But perhaps the most useful article of all was a new form of diving bell called the _Nautilus_, a kind of submarine boat, capable of lateral as well as vertical movement at the will of its occupants. Constructed with double sides, the intervening chambers could be filled either with water or air according as descent or ascent was required. A proper supply of water enabled the machine to descend to depths impossible to be reached otherwise; this water could then be expelled by an ingenious contrivance, which, replacing it with air, enabled the diver to rise towards the surface as fast as he pleased. All these and many other portions of the submarine apparatus which had been employed that very year for clearing the channel, lifting the wrecks and recovering the treasure, lay now at San Francisco, unused fortunately on account of the season of the year, and therefore they could be readily obtained for the asking. They had even been generously offered to Captain Bloomsbury, who, in obedience to a telegram from Washington, had kept his crew busily employed for nearly two weeks night and day in transferring them all safely on board the _Susquehanna_. Marston was the first to make a careful inspection of every article intended for the operation. "Do you consider these buoys powerful enough to lift the Projectile, Captain?" he asked next morning, as the vessel was briskly heading southward, at a distance of ten or twelve miles from the coast on their left. "You can easily calculate that problem yourself, Mr. Marston," replied the Captain. "It presents no difficulty. The Projectile weighs about 20 thousand pounds, or 10 tons?" "Correct!" "Well, a pair of these buoys when inflated can raise a weight of 30 tons." "So far so good. But how do you propose attaching them to the Projectile?" "We simply let them descend in a state of collapse; the diver, going down with them, will have no difficulty in making a fast connection. As soon as they are inflated the Projectile will come up like a cork." "Can the divers readily reach such depths?" "That remains to be seen Mr. Marston." "Captain," said Morgan, now joining the party, "you are a worthy member of our Gun Club. You have done wonders. Heaven grant it may not be all in vain! Who knows if our poor friends are still alive?" "Hush!" cried Marston quickly. "Have more sense than to ask such questions. Is Barbican alive! Am _I_ alive? They're all alive, I tell you, only we must be quick about reaching them before the air gives out. That's what's the matter! Air! Provisions, water--abundance! But air--oh! that's their weak point! Quick, Captain, quick--They're throwing the reel--I must see her rate!" So saying, he hurried off to the stern, followed by General Morgan. Chief Engineer Murphy and the Captain of the _Susquehanna_ were thus left for awhile together.