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XLV. Report made to the Academy of Sciences, 22d of 
August 1825, on the Voyage of Discovery, performed in the 
Years 1822, 1823, 1824, and 1825, under the command of 
M. Durrrrey, Lieutenant of the Navy. 
(Commissioners: MM. pr Humpo tpt, Cuvirr, Desrontaines, 
CorpiEr, LatreiLue, DE Rossei; and Araco, Reporter.) 
[Continued from p. 210.] 
Magnetism. 
"THE phzenomena of terrestrial magnetism, in spite of more 
than a century of researches, are still enveloped in great 
obscurity. M. Duperrey was occupied upon them, during 
the whole of his voyage, with the most persevering attention, 
both when at sea and when in various ports. He journals 
contain a multitude of observations of declination, inclination, 
intensity, and diurnal variations of the declination, made ac- 
cording to the best methods. The Commission is of opinion 
that by here presenting a rapid sketch of the advancement 
which science may expect from this great work, it will fulfill 
the intentions of the Academy. _ 
There exists, as is well known, on the globe, a curve along 
which the magnetic needle maintains a horizontal position. This 
curve, which has received the name of the magnetic equator, 
has been lately the object of the investigations of MM. Hans- 
teen and Morlet. Although these two philosophers have 
used the same data, yet on some points they have arrived at 
results slightly different. In the chaft of the learned Norwe- 
gian, as well as in that of our countryman, the magnetic equa- 
tor is, entirely, to the south of the terrestrial equator, between 
Africa and America. The greatest distance of these two 
curves in latitude, corresponds to about 25° of west longitude: 
it is of 13° or 14°. 
In the first chart we find a node (nceud)in Africa, at 22° of east 
longitude ; the second places it 4° more to the west. According 
to Messrs. Hansteen and Morlet, if we proceed from this node 
advancing to the side of the Indian sea, the line of no dip swerves 
rapidly towards the north of the terrestrial equator, quits Africa 
a little to the south of Cape Guardafui, and comes in the 
Arabian sea to its absolute maximum of northern excursion 
(about 12°), at 62° east longitude. Between this meridian and 
the 174th degree of longitude, the line of no dip constantly 
keeps in the northern hemisphere. It cuts the Indian penin- 
sula a little to the north of Cape Comorin; crosses the Gulf 
of Bengal slightly approaching the terrestrial equator from 
which it is only 8° apart at the entrance of the Gulfof Siam; then 
remounts 
