REPORTS 



THE STATE OF SCIENCE. 



Report on the Relation between Explosions in Coal-mines and Re- 

 volving Storms. By Thomas Dobson, B.A., of St. John's College, 

 Cambridge. 



In coal-mines liable to explosions, there is a continuous discharge of car- 

 buretted hydrogen gas, from the innumerable minute fissures of the fractured 

 coal, into the galleries of the mine. The rate and quantity of this issue of 

 gas depend, cceteris paribus, upon the density of the atmosphere ; being 

 greater when this density is less, and vice versa. The preponderance of air 

 over gas in the atmosphere of the mine never falls below a certain fixed 

 ratio without producing a risk of explosion; hence a due adjustment must 

 be maintained at all times between the rates of ventilation and of gaseous 

 discharge, in order to prevent the mine from becoming charged with gas 

 up to the explosive point. 



It is here proposed to consider the effect of extraordinary fluctuations of 

 the density and temperature of the atmosphere in deranging this delicate 

 adjustment of opposing powers. 



There are two ways in which meteorological agency may render the atmo- 

 sphere of a mine explosive. 



1. During a period of comparatively calm weather, when the mercury in 

 the barometer ranges above 30 inches for several days, the usual escape of gas 

 into the mine is checked by the greater density of the air, and the tension of 

 the pent-up gases increases. If such a period be succeeded by a rapid dimi- 

 nution of atmospheric pressure, indicated by a considerable fall of the mer- 

 curial column, the consequent outpouring of suddenly liberated gas may be 

 so great as to overpower the ordinary ventilation of the mine, and thus an 

 explosive atmosphere may be produced by an excessive issue of gas, owing to 

 a sudden decrease of atmospheric pressure. 



2. Supposing the action of the ventilating mechanism to remain unchanged 

 and the flow of gas into the mine to be steady and constant in quantity, it is 

 evident that the effective ventilation will vary inversely as the temperature of 

 the external air. In fact, the efficiency of the ventilation depends chiefly 

 upon the difference of temperature of the air in the mine and the air above- 

 ground. Hence a considerable rise in the temperature of the external air 

 may so impede the ventilation as to render it inadequate to effect the neces- 

 sary dilution and removal of even the ordinary quantity of gas discharged ; 



1855. B 



