In the progress of our ascent, it is refreshing to pause occasionally, and to cast a glance at the horizon, which widens at every increase of our elevation. By the decomposition of the alkalies and earths, what an immense stride has been made in the investigation of nature!--In sciences kindred to chemistry, the knowledge of the composition of these bodies, and the analogies arising from it, have opened new views, and led to the solution of many problems. In Geology, for instance, has it not shown that agents may have operated in the formation of rocks and earths, which had not previously been known to exist? It is evident that the metals of the earths cannot remain at the surface of our globe; but it is probable that they may constitute a part of its interior; and such an assumption would at once offer a plausible theory in explanation of the phenomena of volcanoes, the formation of lavas, and the excitement and effects of subterranean heat, and might even lead to a general theory in Geology. The reader, for the present, must be satisfied with these cursory hints: I shall hereafter show that our illustrious philosopher followed them up by numerous observations and original experiments in a volcanic country. I remember with delight the beautiful illustration of his theory, as exhibited in an artificial volcano constructed in the theatre of the Royal Institution.--A mountain had been modelled in clay, and a quantity of the metallic bases introduced into its interior: on water being poured upon it, the metals were soon thrown into violent action--successive explosions followed--red-hot lava was seen flowing down its sides, from a crater in miniature--mimic lightnings played around: and in the instant of dramatic illusion, the tumultuous applause and continued cheering of the audience might almost have been regarded as the shouts of the alarmed fugitives of Herculaneum or Pompeii. CHAPTER VIII. Davy's Bakerian Lecture of 1808.--Results obtained from the mutual action of Potassium and Ammonia upon each other.--His belief that he had decomposed Nitrogen.--He discovers Telluretted Hydrogen.--Whether Sulphur, Phosphorus, and Carbon, may not contain Hydrogen.--He decomposes Boracic acid.--Boron.--His fallacies with regard to the composition of Muriatic acid.--A splendid Voltaic Battery is constructed at the Institution by subscription.--Davy ascertains the true nature of the Muriatic and Oxymuriatic Acids.--Important chemical analogies to which the discovery gave origin.--Euchlorine.--Chlorides.--He delivers Lectures before the Dublin Society.--He receives the Honorary Degree of LL.D. from the Provost and Fellows of Trinity College.--He undertakes to ventilate the House of Lords.--The Regent confers upon him the honour of Knighthood.--He delivers his farewell Lecture.--Engages in a Gunpowder manufactory.--His marriage.