102 THE MECHANISM OF LIFE 



regiment is a representation of a body possessing kinetic 

 energy. Potential energy is energy confined to a certain point 

 in space, whereas actual energy is a current of energy, 

 continually changing its place or form. Energy is like water- 

 power — potential in the lake, actual in the waterfall or 

 river. 



Any mechanism capable of causing one form of energy to 

 pass into another is a transformer of energy. A steam engine 

 is a transformer of energy, changing caloric energy into 

 mechanical work. An electrical machine is a transformer 

 of energy, converting mechanical motion into a current of 

 electricity, whilst an electro-motor changes the movement of 

 electrons into mechanical movement. Every living being, and 

 even man himself, is but a transformer of energy, changing 

 the energy derived from the earth and air and sun into 

 mechanical motion, nervous energy, and heat. 



The first law of energetics, that of the conservation of 

 energy, is analogous to Lavoisier's principle in chemistry, the 

 conservation of matter. The sign of equality which unites 

 the terms of a chemical equation expresses the fact that after 

 every chemical reaction the same total mass of matter is 

 present as before the transformation. This is also true of 

 energy ; after every transformation we find exactly the same 

 total quantity of energy as before it. This, however, tells us 

 nothing as to the conditions of the transformation, or the 

 causes, i.e. the anterior phenomena, which determined such 

 transformation. 



The second principle of energetics, that of Carnot, 

 enunciated in 182-i, deals with the conditions under which a 

 transformation of energy is possible. A mass of water at 

 a certain height represents a quantity of potential energy 

 equal to the product of its weight by its height ; but this 

 energy cannot produce mechanical work unless the water is 

 allowed to fall. Consider two lakes at the same altitude and 

 of the same capacity, one of which is entirely landlocked, 

 while the other has an open channel leading to the sea. Each 

 lake represents the same quantity of potential energy, but the 

 energy of the landlocked lake is useless, it cannot be trans- 



