Lodge arranged a mechanical tapper for the purpose which continually administered the small blow to the tube sufficient to keep the filings in a sensitive condition.
Popoff employed an electromagnetic tapper, in fact the mechanism of an electric bell with the gong removed, for this purpose.
The numerous adjustments required by the tapper and the inertia of the apparatus prompted inventors to seek for a self-restoring coherer which should not need tapping.
Do you remember Tapper, Berzerk and Missile Command?