GEYSERS. 



109 



horizontal lines, representing one atmosphere, two atmospheres, three 

 atmospheres, etc., would correctly represent the increasing boiling- 

 points as we pass downward. We shall call this line, ef the curve of 

 toiling -point. The line a g commencing at the surface at 180°, and 

 gradually approaching the boiling-point line, but everywhere within it, 

 would represent the actual temperature in a state of quiescence. We 

 shall call this the line of actual temperature. Now, Bunsen found that, 

 as the time of eruption approached, the temperature at every depth 

 approached the boiling-point for that depth — i. e., the line a g moved 

 toward the line ef. There is no doubt, therefore, that, at the moment 

 of eruption, at some point below the reach of observation, the line a g 

 actually touches the line e f — the boiling-point for that depth is actually 

 reached. As soon as this occurs, a quantity of water in the lower por- 

 tion of the tube, or perhaps even in the subterranean channels which 

 lead to the tube, would be changed into steam, and the expanding steam 

 would lift the whole column of water in the tube, and cause the water 

 in the basin to bulge and overfloiu. As soon as the water overflowed, 

 the pressure would be diminished in every part of the tube, and conse- 

 quently a large quantity of water before very near the boiling-point 

 would flash into steam and instantly eject the whole of the water in 

 the pipe ; and the steam itself would rush out immediately afterward. 

 The premonitory cannonading beneath is evidently produced by the 

 collapse of large steam-bubbles rising through the cooler water of the 

 upper part of the tube ; in other words, it is simmering on a huge scale. 

 An eruption is more quickly brought on by throwing stones into the 

 throat of the geyser, because the 

 circulation is thus more effectu- 

 ally impeded. 



The theory given above is sub- 

 stantially that of Bunsen for the 

 eruption of the Great Geyser, but 

 modified to make it applicable to 

 all geysers. In the Great Geyser, 

 as already stated, Bunsen found a 

 point forty-five feet deep, where 

 the temperature was nearer the 

 boiling-point than at any within 

 reach of observation. This point, 

 forty-five feet deep, plays an im- 

 portant part in Bunsen's theory. 



To illustrate : if ef (Fig. 93) represent again the curve of boiling-point, 

 then the curve of actual temperature in the Great Geyser tube would 

 be the irregular line a g h. At the moment of eruption, this line 

 touched boiling-point at g. Then would follow the instantaneous for- 



3. 100 fi 



Fig. 93. 



