160 
POPULAR SCIENCE REVIEW. 
but for our purpose it is sufficient to confine attention to tlie 
carbon only. 
One pound of pure coal yields, in combining with oxygen in 
combustion, theoretically , an energy equal to the power of 
lifting 10,808,000 pounds one foot high. The quantity of heat 
necessary to raise a pound of water one degree will raise 772 
pounds one foot. A pound of coal burning should yield 14,000 
units of heat, or 772 x 14,000=10,808,000 pounds, as above. 
Such is the theoretical value of a pound of pure coal. Many 
of our coal-seams are about a yard in thickness ; several impor- 
tant seams are much thicker than this, and one well-known 
seam, the thick coal of South Staffordshire, is ten yards in 
thickness. This, however, concerns us no further than that it 
is useful in conveying to the mind some idea of the enormous 
reservoir of power which is buried in our coal formations. One 
square yard of the coal from a yard-thick seam — that is, in fact, 
a cubic yard of coal — weighs about 2,240 pounds avoirdupois ; 
the reserved energy in that cube of coal is equal to lifting 
1,729,200 pounds one foot high. We are raising every year 
about 110,000,000 tons of coal from our coal-beds, each ton 
of coal being about a square yard. The heat of that coal is 
equal to a mechanical lifting power which it is scarcely pos- 
sible to convey to the mind in anything approaching to its 
reality. If we say it is 190,212,000 millions we merely state 
an incomprehensible number. We may do something more 
than this, if we can convey some idea of the magnitude of the 
mass of coal which is raised annually in these islands. 
The diameter of this globe is 7,926 miles, or 13,880,760 
yards ; therefore the coal raised in 1870 would make a solid bar 
more than eight yards wide and one yard thick, which would 
pass from E to W through the earth at the equator. Supposing 
such a mass to be in a state of ignition, we can perhaps imagine 
the intensity of its heat, and its capability, if employed in 
converting water into steam, of exerting the vast force which 
we have endeavoured to indicate. It was intimated last year in 
the House of Commons by a member of the Coal Commission 
that the decision of that body, after a long and laborious 
inquiry, would be that there existed in our coal-fields a supply 
for about one thousand years at our present rate of consumption. 
We have therefore to multiply the above computation by 1,000 
to arrive at any idea of the reserved power of our British coal- 
fields. What must it have been ere yet our coal deposits were 
disturbed ! At the time of the Roman occupation coal was 
used in this country. In the ruins of Roman Uriconium coal 
has been found. Certainly up to the present time a quantity 
of not less than three thousand million tons of coal have been 
dug out of our carboniferous deposits and consumed. All this 
