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  Heavy concessions and reactions have been replaced by direct motions, and cams have been excluded as much as possible.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  But in recent years the drop or four motion feeder has entirely superseded it for such purposes.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 simplified and improved by the use of a single angle clutch, which is found to work even when the surfaces are freely oiled (Fig. 6).

Any motion of the free extremity of the lever upon which the biting clutch is formed binds the latter upon the flange of the wheel, which then advances so long as the lever continues to move in that direction.  When the stitch is completed, the clutch is allowed to recede, and is pulled back by a reacting spring.  The bite of the clutch is given by the two opposite corners.

The feed wheel itself is free to revolve in a forward direction, but is prevented from rocking backward in Singer’s machine by an ingenious little device, recently introduced.  It consists of a small steel roller, situated within the angle formed by an inclined plane and the flange of the wheel, and constantly pulled into the angle by a spiral spring.  Any backward tendency of the wheel binds the roller more firmly in the angle and stops the wheel.  Former feed wheels were checked by a brake spring or block, which retarded the motion of the whole machine when heavily adjusted.