CHAPTER X.. Magnetism.

MAGNETISM.

Magnetic Iron--Knowledge of, by the Ancients--Artificial Magnets--Electro-Magnets--Electro-Magnetism--Magneto- Electricity--Theories of Magnetism--The Magnetic Power of soft Iron and Steel--Influence of Heat on Magnetism--Terrestrial Magnetism--Declination of the Compass-needle--Variation of the Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora Borealis--Magnetic Storms--Magnetic conditions of Matter--Diamagnetism, &c. 235