248 Mr. Christie on the Permanence of 



In order to compare these results, it is necessary to consider 

 the effects produced on the situations of the poles and magnetic 

 centre of a bar by the disturbance of the symmetrical distribu- 

 tion of magnetism in it. When a bar has been carefully mag- 

 netised by double touch from its centre towards its extremities, 

 the magnetic centre is very nearly in its centre of figure, and 

 its poles are very nearly at equal distances from that centre*. 

 If to either pole of such a bar the similar pole of a magnet be 

 applied, the effect will be, to drive the pole at that end nearer 

 to the centre, the other pole further from it, and the magnetic 

 centre towards the other end of the bar. At the same time, 

 the intensity of each pole will be diminished, but that of the 

 pole in the branch to which the magnet has been applied con- 

 siderably more than that of the pole at the untouched end ; 

 and in the former branch, the magnetism will likewise be less 

 concentrated than in the other, having nearly the same degree 

 of intensity over a considerable space. So that any tendency 

 in the magnetism of the bar to return to a state of symmetrical 

 distribution in the two branches, would be shewn by the 

 approach of the untouched, or more intense pole, and of the 

 magnetic centre towards the centre of figure, and the receding 

 of the more diffused pole from that centre ; and as, in the dis- 

 turbance, the effect is greatest on the positions of the magnetic 

 centre and the pole at the end to which the magnet has been 

 applied, so this tendency will be most conspicuous in the 

 change of position of these points. 



In the foregoing table, the changes which took place from 

 one observation to another, in the positions of the poles and 

 magnetic centre, are exhibited in the fourth, eighth, and sixth 

 columns, the sign plus indicating that the change was in the 

 direction corresponding to the resumption of a state of sym- 

 metrical distribution of the magnetism in the bars, and the sign 

 minus that it was in a contrary direction. Now although the 

 changes in all the bars are, upon the whole, of the former cha- 

 racter, yet, as they are the reverse in some cases from one 



* The bars I. and II. having been thus magnetised, the positions of these 

 points were 



Unmarked Pole. Zero. Marked Pole. 



1 3-85 inches. 0-58 inch U. 3*71 inches. 



II. , 377 0-00 3-73 



