Modern electricity and magnetism, theoretically and practically considered (1885)
Avery, Elroy M[cKendree], 1844- [from old catalog] · New York and Chicago, Sheldon and company · leaf 151
Fig. 229. familiar with this alphabet that they understand a message from themere clicks of the lever and do not use any recording apparatus.Such an operator is said to read by sound ; his instrument is calleda sounder. Fig. 229 represents one. The sounder is placed on alocal circuit and has a… … Fig. 230. (&.) With a long main line, the resistance is so great that the cur-rent of the main battery is too feeble to operate the sounders with MAGNETISM. 321 sufficient force. This difficulty is metby introducing a local battery anda relay at each station on the line.The relay (Fig.230) is a…
Electricity · Magnetism
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