time: the refreshing river 



By suitable arrangements, the kinetic energy can be made to 

 perform this task; for example, if the stone is tied to a string 

 it can alternately fall and reascend like a pendulum. But if the 

 stone hits an obstacle its kinetic energy is converted into heat- 

 energy. There is still the same quantity of energy, but even if 

 we could scrape it together and put it through an engine we 

 could not lift the stone back with it. What has happened to 

 make the energy no longer serviceable ? Looking microscopically 

 at the falling stone we see an enormous multitude of molecules 

 moving downwards with equal and parallel velocities — an 

 organised motion like the march of a regiment. We have to 

 notice two things, the energy, and the organisation of the energy. 

 To return to its original height the stone must preserve both of 

 them. 



"When the stone falls on a sujfficiendy elastic surface the 

 motion may be reversed without destroying the organisation. 

 Each molecule is turned backwards and the whole array retires 

 in good order to the starting-point. 



'The famous Duke of York 

 With twenty thousand men. 

 He marched them up to the top of the hill 

 And marched them down again.' 



"History is not made that way. But what usually happens at 

 the impact is that the molecules suffer more or less random 

 collisions and rebound in all directions. They no longer conspire 

 to make progress in any one direction; they have lost their 

 organisation. Afterwards they continue to collide with one 

 another and keep changing their direction of motion, but they 

 never again find a common purpose. Organisation cannot be 

 brought about by continued shuffling. And so, although the 

 energy remains quantitatively sufficient (apart from unavoidable 

 leakage which we suppose made good), it cannot lift the stone 

 back. To restore the stone we must supply extraneous energy 

 which has the required amount of organisation."^ 



A similar use of the term "organisation" occurs at many other 

 places in Eddington's writings.^ In the above example, it seems to 

 mean no more than a group of uniformly directed motions, and such 



^ The Nature of the Physical World, p. 70. 



^ e.g. The Nature of the Physical World, p. 104. 



210 



