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ELECTRICITY
automatically. It is only apparatus of this kind which has practical importance.
As an example of a very simple kind of automatic apparatus we may take Lord Kelvin's "water-dropping machine." Let,
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Fig. 3.
in Fig. 3, A and B be two metal cylinders supported on insulating stands, and a and b two metal funnels likewise supported. A and a are connected by a wire; B and b are similarly connected. To indicate that the two connecting wires at the crossing point in
