26 Proceedings of the Royal Physical Society. 



sible, indeed I think it is highly probable, that Cavendish, not 

 being able to account in the way he did for metals giving off 

 gas when subjected to the treatment referred to, might have 

 made some experiments to ascertain whether the gas did not 

 arise from the other ingredients he was using, and thus have 

 anticipated Lavoisier's great achievement. As the result of 

 all his training, however, his mind was evidently thoroughly 

 imbued with the idea that metals are compounds containing 

 phlogiston, and in the circumstances, what was more natural 

 than to conclude when he saw the metal, during his experi- 

 ment, disappearing, and gas being given off, that the former 

 was being decomposed, and that the gas which was generated 

 was the phlogiston arising from that decomposition. In the 

 year 1781 Cavendish made his great discovery — that one 

 with which his name is inseparably connected. Water, as 

 we all know, had for long been regarded as an element ; by 

 a series of masterly experiments, however, which he carried 

 out at this time. Cavendish clearly proved its compound 

 nature. He was led to his famous discovery by noticing 

 that in making some experiments in which he exploded a 

 mixture of inflammable air, or hydrogen as we now call it, 

 and common air, there was invariably a certain amount of 

 moisture or dew produced. This matter he at once set to 

 investigate, and in his own thorough and accurate fashion — 

 being careful to work quantitatively, as indeed he did in 

 almost all of his investigations. He took an accurately 

 measured quantity of inflammable air and burned it with 

 about two and a half times as much common air, and, in 

 order to be able better to examine the products of the com- 

 bustion, he caused the results of the burning to pass through 

 a long glass cylinder. By this means he got a deposit of 

 dew amounting in all to 135 grains, which, as it had no taste 

 or smell, and did not yield any residue or pungent odour on 

 evaporation, he rightly concluded must be water. In this 

 way, then, but by using many precautions, and making a 

 long series of calculations which it is quite unnecessary to 

 enumerate here, did Cavendish fairly prove the composition 

 of water. It has been suggested, and I believe with good 

 reason, that although Cavendish thus showed how water could 



