The fate of the unhappy Person thrust out of the Vessel by means of the leather bags is too dreadful to contemplate, and the sailors called upon to man a modern war submarine may congratulate themselves that this convenient contrivance imagined by the ingenious prelate has not come into use. As to the taking in of things into the boat one does not quite gather how they would get into the bag, or how the bag would be first untied and then tied again by those inside the vessel. The second difficulty in such an Ark is “the Motion or fixing of it according to occasion: the directing of it to several places as the Voyage shall be designed, without which it would be very useless, if it were to remain only in one Place, and were to remove only blindfold, without any certain Direction: And the Contrivance of this may seem very difficult because these submarine Navigators will want the usual advantages of Wind and Tide for Motion, and the sight of the Heavens for direction.” The progressive motion of the boat would be effected by the help of several oars made to contract and dilate like the fins of a fish, the holes through which they pass into the ship being tied about with the afore-mentioned Leather Bags. “It will not be convenient, perhaps, that the motion in these Voyages should be very swift because of those Observations and Discoveries to be made at the Bottom of the Sea, which in a little space may abundantly recompense the slowness of the Progress.” Dr. Wilkins had grasped the fact that if the Ark were so ballasted as to be equal weight with the like magnitude of Water, it would then be easily movable in any Part of it. As for the ascent and descent of the craft this was to be accomplished by “some great Weight at the Bottom of the Ship (being Part of its Ballast), which by some Cord within may be loosened from it. If this Weight is let loose so will the Ship ascend from it (if need be) to the very Surface of the Water; and again as it is pulled close to the Ship, so will it descend.” The idea of taking in Water-ballast for sinking the Ark does not seem to have occurred to the Author. For directing the course of the Vessel the Mariner’s Needle would be employed, but the patent difficulty of all is this, “How the Air may be supplied for Respiration, How constant Fires may be kept in for light and the Dressing of Food, how those Vicissitudes of Rarefaction and Condensation may be maintained.”