372 Influence of Coal-dust in Colliery Explosions. [Mar. 2, 



doors, in a passage which, connects an intake with a return air-way. Tfie 

 side of the cabin on which the thermometer hangs is separated from the 

 intake air- way by a thickness of 6 yards of coal ; this point of the air- 

 way is 130 yards from the bottom of the downcast shaft, and the cur- 

 rent of air passing it amounts to 21,600 cubic feet per minute. The 

 cabin in the Llwynypia mine is only 16 yards from the bottom of the 

 shaft, and is situated at the side of one of the principal levels, where the 

 quantity of air passing the door is about 30,000 cubic feet per minute. 



The temperatures recorded in these two positions vary very little from 

 day to day ; and although they do not represent the actual variations 

 taking place in the temperature of the ventilating-currents, they may 

 be accepted, in a general way, as indices to the march of temperature in 

 the intake air-courses. Regarding them only in this capacity, then, it 

 is interesting to observe that, in each case, the temperature had reached 

 a minimum about the end of the first week in December. 



The great explosions which furnish the data for figure 10 are those by 

 which nineteen, or more, men were killed ; twenty was originally the lowest 

 figure, but afterwards four others were included, by each of which nine- 

 teen men were killed. In consequence of this restriction the Llan explo- 

 sion (17) is excluded, as well as many others of equal importance. 



Arranging the months according to the number of explosions which 

 took place in each, we have : — ' 



December . . 10 October .... 4 June 3 



February . . 6 November . . 4 January .... 2 



March .... 6 April ...... 3 August .... 2 



July 5 May 3 September . . 1 



The six months ending with March have produced thirty-two of these 

 explosions, and the other six months only seventeen. January is excep- 

 tionally low among the winter months, a circumstance which may per- 

 haps have some connexion with the general cessation of work for several 

 days at the end of the year ; and July is high among the summer months, 

 indicating the effect of a high temperature at the surface in retarding the 

 ventilation. The three explosions in May happened within the same fort- 

 night in 1852 (May 6, 10, and 20) ; and September is particularly ex- 

 empt, having only one. 



It may be said in conclusion that the dangers arising from the presence 

 of dry coal-dust in mines may be greatly diminished by having the coal- 

 dust itself removed as far as possible, and extending the system of water- 

 ing the roadways, now practised in many places for the sake of comfort. 

 The same precautions are recommended in M. Vital's paper already re- 

 ferred to. 



It should also be mentioned in this place that the ventilation of many 

 mines will require to be largely augmented before we can reasonably ex- 

 pect to enjoy comparative immunity from the recurrence of explosions. 



