560 



THE POPULAR SCIENCE MONTHLY. 



Fig. 1. 



If a wire, from a galvanic battery such as is shown in Fig. 1, 

 through which a current of electricity is passing, be wound around a 

 piece of steel or soft iron, as represented in Fig. 2, some curious 

 things will happen. If the bar be soft iron, it will be made magnetic, 

 and kept in that condition as long as the current continues to pass 



round it, and its ends will then at- 

 tract and hold bits of iron, but drop 

 them when the battery is taken 

 away. If the bar be of steel, in- 

 stead of soft iron, it will be mag- 

 netized and attract iron just as be- 

 fore; but, unlike the soft-iron bar, 

 it will keep its magnetism and at- 

 tract the iron even after the battery 

 is removed. Its magnetism will be 

 permanent. Since, however, elec- 

 tricity made the magnet, we can, in 

 turn, make the magnet a source of 

 electricity. Suppose the magnetized 

 steel bar has attracted and is hold- 

 ing on to a piece of iron. We can now take the battery away and 

 join the ends of the wire, as in Fig. 8 ; then, if the piece of iron be 

 pulled off and stuck on again, a current of electricity will run through 

 the wire every time it is done. Electricity produced in this way is 

 called magneto-electricity, and the current in the wire is said to be an 

 induced electric current. If, now, the wire from bar No. 1 (Fig. 4), 

 be extended to a distance, and coiled around another magnetized bar 



(No. 2), the currents induced in it, by mak- 

 ^ ^^^^jg^^^g^^^ ' ing and breaking the contact of the piece 



of soft iron with the first magnet, will 

 simultaneously affect the magnetism in the 

 distant magnet also. Though the magnets be a mile or a hundred 

 miles apart, the disturbance in one is immediately and equally mani- 

 fested in the other. 



But, what is still more remarkable, these induced currents may be 

 sent through the wire without the actual contact of the soft iron with 

 the steel bar. If this piece of iron is brought very near to one 

 magnet without touching it, and then withdrawn, an electric thrill or 

 wave is induced in the wire which is felt in the distant magnet, just 

 as if the contact had been actually made and broken. And so if we 

 play the piece of soft iron backward and forward, before the magnet, 

 no matter how rapidly or slightly, each motion is felt as an electric 

 pulse in the magnet at the other end. To borrow a metaphor from 

 life, it is as if the close approach and quick oscillation of the piece 

 of soft iron fretted or tantalized the magnet, and sent a series of 

 electrical shudders through the iron nerve. 



Fig. 2. 



