August 9, 1894] 



NA TURE 



351 



though our mixture burns under water, yet it does not burn 

 without air, being supplied with enough to serve the turn 

 by the numerous eruptions of the aereal particles of 

 the dissipated nitre." However, he "removes this suspicion " by 

 obtaining nitre crystallised in vacuo. He then suggests the 

 possibility of the nitre supplying "vehemently agitated vapours " 

 which are no true air, but being exceedingly rarefied by the 

 fire " emulate air." Boyle never grasped the true function of 

 air in combustion. P'rom his later experiments on the calcina- 

 tion of metais he drew the same conclusion that we find in the 

 "Sceptical Chemist," namely, that igneous particles combine 

 with other corpuscles to form new bodies. And yet he saw 

 there was a real connection between air and fire. In his tract 

 on Artificial Phosphori, Boyle showed that a piece of phos- 

 phorus sealed up in a glass vessel gradually lost its light. " It 

 seems," he wrote, "that the air included with the phosphorus 

 either had some vital substance preyed upon thereby, or else 

 was tamed by the fumes of the phosphorus and rendered at 

 length unfit to continue the particular flame of our noctiluca. " 



The genius of Robert Hooke was in sharp contrast with that 

 of Boyle. Quick, restless, imaginative, he sprang from dis- 

 covery to discovery. With extraordinary acuteness and powers 

 of invention, he lacked the steady purpose of Boyle, the calm 

 judgment and completeness of Newton — -his two great scientific 

 contemporaries. It might be said of Hooke, as was said of a 

 great poet, he touched nothing he did not strike fire from ; and 

 some would add that his touch had the same effect on persons 

 as on things. We can hardly name a discovery of this age 

 which Hooke had not in part anticipated and claimed as his 

 own. Like a prospector in a newly discovered mining district, he 

 hurried from spot to spot, pegging in his claims and promising 

 to return to work out the ore. And what rich lodes he struck ! 

 The particular claim we are concerned with here is the discovery 

 of the relation between air and flame. In 1665 Hooke pub- 

 lished in the " Micrographia " a description of flame and the 

 phenomena of combution which in my judgment has never been 

 surpassed. How far he was indebted to Boyle will appear 

 directly. 



Born in 1635, Hooke spent five years at Westminster School, 

 then under Ur. Busby, and proceeded to Christ Church in 

 1653. At school and college it.is related of him that he devoted 

 his time to designing flying machines. These mechanical in- 

 ventions attracted the notice of Dr. Wilkins, Warden of Wad- 

 ham, and a leading member of the Philosophical Society. This 

 led to his introduction to Dr. Willis, to whom he became as- 

 sistant in chemistry and natural philosophy. Willis recommended 

 him to Boyle, whose assistant he became. His first work in 

 Boyle's laboratory was the construction of the improved air- 

 pump. In 1662 Eoyle obtained for him the position of curator 

 of experiments in the London Society, soon to be knowc as the 

 Royal Society. Hooke was thus Boyle's assistant when those 

 experiments on combustion I have described were being carried 

 on. Among other experiments made by Boyle were some on 

 the distillation of wood in retorts. 



"Having sometimes distilled such woods as box, whilst our 

 caput mortiium [i.e. the residue] remained in the retort it con- 

 tinued black like charcoal, though the retort were kept red hot 

 in a vehement fire ; but as soon as ever it was brought out of 

 that vessel into the open air the burning coals would degenerate 

 or fall asunder into pure white ashes." ' Hooke saw the experi- 

 ment and a new light flashed on him. " From the experiment 

 of charring coals, " he writes ** (whereby we see that, notwith- 

 standing the great heat, the solid parts of the wood remain, 

 whilst they are preserved from the free access of the air, undissi- 

 pated) we may learn that which has not been published or 

 hinted, nay, not such much as thought of by any ; and that in 

 short is this : — 



" That the air is the universal dissolvent of all sulphurous 

 \i,e. combustible] bodies. . . . 



" That this action of dissolution produces a very great heat, 

 and that which we call fire. 



" That this action is performed with so great a violence, and 

 does so rapidly agitate the smallest parts of the combustible 

 matter, that it produces in the diaphanous medium of the air 

 the action, or pulse of Light. 



" That this dissolution is made by a substance inherent and 

 mixed with the air, that is like, if not the very same with, that 

 which is mixed in saltpetre. 



" That the dissolving parts of the air are but few . . .whereas 

 ' " The Sceptical Cfiemist." 



