20 THE PHYSICAL SIGNIFICANCE OF ENTROPY 



temperature of this particular aggregate no longer change, 

 although molecular collisions are still constantly occurring. 



Well-known examples of the unsettled state of a system are: 

 The turbulent state with its different streams, whirls, and eddies, 

 the state in which the potential and kinetic energy is unequally 

 distributed; for instance, when one part is at a high pressure 

 and another part at a lower pressure, when one part is hotter 

 than another part, and when unmixed gases are present in a 

 communicating system. 



A more specific feature of the unsettled state may be found 

 in the accompaniment to BURBURY'S condition A (already men- 

 tioned at bottom of p. 15) where it is intimated that (at the start 

 and after collision) all directions of the relative velocity R may 

 not be equally likely. 



When such differences have all disappeared to the extent that 

 equal elementary spaces possess their equal shares of the different 

 particles, velocities, and energies, the system will be a settled 

 one, be in thermal equilibrium, and will possess a maximum 

 entropy and a definite temperature. Moreover, BURBURY'S con- 

 dition A is here fully satisfied. 



At this point we again call attention to the fact, that in both 

 the unsettled and settled states of a system all conceivable micro- 

 states are not equally likely to obtain. On p. 9 mention 

 was made that the unsettled and the settled state each pos- 

 sessed a host of conceivable micro-states which agreed with the 

 characteristic averages of their respective macro-states (the 

 unsettled and the settled ones), and yet in each set some of these 

 led subsequently to events which did not accord with experience. 

 Therefore for both the unsettled and the settled state we must 

 limit the manifold character of their micro-states by eliminating 

 all those micro-states which lead to results contrary to experience. 

 This is accomplished by assuming the hypothesis of " elementary- 

 disorder " (elementar-ungeordnet) to obtain for the unsettled as 

 well as the settled state. Now so far as the haphazard character 



