324 Prof . Oersted on Electro-magnetism. [Nov. 



whether it may not also be a law, according to which the pheno- 

 mena are arranged in nature.* It is extremely difficult, and 

 especially for those who are not much accustomed to the repre- 

 sentation of complicated figures, to understand the spiral quite 

 clearly. What I am going to state will be most readily under- 

 stood in the following manner : 



Upon a slip of paper (Plate X), fig. 1, draw the line A B which 

 is to be longitudinally divided into two equal parts ; draw some 

 small triangles so that the summits and the middle of the bases 

 may be cut by the line. Put the sign + at that end towards 

 which the summits point, and the sign— at the end towards which 

 the bases are placed. This piece of paper is to be twisted round a 

 quill, a piece of glass tube, or any other cylindrical body, in such 

 a manner that the triangles, reckoning from the summit to the base, 

 shall be placed from the left to the right hand of the observer. 

 The cylinder enclosed in this manner I call the electro-magnetic 

 indicator. With this indicator, that part of the connecting wire 

 is compared whose effect is to be judged of, by imagining it 

 to be put in the place of the latter in such a position that the end 

 marked + may receive the electricity of the positive extremity 

 of the galvanic apparatus, and the end marked — of the negative. 

 This being done, it will always be found that the south pole of 

 the suspended needle is repelled by negative electricity. For 

 brevity's sake, we will designate positive electricity by -f E, 

 and the negative by — E. But when these forces have assumed 

 their new condition, in which they possess no action upon the 

 electrometer, and affect the magnet, we shall call them electro- 

 magnetic forces, and denote them by the Greek letter + e and — £. 



It would be useless to repeat upon this occasion the descrip- 

 tion of all the experiments mentioned in my Latin memoir; it 

 will be sufficient to say, that with the assistance of the electro- 

 magnetic indicator, all the effects of the connecting wire in the most 

 dissimilar positions which I have described, may be anticipated ; I 

 shall mention one example, as it may make the subject clearer. 

 Place a part of the connecting wire perpendicularly opposite the 

 magnetic needle, and let the upper part of the conductor receive 

 the electricity of the negative end of the galvanic apparatus ; 

 that part of the needle, which receives the effect, will turn 

 towards the east. A, fig. 2, represents the horizontal section of 

 the conductor with the signs above-mentioned to describe the 

 direction of the electro-magnetic forces. B represents a mag- 

 netic needle, whose north pole turns towards the connecting wire. 

 C is another which presents its south pole to the wire. Both will 

 be directed towards the east; the north pole by — s, which 

 comes from the west ; the south pole by + e, which comes also 

 from the west. It will be readily seen that the attraction caused 



* I had intended to develope this matter in the present memoir, but the desire of 

 istating all I am able to say upon so difficult a subject with all possible clearness, hag 

 induced me to defer it to a future opportunity. 



