Action of Magnets on Copper and good Conductors. i65 



2330. If the whole mass be moving parallel to itself, and 

 be small in comparison with the face of the magnetic pole 

 opposite to which it is placed, then, though it pass through 

 the magnetic lines of force, and consequently have a tendency 

 to the formation of magneto-electric currents within it, yet as 

 all parts move with equal velocity and in the same direction 

 through similar magnetic lines of force, the tendency to the 

 formation of a current is the same in every part, and there is 

 no actual production of current, and consequently nothing 

 occurs which can in any way interfere with its freedom of. 

 motion. Hence the reason that though the rotation of the 

 bar or cube (2324. 2328.) upon its own axis is stopped, its vi- 

 bration as a pendulum is not affected. 



2331. That neither the one nor the other motion is affected 

 when the bar or cube is over the vertical pole (2328.), is 

 simply because in both cases (with the given dimensions of the 

 pole and the moving metal) the lines of particles through which 

 the induced currents tend to move are parallel throughout the 

 whole mass; and therefore, as there is no part by which the 

 return of the current can be carried on, no current can be 

 formed. 



2332. Before proceeding to the explanation of the other 

 phaenomena, it will be necessary to point out the fact generally 

 understood and acknowledged, I believe, that time is required 

 for the development of magnetism in an iron core by a current 

 of electricity ; and also for its fall back again when the current 

 is stopped. One effect of the gradual rise in power was re- 

 ferred to in the last series of these Researches (2170.). This 

 time is probably longer with iron not well annealed than with 

 very good and perfectly annealed iron. The last portions of 

 magnetism which a given current can develope in a certain 

 core of iron, are also apparently acquired more slowly than 

 the first portions; and these portions (or the condition of 

 iron to which they are due) also appear to be lost more slowly 

 than the other portions of the power. If electric contact be 

 made for an instant only, the magnetism developed by the 

 current disappears as instantly on the breaking of the current, 

 as it appeared on its formation ; but if contact be continued 

 for three or four seconds, breaking the contact is by no means 

 accompanied by a disappearance of the magnetism with equal 

 rapidity. 



2333. In order to trace the peculiar effect of the copper, 

 and its cause, let us consider the condition of the horizontal 

 bar (2310. 2313.) when in the equatorial position, between the 

 two magnetic poles, or before a single pole ; the point of sus- 

 pension being in a line with the axis of the pole and its ex- 



