278 Historical Sketch of Electro-magnetism. [Oct. 



The direction and constancy of the poles given to the needle 

 by the helices will be directly seen to be a natural consequence 

 of the invariable position of the needle to the connecting wire, 

 pointed out in Oersted's experiments ; for if a small portion of 

 either of the helices, together with the needle magnetised by it, 

 be compared with fig. 1, 2, or 3 (PI. IX), they will be found to 

 be represented by them. Thus in fig. 8, or 9, which represents 

 the helices and the needles in them, every part of the helices 

 will be seen to cross the needles as in 1, 2, or 3 ; or if two of the 

 glass diagrams, fig. 3, be put together with the lines represent- 

 ing the needles together, so as to imply but one, then the lines 

 representing the connecting wires will also represent one round 

 of either helix. 



In the same paper, M. Arago also states, that when the con- 

 necting wire was perfectly straight, a needle placed beneath and 

 parallel to it was not at all magnetised. He also states, that it 

 sometimes happened, though not frequently, that the copper 

 wire connecting the poles of the battery retained its magnetism 

 for a few instants after the connexion had been broken ; and also 

 that M. Boisgeraud had observed the same fact with a platina 

 wire. These wires, it is said, would sometimes take up iron 

 filings, or even a needle, when separated from the battery, but 

 the power soon disappeared, and could not be reproduced at 

 will. 



On Oct. 9, M. Boisgeraud read a paper to the Royal Academy 

 of Sciences, containing the detail of numerous experiments, 

 most of which, however, are variations of Oersted's first experi- 

 ments. He remarked that connecting wires, or arcs, placed any 

 where in the battery would affect the needle — aresult that follows 

 as a consequence from Oersted and Ampere's experiments. He 

 notices the difference of intensity in the effects produced when 

 bad electrical conductors were employed to complete the circuit 

 — a difference which Oersted himself had pointed out in the case 

 of water. M. Boisgeraud, however, proposes to ascertain the 

 conducting power of different substances by placing them in one 

 of the arcs, cells, or divisions, of the battery, and bringing the 

 magnetic needle, or Ampere's galvanometer, towards another 

 arc, i. e. to the wire, or other connecting body, used to complete 

 the circuit in the battery. With regard to the positions M. Bois- 

 geraud notices of the needle and wire, they are all confirmatory 

 of Oersted's statements, and may be represented by the figures 

 before mentioned. 



On Oct. 9, M. Ampere read another memoir on the phenomena 

 of the voltaic pile, and on the method he intended to pursue in 

 calculating the action of two electrical currents. At this sitting, 

 also, he showed the mutual action of two rectilineal electrical 

 currents; i. e. of two straight portions of the connecting wires; 

 foritappears that the phenomena of attraction, repulsion, &c. were 

 first observed with spiral wires. These actions, however, are 



