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in the first channel is extraordinarily intense, while they remain passive when the 

 eruption is less intense. This is undoubtedly the case with many geysers which 

 have two kinds of eruptions. They must be provided with two or more channels 

 beneath the surface of the earth. 



Another reason for two different kinds of eruptions taking place in the same 

 geyser will be mentioned later, [in the dissertation on the eruptions of "Störi 

 Geysir." 



Where violent eruptions take place the spring gas and the vapour in the 

 channels are subjected to great pressure previous to the eruption. The walls of 

 the channels must therefore be very strong, in order to sustain this great pressure. 

 Where the soil is loose and disintegrated, the spring gas makes new passages as 

 soon as the old ones are stopped up. In these localities therefore no great erup- 

 tion can take place. This is evidently the principal reason for the scarcity of 

 geysers where the spring gas contains large quantities of sulphuretted hydrogen. 

 For the soil surrounding the sulphurous springs is always disintegrated. 



In some geysers, Grvla for instance, the real eruption is succeeded by a steam 

 jet period. This is most readily explained by assuming that the form of the spring 

 channel is comparatively regular, so that the steam can easily drive the whole of 

 the water out of the channel. Besides this, the supply of hot water which produces 

 the steam cannot enter into the channel during the eruption. When the spring 

 has spent its accumulated energy, and the steam power is consequently on the 

 decrease, the vapours in the channel become condensed and stop the flow of steam 

 out of the geyser. 



Finally, I will mention somewhat more exhaustively a particular type of periodic 

 spring, namely, the great hot water basins, which evolve gas periodically. The 

 periodicity of these springs is not easily apparent on the surface. The steam and 

 gas bubbles which are periodically ejected from the small holes at the bottom of 

 the basin, diminish very rapidly as soon as they come into contact with the water 

 in the basin, which is kept cooler on account of the evaporation from its large 

 exposed surface. 



These eruptions may therefore appropriately be termed subterranean erup- 

 tions, inasmuch as their energy is exhausted before they reach the surface. 



The periodicity of these springs is easily explained in the same way as in 

 the previous instance. The steam How is not strong enough to keep the water in 

 the basin out of the channels, and by the time the water has entered the channels 

 and hindered or completely stopped the outflow of spring gas, the spring has 

 accumulated sufficient energy to expel it again. 



This class of hot spring claims more attention, inasmuch as "Störi Geysir" 

 must be considered as belonging to it. For besides its characteristic large eruptions, 

 "Störi Geysir" has also small eruptions with regular periods. These small, or as 

 BuNSEN has called them, unsuccessful eruptions, are, like the larger eruptions, 

 accompanied by subterranean detonations. Water and spring gases flow with such 



