COLLIERY EXPLOSIONS. 
225 
latter depends, to some extent, upon the former. Mr. Gallaway,^ 
after referring to the fact that in December, 1875, three great 
explosions occurred within three days when the barometer was 
high and the temperature at the surface low, and that it had 
been often observed that disastrous explosions had happened 
most frequently during the winter months, goes on to say : — 
“ If we assume that the magnitude of some colliery explosions 
has been determined by the presence of coal dust in the 
workings, and that the hygrometric state of coal dust changes 
with the humidity of the air with which it is in contact, then 
it is an obvious conclusion that explosions of this kind will be 
most likely to occur when the air in the mine is driest ; for at 
such times not only will the coal dust be most easily raised into 
the air by the local explosion (which we may always suppose to 
happen at any rate), but it will also be burned more easily than 
w^hen it contains a larger proportion of moisture.” 
“ As an example we may take the case of a dry mine, in 
which the temperature of the workings is 70° F. During warm 
weather the air which descends the shaft has a temperature of 
say 60° when it enters the intake air course ; at this stage it is 
also saturated with vapour, for there is usually a little water 
trickling down the sides of a mine shaft. The temperature rises 
gradually as the current draws near to the “faces,” and at 
length attains its maximum when the newly exposed face of the 
coal has been passed. During this process the humidity has 
also been increasing to some extent, always remaining below 
complete saturation, however, in a mine of this kind.” 
“ In very cold weather, on the other hand, the same current 
may sometimes have a temperature of 32°, or less, when it 
reaches the bottom of the shaft ; and since it passes through the 
same workings, its temperature rises to 70° as before. It is 
^ Ptoc. Boyal Society, No. 168, 1876, pp. 369 — 371. 
