and words, messages are sent over wires charged with electricity, across wide lands and under wide oceans. These dots and dashes of sound are received just as they are sent. So telegraph operators know each other's ways of rattling off messages, just as you know the voices of many friends apart. It was long thought that electric wires would carry words and the very tones of the human voice, if a way could be found to get them on the wire. Of course, a spoken word cannot strike a key, as a finger can. But it can travel on an air wave, strike a rock wall and make an echo of itself.
"Make a wall, then, to catch air waves," was the idea the inventor of the telephone got. "But don’t let the sound bounce back in echoes. Pass them on to an electric wire." The "wall" in the telephone, is a little round thin iron disc about as big as a penny, stretched as tight as a drum head. That is what you have in your ear—a drum head—to catch and pass on sound to the nerve of hearing. The auditory nerve is a sort of telephone wire to the brain.
This little iron drum head in the telephone connects with an electric wire. It catches the air waves made by your voice and passes them to the wire. On the electric waves the sounds travel with the speed of light to a drum-head disc in the receiver held at the ear of your friend. There the electric waves are changed back to air waves again, and your friend hears your words just as you speak them.
Isn’t that wonderful?
THE GAS WE BURN
When coal was first mined in England, it was noticed that an ill-smelling gas often escaped from the seams of the coal and made miners ill. In several mines this gas was accidentally set afire and the flame could not be put out. Around such flames mine owners built brick flues and led the gas out of the mine through iron pipes. There it often burned like a torch, lighting up the mine shaft, for months and years. This gas was called the "spirit of the coal." But no one thought of trying to find out how it was made, or of making any use of it for many years.
It was a Scotch miner named William Murdoch, who earned only five dollars a week, who got to thinking and experimenting with coal gas. Perhaps because he smelled the same gas from the grate fire in his cottage, sometimes, he suspected that, far down in the mine, a seam of coal must be smouldering. He filled a kettle with coal, fitted
