The above books seem to have won popular approval because they appear in several editions. Bishop Wilkins died in 1672 after a life full of strenuosity, variety and action. It is with his scientific publication standing fifth in the above list that we are specially interested. This little book, which treats of a great number of mechanical devices and principles such as wheels, pulleys, screws, engines of war, clocks and other similar machines, contains two chapters, one entitled, “Concerning the Art of Flying. The several ways whereby this hath been, or may be attempted”; and the other, “Concerning the Possibility of framing an Ark for Submarine Navigation. The Difficulties and Conveniences of such a Contrivance.” The latter chapter is the one that bears on our present discussion. Although Wilkins gives credit to Mercennus, who as he puts it, “doth so largely and pleasantly descant upon the making of a ship wherein men may safely swim under the Water,” nevertheless he follows the line of thought of Bourne without giving him credit. He closely imitated Bourne’s scheme of leather attachments. He suggested leather bags open at both ends, one end being without and the other within the ship, the ends capable of being closed like those of a purse. These bags he would use as means of ingress and egress for men and materials. Motion he proposed to obtain by means of oars whose blades would be collapsible on the back stroke, the oars projecting through the ship’s sides, the holes being closed with leather attached to the oars and vessel. Wilkins had in mind the use of such a vessel in attack against a “Navy of Enemies, who by this means may be undermined in the water and blown up.” The submersible power Wilkins would obtain by having his boat or “Ark” ballasted so as to be of “equal weight with the like magnitude of water,” that is, to be at the critical point between floating and sinking, obviously one of greatest danger. He fancied that he could then obtain vertical motion or plunging by attaching a great weight to the bottom of the ship, to be computed, of course, as part of the ballast. If the weight were lowered by means of a cord, so would the boat ascend, and if the weight were raised, it would descend. The method of supplying air to the submerged crew was equally amusing. He depended upon the ability of men to live in a polluted atmosphere by continued practice, or if that were found impossible, the air might be purified by what he calls “refrigeration,” that is, by heating it by lamps and allowing it to cool on coming in contact with the sides of the vessel, the process being assisted by bellows. It is hoped that the theology of the undoubtedly worthy bishop was sounder than his science, and that it emulated rather the particularly high scale of wisdom of his political adaptability. But no matter how ridiculous his details, he, nevertheless, left the main idea more firmly implanted in men’s minds.