A BUBBLE THEOKY. 
127 
the eruptions at two hundred feet, while well-authenti¬ 
cated accounts—when the elevation of the jet has been 
actually measured—make it to have attained a height of 
upwards of one hundred feet. 
With regard to the internal machinery by which 
these waterworks are set in motion, I will only say that 
the most received theory seems to be that which sup¬ 
poses the existence of a chamber in the heated earth, 
almost, but not quite, filled with water, and commu¬ 
nicating with the upper air by means of a pipe, whose 
lower orifice, instead of being in the roof, is at the 
side of the cavern, and below the surface of the subter¬ 
ranean pond. The water kept by the surrounding 
furnaces at boiling point, generates of course a continuous 
supply of steam, for which some vent must be obtained; 
as it cannot escape by the funnel,—the lower mouth of 
which is under water,—it squeezes itself up within the 
arching roof,—until at last, compressed beyond all endur¬ 
ance, it strains against the rock, and pushing down the 
intervening waters with its broad, strong back, forces 
them below the level of the funnel, and dispersing part, 
and driving part before it, rushes forth in triumph to the 
upper air. The fountains, therefore, that we see mount- 
