508 Rev. W. V. Harcourt on Lord Brougham's statements 



B* 



was a different substance from the chalk with which he began 

 it, and that the consequence therefore which he drew from the 

 weight remaining the same was a fallacy. The compounds of 

 sulphur, I perceive, are a stumbling-block even to you * : to 

 Bernoulli's reputation as an experimental philosopher they 

 are more fatal than he deemed them to animal life ; for the 

 wholesomeness of the air from so " benign " an acid as oil of 

 vitriol, and " a globule of the earthy kind, as in his own ex- 

 periment," was an assumption which the first trial would ha've 

 discovered to be false. But it is more surprising that the 

 computations, congenial to his own studies, which he pro- 

 ceeded to make, of the amount of condensation of the air, in 

 the pores of the chalk, should not have apprised him that the 

 globule on which he experimented mast have lost weight, when 

 so great a volume of condensed air was disengaged from it. 



At a later period the younger Bernoulli paid so much re- 

 spect to his father's opinion as to speak of the multiplicity of 

 airs as a doubtful question. " The question," he says, " has 

 long been agitated, whether the factitious elastic aura brought 

 out of bodies, is ordinary air, or not; which question I shall 

 not decide. If however the air of gunpowder be taken to be 

 1000 times denser than natural air, and 10,000 more elastic, 

 then it follows from what precedes, that air compressed by an 

 infinite force cannot be condensed more than 1331 times, and 

 according to the same rule the elasticity of an air four times 

 more dense than the natural air would be to the elasticity of 

 natural air as 4 + ^ to 1. But whether the experiments insti- 

 tuted by others, which make the ratio of these elasticities as 

 4 to 1, were conducted with sufficient accuracy, and whether 

 the heat of the air, whilst under pressure, remained the same, 

 I know not. It is probable however that the same aura which 

 lies latent in the pores of the gunpowder is the cause of the 

 elasticity of elastic bodies, and contractile villous materials ; 

 for when bodies are reduced by any force to an unnatural form, 

 the elastic aura abounding in the little vacuities is compressed, 

 and in giving the form of greatest space to those vacuities 

 brings the body back to its original shape and extent." 



In the English school, however, of pneumatic chemistry, 

 and in the chief successor to the views and experiments of 

 Boyle and Hook, of Mayow and Newton, there was no hesi- 

 tation on this point. You have quoted the opinion of Hales, 

 as representing, instar omnium, the general notion among ex- 

 perimental philosophers before the time of Black, that air was 

 a single and simple element; and your inaccuracy on this 

 point is not to be wondered at; because Hales's opinion has 

 * Note to the Lives of Cavendish, Watt and Black, vol. ii. p. 511. 



