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On Atmospheric Magnetism, 69 





Art. X. — On Atmospheric Magnetism; by Prof. Faraday.* 



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On a former evening (January 24,) it was shown that oxygen 



gas was magnetic, being attracted towards the poles of a mag- 

 net; and that like other magnetic bodies, it lost and gained in 

 power as its temperature was raised and lowered, and that the 

 change occurred within the range of natural temperatures. These 

 J properties it carries into the atmosphere ; and the object, this 



evening, was to show how far they might be apphed to explain 



certani of the observed variations of the terrestrial magnetic 

 force. 



If a source of magnetic power be considered (as a magnet}, it 

 presents us with a system having polarity; and if the parts 

 which are called the poles be taken as representing the most con- 

 centrated condition of the polarity, then the contrary polarities, 

 ttianifest externally in relation to the magnet, are perfectly defi- 

 nite, being exactly equal to each other. If the magnet be irreg- 

 ular in the disposition of its force, still the same definite charac- 

 ter of the sum of the contrary polarities holds good. 



iiixternal to the magnet those concentrations which are named 

 poles may be considered as connected by what are called magnetic 

 ^irves, or lines of magnetic force, existing in the space around. 

 I hese phrases have a high meaning, and represent the ideality 

 of magnetism. They ini'ply not merely the directions of force, 

 which are made manifest when a little magnet, or a crystal, or 

 other subject of magnetic action is placed amongst them, but 

 those lines of power which connect and sustain the polarities, 

 and exist as much when there is no magnetic needle or crystal 

 there as when there is ; having an independent existence analo- 

 gous to (though very different in nature from) a ray of light or 

 neat, which, though it be present in a given space, and even oc- 

 cupies time in its transmission, is absolutely insensible to us by 

 any means whilst it remains a ray, and is only made known 

 through its effects when it ceases to exist. The form of a line 



tnagnetic force may vary exceedingly from a straight line to 

 every degree of curvature, and may even have double and com- 

 pncated curvatures impressed upon it. Its direction is deter- , 

 nnned by its polarity, the two changing together. Its powers 

 are such, that a magnetic needle placed in it finds its place of 

 fest parallel to it ; a crystal of calcareous spar turns until its 

 ^Ptic axis is transverse to it ; and a wire which is unaffected 

 hen moved in or along it, has an electric current evolved the 

 hstant that it j^asses across it : by these and by other means the 



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Proc. Roy. Soc, April 11, p. 56, 



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