A solid brass rod runs from top to bottom, and near the bottom,
and at right angles to it, is fixed a smaller adjustable rod,
terminating in a flat head. Opposite to this flat disk there is a
brass strip secured to the ebonite cap. From the top of this brass
strip hangs a gold or aluminum foil. The foil and strip are placed to
earth, and the solid brass rod is connected to the circuit to be
protected. Should the difference of potential between the foil and the
terminal opposite to it attain more than a certain amount,
electrostatic attraction will cause the foil to touch the disk and
place the circuit to earth. The apparatus, which is a modification of
the Cardew earthing device, is constructed by Messrs. Drake & Gorham,
of Victoria Street.--_The Electrician_.
[Illustration.]
* * * * *
EXPERIMENTS WITH HIGH TENSION ALTERNATING CURRENTS.
Messrs. Siemens and Halske, of Berlin, recently invited the members of
the Elektrotechnische Verein of that city to their works to witness
the demonstration of a series of experiments on alternating currents
under a pressure of 20,000 volts. In order to show that the desired
pressure was really _en evidence_, the high tension was conducted
through a pair of wires of only 0.
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