NO. 1293, VOL. 50] 



saltpetre is a menstruum . . . that abounds more with these 

 dissolvent particles. 



' ' It seems reasonable to think that there is no such thing as an 

 element of fire, . . . but that that shining transient body which 

 we call flame is nothing else but a mixture of air and volatile 

 parts of combustible bodies, which are acting upon one another 

 whilst they ascend ; which action . . . does further rarifie those 

 parts that are acting or are very near them, whereby they, 

 growing very much lighter than the heavy parts of that men- 

 struum they are more remote, are thereby protruded and driven 

 upwards." 



Hooke quotes no other experiments in support of his theory 

 of flame. He states that he has made many; he has, however, 

 only time "to hint an hypothesis," which, if he is permitted 

 opportunity, he will "prosecute, improve, and publish." Some 

 years later he returned to his subject of flame in his tract called 

 " Lampas," published in 1677. "The flame, as I formerly 

 proved, being nothing but the parts of the oyl rarified and 

 raised by heat into the form of a vapour or smoak, the free air 

 that encompasseth this vapour keepeth it into a cylindrical 

 form, and by its dissolving property preyeth upon those parts 

 of it that are outwards, . . . producing the light which we 

 observe ; but those parts which rise from the wick which are 

 in the middle are not turned to shining flame till they rise 

 towards the top of the cone, where the free air can reach and 

 so dissolve them. With the help of a piece of glass anyone 

 will plainly perceive that all the middle of the cone of flame 

 neither shines nor burns, but only the outward superficies 

 thereof that is contiguous to the free and unsatiated air." 



What is practically the same theory of flame was worked out 

 experimentally by John Mayow, Fellow of All Souls : this was 

 published a few years after the " Micrographia." 



But Mayow went -further, and distinctly showed the dual 

 nature of the air. One constituent of air, the nitre air, is con- 

 cerned in respiration and combustion ; the other will neither 

 support flame nor animal life. The ideas, the names, proposed 

 by Hooke and Mayow are so exactly similar that it is impos- 

 sible to imagine that the work was done independently. The 

 two were working at the same time at Oxford, and Mayow, 

 having been an undergraduate at Wadham under Dr. Wilkins, 

 became the pupil of Willis. Yet Mayow nowhere mentions 

 Hooke's name. A writer in the "Dictionary of National 

 Biography"^ tias shrewdly observed that Hooke has brought 

 no charge of plagiarism against Mayow, and even proposed 

 him for the Royal Society four years after the publication of the 

 " Five Tracts." Knowing what we do of Hooke's jealousy, it 

 seems exceedingly unlikely that Mayow was merely working 

 out Hooke's ideas. It seems to me probable that Hooke and 

 Mayow worked together under Boyle between 1660 and 1662 j 

 that in Boyle's laboratory they saw and assisted in the experi- 

 ments which led them jointly to their theory ; that Hooke, busy 

 with other work in London, published the hypothesis in 1665- 

 without further verification : and that Mayow in Oxford sys- 

 tematically worked through the experiments on which he based 

 his conclusions. 



Let me briefly show what the experiments were on which 

 Mayow relied. Combustible bodies will not burn in the 

 vacuous receiver of Boyle's air-pump ; they will burn in vacua 

 or under water when mixed with nitre. There is, therefore, 

 something common to air and to nitre which causes combustion. 

 The fiery particles in air and in nitre both form oil of vitriol by 

 their union with sulphur ; they both form iron vitriol by their 

 union with pyrites. Rust of iron is produced both by the air 

 and by acid of nitre ; the acids of sugar and honey are formed, 

 and wine is soured in the same way. The nitreair (spiritus 

 nitro-aereus), the supporter of combustion and the acid pro- 

 ducer, is therefore the same chemical substance whether it exist 

 in the gaseous form in air or is condensed in saltpetre. 



Mayow heated a weighed quantity of antimony by means of a 

 burning glass, and found it increased in weight during the cal- 

 cination;- the calcined antimony, he adds, has the same pro- 

 perties as the body prepared by heating antimony with nitric 

 acid ; it is impossible to conceive, he says, whence the increase 

 in weight arises except by the fixation of the particles of nitre- 

 air during the heating. 



The nitreair does not make up the whole of the air, but only 

 its more active and subtle part, for a candle under a glass will 



1 Mr. P. J. Hartog. 



- This experiment seems to have been first described by Poppius, Bctsilica 

 .Intit'cQnii. 1625. 



