36 Mv. M. Donovan on the supposed Identity of the Agent 



It is no doubt true that frictional electricity has the power of 

 communicating, reversing and destroying magnetic polarity; 

 but it never docs so while traversing a conductor in the silent 

 quiescent way which \oltaic electricity is known to do. To pro- 

 duce magnetic polarity, it nmst be in the state of high ten- 

 sion, and the circumstances must be otherwise peculiar. In this 

 state it acts with much dynamic violence, and will communicate 

 magnetism, as haunnering, filing, and other mechanical causes 

 are known to do. Of the ])eculiar condition of electricity in the 

 state of flash, and how it diff"ers from a current traversing a con- 

 ductor, we know nothing farther than that there is a great dif- 

 ference. 



The boldest of all the hypotheses of magnetism and the most 

 ingeniously supported is that of Ampere. This philosopher de- 

 nies the existence of a magnetic fluid, or of a magnetic agent 

 called into action by electricity ; but affirms the absolute identity 

 of both powers, an opinion first advanced by Beccaria and sup- 

 ported by Azais. Notwithstanding the address, ingenuity, and 

 resources of invention with which M. Ampere has constructed 

 and applied his hypothesis, it does not seem to have made much 

 advance in public opinion in the British Isles. This doctrine 

 scarcely comes within the province of my essay, as it does not 

 indicate magnetism as a property common to frictional and vol- 

 taic electricitj^, but as identical with both. Mr. Sturgeon's ar- 

 guments* appear to me sufficient to invalidate the assumed iden- 

 tity, yet it may not be superfluous to describe two experiments 

 which I made on this subject ; especially as they both refer to 

 the question whether electricity is magnetism, or whether elec- 

 tricity produces magnetic eff"ects. Their results were of course 

 foreseen ; I made them merely to pemiit me to use them as ar- 

 guments. 



A cylindrical rod of soft iron twelve inches long was wound 

 round in the usual manner, from end to end, with copper wire 

 covered with sewing silk. This was supported in the middle ho- 

 rizontally by an upright glass pillow set in a wooden stand. The 

 ends of the copper wire were connected with a Smee's batteiy con- 

 sisting of four triads of silver and zinc plates, acted on by very 

 dilute sulphuric acid. To the smooth, flat ends of the cylindrical 

 rod were adapted two pendent flat iron armatures, each having a 

 pair of gilt pith-balls attached by means of gilt strings. In this 

 state of things, the cylindrical iron rod being converted into a tem- 

 porary magnet, its ends would hold the pendent ai'matures at- 

 tracted ; and the attractive force would, according to the hypo- 

 thesis of Ampere, be the diflference of electrical state between the 

 ends of the cylindrical rod and the armatures. Application of a 

 * Proceediugs and Transactions of the London Electijcal Society, 1838. 



