INTRODUCTION 283 



body is derived from the food eaten. This undergoes 

 a chemical change during the process of digestion and 

 assimilation, and is transformed into mechanical energy 

 by a process not fully understood. Heat engines make 

 use of the heat liberated by the chemical union of the 

 combustible constituents of fuel and oxygen. Water 

 wheels, tidal machines, and windmills utilize the kinetic 

 energy of masses of moving water or air. Electrical 

 motors depend either upon chemical action or a dynamo 

 to furnish the energy, it being necessary to drive the lat- 

 ter with some form of prime mover. 



Only such motors as are well adapted to agricultural 

 purposes will be considered in this treatise. 



