10 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Energy is not necessarily this power of doing work : 

 for us it is not necessarily causality, for although the sum 

 of energy in a physical system may remain constant, the 

 sum of causality may, indeed generally does, undergo 

 decrease. This leads us to the consideration of the 

 second law of thermodynamics, and for the purpose of 

 our discussion this principle is of vastly greater 

 significance than the first law. In its most general form, 

 as enunciated by Clausius, it says merely that the sum 

 of a mathematical function called entropy tends 

 continually to increase. It can be stated in a more 

 general manner by saying that all the natural processes 

 studied by physics are irreversible and we can most 

 clearly understand this by considering the working of a 

 dynamo. If we cause the machine to revolve, that is 

 supjny a certain amount of mechanical energy to it, a 

 current of electricity is generated, and the amount of this 

 current should theoretically be equal to the energy of 

 the mechanical motion supplied. If now we stop the 

 machine and supply a current of electricity to it equal 

 in amount to that already received the dynamo becomes 

 a motor and begins to supply mechanical energy, and 

 the amount of this should theoretically be equal to the 

 energy supplied to the machine when it worked as a 

 dynamo. That is to say it is perfectly reversible and 

 transforms mechanical energy into electricity and vice 

 versa. 



This perfect reversibility would only exist if we 

 could make a machine with perfectly rigid parts, which 

 revolved without friction, which both conducted and 

 insulated electricity perfectly. As a matter of fact the 

 parts of the machine are not quite rigid, there is friction, 

 its wires conduct electricity with a loss due to imperfect 

 conductivity and insulation ; all this leads to loss in such 



