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II. On the magnetic phenomena produced by Electricity ; in a letter 
from Sir H. Davy, Bart. F. R. S. to W. H. Wollaston, 
M.D. P.R.S. 
Read November 16, 1820. 
My dear Sir, 
The similarity of the laws of electrical and magnetic at- 
traction has often impressed philosophers ; and many years 
ago, in the progress of the discoveries made with the voltaic 
pile, some enquirers (particularly M. Ritter,*) attempted to 
establish the existence of an identity or intimate relation be- 
tween these two powers ; but their views being generally 
* M. Ritter asserted that a needle composed of silver and zinc arranged itself in 
the magnetic meridian, and was slightly attracted and repelled by the poles of a 
magnet ; and that a metallic wire, after being exposed in the voltaic circuit, took a 
direction N. E. and S. E. His ideas are so obscure, that it is often difficult to un- 
derstand them ; but he seems to have had some vague notion that electrical combina- 
tions, when not exhibiting their electrical tension, were in a magnetic state, and that 
there was a kind of electro-magnetic meridian depending upon the electricity of the 
earth. See Annales de Chimiel T. 64, p. 80. Since this letter has been written. Dr. 
Mar cet has been so good as to send me from Genoa, some pages of Aldini onGal- 
vanism, and of Izarn’s Manual of Galvanism, published at Paris more than sixteen 
years ago. M. Mojon, senior, of Genoa, is quoted in these pages as having rendered 
a steel needle magnetic, by placing it in a voltaic circuit for a great length of time. 
This, however, seems to have been dependent merely upon its place in the magnetic 
meridian, or upon an accidental curvature of it; but M. Rom agnesi, of Trente, is 
stated to have discovered that the pile of Volta caused a declination of the needle; the 
details are not given, but if the general statement be correct, the author could not 
have observed the same fact as M. Oersted, but merely supposed that the needle 
had its magnetic poles altered after being placed in the voltaic circuit as a part of the 
electrical combination. 
