d to a mighty clock, or a machine which, as a whole, represents what
can never be found in one of its parts, a _perpetuum mobile_. Let us
however leave aside the idea of a _perpetuum mobile_, and dwell rather on
the comparison with a machine. It seems obvious that in order to be a
machine there must be a closed solidarity in the system. But how could a
machine have come into existence and become functional if it is driven by
wheels, which are driven by wheels, which are again driven by wheels ...
and so on unceasingly? It would not be a machine. The idea falls to pieces
in our hands. Yet our world is supposed to be just such an infinitely
continuous "system." How does it begin to depend upon and be sufficient
unto itself? But further. It is a clock, we are told, which ever winds
itself up anew, which, without fatigue and in ceaseless repetition,
adjusts the universal cycles of becoming, and disappearing, and becoming
again. It seems a corroboration of the old Heraclitian and Stoic
conception, that the eternal primitive fire brings forth all things out of
itself, and takes them back into itself to bring them forth anew. Even
to-day the conception is probably general that, out of the original states
of the world-matter, circling fiery nebulae form themselves and throw off
their rings, that the breaking up of these rings gives rise to planets
which circle in solar systems for many aeons through space, till, finally,
their energy lessened by friction with the ether, they plunge into their
suns again, that the increased heat restores the original state and the
whole play begins anew.

All this was well enough in the days of naively vitalistic ideas of the
world as having a life and soul. But not in these days of mechanics, the
strict calculation of the amount of energy used, and the mechanical theory
of heat. The world-clock cannot wind itself up. It, too, owes its activity
to the transformation of potential energy into kinetic energy. And, since
movement and work take place within it, there is in the clock as a whole
just as in every one of its parts, a mighty process of relaxation of an
originally tense spring, there is dissipation and transformation of the
stored potential energy into work and ultimately into heat. And with every
revolution of the earth and its moon the world is moving slowly but
inexorably towards a final stage of complete relaxation of her powers of
tension, a state in which all energy will be transformed