MAGNETO-ELECTRIC INDUCTION IN DIFFERENT SUBSTANCES. 177 
thousands of miles across the magnetic curves, cutting them in various direc- 
tions within its mass, as well as at the surface, it is possible the electricity 
may rise to considerable intensity. 
192. I hardly dare venture, even in the most hypothetical form, to ask whe- 
ther the Aurora Borealis and Australis may not be the discharge of electricity, 
thus urged towards the poles of the earth, from whence it is endeavouring to 
return by natural and appointed means above the earth to the equatorial 
regions. The non-occurrence of it in very high latitudes is not at all against 
the supposition ; and it is remarkable that Mr. Fox, who observed the deflec- 
tions of the magnetic needle at Falmouth, by the Aurora Borealis, gives that 
direction of it which perfectly agrees with the present view. He states that 
all the variations at night were towards the east *, and this is what would 
happen if electric currents were setting from south to north in the earth under 
the needle, or from north to south in space above it. 
§ 6. General remarks and illustrations of the Force and Direction of Magneto- 
electric Induction. 
193. In the repetition and variation of Arago’s experiment by Messrs. Bab- 
bage, Herschel, and Harris, those philosophers directed their attention to 
the differences of foi;ce observed amongst the metals and other substances in 
their action on the magnet. These differences were very great -J~, and led me 
to hope that by mechanical combinations of various metals important results 
might be obtained (183). The following experiments were therefore made, 
with a view to obtain, if possible, any such difference of the action of two 
metals. 
194. A piece of soft iron bonnet-wire covered with cotton was laid bare and 
cleaned at one extremity, and there fastened by metallic contact with the clean 
end of a copper wire. Both wires were then twisted together like the strands 
of a rope, for eighteen or twenty inches; and the remaining parts being made 
to diverge, their extremities were connected with the wires of the galvano- 
meter. The iron wire was about two feet long, the continuation to the galva- 
nometer being copper. 
* Philosophical Transactions, 1831, p. 202. t Ibid. 1825 ; p. 472, 1831, p. 78. 
2 a 
MDCCCXXXII. 
