Dear cdman,
I'll take a stab at this. The base on your bulb is a porcelain Thomson-Houston base. Originally, these were brass. Around 1897/98, the porcelain version was introduced. By the turn of the century, Thomson-Houston bases were waning as the standard Edison screw base was becoming predominant. So, your lamp likely dates from about 1897-1900 or so.
The other thing I could make out in your picture was the "U" shaped filament, often referred to as a "hairpin" filament. While these were the standard in the earliest bulbs, by the time period of your bulb this kind of filament was primarily used in lower voltage lamps such as 55 volt lamps. If you try to light it up, be sure to use a variac. If I'm correct about this being a lower voltage lamp, as you can imagine, trying it out on a 120 volt circuit will fry the filament.
As to the manufacturer, it's hard to say. Until the early 1920's, light bulbs often had paper labels glued to the outside of the glass envelope giving details such as manufacturer and rating. Often, these labels don't survive the ravages of time. Looks like yours doesn't have a label anymore.
Sometimes a close examination of the glass stem press inside the lamp reveals a possible manufacturer as some are distinctive.
In any case, you have a very nice collector bulb, well over 100 years old.
Regards,
PCris
