relative to Black, Watt, and Cavendish. 489 



sume part of the air, proscribing the rest;" and having ob- 

 served upon it, that " though this opinion is not, as some of 

 the same author's, absurd, it should not be barely asserted, 

 but explicated and proved," proceeded to relate, that " that 

 deservedly famous mechanician and chemist Cornelius Dre- 

 bell contrived for the late learned king James a vessel to go 

 under water," and that on inquiry of Drebell's surviving rela- 

 tives into the principle of his contrivance, it appeared, that " he 

 conceived it to be not the whole body of the air, but a certain 

 quintessence or spiritual part of it that makes it fit for respi- 

 ration, which being spent, the remaining grosser body, or 

 carcase, if I may so call it, of the air, is unable to cherish the 

 vital flame residing in the heart; so that, for aught I could 

 gather," says Boyle, " besides the mechanical contrivance of 

 his vessel, he had a chemical liquor which he accounted the 

 chief secret of his navigation j for when from time to time he 

 perceived that the finer and purer part of the air was con- 

 sumed, or overclogged by the steams and respiration of those 

 that went in his ship, he would, by unstopping a vessel full of 

 this liquor speedily restore to the troubled air such a propor- 

 tion of vital parts, as would make it again for a good while fit 

 for respiration*." 



The experiments which Hook exhibited to the Royal So- 

 ciety in 1764 afforded, it must be allowed, but precarious 

 grounds for the theory of the composition of the atmosphere 

 which his sagacity advanced : he showed that in vessels con- 

 taining a limited quantity of air, combustibles burn and waste 

 for a limited time; and change its quality so that it is no 

 longer capable of supporting combustion ; and he showed that 

 they undergo no loss of substance when heated without air : 

 he took some live coals and put them under a glass vessel — 

 " whereupon the said cole in a little time went out; but being 

 then taken out, and exposed to the free air, recovered its 

 burning:" sulphur in like manner would not burn when 

 "hermetically sealed," and charcoal heated without air — " was 

 not sensibly diminished;" he added — "that a combustible 

 substance kept red-hot, yea in a fire as hot as to melt copper, 

 would not waste, but as soon as fresh air was admitted did 

 burn away and consume." Boyle proposed that trial should 

 be made whether the extinguished combustible could be re- 

 lighted by the burning-glass, or by red-hot iron ; and it was 

 found that it could not be rekindled without the admission of 

 air. * 



Yet nothing can be more accurate than the theoretical ac- 

 count of combustion given in the Micrographia, where, laying 

 * New Exp. Physico-mechanical. 



Phil. Mag. S. 3. Vol. 28. No. 189. June 1846. 2 L 



