WORK 173 



to lift or drag it out. If it is too heavy for this, he may call 

 in his neighbors and thus secure enough men to do the work. 

 If there are no neighbors, it cannot be done. 



The more intelligent races have learned ways of helping 

 themselves which enable them to overcome obstacles of this 

 sort. Let us suppose that a boy owns a boat weighing 2000 

 pounds and that he wishes to pull it out of the water. It is 

 not necessary for him to call in his fellows if he understands 



FIG. 88. The use of pulleys 



By the use of pulleys, rope, and wheels one man may move a much greater weight 

 than he could by pulling directly upon the object 



the use of simple machines. There are several sets of appli- 

 ances which might serve his purpose, but let us suppose that 

 he has at hand some boards, rollers, rope, and two pulley 

 blocks, each of which contains two pulleys. 



The most convenient arrangement the boy could make 

 would be to lay boards on the beach, -with the rollers ready 

 to support the boat, attach one pulley block to the boat and 

 the other to a tree or post, and thread the rope through 

 the pulleys as represented in figure 88. The boat could then 

 be moved along the boards by pulling on the rope. 



192. Decreasing friction by the use of rollers. Everyone 

 knows that if he were to attempt to slide the boat along the 



