304 



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



The first intimation in such a case is the fouling of the currents ; the arti- 

 ficial power may then he increased and the crisis passed without accident, 

 but if an explosion takes place there is no trace of its cause discoverable. 



One example of an explosion which happened under these circumstances 

 may not be out of place. It occurred in winter. The temperature of the 

 air rose for two days in succession to a higher point than it had reached 

 for a considerable time before. On the second day, when natural venti- 

 lation would cease in many shallow mines and become sluggish in deeper 

 ones, an explosion took place by which many men were killed. 



After the accident the Inspector for the district visited the mine ; he 

 described it as having strong natural ventilation, and looked upon the 

 explosion as a mystery. It so happens, however, that for more than three 

 months afterwards the temperature at the surface only reached the point 

 which was observed on the day of the explosion on two occasions — once 

 at midnight three days after the accident, and once on the thirty-second 

 day after it. It is therefore very improbable that the Inspector saw the 

 mine in at all the same state of ventilation as that which had prevailed at 

 the time of the explosion, and hence his description of the phenomena. 

 This explosion and some others like it are marked by triangles on our 

 diagrams. 



There are two groups of accidents during the year 1870, one between 

 the 10th and 14th of February, the other at the end of December, both 

 of which occurred when the temperature was abnormally low, and the 

 atmospherical pressure high and steady. One of these accidents (that on 

 February 14th in South Wales, whereby thirty men were killed) was 

 traced to the escape of gas from a forty-acre goaf, in which it had been 

 most injudiciously pent up until it attained so great a tension that it forced 

 its way through the barriers into one of the air-courses, where it was 

 ignited. 



The others are probably ascribable to the so-called "sharpness" of the 

 fire when ventilation is very active. Under ordinary circumstances, in the 

 lower parts of small accumulations of explosive mixtures, there is a stratum 

 of air containing less gas than is requisite to make it explosive ; and when 

 the miner slowly raises his candle into this stratum, shading all the flame 

 excepting the very top with his hand, he is warned, by the increasing size 

 of the "cap" (the blue flame of the gas seen on the top of the candle- 

 flame), that there is an explosive mixture above. When the air in the 

 mine becomes very pure this stratum disappears in many cases ; there is 

 no longer a space between the pure air, in which fire-damp cannot be di- 

 stinguished, and the explosive mixture above, and the gas is then called 

 " sharp," because it ignites without warning when a candle is raised into it. 



It appears to us, in conclusion, that the evidence we submit fairly jus- 

 tifies the view that meteorological changes are the proximate causes of a 

 large majority of the accidents. It will be remembered, as Mr. Dobson 

 has observed, that the records " contain no account of cases like that of 



