A second descent was made in 1848 from the surface, and a third in the spring of 1870, in both of which Mr. Birkbeck took the lead. The apparatus employed consisted of a windlass (Fig. 3), supported on two baulks of timber, and a bucket, covered with a shield, sufficiently large to hold two people, and two guiding ropes to prevent the revolution of the bucket in mid air. There was also a party of navvies to look after the mechanical contrivances, and two ladders about eight feet long to provide for contingencies at the bottom. Thirteen of us went down, including three ladies. As we descended, the fissure gradually narrowed, until at the bottom it was not more than ten feet wide. The actual vertical descent was a hundred and ninety-eight feet. After running the gauntlet of the waterfall we landed in the bed of the stream, which hurried downwards over large boulders of limestone and lost itself in the darkness of a large cave, about seventy feet high. We traced it downwards, through pools and rapids to the first waterfall, of about twenty feet. This obstacle prevented most of the party going further, for the ladders were too short to reach to the bottom. By lashing them together, however, and letting them down, we were able to reach the first round with the aid of a rope, and to cross over the deep pool at the bottom. Thence we went on downwards through smaller waterfalls and rapids, until we arrived at a descent into a chamber, where the roar of water was deafening. Down to this point the daylight glimmered feebly, but here our torches made but little impression on the darkness. One of the party volunteered to go down with a rope, and was suddenly immersed in a deep pool; the rest, profiting by his misadventure, managed to cling on to small points of rock, and eventually to reach the floor of the chamber. We stood at last on the lowest accessible point of the cave, about 300 feet from the surface. It was indeed one of the most remarkable sights that could possibly be imagined. Besides the waterfall down which we came, a powerful stream poured out of a cave too high up for the torches to penetrate the darkness, and fell into a deep pool in the middle of the floor, causing such a powerful current of air that all our torches were blown out except one. The two streams eventually united and disappeared in a small black circling pool, which completely barred further ingress. [Illustration: FIG. 4.--Diagram of Helln Pot, showing Waterfall at the Bottom.]