120 Hisioncat Sketch of Bkctro-magnethm, [Feb. 



place. As the artiou of" the magnetic pole on the wire waa 

 always independent of the axis joining the extremes or poles of 

 the magnet ; it was concluded that in those motions which 

 would probably be produced by the earth, all consideration of 

 the magnetic axes might be omitted for the time, and the pole 

 considert^d as a point, the position of which is indicated by the 

 dipping needle. Mr. Faraday does not appear to lay much stress 

 on the existence of magnetic poles in the earth, but is rather 

 inclined to consider them as apparent only, and the result of an 

 action analogous to that of the ring before spoken of; but he 

 seems to assume the dipping needle as indicating the resultant 

 of all the terrestrial magnetic forces ; and, therefore, as the datum 

 on which to commence, Mr. Faraday has made a mistake in 



fiving the dip as 72° 30'; it is only 70° 30'. The motions^ 

 owever, do not regard the quantity of dip so as to be confined 

 to a certain range, but probably occur in any part of the earth. 



Judging from the former experiments, the results expected 

 were that a connecting wire would always move laterally, and in 

 a plane at right angles to the dip : this requires the wire to be 

 perpendicular to the dip ; if removed from the perpendicular a 

 little way, it would still, however, move, though with diminished 

 force. To get this result experimentally, a horizontal piece of wire 

 was suspended from the ceiling by a silk thread, its ends dipped 

 into mercury in two basins, and these were connected with the 

 voltaic apparatus ; the wire immediately moved laterally, and that in 

 every azimuth, and the direction of the motion was precisely that 

 described in the former experiments. Thus when the wire was 

 E. and W. the E. end to the zinc, and the W. end to the copper 

 plate, a single pair of plates being used, the motion was towards 

 the N.; when the connexions were reversed, the motion was to- 

 wards the S. When the wire hung N. and S. the N.end to the zinc 

 plate, the S. end to the copper plate, the motion was towards the 

 W. when the connexions were reversed towards the E. and the 

 intermediate positions had their motions in intermediate directions. 



An apparatus was made use of in another experiment resem- 

 bling that described for the revolving motion, but larger and 

 more delicate, and the moveable wire was made to form a greater 

 angle with a perpendicular than that formed by the dipping 

 needle. In these circumstances, the moment the communica- 

 tion was completed, revolution began, and continued by the 

 magnetic force of the earth alone on the wire. 



Mr. F. deduces from these experiments, the cause of the 

 direction taken by Ampere's curve. Considering it as a polygon 

 of an infinite number of sides, he shows that the attempt of 

 those sides to rotate by terrestrial magnetism would place the 

 curve in the position, M. Ampere found it to take in his experi- 

 ments. Mr. Faraday concludes this part of his note by stat- 

 ing his expectation ** that in every part of the terrestrial globe, 

 an electro-magnetic wire, if left to the free action of terrestrial 



