the general law, most substances exhibiting the
opposite thermal effects when stressed. However, here, too, the
action of the stress is opposed by the secondary effects
developed in the substance; for it is found that this substance
contracts when heated, expands when cooled. Again, ice being a
substance which contracts in melting, the effect of pressure is
to facilitate melting, lowering its freezing point. But

64

so soon as a little melting occurs, the resulting liquid calls on
the residual ice for an amount of heat equivalent to the latent
heat of liquefaction, and so by cooling the whole, retards the
change.

Such particular cases illustrate a principle controlling the
interaction of matter and energy which seems universal in
application save when evaded, as we shall see, by the ingenuity
of life. This principle is not only revealed in the researches of
the laboratory; it is manifest in the history of worlds and solar
systems. Thus, consider the effects arising from the aggregation
of matter in space under the influence of the mutual attraction
of the particles. The tendency here is loss of gravitational
potential. The final approach is however retarded by the
temperature, or vis viva of the parts attending collision and
compression. From this cause the great suns of space radiate for
ages before the final loss of potential is attained.

Clerk Maxwell[1] observes on the general principle that less
force is required to produce a change in a body when the change
is unopposed by constraints than when it is subjected to such.
From this if we assume the external forces acting upon a system
not to rise above a certain potential (which is the order of
nature), the constraints of secondary actions may, under certain
circumstances, lead to final rejection of some of the energy, or,
in any

[1] _Theory of Heat_, p. 131.

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case, to retardation of change in the system--dissipation of
energy being the result.[1]

As such constraints seem inherently present in the properties of
matter, we may summarise as follows:

_The transfer of energy into any inanimate material system is
attended by effects retardative to the transfer and conducive to
dissipation._

Was this the only possible dynamic order ruling in material
systems it is quite certain the myriads of ants and pines never
could have been, except all generated by creative act at vast
primary expenditure of energy. Growth and reproduction would have
been