dense white vapor pouring up
into the air. His first impulse was to run forward up the sandy slope
that still remained between the place where he stood and the margin of
the crater; but he checked himself, and stopped where he was, to wait
for the rest of the party. As soon as the portantina bearers reached the
place where he stood, they set down the chair, and immediately the whole
set crowded around Mr. George, and again demanded _buono manos_.

"_Philippe payera_," said Mr. George, pointing down the mountain to the
Hermitage--"_Philippe payera, la bas_," which means, "Philippe will pay
when you go down."

Mr. George said this in a very quiet manner, and then proceeded to help
Rosie out of her chair. The guide who had come up the mountain with
them then led the way, and Mr. George, Rollo, Rosie and Josie followed,
towards the crater.

And here I must stop a moment in my story to explain a little what a
crater is, and how it is formed. A crater is a great circular pit or
depression in the top of a volcano, formed by the sinking of the ground
in that part. This sinking of the ground is caused apparently by the
cooling and shrinking of the melted matter below, after a time when it
has been unusually heated.

Most boys have observed an effect similar to this in casting lead. When
you attempt to cast any thing of lead,--a cannon, for example, or
anchor, or even a bullet,--you will observe that as the lead cools, the
portion of it which comes at the top of the mould shrinks and falls in,
forming a little pit or depression, which you have to fill up by pouring
in a little more lead. The reason is, that lead, as well as most other
melted substances, shrinks when it cools. In the case of the bullet, for
instance, all the lead which forms the mass of the bullet within the
mould shrinks. The effect of this would be to collapse the sides, were
it not that the sides have already become solid by contact with the cold
mould. But the lead at the top, having been poured in last, is still
fluid; and so that settles down as the lead cools below, and forms the
little pit or depression, which the boy presently fills up by pouring in
a little more lead.

It is much the same with a volcano. For some reason or other,--no one as
yet knows what it is,--the interior of a volcano changes its temperature
very much at different times. Sometimes for a period of several months,
or years, it seems to be all the time growing hotter and hotter. T