for Spring 2000:
Edison Demonstration Lamp, late 1879
used this lamp (and about 100 more just like it) to illuminate
Menlo Park on 31 December 1879 when he introduced his invention
to the world. It is currently on display in the exhibition
Lighting A Revolution at the National Museum of American History.
catalog #310,578; negative #13369.
This lamp and a wooden socket (along with several other pieces
relating to Edison) were donated to the Smithsonian in 1933 by Frank
A. Wardlaw, Jr. of Inspiration, Arizona, and his father Frank A.
Wardlaw of New York, New York. The elder Wardlaw had worked for
Edison and at the time of the donation was secretary of the Edison
The lamp may look a bit strange -- it shows many features of experimental
Edison lamps, features that have long since been modified or replaced.
The "base" consists of two copper plates folded against the neck
of the bulb and held in place by a string. Edison designed the first
of several screw-bases in mid 1880 so that his lamps could be installed
upside-down in fixtures.
The filament (broken in this lamp) is a piece
of carbonized Bristol-board - a type of paper - connected
to the lead-in wires with tiny screw-clamps made of platinum. The
lead-in wires are also platinum. Though expensive, platinum expanded
at nearly the same rate as the glass through which it passed, keeping
an air-tight seal as the lamp operated.
Any oxygen inside the bulb would cause carbon
filaments like Bristol-board to burn, hence the need for an air-tight
seal and also the reason for the glass tip on top of the bulb. After
assembly the bulb was connected to a vacuum pump with a thin glass
tube. After the air was exhausted from the bulb, a torch was used
to melt the tube - sealing the lamp and leaving a tip.
This particular bulb was free-blown, but production
demands quickly led to the use of iron molds which allowed fast,
uniform results without the need for a master glass-blower. Later,
machines were developed which could make thousands of bulbs every
hour. The globe on this lamp is dark due to a layer of carbon that
evaporated from the filament and settled on the inside bulb-wall.
For more information
- Robert Friedel
and Paul Israel with Bernard S. Finn, Edison's Electric Light:
Biography of an Invention (New Brunswick, NJ: Rutgers Univ.
Jehl, Menlo Park Reminiscences (Dearborn, MI: Edison Institute,
1936, 1938, 1941). Three volumes.