Magneto-E lectricity, and Electro-magnetical Machines. 125 
Arr. X.—Prof. Locxe on Magneto-Electricity, and Electro- 
magnetical Machines. 
Med. Coll. of Ohio, Jan. 28th, 1838. 
TO PROF. SILLIMAN. 
Dear Sir—I mentionep to you in my last letter, some experi- 
ments which I was about to make in Magneto-Electricity ; I have 
now finished one series of them, part of which T propose to com- 
municate to the public through your Journal. As it is possible, 
that some of your readers may not be sufficiently acquainted with 
the principles of magneto-electricity, to understand fully the ap- 
paratus and experiments which Iam about to describe, I will take 
the liberty to prefix a concise statement of a ote of the most im- 
portant elementary principles. 
1. Whenever a permanent steel magnet or loadstone attracts a 
piece of soft iron, it converts that iron into a magnet, so long only 
as it attracts it, with poles opposite in their character to those by 
which they are attracted. ‘This takes place when the horse-shoe 
magnet attracts its “ keeper.” 
. If the soft iron, thus made magnetical by the attraction of a 
permanent magnet, be forced off and reversed in position, its po- 
larity or magnetism will be reversed. 
3. If the “keeper,” or soft iron attached to the magnet be wrap- 
ped by an insulated coil or “helix” of copper wire, as a spool is 
wrapped by its thread, and be applied to, or detached from, the 
permanent magnet, or be reversed in position so as suddenly 
to acquire, lose, or change polarity ; electricity, at the moment 
of change, will pass through the coil with its usual c 
istics. 
~ 4. If the end of a bar magnet be thrust within a coil, or with- 
drawn from it, an electrical current will be momentarily excited. 
(Farad. 
5. ana the feeble polarity excited by terrestrial magnetism 
on placing a bar of soft iron perpendicularly, and suddenly rever- 
gon nator by a sensible evolution of electricity in a coil 
surrounding that bar. The experiment succeeds still better, by 
making it in the line of the “ dip,” viz. with the upper end inclined 
about 20° to the south. 
