 The professor set about testing our Rumkoff's coil, which would soon be needed to provide us with light in the galleries. While he was doing so, Hans hitched the raft to a projecting rock scarcely 20 paces distant from the gallery. At length, my uncle declared that he was ready, and we advanced in single file, myself in the lead. The opening to the gallery was circular, about five feet in diameter. The floor was roughly at water level, and we were able to enter it without hindrance.