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 deg. 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.

We have before alluded to the fact that Etna is far more thickly
populated than any other part of Sicily or Italy; in fact, more so than
almost any equal area in the world, of course excepting large cities and
their neighbourhood. This is due to the wonderful fertility of the soil,
the salubrity of the climat