  At the end of the nineteenth century \'Edouard Branly discovered that the
electrical resistance of a granular metallic conductor could drop by several
orders of magnitude when excited by the electromagnetic field emitted by a
distant electrical spark [ ]. Despite the fact that this effect was used to
detect radio waves in the early days of wireless telegraphy and more recently,
studied in the field of granular materials, no satisfactory explanation of the
physical origin of the effect has been proposed. In this contribution, we
relate the Branly effect to the induced tunnelling effect first described by
Fran\c{c}ois Bardou and Dominique Boos\'e [ ].
