OF ARTS AND SCIENCES. 



107 



flow through a wire which is wound many times around the iron to be 

 magnetized. Each particle of the iron is supposed to contain, even in 

 its unmagnelic state, currents of electricity, circulating around it. As 

 the direction of these currents is not definite, the particle exhibits no 

 magnetic polarity. As soon, however, as it is exposed to the action of 

 the battery currents, these native currents of the iron assume a direc- 

 tion parallel to one another and to that of the currents in the external 

 wire. When its currents are thus directed, the iron has the properties 

 of a magnet. The magnetism of iron, however developed, consists 

 simply in the magnetic properties of these electrical currents. These 

 currents, moreover, are not created by the inducing agent, but only 

 directed. They are always flowing, but not always in parallel direc- 

 tions. If we take a magnet, in which the currents are already direct- 

 ed, and draw it over a piece of common iron, the currents of the latter 

 are turned round so as to be parallel tg those of the former. The only 

 difference between a magnet made in this way, by ordinary touch, as 

 it is called, and an electro-magnet, consists wholly in the source of the 

 inducing and directing currents. In one case, we take them from a 

 battery ; in the other, we use those of a permanent magnet. 



" If this be so, the difference which is observed in the strength of 

 an electro-magnet and an ordinary magnet must proceed from a cor- 

 responding difference in the inducing currents. The battery currents 

 have a greater magnetizing power than the currents of a well-magnet- 

 ized bar of steel, either because they are stronger in themselves, or 

 because they act from a more favorable position. Now, I have shown 

 by direct experiment that the currents from the galvanic battery are 

 not in themselves so abundant as those which are flowing around a 

 piece of magnetized steel. We suspend a delicate magnetic needle 

 and oscillate it, first in front of one extremity of a helix, through which 

 a battery current is flowing, and then at the same distance from one 

 pole of a steel magnet. From the rapidity of the oscillations we can 

 easily calculate the relative magnetic forces of the helix and the steel 

 bar. It will be necessary to eliminate that part of the motion which 

 belongs to the earth's influence. This is done by oscillating the same 

 needle, when removed from the action both of the helix and steel bar. 

 From this experiment we learn that the battery currents are not nearly 

 so magnetic, and therefore not so abundant, as those of the steel bar. 

 A helix possesses directive power like a compass-needle, but much 

 feebler than a very weak needle of steel, although the current from a 



