Original Socket for Incandescent Lamps, 1880.
Wire Terminal Base Lamp, 1880.
This crude form of lamp base fitted the original form of lamp socket pictured above. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.
This crude arrangement was changed in the latter part of 1880 to a screw shell and a ring for the base terminals, wood being used for insulation. The socket was correspondingly changed. This was a very bulky affair, so the base was changed to a cone-shaped ring and a screw shell for terminals. Wood was used for insulation, which a short time after was changed to plaster of Paris as this was also used to fasten the base to the bulb. It was soon found that the tension created between the two terminals of the base when the lamp was firmly screwed in the socket often caused the plaster base to pull apart, so the shape of the base was again changed early in 1881, to the form in use today.
An improved method of connecting the ends of the filament to the leading-in wires was adopted early in 1881. Formerly this was accomplished by a delicate clamp having a bolt and nut. The improvement consisted of copper plating the filament to the leading-in wire.
Original Screw Base Lamp, 1880.
This first screw base, consisting of a screw shell and ring for terminals with wood for insulation, was a very bulky affair. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.