ELECTRICITY.
[Sidenote: Lightning in a cat’s back.]
[Sidenote: Lighting gas.]
When you see the lightning in a thunder-storm, you would think it
strange if I should tell you that there is lightning in every thing;
but so it is, as you will see. Did you ever have your fingers tingle,
and hear a snapping when you stroked a cat’s back? This is because you
waked up, as we may say, the lightning in her fur and in your hand
together. There is lightning in you as well as in the cat. It only
needs a little rubbing to show it. I have known persons to light the
gas with the lightning that is in them as readily as you would with
a match. They wake up or excite the lightning by walking across the
carpet, rubbing their feet on it as they go, and then put a finger to
the open gas-burner. A spark of lightning goes to it from the finger
and lights the gas.
It is in very clear cold weather that it is most easy to excite the
lightning or electricity that is in different things. It is then that
you can make the cat’s fur snap. Then, too, silk things will snap when
you rub them or fold them up.
[Sidenote: Lightning is electricity.]
Though it is really lightning that is made by rubbing things, we do
not call it so. We call it electricity. We did not know that lightning
and electricity were the same thing till Dr. Franklin showed that they
were. He found it out by an experiment with a kite, which I will relate
to you after I have told you some other things about electricity.
You can make electricity more easily by rubbing some things than by
rubbing others. I have already told you how easily it is waked up on
the cat’s back by stroking it. If you rub a stick of sealing-wax back
and forth rapidly across your coat sleeve, you wake up a good deal
of electricity for so small a thing. It is shown in this way: If you
bring the sealing-wax near some light thing like down, this will cling
to it for a moment, and then fly off again, as if it did not like the
sealing-wax. It is the electricity which you have excited that does
this.
A good deal of electricity can be made by rubbing glass. In the machine
which is used in making electricity for experiments there is a large
glass cylinder, which is turned round quickly against a leather rubber
that has a preparation of mercury on it.
[Sidenote: Description of an electrical machine.]
[Illustration]
In this machine, represented here, _a_ is the glass cylinder, and _b
b_ are the wheels by which it is made to turn round. These wheels
are worked by the handle which you see on the lower one. The rubber
is pressed against the glass cylinder on the side of it that you do
not see. You can see the standard that holds the rubber. At _c_ is a
piece of oiled silk that is fastened to the rubber, and lies upon the
glass cylinder, serving to keep it free from dust. At _d_ you see a
receiver, as it is called, which receives the electricity as fast as it
is produced. This is made of brass, and has a glass standard, _e_. Now,
as the machine is worked, the electricity excited by the rubber and
the glass passes off continually to this receiver, and there it stays
collected on the surface of it, for it can not go down the standard.
Why is this? you will ask. It is because glass, though a very good
thing to make electricity with, is very slow to let the electricity
pass over it. I shall tell you more about this soon.
[Sidenote: Electricity in the receiver.]
Well, here is the electricity all over this receiver. It stays there
because it can not get away. It is ready to go whenever it can get a
chance. You would find this out if you should put your finger near
that knob that you see on the end of the receiver. Almost all of the
electricity in the receiver would pass through your finger into your
body, and give you a shock; and if there was much electricity in the
receiver, the shock would be harder than you would wish to bear.
[Illustration]
[Sidenote: How a person can be a receiver.]
Now a person can act as a receiver and be charged with electricity
just as this brass receiver is. It can be done in this way. The person
stands on a stool, such as you see here. The top of this, _a_, is
wood, and the legs, _c_, _c_, are glass. These glass legs answer for
him as the glass standard does for the receiver of the machine. They
prevent the electricity that he gets from passing off. If he stood on
the floor, it would pass to the floor as fast as it came to him. As he
stands on this stool, he holds in his hand a chain that is fastened
to the knob on the end of the brass receiver. You can see now what
will happen when the machine is worked. The electricity that goes
from the glass cylinder to the receiver does not all stay there, but
most of it goes on through the chain to the person on the stool. It
can not get from him to the floor, for the glass legs prevent this.
Therefore, after working the machine some time, he becomes filled with
electricity, just as the brass receiver does on its glass standard, and
you can receive a shock from him, for he is now a receiver. If you put
your finger to his nose, or chin, or any other part, the electricity
will pass to you with a spark, and will give you a shock.
[Illustration]
[Sidenote: How electricity affects the hair.]
A curious effect is produced on the hair when one is thus charged with
electricity. The hair stands out straight. This effect is seen in a
very amusing way by having a figure of a head with hair on it fastened
to the receiver. The hair will stand out as you see here.
[Illustration]
[Sidenote: Bottling it up in the Leyden jar.]
The electricity that is collected on the brass receiver can be taken
off and be bottled up, as we may say, so as to be convenient for use.
This can be done with what is called the Leyden jar, as represented
here. This is a glass jar coated inside and out with tin foil to within
a few inches of the top. Then there is a knob on the end of a wire
that extends down into the jar. Now see how we do this bottling up of
the electricity. The knob of the jar is held close to the knob of the
receiver as the machine is worked. The electricity, therefore, passes
to the knob of the jar, and by the wire to all the inside of the jar
where the tin foil is. It can not get outside, because it can not pass
over or through the glass.
So, then, the electricity is shut up in the jar, but it is ready to
come out when it has a way made for it to come. If the inside foil and
the outside foil be connected together by something that will let the
electricity pass through it, it will come out of the jar. You can be
that something if you please. If you put one hand on the tin foil on
the outside, and touch the other to the knob on the end of the wire,
the electricity will come out by the wire, and give you a shock in your
wrists, and elbows, and chest.
[Sidenote: Taking shocks from the jar.]
A great many persons can take a shock in this way at the same time.
Suppose there are a hundred persons standing in a ring and taking
hold of each other’s hands. Let there be two in this ring that do not
have hold of each other. Now, if one of these touches the jar on the
outside, and the other touches the knob, the whole hundred will feel a
shock at the same time, for the electricity will go through them all
around the whole ring as quick as lightning, as we say; and it is, in
this case, really so, for the electricity is lightning. And so, when in
the telegraph the electricity passes along the wire, it takes almost no
time for it to go very great distances.
[Sidenote: An electrical battery.]
[Illustration]
Sometimes a great deal of electricity is collected in a number of these
jars, which are connected together in such a way that the electricity
can be discharged from them all at once. A collection of jars thus
connected, as represented here, is called an electrical battery. There
is need of great care in experimenting with a battery; for if, when
the jars are well filled, they should all be discharged into any one,
he would be killed in the same way that one is who is struck with
lightning.
[Sidenote: 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?