Just when the ancient lamp was invented in the form of a vessel filled with oil into which some kind of wick was dipped, cannot be ascertained, but its invention certainly antedated the Christian Era by several centuries. And it is equally certain that once this smoky, foul-smelling lamp had been discovered, it remained in use, practically without change or improvement, until the end of the twelfth century, the date of the invention of the candle. Such lamps were used by the Greeks and Romans, great quantities of them being still preserved. They were simply shallow, saucer-like vessels for holding the oil, into which the wick was laid, so arranged that the upper end rested against the edge of the vessel. Here the oil burned and smoked, capillarity supplying oil to the burning end of the wick, which was pulled up from time to time as it became shortened by burning, either with pincers made for the purpose, or perhaps more frequently by the ever useful hairpin of the matron. As the thick wick did not allow the air to penetrate to burn the carbon of the oil completely, a nauseous smoke was given off constantly which was stifling when a draught of air prevented its escape through the hole in the roof--the only chimney used by the Greeks. And since this was the only kind of lamp known at the time, the palace of the Roman Emperor and hut of the Roman peasant were necessarily alike in their methods of lighting if in little else. The Emperor's lamps might be modeled of gold and set with precious stones, while those of the peasant were of rudely modeled clay; but each must have evoked, along with its dim light, an unwholesome modicum of smoke and malodor. It was this form of lamp, practically unaltered except occasionally in design, that remained in common use during the Middle Ages; and when, at the close of the twelfth century, the "tallow candle" was invented, that now despised device must have been almost as revolutionary in its effect as the incandescent burner and the electric bulb were destined to be in a more recent generation. It burned with dazzling brilliancy in comparison with the oil lamp; it gave off no smoke and little smell; it needed no care, and it occupied little space. Then for the first time in the history of the world reasonably good house illumination became possible. Several additional centuries elapsed, however, before the idea was developed of placing a candle in a covered glass-sided receptacle, to form a lantern or a street lamp.