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 appear at the surface until they have heated the water to their own temperature.

“’When so much vapor has escaped that the expansive force of that which remains has become less than the pressure of the confining column of water, tranquility is restored, and this lasts until such a quantity of vapor is again collected as to produce a fresh eruption.  The spouting of the spring is therefore repeated at intervals, depending on the capacity of the cavern, the height of the column of water, and the heat generated below.’” Dr. Peal continues: 

“Bishof says that the eruptions of the Geyser and Strockr agree exactly with this explanation and he accounts for the two distinct classes of eruption observed in the Geyser as follows: 

“’The two distinct classes of eruption in the geyser which we have already mentioned seem to be attributable to two different cavities.  A small cavity fills quicker, and, therefore, empties itself more frequently; a larger one fills slower, empties itself seldomer, but with greater violence.’”

Bunsen’s theory is the next considered and is somewhat similar to Bischof’s but with notable differences.  After taking temperatures at different points in the Geyser tube his first conclusions are that: 

(1) The temperature in the geyser tube increases as we descend.

(2) At no point does the water in the tube attain the temperature of ebullition which it should have under the pressure to which it is subjected, but the temperature depends on the time that has elapsed since the last eruption.  As a great eruption comes near it approaches the boiling point.

(3) At the depth of about forty-five feet the difference between the temperature of the water and the calculated boiling point for that pressure is the least.

The main point of his theory appears to be that an eruption takes place when the water in the tube reaches the boiling point, and to account for it, “He supposes that the column in the central tube communicates by a long and sinuous channel with some space, be it what it may, which is subjected to the action of the direct source of subterranean heat.  The temperature gets raised above the boiling point, due to the pressure, and a sudden generation of steam is the result.  This steam rises in the column of water, which, being cooler, causes it to condense.  Gradually the heat of the water is raised until the water of the channel must boil, and the steam therefore cannot condense, but must accumulate and acquire a gradually increasing tension.  The condensation of the bubbles possesses a periodic character, and to this is due the uplifting of the water in what Bunsen calls conical water hills, which are accompanied by the subterranean explosions.”