MT. PLEASANT COAL AND IRON COMPANY. 217 



which grip the skips by the wheels. The coal is then loaded 

 into hopper trucks, wooden or iron, and drawn by horses to 

 the top of a self-acting incline, which is about three-quarters 

 of a mile long. The line has three rails above and below the 

 passing, where of course there are four. The speed is regu- 

 lated by brakes having cast iron shoes instead of the customary 

 wooden blocks, and these brakes are manipulated by the usual 

 ships' steering wheel by the man in charge. At the bottom 

 of the steep incline there is another incline, nearly flat, for 

 half a mile, having three raik at the top end, four in the 

 centre, and two at the lower end. At the bottom of this 

 incline is a Pooley's weighing machine, and after that the 

 trucks are taken in charge by a small locomotive. The line 

 is continued for another one and a half miles to the Wollon- 

 gong basin, where most of the coal is shipped, but occasionally 

 some is shipped to Port Kembla or Darling Harbour. 



On the south coast, where there are so many self-acting 

 inclines, the following notes, mostly abstracted from Alex- 

 ander Bowie's paper on "Problems in Hauling and Hoisting"" 5 

 may be of interest : 



Let (a) be the angle of inclination. 



(C) the coefficient of friction of trucks and ropes. 

 (W) the weight in Ibs. of the loaded truck. 

 (w) the weight in Ibs. of the empty truck, 

 (r) the weight of the rope for the length of the in- 

 cline in Ibs. 



(C 1 ) the coefficient of friction for the drum. 

 (f) the amount of resistance due to friction for drum 

 in Ibs., or = 2 C 1 [(w + r) sin a + C (w + r) 



cos a]. 



The coefficient of friction is equal to the tangent of the 

 angle of inclination on which the force exerted by gravity is 

 exactly counterbalanced by the frictipnal resistance. This 

 angle is known as "the angle of friction," the "angle of re- 

 pose," or "the limiting angle of frictional stability." 



When a waggon (W) is placed on an inclined plane, the 

 force with which it tends to move down the plane, disregard- 

 ing friction, is 



W sin a. 



As the amount of friction equals the pressure multiplied by 

 the coefficient of friction, the amount of friction encountered 

 in moving a waggon (W) on an inclined plane is 



WC cos a. 

 sin a 



When W sin a = AYC cos a, or - = tan a = C 



cos a 



*T. Am. I. M. E., 1901. Vol. XXXI., p. 265. 



