Robert Chielly. age 13. of Rochester,NY

What are those cups on telephone poles?

Telephone and telegraph wires carry loads of electricity. The huge pylons; that march over the land carry enormous loads of electricity: And these electric currents have to be kept in line. They must stay in their high wires until needed. They must not leak and waste their precious power. Electricity leaking from the wires could also be dangerous.

The job of those little cups is to help keep the electric current in line. Electricity is very choosy about where and how it will flow. It. will flow only in an unbroken circle to and front the generator. It will flow: merrily through some substances. It refuses to flow through other substances.

The substances through which it flows well are called good conductors. They do a good job of conducting an electric current. Silver is tops as a conductor, gold and aluminum are quite good. Copper is almost as good as silver. Most electric wires are made of copper because it is plentiful and therefore cheap.

Now for the poor conductors. Electric current balks at passing through the mineral mica. It will not go through paraffin or vulcanized rubber. And it refuses to pass through glass or porcelain. But poor conductors are good pat something else. They are good at insulating or separating the electricity from' things round about. They act like policemen to keep the electric traffic: flowing in the wires there it belongs.

See how a good conductor and a good insulator work together in s lamp cord. The inside of the cord is made of copper. Threads of ware wound. together carry the current to and fr® in the electric circuit. These wires are encased in rubber. the good insulator. Without this shield. the electricity would leap and leak out of the wire and cause trouble.

Current in the outdoor wires also needs insulating. Here we use glass or porcelain knobs. cups or saucers. They are placed at certain spots; along the wires. These are the places where the current is most likely to leak due to the stresses and weaknesses in the miles of wire

Electricity is not too fond of passing through the air. So the Wires hanging between the poles and pylons do not need extra insulation. Danger spots are where the wires touch the wooden poles and the metal framework of the tall pylons.

Here is where the glass and porcelain cups do their work. Electricity that tries‑to leap into the poles mind metal is stopped in its tracks. Sturdy policemen of glass or porcelain turn it back. It cannot pass. So it. stays; in the wires where it belongs. It flows along to do the work waiting for it in homes and factories.

Glass and porcelain insulators come. in different shapes and sizes. Depending upon the job to be done. A glass or white porcelain knob. Its usually enough to keep a telephone wire in line. The big pylons need more. You often see stacks of glass saucers hanging from their riggings. They look like. jeweled pen dents. Actually they are policemen dividing the traffic duty between them to keep a tremendous current where it belongs.