Mr. W. Sturgeon on the Theory of Magnetic Electricity. 369 



cerned, the vigorous retention of magnetic polarity exhibited 

 by some of them, and the almost total absence of this quality 

 in others, may very easily be explained upon the principles 

 already advanced ; and perhaps it would only require that we 

 should consider copper and other non-ferruginous metals to 

 be still better magnetic conductors than soft iron, to reconcile 

 the sudden and total disappearance of polarity in them to the 

 same principles, whether the exciting agent be magnetic or 

 electric. 



I have deflected a magnetic needle by an electric current 

 traversing an ignited charcoal conductor, as was first shown 

 by the very interesting experiments of JVlr. Kemp ; but as we 

 are not aware of the total absence of the magnetic matter in 

 charcoal, the experiment is inconclusive, any further than as 

 an interesting fact, which has no particular bearing on the 

 present discussion. 



The energies of ferruginous electro- magnets are invariably 

 exalted by multiplying, to a certain extent, the number of coils 

 of conducting wire. My large electro-magnet, described in 

 a former communication, requires twelve coils to accomplish 

 its maximum of power (400 pounds). The general explana- 

 tion of this fact is, I believe, that one wire alone is incapable 

 of transmitting or conducting the whole of the electric force; 

 and therefore a multiplicity of conducting wires becomes ne- 

 cessary in order that the battery may be enabled to give a full 

 and complete display of its electric energies. And in order to 

 accomplish this object the more completely, the extremities 

 of all the wires are brought as close as possible to the voltaic 

 plates. The wires of the large American magnet are even 

 soldered to the plates of the battery. 



I find, however, that although an addition of coils is attend- 

 ed with an accession of magnetic power until a maximum of 

 polarity is accomplished, it is by no means essential that all 

 those wires arrive immediately at the battery. A single cop- 

 per wire may intervene between the coils round the iron and 

 the poles of the battery without deteriorating the energies of 

 the magnet, which will still be displayed to a maximum, as 

 decidedly as if the whole system of wires were soldered directly 

 to the plates. 



My large electro-magnet is still capable of supporting its 

 400 pounds, notwithstanding the electric force has to traverse 

 six inches of bell-wire before it arrives at the coils ; and also 

 six inches more from its quitting the coils till its arrival at the 

 other pole of the battery; — in all, twelve inches of single bell- 

 wire. There is a limit, however, to the dimensions of the in- 

 tervening wires. If they be too long or too thin, the magnet 



Third Series. Vol. 2. No. 1 1 . May 1833. 3 B 



