differential or variable motion. The space between the carrier and the
sides of the recess is sufficient to permit the free passage of the thread
in encircling the shuttle, and the differential movement ingeniously
releases the contact between the hook and carrier. The skeleton of this
device is only one-sided, and does not really carry its bobbin in the
course of its revolution. The bobbin is placed in a cup-like holder, which
lies within the shuttle or hook body, and is retained in position by a
latch hinged to the bed of the machine. The cup and bobbin are prevented
from partaking of the rotatory movement by a steel spur projecting from the
cup, and fitting loosely into a notch in the latch. Tension upon the under
thread is obtained by passing it under a tension plate upon the bobbin cup.
Twisting of the thread is by these means entirely obviated. In this
apparatus, the disk-like appearance of the bobbin is partially lost in its
considerable breadth, and there is thus a distinct departure from the lines
of the ring shuttles before mentioned. The diagrams exhibit the hook in
several positions during its revolution, and the position of the threads
corresponding thereto.

[Illustration: FIG. 2]

_Fixed Rotating Hooks_.--Wilson's rotating hook for lock stitch machines,
and Gribbs' hook for single thread machines, are both well known. In the
year 1872, the Wheeler & Wilson company introduced a new hook, forming an
improvement upon Wilson's original device (Fig. 3). Its chief peculiarity
consists in the extension of the termination of the periphery, forming a
long tail piece, quite overlapping the point, and serving as a guard, both
to keep off the bobbin thread and to prevent collision between bobbin and
needle.

[Illustration: FIG. 3.]