The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 27
2 Induction of Electric Currents. variation of current would only have been one hundredth of the percentagevariation of resistance of the transmitter. Thus vfe see that the longer theline the weaker is the speaking, since the speaking depends not upon thecurrent flowing through the telephone, but… … Figure 5. The solution of this problem was found in the induction coil. Theinduction coil consists of an electro-magnet around which a second set ofwindings are placed. The first set of windings is termed the primary coil,and the second set the secondary coil, and the currents sent through…
Telephone · Postal service
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