1817-] On Explosions in Coal-Mines. i3l 
ARTICLE IX. 
The Conclusion of the Essay on the Explosions in Coal-Mines. 
By Mr. John B. Longmire. 
(To Dr. Thomson.) 
DEAR SIR, Nov. 9, 1816. 
In my former communication on the explosion of.coal-mines, 
which you did me the favour to insert in the Annals of Philosophy 
for November, I described the properties of the air’s explosive mo- 
tion: in this paper I will give an example of its effects on the mine. 
Let ABCD, [Plate LVHI. Fig. A] (see the number for No- 
vember) be part of a coal-mine, in which A is the pit shaft; AB, 
AD, lc, aC, ed, are ranges, that contain doors and stops in all 
the thirls, or cross workings. A door is represented by two lines, 
as at k, and a stop by one line, as at f. By means of these doors 
and stops, the current of air, which descends from the surface 
down the shaft A, passes round the mine, as the dotted line A, B, 
c, C, n, i,m, q, l, g, represents: at g it commences to circulate 
round other workings till it reaches the up-air pit. 
Let inflammable air enter the mine at the forehead, h, of the 
working hi. As the current of air does not traverse this working, 
it is filled with inflammable air from h to i; and the current of air 
moving along the working 7 D carries the infammable air with it 
as it enters this working. But if the door e be left\open, the air 
passes to g by a route, e 2 9, shorter than its usual way. Hence 
the gas accumulates in the working Dat 7; and if a miner travel 
along this working, without detecting the change in the current of 
air, he sets the gas on fire, and an explosion is the consequence. 
The explosion flies with an equal velocity, in the directions 7 A, 
tk, andi D. It is soon stopped by the doors in the direction i A, 
It proceeds to D, gives small concussions to the air in the thirls, 7, 
.l, &c. as it passes them ; and after it has reached the forehead, it 
returns up the working with a decreasing velocity. This rebound 
the workmen call a return. If all the stops in the thirls of the 
range n D withstand the shocks given to the air in them, by the 
advancing and retreating motion, this part of the explosion soon 
breaks through the thirl m, and there meets another part coming 
down the working k¢. The air in this part of the explosion passes 
along the inclined thirl 7%. It there blows down the door ks which 
for a moment retards its progress, and produces a small rebound. 
But the door being overturned, the explosion strikes the side at k, 
flies to the opposite side at n, returns to e, then passes alternately 
from ¢ to l, and from b to p; from p a part of it enters the work- 
ing p q, and the other part flies to 7, and displaces the door 7; from 
that place it passes to the opposite side s, and then strikes the fore- 
head at ¢, and rebounds up the working from side to side. 
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