the bottom of the shaft, connects
the bottoms of the cages, so that the dead weight of cage, tubs and rope
is completely counterbalanced at all positions of the cages, and the
work of the engine is confined to the useful weight of coal raised.
Motion is communicated to the rope by frictional contact with the drum,
which is covered through about one-half of the circumference. This
system has been used in Nottinghamshire, and at Sneyd, in North
Staffordshire. In Belgium it was tried in a pit 940 metres deep, where
it has been replaced by flat hempen ropes, and is now restricted to
shallower workings. In Westphalia it is applied in about thirty
different pits to a maximum depth of 761 metres.

A novelty in winding arrangements is the substitution of the
electromotor for the steam engine, which has been effected in a few
instances. In one of the best-known examples, the Zollern colliery in
Westphalia, the Koepe system is used, the winding disk being driven by
two motors of 1200 H.P. each on the same shaft. Motion is obtained from
a continuous-current generator driven by an alternating motor with a
very heavy fly-wheel, a combination known as the Ilgner transformer,
which runs continuously with a constant draught on the generating
station, the extremely variable demand of the winding engine during the
acceleration period being met by the energy stored in the fly-wheel,
which runs at a very high speed. This arrangement works admirably as
regards smoothness and safety in running, but the heavy first cost and
complication stand in the way of its general adoption. Nevertheless
about 60 electric winding engines were at work or under construction in
May 1906.

Surface arrangements.

The surface arrangements of a modern deep colliery are of considerable
extent and complexity, the central feature being the head gear or pit
frame carrying the guide pulleys which lead the winding ropes from the
axis of the pit to the drum. This is an upright frame, usually made in
wrought iron or steel strutted by diagonal thrust beams against the
engine-house wall or other solid abutments, the height to the bearings
of the guide pulleys being from 80 to 100 ft. or more above the ground
level. This great height is necessary to obtain head-room for the cages,
the landing platforms being usually placed at some considerable height
above the natural surface. The pulleys, which are made as large as
possible up to 20 ft. in diameter to diminish the e