Antique, Harvey Hubbell vintage, brass and porcelain dimming socket for early electric lights. This old socket still has the early mica insulator disk at the bottom of the socket. It is made by the Wirt Company of Philadelphia, PA and is marked on the brass shell "Dim-A-Lit" and carries a patent date of Nov 24, 1908.
This measures about 12" long over the original pull cords used to control the light socket. It is rated for 40 watts at 110 volts. We've tested this and it works well. It has a lovely patina of tarnish and age, but it does have a stress crack to the backside of the outer brass shell.
This vintage dimmer socket works by running the electrical current through a coil of high resistance wire with a contact that can move up and down along the wire, thus increasing or decreasing the amount of resistance in the circuit. This is known as a potentiometer or a rheostat.
By pulling on the two cords the outer portion of the rheostat turns, thereby changing the amount of resistance and allowing more electricity reach the light bulb. Because you can vary the amount of power reaching the light bulb, this type of socket is ideal for displaying antique and vintage light bulbs (Mazda, figural etc) by allowing you to slowly increase the power, rather then applying the electrical current all at once.