An unusual antique hearing aid from France which was in effect no more than quackery. These usually come in double sets but this one is a cased single aid for the left ear.
The metal plate is designed to fit behind the ear and is flesh coloured (hence ‘Invisible’). The improved hearing was attributed to magnetism and the box comes with its own ‘Galvanometer’. Each plate is marked “Audiphone, Bernard Cie, 7 Rue De Londres Paris”. The silk lined box is also engraved as shown and is in good condition.
You can read a French newspaper clipping from Feb 1901 extolling their virtues.