1821.] Prof '. Oersted on Electro-magnetism. 333 



agree with the opinion, that S' N' should be considered as a mag- 

 net. As there is not in this case any question as to the length 

 of the axis of the magnet, in making the experiment it is only 

 requisite to employ a wire curved like A B C D E F, fig. 12, 

 which receives + * at A and — e at F. The moveable magnet 

 S N may also be mounted in the manner shown in fig. 3, only it 

 is necessary to observe that C D should be so turned in the 

 cylinder A B, that S N should be in a horizontal position. 



The experiment cited by M. Ampere as particularly favourable 

 to his theory, that a magnetic needle properly suspended is either 

 totally attracted or repelled by the connecting wire in complete 

 conformity with his theory, cannot be considered as contrary to 

 mine, and has not moreover been so considered by M. Ampere, 

 especially as he did not intend to criticise the theory which I 

 had in few words proposed, and but very slightly explained ; but 

 the explanation of this account will increase the facility of com- 

 prehending that which I am here going to describe. 



A, fig. 13, is a transverse section of an electro-magnetic con- 

 ductor ; B and C are two magnetic needles. It will be readily 

 conceived that C will be repelled, and B attracted ; for — e in A 

 will meet the north pole, and + e the south pole of C ; on the 

 contrary + e of A will meet the north pole, and — s the south 

 pole ofB. This phenomenon is, therefore, a consequence which 

 results with equal facility from both theories. 



One of the difficulties of M. Ampere's theory is the explana- 

 tion of the common manner of magnetizing steel, as has been 

 already remarked by the celebrated Erman. It is unintelligible 

 how by touching or rubbing the side of a steel wire, a galvanic 

 circle can be placed around the whole of the wire. As the theory 

 here sanctioned differs from the common one only in the deriva- 

 tion of the magnetism, and not in the idea which ought to be 

 formed of the distribution of the magnetic forces in the magnet, 

 the common theory may also be adopted. That which neither 

 one theory nor the other can yet explain is the peculiar power 

 which some bodies, especially iron, nickel, and cobalt, possess 

 of receiving a high degree of magnetism, while almost all others 

 are susceptible of it only in a very slight degree. 



I shall not explain more at length my objections against the 

 theory of the celebrated Ampere. If I have perfectly understood 

 it, what I have already said will be sufficient. If I am deceived 

 upon any point of his theory, I flatter myself that I have giveu 

 him an opportunity of shedding new light upon this important 

 matter. 



(E.) Magnetism of the Earth. 



The daily course of the light of the sun round the earth pro- 

 duces warmth, evaporation, and chemical agency, from the east 

 to the west. From this also proceeds an alternation of the 

 destruction and renovation of electrical equilibrium, and the 

 effect of it must be similar to that of a galvanic circle applied 



