Electrical batteries in some animals.
You remember that I told you, in Part Second, Chapter XXV., that there are some animals that have electrical machines or batteries in them. There are only a few such animals, and they are great curiosities. They can fire off their batteries when they please, but exactly how they do it we do not know. These batteries are more nicely and curiously made than any that man makes, and have much more power. They are so small that it is wonderful that they can give such severe shocks.
Questions.—Why does the fur of a cat sometimes snap when it is stroked? How can some persons light the gas by their electricity? When is the best time to wake up electricity? Who discovered that lightning and electricity were the same thing? What things will give out electricity easily when rubbed? Describe the electrical machine. Why does the electricity stay on the receiver? What will happen if you put your finger near the knob on the end of it? Tell how a person can be made to act as a receiver. Why can not the electricity go from him into the floor? Tell about taking shocks from him. What effect is produced on his hair? Tell how electricity can be bottled up. How can you get it out of the bottle again? Tell how a great many persons can take a shock from the jar at the same time. What is said about the quickness with which electricity goes? What is an electrical battery? What is said about electricity in some animals?
CHAPTER XXX.
MORE ABOUT ELECTRICITY.
Electricity passes through some things more easily than it does through others. Those that it passes through easily are said to be good conductors of electricity. There are some things that let so very little pass through or over them that they are called non-conductors. Such are glass and silk. The different metals, copper, silver, iron, etc., are good conductors.
The supports of lightning-rods and telegraph wires.
You have seen how a lightning-rod is fastened to a house. It rests against pieces of wood. Observe what the object of this is. Iron lets the electricity or lightning pass much more easily than the wood does. Now, if the rod was fastened to the house by iron supports, the lightning, as it came down the rod, might go into the house by some of these supports, instead of going down by the rod into the ground.
The iron is called a good conductor, while the wood is a poor conductor. Glass is a poorer conductor still. It is so poor a conductor that it is called a non-conductor, as I have before told you. It is for this reason that the telegraph wires are fastened to glass knobs on the posts. The object is to have all the electricity go along on the wires, and not let any of it escape down the posts. If a very little of it should escape down each post, by the time it came to the end of the journey there might not be enough left to do any good.