68 HOT springs; steam- jets. 



Great Geyser and the Strokkr, have the highest 

 claim on the attention of the observer. The only 

 esssntial difference, according to Bunsen's account, 

 between these and those that I have just been 

 describing, are the great circumference and pro- 

 portionally small discharge of the latter. The 

 cylindrical tube of the Geyser built up by the gradual 

 deposition of the flint-sinter is 64 feet deep, by 

 9 8 feet across. It widens out at the top into a flat 

 saucer-shaped basin of at least 50 feet diameter. 

 Immediately after one of the discharges of the 

 Geyser, Bunsen found this basin empty, and the 

 water standing four or five feet below the mouth 

 of the tube. It required several hours for the 

 basin to become filled again; the water then 

 began to flow quietly over its edge in a little cas- 

 cade, while the liquid column was heated more 

 and more by the steam or water coming up from 

 below. But the water was considerably cooled at 

 the surface, by reason of the great width of the 

 basin, and the slowness of the overflow. Being 

 thus made heavier, it returned partially into the 

 tube, and made the temperature, to a certain depth 

 within, fall below the boiling-point. On this 

 simple circumstance depends the long period of 

 rest that follows each outbreak of the Geyser. 

 The effect of these two opposite agencies, — the 

 heating from below, and the cooling from above, — 

 may be clearly seen from the following obser- 



