132 On Explosions in Coal-Muines. [Frs. 
The other part of the explosion, which continues to the side p of 
the working p q, flies from p to uw, and from uw tov; from v it 
passes to w, in the open thirl wa, and then from w to x; from x 
it strikes the far side of the working y g at 3; it then moves to y, 
and from y it reaches the corner 2 of the pillar 5 d, one half being 
reflected to 1, and the other to 4. From 1 it flies to 2, from 2 it 
strikes obliquely the corner of the forehead g, and from thence 
retreats backwards along the thirl 2, 1, and down the working gq p. 
The other part of the explosion passes through the strait thirl, from 
2 to 4, and from 4 to 5; at 5 it displaces the stop, and flies to 6 on 
the opposite side of the working dé; from 6 it passes to 7, and 
from 7 to 8. In this irregular course it proceeds through the 
workings in the part C E e; and gives successive shocks to the air in 
every one of them. When the explosive motion has pervaded all 
the workings in the part EC, it can only escape through the narrow 
working 9, and the stone tunnel at B. But the displaced air cannot 
pass through these outlets as fast as the heat dilates it, without 
having first obtained an augmentation of pressure in every part of 
the workings. In acquiring a greater degree of pressure, a current 
in the contrary direction takes place; for as soon as the air in 
motion receives a check by the narrowness of the outlets, it re- 
bounds up the workings towards the centre of motion, 7, and con- 
tinues retreating so long as the displaced air is kept in. But when, 
partly by an increased degree of pressure, and a diminution in the 
force of the explosion, the pressure is adequate to send the air 
through the outlets, the backward motion then ceases. It may not 
cease, however, till after two or more repetitions of this motion 
have taken place: one commencing at the outlets, as soon as a 
former has ceased at 7. Though this returning motion tends gene- 
rally towards the place of combustion 7, it is carried in other direc- 
tions by the workings: for, as soon as the returning motion has 
reached the end of the thirl d, it spreads into that working as well 
as down the working g x; and on arriving at the thirl 1 g, it enters 
this place while it continues down the working 2. Again this 
retrograde motion passes from B to the end of the first working, and 
then spreads into it also; andas it continues to move in the direction 
Bk, it fills all the workings as it passes them. When the mine is 
thus filled with compressed air, a considerable force acts against 
the doors, and stops in the range B a, and against the doors between 
A and fh. If these doors and stops are strong enough to support 
this pressure, all the heated air escapes through the two outlets 
only; but if the quantity of burning gas be great, the pressure will 
displace the weakest of them, which suppose the stop f and the 
door next the pit, and then the explosion will fly along the working 
AB, and also up the pit A, until the whole of the displaced air is 
expelled out of the mine. When the explosion is over at the top of 
the pit, a momentary stillness ensues; and then a quick current 
passes down the pit, but which decreases, and very soon becomes 
only the regular current of the air course. 
