is broken, and A makes fresh contact with the screw H,
by means of the spring Z {88} fastened to the underside of A. The armature,
once it has been attracted, is held in permanent contact with H by the
catch S, independent of the magnets N. As soon as contact is made with H,
the clutch (F, Fig. 35) circuit is completed, and the circuit of the relay
K is broken. When the circuit of the clutch F is broken by means of the
circuit breaker C on the machine (Fig. 36), the stop S is pulled back by
hand, allowing the contact arm A to rise, and again make fresh contact with
the contact screw T.

[Illustration: FIG. 44.]

DRIVING APPARATUS

_The Friction Brake._--This consists of a steel disc A, Fig. 45, about
2-1/2 inches diameter and 3/8 inch or 1/2 inch wide on the face, secured to
the main shaft of the driving motor. The arm H, pivoted at C, carries at
one end the curved block B, which is faced with a pad of tow F. The other
extremity is pivoted to the steel rod P, which slides {89} [Illustration]
in holes bored in the standards J. One end of the rod P is screwed with a
fine thread, about 75 to the inch, and is fitted with a regulating wheel T,
by means of which the block B can be made to press upon the disc A with any
required degree of pressure. A fairly stiff steel spring R is placed upon
the rod P, between one standard J and the collar N. As the speed of the
driving motor is slightly in excess of that required by the machine, the
block B, by means of the wheel, is made to press upon the disc A, setting
up friction which reduces the motor speed until the isochroniser indicates
that the correct working speed has been attained.

_The Clutch_.--The details of this will be seen from Figs. 46 and 47. It
consists of a steel shaft coned at both ends running between two
countersunk bearings, one of which is adjustable. This shaft carries the
two portions of the clutch A and B, the portion A being a fixture on the
shaft, and the portion B running free upon it. The portion B is a gun-metal
casting bored to run accurately upon the steel shaft. A soft iron annular
ring is fastened to the face.

[Illustration: FIG. 46.

E, spindle; R, bobbins; P, iron cores; D, copper rings; T, brushes; N, back
plate; V, front plate; J, gearing; S, spring; H, collar; Z, iron ring; F,
fixed bearing; C, insulating bush.]

The portion A consists of a gun-metal casting {90} [Illustration] bored a
tight fit for the shaft E, secured by means of a set