SECT. XXIX. VOLTAIC ELECTRICITY. 297 



SECTION XXIX. 



Voltaic Electricity The Voltaic Battery Intensity Quantity^. 

 Static Electricity, and Electricity in Motion Luminous Effects Mr, 

 Grove on the Electric Arc and Light Decomposition of Water Forma- 

 tion of Crystals by Voltaic Electricity Photo-galvanic Engraving 

 Conduction Heat of Voltaic Electricity Electric Fish. 



VOLTAIC or Dynamic electricity is elicited by the force of chemi- 

 cal action. It is connected with some of the most brilliant 

 periods of British science, from the splendid discoveries to which 

 it led Sir Humphry Davy and Dr, Faraday, 



In 1790, while Galvani, Professor of Anatomy in Bologna, was 

 making experiments on electricity, he was surprised to see con- 

 vulsive motions in the limbs of a dead frog accidentally lying 

 near the machine during an electrical discharge. Though a 

 similar action had been noticed long before his time, he was so 

 much struck with this singular phenomenon, that he examined all 

 the circumstances carefully, and at length found that convulsions 

 take place when the nerve and muscle of a frog are connected by 

 a metallic conductor. This excited the attention of all Europe ; 

 and it was not long before Volta, Professor at Pavia, showed that 

 the mere contact of different bodies is sufficient to disturb elec- 

 trical equilibrium, and that a current of electricity flows in one 

 direction through a circuit of three conducting substances. From 

 this he was led, by acute reasoning and experiment, to the con- 

 struction of the Voltaic pile, which, in its early form, consisted 

 of alternate discs of zinc and copper, separated by pieces of wet 

 cloth, the extremities being connected by wires. This simple 

 apparatus, perhaps the most wonderful instrument that has been 

 invented by the ingenuity of man, by divesting electricity of its 

 sudden and uncontrollable violence, and giving in a continued 

 stream a greater quantity at a diminished intensity, has exhibited 

 that force under a new and manageable form, possessing powers 

 the most astonishing and unexpected. The expression current has 

 no relation to a fluid, which is now considered to be as inconsis- 

 tent with the phenomena of dynamic as with static electricitv. 



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