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APPENDIX. 
On the Production of Currents and Sparks of Electricity from 
Magnetism; by Prof. J. Henry. 
AttnoueHs the discoveries of Oersted, Arago, Faraday, and oth- 
ers, have placed the intimate connection of electricity and magnetism 
in a most striking point of view, and although the theory of Ampere 
has referred all the phenomena of both these departments of science 
to the same general laws, yet until lately one thing remained to be 
proved by experiment, in order more fully to establish their identity ; 
namely, the possibility of producing electrical effects from magnetism. 
It is well known that surprising magnetic results can readily be ob- 
tained from electricity, and at first sight it might be supposed that 
electrical effects could with equal facility be produced from magnet- 
ism; but such has not been found to be the case, for although the 
experiment has often been attempted, it has nearly as often failed. 
It early occurred to me, that if galvanic magnets, on my plan, were 
substituted for ordinary magnets, in researches of this kind, more suc- 
cess might be expected. Besides’ their great power, these magnets 
possess other properties, which render them important instruments in 
the hands of the experimenter ; their polarity can be instantaneously 
reversed, and their magnetism suddenly destroyed or called ito full 
action, according as the occasion may require. With this view, I 
commenced, last August, the construction of a much larger galvanic 
magnet than, to my knowledge, had before been attempted, and also 
made preparations for a series of experiments with it on a large scale, 
in reference to the production of electricity from magnetism. I was, 
however, at that time, accidentally interrupted in the prosecution of 
these experiments, and have not been able since to resume them, 
until within the last few weeks, and then on a much smaller scale 
than was at first intended. In the mean tine, it has been announced 
in the 117th number of the Library of Useful Knowledge, that the 
result so much sought after has at length been found by Mr. Fara- 
day of the Royal Institution. It states that he has established the 
general fact, that when a piece of metal is moved in any direction, 
in front of a magnetic pole, electrical currents are developed in the 
metal, which pass in a direction at right angles to its own motion, 
and also that the application of this principle affords a complete and 
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