n the earth, out of
which come little jets of steam, and which give the idea that it would
not require a very heavy blow to break in, at any point, the crust of
the earth, and let the adventurous traveller drop down into the
boiling mass below.

In Iceland the Geysers are not quite so terrible in their aspect as
those in California, but they are bad enough. Their contents are
generally water, some hot and bubbling, and some hot and still; while
the Great Geyser, the grandest work of the kind in the world, bursts
forth at times with great violence, sending jets of hot water hundreds
of feet into the air.

These wonderful hot springs, wherever they have been found, have
excited the greatest attention and interest, in travellers and
scientific men, and their workings have been explained somewhat in
this way:--

Water having gradually accumulated in vast underground crevices and
cavities, is heated by the fires, which, in volcanic regions, are not
very far from the surface of the earth. If there is a channel or tube
from the reservoir to the surface, the water will expand and rise
until it fills the basin which is generally found at the mouth of hot
springs. But the water beneath, being still further heated, will be
changed into steam, which will at times burst out with great force,
carrying with it a column of water high into the air. When this water
falls back into the basin it is much cooler, on account of its contact
with the air, and it cools the water in the basin, and also condenses
the steam in the tube or channel leading from the reservoir. The
spring is then quiet until enough steam is again formed to cause
another eruption. A celebrated German chemist named Bunsen
constructed an apparatus for the purpose of showing the operations of
Geysers. Here it is.

[Illustration: THE ARTIFICIAL GEYSER.]

You see that the two fires in the engraving--one lower and larger than
the other, because the heat of the earth increases as we get farther
from the surface--will heat the water in the iron tube very much as
water is heated in a real Geyser; and when steam enough is formed, a
column of hot water is thrown out of the basin. The great subterranean
reservoir is not imitated in this apparatus, but the action is the
same as if the tube arose from an iron vessel. There is a great deal
in Bunsen's description of this contrivance, in regard to the
difference in the temperature of the water in that part of the tube
between t