hose which
spurt a few feet into the air have been classed as pseudo-geysers.

"It has been noticed that geysers occur where the intensity of volcanic
action is decreasing. In the neighborhood of active volcanoes, such as
Vesuvius, the temperature appears to be too high, and the vapor escapes
as steam from what are called stufas. When the rocks at the surface are
more cooled the water comes forth in liquid form.

"We will now pass to the various geyser theories that have been proposed
by different writers."

Dr. Peal then proceeds to give the theories of Sir J. Herschell and Sir
George McKenzie, but as they are accepted and extended by others, we may
pass on to Bischof's, of which Dr. Peal says: "Very similar to
McKenzie's theory is the one adopted by Bischof in his Researches on the
Internal Heat of the Globe (pages 227, 228). It is really the theory of
Krug Von Nidda, who examined the geyser in 1833. Bischof says:

"'He (Krug Von Nidda) takes it for granted that these hot springs derive
their temperature from the aqueous vapors rising from below. When these
vapors are able to rise freely in a continued column the water at the
different depths must have a constant temperature equal to that at which
water would boil under the pressure existing at the respective depths;
hence the constant ebullition of the permanent springs and their boiling
heat. If, on the other hand, the vapors be prevented by the complicated
windings of its channels from rising to the surface; if, for example,
they be arrested in caverns, the temperature in the upper layers of
water must necessarily become reduced, because a large quantity of it is
lost by evaporation at the surface, which cannot be replaced from below.
And any circulation of the layers of water at different temperatures, by
reason of their unequal specific gravities, seems to be very much
interrupted by the narrowness and sinuousity of the passage. The
intermitting springs of Iceland are probably caused by the existence of
caverns, in which the vapor is retained by the pressure of the column of
water in the channel which leads to the surface. Here this vapor
collects, and presses the water in the cavern downward until its elastic
force becomes sufficiently great to effect a passage through the column
of water which confines it. The violent escape of the vapor causes the
thunder-like subterranean sound and the trembling of the earth which
precedes each eruption. The vapors do not