GEYSERS AND HOW THEY ARE EXPLAINED. 415 



proaching the boiling-point line, but everywhere within it, would rep- 

 resent the actual temperature in a state of quiescence. 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 ef the boiling-point for that 

 depth is actually reached. As soon as this occurs, a quantity of water 

 in the lower portion 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 overflow. As soon as 

 the water overflowed, the pressure would be diminshed in every part 

 of the tube, and consequently 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 evi- 

 dently 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 circula- 

 tion is thus more effectually impeded. 



The theory given above is substantially 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 with- 

 in reach of observation, though 

 doubtless beyond the reach of 

 observation the temperature 

 again approached and touched 

 the boiling-point. This point, 

 forty-five feet deep, plays an 

 important part in Bunsen's 

 theory. To illustrate : if ef 

 (Fig. 9) represent again the 

 curve of boiling-point, then 

 the curve of actual tempera- 

 ture in the Great Geyser tube 

 would be the irregular line a 

 g h. At the moment of erup- 

 tion, this line touched boiling-point at some depth, h, beyond the reach 

 of observation. Then followed the lifting of the column, the overflow 

 of the basin, the relief of pressure by which the point g was brought 

 to the boiling-point, the instantaneous formation of steam at g, and 

 the phenomena of an eruption. But it is extremely unlikely that this 



a 



Fig. 9. 



h33-ft 



66ft 



d 100 ft 



