Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

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    E E is fixed to an iron frame to which also is attached a soft iron armature A, by means of a straight spring s. At the end of the armature is the hammer h, which strikes the gong g whenever an electric current of sufficient strength circulates around the coils of the electro-magnet. There are two methods of arranging the circuit for signalling. (1) A complete wire circuit may be used, as seen in Fig. 140, where b is the battery and the “key” or arrangement. for closing and opening readily the circuit. (2) The return wire may be substituted for an earth connec- tion, asseenin Fig. 141, where K is thekey. The earth connection Bell Fig. 140. may be made by means of the water pipes or by the help of me- tailic plates e E, buried in the earth. The expense of half the A\-ire is thus saved, and the current is increased with the 'sarrie battery owing to the reduction of the resistance. It must, however.
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