Mr. W. Sturgeon on the Theory of Magnetic Electricity. 367 



rent and the magnet employed ; but the illustrations which 

 have been advanced by that gentleman might possibly re- 

 quire considerable modification to establish a theory on those 

 principles. 



I have heard brought forward, as an argument against the 

 hypothesis of magnetic polarity of the conducting wire, an 

 experiment of Sir H. Davy's, which showed the deflection of 

 an electric current passing through air between the charcoal 

 points of a voltaic battery, by the presentation of a magnetic 

 pole. Such arguments can have but very little force in dis- 

 cussions of this character; for the experiment develops nothing 

 different to the generality of electro-magnetic phaenomena. 

 If an electric current be capable of rousing into activity the 

 dormant magnetic powers of ferruginous matter, no doubt 

 can possibly be entertained of its susceptibility of being put 

 into motion by the energies of an already formidable polarized 

 bar. 



This is the extent of reasoning to which the experiment 

 can be applied even under the supposition of the electric 

 current being the immediate agent in the process of magneti- 

 zing iron or steel, and that no intervening polarization of the 

 conducting wire is concerned in the operation; which, in fact, 

 is no argument whatever, further than might be advanced from 

 any other electro-magnetic experiment. 



On the other hand, it might be inferred with a great deal 

 of propriety, that if the electric current is capable of calling 

 forth the latent magnetism of hard steel, in which it is pent 

 up and retained with a degree of vigour which requires the 

 greatest efforts of the exciting agent to extricate it and accom- 

 plish its polarity even to a comparatively small extent ; — it is 

 but reasonable to expect that in those metals which do not 

 possess so exalted a degree of retention as hard steel, the same 

 exciting agent would accomplish a polarity to a much greater 

 extent. 



This simple induction is beautifully illustrated and substan- 

 tiated by demonstrable facts, by comparative experiments on 

 soft iron and hard steel; and it was by the same mode of 

 reasoning that I was first led to construct electro-magnets of 

 soft iron * ; since which time the practice has been pursued 

 with more than anticipated success. 



The facility of polarizing the magnetic matter, or of ar- 

 ranging it into active polar lines by any constant exciting 

 force, appears to be inversely proportional to the retentive 

 quality of the metal on which the process is performed. 



* See Transactions of the Societv of Arts,&c. vol. xliii. ; Phil. Mag. and 

 Annals, N.S., vol. xi. p. 194. 



