These would prove of invaluable advantage in all operations performed at great sea depths, as its distinctive feature, "the regulator," could maintain, what is not done by any other diving armor, a constant equality of pressure on the lungs between the external and the internal air.
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.