Faraday as a Discoverer HTML version

Chapter 14
Unity and convertibility of natural forces: theory of the electric current.
The terms unity and convertibility, as applied to natural forces, are often employed in
these investigations, many profound and beautiful thoughts respecting these subjects
being expressed in Faraday's memoirs. Modern inquiry has, however, much augmented
our knowledge of the relationship of natural forces, and it seems worth while to say a few
words here, tending to clear up certain misconceptions which appear to exist among
philosophic writers regarding this relationship.
The whole stock of energy or working-power in the world consists of attractions,
repulsions, and motions. If the attractions and repulsions are so circumstanced as to be
able to produce motion, they are sources of working-power, but not otherwise. Let us for
the sake of simplicity confine our attention to the case of attraction. The attraction
exerted between the earth and a body at a distance from the earth's surface is a source of
working-power; because the body can be moved by the attraction, and in falling to the
earth can perform work. When it rests upon the earth's surface it is not a source of power
or energy, because it can fall no further. But though it has ceased to be a source of
energy, the attraction of gravity still acts as a force, which holds the earth and weight
The same remarks apply to attracting atoms and molecules. As long as distance separates
them, they can move across it in obedience to the attraction, and the motion thus
produced may, by proper appliances, be caused to perform mechanical work. When, for
example, two atoms of hydrogen unite with one of oxygen, to form water the atoms are
first drawn towards each other--they move, they clash, and then by virtue of their
resiliency, they recoil and quiver. To this quivering motion we give the name of heat.
Now this quivering motion is merely the redistribution of the motion produced by the
chemical affinity; and this is the only sense in which chemical affinity can be said to be
converted into heat. We must not imagine the chemical attraction destroyed, or converted
into anything else. For the atoms, when mutually clasped to form a molecule of water, are
held together by the very attraction which first drew them towards each other. That which
has really been expended is the pull exerted through the space by which the distance
between the atoms has been diminished.
If this be understood, it will be at once seen that gravity may in this sense be said to be
convertible into heat; that it is in reality no more an outstanding and inconvertible agent,
as it is sometimes stated to be, than chemical affinity. By the exertion of a certain pull,
through a certain space, a body is caused to clash with a certain definite velocity against
the earth. Heat is thereby developed, and this is the only sense in which gravity can be
said to be converted into heat. In no case is the force which produces the motion
annihilated or changed into anything else. The mutual attraction of the earth and weight
exists when they are in contact as when they were separate; but the ability of that
attraction to employ itself in the production of motion does not exist.