ng a black dye for the use of calico
printers.

_Accumulation of Power_ arises from lifting a weight and then allowing
it to fall. A man, even with a heavy hammer, might strike repeated blows
upon the head of a pile without producing any effect. But if he raises a
much heavier hammer to a much greater height, its fall, though far less
frequently repeated, will produce the desired effect.

_Regulating Power._--A contrivance for regulating the effect of
machinery consists in a vane or a fly, of little weight, but presenting
a large surface. This revolves rapidly, and soon acquires an uniform
rate, which it cannot greatly exceed, because any addition to its
velocity produces a much greater addition to the resistance it meets
with from the air. The interval between the strokes on the bell of a
clock is regulated by this means; and the fly is so contrived, that this
interval may be altered by presenting the arms of it more or less
obliquely to the direction in which they move. This kind of fly or vane
is generally used in the smaller kinds of mechanism, and, unlike the
heavy fly, it is a destroyer instead of a preserver of force. It is the
regulator used in musical boxes, and in almost all mechanical toys.

_Increase and Diminution of Velocity._--Twisting the fibres of wool by
the fingers would be a most tedious operation; in the common
spinning-wheel the velocity of the foot is moderate; but, by a very
simple contrivance, that of the thread is most rapid. A piece of cat-gut
passing round a large wheel, and then round a small spindle, effects
this change. The small balls of sewing cotton, so cheap and so
beautifully wound, are formed by a machine on the same principle, and
but a few steps more complicated. The common smoke-jack is an instrument
in which the velocity communicated is too great for the purpose
required, and it is transmitted through wheels which reduce it to a more
moderate rate.

_Extending the Time of Action in Forces._--The half-minute which we
daily devote to the winding up of our watches is an exertion of labour
almost insensible; yet, by the aid of a few wheels its effect is spread
over the whole twenty-four hours. Another familiar illustration may be
noticed in our domestic furniture: the common jack by which our meat is
roasted, is a contrivance to enable the cook in a few minutes to exert a
force which the machine retails out during the succeeding hour in
turning the loaded spit.

_Saving Time in