54 THE PHILOSOPHY OF BIOLOGY 



energy. It may pass through numerous transfor- 

 mations — the chemical potential energy of coal may 

 be transformed into the kinetic energy of water 

 molecules (steam at high temperature), and this into 

 the kinetic energy of the revolving armature of a 

 dynamo, and this again into the energy of moving 

 electrons (the current of electricity in the circuit of 

 the dynamo) , and then again into the energy of ethereal 

 vibration (light, heat, X-rays, or other electro-magnetic 

 waves), and these again into mechanical or kinetic 

 energy, and so on. When we say that we can control 

 energy we say that we can produce these transfor- 

 mations ; we can cause things to happen, we bring 

 becoming into being. In this sense energy is causalit3^ 

 But while the sum-total of energy in the universe 

 remains constant, the sum of causality continually 

 diminishes. Energy is the power, or condition, of 

 producing diversity, but while energy can suffer no 

 diminution of quantity, diversity tends continually 

 to decrease. 



In the last two sentences we state, in one way, 

 the second law of thermodynamics — in some respects 

 the most fundamental result of our experience 

 in the physical investigation of the universe. In 

 its most technical form, as enunciated by Clausius, 

 this law states that the value of a certain mathe- 

 matical function, called entropy,^ tends continually 

 towards a maximum, when it is applied to the 

 universe as a whole. When we say the " universe," 

 we mean all that comes within our power of physical 

 investigation. Let us now see what this statement 

 means. 



^ See appendix, p. 369. Entropy is a shadowy kind of concept, difficult 

 to grasp. But again we may point out that the reader who would extend 

 the notion of mechanism into life simply must grasp it. 



