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



scientific men at the period immediately preceding Black's dis- 

 coveries. The article f Air,' in the French Eficyclopedie, was 

 published in 1751, and written by D'Alembert himself. It is, 

 as might be expected, able, clear and elaborate. He assumes 

 the substance of the atmosphere to be alone entitled to the 

 name of air, and to be the foundation of all other permanently 

 elastic bodies. When D'Alembert wrote this article, he gave 

 the doctrine then universally received, that all the other kinds 

 of air were only impure, and that this fluid alone was perma- 

 nently elastic, all other vapours being only like steam, tempo- 

 rarily aeriform. Once the truth was made known, that there 

 are other gases in nature, only careful observation was re- 

 quired to find them out*." 



After all this, should I venture to affirm that you have post- 

 dated our knowledge of permanently elastic gases, other than 

 the atmosphere, by about a hundred years, were I to suggest 

 that in this case also the old story is the true one, and that 

 Priestley has correctly recorded the real historical fact when 

 he said, " Mr. Boyle, I believe, was the first who discovered 

 that what we call fixed air, and also inflammable air, are really 

 elastic fluids capable of being exhibited in a state unmixed with 

 common air," were I to add that the existence of various 

 elastic fluids was generally recognised by the philosophers of 

 Europe, and particularly by those whom you have quoted as 

 instances to the contrary, during the century which preceded 

 Black's essay, as distinctly, and more distinctly, than by Black 

 himself, — I know not what you would think of me. Neverthe- 

 less, since this is a passage in the history of science which de- 

 serves to be told with a strict regard to dry matter of fact, I 

 must beg you to listen with patience to an account of it cer- 

 tainly very different from your own. 



It was in December 1659 that Boyle published his " New 

 Physico-mechanical Experiments," among which is to be 

 found a description of two of those gases separable from fixed 

 bodies, which he subsequently denominated factitious airs. 

 The high interest which may be justly attached to all the 

 circumstances of discoveries so important as this, induces me 

 to give the details of it in the words of the author. 



" Contenting myself," he says, " to have mentioned our 

 author's (Kircher's) experiment as a plausible, though not de- 

 monstrative, proof that water may be transmuted into air, we 

 will pass on to mention, in the third place, another experi- 

 ment which we tried in order to the same inquiry. We took 

 a clear glass bubble, capable of containing by guess about 

 three ounces of water, with a neck somewhat long and wide of 

 * Life of Black, pp. 331-36. 



