[54] M. Humboldt (_Ueber die gereize Faser_, l. 473, 1797,) quotes part of a letter from Dr. Ash, in which it is said that, "if two finely polished plates of homogeneous zinc be moistened and laid together, little effect follows; but if zinc and silver be tried in the same way, the whole surface of the silver will be covered with oxidated zinc. Lead and quicksilver act as powerfully upon each other, and so do iron and copper." M. Humboldt says, that, in repeating this experiment, he saw air bubbles ascend, which he supposes to have been hydrogen gas from the decomposition of water. In the Bakerian Lecture[55] read before the Royal Society in 1826, Davy, in giving a retrospective view of the progress of Electro-chemical Science, very justly remarks, that the true origin of all that has been done in this department of philosophy was the accidental discovery of Nicholson and Carlisle, of the decomposition of water by the pile of Volta, on the 30th of April, in the year 1800; which was immediately followed by that of the decomposition of certain metallic solutions, and by the observation of the separation of alkali on the negative plates of the apparatus. Mr. Cruickshank, in pursuing these experiments, obtained many new and important results, such as the _decomposition of the muriates of magnesia_, _soda_, and _ammonia_; and also observed the fact, that alkaline matter always appeared at the negative, and acid matter at the positive pole.[56] [55] As this lecture will be frequently mentioned in the progress of these Memoirs, in connexion with most important discoveries, it may be interesting to the reader to learn something of its foundation and design. I have therefore collected the necessary information from the Minutes of the Royal Society. Mr. Baker is well known in the history of Science, as an accurate observer with the microscope, and as the author of several works on the subject. By his will, dated July 1763, he bequeathed the sum of one hundred pounds, the interest of which he directed "to be applied for an Oration or Discourse, to be read or spoken yearly by some one of the Fellows of the Royal Society, on such parts of Natural History, or Experimental Philosophy, at such time, and in such manner, as the President and Council of the said Society shall please to order and appoint; on condition, nevertheless, that if any one year shall pass after the payment of the said hundred pounds, without such oration or discourse having been read or spoken at some Meeting of the said Royal Society, the said hundred pounds shall then become forfeited, and shall be repaid by the said Society to his executors," &c. Baker died in November 1774, and in the following year a Fellow was nominated to read the lecture. It is a whimsical circumstance, that the first lecturer should have been PETER WOULFE, the last of the alchemists. The names of the successive lecturers were as follow:--Dr.