Electric Currents. 55 



that the atom is active; that it has the power 

 to pick itself up again in an infinitesimally 

 short time and is again knocked down (fol- 

 lowing the illustration of the bricks) by the 

 next discharge along Its line or chain of atoms. 



If you could get a mental picture of this 

 action you would see that the whole conductor 

 is in a most violent state of atomic motion of 

 a peculiar kind. At the same time a part of 

 this electrical motion is being converted into a 

 heat motion of the atoms, and finally it all re- 

 turns to heat unless some of it is stored up 

 somewhere as potential energy. If the current 

 has driven a motor that has wound up a weight, 

 a part is stored up in the weight, which has the 

 ability to do work if it is allowed to run down. 

 If it drives machinery as it runs down, the 

 mechanical motion is the expression of the 

 stored energy. When the weight has run down 

 the energy will be represented by the heat 

 rn-ated by friction of the journals of the 

 \vh< -els and pulleys and the heating of the air. 

 If the weight is allowed to fall suddenly it 

 will heat the air to some extent, but mostly the 

 earth and the weight itself will be heated. If 

 .)' energy (the battery) is groat and 

 the Mvssure high and the conductor is too 

 small to carry the energy developed in the bat- 

 tery as electricity, IK at i> developed, and if the 

 heat is sullieiently inten-e. light also. 



We have ceen (Vol. II) that heat motion 



