of the various Forms of Energy. 285 



The unknown, or electrical, energy appears to rank distinctly 

 above the energy of molecules ; because we haye found some 

 remarkable and indirect means of transferring the energy of 

 electric currents to ordinary masses, by the intervention of 

 electromagnetism, with a comparatively small waste. 



20. "When energy passes from a higher to a lower form it 

 is said to be degraded ; and when it has no availability at all 

 it is called dissipated* . 



Energy is degraded when it is transferred from masses of 

 ordinary size to the molecules of which they or others consist 



(§ 18). 



The two fundamental forms of energy are those due to mo- 

 tion and those due to strain (§9). Now whenever motion 

 takes place against friction, some energy is always transferred 

 to the molecules of the rubbing surfaces. And whenever strain 

 is produced in imperfectly elastic bodies, some energy always 

 passes to the molecules. 



But in practice no motion takes place without friction, and 

 all bodies are imperfectly elastic. Hence energy is continually 

 getting dissipated; or, in other words, at every transfer of 

 energy between ordinary bodies under ordinary circumstances, 

 some of it is always and necessarily degraded into a lower and 

 less available formf . 



It may be useful to append the following summary of the 

 contents of the sections : — 



1. Newton's third law. 



2. Definition of work, + and — . 



3. Denial of-" action at a distance." 



4. Definition of working-power. 



5. Definition of energy. 



6. Conservation of energy, and first law of thermodynamics. 



7. Possibility of various forms of energy. 



8. Classification of the forms of energy. 



9. The fundamental forms of energy. 



10. Kinetic and potential energy are related to the two fac- 

 tors in the product work. 



* It is then of no more use to us than is our money to the inhabitants of 

 Mars, who have no means of getting at it. Its terrestrial transferences 

 are to them useless. 



t For instance, during every quarter-swing of a free pendulum, energy 

 is being transformed from kinetic to potential, or vice versa; and is being 

 transferred from the unknown gravitation agent to the mass of the pen- 

 dulum, or back again. Some, however, is dissipated every time, and ulti- 

 mately the pendulum must stop. 



