ion being
especially great in the case of iron smelting. For this last operation
some kinds of raw coal are unsuitable, and such coal is converted into
coke before being used in the blast furnace. The fact that the iron ore
and the coal occur in the same district is another cause of our high rank
as a manufacturing nation.

It has often been a matter of wonder that iron ore and the material
essential for extracting the metal from it should be found associated
together, but it is most likely that this combination of circumstances,
which has been so fortunate for our industrial prosperity, is not a mere
matter of accident, but the result of cause and effect. It is, in fact,
probable that the iron ore owes its origin to the reduction and
precipitation of iron compounds by the decomposing vegetation of the
Carboniferous period, and this would account for the occurrence of the
bands of ironstone in the same deposits with the coal. In former times,
when the area in the south-east of England known as the Weald was thickly
wooded, the towns and villages of this district were the chief centres of
the iron manufacture. The ore, which was of a different kind to that found
in the coal-fields, was smelted by means of the charcoal obtained from the
wood of the Wealden forests, and the manufacture lingered on in Kent,
Sussex, and Surrey till late in the last century, the railings round St.
Paul's, London, being made from the last of the Sussex iron. When the
northern coal-fields came to be extensively worked, and ironstone was
found so conveniently at hand, the Wealden iron manufacture declined, and
in many places in the district we now find disused furnaces and heaps of
buried slag as the last witnesses of an extinct industry.

From coal we not only get mechanical work when we burn it to generate heat
under a steam boiler, but we also get chemical work out of it when we
employ it to reduce a metallic ore, or when we make use of it as a source
of carbon in the manufacture of certain chemical products, such as the
alkalies. We have therefore in coal a substance which supplies us with the
power of doing work, either mechanical, chemical, or some other form, and
anything which does this is said to be a source of energy. It is a
familiar doctrine of modern science that energy, like matter, is
indestructible. The different forms of energy can be converted into one
another, such, for example, as chemical energy into heat or electricity,
he