[ 493 ] 
XX. An Account of the Magnetical Experiments made on the western coast of 
Africa , 1830-1, hy Commander Edward Belcher, of H. M. S. JEtna. 
Communicated by the Rev. George Fisher, through Captain Beaufort, R.N. 
F.R.S. 
Read June 21, 1832. 
I HAVE the honour of communicating the results of some experiments made 
on the western coast of Africa, by Commander Edward Belcher, of His 
Majesty’s ship /Etna, for the purpose of determining the relative horizontal 
intensities of the magnetic force, on the different parts of the coasts he has 
been lately surveying. 
The experiments were made with four needles, constructed for the purpose, 
on nearly the same plan as that adopted by Professor Hansteen, and made 
by Mr. Dollond. They were nearly cylindrical, and furnished with a move- 
able collar or suspension stirrup, for the purpose of adjusting them horizon¬ 
tally, and were respectively four, three and a half, three, and two and a half 
inches in length. 
Captain Belcher has kindly sent me his observations with these needles, 
which he has most accurately made, together with similar ones made in En¬ 
gland since his return; and the near agreement between these and others 
made by myself before their embarkation, affords a satisfactory proof that the 
magnetism of the needles has not undergone any material change during the 
period of the voyage; a proof most essential in obtaining a correct result in 
experiments of this nature, and the want of which has rendered many others 
made of late years in different parts of the world, little better than useless. 
The sudden changes in the intensities of magnetic needles, particularly those 
kept on ship-board, arising from a variety of causes, are well known to those 
accustomed to use them. Hence arises the necessity in experiments, such as 
those described in this paper, of frequently repeating them at the same place 
3 s 
MDCCCXXXII. 
