Marvels of Modern Science

by Paul Severing

There are other inventions on which the action is the reverse. These are called anti-coherers. One of the best known of these is a tube arranged in a somewhat similar manner to the filings tube but with two small blocks of tin, between which is placed a paste made up of alcohol, tin filings and lead oxide. In its normal state the paste allows the battery current to get across from one block to another, but when electric waves touch it a chemical action is produced which immediately breaks down the bridge and stops the electric waves, the paste resumes its normal condition and allows the battery current to pass again. Therefore by this arrangement the signals are made by a sudden breaking and making of the battery circuit.

Then there is the magnetic detector. This is not so easy of explanation. When we take a piece of soft iron and continuously revolve it in front of a permanent magnet, the magnetic poles of the soft iron piece will keep changing their position at each half revolution. It requires a little time to effect this magnetic change which makes it appear as if a certain amount of resistance was being made against it. (If electric waves are allowed to fall upon the iron, resistance is completely eliminated, and the magnetic poles can change places instantly as it revolves.)

From this we see that if we have a quickly changing magnetic field it will induce or set up an electric current in a neighboring coil of wire. In this way we can detect the changes in the magnetic field, for we can place a telephone receiver in connection with the coil of wire.

In a modern wireless receiver of this kind it is found more convenient to replace the revolving iron piece by an endless band of soft iron wire. This band is kept passing in front of a permanent magnet, the magnetism of the wire tending to change as it passes from one pole to the other. This change takes place suddenly when the electric waves form the transmitting station, fall upon the receiving aerial conductor and are conducted round the moving wire, and as the band is passing through a coil of insulated wire attached to a telephone receiver, this sudden change in the magnetic field induces an electric current in the surrounding coil and the operator hears a sound in the telephone at his ear. The Morse code may thus be signalled from the distant transmitter.

There are various systems of wireless telegraphy for the most part called after the scientists who developed or perfected them. Probably the foremost as well as the best known is that which bears the name of Marconi. A popular fallacy makes Marconi the discoverer of the wireless method. Marconi was the first to put the system on a commercial footing or business basis and to lead the way for its coming to the front as a mighty factor in modern progress. Of course, also, the honor of several useful inventions and additions to wireless apparatus must be given him. He started experimenting as far back as 1895 when but a mere boy. In the beginning he employed the induction coil, Morse telegraph key, batteries, and vertical wire for the transmission of signals, and for their reception the usual filings coherer of nickel with a very small percentage of silver, a telegraph relay, batteries and a vertical wire. In the Marconi system of the present time there are many forms of coherers, also the magnetic detector and other variations of the original apparatus. Other systems more or less prominent are the Lodge-Muirhead of England, Braun-Siemens of Germany and those of DeForest and Fessenden of America. The electrolytic detector with the paste between the tin blocks belongs to the system of DeForest. Besides these the names of Popoff, Jackson, Armstrong, Orling, Lepel, and Poulsen stand high in the wireless world.

A serious drawback to the operations of wireless lies in the fact that the stations are liable to get mixed up and some one intercept the messages intended for another, but this is being overcome by the adoption of a special system of wave lengths for the different wireless stations and by the use of improved apparatus.

In the early days it was quite a common occurrence for the receivers of one system to reply to the transmitters of a rival system. There was an all-round mix-up and consequently the efficiency of wireless for practical purposes was for a good while looked upon with more or less suspicion. But as knowledge of wave motions developed and the laws of governing them were better understood, the receiver was "tuned" to respond to the transmitter, that is, the transmitter was made to set up a definite rate of vibrations in the ether and the receiver made to respond to this rate, just like two tuning forks sounding the same note.

In order to set up as energetic electric waves as possible many methods have been devised at the transmitting stations. In some methods a wire is attached to one of the two metal spheres between which the electric charge takes place and is carried up into the air for a great height, while to the second sphere another wire is connected and which leads into the earth. Another method is to support a regular network of wires from strong steel towers built to a height of two hundred feet or more.

Long distance transmission by wireless was only made possible by grounding one of the conductors in the transmitter. The Hertzian waves were provided without any earth connection and radiated into space in all directions, rapidly losing force like the disappearing ripples on a pond, whereas those set up by a grounded transmitter with the receiving instrument similarly connected to earth, keep within the immediate neighborhood of the earth.

For instance up to about two hundred miles a storage battery and induction coil are sufficient to produce the necessary ether disturbance, but when a greater distance is to be spanned an engine and a dynamo are necessary to supply energy for the electric waves.