174 GEYSERS. 
tion of the action of these natural steam engines. This theory, which 
bears the name of the illustrious Bunsen, depends upon the well- 
known fact that the boiling point of water rises with the pressure, 
and is therefore higher at the bottom of a tube of water than at the 
surface. The temperature of water heated in any vessel is generally 
equalized by convective currents, but in a long and narrow or an 
irregular tube this circulation is impeded, and while the water at the 
surface boils at 100° C. (at sea level), ebullition in the lower part of 
the tube is only possible at a much higher temperature, owing to the 
weight of the water column above it. In the section of Geyser shown 
in the figure the observed temperatures are given on the left, and the 
temperatures at which the waters would boil, taking into account the 
pressure of the water column, are given on the right. In Geyser the 
nearest approximate to the boiling point is at a depth of 45 feet oppo- 
NA 
LY SV //p Z UY, \-10 
ty 
Observed Temp. ///- SSA 
Y Yyyy 
: =— $Y 
Yj Yy Yj 20 
ijpj§— Vj 
Yj; =e L 30 
——/7/ i 
) jececeacedseqeced Yw$7y i 
(i ///aeee 
Yn YY, 
Y Mj Yy 50 
2s Gj mecisv 60 
YY ty Y GY 4 
Yj. Yy 70 
QM ee 
Geysir 
Sections of Geyser and Strokr showing fissures supplying geyser tubes (after Campbell). 
site a ledge and fissure discovered subsequent to Bunsen’s experiments. 
At this depth the temperature is 2° C. below the temperature at which 
the water can boil. If by the continued heating of this layer by steam 
from the fissure it attains the temperature at which it can boil, steam 
is formed, whose expansive force lifts the superincumbent column of 
water, causing a slight overflow at the top, which, shortening the col- 
umn, brings the layer B to the position C, where its temperature is 
above the boiling point of C, wherefore steam is formed at this point and 
a further lifting and relief of pressure ensues, followed by an eruption. 
In illustration of this theory a model geyser is easily constructed of 
a glass tube of an inch or so in diameter and several feet long. When 
