Is it ensure, insure, or assure?
vessel containing kerosene with a wick for burning to provide light. Such lamps were widely used from the 1860s, when kerosene first became plentiful, until the development of electric lighting. Compared with other oil lamps, they were safe, efficient, and simple to operate. The kerosene fed the wick by capillary action alone. An adjustment knob, the only mechanism needed, controlled the lamp's brightness by raising or lowering the wick to vary the size of the flame. A glass chimney, which was used more widely and effectively on kerosene lamps than on any previous lamps, enhanced the steadiness, brightness, and cleanness of the flame.