CAVENDISH. D3 



compared in this respect air with water. It is, how- 

 ever, sufficiently clear, that neither of these experi- 

 ments gave the relative measure of one air with an- 

 other: nor, indeed, could they be said to compare 

 common air with either mercury or water, although 

 they certainly showed the relative specific gravities of 

 the two bodies, taking air for the middle term or com- 

 mon measure of their weights. 



The common accounts in chemical and in biographi- 

 cal works are materially incorrect respecting the man- 

 ner in which Mr. Cavendish was led to make his great 

 experiment upon the composition of water in 1781 

 and the following years. It is said, that while making 

 his experiments on air in 1765 and 1766, he had ob- 

 served for the first time, that moisture is produced by 

 the combustion of inflammable air, and that this led 

 him, sixteen or seventeen years later, " to complete the 

 synthetical formula of water, and to find that the moist- 

 ure that he had before observed was simple water."* 

 Nothing can be more erroneous than this whole state- 

 ment. In Mr. Cavendish's paper, of 1766, upon fixed 

 and inflammable airs, there is not one word said of the 

 moisture formed by the combustion ; and respecting 

 inflammable air, the experiments are confined entirely 

 to its burning or exploding, to its specific gravity, and 

 to its production. The paper of 1 784 is, in fact, en- 

 titled ' Experiments upon Air,' and it commences with 

 stating, not that those experiments were undertaken 

 with any view to the water formed by burning inflam- 

 mable air, but that they were made " with a view to 

 find out the cause of the diminution which common 



Penny Cyclopaedia, vol. vi., p. 392. This and other similar accounts 

 are plainly given by some persons who never read Mr. Cavendish's writ- 

 ings. But a still greater error occurs in them ; they represent him as 

 having first shown that fixed and inflammable airs are separate bodies 

 from common air; whereas Dr. Black, in his Lectures from 1755 down- 

 wards, showed this distinctly by his experiments, proving clearly that 

 these gases have nothing in common with the atmospheric air (vol. ii., 

 f. 87, 88). 



