48 



MECriAXICS. 



Fi<r. 45. 



more nearly balanced. An observance of this rule would 

 often save a great deal of needless waste of strength. 



A sack-barrow, used in barns and mills for conveying 

 heavy bags of grain from one part oftlie floor to another, 



and in warehouses 

 for boxes, is a lever 

 nearly intermediate 

 between the first and 

 second kind, the 

 weight usually rest- 

 ing very nearly over 

 the fulcrum or 

 wheels. When the 

 bag of grain is 

 thrown forward of 

 the wheels, it be- 

 comes a lever of the 

 first kind ; w^hen 

 back of the wheels, 

 it is a lever of the 

 second kind. As it 

 is used only on hard 

 and smooth floors, 

 and not, like the whoel-barro^\, on soft earth, the more 

 nearly the load is placed directly over the wheels, the 

 more easily they will run. 



3. In a lever of the third kind, the weight being further 

 from the fulcrum than the power, it is only used where 

 great power is of secondary importance when com- 

 pared with rapidity and dispatch. A hand-hoe is of this 

 class, the left hand acting as the fulcrum, the right hand 

 as the power, and the resistance overcome by the blade 

 of the hoe as the weiglit. A hand-rake is similar, as well 

 as a fork used for pitching hay. Tongs are double levers 

 of this kind, as also the shears used in sheariiilg sheep. 

 The limbs of animals, generally, are levers of the third 



Sack-barrow. 



