This base, which came out in late 1881 or early 1882, is similar to that of earlier bulbs except that the cone-shaped copper ring which served as a second contact terminal is eliminated.  This base has a copper screw shell with two or three threads (which serve as one terminal) over a plaster of paris insulator.  (NOTE: Plaster of paris is white in color, somewhat rough and porous and easy to scratch.)  The bottom of the base has straight-sided copper contact for the second contact terminal (eliminating the separate cone-shaped copper ring) also over plaster of paris insulator.  The base is cemented to the neck of the bulb by a thick ring of plaster of paris between the bulb and base.  This light bulb still retains the small plaster of paris collar above the base for holding and screwing the bulb into a socket.  The socket itself would have female threads to place and tighten the base in.

Note: The base of this bulb will even fit into today’s sockets.



 
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