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during our stay at Hveravellir. If this be so, the spring water must have found 

 another outlet. The water standing in the old channel would then rise or sink 

 according to the pressure prevailing in the water in the earth below. It is quite 

 possible that similar channels are found in many places in the neiglil)ourhoüd of 

 the periodic springs, although they are not yet discovered, as Ihe water in such 

 channels does not necessarily reach up to the surface of the earth. 



It is not difficult to perceive that a natural channel of a similar form to that 

 shown in Fig. 15 may suffice to explain how the air is mixed with the spring 

 gases, provided that the channel has suitable dimensions. 



We may assume that the channel b is at the beginning entirely filled with 

 water. When the pressure down in the earth is reduced, the water recedes down 

 the channel, and as soon 

 as the surface of the water 

 has fallen as low as the 

 bend, the atmospheric air, 

 forcing its way through 

 the water, enters the re- 

 servoir B, where it is stored 

 up, and also in the upper 

 part of the channel c. 

 When the pressure below 

 increases again, the water 

 rises in the channels b 

 and c, and expels the air 

 from them; but the air 

 remains in the reservoir B. 

 By the subsequent reduc- 

 tion of the pressure in d, 

 the air in B is forced 

 down the channel c by 

 the pressure of the water 

 column in the channel b. 

 Supposing d to be in 

 communication with the 

 channel of a geyser, the 

 periodic variations of the 

 pressure in the gej'ser 

 channel will be sufficient 

 to produce the required variations in the pressure in the channel d. 



Inasmuch as channels similar to that shown in Fig. 15 are undoubtedly very 

 common, especially in periodic springs, one can readily understand that when such 

 a channel falls into inactivity on account of the spring water finding an outlet on 

 a lower level, it is very likely that the vacant channel serves as a kind of pumping 



33* 



l-isi. 1,-,. 



