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.

    447/502 page 427
    have been scattered, inside the coil. The filings will place themselves along the lines of force as shown in Fig. 135,?^. The lines are parallel in the centre of the coil, but diverge at the ends. When a secondary coil is placed so as to enclose certain of these lines whenever a change is produced in the number of lines so enclosed, an induced current will be produced as long as the clia7ige is taking place. By placing iron within the primary of Fig. 135^, since magnetic effect is stronger, and Fig. i35^'. hence the number of lines is increased, the induced currents will be intensified. A further increase of effect will be pro- duced by placing iron within the secondary, for now more lines of force will pass through this coil. All. Induction Machines.—There are two kinds of elec- trical machines which depend for their action on the laws of induction. The object of the one set of machines is to transform the energy of work into the energy of electricity in motion, and to get powerful currents without the necessity of a voltaic battery. These are called magneto-electrical or dynamo- electric machines. The object of the other is to transform the ordinary current, which is deficient in electro-motive force, into a spark possess- ing great electro-motive force, and resembling in this respect the spark of the electric machine. These are called intensity coils or transformers. A12. Magneto-electrical Machines.—The machines for transforming work into electricity in motion by the .aitl of a permanent magnet go by this name. They consist of a station- ary permanent magnet, and of a coil which is made to revolve in front of the poles of this magnet. Under these circum- stances an electric current will, as we have seen, bo produced in the coil. In Clarke's machine (see Fig. 1354), two coils, t and con-
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