134 On the Ancient Purpurissum. (Fes. 
The mine is injured by the explosion, either by driving out of 
their situations such doors and stops as it meets with in traversing 
the mine, or by displacing them in obtaining an increased pressure. 
The impinging force is certainly more powerful, and does greater 
injury to the mine, where it acts only on a few doors and stops ; 
but the pressure, by acting on a great number, exerts its force 
equally against the weak and the strong, so that those which are the 
least able to resist it are sure to be displaced. The displacement of 
stops and doors prevents the circulation of the atmospheric air, and 
the miners who cannot quickly escape out of the part affected by 
the fire are suffocated by the noxious gases of combustion. It is 
difficult to prevent the fatal effécts of an explosion ; as, should we 
know its place of departure, the course that it may take through the 
mine is not to be calculated with any degree of accuracy; as the 
smallest deviation in the situation of the side impingements will 
either make the explosion take this or that working. Thus, had 
the explosion struck the pillar v a little further on than p, none of 
it would have entered the working p g; or, had it reached the side 
of the pillar w 2a little below y, it would have passed altogether 
through the opening 4, 5, and none of it have gone in the direction 
, 2. This uncertainty as to the direction which the blast may 
take makes the safety of the miners very precarious in any situation 
in the vicinity of a fire. 
This description will suffice to show the effects of an explosion 
on the mine. I might have given a more extensive example, and 
carried the ravages of the explosion into other districts of the mine; 
but it would only have been a repetition of the same motions varied 
a little in every instance, according to certain differences in the 
affected parts of the mine. 
This communication, Sir, concludes my Essays on Fire-damp; 
but I shall shortly have for your consideration an Essay on the 
Choak-damp of Miners. 
Tam, Sir, with great esteem, 
Your humble servant, 
Joun B. Lonemire: 
ARTICLE X. 
On the Ancient Purpurissum: the State of Turkey Red Dyeing in 
the Greek Empire: and the Means of procuring a Substitute 
jor Purpurissum. 
(fo Dr. Thomson.) 
SIR, 
SHoucp the accompanying observations on the ancient purpu- 
rissum, on the state of Turkey red dyeing in the Greek empire, 
