suddenly there was the momentary gleam of a light up in the direction of the ventilator, which vanished immediately, but was succeeded by a strong smell of burning oil and heated metal. someone in the next room had lit a dark-lantern. i heard a gentle sound of movement, and then all was silent once more, though the smell grew stronger. for half an hour i sat with straining ears. then suddenly another sound became audible—a very gentle, soothing sound, like that of a small jet of steam escaping continually from a kettle. the instant that we heard it, holmes sprang from the bed, struck a match, and lashed furiously with his cane at the bell-pull.