VOLTAIC ELECTRICITY. 253 



is called electro-positive; that which goes to the 

 positive electrode is called electro-negative, these 

 terms being based upon the idea of attraction between 

 opposite electricities. 



402. Physiological Effects of Voltaic Elec- 

 tricity. The physiological effects are shocks and spas- 

 modic muscular contractions more or less violent. When 

 the electrodes of a strong battery, or the electrodes of a 

 Ruhmkorff coil ( 410), are held in moistened hands, the 

 passage of the current through the body produces a pecu- 

 liar sensation easily recognized thereafter. The current 

 may be made to pass through a series of persons who have 

 joined hands. 



403. Induced Currents. From our study of 

 f rictional electricity, we are familiar with the term induc- 

 tion, by which we understand the influence which an 

 electrified body exerts upon a neighboring unelectrified 

 body. In 1831, Faraday discovered an analogous class of 

 phenomena produced by Voltaic electricity or by mag- 

 netism. An induced cun*ent is an instantaneous 

 cuwent produced in a conductor by the influence 

 of a neighboring current or magnet. A current used 

 to produce such an effect is called an inducing current. 



404. Inductive Effect of Closing or Break- 

 ing a Circuit. In Fig. 199, B represents a double 

 coil made as follows: On a hollow cylinder of wood or 

 card-board is wound several layers of stout copper wire, 

 insulated by being covered with silk. The two ends of 

 this wire, which constitute the primary coil, are seen 

 dipping into the cups gcj '. Upon this coil, and carefully 

 insulated from it, is wound a much greater length of finer 



