电话 The TelephonePDF电子书下载

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How telephones began 1

How Edison improved on the early telephone 4

How the sound of your voice travels 6

Sound waves into electric currents 7

The Transmitter 8

The Receiver 9

Telephone exchanges 12

Manual exchanges 14

Automatic exchanges 15

How the selectors work 17

Automanual switchboards 18

Dialling codes 20

Exchange systems 23

Long distance telephoning 24

Helping the electric currents over long distances 26

International services 29

Radio-telephones 30

The Post Office Tower 31

Telephoning by Satellite 32

Special services 34

Emergency services 35

Public services 37

Learning more about the telephone 38

Vocabulary 40

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