70 HOT SPRINGS; STEAM- JETS. 



from above. This is brought about by the for- 

 mation of single bubbles, which always occurs 

 before boiling properly commences. The column of 

 water at any given depth, for instance at 32*5 feet, 

 has just reached the boiling-point; therefore the 

 higher temperature of the water rising from below 

 cannot be employed in heating this layer of water 

 any more, so that this excess must give rise to 

 some bubbles, which have elasticity enough to up- 

 heave the water above them. That this is taking 

 place may be known by the surface of the water 

 in the basin suddenly rising into a mound. But 

 when these bubbles have reached a layer of water, 

 which is still below the boiling-point, they are 

 again condensed into liquid, and thus the balance 

 is restored. This process is often repeated, each 

 time more quickly following the last, for several 

 hours before the outburst, and is always accom- 

 panied with a loud noise, caused by the striking 

 of the water-surfaces where the bubbles are con- 

 densed. — By degrees more and more of the column 

 approaches the boiling-point; any steam-bubble 

 now coming up cannot be condensed so quickly, 

 but increases more and more in size as it rises, 

 and at last heaves up the water in the middle of 

 the tube through several feet. A part of the 

 water-column is thus removed; the pressure that 

 restrains the bubbling up of the steam is lessened ; 

 and steam must begin to be formed at all parts 



