Scientific American Supplement, No. 433, April 19, 1884Various
Science
Scientific American Supplement, No. 433, April 19, 1884
Various
Science -- Periodicals
Up to this point we have assumed that, while touching two points in the
wire, the rest of the circuit is perfectly insulated, so that no current
can leak, in other words, that the circuit is nowhere "grounded." If
this is not the case we may, under suitable conditions, receive a
shock by touching only _one_ point of the wire. This becomes clear
by considering the current to leak from another spot of different
potential, to pass through the ground and into the body; thus, on
touching the wire the body virtually makes a connection between the
two points of the circuit. In clear dry weather such leaks are
insignificant; but in damp and rainy weather, and with poor insulation,
they may rise to such a point at which it would be dangerous to touch
the circuit even with one hand, the leaks being sometimes so great as
to cause the lamps to burn in a fitful, desultory manner, and to go out
entirely.
There is still another factor which enters into the discussion of the
danger of electric light wires. This must be looked for in the fact that
the physiological effects are greatest at the moment of the opening or
the closing of the circuit; or in a closed circuit they are the more
marked when the flow of current stops and starts, or diminishes and
increases. In dynamo electric machines the current is not absolutely
continuous or uniform, since the coils on the armature being separated a
distance cause a slight break or diminution of the current between each.
This break is so short that it does not interfere with the practical
work for lighting; in some constructions, nevertheless, the distances
apart is so great that, while not interfering with light, its effects
upon the muscles are greatly increased over those of other constructions
which give a more uniform current.
All these statements might lead to the conclusion that arc light wires
are dangerous under any circumstances; but this is not the case. The
first and only requisite is, that they be perfectly insulated. When thus
protected accidents from them are impossible, and all mishaps that have
occurred through them can be traced directly to the lack of insulation.
Nevertheless, we would warn our readers against experimenting upon arc
wires by actual trial, because unforeseen conditions might lead to
disagreeable results.
* * * * *
ROBERT CAUER'S STATUE OF LORELEI.
The statue of Lorelei, the mythical siren of the Rhine, represented in
the annexed cut, which is taken from the _Illustrirte Zeitung_, was
modeled by Robert Cauer, of Kreuglach on the Rhine. He was born at
Dresden in 1831, and is the son of the well-known sculptor Emil Cauer,
and a brother of the sculptor Karl Cauer.
[Illustration: LORELEI STATUE BY ROBERT CAUER.]
* * * * *
REDUCING AND ENLARGING PLASTER CASTS.
Public-domain text, read in full here on John Shaqi.
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