299 
Force has the power of imparting it, but energy can impart or 
transfer itself, without force. Heat, light, and the rest, are not 
forces, but forms of energy. They are brisk, vibratory agita- 
tion. Yet neither are they “ modes of motion,” but forms or 
kinds of energy. All this hopeless labyrinth of confusion arises 
from confounding two distinct ideas under one ambiguous 
name, and then fancying that we have discovered a third object 
of thought, distinct from both, and hereby effected a grand 
scientific discovery. 
To recover clearness of thought we must hold fast this simple 
truth : Kinetic Energy is one thing, and Potential Energy 
anothei’, quite distinct. The first is motion, the second, force, 
the conceived cause of motion. The first is actual motion. The 
second is not actual force, but a summation of possible future 
forces. Assume that forces depend only on the distances, and 
have acted and will act, only within limits of distance somehow 
defined; and the increase or diminution of motion will of 
course answer to the sum total of past force exercised ; and 
when the remaining possibilities of force, up to the conceived 
limit, are added to this past effect, we shall have not really but 
numerically, a constant sum. 
Like Force, Energy produces motion, and still is not Force. 
It is transferred when Motion is transferred, and is not Motion. 
Force and Motion both convey it, and still it is neither. Heat, 
Light, and Sound are not forces, nor, as some illogically say, 
modes of motion, but forms of energy. Yet Bacon and Locke 
have well defined the first, and might have defined the others, 
as “ brisk, vibratory agitations.” 
All this confusion is the natural result of mixing up two ideas 
under one ambiguous name. Sometimes it means one, some- 
times the other. All the properties of each may thus be affirmed 
and denied of it in turn, and with equal truth. Kinetic Energy 
has all the characters of motion, not of actual or possible force. 
Potential Energy has those of a sum total of possible forces, but 
not of actual force, or of actual or possible motion. This third 
something, called Energy, distinct alike from force and motion, 
is an idol of the marketplaces of science. It is an illusion and 
shadow, though some dare attempt to place it on the throne of 
the universe. 
Let us examine the doctrine, freed from this ambiguous and 
deceptive phrase, on the side of induction and experience. The 
conservation of motion, to pass from an hypothesis into reality, 
requires three conditions to be fulfilled. First, in Physics, it 
excludes the notion of ultimate incompressibility, which Sir W. 
Hamilton and Mr. Spencer alike accept as a fundamental law 
