358 



THE CENTURY BOOK OF FACTS. 



to devise means for using it for sending mes- 

 sages. Many of these devices were tried and 

 failed. Some of them seem now to us absurd, 

 because they were attempted before even the 

 battery was invented, when the current was 

 obtained by friction. In 1832 an American, 

 Morse, while on a voyage home from Europe in 

 a sailing vessel, began to think of making 

 what we now know as a telegraph. After 

 more than eight years of waiting, Congress 

 made an appropriation for building a line be- 

 tween Baltimore and Washington. The story 

 of this first line is curious, almost absurd, 

 showing how little the inventor knew when he 

 began it, and how much was learned during 

 its construction. Morse had an assistant named 

 Alfred Vail, who is the author of most of the 

 features of the telegraph which have proved 

 useful, as we now know it. 



In principle, and even in practice, the tele- 

 graph is one of the simplest of electrical ap- 

 pliances. Any two operators can communi- 

 cate with each other over a great distance with 

 two parts only ; a battery and a wire, for the 

 wonderful alphabet of Vail, the dots and 

 dashes, can be read in any language, and by 

 sight, hearing, tasting, or feeling. Something 

 to produce a current, and a wire to carry it, 

 are all that are absolutely necessary. There is 

 usually only one wire. There would be two, 

 but the earth acts in place of the return wire, 

 and the connection is simply made at the bat- 

 tery, along the wire, and into the ground. 

 The only machine, so' to speak, that is neces- 

 sary in practice is the small electro-magnet 

 which one hears pulling down the armature to 

 it every time a connection is made by the op- 

 erator at the other end of the circuit who is 

 sending a message, and spelling out the words 

 of it with the click and pause sound which 

 would be the dpt and dash of the old roll of 

 paper indented by a pointed stylus, now dis- 

 carded. This electro-magnet and its action 

 with an interrupted current has been briefly 

 explained. The key with which the message 

 is spelled out is a lever with a button at the 

 end, which, when pressed down, makes a con- 

 tact and completes the circuit over the wire 

 and the windings of the electro-magnet, and, 

 when released, breaks it again. 



Telephone, The. This wonderful ad- 

 vance in electrical science was made practical 

 in 1875, and is the invention of Prof. A: G. 

 Bell, Chicago. There were simultaneous in- 

 ventions by Gray, Edison, and others. In 

 reality, the telephone is simple in construc- 

 tion, but it is difficult to explain in words. 

 The human voice, recognizable in articulate 

 words, is apparently carried for miles on a 

 wire. Yet it is well to understand in the be- 



ginning that such is not the case. The lis- 

 tener does not hear any person talk. All that 

 goes over the wire is thousands of varying 

 impulses of electricity. The entire secret lies 

 in electrical induction. 



It has been shown that electricity produces 

 magnetism. Following it has been shown that 

 this process can be reversed, and that mag- 

 netism produces electricity. This last fact was 

 made use of in the original Bell telephone. 

 The Blake transmitter is now used, slightly 

 modifying the action, but not altering the 

 principle of the instrument, and an endeavor 

 to explain this will be made. Ft has been 

 shown that an approach to, or a receding from, 

 a wire carrying a current, produces an induced 

 current. Then it was shown that if one of the 

 pieces were a magnet, and there was a rapid 

 approach and receding by a piece of soft iron, 

 an induced current would also be produced. 



Now there is in the transmitting instrument 

 of a telephone a bar magnet, and on one end 

 of this is wound several layers of fine insulated 

 wire. The ends of this wire run off and be- 

 come a part of the circuit between two tele- 

 phones. No current passes over this circuit 

 ordinarily, but one can be induced if a piece of 

 iron is made to move quickly, to tremble, near 

 the bar. This is accomplished by placing 

 crosswise to the end of the bar magnet the 

 thin black disc of sheet-iron against which, so 

 to speak, one talks when using the telephone. 

 The voice impinging upon this, causes it to 

 tremble ; to approach to and recede from the 

 magnet, not vaguely and without rule, but pre- 

 cisely in proportion to the tone of the voice. 

 Every time one of these very small movements 

 of the disc occurs a small impulse is sent from 

 the magnet out over the circuit whose coil in- 

 closes it. 



At the other end of the circuit there is a pre- 

 cisely similar arrangement of bar magnet and 

 coil and disc, inclosed in that trumpet-shaped 

 receiving instrument which is held to the ear. 

 The magnetism in this last magnet is increased 

 with each impulse in precise proportion to the 

 power of the impulse, and this disc of the re- 

 ceiving instrument is drawn toward its mag- 

 net and released again in unison with the 

 movements of the disc in the transmitter, 

 which movements, as stated, are great or 

 small, or slow or fast, in accordance with the 

 tones of the voice of the speaker. 



It follows that the mechanical rattle of a 

 disc of sheet-iron held close to the ear pro- 

 duces sounds that vary in pitch and intensity 

 precisely as those do which are produced by 

 the impinging of the human voice upon the 

 other disc, a mile or more away. The move- 

 ment of the transmitting disc controls those 



