed in the manner and with the results 
described in the subjoined memorandum. 
“The observations were made in the instrument room attached to Lieut. -Colonel 
Sabine’s office in the Royal Military Repository, Woolwich. 
“ The instruments rested on wooden stands detached from the floor. 
“ The deflections were observed with one of Weber’s transportable magnetometers ; 
the variations of declination and horizontal force with the larger instruments. 
“The needles were placed upon open Y supports, in the centre of a wooden trough 
about nine inches in length, six broad and six deep, and were fixed so that their 
magnetic axes should be in the line passing through the centre of the suspended 
magnet perpendicular to the magnetic meridian. 
“The trough was filled alternately with warm and cold water, and the instruments 
were registered after a sufficient time had elapsed to allow the needles to take up the 
temperature of the water; care was taken not to raise the temperature of the water 
above 110° or 120°, to avoid the permanent loss of magnetism which might have been 
occasioned thereby. 
