THE TELEPHONE 



273 



Experiment 167. How does the electric bell work? 



Remove the metal box cover from an electric bell and 

 study the construction. Connect the bell with a dry cell and 

 a push button as shown in Figure 445. Study the motion of 

 the clapper. What causes it to move toward the electro- 

 magnets? What causes it to fly back? Why docs it repeat 

 this? Trace the current through the bell. 



Summarize your results of this experiment in a short, 

 clearly written paragraph. 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



What is the early history of the telephone? The 

 invention and development of the electric telegraph 

 opened the way for the next step in communication, 

 which was to send the human voice over wires as elec- 

 tric currents. In 1854 Charles Bourseul outlined a 

 method by which he thought that speech could be 

 sent by wire. In 1861 a German, Phillip Reis, designed 

 a device which would transmit a tone but not the 

 variations of the human voice. 



Courtesy Bell Telephone Laboratories 



FIG. 444. BELL'S FIRST TELEPHONE / 



The telephone was invented in Boston by Alex- 

 ander Graham Bell, a young Scotchman who came to 

 this country in 1871. Being a teacher of deaf mutes, he 

 was greatly interested in sound and especially in the 

 human voice. Bell had experimented with a device 

 called the "harmonic telegraph" with which he hoped 

 to send several messages by telegraph over one wire 

 at the same time. Out of this harmonic telegraph the 

 first telephone was developed. 



In the course of his experiments Bell made the ac- 

 quaintance of a young machinist-instrument maker by 

 the name of Watson, who made the first instruments 

 after Bell's plans. On June 2, 1875, these two were ex- 

 perimenting with the harmonic telegraph in an attic ; 

 Watson was in one room with the sending instru- 

 ments, and Bell was in another room with the re- 



ceivers. An accidental touch of one of the senders by 

 Watson caused a sound to be sent over the wire to 

 the next room, and this sent Bell running in. He 

 asked, "What did you do then?" Watson showed him ; 

 it was repeated many times that day, and the prin- 

 ciple of the first telephone was born. A few days later 

 with improved instruments Watson was able to hear 

 Bell's voice over the wire. On March 10, 1876, Bell 

 spoke those memorable words, "Mr. Watson, please 

 come here ; I want you," which sent Watson bounding 

 up two nights of stairs. The transmitter and receiver 

 of this first telephone worked very much like a mod- 

 ern telephone receiver. A telephone line which uses 

 only receivers may be set pp. When a person speaks 

 into one receiver he can be heard through the other. 



Professor Bell exhibited his telephone in the sum- 

 mer of 1876 at the Centennial Exposition in Philadel- 

 phia, but it was not well received. Many practical men 

 of the day believed it only a toy. They saw for it no 

 future in the social and industrial life of the world. 

 Great difficulty was found in interesting people in in- 

 vesting money in the new company or even in using 

 the discovery in business. In 1877 there were only 234 

 telephones in the whole country. There are now about 

 twenty million in this country alone. 



How does the electric bell work? The electric bell is 

 a very important part of any telephone system and so 

 should be thoroughly under- 

 stood. In an experiment at the 

 beginning of this topic a study 

 was made of the electric bell in 

 which it was connected in a cir- 

 cuit with a push button and 

 switch. When the button was 

 pushed, current from the battery 

 flowed through the complete cir- 

 cuit and the bell rang. Study the 

 diagram in Figure 445 and see 

 how the electricity is able to ring 

 the bell. A and B are electro- 

 magnets, G is the armature or 

 moving part, D is a contact point, 

 and is a spring. When the but- 

 ton is pushed, current flows from 

 the battery to the electromag- 

 nets, which pull the armature G 

 toward them. The circuit is 

 broken at D because the spring 

 F has been pulled away from the 

 contact. When the circuit is broken no electricity 

 flows and the electromagnets lose their power of at- 

 traction. The armature is moved backward by a spring 

 at E until contact is again made at D. This again 

 completes the electrical circuit, current flows, and the 

 magnets again pull the armature and spring away 

 from the contact. This process, repeated many times 



FIG. 445 



