Explanatory Notes 109 



of material activity. Energy is protean in change of form, 

 but when once converted into heat it is likely to retain 

 that form, unless some ingenious machine is employed 

 to transform it into other forms of energy and to assist 

 it to do work, as when the vapour of boiling water is en- 

 abled to pump a mine or drive a flywheel by aid of a steam 

 engine. Moreover, there is a tendency for all contiguous 

 bodies, unless specially prevented, to become equal in 

 temperature, a condition in which no more work can be 

 obtained by any thermal process; and the energy is then 

 said to be degraded or dissipated. 



Ultimately therefore, in process of time, it has been sug- 

 gested that all the energy of the Universe may be expected 

 to take the low form of heat at a uniform temperature, *. e. 

 practically at an exceedingly low, nearly zero, temperature 

 an epoch being foreshadowed at which every activity 

 will thus ultimately cease. 



This dismal foreboding is not, or should not be, set for- 

 ward with any certainty; because processes whereby energy 

 may be pumped up again, as it were, from lower to higher 

 forms through the agency of life perhaps, or through the 

 agency of special intelligence for which the crude average 

 terms heat and temperature have no dominating meaning 

 can be imagined, and it only remains for us to discover 

 them in action somewhere. 



A description of how such intelligences could act was 

 first given by Clerk Maxwell, and was vividly elaborated 

 by Lord Kelvin. They are known as " Maxwell's demons." 

 Some biologists have suspected the real existence of such, 

 agents, in nitrifying bacteria and the like; and although no 

 definite discovery of agencies which will reverse results 

 attributed to the second law of Thermodynamics has yet 

 been made, it would be a mistake to limit the possibility of 

 discovery. 



And anyhow the material universe is manifestly in full 

 blast at present; it has not by any means reached the stage 



