1876.] 



of Coal-dust in Colliery Explosions. 



371 



Figs. 9 & 10. Fires are kindled near the mouth of the Llwynypia downcast shaft to 

 heat somewhat the air which enters it when its normal temperature is at or 

 below the freezing-point. This is necessary in order to prevent the formation 

 of large masses of ice on the walls, which would be the result if the numerous 

 springs which percolate the brickwork were permitted to freeze for a consider- 

 able time. In this way the apparent irregularity of the temperature observed 

 in the cabin of this mine at the beginning of December may be partly or wholly 

 accounted for. 



Llwynypia shafts, in the South Wales district, for six weeks before and 

 after the explosions of the 4th and 6th of December last (these dates are 

 marked above each curve by short thick lines); fig. 11 represents the 

 numbers of great explosions which have occurred in each month of the 

 year for the last twenty-five years (1851 to 1875 inclusive). 



Ferndale and Llwynypia shafts are 286 and 380 yards deep respectively. 

 The cabins, in which the observations of temperature are made daily, are 

 small chambers 8 to 9 feet square by 7 to 8 feet high, formed in the coal 

 on one side of a roadway. Each cabin is separated from the roadway by 

 a brick wall with a door in it, which is usually kept shut. The door of 

 the cabin in the Ferndale mine opens into the space between two trap- 



