I have tried to have this question answered, without luck, I might
add, in the "Antiques" list.  Perhaps someone here can help?
 
I have an old light bulb which appears to be hand-blown, as
it has a small nipple on top.  The filament, which appears to
be silver wire, has three turns, each loop about 7/8 inch in
diameter.  The bottom portion of the filament runs through a
cylinder of glass, about 1 1/2 inches high, pinched flat at
the top.  The bottom inside portion of the bulb appears to be
lined with porcelain.
 
The base of the bulb is a real mystery to me.  Instead of
this bulb screwing into a socket, the socket screws into it!
The brass base's underside is porcelain, with a large ring of
brass around the outside diameter of the base, and a threaded
ring insert in the center of the base, 3/8 inch across. It is
into this hole that the porcelain socket screws.
 
Could anyone tell me approximately when it was manufactured, by
what company, and whether it was used for a specific purpose
(i.e., industrial, interior lighting for a streetcar, etc.)?
 
Failing that, can anyone recommend any reference works that may be
of help?
 
Thanks...
Daniel
 
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Daniel M. Dumych          | "The whole earth is full of monuments
[log in to unmask] | to nameless inventors."  Otis T. Mann