A FEW WORDS ABOUT COAL. 309 



perature, is purely voluntary. The increase has been 

 calculated at a rate for which there is no authority ; 

 and while we are saying our coal-beds cannot be worked 

 below 4,000 feet, a colliery in Belgium has nearly ap- 

 proached that depth, and no inconvenience is experi- 

 enced by the miners.' But unfortunately this sanguine 

 view has not been supported by recent researches. It 

 will be known to our readers that in '1865 commission- 

 ers were appointed for discussing the whole subject of 

 our coal supply. Among their ranks were several of 

 the most eminent geologists, as well as some of the 

 highest authorities on the practical questions involved 

 in the subject. The question of the possible depth to 

 which our mines could be worked, was necessarily one 

 to which the commissioners were bound to give veij 

 close attention ; and we may fairly accept the result of 

 their inquiries as representing the most trustworthy 

 conclusion which has yet been reached on this particular 

 point. Now they stated that, according to the ordinary 

 method of working, the depth at which the temperature 

 of the mine would reach blood heat (or ninety-eight 

 degrees Fahrenheit) is about 3,000 feet. They ex- 

 pressed a belief that, by the 'long-wall' system of 

 working, a depth of 3,420 feet might be reached 

 before this temperature was attained ; but whether 

 this will prove to be the case or not remains to be seen. 

 Now, although the human frame' can bear for a while a 

 greater heat than 100 or even 200 degrees Fahrenheit,* 



* Brewster mentions that Chantrey's workmen used to enter the fur- 

 nace which the sculptor employed in drying his moulds, when the tem- 

 perature was as high as 340, ' walking over the floor with wooden 



