The first year of the nineteenth century is further memorable on account of the invention of the voltaic pile, and by reason of its application by =William Nicholson= and =Sir Anthony Carlisle= to the electrolytic decomposition of water. This mode of resolving water into its constituents made a great sensation at the time, mainly because of the extraordinary method by which it was effected. It afforded an independent and unlooked-for proof of the compound nature of water by a method altogether differing in principle from that by which its composition had been previously ascertained. The formation of water by the combustion of hydrogen brought no conviction of its real nature to a confirmed phlogistian like Priestley; and it is even doubtful whether Cavendish ever fully realised the true significance of his great discovery. But the fact that the quantitative results of the analysis thus effected were identical with those of its synthesis, as made by Cavendish and Lavoisier, admitted of only one interpretation. This cardinal discovery may be said to have completed the downfall of phlogiston. The value of the voltaic pile as an analytical agent was nowhere more quickly appreciated than in England. In the hands of Humphry Davy its application to the analysis of the alkalis and alkaline earths led to discoveries of the greatest magnitude. =Humphry Davy= was born in Penzance in 1778. In the course of his studies for the profession of medicine he was attracted to chemistry; and he became chemical assistant to Dr. Beddoes, a former teacher of chemistry at Oxford, but then living at Clifton, near Bristol. While in the capacity of assistant and operator in Beddoes’s Pneumatical Institute, Davy discovered the intoxicating properties of _nitrous oxide_ (so called laughing gas), which brought him into prominence and led to his engagement by the managers of the newly-created Royal Institution in London as lecturer in chemistry in succession to Garnett. He early began to experiment on galvanism, and soon succeeded in developing the fundamental laws of electro-chemistry; and in 1807 he effected the _decomposition of potash and soda_ by the application of voltaic electricity—thereby establishing, what indeed had been surmised previously, that the alkalis are compound substances. He subsequently proved that this was also the case with the alkaline earths. Davy thus added some five or six metallic elements to those already known. These discoveries, perhaps the most brilliant of their time, afforded additional evidence of the invalidity of Lavoisier’s assumption that oxygen, as the name implies, was the “principle of acidity.” The surmise, in fact, was already disproved by the case of water—a neutral substance and devoid of all the recognised attributes of an acid. It was still further disproved by the cases of potash and soda—strongly alkaline compounds.