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 0.2 mm. diameter to a battery of 200
100-volt incandescent lamps, all connected up in series. An ordinary
Siemens electric light cable was inserted, and broke down at a
pressure of some 15,000 volts.
At the end of the meeting a few experiments on the formation of the
arc under this enormous pressure were shown. The sparking distance
varied considerably, according to the shape of the electrodes. At
20,000 volts a spark jumped from a ball to a ball about 10
millimeters, while between two points a sparking distance of 30
millimeters, and sometimes even more, was reached. This arc is shown
half size in the accompanying engraving.
[Illustration: A 20,000 VOLT ALTERNATING ARC (half size).]
The arc which followed the jumping over of a spark made a loud humming
and clapping noise, and flapped about, being easily carried away by
the slightest draught. The arc could be drawn out horizontally to
something like 100 millimeters distance between the electrodes, and
even to a distance of 150 millimeters, when carbon pencils were used
as electrodes, but it always remained standing up in a point.
--_Electrical Engineer._
* * * * *