240 
This rule would, I think, help to produce a greater immu- 
nity from explosions of gas, for most of them are traced to 
the incautious practice of firing shots in the neighbourhood 
of accumulations of gas ; hence the importance of this duty- 
being attended to by an intelligent workman — and it can 
be practically carried out more efiectually under the 
necessary discipline of ''Longwall," than by any other 
method. 
The writer is of opinion that the extension of this system 
of ''Longwair^ in Coal mining, is the pioneer paving the way 
for the working of this mineral at greater depths than we are 
accustomed to at present, for under no system of pillar work- 
ings could we get adequate ventilation at such depths as 
necessity will compel those following after us to venture to, for 
when we come to work at depths of 1,200 yards and upwards, 
we shall strive to convey all the air we can collect direct to 
the working faces unimpaired, avoiding all circuitous air 
courses, which would so diminish as to render the ventilation 
totally inadequate. 
Associated with this portion of my subject, I may state 
that the deepest mines in existence, where we may collect 
evidence as to the temperature under the above circum- 
stances, are Rosebridge Colliery, in Lancashire, 806 yards 
deep, the normal temperature of the Coal at that depth 
being 93 deg., while the temperature of the air passing 
through the workings is 78 deg. ; at Denaby Main Colliery, » 
440 yards deep, the deepest and nearest mine to Doncaster, 
the temperature of the air passing through the workings 
averages about 68 deg. 
In Belgium, Coal Mining has descended to a depth of 
nearly 1,200 yards, and from some observations that I made 
during a recent visit to the Coal fields of that country, and 
also from personal experiments that I have made at depths up 
to 500 yards, I have found the average increase of tempera- 
