a closer look at a rare bergmann-edison 19th century incandescent electric lamp "moving tongue" socket

the bergmann socket was designed to be compact and simply constructed with as few parts as possible, including the amount of insulation used and possess a very simple form of "circuit-controller."

the stout copper-plated two-part shell or casing, containing several lightly incised patents, conceals the socket, consisting of the threaded sleeve that receives the light bulb that screws into place in order for a connection to be made by the terminals. the larger section of the casing contains an opening or slot for the protruding circuit controlling ornamented key or paddle switch that extends from the brass disk or ring containing the binding screws used to receive the circuit wires.

the aforementioned top ring or plate is covered by a cap that is held down with two flat-headed screws inserted directly into the ring. the internally threaded tube used to connect the socket to a light fixture arm, is soldered directly against the cap (in some cases, the cap and tube are a single piece). a flanged ring consisting of hardened rubber or an equally equivalent insulating material is screwed between the internal sleeve and casing to hold the components tightly in place.  

all of the circuit connections employed used, incorporated a single insulating disk that is comprised of a non-carbonizable material known as black lava. since the contacts and terminals are arranged close to each other, there was always the possibility of a short-circuit, especially as the circuit is open and closed when engaging the socket key or paddle switch. a patent pertaining to this matter was issued to sawyer & man at an earlier time.

advertising and portrait images courtesy of antique light sockets