consist of numerous individuals.

Of that class of mechanical agents by which motion is
transmitted--the lever, the pulley, the wedge, and many others--
it has been demonstrated, that no power is gained by their use,
however combined. Whatever force is applied at one point can only
be exerted at some other, diminished by friction and other
incidental causes; and it has been further proved, that whatever
is gained in the rapidity of execution is compensated by the
necessity of exerting additional force. These two principles,
long since placed beyond the reach of doubt, cannot be too
constantly borne in mind. But in limiting our attempts to things
which are possible, we are still, as we hope to shew, possessed
of a field of inexhaustible research, and of advantages derived
from mechanical skill, which have but just begun to exercise
their influence on our arts, and may be pursued without limit
contributing to the improvement, the wealth, and the happiness of
our race.

16. Of those machines by which we produce power, it may be
observed, that although they are to us immense acquisitions, yet
in regard to two of the sources of this power--the force of wind
and of water--we merely make use of bodies in a state of motion
by nature; we change the directions of their movement in order to
render them subservient to our purposes, but we neither add to
nor diminish the quantity of motion in existence. When we expose
the sails of a windmill obliquely to the gale, we check the
velocity of a small portion of the atmosphere, and convert its
own rectilinear motion into one of rotation in the sails; we thus
change the direction of force, but we create no power. The same