off, operating the faller wire, rotating the
spindles and pushing the carriage home. In the year 1785 the first
steam-engine was employed for cotton spinning, and in 1792 William
Kelly placed the headstock of a mule, in which the chief mechanism is
situated, in the middle of the carriage, instead of at one end. By
this device one machine was doubled in length, and shortly afterwards
two mules, each of 300 to 400 spindles, were allotted to one spinner
and his assistants. Kelly also attempted to control all parts of the
machine mechanically, but in this he failed, as did Eaton, Smith and
many others, although each contributed something towards the solution
of the problems involved in automatic spinning. Eventually the hand
mule became a machine in which most of the work was done
automatically; the spinner being chiefly required to regulate the
velocity of the backing off, and the inward run of the carriage, and
to actuate the fallers. As a result of these alterations the machine
was made almost double the length of Kelly's. In this state many mules
continued to be used until the last decade of the 19th century, and a
few are still in use. Between the years 1824 and 1830 Richard Roberts
invented mechanism that rendered all parts of the mule self-acting,
the chief parts of which are shown at (I, J), and they regulate the
rotation of the spindles during the inward run of the carriage. At
first his machine was only used to spin coarse and low-medium counts,
but it is now employed to spin all counts of yarn. Although numerous
changes have since been made in the self-acting mule, the machine
still bears indelible marks of the genius of Roberts.

[Illustration: FIG. 9.]

For many purposes the threads as spun by the ring frame or the mule
are ready for the manufacturer; but where extra strength or smoothness
is required, as in threads for sewing, crocheting, hosiery, lace and
carpets; also where multicoloured effects are needed, as in
Grandrelle, or some special form of irregularity, as in corkscrewed,
and knopped yarns, two or more single threads are compounded and
twisted together. This operation is known as doubling. In order to
prepare threads for doubling it may be necessary to wind side by side
upon a flanged bobbin, or upon a straight or a tapering spool, from
two to six threads before twisting them into one.

_Winding machines_ for this purpose are