This bulb has the following features - a longer copper threaded base with 4 to 6 threads and one straight-sided copper contact terminal on the bottom of the base, all over plaster of paris insulator.
Base is cemented to the neck of the bulb by a thick ring of plaster of paris between the bulb and base. The carbonized split Japanese bamboo filament is connected to the platinum lead in wires by carbon paste joints. The use of this longer base was introduced in 1888. The bulb pictured above was itself manufactured in that same year.
NEXT PAGE in the Evolution of Incandescent Light Bulbs