THE LEVEK. EXAMPLES. 47 



This is owing to the power "being expended through a 

 greater distance near the points, according to the rule al- 

 ready explained. Pincers, nippers, and other similar in- 

 struments are also double levers of the first kind. 



A common steelyard is another example, the sliding 

 weight becoming gradually more efiective as it is moved 

 further from the fulcrum or hook supporting the instru- 

 ment. The brake or handle of a pump is a lever of this 

 class, the pump-rod and piston being the weight. 



The common balance is still another, the two arms being 

 exactly equal, so that one weight will always balance the 

 Yig. 44. other, and on this its usefulness 



and accuracy entirely depend. 

 The most sensitive balances have 

 Yio-ht beams with loner arms, and 

 the turning-point of hardened 

 -^ steel or agate, in the form of a 

 .!iihiiiiijii!!i4ii;iiiwii!iii-.!iiiiiiiiiiitiiiiiiiiii^^ thin wedge, on which the balance 

 turns almost without friction. Small balances have been 

 BO skillfully constructed as to turn with one-thousandth 

 part of a grain. 



2. Levers of the second kind are less numerous, but not 

 uncommon. A handspike used for rolling a log is an ex- 

 ample. A wheel-barrow is a leverof the second kind, the 

 fulcrum being the point where the wheel rests on the 

 ground, and the weight the centre of gravity of the load. 

 Hence, less exertion of strength is required in the arm 

 when the load is placed near the wheel, except where the 

 ground is soft or muddy, when it is found advantageous 

 to place the load so that the arm shall sustain a consider- 

 able portion, to prevent the wheel sinking into the soil. 

 A two-wheeled cart is a similar example ; and, for the same 

 reason, when the ground is soft, the load should be placed 

 forward toward the horse or oxen ; on the other hand, on 

 a smooth and hard, or on a plank road, the load should be 



