A singular result of the application of this invention occurred to an accomplished traveller, who ascended Mount Etna, in order to obtain representations of that remarkable volcano. No sooner was the camera fixed on the edge of the crater, and the sensitive paper introduced, than a partial irruption took place, and the traveller had to fly for his life. On the cessation of the irruption, he returned; doubtless, with the expectation of merely collecting the fragments of his valuable instrument; when, to his great astonishment and delight, he discovered not only that his camera was absolutely uninjured, but that it contained an admirable representation of the crater and the irruption. A brief account of the process of the Daguerreotype may now be given. A plate of silvered copper, about as thick as a shilling, is well cleaned and polished by rubbing it with cotton, fine pumice powder, and dilute nitric acid, and afterwards exposed to the heat of a spirit-lamp, placed below it, till a strong white coating is formed on the polished surface. On the plate being cooled suddenly by means of a cold slab of stone or of metal, the white coating is removed by repeatedly polishing it with dry pumice and cotton, and then three times more with the dilute nitric acid and pumice powder. A careful cleaning being thus given to the plate, it is placed in a box containing iodine, till it becomes visibly covered with a golden film of that substance, which must neither be pale nor purple. It is then placed in the camera till a distinct picture of whatever appears before it is formed upon the surface; it remains there for a period depending on the intensity of the light, and is then removed to a metallic box, having in it a cup containing at least three ounces of mercury. Placed below the cup is a spirit-lamp, which throws off the mercurial vapour; and, in exact proportion as this vapour deposits itself on the parts of the plate which have been acted upon by the light, is the picture developed on the surface of the plate, by the adhesion of the white mercurial vapour to the different parts which had been impressed by the light. As soon as the picture appears complete, the plate is placed in a trough of sheet-copper, containing either a saturated solution of common salt, or a weak solution of hyposulphite of soda. Thus, the coating of iodine will be dissolved, the yellow colour quite disappearing; hot, but not boiling, distilled water is then poured over the plate, and any drops which remain are removed by blowing upon them.