The Story of Great Inventions

by Elmer Ellsworth Burns

I will tell you a fable to make the meaning clear. There once lived a race of blind men. Not one of them could see. They built houses and cities, railroads and steamships, but they did everything by touch and sound. When they met they touched each other and spoke, and each man knew his friend by the sound of his voice. One day a wise man among them said he believed there was something besides the sound of the voice with which they could make signals to each other. Another wise man thought upon this matter for some time and brought forth a proof that there is something called light, though no man could see it. Another, wiser and more practical, invented an eye which any man could carry about with him and see the light when he turned it in the direction from which the light was coming. Thereafter each man carried a light that flashed like the flashing of a firefly. Each man also carried an eye, and each could see his friend as well as hear the sound of his voice.

The fable is true. The light which no man had seen we now call electric waves. The eye with which any one can perceive this light is the receiving instrument of the wireless telegraph. The strange light flashed out whenever an electric spark passed from an electrical machine, a Leyden jar, an induction-coil, or as lightning in the clouds, but for hundreds of years this light was unseen. The human eye could not see it, and no artificial eye that would catch electric waves had been invented. A man in England, James Clerk-Maxwell, first proved that there is such a light. Heinrich Hertz, a German, first made an eye that would catch the waves from the electric spark, and the man who first perfected an eye with which one could catch the electric waves at a great distance and improved the instruments for sending out such waves was Marconi.

The fable is true, for electric waves are like the light from the sun. They go through space in all directions as light does. They will not merely go through air, but through what we call empty space, or a vacuum, as light will. If we think of waves somewhat like water waves, but not exactly like them, rushing through space, we have about as good a picture of electric waves as we can well form in our minds. As the light of a lamp goes out in all directions, so do the electric waves go out in all directions from the place where the electric spark passes. Since these waves go through what we call empty space, we must think of something in that space and that it is not really empty. Examine an incandescent electric lamp. The bulb was full of air when the carbon thread was placed in it. The air was then pumped out until only about a millionth part remained. The bulb was then sealed at the tip and made air-tight. We say the space inside is a vacuum. If the bulb is broken there is a loud report as the air rushes in. Is the bulb really empty after the air is pumped out? Is anything left in the bulb around the carbon thread? Turn on the electric current and the carbon thread becomes white hot. The light from the white-hot carbon thread goes out through the vacuum. There is nothing in the vacuum that we can see or feel or handle, but something must be there to carry the light from the carbon thread. The light of the sun comes to the earth through ninety-three million miles of space. Is there anything between the earth and the sun through which this light can pass? Light, we know, is made up of waves, and we cannot think of waves going through empty space. There must be something between the sun and the earth. That something through which the light of the sun comes to the earth we call the ether. It is the ether that carries the light across the vacuum in the light bulb as well as from the sun to the earth. Electric waves used in wireless telegraphy go through this same ether. The light of the sun is made up of the same kind of waves, and we do not think it strange because it is so common. It is true we do not see light waves, but they affect our eyes so that by means of them we can see objects and perceive the flashing of a light. So with the wireless receiving instrument we do not see the electric waves, but we perceive the flashing of the strange light. Electric waves and light travel with the same speed—186,000 miles in a second. A wireless message will go around the earth in about one-seventh of a second.

Electric waves will go through a brick wall as readily as sunlight will go through a glass window, but that is not so strange as it may seem. Red light will not go through blue glass. Blue glass holds back the red light, but lets the blue light go through. So the brick wall holds back common light, but allows the light which we call electric waves to go through.

Some waves on water are longer than others. So electric waves are longer than light waves. That is the only difference between them. In fact, the light of the sun is made up of very short electric waves. These short waves affect our eyes, but the longer electric waves do not. We are daily receiving the wireless-telegraph waves from the sun, which we call light. Electric waves used in wireless telegraphy vary from about six hundred feet to two miles in length, while the longest light waves that affect our eyes are only one thirty-three-thousandth of an inch in length.

The sensitive part of the Marconi receiving apparatus is the coherer. The first coherer was made in 1890 by Prof. Edward Branly, of the Catholic University of Paris. Very fine metal filings were enclosed in a tube of ebonite and connected in a circuit with a battery and a galvanometer. The filings have so high a resistance that no current flows. The waves from an electric spark, however, affect the filings so that they allow the current to flow. The electric waves are said to cause the filings to cohere—that is, to cling together more closely. It is a peculiar form of electric welding. Branly discovered that a slight tapping of the tube loosens the filings and stops the flow of the current.

All that was needed for wireless telegraphy was at hand. Men knew how to produce electric waves of any desired length. They knew how they would act. A sensitive receiver had been discovered. There was needed the practical man who should combine the parts, improve details, and apply the wireless telegraph to actual use. This was the work of Guglielmo Marconi. In 1894, at the age of twenty, Marconi began his experiments on his father's estate, the Villa Grifone, Bologna, Italy. Fig. 108 is from a photograph of Marconi and his wireless sending and receiving instruments.

FIG. 108–MARCONI AND HIS WIRELESS-TELEGRAPH SENDING AND RECEIVING INSTRUMENTS