MAGNETIC IRON ORE. 



235 



CHAPTER X. 



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 Therm o-Magnetisrn Aurora Borealis 

 Magnetic Storms Magnetic conditions of Matter Dia- 

 Magnetism, &c. 



AGREEABLY with the view now generally received, that 

 magnetism and electricity are but modifications of one 

 force, since they are found to stand to each other in the 

 relation of cause and effect, the separation which is here 

 adopted, of the consideration of their several phenomena, 

 may appear inappropriate. The importance, however, 

 of all that is connected with magnetism, and the very 

 decided difference which is presented by true magnetic 

 action, and that of frictional or chemical electricity, i& 

 so great that it has been thought advantageous to adopt 

 the present arrangement in reviewing the influence of 

 terrestrial magnetism with which science has made us 

 acquainted. 



From a very early period a peculiar attractive force 

 has been observed in some specimens of iron ore. 

 Masses of this kind were found in Magnesia, and from 

 that locality we derive the name given to iron in its 



