“He built a ship in which one could row and navigate under water from Westminster to Greenwich, the distance of two Dutch miles; even five or six miles, or as far as one pleased. In this boat a person could see under the surface of the water and without candle-light, as much as he needed to read in the Bible or any other book. Not long ago this remarkable ship was yet to be seen lying in the Thames or London river.” As to what Drebbel’s “Chymicall Liquor” really was there is no chance of discovering. Professor W. P. Bradley has pointed out that the name “Quintessence of Air” is very suggestive of oxygen. The life-giving component of air (not discovered until a century and a half after Drebbel’s time) is volumetrically the “quintessence,” the fifth part of air. “Is it possible,” he asks, “that Drebbel had discovered some liquid which easily disengaged the then unknown oxygen gas and thus was able to restore to vitiated air that principle of which respiration deprives it? Undoubtedly not. It is much more likely that he possessed a solution capable of absorbing the carbonic acid gas which is produced by respiration, and that the name given it was entirely fanciful and without special significance. But even if Drebbel’s claim was a piece of pure quackery with no substantial basis at all, it is nevertheless not without interest, for it shows, as we might have anticipated, that the problem of ventilation, one of the most important with which the inventors of submarines have to deal, was at least appreciated by Drebbel the pioneer.” A writer of the period, one Harsdoffer, tells how Drebbel was led to the construction of his boat:— “One day when walking along the banks of the Thames Drebbel noticed some sailors dragging behind their barques baskets full of fish; he saw that the barques were weighed down in the water, but that they rose a little when the baskets allowed the ropes which held them to slacken a little. The idea occurred to him that a ship could be held under the water by a somewhat similar method and could be propelled by oars and poles. Some time afterwards he constructed two little boats of this nature, but of different sizes, which were tightly closed with thick skin, and King James himself journeyed in one of them on the Thames. There were on this occasion twelve rowers besides the passengers, and the vessel during several hours was kept at a depth of twelve to fifteen feet below the surface.” This royal excursion under water terminated, we read, “fort hereusement.” The Abbé de Hautefeuille, in a brochure which appeared in 1680 entitled “Manière de respirer sous l’Eau,” writes thus:—