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That is a heat-lamp bulb probably dating to around the 1920s-30s or so. Thick carbon filament of 250 - 300 watts at 120 volts, it puts out a lot of heat that would have been used in a handheld fixture with a reflector for medicinal purposes - relieving muscle pain, etc. A concept that is still in use today, and by much the same means too.
The cone shaped spiral filament is known as the "stereopticon" shape, and helps concentrate the filament in to a small area. These lamps are very bright as well as giving out a lot of heat and as such were also used for projection in "magic lanterns" and possibly cinema projectors too. The stereopticon filament makes for a solid, bright light source when aligned properly, that could be focussed rather precisely making it ideal for projection. In the days before coiled tungsten filaments they were essentially all there was, asides from arc lamps.
They are often found with standard 4 or 5 loop filaments intended for medicinal uses only, the Stereopticon filament shape is a bit less common but still not that rare. I have also seen blue-glass and red-glass versions, presumably with standard filaments, which are likely to be more medicinal than decorative. For when the warmth is required but the bright glare would be undesirable, the dark glass would block out a lot of the light but not the heat. Those are quite rare and hard to find, so worth a fair amount ($40-ish?). The clear ones are worth less - unfortunately lamps like this are not hugely valuable, fetching maybe $10-15 or so, at least the last time I looked.
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