d if there is
any reason to believe that any one of them may have had some influence
in determining an observed result, then it is foolish to exclude these
things from philosophic consideration, on the ground that they are out
of place in the realm of Natural Philosophy, that they are not allowed
for in its scheme, and therefore cannot possibly be supposed capable of
exerting any effective interference, any real guidance or control.

[4] It is on a similar basis that there is a science of rigid
dynamics, with elasticity and fluidity excluded; and thus also
can there be a hydrodynamics in which the consequences of
viscosity are ignored.

My contention then is--and in this contention I am practically speaking
for my brother physicists--that whereas life or mind can neither
generate energy nor directly exert force, yet it can cause matter to
exert force on matter, and so can exercise guidance and control: it can
so prepare any scene of activity, by arranging the position of existing
material, and timing the liberation of existing energy, as to produce
results concordant with an idea or scheme or intention: it can, in
short, "aim" and "fire."

Guidance of _matter_ can be affected by a passive exertion of force
without doing work; as a quiescent rail can guide a train to its
destination, provided an active engine propels it. But the analogy of
the rail must not be pressed: the rail "guides" by exerting force
perpendicular to the direction of motion, it does no work but it
sustains an equal opposite reaction.[5] The guidance exercised by life
or mind is managed in an unknown but certainly different fashion:
"determination" can sustain no reaction--if it could it would be a
straightforward mechanical agent--but it can utilise the mechanical
properties both of rail and of engine; it arranged for the rail to be
placed in position so that the lateral force thereby exerted should
guide all future trains to a desired destination, and it further took
steps to design and compose locomotives of sufficient power, and to
start them at a prearranged time. It "employs" mechanical stress, as a
capitalist employs a labourer, not doing anything itself, but directing
the operations. It is impossible to explain all this fully by the laws
of mechanics alone, that is to say, no mechanical analysis can be
complete and all-embracing, though the whole procedure is fully subject
to those laws.

[5] It is well to be