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THE ANIMAL AS A MACHINE. 



10. The Object of all Mechanism is to produce 

 a certain definite motion of some part or parts — the 

 position and form and the methods of connection of 

 which are known and fixed — against any resistance 

 that may be met with in the course of such movement. 

 Every machine and every train of mechanism is there- 

 fore a contrivance by means of which energy or power 

 available at one point, usually in definite amount and 

 acting in a definite direction and with definite velocity, 

 is transferred to other points, there to do work of 

 definite amount, and there to overcome known resist- 

 ances with known velocities. 



The object of the engineer in designing mechanism 

 is to effect this transfer of energy and these trans- 

 formations at the least cost and with least running 

 expense," and hence with maximum efficiency of 

 apparatus. It is often important to secure minimum 

 volume and weight of machine, as well as maximum 

 effectiveness in operation. 



The work of a machine is measured by the magnitude 

 of the resistance encountered and the velocity with 

 which it is overcome. The nature of the work, aside 

 from its simple kinetic character, is as widely variable 

 as are the details of human industry. 



Prime Movers are those machines which receive 

 energy directly from natural sources, and transmit it 

 to other machines which are fitted for doing the various 

 kinds of useful work. Thus, the steam-engine derives 

 its power from the heat-energy hberated by the com- 

 bustion of fuel ; water-wheels utilize the energy of 

 flowing streams ; windmills render available the power 

 of currents of air ; the voltaic battery develops the 

 energy of chemical action in its cells ; and, through 



