Sddntific Intelligence — Geology, 171 



it becomes more and more, abundant in proportion as this pres- 

 sure is diminished. Besides, the pressure under which the gas 

 commences to be evolved from the pores of the coal, varies in 

 different mines. It is sometimes scarcely superior to the common 

 pressure of the atmosphere, as without doubt is the case in many 

 of the mines in Northumberland, in which, according to Mr 

 Buddie, the atmosphere becomes explosive when the barometer 

 is low, whilst scarcely a trace of inflammable air is to be found 

 when the barometer is very high. At other times, it exceeds con- 

 siderably the pressure of the atmosphere. Monsieur Combes states 

 the following as a proof of this. We give the statement in his 

 own words. " In the year 1830, 1 caused the shaft of a coal-pit 

 at Latour, near Firmini, Department of the Loire, to be emptied 

 of the water it contained. This pit had for many years been 

 abandoned, on account of the immense quantities of inflammable 

 air which had been generated in the galleries, which had occa- 

 sioned so many deplorable accidents, that the working could not 

 be continued, on account of the imminent risk. The pit was 

 230 feet deep at the place where it reached the roof of the gal- 

 leries in the coal, and it was filled with water to within Q5 feet 

 of the surface. This free portion of the pit contained only at- 

 mospheric air, without a single trace of carburetted hydrogen. 

 When the water was pumped out to the depth of 193 feet from 

 the surface, the roof of the galleries being still covered with wa- 

 ter to the extent of 37 feet, the gas began to be disengaged 

 through the column of water still in the pit, with a noise such as 

 a copious spring would have made by faUing from the upper 

 part of the shaft. After this event, the air in the pit continued 

 to be in the highest degree explosive. One day two workmen 

 incautiously descended into the pit to discover the spring, which 

 they supposed issued from the upper part of the shaft ; they 

 took a common lamp along with them, and when they had de- 

 scended about 45 feet, their lamp set fire to the gas ; when, for- 

 tunately enough, only the upper layer exploded. One of the 

 workmen was severely scorched. When they had ascended to 

 the surface, and a wisp of burning straw was thrown into the 

 pit, a very great explosion was the immediate result. Thus, in 

 this mine, the inflammable gas was evolved under a pressure at 

 least equal to two atmospheres, and probably much more ; the 



