320 Mr HARRIS'S Experimental Inquiries concerning 



the induced force variable, the distances a b, a' b' being varied 

 (36) ; and 3, when both the distances and forces were varied ; 

 that is to say, when the distance c d, and the distances a b, a'b' 

 were varied simultaneously. The experiment being thus ar- 

 ranged, the forces set free, as expressed by the index, at the ex- 

 tremity d of one of the masses of iron, were found to vary with 

 the distance cd, when the induced forces were the same, and 

 with the induced forces when the distance c d was the same ; 

 and, finally, with these quantities conjointly, when they were both 

 made variable. 



55. Now, by whatever artificial method we suppose a bar of 

 steel to be made a magnet, whether by the single or double 

 touch, it would not be difficult to shew, that the first states of 

 the magnetic disturbance, as measured from the magnetic centre, 

 would be in an arithmetical progression. Thus, if we suppose a 

 bar of steel a 6, Fig. 20, to have been magnetized, then the 

 forces impressed on each side of zero may at first be conceived 

 to go on in the arithmetical progression 1, 2, 3, or 1', 2', 3', &c. 

 If we conceive these forces to be all united in the centre, their 

 free action would be zero. Let us now suppose these opposite 

 forces to be withdrawn through the distances 1 I', 2 2', 3 3', &c. 

 successively ; then, by the preceding experiments (54), the forces 

 set free in the points 1, 2, 3, &c. 1', 2', 3', &c. would vary direct- 

 ly as the square of the distances from the magnetic centre, since 

 they vary directly with the magnetic intensities, and directly 

 with the distances. 



In the few theoretical illustrations found in the preceding 

 observations, it has been my endeavour to wander as little as 

 possible from experimental facts. I have not the vanity to sup- 

 pose that my researches are such as to defy the scrutiny of a 

 critical examination, or that, in so difficult an inquiry, I have 

 obtained perfection. It is only by examining nature in a great 



