While our author will not go so far as to say that a man may by custom, “which in other things doth produce such strange incredible effects,” be enabled to live in the open Water as do the fishes, yet he thinks that long use and custom may strengthen men against many such inconveniences of this kind which to inexperienced persons may prove very hazardous: thus it will not perhaps be so necessary to have the air for breathing so “pure and desecated” as is required for others. The difficulty of respiration under water may be met in several ways. “The submarine ark should be of such a large capacity that as the air is corrupted in one part so it may be purified and renewed in the other: if the mere refrigeration of the air would fit it for breathing, this might be somewhat helped with bellows, which would cool it by motion: it is not altogether improbable,” says the doctor, “that the lamps and fires in the middle of it like the reflected beams in the first region rarefy the air and the circumambient coldness towards the sides of the vessel like the second region, cooling and condensing of it would work such a Vicissitude and change of air as might fit it for all its proper uses.” Finally, if none of these conjectures will help, the author mentions that there is in France one Barrières, a diver, who hath found out the art whereby a man might easily continue under water for six hours together, “whereas Ten Cubical Feet of Air will not serve another Diver to breathe in for Half an Hour, he by the help of a Cavity not above one or two Foot at most will have Breath enough for six hours and a Lanthorne scarce above the usual size to keep a candle burning as long as a Man please. Which (if it be true and were commonly known) might be sufficient help against the greatest difficulty.” Dr. Wilkins makes no mention of the “Chymicall Liquor” which Drebbel is reported to have discovered for the purifying of the air inside the boat when under water, and it is probable that he attached little value to the accounts of this remarkable substance. Having so far dealt with the difficulties of submarine navigation and their remedies, the author proceeds to discuss the many advantages and conveniences of such a contrivance. _First of all_, says he—“’Tis private; a Man may thus go to any Coast of the World invisibly without being discovered or prevented in his journey.” Certainly this would be a convenience to the criminal fleeing from justice, to a deposed ruler wishing to escape from his conquerors, and to others desirous of effacing themselves for a time.