At length the hauling-chains, the air-chambers, and the automatic grappling-irons were put on board. J. T. Maston, Engineer Murchison, and the delegates of the Gun Club, were already in their cabins. They had but to start, which they did on the 21st of December, at eight o'clock at night, the corvette meeting with a beautiful sea, a north-easterly wind, and rather sharp cold. The whole population of San Francisco was gathered on the quay, greatly excited but silent, reserving their hurrahs for the return. Steam was fully up, and the screw of the Susquehanna carried them briskly out of the bay. It is needless to relate the conversations on board between the officers, sailors, and passengers. All these men had but one thought. All these hearts beat under the same emotion. Whilst they were hastening to help them, what were Barbicane and his companions doing? What had become of them? Were they able to attempt any bold maneuver to regain their liberty? None could say. The truth is that every attempt must have failed! Immersed nearly four miles under the ocean, this metal prison defied every effort of its prisoners. On the 23rd inst., at eight in the morning, after a rapid passage, the Susquehanna was due at the fatal spot. They must wait till twelve to take the reckoning exactly. The buoy to which the sounding line had been lashed had not yet been recognized. At twelve, Captain Blomsberry, assisted by his officers who superintended the observations, took the reckoning in the presence of the delegates of the Gun Club. Then there was a moment of anxiety. Her position decided, the Susquehanna was found to be some minutes to westward of the spot where the projectile had disappeared beneath the waves. The ship's course was then changed so as to reach this exact point. At forty-seven minutes past twelve they reached the buoy, it was in perfect condition, and must have shifted but little. "At last!" exclaimed J. T. Maston. "Shall we begin?" asked Captain Blomsberry. "Without losing a second." Illustration: THE DESCENT BEGAN. Every precaution was taken to keep the corvette almost completely motionless. Before trying to seize the projectile, Engineer Murchison wanted to find its exact position at the bottom of the ocean. The submarine apparatus destined for this expedition was supplied with air. The working of these engines was not without danger, for at 20,000 feet below the surface of the water, and under such great pressure, they were exposed to fracture, the consequences of which would be dreadful.