THE GREAT GEYSER. 159 



Geyser tube is so wide, that although the water 

 at the bottom is heated, and partly converted 

 into vapour, yet the loss of heat at the surface 

 by evaporation and radiation is so great, that 

 the whole volume of water in the tube. is not 

 brought up to the boiling point excepting at 

 stated times. When this is the case, then, it 

 appears that a powerful volume of vapour accu- 

 mulates at the lower part of the tube, which, 

 acquiring fresh elastic force, at length lifts the 

 immense body of water above it into the air, 

 driving it in a roaring, rushing column 28 feet 

 in circumference, and 100 in altitude; after 

 this the spring becomes .quiet again, until its 

 column is again heated up to the boiling point. 



As the incrustation continues, the sides of the 

 tube rise, higher and higher, until they and the 

 surrounding ground attain a height which puts 

 an end to these singular phenomena. As soon 

 as the supply of heat from below and the cooling 

 at the surface are so far in equilibrium that the 

 temperature of the mass of water is not any- 

 where able to reach the boiling point, the ac- 

 tion of the spring ceases spontaneously. Large 

 reservoirs rilled with hot stagnating or running 

 water are thus formed. Old geysers abound in 

 various districts, appearing in the form of large 

 reservoirs filled with hot water, in the depths of 

 which the old mouths may still be seen. These 



