236 REPORT— 1861. 



of the laminae in the direction of the line of fire, i. e. perpendicular to the 

 faces of the work; for on inspecting the last column in Table XII. which con- 

 tains the values of T, under the several conditions of rock and of compres- 

 sion, it is at once apparent how much greater is the " work done" in crushing 

 the slates and the quartz in their toughest and most compressible direction, 

 i. e. in the direction of the lamina. Twice as much tvork is, upon the average, 

 consumed in crushing the rock in this direction, that suffices to destroy 

 its cohesion in the one transverse to the lamina ; and the proportion in the 

 two, in the case of the softest quartz (Nos. 5 and 8), is as much as about ^/Je 

 to one. 



It would be unsuitable, however, to the present memoir to pursue further 

 here such practical deductions suggested by the results obtained experi- 

 mentally. 



On the Explosions in British Coal-Mines during the year 1859. By 

 Thomas Dobson, B.A., Head Master of the School Frigate " Con- 

 way" Liverpool. 



In my Report " On the Relation between Explosions in Coal-mines .and Re- 

 volving Storms," read at the Meeting of this Association, at Glasgow, in 

 1855, 1 have given my reasons for tliinking that the freedom of the atmo- 

 sphere of a mine from noxious gases, and the occasional abundant issue of 

 such gases into a mine, are in a great measure dependent upon certain con- 

 ditions of the pressure and temperature of the external atmosphere. This 

 dependence is, indeed, a consequence so direct and obvious of the first prin- 

 ciples of pneumatics, that we may speak with certainty of the ki7id of influ- 

 ence exerted by the atmosphere in restraining or augmenting the flow of in- 

 flammable gases into a mine ; and we have only to inquire whether this influ- 

 ence is ever exercised to such a degree as to charge a mine up to the point 

 of explosion. 



It is, I think, now generally admitted that a high atmospheric pressure 

 tends to check the issue of gases into the workings of amine, and that a low 

 pressure favours their copious efi"usion from the broken coal and deserted 

 goaves. 



It is also evident that a low temperature of the external air makes the 

 ventilation of a mine brisk and effective, while a high temperature of the air 

 above renders the ventilation sluggish, and causes the gases to accumulate 

 below. 



I have compared the dates of all the fatal explosions in British coal-mines, 

 as given in the Reports of the Government Inspectors of Mines, with the 

 corresponding barographical and thennographical records for several years, 

 and find that this comparison tends to confirm in a very striking manner the 

 conclusions arrived at in my Report of the year 1855. 



Were the Government Inspectors to give in their Reports the dates of all 

 explosions of gases in mines, whether fatal or not, and also the dates of days 

 when mines have been in a dangerous state from the abundance of gas, but 

 explosion avoided, the evidence of atmospheric influence would soon be placed 

 beyond doubt. Seeing that the great atmospheric disturbances with which 

 we are here concerned generally extend nearly simultaneously over Britain 

 and the adjacent countries of the Continent, I have been at some pains to 

 obtain the dates of all the great explosions in the coal-mines of France and 

 Belgium; but I was told at the Ecole des Mines, in Paris, that they had no 



