to Magnecrystallic Action. 131 



greater leverage possessed by the force acting on the more distant 

 parts. When the shape of the poles is such that the diminution 

 of the force with the increase of distance is too speedy for the 

 above condition to be fulfilled, the phsenomena no longer exhibit 

 themselves. It is plain that the diminution of the force as we 

 recede from a pointed pole must be more speedy than when we 

 recede from a magnetized surface, and hence it is that Mr. Fa- 

 raday finds that " conical poles are not good." It is also essen- 

 tial that the length of the lever which supports the magnecry- 

 stallic body shall bear a sensible ratio to the distance between the 

 two points of application of the magnetic force. If the lever be 

 long, recession will take place in cases where, with a shorter 

 lever, approach would be observed. 



It is well known that a piece of soft iron is attracted most 

 strongly by the angles and corners of a magnet, and hence it is 

 inferred that the magnetic force emanating from these edges and 

 corners is more intense than that issuing from the central parts 

 of the polar surfaces. Such experiments, however, when nar- 

 rowly criticised, do not justify the inference drawn from them. 

 They simply show that the difference between attraction and 

 repulsion, on which the final attraction depends, is greater at 

 the edges than elsewhere ; but they do not enable us to infer 

 the absolute strength of either the attraction or the repulsion, 

 or in other words, of the force of magnetization. The fact 

 really is, that while the attraction of the mass is nearly absent 

 in the central portion of a magnetic field bounded by two flat 

 poles, the magnetization is really stronger there than between the 

 edges. This is proved by the following experiment : — I suspended 

 a cube of crystaUized bismuth from a fibre of cocoon silk, and 

 when the magnet was excited, the cube set its planes of prin- 

 cipal cleavage equatorial. When drawn aside from this position 

 and liberated, it oscillated round it. Between the upper edges 

 of the moveable poles the number of oscillations performed in a 

 minute was seventy-six; in the centre of the field the number 

 performed was eighty-eight, and between the lower edges eighty. 

 A cube of magnetic slate, similarly suspended, oscillated in the 

 centre of the field forty-nine times, and between the edges only 

 forty times, in fifteen seconds. In the former position there was 

 no sensible tendency of the cube to move towards either pole ; but 

 in the latter position, though the magnetization was considerably 

 less intense, the cube was with difficulty prevented from moving up 

 to one or the other of the edges. The reason of all this manifestly 

 is, that while the forces in the centre of the field nearly neutralize 

 each other as regards the translation of the mass, they are eff"ect- 

 ive in jjroducing its oscillation ; while between the edges, though 

 the absolute forces acting on the north and south poles of the 



