DESCARTES' THEORY OF MAGNETISM. 361 



these conduits and back to the origin, hence but a small 

 proportion of the total number of streams reaches the air. 

 That is the first notion of "short circuiting" and "leak- 

 age." 



Some of the explanations are curiously ingenious, such, 

 for example, as that of magnetic attraction and repulsion. 

 If two magnets are placed with iinlike poles in proximity, 

 the spirals from one may enter the conduit ends of the 

 other. Then the air between the juxtaposed poles is 

 driven out and forced around to the rear of the two mag- 

 nets so that it pushes them together. If, on the other 

 hand, like poles are opposed, the spirals from one magnet 

 cannot enter the conduits of the other, and the spirals 

 force the stones apart. 



Iron is adapted to become magnetic because it has con- 

 duits suitable to receive the spirals; but it is not normally 

 magnetic, because the little branches or projections in the 

 pores are turned naturally in all sorts of directions. If, 

 however, a magnet through which a strong stream of spi- 

 rals is passing be approached to the iron, the force of that 

 stream is enough to drive the spirals through the conduits 

 in the iron, and in so doing to turn all the little branches 

 in one way. After that the iron constantly receives 

 streams, and is magnetic. 



The mode of answering that standing puzzle, how is it 

 that the magnet in communicating its virtue to large 

 quantities of iron still retains its own unimpaired? is espe- 

 cially felicitous. "There happens no change in the mag- 

 net, because the spirals which leave its pores enter iron 

 rather than some other body. In fact, they pass even 

 more freely and in greater quantity through the magnet 

 when there is iron around it than when there is none. 

 Hence, instead of the magnet's virtue being in anywise 

 thus impaired it is increased, besides being communicated 

 to the iron." Yet he does not account for the strengthening 

 effect of the armature in this way, but agrees with Gali- 

 leo's hypothesis concerning it. 



