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Art. IX. — Account qf the Recent Magnetlcal Discoveries qf 
Frqfessor Ha^qsteen. Being the substance of a Letter 
from Professor Hansteen to M. IIumker, Director of the 
Nautical Academy of Hamburgh. 
In two of the preceding Numbers of this Journal, (Vol. III. 
p. 124., and Vol. IV. p. 114.) we have laid before our readers 
an account of the very interesting inquiries of Professor Han- 
steen respecting the Magnetism of the Earth, as contained in 
his elaborate work, entitled, Untersuclmngen iiher den Magne^ 
tismus der Erde, and published at Christiania in 1819. 
Through the kindness of our learned correspondent M. Rum- 
ker, we have the pleasure of publishing an account of the recent 
magnetical discoveries of the same eminent natural philosopher, 
drawn up and transmitted by himself, and which have not yet 
appeared in any other work. 
The observations on the diurnal variation of the needle given 
in our last Number, (Vol. IV. p. 199.)j and transmitted to us by 
M. Rumker, -were the result of a series of experiments which M. 
Hansteen made with an oscillating apparatus, the description 
and use of which forms the subject of his letter to M. Rumker. 
D. B. 
The instrument which I use, is a small^well hardened mag- 
netic cylinder of steel a 6, about 2| inches long and /^th thick, 
suspended by a thread cd, (drawn from the cod of the silk- worm), 
in a square box, as shewn in Plate VI. Fig. 3. The cover MN 
of the box consists of three parts, of which the two outermost 
ones M, N, have glass windows, which may be drawn out. A 
hollow tube T, is screwed to the middle part P, in which the 
cylinder is suspended. The box rests on three screws, S, S, S, by 
which it is set horizontally. At the bottom of the box a divided arc 
q/*is fixed, to read off the vibrations of the cylinder a b. This 
cylinder is drawn out of its magnetic meridian, by applying to the 
end of the box a little iron rod, which being held vertically, has 
in its lower part a north pole. On removing it, the cylinder 
