1881

In early 1881, the base was further modified by substituting plaster of paris for the wood as the insulator.  This base also had a copper screw shell with two or three threads (which served as one contact terminal) molded over the plaster of paris insulator as well as the separate cone-shaped copper ring (being the second contact terminal) also molded over the plaster of paris insulator and above the threads.  The collar, also made of plaster of paris, was retained for holding and screwing the bulb into a socket.  The base is cemented to the neck of the bulb by a thick ring of plaster of paris insulator between bulb and base.  The wooden socket itself would have female threads to place and tighten the base in.  This base was introduced in early 1881 but 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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