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most natural and active repugnance. The water must be 
raised by virtue of mechanical appliances, which bring it 
under the secondary action of atmospheric pressure — it may 
be at a considerable pecuniary and other form of expense. 
And during the whole operation there is not a globule which 
yields a voluntary impulse, but all the particles, to the very 
last drop of the fluid, exert an active effort to elude the 
objects of their expulsion. And when command has been 
exercised on all within reach of the pump, the exposed bed 
of the reservoir will exhibit the numerous little pools and 
irregularities of surface which the last dregs of the fluid has 
occupied, rather than surrender itself voluntarily to the 
compulsory effect which it was sought to bring into contact 
with it. What truer analogy can be conceived, than that 
which exists between this, and the underground reservoir 
already described ? We have only to turn the description 
upside down, reading top for bottom, and vice versa, and the 
two cases are perfect and most beautiful types of each other. 
The subterranean reservoir is " pumped" out, when drained 
of its gases by means of a dip-outlet. The action of the 
furnace or similar expedient, is precisely analogous to the 
vacuum-creating action of the pump. So also is it limited 
by the involuntary habit of the gas, towards all operations 
with which it has not a direct natural sympathy. Perforated 
at the bottom of the reservoir, the water escapes by its own 
natural impulse ; and all the operations for cleansing the 
pool, so long as they preserve the gravitating influence, 
become simple, easy, and certain. In like manner when 
perforated at the top, will gases exude from a mine. And 
harmonized with this quality of their being, all the processes 
of ventilation become simplified, certain in their action, and 
comparatively inexpensive in their provision and maintenance. 
The time is not distant when such a picture as this would 
have been regarded as purely imaginary — and, for all 
