THE BALANCE. 121 



beam A, than at the end of B, because the smaller 

 weight descends for the same deflection through a 

 larger space at A, than at B t Hence the sensibility of 

 a balance increases with the length of the beam. There 

 is, however, a limit to the length, for the longer the 

 beam the less is its rigidity, other conditions being 

 equal. 



It will be obvious from the principle of the lever that 

 the scale-pans must be sus- 

 pended in a manner which 

 ensures their being always at 

 the same distance from the 

 fulcrum ; they are therefore FIG. 89. (an. proj. real size}. 

 suspended by hooks which rest upon knife-edges 

 turned upwards, as shown in fig. 89. These knife- 

 edges should be parallel to each other and also to the 

 one which supports the beam, and all three should be 

 in the same horizontal plane. This condition is ful- 

 filled, in the best modern balances, by placing the 

 points of suspension a very little above the plane of the 

 fulcrum ; when the balance is used, the load bends the 

 beam a little and brings the points of suspension into 

 the desired position. 



Along index or pointer (which in the better balances, 

 which are usually supported upon a pillar, points down- 

 wards to a graduated arc near the foot of the pillar) 

 is fixed to the middle of the beam in order to show 

 whether it is horizontal. 



In order to preserve the edge of the fulcrum as much as possible 

 :he better kinds of balances are provided with an arrangement which 

 illows of raising the whole beam with its fulcrum from the support 

 m which the latter rests. For our purposes a common balance is 

 }uite sufficient. When anything is to be weighed, the balance may be 



