VOLTAIC ELECTRICITY. 237 



5. (a.) A minute after the discharge of a Leyden jar, a second and 

 feebler spark may generally be obtained. Explain ( 356.) (&.) State 

 two uses of lightning-rods. 



6. (a.} Having a metal globe positively electrified, how could you 

 with it negatively electrify a dozen globes of equal size without 

 affecting the charge of the first ? (6.) How could you charge posi- 

 tively one of the dozen without affecting the charge of the first ? 



7. Can you devise a plan by which a series of Leyden jars, placed 

 upon a glass plate, may be simultaneously charged, the first posi- 

 tively, the second negatively, the third positively, the next nega- 

 tively, and so on ? 



Recapitulation. In this section we have considered 

 the Condensation of electricity ; the Leyden Jar ; 

 the Leyden Battery ; the Distribution of elec- 

 tricity on conductors; Atmospheric Electricity; 

 electrified Clouds and Lightning ; Lightning 

 Rods and their action ; the Velocity of the electric 

 current and the Duration of the electric spark; six 

 Classes of Effects of electricity and many electric 

 experiments. 



IV. 



VOLTAIC ELECTRICITY. DYNAMO-ELECTRICITY 

 AND THERMO-ELECTRICITY. 



373. Chemical Action. All chemical changes 

 produce electric separation. This is true whether the 

 substances subjected to chemical action be solid, liquid or 

 aeriform ; but the chemical action between liquids and 

 metals gives results the most satisfactory. Electricity 

 thus developed is called Voltaic or Galvanic electricity. 



