But if a diver feels helpless in the bag of a suit now commonly worn, what would he do when encased in a steel boiler; for that is virtually what the armored suit is! A common mistake that inventors of armor units have made is to fail to consider the effects of the enormous hydraulic pressure on the joints of the suit. In order to make them perfectly tight, packings must be employed, and these are liable to be so jammed by the hydraulic pressure that it is well nigh impossible to articulate the limbs. Again, the construction of the suit should be such that when a limb is flexed it would not displace any more water than when in an extended position, and vice versa. A diver may find that he cannot bend his arm, because in doing so he would expand the cubical content of his armor by a few cubic inches, and to make room for this increment of volume it would be necessary for him to lift several hundred pounds of water. The hydraulic pressure will reduce the steel suit to its smallest possible dimensions, which may result either in doubling up the members or extending them rigidly. But these difficulties are not insuperable. There is no reason why a steel manikin cannot be constructed with a man inside to direct its movements. THE SALVOR'S SUBMARINE Other schemes have been devised to relieve the diver of abnormally high air-pressure. One plan is to construct a large spherical working-chamber strong enough to withstand any hydraulic pressure that might be encountered. This working-chamber is equipped with heavy glass ports through which the workers can observe their surroundings in the light of an electric search-light controlled from within the chamber. The sphere is to be lowered to the wreck from a barge, with which it will be in telephonic communication and from which it will be supplied with electric current to operate various electrically driven mechanisms. By means of electromagnets this sphere may be made fast to the steel hull of the vessel and thereupon an electric drill is operated to bore a hole in the ship and insert the hook of a hoisting-chain. This done, the sphere would be moved to another position, as directed by telephone and another chain made fast. The hoisting-chains are secured to sunken pontoons and after enough of the chains have been attached to the wreck the pontoons are pumped out and the wreck is raised. It is a pity that ship-builders have not had the forethought to provide substantial shackles at frequent intervals firmly secured to the framing. A sunken vessel is really a very difficult object to make fast to and the Patent Office has recorded many very fantastic schemes for getting hold of a ship's hull without the use of divers. One man proposes the use of a gigantic pair of ice-tongs; and there have been no end of suggestions that lifting-magnets be employed, but no one who has any idea of how large and how heavy such magnets must be would give these suggestions any serious consideration.