omes, in the end, to employ it entirely in making his
lungs breathe and his heart beat.

From this point of view, a world like our solar system is seen to be
ever exhausting something of the mutability it contains. In the
beginning, it had the maximum of possible utilization of energy: this
mutability has gone on diminishing unceasingly. Whence does it come? We
might at first suppose that it has come from some other point of space,
but the difficulty is only set back, and for this external source of
mutability the same question springs up. True, it might be added that
the number of worlds capable of passing mutability to each other is
unlimited, that the sum of mutability contained in the universe is
infinite, that there is therefore no ground on which to seek its origin
or to foresee its end. A hypothesis of this kind is as irrefutable as it
is indemonstrable; but to speak of an infinite universe is to admit a
perfect coincidence of matter with abstract space, and consequently an
absolute externality of all the parts of matter in relation to one
another. We have seen above what we must think of this theory, and how
difficult it is to reconcile with the idea of a reciprocal influence of
all the parts of matter on one another, an influence to which indeed it
itself makes appeal. Again it might be supposed that the general
instability has arisen from a general state of stability; that the
period in which we now are, and in which the utilizable energy is
diminishing, has been preceded by a period in which the mutability was
increasing, and that the alternations of increase and diminution succeed
each other for ever. This hypothesis is theoretically conceivable, as
has been demonstrated quite recently; but, according to the calculations
of Boltzmann, the mathematical improbability of it passes all
imagination and practically amounts to absolute impossibility.[89] In
reality, the problem remains insoluble as long as we keep on the ground
of physics, for the physicist is obliged to attach energy to extended
particles, and, even if he regards the particles only as reservoirs of
energy, he remains in space: he would belie his role if he sought the
origin of these energies in an extra-spatial process. It is there,
however, in our opinion, that it must be sought.

Is it extension in general that we are considering _in abstracto_?
_Extension_, we said, appears only as a _tension_ which is interrupted.
Or, are we considering the c