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324 THE ATMOSPHERE AND METEOROLOGY.
CHAPTER XXI.
TERRESTRIAL MAGNETISM.—DECLINATION, INCLINATION, AND INTENSITY OF
THE MOVEMENTS OF THE NEEDLE. MAGNETIC POLES AND EQUATOR.
ISOGONAL LINES, AND THEIR SECULAR ANNUAL AND DIURNAL VARIATIONS.
ISOCLINAL LINES. ISODTNAMIC LINES.
The incessant mobility so characteristic of all the phenomena of climate is most especially manifested in the perpetual oscillations of the
electric currents. Magnetism—this force as mysterious as the nervous
fluid of organized bodies, in its invisible undulations vibrating from the
poles to the equator—transforms this planet into a gigantic loadstone.
The heat of the sun, which gives life to our globe, causes a continual
tremor in the crust of the earth; currents of electricity (whose incessant
movement from east to west in an opposite direction to the rotation of
the globe, was discovered by Ampere) vibrate round the terrestrial surface like an immense coil, and maintain between the two poles a magnetic activity exactly similar to that which is produced in an induction
coil.* All bodies are more or less influenced by these currents, and
would arrange themselves in certain regular directions did not the bulk,
weight, and cohesion of their particles hinder them from obeying the
force acting upon them. The magnetic power of the earth is estimated
by Gauss at 8464 trillion times that of our strongest artificial magnets,
and yet this immense power has only been known for a comparatively
short time. It was only in the year 1700 that Halley drew the first magnetic chart, and it is scarcely seven hundred years since the sailors of
Amalfi, Provence, and Liguria learned from the Arabs, or discovered for
themselves, the movements of the magnetic needle, and this was the earliest recognition of this magnetic current pervading every atom of the
planet. The Chinese navigators had known the remarkable properties of
the compass for more than two thousand years before this.
In the earliest times it was believed that the needle pointed constantly
toward the polar star, or rather toward the pole of our planet; but the
mariners who ventured as far as the Canaries and Iceland, or even those
who confined their voyages to the Mediterranean^ ascertained that the
point of the compass did not invariably indicate the north, and that it
diverged according to the latitudes, by a greater or fewer number of
degrees, to the right or left of the normal direction. In 1268, Pierre
Pelerin de Maricourt observed that it pointed seven.and a half degrees
toward the east at Lucera, in Southern Italy.f Columbus, on the voy-
* Barlow, Ampere, Becquerel, Sabine. See, also, les Phenomenes de la Physique, by Ame-
de'e Guillemin, pp. 702, 703.
t Detvezac, Bulletin de la Societe de Ge'ographie, 1859.
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000355 |
| Type | Books/Pamphlets |
| Transcript | 324 THE ATMOSPHERE AND METEOROLOGY. CHAPTER XXI. TERRESTRIAL MAGNETISM.—DECLINATION, INCLINATION, AND INTENSITY OF THE MOVEMENTS OF THE NEEDLE. MAGNETIC POLES AND EQUATOR. ISOGONAL LINES, AND THEIR SECULAR ANNUAL AND DIURNAL VARIATIONS. ISOCLINAL LINES. ISODTNAMIC LINES. The incessant mobility so characteristic of all the phenomena of climate is most especially manifested in the perpetual oscillations of the electric currents. Magnetism—this force as mysterious as the nervous fluid of organized bodies, in its invisible undulations vibrating from the poles to the equator—transforms this planet into a gigantic loadstone. The heat of the sun, which gives life to our globe, causes a continual tremor in the crust of the earth; currents of electricity (whose incessant movement from east to west in an opposite direction to the rotation of the globe, was discovered by Ampere) vibrate round the terrestrial surface like an immense coil, and maintain between the two poles a magnetic activity exactly similar to that which is produced in an induction coil.* All bodies are more or less influenced by these currents, and would arrange themselves in certain regular directions did not the bulk, weight, and cohesion of their particles hinder them from obeying the force acting upon them. The magnetic power of the earth is estimated by Gauss at 8464 trillion times that of our strongest artificial magnets, and yet this immense power has only been known for a comparatively short time. It was only in the year 1700 that Halley drew the first magnetic chart, and it is scarcely seven hundred years since the sailors of Amalfi, Provence, and Liguria learned from the Arabs, or discovered for themselves, the movements of the magnetic needle, and this was the earliest recognition of this magnetic current pervading every atom of the planet. The Chinese navigators had known the remarkable properties of the compass for more than two thousand years before this. In the earliest times it was believed that the needle pointed constantly toward the polar star, or rather toward the pole of our planet; but the mariners who ventured as far as the Canaries and Iceland, or even those who confined their voyages to the Mediterranean^ ascertained that the point of the compass did not invariably indicate the north, and that it diverged according to the latitudes, by a greater or fewer number of degrees, to the right or left of the normal direction. In 1268, Pierre Pelerin de Maricourt observed that it pointed seven.and a half degrees toward the east at Lucera, in Southern Italy.f Columbus, on the voy- * Barlow, Ampere, Becquerel, Sabine. See, also, les Phenomenes de la Physique, by Ame- de'e Guillemin, pp. 702, 703. t Detvezac, Bulletin de la Societe de Ge'ographie, 1859. |
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