Davy had sent a letter to Pavia to announce his intended visit; and on the appointed day and hour, Volta, in full dress, anxiously awaited his arrival. On the entrance of the great English philosopher into the apartment, not only in _déshabille_, but in a dress of which an English artisan would have been ashamed, Volta started back in astonishment, and such was the effect of his surprise, that he was for some time unable to address him. From Milan, which he left on the 22nd of June, he went to Como, Domo D'Ossola, and then over the Simplon, to Geneva, where he arrived on the 25th of that month, and remained until the 18th of September. During this visit he made various experiments on Iodine, at the house of De Saussure, which was situated near the edge of the Lake, and about three miles from Geneva. He also worked at M. Pictet's house, on the subject of the heat in the solar spectrum. Here also he met with a number of celebrated persons, whose society he greatly enjoyed; amongst whom were Madame de Stael, Benjamin Constant, Necker, and Talma. Lausanne, Vevay, Payerne, Berne, Zurich, Schaffhausen, and Munich, were successively visited by him. His route was then continued through Tyrol, Inspruck, Calmar, Bolsenna, Trent, Bassano, Vicenza, Padua, to Venice; where having remained two days, he returned to Padua on the 16th of October, and then proceeded to Ferrara, Bologna, and Pietra-Mala; near which latter place, in the Apennines, he examined a fire produced by gaseous matter constantly disengaged from a schist stratum, and from the results of its combustion, he concluded it to be pure fire-damp. On again reaching Florence, he found that the Professors had been dismissed, but he nevertheless resumed his researches, first at home, and afterwards in the laboratory of the Grand Duke, where he submitted to analysis some gas which had been collected by his attendant Mr. Faraday, from a cavity in the earth, about a mile from Pietra-Mala, then filled with water, and which from the quantity of gas disengaged is called _Aqua Buja_. It was found to be pure light carburetted hydrogen, requiring two volumes of oxygen for its combustion, and producing a volume of carbonic acid gas. "It is very probable," says he, "that these gases were disengaged from coal strata beneath the surface, or from bituminous schist above coal; and at some future period new sources of wealth may be opened to Tuscany from this invaluable mineral treasure." On the 29th he left Florence, and passing through Levano, Tortona, and Terni, arrived again at Rome, on the 2nd of November, where he remained till the 1st of March 1815.