"Drebbel conceiv’d, that 'tis not the whole body of the Air, but a certain Quintessence (as Chymists speake) or spirituous part of it, that makes it fit for respiration, which being spent, the remaining grosser body, or carcase to cherish the vitall flame residing in the heart: So that (for ought I could gather) besides the Mechanicall contrivance of his vessell he had a Chymicall liquor, which he accounted the chiefe Secret of his submarine Navigation. For when from time to time he perceiv’d, that the finer and purer part of the Air was consum'd, or over clogg’d by the respiration, and steames of those that went in his ship, he would, by unstopping a vessell full of this liquor, speedily restore to the troubled Air such a proportion of Vitall parts, as would make it againe, for a good while, fit for Respiration, whether by dissipating, or precipitating the grosser Exhalations, or by some other intelligible way, I must not now stay to examine; Contenting my selfe to add, that having had the opportunity to do some service to those of his Relations, that were most Intimate with him, and having made it my business to learne what this strange Liquor might be, they constantly affirm'd that Drebell would never disclose the Liquor unto any, nor so much as tell the matter whereof he made it, to above one Person, who himselfe assur'd me that it was. ...I have been sometimes inclin'd to favourable thoughts of their opinion, who would have the Aire necessary to ventilate, and cherish the vitall flame, which they do suppose to be continually burning in the heart. For we see, that in our Engine the flame of a Lamp will last almost as little after the Exsuction of the Air, as the life of an Animall ..."