574 
forms a perfect magazine of destruction, whenever, by acci- 
dent or otherwise, the smallest atom of flame is brought into 
contact with it. 
It will be argued in support of the system as it now exists, 
that superior elevations attained in the up-cast shaft, and the 
vigour with which, by rarefaction, the air is caused to move 
in it, must have the desired effect, and equally answer all the 
purposes we are contending for, of extracting the explosive 
gases from the mine. 
The shaft may be, and no doubt is, in the manner referred 
to, made to operate as a " head" in impelling the currents of 
ventilation along the passages, in which, but for some artifi- 
cial stimulus, the motion of air would be very trivial indeed. 
But the influence of an up-cast shaft, approached by descend- 
ing passages, and placed on the dip-side of the active workings 
of the colliery, must be maintained in opposition to, and 
independently of, the laws which explosive gases naturally 
and voluntarily obey. And hence the complicated system 
of trapping and splitting, and coursing and heating, for 
the purpose of carrying the air to all parts of the mine, 
where its presence is desired in the capacity of scavenger, 
to withdraw the agents of mischief by channels along which 
they have of themselves no disposition to retreat. 
The insidious and ever active force with which the lighter 
and dangerous gases seek out and obtain possession of all 
the most elevated cavities of a mine, indicates in language 
which cannot be mistaken, the soundness in theory of any 
plan of ventilation which harmonises with this voluntary 
habit of their nature. We have already shown, and expe- 
rience abundantly proves, that the systems of working now 
in operation are not so harmonised; but, on the contrary, 
are in a most active sense directly opposed to it. Let there 
be vent provided on the " rise," and the gases themselves 
supply the place of the cupola furnace. Their tendency 
