'^•Xli^ 



ato 





■\i 



-am 



c\ 



) 



J 



an of 

 ?lliiot 



mete 



J 



■•.uSCi 



ds by 



V 



freed 



mucli 

 tier 



« 



boiled 

 . verv 



i^ 



J his 

 of 



an 



) 



fliot 



nori- 

 3toa 



riiV^ 

 tic 



rfi 



a 



iref 



Ch. XXXIII.] 



AGENCY OF STEAM IN VOLCANOS. 



221 



the mouth of the tube were ejected to a height of 100 feet, 

 other experiments also were made^ tending to demonstrate tlie 

 singular fact^ that there is often scarcely any motion below, 

 when a violent rush of steam and water is taking place above. 

 It seems that when a lofty column of water possesses a 

 temperature increasing with the depth, any slight ebullition 

 or disturbance of equilibrium in the upper portion, may first 

 force up water into the basin, and then cause it to flow over 

 the edge. A lower portion, thus suddenly relieved of part of 

 its pressure, expands and is converted into vapour more 

 rapidly than the first, owing to its greater heat. This allows 

 the next subjacent stratum, which is much hotter, to rise and 

 flash into a gaseous form ; and this process goes on till the 

 ebullition has descended from the middle to near the bottom 

 of the funnel.*^ 



mechanism 



may 



some 



the earth, in 



accumulates : and when 



water containing the usual mixture of air penetrates into 



may 



same manner 



column 



may 



n up the pipe of a Geyser. In other 

 a continuous column of liquid lava 



may 



under 



column may have a temperature 



downwards. 



quilibrium 



an eruption near the surface, by the expansion and conversion 

 into gas of entangled water and other constituents of what 

 we call lava, so as to occasion a diminution of pressure. More 

 steam would then be liberated, carrying up with it jets of 

 melted rock, which being hurled up into the air may fall in 

 showers of ashes on the surrounding country, and at leno-th 

 by the arrival of lava and water more and more heated at'the 

 orifice of the duct or the crater of the volcano, expansive 



* Liebig's Annaleii dor Chlmie imd Memoirs ' of Cavendish Soc. London 

 Pharmacie, translated in ' Eeports and 1848, p. 351. 



iii 



