418 REPORT UNITED STATES GEOLOGICAL SURVEY. 



under high pressure. This pressure is sufficient to sustain the column 

 of water P M to the height P. If there is a sudden addition of heat 

 under b, a quantity of steam will be i)roduced in starts and the expan- 

 sive force will be so great that the water will overflow at P. All the 

 water in b will be forced into the pipe, and the steam will rush through 

 it with great violence, and the eruption takes place. The shakiug of 

 the ground and the noises like the discharge of artillery he refers to the 

 evolution of steam in starts, due to the sudden accessions of heat. 



McKenzie admitted that his theory could only be a partial exi^lana- 

 tion. He, however, recognized the fact that the sudden evolution of 

 steam is the proximate cause of the eruptions. He could not account 

 for the frequent and periodical x)roduction of the phenomena. Bunsen 

 thought that McKenzie's theory would account for the action of the 

 Little Geyser, but not for the eruptions of the Great Geyser. 



Bischof^s theory. — Very similar to McKenzie's theory is tl}e one 

 adopted by Bischof in his Researches on the Internal Heat of the Globe 

 (pages 227, 228). It is really the .theory of Krug Yon Nidda, who exam- 

 ined ,the geyser in 1833. Bischof says : 



He [Krug Vou Nidda] takes it for granted that these hot springs derive their tem- 

 perature from tlie 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 con- 

 stant temperature equal to that at which water would boil under the pressure exist- 

 ing 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 com- 

 plicated 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 sinuosity of the passage. The intermitting 

 springs of Iceland are ]3robably 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 jiresses the water in the cavern down- 

 ward until its elastic force becomes sufhciently great to effect a passa.ge through the 

 column of water which confines it. The violent escape of the vapor causes the thun- 

 der-like subterranean sound and the trembling of the earth which precedes each 

 eruption. The vapors do not ai^pear at the surface till 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, tranquillity is restored, and this lasts until such a quantity of vapor is again 

 collected as to produce a fresh eruption. The spouting of the spriug is therefore re- 

 peated at intervals, depending upon the capacity of the cavern, the height of the 

 column of water, and the heat generated below. 



Bischof says that the eruptions of the Geyser and StrocTcr 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 smaller cavity fills quicker, and, 

 therefore, empties itself more frequently; a larger one fills slower, empties itself 

 seldomer, but with greater violence. 



Bunsen'' s theory. — In July, 1846, Bunsen and Descloizeaux spent eleven 

 days in studying and experimenting upon the Great Geyser of Hauka- 

 dal, in Iceland. They took temperatures at different points in the tube. 

 These temperatures are given on the right-hand side of the column in 

 Fig. 22. On the middle left-hand side are the figures that represent the 

 boiling points of the water for the different depths, calculated accord- 

 ing to the ordinary laws. Bunsen's 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 sub- 



