One of his first discoveries at the Pneumatic Institution on the 9th of April 1799 was that pure nitrous oxide (laughing gas) is perfectly respirable, and he narrates that on the next day he became "absolutely intoxicated" through breathing sixteen quarts of it for "near seven minutes." This discovery brought both him and the Pneumatic Institution into prominence. The gas itself was inhaled by Southey and Coleridge among other distinguished people, and promised to become fashionable, while further research yielded Davy material for his _Researches, Chemical and Philosophical, chiefly concerning Nitrous Oxide_, published in 1800, which secured his reputation as a chemist. Soon afterwards, Count Rumford, requiring a lecturer on chemistry for the recently established Royal Institution in London, opened negotiations with him, and on the 16th of February 1801 he was engaged as assistant lecturer in chemistry and director of the laboratory. Ten weeks later, having "given satisfactory proofs of his talents" in a course of lectures on galvanism, he was appointed lecturer, and his promotion to be professor followed on the 31st of May 1802. One of the first tasks imposed on him by the managers was the delivery of a course of lectures on the chemical principles of tanning, and he was given leave of absence for July, August and September 1801 in order to acquaint himself practically with the subject. The main facts he discovered from his experiments in this connexion were described before the Royal Society in 1803. In 1802 the board of agriculture requested him to direct his attention to agricultural subjects; and in 1803, with the acquiescence of the Royal Institution, he gave his first course of lectures on agricultural chemistry and continued them for ten successive years, ultimately publishing their substance as _Elements of Agricultural Chemistry_ in 1813. But his chief interest at the Royal Institution was with electro-chemistry. Galvanic phenomena had already engaged his attention before he left Bristol, but in London he had at his disposal a large battery which gave him much greater opportunities. His first communication to the Royal Society, read in June 1801, related to galvanic combinations formed with single metallic plates and fluids, and showed that an electric cell might be constructed with a single metal and two fluids, provided one of the fluids was capable of oxidizing one surface of the metal; previous piles had consisted of two different metals, or of one plate of metal and the other of charcoal, with an interposed fluid. Five years later he delivered before the Royal Society his first Bakerian lecture, "On some Chemical Agencies of Electricity," which J. J. Berzelius described as one of the most remarkable memoirs in the history of chemical theory. He summed up his results in the general statement that "hydrogen, the alkaline substances, the metals and certain metallic oxides are attracted by negatively electrified metallic surfaces, and repelled by positively electrified metallic surfaces; and contrariwise, that oxygen and acid substances are attracted by positively electrified metallic surfaces and repelled by negatively electrified metallic surfaces; and these attractive and repulsive forces are sufficiently energetic to destroy or suspend the usual operation of elective affinity." He also sketched a theory of chemical affinity on the facts he had discovered, and concluded by suggesting that the electric decomposition of neutral salts might in some cases admit of economical applications and lead to the isolation of the true elements of bodies. A year after this paper, which gained him from the French Institute the medal offered by Napoleon for the best experiment made each year on galvanism, he described in his second Bakerian lecture the electrolytic preparation of potassium and sodium, effected in October 1807 by the aid of his battery. According to his cousin, Edmund Davy,[1] then his laboratory assistant, he was so delighted with this achievement that he danced about the room in ecstasy. Four days after reading his lecture his health broke down, and severe illness kept him from his professional duties until March 1808. As soon as he was able to work again he attempted to obtain the metals of the alkaline earths by the same methods as he had used for those of the fixed alkalis, but they eluded his efforts and he only succeeded in preparing them as amalgams with mercury, by a process due to Berzelius. His attempts to decompose "alumine, silica, zircone and glucine" were still less fortunate. At the end of 1808 he read his third Bakerian lecture, one of the longest of his papers but not one of the best.