*Project Gutenberg*. Public domain.

43. *Q.* Cannot the operation of a governor be
deduced merely from the consideration of centrifugal
and centripetal forces?

*A.*—It can; and by a very simple
process. The horizontal distance of the arm from
the spindle divided by the vertical height, will give
the amount of centripetal force, and the velocity
of revolution requisite to produce an equivalent centrifugal
force may be found by multiplying the centripetal
force of the ball in terms of its own weight by 70,440,
and dividing the product by the diameter of the circle
made by the centre of the ball in inches; the square
root of the quotient is the number of revolutions per
minute. By this rule you fix the length of the
arms, and the diameter of the base of the cone, or,
what is the same thing, the angle at which it is desired
the arms shall revolve, and you then make the speed
or number of revolutions such, that the centrifugal
force will keep the balls in the desired position.

44. *Q.*—Does not the weight of the
balls affect the question?

*A.*—Not in the least; each ball may
be supposed to be made up of a number of small balls
or particles, and each particle of matter will act
for itself. Heavy balls attached to a governor
are only requisite to overcome the friction of the
throttle valve which shuts off the steam, and of the
connections leading thereto. Though the weight
of a ball increases its centripetal force, it increases
its centrifugal force in the same proportion.

## THE MECHANICAL POWERS.

45. *Q.*—What do you understand by
the mechanical powers?

*A.*—The mechanical powers are certain
contrivances, such as the wedge, the screw, the inclined
plane, and other elementary machines, which convert
a small force acting through a great space into a great
force acting through a small space. In the school
treatises on mechanics, a certain number of these
devices are set forth as the mechanical powers, and
each separate device is treated as if it involved
a separate principle; but not a tithe of the contrivances
which accomplish the stipulated end are represented