, and that this
conductivity is easily destroyed; as, for instance, by turning the
tube over and over.
In several memoirs published in 1890 and 1891, M. Ed. Branly
independently pointed out similar phenomena, and made a much more
complete and systematic study of the question. He was the first to
note very clearly that the action described could be obtained by
simply making sparks pass in the neighbourhood of the radio-conductor,
and that their great resistance could be restored to the filings by
giving a slight shake to the tube or to its supports.
The idea of utilising such a very interesting phenomenon as an
indicator in the study of the Hertzian waves seems to have occurred
simultaneously to several physicists, among whom should be especially
mentioned M. Ed. Branly himself, Sir Oliver Lodge, and MM. Le Royer
and Van Beschem, and its use in laboratories rapidly became quite
common.
The action of the waves on metallic powders has, however, remained
some what mysterious; for ten years it has been the subject of
important researches by Professor Lodge, M.
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