VALE OF CLWYDD COLLIERY. 



113 



steelyard is suspended from a strong beam (Fig. 51). The 

 average tare of the skip is placed on the disc at the end of the 

 steelyard. The jockey, or sliding poise, on the main beam, 

 weighs up to 15cwt., while that on the auxiliary beam on the 

 side is divided into quarters, and weighs up to 5cwt. The 

 hooks (a) keep the frame, on which the skip is weighed, 

 -steady. 



Fig. 51. Steelyard. 



In principle the steelyard is a lever with arms of unequal 

 length, which rest on a fulcrum. In Fig. 52, (F) is the ful- 

 crum; (FP) a graduated scale divided into equal parts; (p) is 

 a sliding counterpoise ; (A) a hook on the shorter arm, from 

 which the thing to be weighed is suspended ; (w) the pan for 

 various weights. The parts that vary are the position of the 

 counterpoise (p) and the weight on (W), The weight, multi- 



T" 7 



Fig. 53. 



plied by its distance from the fulcrum, is equal to the resis- 

 tance multiplied by its distance from the fulcrum. Thus W 

 x PF = U x AF where R equals the thing to be weighed. 



