300 Messrs. Scott and Galloway on the Connexion [Apr. 18, 



but on the 11th of December a serious fall is observed, and two accidents 

 occurred next day. The explosions which appear at the end of the year 

 do not seem to be referable to pressure. 



On the whole, we find in 1 870 1 79 explosions (67 of them fatal), of which 

 92 are due to the state of the barometer, 43 to the temperature, while 44 

 remain unaccounted for by either of these agencies. 



As a general summary, we consider that out of 525 explosions recorded 

 in the three years, 49 per cent, may be reasonably connected with dis- 

 turbance of the barometer, 22 per cent, with abnormally high tempera- 

 ture, while 29 per cent, are not traceable to atmospherical agency. 



[Since handing in the paper, we have received the statistics of non-fatal 

 explosions in the mines of Yorkshire during the years 1869 and 1870. 



In 1869 there were eight occurrences, of which we attribute four to the 

 state of the barometer, one to temperature, while three are unaccounted for. 



In 1870 there were seventeen occurrences, of which we attribute six to 

 the state of the barometer, four to temperature, while seven are unac- 

 counted for. 



These figures raise the total number of accidents to 550, but do not ma- 

 terially alter the percentages given in the text. The facts have been in- 

 serted in the diagrams. — April 13, 1872.] 



It may not be out of place to discuss briefly the manner in which an in- 

 creased supply of gas or a diminished supply of air brought about by any 

 of the causes just alluded to, leads to a fouling of the ventilating-current 

 in its passage through the workings ; and also how the comparative purity 

 or foulness of the ventilating-current affects the condition of the air in 

 places adjoining its course. 



The gas flows from the fissures of the coal and stone either into a venti- 

 lating-current, by which it is carried out of the mine, as when it escapes at 

 the face of a long-wall working or bratticed bord, or from the sides of an 

 air-course ; or, secondly, it flows into a quiet atmosphere, such as that in 

 goaves and cavities in the roof whence stone has fallen, in unbratticed bords, 

 or in recesses between pack-walls in long-wall workings. In any of these 

 latter cases it diffuses itself into the surrounding air, and an accumulation 

 of a more or less explosive character is generated. 



As long as the average quantity of air is circulating in the mine and the 

 quantity of gas which escapes into the workings is not suddenly increased, 

 we may take it for granted that little danger exists ; for the districts of the 

 mine in which explosive mixtures are to be met with are clearly defined and 

 well known, so that precautions can be taken to prevent ignition. 



As soon as these conditions are in any way changed (i. e., if the supply 

 of air be diminished in quantity or deteriorated in quality by an increased 

 escape of gas), explosive mixtures may make their appearance in places 

 where no danger had previously existed. 



It may be assumed that a ventilating-current consists of pure air 



