Part 99

Sketch showing arrangement of aerial on ship equipped with the Marconi Direction Finder, an instrument which tells the sea captain the exact points of the compass from which wireless distress signals are being sent and enables ships to avoid collisions in fog.]

The Story in the Wireless

What is the Principle of the Wireless Telegraphy?

Drop a stone in a pool of water. Circular waves or ripples will travel outward in all directions. That is the principle of wireless telegraph.

If a chip be floating on the water it will be rocked by each ripple, just as a wireless receiving station will respond to the electrical waves or impulses that make up a wireless message. It is not known just how the invisible wireless waves are propelled through space, but they travel through the ether in the air in very much the same way as do sound waves. The electrical signals, too, are received only by apparatus that is attuned to them; that is, they can not be heard except at wireless stations, any more than sound can be heard by the ears of a deaf person.

The wireless waves have a definite length, can be measured in feet or meters, and are regulated according to the distance the message is to travel. Stations that send a few hundred miles use a wave length of six hundred meters, or less, while at the powerful land stations used for trans-atlantic work the wave lengths used run into as many thousands.

Why Don’t the Messages Go to the Wrong Stations?

So that the hundreds of messages hurtling through space at the same time will not interfere, the wireless stations are equipped with tuning-apparatus through which they can adjust their wave length to receive the particular message desired. A different wave length is used by each ship or wireless shore station, and even though dozens of messages fill the air, the minute the wireless operator adjusts his tuner to the length of the station he is after, that particular message stands out very strongly and all the others grow dim.

How Does the Wireless Reach Ships at Sea?

All ships at sea report their positions regularly; thus it is a simple matter for a shore station to send a wireless message to the ship to which it is addressed. For example, the Marconi station at Sea Gate, New York, wants to reach the Lusitania. The operator looks up that vessel on the list and notes her call signal and wave length. He adjusts his tuner to correspond and calls her signal, M F A, repeating it three times.

The wireless man on the vessel, knowing that he is within range of a shore station, has set his tuner at the wave length assigned to him and is listening. When his call letters are heard, he acknowledges them and signals to go ahead with the message. When it has been given, the Sea Gate station “signs off” with its call letters W S E and the ship operator enters in his record that that particular message reached him via the Marconi station at Sea Gate. Thus, with the wide variety in wave lengths, no confusion of messages exists and any desired ship or shore station can be called, just as a direct telephone connection is secured by giving the central station the call number of the subscriber wanted.

What Kind of Signs Are Used in the Wireless?

The actual wireless message is composed of dots and dashes, which, in certain combinations, stand for certain letters of the alphabet. This is done through opening and closing the electrical circuit by pressing a key, a sharp touch forming a dot and a longer pressure a dash, as with the wire telegraph.

If secrecy in a wireless message is wanted, the words are sent in cipher which, of course, cannot be understood by outsiders. The Government sends thousands of words each day without a single word meaning anything to the wireless stations that happen to be “listening in.” While it is true that any one owning a wireless receiving set may listen to messages flying through the air, every person within hearing who understands the Morse Code can read the telegrams that come into a telegraph office. Knowledge thus gained, however, is of little value, as the law provided heavy penalties for disclosing the contents of any kind of telegraph message.

What Does a Wireless Equipment Consist of?

The various apparatus that comprises a wireless equipment can not be properly explained without the use of technical language, but the general principle of operation is somewhat as follows: If a small loop of copper wire, with a slight separation between the ends, is placed across a room from an electric spark, it will be slightly affected. Increase the electrical current to far greater power and control it, and the invisible electrical wave may be thrown many miles. To send a message across the ocean, the current used by the modern wireless station is so powerful that it will pass through storm and fog, even through mountains, without losing much of its force. When this tremendous force is released by pressing the telegraph key, it leaps from the aerial wires, or antennae, travels across the Atlantic and is picked up by a corresponding aerial, attuned to receive the signal.

Station set up and working.

WORKING THE WIRELESS IN THE ARMY.]

The aerial, or antennae, as it is called in a wireless work, is made up of copper wires. On a ship these are strung between the masts, usually consisting of two, four or six wires held apart by crosspieces. Two or more wires lead down from this to the wireless cabin.

The coil or transformer is the apparatus which produces the spark that forms the electrical waves. In small stations, the length and thickness of the spark and the speed of vibration is regulated by a thumb screw. Transformers are used when the power is taken from the alternating current of an electric light circuit.

The gap, which the electrical current jumps when the telegraph key is pressed down, is composed of two rods which slide together or apart to vary the length of the spark.

The simplest type of sending station consists of the antenna, battery, coil, wireless key and spark gap. If a change in wave length is desired a transmitting tuning coil must be added.

The receiving apparatus contains a detector, which is chiefly two mineral points lightly touching and connected with a sensitive head telephone. The incoming signals are heard as long and short buzzing sounds corresponding to the dots and dashes. The receiving tuning coil, used to adjust wave lengths, is operated by simply moving sliding contacts along a bar until the signals are more plainly heard. While the large stations have more complicated apparatus, the principle remains the same.

THE WIRELESS IN THE ARMY]

How High Do Wireless Masts Have to be?

The towering masts of the Marconi Trans-Oceanic stations are often supposed to rise to their great height, so that an antennae will be raised above the obstructions between. If this were necessary, two wireless stations separated by the Atlantic would have to have masts one hundred and twenty-five miles high to rise above the curvature of the earth. The path of the wireless waves, however, is not in a straight line, but follows the curvature of the earth. Scientists explain this by saying the rarefied air above the earth’s surface acts as a shell enclosing the globe.

The speed of wireless messages is placed at 186,000 miles per second. A wireless message will thus cross the Atlantic in about one-nineteenth of a second--a period of time too small for the human mind to grasp. In other words, the wireless flash crosses in a fraction of a second a distance that the earth requires five hours to turn on its axis and the fastest ships take nearly a week to cross.

The longest distance over which a wireless message can be sent is not definitely known; the present record was made in September, 1910, by Marconi from Clifden, Ireland, to Buenos Aires, Argentina, a distance of 6700 miles.