CHAP. III.] STATIC AND KINETIC ENERGY. 33 



that has just been suddenly released from tension, will, 

 if it is elastic enough, vibrate rapidly for some time ; 

 the energy of motion due to its vibrations has been pro- 

 duced by transforming the static energy that was due 

 to the straining of its elasticity: and the vibrations 

 continue until their motion is carried away by being 

 transferred to the air and to the substances surrounding 

 the spring. 



So, when the string of a musical instrument is drawn Vibrating- 

 to one side, the energy that has done work in drawing it ^ "°^^' 

 is transformed into the energy due to its tension : and as 

 it vibrates, the energy vibrates back and forward between 

 the static and kinetic forms : being static at the ex- 

 tremities of the vibration, where the string has no velocity, 

 and kinetic in the middle, where its velocity is at the 

 greatest. This is an exactly parallel case to that of the 

 oscillatory transformation of energy between the potential 

 and actual forms in the motion of the pendulum : ^ for 

 the principle of the transformation is not affected by the 

 fact that, in the case of the pendulum, the energy at the 

 extremity of the stroke assumes the static potential form, 

 and in the case of the vibrating string it assumes the 

 static actual form. 



Energy of motion, heat, and radiance are all kinetic 

 forms of energy : and so is current, or voltaic, electricity. 

 Static electricity is a form of static actual energy : and in 

 a note to this chapter I shall give reasons for believing 

 that, as heat consists in molecular motion, so magnetism, 

 and probably electricity, consist in the straining of pecu- 

 liar molecular tensions. 



But in the chapters on chemical energies and on vital 

 energy I shall have to describe forms of static actual 

 energy of which we cannot give any such explanation, or 

 indeed any explanation whatever. 



It ought to be mentioned here, that it is possible for Trans- 

 one form of static energy to be transformed into another of static 

 without passing through any intermediate kinetic state, energy. 

 For instance, the water that descends in the buckets of an 



1 See p. 20. 



