624 
indemnifies us, where the atmosphere without it would be 
instantly fatal we freely admit. The grander question, how- 
ever, at the present moment is — whether any such atmos- 
phere ought ever to exist, and whether the proper business 
of ventilation has been performed, where in the ordinary 
operations of a mine, the safety lamp becomes necessary ? 
On this issue the vital question of mining security must be 
fairly tried. 
It has already been more than insinuated, that descending 
currents and effective ventilation are, for colliery purposes, 
incompatible in theory, and inoperative in practice. The air, 
we admit, is capable of being attracted by the agency of high 
rarifying power along the downward courses of a mine, and 
currents may thus be established which indicate a total 
volume sufficient for every purpose, if they were diffused in 
the mine, and made to scour its cavities as the very idea of 
ventilation imports. But here we encounter the difficulties 
and uncertainties of the entire system. The air impelled 
against the law which its own gravity stamps upon it, is ever 
struggling to escape by the shortest possible tracks which 
lead to its exit; and hence it is, that ventilation by the 
processes in most general use is made to assume the form 
of sharply-defined jets, which pierce the apertures and 
passages of the mine, in the direction, and with a form, pro- 
portionate to the degree of coercive influence which compels 
their obedience, and beyond this any such principle as that 
of voluntary diffusion is utterly abortive. 
Another aspect of the difficulty arises when we turn from 
the ventilating air to consider the gases generated in the 
mine, which it is requisite to dilute and expel. 
The most prominent gas, because that which imparts the in- 
flammable constituent — carburetted hydrogen — is well known 
to possess a remarkable degree of lightness, its specific gravity 
being very little more than one-half that of ordinary atmos* 
