The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

306 THE STEAM ENGINE.
and its height above the level of the water is 120 feet: its
mass might be lifted from the level of the water to its present
position by the combustion of 4 bushels of coals.'
The enormous consumption of coals in the arts and manufactures, and in steam navigation, has of late years excited
the fears of some persons as to the possibility of the exhaustion of our mines. These apprehensions, however, may be
allayed by the assurance received from the highest mining
and geological authorities, that, estimating the present demand
from our coal mines at 16 millions of tons annually, the coal
fields of Northumberland and Durham alone are sufficient to
supply it for 1700 years, and after the expiration of that time
the great coal basin of South Wales will be sufficient to
supply the same demand for 2000 years longer.
But, in speculations like these, the probable, if not certain,
progress of improvement and discovery ought not to be
overlooked; and we may safely pronounce that, long before a
minute fraction of such a period of time shall have rolled over,
other and more powerful mechanical agents will altogether supersede the use of coal. Philosophy already directs her finger
at sources of inexhaustible power in the phenomena of electricity and magnetism. The alternate decomposition and recomposition of water, by magnetism and electricity, has too
close an analogy to the alternate processes of vaporization
and condensation, not to occur at once to every mind: the
developement of the gases from solid matter by the operation of the chymical affinities, and their subsequent condensation into the liquid form, has already been essayed as a
source of power. In a word, the general state of physical
science at the present moment, the vigour, activity, and sagacity with which researches in it are prosecuted in every
civilized country, the increasing consideration in which
* Some of these examples were given by Sir John Herschel, in his Preliminary Discourse on Natural Philosophy; but since that work was written an
increased power has been obtained from coals, in the proportion of 7 to 12a.