“It will not be altogether impertinent,” says the author, “with the Discourse of these gradient _Automata_ to mention what Mersennus doth so pleasantly and largely descant upon concerning the making of a ship wherein men may safely swim under the water. That such a Contrivance is feasible, and may be effected, is beyond all question, because it hath been already experimented here in _England_ by _Cornelius Dreble_; but how to improve it unto Publick Use and Advantage, so as to be serviceable for remote Voyages, the carrying of any considerable Number of Men, with Provisions and Commodities, would be of such excellent Use, as may deserve some further enquiry.” The difficulties are divided into three heads:— 1. “The letting-out or receiving in anything as there shall be occasion without the admission of Water. If it hath not such a convenience these kind of Voyages must needs be very dangerous and uncomfortable both by Reason of many noisome and offensive Things which should be thrust out, and many other needful Things which should be received in. Now herein will consist the Difficulty, for to contrive the opening of the Vessel so that anything may be put in or out, and yet the Water not rush into it with much Violence as it doth usually in the leak of a Ship.” The learned Doctor’s remedy is as follows: “Let there,” he says, “be certain leather bags made of several bignesses, long and open at both ends, and answerable to these let there be divers windows made in open places in the frame of the ship round the sides, to which one end of these bags might be fixed, the other end coming within the ship. The bag being thus fastened and tied close about towards the window, then any thing that is to be sent out might be safely put into that end within the ship: this being again close shut, and the other end loosened, the thing may be safely sent out without the admission of any water.” In taking anything in, it was to be first received into that part of the bag towards the window, which being close tied down at the other end may then be safely opened. [Illustration: A CONCERT IN A SUBMARINE. The _Diable Marin_ of W. Bauer. (1855.) ] “It is easy to conceive, how by such means as these a Person may be sent out or received in, as there shall be occasion; how the water which will perhaps by Degrees leak into several parts may be emptied out again, with divers other like advantages. Tho’ if there should be a leak at the bottom of the vessel, yet very little Water would get in, because the Air would get out.”