The glow of phosphorescent bodies, suggested by the monk Mersenne for illuminating the interior of a submarine, later in the seventeenth century and actually so used by Bushnell in the eighteenth, might have furnished sufficient light for Bible- and compass-reading on this voyage. But how did King James--the first and last monarch to venture on an underwater voyage--the other passengers, and the twelve rowers get enough air? “That deservedly Famous Mechanician and Chymist, Cornelius Drebell ... conceived, that ’tis not only the whole body of the air but a certain Quintessence (as Chymists speake) or spirituous part that makes it fit for respiration ... so that (for aught I could gather) besides the Mechanicall contrivance of his vessel he had a Chymicall liquor, which he accounted the chief secret of his Submarine Navigation. For when from time to time he perceived that the finer and purer part of the air was consumed or over-clogged by the respiration and steames of those that went in his ship, he would, by unstopping a vessel full of liquor speedily restore to the troubled air such a proportion of vital parts as would make it again for a good while fit for Respiration.”[3] Did Van Drebel anticipate by one hundred and fifty years the discovery of oxygen: the life-giving “Quintessence” of air? Even if he did, it is incredible that he should have found a liquid, utterly unknown to modern chemistry, capable of giving off that gas so freely that a few gallons would restore the oxygen to a confined body of air as fast as fifteen or twenty men could consume it by breathing. Perhaps his “Chymicall liquor” instead of producing oxygen directly, increased the proportion of it in the atmosphere by absorbing the carbonic acid gas. The Abbé de Hautefeullie, who wrote in 1680 on “Methods of breathing under water,” made the following shrewd guess at the nature of the apparatus: “Drebel’s secret was probably the machine which I had imagined, consisting of a bellows with two valves and two tubes resting on the surface of the water, the one bringing down air and the other sending it back. By speaking of a volatile essence which restored the nitrous parts consumed by respiration, Drebel evidently wished to disguise his invention and prevent others from finding out its real nature.” [Illustration: Courtesy of the Scientific American. The _Rotterdam Boat_.]