OSBORNE-WALLSEND COLLIERY. 223 



the pulley five times, takes off on the higher side. The tension 

 varies in all parts of the rope, being greatest whereat passes 

 on to the driving pulley, and least where it passes 

 off it. Fisher's friction clutches are used to throw the rope 

 systems into gear (Figs. 141 and 142). The rope pulley (f) 

 and brake path (k) run loose on the main shafting (h), "but a 

 driving drum (g) is keyed to the shafting, and revolves with 

 it. The clutch consists of three segments (a) which surround 

 the driving drum, and are bolted through oblong slots in the 

 firms of the pulley. The segments of the clutch are united to- 



Fig. 141. Fisher's Friction Clutch (elevation). 



gether by right and left hand screws (c, c), the clutch is put in or 

 out of gear by the ordinary fork (i) and lever (j) arrangement, 

 which brings a system of levers into play, and either forces 

 the segments to press on the driving drum, when the levers 

 are pushed towards it, or causes them to be withdrawn 

 when the motion is reversed. The segments are shod with 

 brass so as to get more adhesion, and save the wearing of the 

 driving drum and segments. As the segments are attached 

 to the rope pulley, when they grip the revolving driving drum, 

 they cause the rope pulley to become a part of the moving 

 body. When the clutch is thrown into gear, the friction slips 

 at first, thereby avoiding a strain on the machinery, and the 

 pulley moves slowly until the inertia of its load is overcome. 

 The endless rope system is suitable for undulating ground, as 



