Mining and Engine House Telephones
Pattern No. B385
Comprises an Enclosed; Wood Wall Box saturated with oil, (and outwardly covered with Sheet Lead to prevent the corrosive action of the acid liquids
and vapours met with in Mines), Solid Back Transmitter, Fixed Receiver with Flexible
Tube, Induction Coil, two Dry Cells, a Knob-handle Switch, and the separate large size extension Bell.
The exposed metal work is also all covered with a layer of lead, and the fronts of the instrument and bell box respectively are provided with India rubber gaskets to make them watertight. No automatic switch is provided, but an outside knob is arranged to be turned and held whilst speaking is going on.