“Two years ago[43] it was proved by conclusive experiments that
Hertzian waves travelling along an iron wire magnetise transversely
the very thin layer into which the alternating current penetrates, and
whose thickness does not exceed some thousandths of a millimetre. Once
proved that alternate magnetisation can be produced with such rapidity,
other questions present themselves. One asks, for instance, if it is
not possible to demonstrate in magnetic cylinders stationary magnetic
waves analogous to the electric stationary waves along metallic wires.”
[42] Abstracted from _Comptes Rendus_, June 11, 1894, and communicated
by Dr. Oliver Lodge.
[43] Why two years ago? It was practically proved by Savart early in
the century, and has been observed over and over again since. However,
it is true that experiments have been more numerous and conclusive of
late, and have been pushed to very high frequencies.--O. J. L.
The author finds that the conductivity of massive iron makes it an
unsuitable substance, and uses instead a mixture of iron filings, or of
chemically-obtained iron powder, with paraffin, to which he sometimes
adds powdered quartz. This he moulds into cylinders, and inserts as the
core of a spiral in an otherwise ordinary Hertz resonator.
Fig. 67 shows emitter and receiver drawn to scale; the magnetic cores
are introduced into the spiral A, and their effect on the length of
the resonator spark is observed. With this arrangement of exciter the
_electric_ effect of the spiral is negligible, since it is well removed
from electrostatic disturbance, and subject only to magnetic. The
spiral is of 12 well-insulated turns, the spark gap is a micrometer
with point and knob, and a pair of adjustable plates to vary the
capacity for purposes of tuning.
He employed 12 different types of cylinder, all about 20 centimetres
long, and 4 centimetres diameter.