352 



Henry Woodward — On Volcanos. 



The Great Geyser has a cone-like elevation around its basin made up 

 of layers of travertin. The following are its principal measurements : — 



Diameter of basin 56 feet. 



Depth of tube 74 



Diameter of tube 8-10 



Professor Bunsen, in 1846, took the temperature of the Great 

 Geyser tube by a thermometer suspended by a string. The results 

 of his observations are given in the annexed woodcut (Fig. 11) : — 



Observed 

 Temperatures. 



■I- 



241° 20 feet. 



Known Boiling 



Temperature 



of Water. 



248° 38 feet. 



254° 44 feet. 



266° 60 feet. 



277° 74 feet. 



Fig. 11. — Section of Tube of the Great Geyser in Iceland. (After diagram in 

 Prof. Tyndall's "Heat a Mode of Motion," p. 126.) 



How does the water rise, under pressure, so much above the ordi- 

 nary boiling point for water at the surface? — Because, being de- 

 prived of air by frequent boiling, it refuses to circulate freely up and 



