J 12 Mr, Christie on the Magnetism of Iron [A!J4. 



to suppose ia order to account for the pheenomena which take 

 place ot* attraction and repulsion, as they have been called. 

 Immediately, then, that the iron becomes stationary in any 

 position, the deviation of the needle ought, on this hypothesis, 

 to become the same, whether the iron has been brought into 

 that position by revolving in one direction, or in the contrary. 

 It is hardly necessary for me to say that this would not be the 

 case, since I have stated, that, in all the preceding observa- 

 tions, the iron was stationary previous to the observation being 

 made. 



" Whatever are the effects produced on the iron by its revo- 

 lution, so far from these effects being of the transient nature 

 which we must suppose them to be on this hypothesis, they 

 appear to have been quite permanent, that is, so long as the 

 iron remained in the same position. The following observar 

 tion will show the small changes which took place during 12 

 hours. 



" In order that the needle might be quite free to move, it was 

 suspended in a balance of torsion by a brass wire, of the same 

 diameter as the finest gold wire used for transits, free from 

 torsion, 21.15 inches long. The plane of the plate was in the 

 plane of the secondary to the equator and meridian, its centre 

 m latitude 0°, longitude 180°; and it was fixed to a wooden 

 axis passing through its centre perpendicular to its plane : the 

 ends of this axis, which revolved with the plate, being made of 

 brass, that I might ascertain whether the effect was independ- 

 ent of friction on the plate itself. The plate was made to 

 revolve in contrary directions, as usual, and the direction of the 

 north end of the needle noted, when the point 180° on the plate 

 coincided with the upper part of a plane parallel to the meri<p 

 dian, and passing through the plate's centre. After having 

 made the plate revolve so that its upper edge moved from west 

 to east, and noted the direction of the north end of the needle 

 when 180° coincided with the above plane, it was made to 

 revolve from east to west, and 180° being again brought to 

 coincide with this plane, the direction of the north end of the 

 needle was noted at different times for more than 12 hours, 

 the plate remaining stationary during that time. 



