COAL MINING. 311 
is lost by the massive falls of overlying strata, though, under favorable 
conditions ninety per cent. of the whole seam is recovered ; generally, 
however, not more than 70 to 80 per cent of the whole is won. A rule 
of mining engineers in computing the yield of solid coal in the mine, is 
1,000 tons to the acre for every foot of thickness; this is 62 per cent. ; 
but in this calculation allowance is made for slack, which is not un- 
merchantable, and which frequently amounts from 12 to 15 per cent. of 
the whole. 
In the third system, which was devised by John Buddle, to whom 
the British nation is indebted for a number of important improvements 
in the art of mining, the pillars may be removed at any time. By this 
system, instead of carrying forward the workings to the boundary of 
the mining property before attacking the pillars, the mine is laid out in 
a series of quadrangular panels; each panel covering 10 or 12 acres of 
land, and including from 16 to 25 rooms. On all sides of the panel a 
solid wall or pillar of coal is left, varying in thickness according to the 
resisting power of the coal and floor of the mine. Air-waysand hauling- 
roads are cut through the panel walls at proper distances, the rooms 
being opened from an inner parallel gallery, and carried forward on the 
face or rise of the coal until the back end of the panel is reached; the 
pillars are then attacked and withdrawn, and the superincumbent strata 
of the excavated area are allowed to fall and close in. 
While the work of withdrawing pillars is going on in one panel 
the rooms of an adjoining panel are advancing forward, the strong and © 
solid pillars surrounding the excavated panel resist the crush, and con- 
fine it at home. 
The following interesting description of this system of working, 
taken from Ure’s Dictionary of Arts, Manufactures and Mines, explains 
in detail the manner of panel working, as devised by Mr. Buddle in 
the New Castle coal field in the north of England: 
“‘ By this plan of Mr. Buddle, the pillars of a panel may be worked 
out at any time most suitable for the economy of the mining operations, 
whereas, formerly, though ‘the size of the pillars and general arrange- 
ments of the mine were made with the view of taking out ultimately 
a great proportion of the pillars, yet it frequently happened that before 
the workings were pushed to the proposed extent, some part of the 
mine gave way, and produced a crush; but the most common misfortune 
was the pillars sinking into the pavement, and deranging the whole 
