The base of this bulb, introduced in 1881, has a copper screw shell with two or three threads (which serve as one contact terminal) over a plaster of paris insulator in place of wood.  It also has a separate cone-shaped copper ring (being the second contact terminal) also over the plaster of paris and above the threads.  The collar at the top of the base is used for holding and screwing the bulb into a socket and is also made of plaster of paris.  (NOTE: Plaster of paris is white is color, somewhat rough and porous and easy to scratch.)  The base is cemented to the neck of the bulb by a thick ring of plaster of paris insulator between bulb and base.  Socket itself would have female threads to place and tighten the base in.  Note: It was soon discovered that screwing this type of base into a socket would produce a tension inside the plaster of paris insulator between the two terminals and as a result the plaster of paris would eventually crack.  Hence a newer base would come along later in that year.



 
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