ELECTRICITY. A 33 
and this crack are lightning and thunder in miniature, for the black thunder- 
clouds that we see in a thunder-storm are clouds charged with electricity. 
When two thunder-clouds approach each other, induction takes place, and 
owing to the immense quantity of electricity the two contain, when it passes 
from the one to the other, the flash is of exceeding brightness, and the report 
deafening. Sometimes the induction takes place between a cloud and a 
prominent object on the ground, such as a steeple, a tall chimney, a tree, 
oran animal. Anything will do, if it form a point near enough the cloud 
to cause the electricity to overcome the resistance of the intermediate 
space ; and the consequences are generally fatal to the object in this 
position. But it is not necessarily so; the destructive effects of lightning, 
or of electricity rather, only take place when it meets with resistance— 
that is, when induction takes place between a thunder-cloud and some 
ebject which is a bad conductor of electricity. Hence the object of 
lightning-conductors. Metals being good conductors, if a rod of metal 
have its point extending beyond the top of any prominent object, and 
pass down into the ground, when a thunder-cloud happens to be near, 
and induction takes place, the electricity, which would otherwise have 
shivered the non-conducting steeple or chimney, passes harmlessly down 
the metal rod. 
It may now be asked where this vast quantity of electricity in the 
thunder-cloud comes from. We saw that electricity is produced by 
friction ; this, in the case of the thunder-cloud, is one source of it, for 
there are many different kinds of friction going on in nature. The friction 
produced by the wind in various ways is very great; thus electricity may 
be produced in a piece of glass by a blast of air from a bellows, instead 
of by rubbing. But, besides friction and all other forms of mechanical 
action, electricity is produced by all kinds of physical and chemical 
action; it is produced by the great system of evaporation which is con- 
tinually going on from all bodies of water, and also from the processes of 
vegetation in which water is being continually separated and evaporated 
from plants, so that the vapours and gases that rise into the air are all 
more or less charged with electricity; and this electricity, which is 
generally diffused through the atmosphere, becomes occasionally concen- 
trated in clouds, and is then liberated in the form of lightning. 
The Electric Telegraph. 
In the form of lightning, electricity is often very destructive, and is at 
all times very terrible; but the reason and skill of man have enabled him 
to turn it to account in a most useful manner. By means of the electric 
telegraph, a message can now be sent half round the world in a few 
hours. 
We have said that one of the sources of electricity is chemical action ; 
c 
