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these definitions, in fact, appear to comprise both force and 
energjr. 
8. The definition of force which appears to the writer least 
open to objection, is — that which produces a mutual action 
BETWEEN DIFFERENT PORTIONS OR PARTICLES OF MATTER, BY 
WHICH THEY ARE EITHER ATTRACTED TOWARDS OR REPELLED 
from each other. Hence, force must be essentially either 
attractive or repulsive in its character. By this action “ energy ” 
is imparted to the matter put in motion : hence force may be 
further characterized as having the power of imparting energy. 
But for the same reasons as those above stated, “ the power 
of imparting energy ” will not serve as a definition of force, 
because energy may be imparted by other matter possessing 
energy, without the intervention of any force. 
9. Cohesive attraction may be quoted as a force acting 
between contiguous atoms or molecules of a body ; electric and 
magnetic attraction and repulsion as forces acting between 
certain particles and masses under certain conditions only ; 
gravitation, or weight attraction, as a force acting indis- 
criminately between all portions of matter : the mutual actions 
of masses being only the aggregate of the actions of their 
component particles. Heat, or more correctly speaking 
thermic energy, is an universal source of repulsive force acting 
between the particles of all kinds of matter. 
10. Energy was first (as the writer believes) defined by 
Thomas Young to be The Power of Doing Work, and this 
definition does not appear to require any amendment. 
11. Energy, as it exists in moving matter, is called actual or 
kinetic : and this kind of energy implies the existence of 
motion and vice versa , but it is not (as it has frequently been 
assumed to be) identical or synonymous with motion. 
12. When energy, from the circumstances of the case, 
remains undeveloped in matter, inactive but capable of being 
called into action, it is termed “ potential energy.” Thus the 
energy of chemical affinity existing between the elements of 
gunpowder is potential; but when called into action by 
elevation of temperature, the repulsive force existing between 
the particles of the highly-condensed and heated gases into 
which the gunpowder is resolved imparts actual or kinetic 
energy to the shot. 
13. If a weight be raised, a certain amount of energy is ex- 
pended in raising it, and so long as the body is supported, the 
energy expended in raising it remains potential in it ; but when 
allowed to fall freely in vacuo to the level from which it was 
raised, the body acquires, in an active or kinetic form, exactly the 
amount of energy that was expended in raising it. Similarly 
