IS THE BODY A MACHINE T 31 



only be necessary for us to turn our attention to 

 the life activities of the higher animals. 



WHAT IS A MACHINE? 



Turning now to our more immediate subject 

 of the accuracy of the statement that the 

 body is a machine, we must first ask what is 

 meant by a machine ? A brief definition of a 

 machine might be as follows : A machine is a 

 piece of apparatus so designed that it can change one 

 kind of energy into another for a definite purpose. 

 Energy, as already noticed, is the power of 

 doing work, and its ordinary active forms are 

 heat, motion, electricity, light, etc. ; but it may 

 be in a passive or potential form, and in this 

 form stored within a chemical molecule. These 

 various forms of energy are readily convertible 

 into each other; and any form of apparatus 

 designed for the purpose of producing such a 

 conversion is called a machine. A dynamo is 

 thus a machine so adjusted that when mechanical 

 motion is supplied to it the energy of motion is 

 converted into electricity; while an electromotor, 

 on the other hand, is a piece of apparatus so de- 

 signed that when electricity is applied to it, it is 

 converted into motion. A steam engine, again, 

 is designed to convert potential or passive energy 

 into active energy. Potential energy in the form 

 of chemical composition (coal) is supplied to the 

 engine, and this energy is first liberated in the 

 active form of heat and then is converted into 

 the motion of the great fly-wheel. In all these 

 cases there is no energy or power created, for 



