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oxygen gas of the atmosphere, of which each particle is a small 
magnet having its north and south pole. Now substances 
which are magnetic lose this property at high temperatures, 
and the late Professor Barlow, of Woolwich, in his treatise on 
magnetism, states that white hot iron ceases altogether to be 
magnetic. So that, if the magnetic metals exist in large quan- 
tities in the interior of the earth, they will cease to be mag- 
netic, from the high temperature of the internal heat. — From 
these considerations, it is probable that the earth owes its claim 
to be a magnetic body to the oxygen of the atmosphere, and 
the coldest parts on the earth’s surface are the localities of the 
magnetic poles, the definition of the magnetic pole being the 
place where the dipping needle takes the vertical position ; the 
north magnetic pole, in round numbers, being in 70° North 
latitude, and 100° West longitude. 
According to Professor Barlow and Mr Charles Bonnycastle, 
the investigation of the magnetic meridians in various places 
shews that they only converge ultimately towards some places 
within the arctic and antarctic circles. 
The moon having no visible atmosphere we have no like 
reasons to offer for her being a magnetic body, and the vol- 
canic appearance of her surface has all the appearance of 
the diamagnetic substances, and the interior still fluid, as shewn 
by the occasional voleanic eruptions which are noticed, will 
also from the great heat be diamagnetic. 
The relations of the earth and moon are therefore those 
of a smaller diamagnetic body in the presence of a larger 
magnetic body, and the phenomena of magneto-electricity will 
be effective between them, since the magnetic force acts freely 
through a vacuum as well as through dense bodies. 
About the year 1825, M. Arago made the discovery that if 
a circular disk of copper be set rotating rapidly parallel to and 
under a bar magnet which is suspended so as to be free to move 
parallel to the disc, then the magnet goes into rapid rotation 
