A crank pin is attached to each, and these pins are
connected together by a simple link. An examination of the device itself
shows that, while the motion of the main shaft portion is uniform, that of
the hook shaft is alternately accelerated and retarded.

The picture on the screen gives a general view of the No. 10 D machine, in
which these motions are embodied, and showing the position of the positive
take-up affected by those motions, a position which is preferred for very
high speeds in this machine, especially for threads possessing little
elasticity.

_Motions of the Feeder_.--The speed attained by the fastest sewing machines
is due more to the reduction and simplification of the movements than to
any other improvement. Heavy concessions and reactions have been replaced
by direct motions, and cams have been excluded as much as possible. Mr.
A.B. Wilson's famous invention of the four motion feeder depended upon both
gravity and a reacting spring for two motions. Singer improved upon it by
making three of the motions positive, a spring being used for the drop. But
a really positive four motion feeder was long sought by inventors.

Hitherto the reaction of the feeder--that is, its descent and
recession--was generally attained by means of a spring. The drop and ascent
are now effected by means of a separate eccentric in Singer's machine.
Uncertainty of action in the feed, once a cause of much inconvenience, may
now be said to be overcome. A peculiarity of the four motion feeder in
Wheeler & Wilson's machine is an arrangement enabling the operator to feed
in either direction at will.

Not less worthy of note are improvements that have been made in wheel
feeders. The wheel feed was originally much used for cloth sewing machines,
especially in Singer's system. But in recent years the drop or four motion
feeder has entirely superseded it for such purposes. The wheel feed still
holds its own, however, for sewing leather, especially in the "closing" of
boot uppers, in this country. Singer's original wheel feeder was actuated
by a friction shoe riding upon the flange of the wheel. The friction grip,
however, had certain faults, owing to the tendency of the shoe to slip when
the surfaces became covered with oil.

[Illustration: FIG. 6.]

A later form of Howe's machine used a pair of angular clutches, embracing
the flange of the wheel. In both Singer's and Wheeler & Wilson's latest
styles of machines this arrangement is s