During our descent from the mountain we were much struck by the apparent nearness of the minor cones beneath us, and of the villages at the base of the mountain. They seemed to be painted on a vertical wall in front of us, and although from ten to fifteen miles distant they appeared to be almost within a stone's throw. This curious effect, which has often been observed before, is due to refraction. At the summit of Etna we have left one-third of the atmosphere beneath us, and the air is now pressing upon the surface of the earth with a weight of ten pounds on the square inch, instead of the usual fifteen pounds experienced at the level of the sea. In looking towards the base of the mountain we are consequently looking from a rarer to a denser medium; and it is a law of optics, that when light passes from a denser to a rarer medium it is refracted away from the perpendicular, and thus the object, from which it emanates, appears raised, and nearer to us than it really is. The objects around Etna appear near to us and raised vertically from the horizon for the same reason that a stick plunged in water appears bent. We reached Nicolosi again about noon, having left it eighteen hours before. The ascent of the mountain, although it does not involve much hard walking, is somewhat trying on account of the extremes of temperature which have to be endured. In the course of the morning of our descent we had experienced a difference equal to more than 40° F. As to the ascent, you are moving upwards nearly all night; you have six hours of riding on a mule, some of it in a bitterly cold atmosphere; you get very much heated by the final steep climb of 1100 feet, and you find at the summit a piercing wind; of course there is no shelter, and you sit down to wait for sunrise on cinders which are gently giving off steam and sulphurous acid; the former condenses to water as soon as it meets the cold air, and you find your great coat, or the rug on which you have sat down, speedily saturated with moisture. CHAPTER IV. TOWNS SITUATED ON THE MOUNTAIN. Paterno.--Ste. Maria di Licodia.--The site of the ancient town of Aetna.--Biancavilla.--Aderno.--Sicilian Inns.--Adranum.--Bronte.-- Randazzo.--Mascali.--Giarre.--Aci Reale.--Its position.--The Scogli de'Ciclopi.--Catania, its early history, and present condition.