of various kinds. There are
those in which the threads are laid evenly between the flanges of a
bobbin, and those that coil the threads upon a straight or a tapering
tube to form "cheeses." In the latter the tubes may be laid upon
diagonally split drums and rotated by frictional contact. By placing
each group of threads to be wound in the slit of a rotating drum, it
is drawn quickly to and fro and coiled upon a spool. If solid instead
of split drums be used, the guides for all the threads on one side of
a machine are attached to a bar, which is traversed by a cam placed at
one end of the frame. Or independent mechanism may be provided
throughout for treating each group of threads to be wound. The bobbins
or tubes may be filled from cops, ring spools or hanks, but a stop
motion is required for each thread, which will come into operation
immediately a fracture occurs.

_Doublers_.--In action doublers are continuous and intermittent. The
former resemble throstle and ring spinning machines, but since they do
not attenuate the material, only one line of rollers is provided. The
folded material is placed in a creel and led through the rollers to
the spindles to be twisted in a wet or dry condition. If wet, the
moisture flattens down most of the protruding ends of the fibres and
produces a comparatively smooth thread; if dry, the doubled yarn
retains some of its furry character. There are two types of continuous
doublers, which are known respectively as English and Scotch. By the
English system of dry doubling the yarn from the creel may be treated,
on its way to the spindle, in various ways to obtain the desired
tension. It may be led under a rod, over a guide, round and between
the rollers, and round a glass peg. For wet doubling, a trough
containing water is placed behind the rollers, and the yarn passes
beneath a glass rod in the water, thence over a guide, beneath,
between and over the rollers to the spindles. By the Scotch system the
trough is placed below the rollers, and the bottom roller is partly
immersed in water. It is claimed that this system wets the fibres more
thoroughly than the English one. For the purpose of twisting the
strands together the spindles may be provided either with flyers, as
in throstle spinning, or with rings and travellers, as in ring
spinning. The twist is generally in the opposite direction to that in
the single thread