436 Life of Cavendish 



to his eye ; and all the operations of his intellectual powers exhibit a degree of 

 caution almost unparalleled in the annals of science, for there is scarcely a single 

 instance in which he had occasion to retrace his steps or to recall his opinions. 

 In 1760 he became a Fellow of the Royal Society, and continued for almost 

 fifty years to contribute to the Philosophical Transactions some of the most 

 interesting and important papers that have ever appeared in that collection, 

 expressed in language which affords a model of concise simplicity and unaffected 

 modesty, and exhibiting a precision of experimental demonstration com- 

 mensurate to the judicious selection of the methods of research and to the 

 accuracy of the argumentative induction; and which have been considered, 

 by some of the most enlightened historians, as having been no less instru- 

 mental in promoting the further progress of chemical discovery, by banishing 

 the vague manner of observing and reasoning that had too long prevailed, 

 than by immediately extending the bounds of human knowledge with respect 

 to the very important facts which are first made public in these communications. 



i. Three Papers containing Experiments on Factitious Air. (Phil. Trans. 

 1766, p. 141.) It had been observed by Boyle, that some kinds of air were unfit 

 for respiration; and Hooke and Mayow had looked still further forwards into 

 futurity with prophetic glances, which seem to have been soon lost and for- 

 gotten by the inattention or want of candour of their successors. Hales had 

 made many experiments on gases, but without sufficiently distinguishing their 

 different kinds, or even being fully aware that fixed air was essentially different 

 from the common atmosphere. Sir James Lowther, in 1733, had sent to the 

 Royal Society some bladders filled with coal-damp, which remained inflammable 

 for many weeks little imagining the extent of the advantages which were one 

 day to result to his posterity from the labours of that society by the prevention 

 of the fatal mischiefs which this substance so frequently occasioned. Dr Seip 

 had soon after suggested that the gas which stagnated in some caverns near 

 Pyrmont was the cause of the briskness of the water; Dr Brownrigg of White- 

 haven had confirmed this opinion by experiments in 1741 ; and Dr Black, in 

 1755, had explained the operation of this fluid in rendering the earths and 

 alkalis mild. Such was the state of pneumatic chemistry when Mr Cavendish 

 began these experimental researches. He first describes the apparatus now 

 commonly used in processes of this kind, a part of which .had been before 

 employed by Hales and others, but which he had rendered far more perfect 

 by the occasional employment of mercury. He next relates the experiments 

 by which he found the specific gravity of inflammable air to be about -,-\ of 

 that of common air] whether it was produced from zinc or otherwise: first 

 weighing a bladder filled with a known bulk of the gas, and then in a state of 

 collapse; and also examining the loss of weight during the solution of zinc in 

 an acid, having taken care to absorb all the superfluous moisture of the gas by 

 means of dry potass. He also observed that the gas obtained during the solu- 

 tion of copper in muriatic acid was rapidly absorbed by water, but he did not 

 inquire further into its nature. The second paper relates to fixed air, which was 

 found to undergo no alteration in its elasticity when kept a year over mercury; 





