Measurement of Weight 61 



chemists' shops, affords another example of the applica- 

 tion of the Principle of Moments. It is constructed 

 on the model of the simple steelyard, of which an 

 illustration is shown in Fig. 23. It resembles an 

 ordinary balance in that it has a beam pivoted about 

 one point but this point is not situated at the centre 

 of the beam, being much nearer to one end than the 

 other. Let us suppose that the point about which the 

 beam turns is 2" from one end of the beam and 20" 

 from the other. Applying the Principle of Moments, 

 it is evident that a weight of 1 Ib. attached to the 

 end of the longer arm will balance a weight of 10 Ib. 

 at the other end of the beam. When placed halfway 

 along the longer arm, the 1 Ib. weight will balance 

 5 Ib. at the other end, and so on. The. longer arm 

 of the beam is usually graduated in such a way that 

 the weight of the object attached to the end of the 

 shorter arm may be read directly from the scale when 

 an exact balance has been effected, by noting the 

 position of the weight which slides along the longer 

 arm. In the weighing-machines used to determine the 

 weights of heavy objects, a set of weights, suspended 

 from the end of the long arm, is used in conjunction 

 with the sliding weight. They are marked with values 

 which bear the same ratio to their actual weights 

 as the length of the longer arm bears to that of the 

 shorter. Large machines of this character may be 

 found in market-places, where they are of use in 

 weighing cattle, loads of hay, and similar heavy bodies. 



