The bulb you have is often referred to as a "turn down lamp" or simply a "hilo" or "hylo" type lamp. Turn down lamps had two filaments - a normal wattage type and a smaller low wattage filament. The filaments could be controlled by various ways depending on the type of turn down lamp. The most common turn down lamps are probably those with the pull strings that activated a switching mechanism in or on the lamp's base. Your bulb probably dates to about 1900, give or take a couple of years, but this is just a guess since I have not seen the bulb. If possible, consider posting a photo here of the bulb.
