612 
[October, 
The Vehicle of Force. 
tending the one to, the other from, the same point, are forced 
to recede from each other. And the vigour of this influence 
is probably governed only by the energy of the motions and 
the distance separating them, — net at all by their degree of 
approach to parallelism. 
All motions, whatever their direction, must, under the 
operation of the above law, exert an influence, either at- 
tractive or repulsive, upon all other motions. There can be 
no neutral state in which both these influences will disappear. 
For a close observance of the possible directions of two 
lines of motion, which end in or tend towards the same 
point, shows that they must hold toward each other one of 
the above relations, and that no intermediate relation is 
possible. They must either both approach or both recede 
from this point, or one must approach and the other recede. 
But in the case of motions which do not tend to or from 
such a point, and are not parallel, conditions of both attrac- 
tion and repulsion might exist between their different parts. 
A great variety of relations might thus arise, in some of 
which the opposite influences might become balanced, and 
neutrality arise through opposition, not through loss of 
force. 
Motions also may readily become reversed, with a conse- 
quent reversal of their forces ; and if this reversal is rapid 
and incessant the effeCt of neutralisation will be produced. 
Such is the case in heat vibration. A vibrating particle 
reverses its relations of motion to all contiguous particles 
at every change of phase in its vibration. Thus its influence 
constantly shifts from attractive to repulsive, and the con- 
trary, and its force effect is virtually neutralised. An 
analogous condition may arise in the case of magnetic sub- 
stance. When its internal movements are largely in the 
same direction the magnetic phenomena appear. When not 
largely in the same direction their external influence becomes 
neutralised, the attractive and repulsive forces of the various 
particles balancing each other. 
But although positive neutrality cannot exist between two 
motions, it may easily exist between motion and rest ; for if 
force is an attribute of motion, changing in vigour as motion 
changes in energy, a particle at rest must cease to exist so 
far as the exertion of force is concerned, since with the dis- 
appearance of its motion its force display must likewise 
disappear. In like manner a particle approaching rest must 
decrease in force through the diminution of its momentum ; 
at the same time the force exerted upon it by other matter 
must similarly decrease. The force exerted between any 
