34 MECHANIC POWERS, 



5. The pivots, which form the axis or fulcrum, 

 should be in a straight line, and at right angles to 

 the beam. 



6. The arms should be as long as possible, rela- 

 tively to their thickness, and the purposes for 

 which they are intended ; as the longer they are, 

 the more sensible is the balance. 



They should also be made as stiff and inflexible 

 as possible \ for if the beam be too weak, it will 

 bend, and become untrue. 



7. The rings, or the pieces on which the axis 

 bears, should be hard and well polished, parallel 

 to each other, and of an oval form ; that the axis 

 may always keep its proper bearing, or remain 

 always at the lowest point. 



8. If the arms of a balance be unequal, the 

 weights in equipoise will be unequal in the same 

 proportion. The equality of the arms is of use, 

 in scientific pursuits, chiefly in the making of 

 weights by bisection. A balance with unequal 

 arms will weigh as accurately as another of the 

 same workmanship with equal arms, provided the 

 standard weight itself be first counterpoised, then 

 taken out of the scale, and the thing to be weighed 

 be put into the scale, and adjusted against the 

 counterpoise. Or, when proportional quantities only 

 are considered, the bodies under examination may 

 be weighed against the weights, taking care always 

 to put the weights in the same scale ; for then, 

 though the bodies may not be really equal to the 

 weights, yet their proportions amongst each other 

 will be the same as if they had been accurately so. 



9. Very delicate balances are not only useful in 

 nice experiments, but are likewise much more ex- 

 peditious than others in common weighing. If a 

 pair of scales with a certain load be barely sensible 



