12. Lead, which I first discovered in the fumaroles of the lavas of 1855, is a constant product of fumaroles which have a certain duration. It is often obtained as a distinct and crystallized chloride, and often is found in combination with other products. 13. Oxide of copper is also a constant and primary (_primitivo_) product of fumaroles. The chloride and sulphate of copper are formed from the oxide, directly contrary to general belief. 14. I do not think that the chloride of calcium, which I found on this occasion in almost all the deliquescent sublimations, is a product peculiar to this eruption only, in which alone, however, I found it. I was, therefore, induced to look for it in other sublimates, in which I might possibly have overlooked it, as, without doubt, my predecessors have done, owing to the deliquescence of the chloride of iron with which it was constantly combined. I think that this chloride, in accordance with the general law, is transformed into a sulphate--a transformation which readily occurs on Vesuvius. 15. Copious and well-crystallized sal ammoniac is only found on the fumaroles of those lavas which have covered cultivated or wooded ground. 16. The scarcity of oxygen in the gases of fumaroles may possibly arise from the formation of the oxides which precede the chlorides. 17. Lavas give a continuous spectrum, although covered with smoke, when looked at with Hoffmann's spectroscope with direct vision.[G] 18. The smoke gives positive electricity, and the falling ashes negative electricity. REFERENCE TO THE PLATES. PLATE Ia. The Cone of Vesuvius, in 1870, from a Photograph taken near the Observatory. _a._ The Atria del Cavallo. _b b._ Fossa della Vetrana. _c._ Punta del Crocella. _d._ Lava of 1858 and 1867. _e._ Police Barrack near the Observatory. _f._ Part of Monte Somma. IIa. Profile of Vesuvius, taken from a Photograph of the Observatory in the month of September, 1871. 1. The Cone, on the 13th January, 1871. 2, 2. Lava of 1871. IIIa. Profile of Vesuvius on the 16th April, 1872, about ten days before the last Conflagration. IVa. Vesuvius, on the 26th April, 1872, from a Photograph taken in the neighbourhood of Naples. 1. The Observatory. 2. Fossa della Vetrana. 3. Eruption of Smoke and Ashes, with Stones, from the surface of the Lava. 4. The Novelle, St. Sebastiano, and Massa. 5. Lava which took the direction of Resina. 6. Lava which, from the Crater, took the direction of the Camaldoli. 7. The Grain Stores, near Naples. 8. Resina. 9. Torre del Greco. 10. The Camaldoli. Va. Profile of Vesuvius after the Eruption of the 26th April, 1872, from a Photograph taken near the Observatory.