296 On the Ventilation of Coal-Mines. [Aprit, 
keep his spirits up with the hopes (too often fallacious!) that explo- 
sions may not often occur, and that when they do, they may be 
trifling ; well knowing, that if a sufficient quantity of fire-damp 
takes fire, he must be blown to pieces in the first instance, or suf- 
focated in the second. 
Tke results then of the comparison which has been thus far pur- 
sued are: 1. That the proposed system of ventilation affords to the 
fire-damp every facility of making its escape. 2. Having so many 
other channels to escape by, it will take a considerable time to col- 
lect, in a passage which may be accidentally choaked. 3. By 
limiting the fire-damp, which cun possibly accumulate, toa fixed 
quantity, we necessarily restrict in the same proportion its destructive 
effects if it should explode. 4. By affording to this limited quan- 
tity of fire-damp a free passage in every direction when it acci- 
dentally inflames, we prevent it from extending its ravages to 
distant quarters of the mine. ‘This part of the subject may be 
here concluded by observing; that these important advantages will 
be in vain sought for in examining the arrangements of the existing 
system of ventilation. 
There are still some points, the discussion of which, from their 
intimate connexion with the subject, it would be inconsistent with 
the objects of this paper to omit. After having described the mode 
of ventilating the Felling colliery, Mr. Hodgson goes on to say, 
“Fyrom this explanation it will easily be perceived, that the purity 
and wholesomeness of a coal-mine has no reference to its depth.” 
This assertion appears to have been made without due consideration, 
In the first place, it is not attempted to be supported by facts, but 
by inconclusive reasoning. In the next place, it is at variance with 
numerous facts: and though an attempt has been made by an 
anonymous writer in the Philosophical Magazine, to evade the 
application of these facts,-this writer must “submit to be told,” 
~ (as he phrases it,) that evidence of this kind can never be super- 
seded by any species of reasoning, while the facts themselves are 
- unassailed. _ 
From the constitution of carbureted hydrogen gas, it is evident, 
- that we cannot retain it at the surface of the earth, much less at 
any considerable depth below that surface, but by absolute force ; 
- hence this gas can. never exist in a coal-mine, but in a state of 
compression, more or less forcible, from the moment it is evolved, 
until it is liberated by ascending into the atmosphere. But we 
know that atmospheric pressure increases as we descend below the 
surface of the earth, in the same proportion as it diminishes when 
- we ascend above it. The degree of compression in which fire- 
damp is held below ground must, therefore, be regulated by the 
depth of the mine. But we also know, that compression is one of 
the principal conditions of explosion, and that the more forcible 
the compression, the more violent the explosion, and vice versd. 
Another. remarkable fact, but well established, is, “ that the 
workings of a colliery are often inaccessible with candles near the 
