SECT. XXIX. THE VOLTAIC BATTERY. 291 



uncontrollable violence, and giving in a continued stream 

 a greater quantity at a diminished intensity, has exhibited 

 that fluid under a new and manageable form, possessing 

 powers the most astonishing and unexpected. As the 

 Voltaic batteiy 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 devel- 

 opment of electricity, invariably accompany the chem- 

 ical action of the fluid on metallic substances, and are 

 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 nega- 

 tively electric. It has not yet been ascertained why 

 equilibrium is not restored by the contact of these two 

 substances, which are both conductors, 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 accu- 

 mulated 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 oxidation of the zinc will go on rapidly. (Thus 

 three substances are concerned in forming a voltaic 

 circuit, but it is indispensable that one of them should 

 be a fluid, j The electricity so obtained will be very 

 feeble in overcoming resistances offered by imperfect 

 conductors interposed in the circuit, or by very long 

 wires, but it may be augmented by increasing the num- 

 ber of plates. In the common Voltaic battery, the 

 electricity which the fluid has acquired from the first 

 plate of zinc, exposed to its action, is taken up by the 



