SOURCES OF ELECTRICITY. 
20 7 
continuously through the sides of the triangle. But the 
moment any one of the sides of the triangle is removed, 
whether it be the zinc, the copper, or the liquid, the force 
ceases to act. The action can, however, be restored by means 
of a wire, though it may be a very long one, connecting the 
two poles of the combination, or even if each pole be con¬ 
nected through wires with the earth. These results can easily 
be demonstrated by very ordinary appliances ; but when the 
size of the apparatus is increased, and arrangements are made 
for magnifying the effects, the phenomena are very marked, 
and can be made to give rise to very decided mechanical 
effects. 
A wire placed in the positions just mentioned acquires those 
magnetic properties upon which the telegraph is based. If the 
wire be wound round a soft iron core, the latter is magnetized 
while the current passes through the wire, and the magnet so 
formed will attract other pieces of iron, so that movement can 
thus be imparted to a piece of machinery. Or again, if this 
wire is placed round or near a magnetized needle, the latter 
can be at will deflected to the right or left by the current, and 
thus produce the visual signals of a preconcerted code. 
Let us now see how the wire must be used, and how the 
power it possesses can be multiplied or re-inforced, so that it 
becomes capable of practically producing the effects required 
for electric telegraphs. The properties acquired by the wire 
affect its whole length, but their intensity is modified by that 
length. The wire must always be considered as offering a 
resistance to the passage of electricity, and the longer it is, and 
the thinner it is, the greater is that resistance. This resistance, 
however, does not affect the practical rapidity with which the 
force is transmitted, and it is most important to understand 
that it diminishes the effect only by reducing the quantity of 
electricity that is put in motion. Again, the amount of the 
force is the same at every part of the circuit; so that, if the 
wire is made thicker at any part of the circuit, the general 
resistance is diminished, and in a given time a greater amount 
of electricity passes through each part of the circuit. 
If a wire joining the two metals be bent into this form y\, the 
current passes up one side and down the other, but if the sides 
be connected by a cross-piece, made of wire of the same thick™ 
