ANNALS 



OF 



PHILOSOPHY. 



AUGUST, 1821. 



Article I. 



On the Magnetic Phenomena produced by Electricity. In a 

 Letter from Sir H. Davy, Bart. FRS. to W. H. Wollaston, 

 MD. PRS * 



MY DEAR SIR, 

 The similarity of the laws of electrical and magnetic attrac- 

 tion has often impressed philosophers ; and many years ago, in 

 the progress of the discoveries made with the voltaic pile, some 

 inquirers (particularly M. Ritter,f) attempted to establish the 

 existence of an identity or intimate relation between these two 

 powers ; but their views being generally obscure, or their expe- 

 riments inaccurate, they were neglected : the chemical and elec- 



* From the Philosophical Transactions, 1821. 



f M. Ritter asserted that a needle composed of silver and zinc arranged itself in die 

 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 NE 

 and SE. His ideas are so obscure that it is often difficult to understand them; but he 

 seems to have had some vague notion that electrical combinations, 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 Annates de Chi- 

 mie, torn. 64, p. 80.) Since this letter has been written, Dr. Marcet has been so good 

 as to send me from Genoa some pages of AJdini on Galvanism, and of Izarn's Manual 

 of Galvanism, published at Paris more than 16 years ago. Mr. 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 curva- 

 ture of it; but M. Romagnesi, 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 iu 

 the voltaic circuit as a part of the electrical combination. 



New Series, vol. it. g 



