224 



COALFIELDS AND COLLIERIES OF AUSTRALIA. 



the up and down grades help to balance one another ; the uni- 

 form conveyance of single skips or small sets is better adapted 

 to colliery work than long- trains, which require an accumula- 

 tion of skips at flats and at the surface ; also as the engine is 

 running the whole time, power is more evenly used, and less 

 powerful engines are required than with the main and tail rope 

 system for equal distances. For the underground haulage, 

 screw clips are used. If they used Fisher's clips, the thimble 

 would become pushed up while passing round the sheaves at 

 horizontal curves ; besides they are found to be not strong 

 enough to hold four loaded skips at a time travelling up hill. 

 When a rail crosses the track of a rope, the rail is cut through 

 as far as the flange, so as to leave a space for the rope to pass 



Fig. 142. Fisher's Friction Clutch. 



through. At a kip, the rails are fastened to longitudinal 

 sleepers, so as to allow the rope to keep down out of the way. 

 At a horizontal curve a series of vertical sheaves, called 

 "tommy dodds," are arranged near the centre of the track, so 

 as to guide the rope. In one place where the track had a curve 

 when on an incline, they originally had a good deal of trouble, 

 as the rope used to rise. Now the grade is eased before rounding 

 the corner, so the rope tends to travel faster than the skip, 

 and this causes the clip to be pulled under the skip, and 

 drag it along, which has the effect of keeping the rope down 

 instead of allowing it to rise. In one place, where a. single 

 track is laid along a heading over which both full and empties 

 run to serve a horse track that branch off from it, an arrange- 

 ment is laid out. ns shown in Fisr. 143, where the empties are 



