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On Atmospheric Magnetism. By Professor Faraday.* 



On a former occasion it was shewn that oxygen gas was 

 magnetic, being attracted towards the poles of a magnet ; 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 properties it carries into the atmosphere ; and the 

 object of this lecture was to shew how far they might be ap- 

 plied to explain certain 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 

 concentrated condition of the polarity, then the contrary 

 polarities, manifest externally in relation to the magnet, are 

 perfectly definite, being exactly equal to each other. If the 

 magnet be irregular in the disposition of its force, still the 

 same definite character of the sum of the contrary polarities 

 holds good. 



External to the magnet those concentrations which are 

 named poles may be considered as connected by what are 

 called magnetic curves, or lines of magnetic force, existing 

 in the space around. These phrases have a high meaning, 

 and represent the ideality of magnetism. They imply 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 analogous to (though 

 very different in nature from) a ray of light or heat, which, 

 though it be present in a given space, and even occupies 

 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 



* Abstract of a Lecture read to the Royal Institution of Great Britain, on 

 the 14th April 1851. 



