196 Ilev.W.V. Harcourt on Lord Brougham's statements 



into the blood, which whatever it be being exhausted the rest 

 of the air is made useless, and no more fit for respiration ; 

 where yet he doth not exclude this use, that, together with 

 the expelled air, the vapours also steaming out of the blood 

 are thrown out. And inquiring what that may be in the air 

 so necessary to life he conjectures that it is the more subtle 

 and nitrous particles with which the air abounds which are 

 communicated to the blood through the lungs, and this aerial 

 nitre he makes so necessary to all life, that even plants them- 

 selves do not grow in earth deprived thereof*." 



In 1 673-74 he gave a fuller account of his opinions in an- 

 other treatise f, the views contained in which exhibit one of 

 the finest examples extant of the success with which a man of 

 philosophical genius, having seized a true principle, may de- 

 duce from the observation of a few facts distinctly apprehend- 

 ed a whole train of real and important consequences, long be- 

 fore the principle itself can be deemed to have been proved 

 by demonstrative experiments. 



In reproducing the theory of the Micrographia, he took no 

 care to give the original author of it the credit which was due ; 

 and in his own turn is passed unmentioned by Lavoisier, who 

 did not distinguish this precursor of his own discoveries from 

 the rest of his chemical predecessors, on whom he pronounces 

 this general censure — that " they all allowed themselves to be 

 carried away by the spirit of their age, which contented itself 

 with assertions without proofs, or at least often regarded very 

 slight probabilities as such!," — a censure which it is but just 

 to qualify by the reflection, that in experimental philosophy 

 solid proofs are not to be discovered without the preliminary 

 of happy conjectures. 



In this tract Mayow expressly says, " Though the particles 

 of air are very minute, and are vulgarly taken for an element 

 of the greatest simplicity, it appears to me necessary to judge 

 them to be a compound §; and he adds, — " it is manifest that 

 the air is deprived of its elastic force by the respiration of 

 animals much in the same manner as by the deflagration of 

 flame." The latter assertion he made good by experiment : 

 he not only observed, but measured, the amount of elastic 

 force lost in both these cases; and he proved that animals, 

 when confined in air which has been already diminished by 

 combustion, survive but half the time that they would have lived 



* " An account of two books — Tractatiis duo, prior tie Respiratione, 

 a Joh. Mayow, Oxon. 1668." Phil. Trans. No. 41. p. 833. 

 f Tract 5. Med. Phys. Imprini. Jul. 17, 1673. 

 \ Traite de Chimie. Discours preliminaire, tome i. p. 16. 

 § Tract, de parte aerea igncaque Spiritus Nitri, cap. 7« p. 114. 



