erse may be represented in the imagination as an aggregate of bodies
participating in motions of extraordinary complexity, but of one type.
But now let the emphasis be placed upon the determining causes rather
than upon the moving bodies themselves. In other words, let the bodies
be regarded as attributive and the forces as substantive. The result is
a radical alteration of the mechanical scheme and the transcendence of
common-sense imagery. This was one direction of outgrowth from the work
of Newton. His force of gravitation prevailed between bodies separated
by spaces of great magnitude. Certain of the followers of Newton,
notably Cotes, accepting the formulas of the master but neglecting his
allusions to the agency of God, accepted the principle of action at a
distance. _Force_, in short, _was conceived to pervade space of itself_.
But if force be granted this substantial and self-dependent character,
what further need is there of matter as a separate form of entity? For
does not the presence of matter consist essentially in resistance,
itself a case of force? Such reflections as these led Boscovich and
others to the radical departure of defining material particles _as
centres of force_.

[Sidenote: The Development and Extension of the Conception of Energy.]

Sect. 108. But a more fruitful hypothesis of the same general order is
due to the attention directed to the conception of _energy_, or capacity
for work, by experimental discoveries of the possibility of reciprocal
transformations without loss, of motion, heat, electricity, and other
processes. The principle of the conservation of energy affirms the
quantitative constancy of that which is so transformed, measured, for
example, in terms of capacity to move units of mass against gravity. The
exponents of what is called "energetics" have in many cases come to
regard that the quantity of which is so conserved, as a substantial
reality whose forms and distributions compose nature. A contemporary
scientist, whose synthetic and dogmatic habit of mind has made him
eminent in the ranks of popular philosophy, writes as follows:

"Mechanical and chemical energy, sound and heat, light and
electricity, are mutually convertible; they seem to be but
different modes of one and the same fundamental force or
_energy_. Thence follows the important thesis of the unity of
all natural forces, or, as it may also be expressed, the
'monism of energy.'"[23