GEYSERS. 175 
this tube is closed at one end, filled with water and placed upright we 
have all the mechanism necessary to produce all the phenomena of a 
geyser. By heating the water at the bottom by the introduction of 
steam (or with a spirit lamp), we can produce eruptions whose period 
will depend upon the intensity of the heat. At first the bubbles of 
steam collapse in the cool waters at the bottom of the tube, but as the 
temperature rises the bubbles rise part way up the tube and heat the 
lower part of the column to a high temperature while the water near 
the surface is still cool. Eventually the water at the bottom reaches 
the pressure boiling point, when steam is formed, lifting the water 
above it and causing an overflow at the top. This overflow or its 
equivalent, the filling of a shallow basin at the top of the tube, relieves 
the pressure and all that part of the column whose temperature was 
previously below the boiling point but now exceeds it, flies into steam 
and ejects the water above with great violence. The glass walls of our 
geyser tube permit us to watch the gradual heating of the water by 
means of thermometers suspended in the tube, the ascent and collapse 
of steam bubbles, the overflow and abortive attempts to erupt and the 
final ejection of the water from the tube. 
Where the tube is surrounded at the top by a basin no actual over- 
flow need occur. Indeed there is in the Yellowstone a miniature gey- 
ser, aptly named the Model, with a tube but 2 inches in diameter, sur- 
rounded by a shallow, saucer-like basin, which has eruptions about 
every fifteen minutes of 5 feet to 5 feet in height in which scarcely a 
drop of water is wasted, but flows back into the tube after the erup- 
tion. During the interval between eruptions no water can be seen in 
the tube, whose basin and upper part are dry and cool. The first sig- 
nal of the coming display is a quiet welling up of the water in the tube 
filling the little basin, which being relatively large and shallow relieves 
the water column of a considerable height. During the eruption which 
follows, the spray is chilled by the air, falling back into the basin; at 
the end of the display the water is quickly sucked back into the tube 
and re-heated for the ensuing eruption. 
At first thought the constant boiling of the waters in the tube of 
Strokr, Old Faithful and many other geysers seems to oppose the 
theory which we have just given. Observations show however that 
in many: cases the boiling is confined to the surface and deep tempera- 
tures do not reach the boiling point corresponding to the depth. It is 
quite likely also that in some cases a lesser and independent supply of 
heat may connect with the upper part of a geyser tube; Strokr, we 
know, has two vents (see figure), one of which is the geyser tube, the 
funnel-like throat of Strokr being really but a nozzle to the geyser. 
It is unnecessary to describe the numerous other theories of geyser 
action; they all suppose caverns or systems of chambers and tubes, of 
definite arrangement, a supposition most unlikely to occur in many 
cases, and made unnecessary by Bunsen’s theory. Local expansions 
and irregularities of the tube do exist, and to them we owe many of 
