1821.] Prof . Oersted on Electro-magnetism. 323 



I deferred a minute examination of it to a period at which I 

 hoped for more leisure.* 



At the beginning of the month of July, my experiments were 

 repeated and continued without interruption until I obtained the 

 results which have been published. 



(B.) Explanation of the first Lata of Elect -fo-magnetit Effects. 



The electro-magnetic effect which I discovered by the aid of 

 the galvanic apparatus, has since been produced by common 

 electricity, so that the expression of electro-magnetic effect is 

 perfectly justified by experiment. It is well-known that for the 

 first experiments on this subject we are indebted to M. Arago, 

 who has been equally successful in enriching both physics and 

 astronomy with his discoveries ; the illustrious President of the 

 Royal Society of London has also made an important series of 

 experiments on this subject. 



I shall here state, rather more in detail than I have done in my 

 first publication, the rule by which I think all electro-magnetic 

 effects are governed. It is this : When opposite electrical poiversf 

 meet under circumstances which offer resistance, thei/ are subjected 

 to a new form of action, and in this stale they act upon the magnetic 

 needle in such a manner that positive electricity repels the south, 

 and attracts the north pole of the compass ; and negative electriciti/ 

 repels the north, and attracts the south pole ;J bid the direction 

 followed by the electrical poivers in this state is not a right line, 

 but a spiral one, turning from the left hand to the right. Many 

 philosophers, and some of them of great merit, have thought the 

 spiral motion of electrical powers to be improbable. I shall 

 endeavour in the sequel to show, that this supposition is less 

 arbitrary than it may appear to be at first ; but to prepare for 

 this, it is necessary first to explain the meaning of this supposi- 

 tion, and then to prove that all electro-magnetic phenomena 

 so completely harmonize with the rule given, that it' will suffice 

 even to anticipate those among them which were not known before 

 experiment. I have not discovered so perfect an agreement with 

 facts in any other theory which has been hitherto advanced. 

 When I have shown that the rule is quite sufficient to compre- 

 hend all the facts under one point of view ; that is to say, that 

 it is a correct rule, I shall invite the reader to examine with me, 



• All my auditors are witnesses that I mentioned the result of the experiment before- 

 hand. The discovery, therefore, was not made by accident, as Prof. Gilbert has con- 

 cluded from the expression* which" I made use of in my first announcement. 



•f I here repeat what I have already stated in other works, that by electrical forces, I 

 mean only the unknown cause of electrical phenomena, whether it belong to impercep- 

 tible matter or independent motion. 



X In my tirst memoir, I grounded all explanations upon- the repulsions only which 

 are exerted by electrical and magnetic forces ; but I soon discovered, that from the fear 01 

 assuming more than the phenomena required, I drew an unjust inference ; for if mag- 

 netic forces are the -same as electrical under another form of action, it follows, that oppo- 

 site forces ought to attract each other reciprocally, and forces of the same kind to repel 

 each other. 



y2 



