ON EXPLOSIONS OF FIKE-DAMP IN COAL MINES. 
19 
force it out into the mine, or from which sudden 
decrease in the pressure of the surrounding air allows it 
to escape. This makes the “goaf” a constant source of 
danger, which should be entered or traversed as little as 
possible, and, as far as may be, cut off from communication 
with workings in progress. Putting these facts together, 
it is clear that the safest combination is to have the 
“ goaf ” in the rear and to the rise of the workings ; and that, 
coeteris paHbus, the safest way of getting the coal is that 
known as “ long wall,” by which all the mineral is extracted 
at the first working ; and that the “ pillar and stall ” method. 
Fig. 1. 
by which portions are left to support the roof, and afterwards 
got out by a second working, is liable to objection, because it 
involves the carrying on of operations in the middle of a mass 
of abandoned workings, loaded with fiery gas. It is also clear 
that several advantages will be gained by placing the downcast 
shaft on the extreme dip of the mine, and making it the shaft 
by which the mineral is raised to the surface. For by this 
means the intake air drives the light fire-damp in the direction 
in which it naturally tends to move, and the coal may be run 
down to the shaft bottom by its own gravity. 
Fig. 1 shows a plan of what may be called a coal mine 
under its simplest form, in which all these ad vantage, s have 
