Page:On the Magnet - Gilbert (1900 translation of 1600 work).djvu/21

Book 4.
Chap. 1.	On Variation.
Chap. 2.	That the variation is caused by the inæquality of the projecting parts of the earth.
Chap. 3.	The variation in any one place is constant.
Chap. 4.	The arc of variation is not changed equally in proportion to the distance of places.
Chap. 5.	An island in Ocean does not change the variation, as neither do mines of loadstone.
Chap. 6.	The variation and direction arise from the disponent power of the earth, and from the natural magnetick tendency to rotation, not from attraction, or from coition, or from other occult cause.
Chap. 7.	Why the variation from that lateral cause is not greater than has hitherto been observed, having been rarely seen to reach two points of the mariners' compass, except near the pole.
Chap. 8.	On the construction of the common mariners' compass, and on the diversity of the compasses of different nations.
Chap. 9.	Whether the terrestrial longitude can be found from the variation.
Chap. 10.	Why in various places near the pole the variations are much more ample than in a lower latitude.
Chap. 11.	Cardan's error when he seeks the distance of the centre of the earth from the centre of the cosmos by the motion of the stone of Hercules; in his book 5, On Proportions.
Chap. 12.	On the finding of the amount of variation: how great is the arc of the Horizon from its arctick to its antarctick intersection of the meridian, to the point respective of the magnetick needle.
Chap. 13.	The observations of variation by seamen vary, for the most part, and are uncertain: partly from error and inexperience, and the imperfections of the instruments: and partly from the sea being seldom so calm that the shadows or lights can remain quite steady on the instruments.
Chap. 14.	On the variation under the æquinoctial line, and near it.
Chap. 15.	The variation of the magnetick needle in the great Æthiopick and American sea, beyond the æquator.
Chap. 16.	On the variation in Nova Zembla.
Chap. 17.	Variation in the Pacifick Ocean.
Chap. 18.	On the variation in the Mediterranean Sea.
Chap. 19.	The variation in the interior of large Continents.
Chap. 20.	Variation in the Eastern Ocean.
Chap. 21.	How the deviation of the versorium is augmented and diminished by reason of the distance of places.
Book 5.
Chap. 1.	On Declination.
Chap. 2.	Diagram of declinations of the magnetick needle, when excited, in the various positions of the sphere, and horizons of the earth, in which there is no variation of the declination.
Chap. 3.	An indicatory instrument, showing by the virtue of a stone the degrees of declination from the horizon of each several latitude.

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