198 THE REALITIES OF MODERN SCIENCE 



They had learned to speak in terms of force and to 

 recognize that like charges repel, while unlike attract. 

 A body which did not test as being either positive or 

 negative, that is, a neutral body, contained equal and 

 opposite charges. Such a body might, however, serve 

 as a conductor of electricity. Two parallel conductors 

 did not attract each other electrically, for the attrac- 

 tion of their unlike charges was balanced by the repul- 

 sion of their like charges. Nevertheless, when currents 

 flowed through them in parallel directions they trac- 

 tated. Therefore, men reasoned that electricities in 

 motion attracted if going in parallel directions. When 

 it came to electricity in motion they forgot Coulomb's 

 law and treated it as a new entity, calling it " voltaic 

 electricity," building up the subject of " electro- 

 magnetism, " so called because such currents also affect 

 magnets, and making new definitions for such electrical 

 magnitudes as current, quantity, and potential difference. 

 Let us, however, express this phenomenon in terms 

 of energy and electrons. Consider first two wires, 

 say A and B, which are not carrying currents. We 

 analyze this system into four component systems, 

 namely those comprised by (1) the free electrons of 

 A and of B, (2) the positive molecules, (3) the elec- 

 trons of A and the positives of B, and conversely, 

 (4) the electrons of B and the positives of A. These 

 potential energies exist but are absolutely not avail- 

 able, e.g. systems (1) and (3) are equal in their space 

 rates, and the parts of (1) pellate while those of (3) 

 tractate. If we could isolate one system we should 

 find that the energy which we made available would 

 just be equal to the work which we had done. 



