Magnetism of the Earth. 149 
It may be remarked of the Siberian curve, that the space which it 
encloses is considerably less than its parallel in America; a circum- 
stance consistent with the supposition already noticed, that the maxi- 
mum intensity in Siberia is inferior in attractive force to the maximum 
in Hudson’s Bay: consequently curves of equal intensity are encoun- 
tered at a less distance from the point of maximum in Siberia than in 
_America. 
The second curve on the American side connects those places 
where the needle, introduced for illustration, would perform its one 
hundred vibrations in two hundred and seventy eight seconds. ‘The 
points which have determined it are, Melville Island in the north West ; 
several stations on the west side of Greenland, from lat. 76° to lat. 
66°, im the north east; and finally a greater intensity observed at 
New York and a lesser at the Havanna ; whence it is concluded that 
this curve intersects the sea board of the United States at an inter- 
mediate point between those cities. A corresponding intensity has 
been traced by Dr. Erman of Berlin, (who accompanied M. Han- 
steen to Siberia,) from the mouth of the River Oby, in lat. 68° and 
long. 70° E. preserving nearly the direction of a meridian, to lat. 60°, 
whence it bends gradually to the eastward, passes between Tobolsk 
and Naryon, and has been observed at Kainsk by M. Hansteen, on 
its way to its probable southern limit on the Asiatic side, a few d 
grees south of Lake Baikal. 
No. 3 is that in which the needle would perform one hundred vi-- 
brations in two hundred and eighty seven seconds. Its points of ob- 
servation have been, north of the Havanna, east of the Pendulum Isl- 
ands on the eastern side of Greenland in lat. 74° 5’, between the 
North Cape and Spitzbergen, by myself in 1823, and by M: Keilhaw 
in 1827. By M. Hansteen’s observations it enters the continent of 
Europe between Archangel and Nova Zembla, and was crossed by 
him, on the route from Moscow to Tobolsk, in 56° and 57° east lon- 
itude, and 57° and 58° latitude. 
aie curve marked No. 4 is that in which the needle would frake 
one hundred vibrations in two hundred and ninety eres seconds. 
Its tracing by observation commences on the American side, with the 
islands of Caymen and Jamaica. Crossing the Atlantic, it passes 
through the northern parts of the British islands, and oa Norway 
south of Bergen. It there became subject to M. Hansteen’s observ~ 
ation, who has ascertained its northern limit, and where it begins — 
bend to the southward, to be on the shores of the gulf of Bothnia, 
