TELEGRAPHING WITHOUT WIRES 



279 



light waves, ultra-violet waves, and infra-red waves 

 are supposed to be carried. These waves together with 

 wireless waves, radio waves, and some others have 

 come to be known as ether waves. 



In Unit V, Topic 2, you studied about the visible 

 spectrum and how it could be produced from white 

 sunlight by means of a prism. You will recall that the 

 colors produced in the descending order of their 

 wave lengths were red, orange, yellow, green, blue, 

 indigo, and violet. As has been noted, this is only 

 a small portion of the entire ether spectrum. There 

 are wave lengths longer than the red and shorter than 

 the violet waves that are not detected by the human 

 eye. 



Light waves and wireless waves are similar. About 

 the time of our Civil War there lived in Edinburgh, 

 Scotland, a young mathematician, J. Clerk Maxwell. 

 By applying his great knowledge of mathematics he 

 was able to prove that light waves and other ether 

 waves are similar. He thought that it should be pos- 

 sible to set up these other ether waves just as light 

 waves can be created and controlled by man. 



Many scientists began working on this problem, 

 but it was not until 1888 that a young German scien- 

 tist, Heinrich Hertz, made and detected waves of this 

 kind. While working in his laboratory with a spark 

 coil similar to the one which was used in Experiment 

 168, he was able to send out wireless waves. He at- 

 tached a metal plate to each of the secondary termi- 

 nals of his coil as shown in Figure 457. When the cur- 

 rent was turned on in the coil and a spark jumped 

 across the gap, these plates formed the aerial of his 

 simple broadcasting set. Hertz discovered that when 

 a loop of wire of certain length was placed near the 

 spark coil in which current was flowing, a spark would 

 jump between the ends of the loop. The coil was the 

 first wireless sending set and the loop of wire the first 

 receiving set. 



How are wireless waves set up and messages sent? 

 In making sound waves and light waves there must 

 be some sort of disturbance such as a ringing bell or 



FIG. 457. HERTZ'S EXPERIMENT 



a source of light. To set up water waves in a still pond 

 something must disturb the water. So it is with the 

 making of wireless waves ; there must be a disturbance 

 to create them. Surging electrons in an electric spark 

 between two pieces of metal will cause wireless waves 

 to start up in the ether. The spark plugs of every 

 automobile are little broadcasting stations, and the 

 wireless waves which are sent out by the surging elec- 

 trons can be picked up by some receiving sets. Sparks 

 are frequently seen when electrons surge between the 

 trolley wheel of the street car and the trolley wire. 

 This also sends out a wireless wave into the ether. 

 In fact, wherever an electric spark, caused by mov- 

 ing electrons, occurs, wireless waves are set up and 

 radiate into the ether in every direction from the 

 source. 



To have sufficient energy to flow across a spark 

 gap the electrons must have a very high pressure or 

 voltage behind them. Dry cells and storage batteries 

 might be used, but many of them would be required 

 to produce this high voltage. A spark coil similar to 

 the one which you used in Experiment 168 is a part of 

 every automobile and is simply a device to raise the 

 pressure or voltage back of the electrons so that they 

 can flow across the gap in the spark plug and explode 

 the gasoline. Low voltage battery currents are 

 changed into high voltage currents by the spark coil. 

 This enables the electrons to flow across a spark gap 

 and become the center of disturbance in the ether, pro- 

 ducing wireless waves. If a telegraph key is placed in 

 the circuit of the spark coil with the batteries, long 

 and short surges may be made with it. These will 

 then be sent out as wireless waves in the ether, each 

 wave series representing a dot or a dash, and thus 

 messages may be sent. If one side 

 of the spark gap is connected to an 

 aerial and the other side to a water 

 pipe, the wireless waves will be 

 given a better start on their jour- 

 ney through the ether. 



Spark transmitters, which were 

 used for many years to send wire- 

 less messages, have now been re- 

 placed because of better ways 

 which have been discovered to 

 make electrons surge back and 

 forth. Dr. Alexanderson, an Ameri- 

 can, has discovered how an alter- 

 nating-current electric generator 

 may be used to move electrons back 

 and forth rapidly and thus create 

 ether waves. 



Vacuum tubes may also be used 

 to control electrons and cause them 

 to set up ether waves. Figure 45S 

 shows a vacuum tube of the type 



FII.. 458. VACUUM 

 TUHE USED IN 

 BROADCASTING 



