Wb have considered the effects of the first movers of
machinery, and we must now direct our attention to the
subject of Friction, which, as we have frequently noticed,
tends to diminish these eflects. On this subject it is not
our intention to dwell long, as all the researches that have
been hitherto made in this branch of mechanical science,
are not of such a nature as to furnish means of deducing
satbfactory laws. The resistance arising from one surface
rubbing against another is denominated friction; and it is
the only force in nature which is perfectly inert — its ten-
dency always being to destroy motion. Friction may thus
be viewed as an obstruction to the power of man in the
construction of machinery ; but, like all the other forces
in nature, it may, when properly understood, be turned to
his advantage, — for friction is the chief cause of the sta*
biiity of buildings or machinery, and without it animals
could not exert their strength.
The friction of planed woods and polished metals, without
grease, on one another is about one-fourth of the pressure.
The friction does not increase on the increase of the rub»
bing surfaces.
1



310 FRICTION.
The friction of metals is nearly constant.
The friction of woods seems to increase after they are
sometime in action.
The friction of a cylinder rolling down a plane, is in*
versely as the diameter of the cylinder.
The friction of wheels is as the diameter of the axle
directly, and as the diameter of the wheel inversely. The
following^ hints may be of use for the purpose of diminish-
ing friction.
