174 



MAWS WAY OF HELPING HIMSELF 



If the force required by a machine is 150 pounds, while 

 that calculated as necessary is 100 pounds, the loss due to 

 friction is 50 pounds, and the machine, instead of being 

 thoroughly efficient, is only two thirds efficient. 



Machinists make every effort to eliminate from a ma- 

 chine the waste due to friction, leveling and grinding to the 

 most perfect smoothness and adjustment every part of the 

 machine. When the machine is in use, friction may be further 

 reduced by the use of lubricating oil. Friction can never 

 be totally eliminated, however, and machines of even the finest 

 construction lose by friction one tenth of their efficiency, while 

 poorly constructed ones lose by friction as much as one half 

 of their efficiency. 



170* Man's Strength not Sufficient for Machines. A machine, 

 an inert mass of metal and wood, cannot of itself do any work, 



but can only distribute the 

 energy which is brought to it. 

 Fortunately it is not neces- 

 sary that this energy should 

 be contributed by man alone, 

 because the store of energy 

 possessed by him is very 

 small in comparison with the 

 energy required to run loco- 

 motives, automobiles, saw- 

 mills, etc. Perhaps the great- 



FIG. us. Man's strength 

 for heavy work. 



est value of machines lies in 

 nsufficient the fact that they enable man 



to perform work by the use of 

 energy other than his own. 



Figure 1 18 shows one way in which aJiorse's energy can be 

 utilized in lifting heavy loads. Even the fleeting wind has 

 been harnessed by man, and, as in the windmill, made to work 



