Bodies are repelled from the Poles of a Magnet. 285 



Let us apply this reasoning to the experiment with the bis- 

 muth prisms ah-eady described. The motion of the magnetic 

 needle in the case referred to is not more inexplicable, on the 

 assumption of a purely attractive force, than is the motion of our 

 rectangular box on the assumption of a purely repulsive one; 

 and if the above experiment would lead to the conclusion that 

 the end h of the magnetic needle is repelled, the experiment 

 with the bismuth leads equally to the conclusion that the end/ 

 of the prism hf, fig. 2, must be attracted by the pole N. The 

 assumption of such an attraction, or in other words, of diamag- 

 netic polarity, is alone capable of explaining the effect, and the 

 explanation which it offers is perfect. 



On the hypothesis of diamagnetic polarity, the prism hf turns 

 a hostile end h to the magnetic pole N, and a friendly pole / 

 away from it. Let the repulsive force acting upon the former 

 be ^, and the attractive force acting vipon the latter <^'. It is 

 manifest that if (^ were equal to ^', as in the case of the earth's 

 action, or in other words, if the field of force were perfectly uni- 

 form, then, owing to the greater distance of ^' from the axis of 

 rotation, from the moment at which the rectangular box quits 

 the equatorial position, which is one of unstable equilibrium, to 

 the moment when its position is axial, the box would be inces- 

 santly drawn towards the position last referred to. 



But it will be retorted that the field of force is not uniform, 

 and that the end h, on account of its greater proximity to the 

 magnet, is more forcibly repelled than the end / is attracted : to 

 this I would reply, that it is only in " fields ■'•' which are approxi- 

 mately uniform that the effects can be produced ; but to produce 

 motion towards the pole, it is not necessary that the field should 

 be perfectly uniform : setting, as before, the distance of the direc- 

 tion of the force ^ from the axis of rotation = d, and that of the 

 force <p' = d', a motion towards the pole N will always occui* 

 whenever 



d (}>'' 



To ascertain the diminution of the force on receding from a 

 polar surface such as that here used, I suspended a prism of 

 bismuth, similar to those contained in the rectangular box, at a 

 distance of 0'9 of an inch from the surface of the pole. Here, 

 under the action of the magnet excited by a current of ten cells, 

 the number of oscillations accomplished in a second was 17; at 

 0"7 of an inch distant the number was 18; at 0'5 of an inch 

 distant the number was 19 ; at 0"3 distant the number was 19*5 ; 

 and at 0*2 distant the number was 20. The forces at these 

 respective distances being so very little difiPerent from each other. 



