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III. Experimental Researches in Electricity. — Twenty-eighth Series. By Michaei. 
Faraday, Esq., D.C.L., F.R.S., Fullerian Prof. Chem. Royal Institution, Foreign 
Associate of the Acad. Sciences, Paris, Ord. Boruss. Pour le Mdrite, Eq., Memh. 
Royal and Imp. Acadd. of Sciences, Petershurgh, Florence, Copenhagen, Berlin, 
Gottingen, Modena, Stockholm, Munich, Bruxelles, Vienna, Bologna, S^c. &fc. 
Received October 22, — Read November 27 and December 11, 1851. 
\ 36. On Lines of Magnetic Force ; their definite character ; and their distribution 
within a Magnet and through Space. 
3070. From my earliest experiments on the relation of electricity and magnetism 
(114. note), I have had to think and speak of lines of magnetic force as representa- 
tions of the magnetic power ; not merely in the points of quality and direction, but also 
in quantity. The necessity I was under of a more frequent use of the term in some 
recent researches (2149. &c.), has led me to believe that the time has arrived, when the 
idea conveyed by the phrase should be stated very clearly, and should also be carefully 
examined, that it may be ascertained how far it may be truly applied in representing 
magnetic conditions and phenomena; how far it may be useful in their elucidation; 
and, also, how far it may assist in leading the mind correctly on to further concep- 
tions of the physical nature of the force, and the recognition of the possible effects, 
either new or old, which may be produced by it. 
3071. A line of magnetic force may be defined as that line which is described by a 
very small magnetic needle, when it is so moved in either direction correspondent 
to its length, that the needle is constantly a tangent to the line of motion ; or it is 
that line along which, if a transverse wire be moved in either direction, there is no 
tendency to the formation of any current in the wire, whilst if moved in any other 
direction there is such a tendency ; or it is that line which coincides with the direc- 
tion of the magnecrystallic axis of a crystal of bismuth, which is carried in either 
direction along it. The direction of these lines about and amongst magnets and 
electric currents, is easily represented and understood, in a general manner, by the 
ordinary use of iron filings. 
3072. These lines have not merely a determinate direction, recognizable as above 
( 3071 .), but, because they are related to a polar or antithetical power, have opposite 
qualities or conditions in opposite directions ; these qualities, which have to be 
distinguished and identified, are made manifest to us, either by the position of the ends 
of the magnetic needle, or by the direction of the current induced in the moving wire. 
MDCCCLTI. E 
