OUTBURSTS OF THE GEYSERS. 71 



of the water, which were nearly boiling before. 

 As the bulk of steam in the tube increases, greater 

 masses of water are displaced upwards, and the resist- 

 ance from above diminishes more and more. Steam 

 is now given off very fast, and sets in motion the 

 water that still remains liquid, which mingled with 

 the vapour is hurled into the air in a mighty jet, 

 ten feet thick, to a height of more than a hundred 

 feet. But this phenomenon lasts only a very short 

 time. The water cooled in the air sinks partly 

 back into the tube ; the escape of steam ceases ; 

 and all returns again to perfect rest; the out- 

 bursts follow each other after unequal periods. It 

 is evident that differences in the rate of cooling 

 from above must have a great influence in causing 

 these variations. 



In the other great spring near the Geyser, the 

 Strokkr, the same behaviour may be observed as 

 in the former. But its shaft is not cylindrical, 

 but narrows off towards the bottom, so that the 

 lower opening may be stopped by throwing in turf 

 and stones. There then always follows after a 

 short time a more violent outburst of the water, 

 by which the substances thrown in are hurled up 

 into the air. 



Bunsen distinguishes yet another kind of inter- 

 mittent springs, of which great numbers occur 

 in Iceland, and of which the discharges do not 

 take place in shocks, as is the case with the Great 



