histle may be regarded as a
means of raising the wind, because the wind whistles; and rain-wizards
may make a victim shed tears that the clouds also may weep.

Sec. 7. Another consideration arises out of the complex character of causes
and effects. When a cause consists of two or more conditions or forces,
we may consider what effect any one of them would have if it operated
alone, that is to say, its _Tendency_. This is best illustrated by the
Parallelogram of Forces: if two forces acting upon a point, but not in
the same direction, be represented by straight lines drawn in the
direction of the forces, and in length proportional to their
magnitudes, these lines, meeting in an angle, represent severally the
tendencies of the forces; whilst if the parallelogram be completed on
these lines, the diagonal drawn from the point in which they meet
represents their _Resultant_ or effect.

Again, considering the tendency of any force if it operated alone, we
may say that, when combined with another force (not in the same
direction) in any resultant, its tendency is _counteracted_: either
partially, when the direction of the resultant is different; or wholly
when, the other force being equal and opposite, the resultant is
equilibrium. If the two forces be in the same direction, they are merely
added together. Counteraction is only one mode of combination; in no
case is any force destroyed.

Sometimes the separate tendencies of combined forces can only be
theoretically distinguished: as when the motion of a projectile is
analysed into a tendency to travel in the straight line of its
discharge, and a tendency to fall straight to the ground. But sometimes
a tendency can be isolated: as when,--after dropping a feather in some
place sheltered from the wind, and watching it drift to and fro, as the
air, offering unequal resistances to its uneven surface, counteracts its
weight with varying success, until it slowly settles upon the
ground,--we take it up and drop it again in a vacuum, when it falls like
lead. Here we have the tendency of a certain cause (namely, the relation
between the feather and the earth) free from counteraction: and this is
called the _Elimination_ of the counteracting circumstances. In this
case indeed there is physical elimination; whereas, in the case of a
projectile, when we say that its actual motion is resolvable (neglecting
the resistance of the air) into two tendencies, one in the line of
discharge, the