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the animal body, a natural mechanism for moving and circu- 
lating a fluid substance, the blood. Now, as regards this, 
one side of the instrument, the heart, effects the object by 
creating a vacuum by its action. When the right auricle or 
cavity of the heart empties itself, the blood immediately 
rushes in from the veins to fill up the vacuum ; but this action 
of the blood operates upon the whole column in the veins 
down to the remotest capillaries. The whole of the blood 
is moved forwards and upwards to the extent of the quantity 
required to occupy the space described by the emptied auricle 
or cavity of the heart. This movement is aided by the 
presence of valves in the course of the veins, which act by 
preventing any retrograde movement of the blood. 
The object I have in view is to apply the principle of this 
natural hydraulic machine, to pneumatics, or to operate upon 
gaseous substances in a similar simple way. 
There may be difficulties in the way of its application to 
coal mines for the purpose of drawing off fire damp which I 
may not have foreseen, inasmuch as I have never been in a 
coal pit; and I am told there occur breaks or "fallings in," 
which would obstruct the application of the arterial tubes ; 
I can only say that the system I speak about would not 
require an uniformity of level or of direct course, but might 
deviate in any serpentine form, without thereby being im- 
paired in its efficiency : the pipes might be conveyed through 
the breaks or round them. 
To effect a circulation of air through the arterial tubes, 
there must, at the outlet or evacuating pipe, be a system of 
exhaustion or rarefaction kept up, either by heat or by an 
exhausting air pump of large capacity, and worked by the 
steam engine or power of the mine. This would maintain 
the circulation of the air from the interior of the mine, and 
as fast as the foul air was withdrawn, fresh atmospheric air 
would descend down the shaft to supply its place; thus a 
