280 M. Wartmann's First Memoir 



§ VI. Examination of tisoo circumstances under 'which the elec- 

 tric curreiits and the magnets do not produce induction. 



48. Since the labours of Ampere and Mr. Faraday upon 

 electro-magnetism and magneto-electricity, no attempts have 

 been made, that I am aware, to ascertain whether the presence 

 of a magnet or an electric current alwai/s induces electricity 

 in the neighbouring conductors, and whether induction takes 

 place in the same manner in all directions. 



49. To obtain some datum upon those problems which are 

 at the foundation of every solid theory of induction, it was ne- 

 cessary to examine whether a rectilinear current induces sphe- 

 rical electricity around every molecule of the conductor, sup- 

 posed to be electrically isotropic (?) (that is to say, having an 

 equal conductibility in all directions). The experiments of 

 Mr. Faraday had shown us that induction takes place in a 

 wire placed parallel to the inductor wire, whether the two 

 wires were or were not twisted into a helix. My experiments 

 have proved to me, that induction does not take place in a 

 sensible manner in a wire which is at a right angle to the cur- 

 rent. 



50. I arrived at this conclusion by the two following me- 

 thods : — I placed the brass wire No. 1 in the small hollow 

 helix for magnetizing, and after having united the extremities 

 of the latter with the thermo-electric rheometer, I closed with 

 a wire the circuit of a strong voltaic element. At the break- 

 ing, as at the closing of the circuit, the needle remained per- 

 fectly immoveable, when even a bright spark upon the mer- 

 cury proved the intensity of the current and its induction upon 

 itself. 



51. I substituted for the preceding apparatus an electro- 

 magnet, and I closed the circuit of the pile by the iron of the 

 instrument. The needle of the rheometer, which communi- 

 cated with its external helix by copper wire and by insulated 

 spirals, one with another, in no degree deviated, even on 

 placing in the circuit a large spiral plate {coil). 



52. Thus a voltaic conductor induces currents in neigh- 

 bouring conductors only parallel to its own direction. It is 

 from the parallelism between the currents which surround the 

 magnets (according to M. Ampere) and the coils of the ex- 

 terior helix of the electro-magnet, that the approach of a mag- 

 netic body near soft iron determines induced currents in the 

 helix, and that the passage of the current in the latter mag- 

 netizes the bar. The same fact also accounts for the action 

 of the voltaic current on the magnetized needle, — an action 

 discovered by M. Oersted, and which is the foundation of 

 electro-magneti sm . 



