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muth, phosphorus, &c. from the poles of magnets is a very 
weak force compared with the attraction of the more magnetic 
metals. We recognize also that magnetic bodies have the 
property of polarity, which does not exist in diamagnetic 
bodies. 
The discovery of Dr Faraday that oxygen gas is magnetic 
was a most important step, and we may now conclude that the 
earth’s magnetism resides very greatly, if not entirely, in the 
oxygen gas of the atmosphere, for the greater part of the 
earthy materials of the earth’s crust are diamagnetic substances, 
and the abundant mineral per-oxide of iron is still small in 
quantity compared with the others, and only feebly magnetic. 
Tt is not easy to find the place of oxygen gas amongst the 
magnetic substances from the small weight contained in such 
glass globes as we can use in experiments, but the black or 
protoxide of iron is very magnetic. In the original experiment 
exhibited by Dr Faraday, when he made known his discovery at 
the meeting of the Royal Institution, at which I was present, 
the weight of the oxygen gas in the globe of perhaps 2 inches 
diameter would be less than 14 grains, and the flint-glass of 
the globe was feebly diamagnetic yet though surrounded by 
atmospheric air of which about 4" of the volume is oxygen 
gas; and notwithstanding the resistance to motion which such 
a globe would experience, and its inertia, yet it was evidently 
steadily though slowly attracted to the poles of the magnet. 
Since that time, I, every session of my lectures, exhibited the 
same result without a single case of failure, to my experimental 
class of Natural Philosophy in University College, London. 
If we consider that the weight of the oxygen gas of the 
atmosphere is more than 4" of the weight of the barometric 
column or more than the weight of 6 inches depth of mercury 
covering the whole surface of the earth or considerably more 
than that of 10 inches depth of iron, we may conclude that 
the earth’s magnetism lies very greatly if not entirely in the 
