ELECTRICITY. 35 
made by rubbing a piece of iron with a natural magnet; but the strongest 
magnets are got by coiling the wire of a galvanic battery round a piece 
of iron. While the electric current is passing through the wire, the iron 
becomes strongly magnetic, and ceases to be so as soon as the current is 
stopped. Magnets are of different forms. Perhaps the most common form is 
that of the horse-shoe magnet (fig. 36), the object being to bring together 
the two ends, called the poles, N and 8, in which the strength of the 
magnet is concentrated. The part sn is not properly a portion of the 
magnet, but is a piece of iron, called an armature, used partly for con- 
venience, but chiefly for keeping in the magnetism. Fig. 37 shews an 
electro-magnet, which is a piece of iron that can be rendered magnetic 
by an electric current, as described above. Neither the horse-shoe nor the 
armature is magnetic in itself, and therefore they will not remain in 


contact; but as soon as the electric current is sent through the wire coiled 
tound the magnet, the armature is pulled to it with a sharp click. We 
now proceed to describe the working of the Electric Telegraph. 
There is one kind of telegraph which depends on the effect that an 
electric current has on a magnetic needle placed near it, as in fig. 34, of 
turning it out of its natural position, in which it points north and south ; 
but as we can only describe one, it will be one on another principle, which 
is perhaps the best and the one now most extensively adopted, namely, 
the electro-magnetic. Of this, again, there are various modifications ; the 
instrument here described is Morse’s. 
We have seen that an electro-magnet is only magnetised when the 
current is passing, and this can only be when the circuit is complete, as in 
fig. 34, by the wire and the liquid. Now, everybody knows how the wire 
of the telegraph passes from one station to another; but how about the 
1 From Latin armatura, armour, protection. 
