possessed a speed equal to its own, moving in the same direction, it
would no longer exist so far as our sense of touch is concerned.

[Footnote 5: "Nothing is created; nothing is lost"--ED.]

On this hypothesis, matter would only be the capacity for kinetic
energy, its pretended impenetrability energy of volume, and its weight
energy of position in the particular form which presents itself in
universal gravitation; nay, space itself would only be known to us by
the expenditure of energy necessary to penetrate it. Thus in all
physical phenomena we should only have to regard the quantities of
energy brought into play, and all the equations which link the
phenomena to one another would have no meaning but when they apply to
exchanges of energy. For energy alone can be common to all phenomena.

This extreme manner of regarding things is seductive by its
originality, but appears somewhat insufficient if, after enunciating
generalities, we look more closely into the question. From the
philosophical point of view it may, moreover, seem difficult not to
conclude, from the qualities which reveal, if you will, the varied
forms of energy, that there exists a substance possessing these
qualities. This energy, which resides in one region, and which
transports itself from one spot to another, forcibly brings to mind,
whatever view we may take of it, the idea of matter.

Helmholtz endeavoured to construct a mechanics based on the idea of
energy and its conservation, but he had to invoke a second law, the
principle of least action. If he thus succeeded in dispensing with the
hypothesis of atoms, and in showing that the new mechanics gave us to
understand the impossibility of certain movements which, according to