228 GREAT MEN OF SCIENCE 



publication, and relating only to his grasp of the matter, im- 

 mediately led him to the 'lefthand rule' still in use to-day, 

 for indicating the direction in which a north pole is de- 

 flected by a given current. This was an improvement on 

 Oersted's form of statement, which of course led to exactly 

 the same result. Ampere on this occasion also introduced 

 for the first time a clear distinction between electrostatics 

 (the science of stationary electricity) and electrodynamics 

 (science of moving electricity, that is of current eff"ects), and 

 invented these terms themselves. 



To all this Ampere immediately also added an entirely new 

 discovery. It was known that electric charges exert forces 

 upon one another, and likewise magnetic poles - both ac- 

 cording to Coulomb's law - and it was now known from 

 Oersted's work, that electric currents act on magnetic poles 

 as if they were themselves magnets. This at once gave rise 

 for Ampere to the question whether currents might not also 

 exert forces on other currents. He decided the question in 

 the year of Oersted's discovery (1820), by experiments, and 

 in the affirmative. He found that parallel currents in the 

 same direction attract one another, and those in opposite 

 directions repel one another, it being a matter of indifference 

 whether the two currents acting upon one another be- 

 long to the same circuit or to separate circuits. The re- 

 sult was the discovery of again a new and unknown kind of 

 force. 



The fundamental experiments were of a simple descrip- 

 tion, although at that time by no means quite obvious; it was 

 merely a matter of making current-carrying conductors 

 easily mobile, which Ampere effected by suspending them 

 from mercury cups and by similar means. A very re- 

 markable fact in this connection was that here like attracted 

 like, and opposites repelled one another, a reverse case to 

 that of static electricity. The newly discovered electro- 

 dynamic force was thereby immediately distinguished from 



