114 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



This principle of the lever holds good, though there are more 

 than two forces, as in Fig. 53, where W x PF = ]J -x BF + 

 A x AF. The steelyard may have a supplemental arm at- 

 tached parallel to the longer arm, which carries a second 

 counterpoise. The mechanical effect of this is the same as if 

 the second counterpoise were made to slide over the same arm 

 us the first. The main bar carries the hundredweight poise, 

 while the minor bar carries a slide which indicates quarters. 

 The counterpoise must, of course, be in proportion to the class 

 of weight used. When weighing with such a steelyard as 

 shown in Fig. 51, -the average tare of an empty skip is placed 

 on the disc (w) at the end of the larger arm; the hundred- 

 weight counterpoise is placed at the minimum weight of a 

 skip load of coal ; while the auxiliary counterpoise is shifted 

 about to obtain the exact weight of each load, and is the only 

 one it is necessary to read off'. 



The Zig Zag Colliery. 



This colliery has been managed for about six years by Mr. 

 J. Durie. 



The hoisting shaft is 210ft. in depth, being 14ft. by 7ft., 

 divided into two hoisting compartments, and another compart- 



Fig. 54. The Travelling Road. 



