In 1811, Hansteen took up the subject, and in 1819 published his celebrated work, clearly demonstrating the fluctuations which this element has undergone during the last two centuries; confirming in great detail the position of Halley, that “the whole magnetic system is in motion, that the moving force is very great as extending its effects from pole to pole, and that its motion is not _per saltum_, but a gradual and regular motion.”
The knowledge of the geographical position of both Magnetic Poles is due to the scientific energy of the same navigator, Sir James Ross. His observations of the Northern Magnetic Pole were made during the second expedition of his uncle, Sir John Ross (1829-1833); and of the Southern during the Antarctic expedition under his own command (1839-1843). The Northern Magnetic Pole, in 70° 5′ lat., 96° 43′ W. long., is 5° of latitude farther from the ordinary pole of the earth than the Southern Magnetic Pole, 75° 35′ lat., 154° 10′ E. long.; whilst it is also situated farther west from Greenwich than the Northern Magnetic Pole. The latter belongs to the great island of Boothia Felix, which is situated very near the American continent, and is a portion of the district which Captain Parry had previously named North Somerset. It is not far distant from the western coast of Boothia Felix, near the promontory of Adelaide, which extends into King William’s Sound and Victoria Strait.
The Southern Magnetic Pole has been directly reached in the same manner as the Northern Pole. On 17th February 1841, the _Erebus_ penetrated as far as 76° 12′ S. lat., and 164° E. long. As the inclination was here only 88° 40′, it was assumed that the Southern Magnetic Pole was about 160 nautical miles distant. Many accurate observations of declination, determining the intersection of the magnetic meridian, render it very probable that the South Magnetic Pole is situated in the interior of the great Antarctic region of South Victoria Land, west of the Prince Albert mountains, which approach the South Pole and are connected with the active volcano of Erebus, which is 12,400 feet in height.--_Humboldt’s Cosmos_, vol. v.
The mysterious course of the magnetic needle is equally affected by time and space, by the sun’s course, and by changes of place on the earth’s surface. Between the tropics the hour of the day may be known by the direction of the needle as well as by the oscillations of the barometer. It is affected instantly, but transiently, by the northern light.