ame
of heat.

And when we reverse the process, and employ those tremors of heat to
raise a weight, as is done through the intermediation of an elastic
fluid in the steam-engine, a certain definite portion of the molecular
motion is destroyed in raising the weight. In this sense, and this
sense only, can the heat be said to be converted into gravity, or
more correctly, into potential energy of gravity. It is not that the
destruction of the heat has created any new attraction, but simply that
the old attraction has now a power conferred upon it, of exerting a
certain definite pull in the interval between the starting-point of the
falling weight and its collision with the earth.

So also as regards magnetic attraction: when a sphere of iron placed
at some distance from a magnet rushes towards the magnet, and has its
motion stopped by collision, an effect mechanically the same as that
produced by the attraction of gravity occurs. The magnetic attraction
generates the motion of the mass, and the stoppage of that motion
produces heat. In this sense, and in this sense only, is there a
transformation of magnetic work into heat. And if by the mechanical
action of heat, brought to bear by means of a suitable machine, the
sphere be torn from the magnet and again placed at a distance, a power
of exerting a pull through that distance, and producing a new motion of
the sphere, is thereby conferred upon the magnet; in this sense, and in
this sense only, is the heat converted into magnetic potential energy.

When, therefore, writers on the conservation of energy speak of tensions
being 'consumed' and 'generated,' they do not mean thereby that old
attractions have been annihilated and new ones brought into existence,
but that, in the one case, the power of the attraction to produce
motion has been diminished by the shortening of the distance between
the attracting bodies, and that in the other case the power of producing
motion has been augmented by the increase of the distance. These remarks
apply to all bodies, whether they be sensible masses or molecules.

Of the inner quality that enables matter to attract matter we know
nothing; and the law of conservation makes no statement regarding that
quality. It takes the facts of attraction as they stand, and affirms
only the constancy of working-power. That power may exist in the form
of MOTION; or it may exist in the form of FORCE, with distance to act
through. The former is dynamic en