SECT, xxix.] VOLTAIC PILE. 331 



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 elec- 

 tricity of its sudden and uncontrollable violence, and giving 

 in a continued stream a greater quantity at a diminished 

 intensity, has exhibited that fluid under a new and manage- 

 able form, possessing powers the most astonishing and un- 

 expected. As the Voltaic battery has become one of the 

 most important engines of physical research, some account 

 of its present condition may not be out of place. 



The disturbance of electric equilibrium, and a development 

 of electricity, invariably accompanies the chemical action of 

 a fluid on metallic substances, and is most plentiful when that 

 action occasions oxidation. Metals vary in the quantity of 

 electricity afforded by their combination with oxygen. But 

 the greatest abundance is developed by the oxidation of zinc 

 by weak sulphuric acid. And, in conformity with the law that 

 one kind of electricity cannot be evolved without an equal 

 quantity of the other being brought into activity, it is found 

 that the acid is positively, and the zinc negatively electric. 

 It has not yet been ascertained why equilibrium is not restored 

 by the contact of these two substances, which are both con- 

 ductors, and in opposite electrical states. However, the 

 electrical and chemical changes are so connected, that, unless 

 equilibrium be restored, the action of the acid will go on 

 languidly, or stop as soon as a certain quantity of electricity 

 is accumulated in it. Equilibrium, nevertheless, will be 

 restored, and the action of the acid will be continuous, if a 

 plate of copper be placed in contact with the zinc, both 

 being immersed in the fluid ; for the copper, not being acted 

 upon by the acid, will serve as a conductor to convey the 

 positive electricity from the acid to the zinc, and will at 

 every instant restore the equilibrium, and then the oxida- 

 tion of the zinc will go on rapidly. Thus three substances 



