**
[footnote] *William Gilbert, of Colchester, whom Galileo pronounced "great
to a degree that might be envied," said "magnus magnes ipse est globus
terrestris." He ridicules the magnetic mountains of Frascatori, the great
contemporary of Columbus, as being magnetic poles: "rejicienda est vulgaris
opinio de montibus magneticis, aut rupe aliqua magnetica, aut polo
phantastico a polo mundi distante." He assumes the declination of the
magnetic needle at any give point on the surface of the Earth to be
invariable (variatio uniuscujusque loci constans est), and refers the
curvatures of the isogonic lines to the configuration of continents and the
relative positions of sea basins, which possess a weaker magnetic force than
the solid masses rising above the ocean. (Gilbert, 'de Magnete', ed. 1633,
p. 42, 98, 152 and 155.)
[footnote] ** Gauss, 'Allgemcine Theorie des Erdmagnetismus', in the
'Resultate aux den Beob. des Magnet. Vereins', 1838, s. 41, p. 56.
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.
Pages:
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371