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Art. XI . — An account of the Experiments of Mr Barlow of the 
Royal Military Academy , and those of M . Arago, on the 
Magnetism induced or exhibited in Iron , and in other Metals, 
by Rotation , with some new Experiments on the same subject , 
by Mr James Marsh. Communicated by Professsor Barlow. 
Dear Sir, 
Mr Marsh having consulted me on the propriety of forward- 
ing to you the inclosed papers, containing a statement of mine 
and Mr Arago’s experiments, with some additional ones of his 
own, on the influence of rotation on the magnetic state of bodies, 
I am inclined to trouble you with the article ; and, as the re- 
sults are at least of a novel kind, I have no doubt you will find 
room for the papers in your next number. 
Dear Sir, yours truly, 
Royal Military Academy, Peter Barlow. 
May 11. 1825. 
Mr Barlow having requested me to ascertain, by means of 
one of the turning lathes in the Royal Arsenal, whether, by 
giving to an iron body a rapid rotation, any change could be 
distinguished in its magnetic state during the motion, or after it 
had subsided ; I did, accordingly, about the beginning of last 
December, attach a small howitzer shell to a lathe, admitting of 
a rapid motion, and having placed a small compass very near 
to it, I perceived, at once, that the needle was considerably de- 
flected, but it returned to its original direction as soon as the 
motion ceased. Having communicated to Mr Barlow the result 
of the experiment, he came down himself, a few days after, and 
caused a thirteeen inch shell to be fixed to the mandrel of one 
of the large lathes worked by the steam-engine, and the effect 
obtained was, of course, proportionally greater. In fact, with 
this shell the direction of the needle was, in many cases, reversed 
by the motion of the former ; but there were other points in 
which no motion could be observed. Moreover, in some places 
the deviation of the needle was made in a contrary way to what 
it was in others, and varying in quantity, as stated above, from 
