All this must be taken into consideration when magnets are being made. In the first place, the wire we wind around steel or iron to make magnets must always be covered with an insulator of electricity. Magnet wire is usually covered with cotton or silk. If it were left bare, each turn of the wire would touch the next turn, and so we should make such an easy path for the electricity that it would all go back to the battery by a short circuit, and then we would get no magnetic effect in the steel or iron. The only way we can get electricity to do useful work for us is to put some resistance or opposition in its way. So you see that if we make it travel through the wire around the iron or steel, there is just enough resistance or opposition in its way to give it work to get through the wire, and this work produces the peculiar effect of making the iron or steel magnetic.
The covering on the wire, as you will remember, is called "insulation."
IV
THE TELEGRAPH
Every one knows how very convenient the telegraph is, but there are not many who think how wonderful it is that we can send a message in a few seconds of time to a distant place, even though it were thousands of miles away. And yet, though the present system of telegraphing is a wonderful one, the method of sending a telegram is simple enough. The apparatus that is used in sending a telegram is as follows:
The Battery.
The Wire.
The Telegraph Key.
The Sounder.
The different kinds of electric batteries will be mentioned afterward, so we will not stop now to describe them, but simply state that a battery is used to produce the necessary electricity. As you all know what wire is, there is no necessity of describing it further.
The telegraph key is shown in the sketch below. (Fig. 6.)