Chance. I 4Ub [May 6, 



The table is arranged to show the number of explosions occuring in each 

 month of the year for ten years, and the right hand column the number 

 for each month of the whole period. 



An inspection of latter column shows at once that from April to October 

 the number of explosions is far greater than that of the remaining months 

 of the year. In these seven months 463 explosions are recorded, an aver- 

 age of sixty-six for each month, but for the remaining five months (Jan., 

 Feb., March, Nov. and Dec.) we find but 216 explosions, an average of 

 but forty-three for each of these months. 



Temporary or partial suspension of mining during some part of these 

 months in certain years may partly account for this difference, but is inade- 

 quate to explain so marked a contrast between the groups of warm and 

 cold months. 



It seems probable, that if a closer differentiation could be made, it would 

 be found that many of the explosions occurring during the warm months, 

 happened at or immediately following a short period of unusual warmth, 

 during which the ventilating current was somewhat diminished in strength. 

 At such a time, when unusual warmth with higli barometer had existed for 

 one or two days, a sudden fall in the barometric column, presaging a local 

 or general storm would surely be followed by an increased outflow of gas 

 which might readily become explosive at the working face while the air 

 still remained safe in the upcast.* 



The low rate of July may be due in part to partial suspension of opera- 

 tions during that month, and the high rates of November and December, 

 high compared to those of January, February and March, are probably due 

 in part to steady working to supply the winter demand, and the low rates 

 of the remaining winter months to partial suspension of work. 



The maximum rate in May, and the next in rank, October, are just five 

 months apart. Are these months subject to greater and more sudden and 

 frequent barometric changes than others in this part of the United States ? 



A list of the most serious colliery disasters in Great Britain, from 1778 to 

 1866 inclusive, develops the interesting fact that out of forty -five explosions, 

 ten occurred in June and eight in December, periods just six months apart. 



The table is as follows : 



Months. '^^- °/ 



Explosions. 



January 2 



February 1 



March 4 



April 



May 4 



*If one per cent, of gas in the upcast corresponds to a maximum of Ave per 

 cent, at the working face (in places where "accumulations" are found) an in- 

 crease of two per cent, in the upcast, making three per cent, in all, a perfectly 

 safe percentage— means an increase to seven per cent, at the working face; a 

 condition of great danger. The .above described meteorological conditions may 

 often bring about just such a result. 



