402 WELLS'S NATURAL PHILOSOPHY. 



uid, to the copper, and from the copper along the conducting-wires to the 

 zinc, as indicated by the arrows in the figure. A current of negative elec- 

 tricity at the same time traverses the circuit also, from the copper to the 

 zinc, in a direction precisely reversed. 



Such an arrangement is called a simple galvanic battery. 



What are the The two metals forming the elements of the 

 vanl^ bLttefy ?" battery are generally connected by copper 

 wires ; the ends of these wires, or the terminal 

 points of any other connecting medium used, are called the 

 poles of the battery. 



Thus, when zinc and copper plates are used, the end of the wire conveying 

 positive electricity from the copper would be the positive pole, and the end of 

 the wire conveying negative electricity from the zinc plate would be the 

 negative pole. Faraday describes the poles of the battery as the doors by 

 which electricity enters into or passes out of the substance suffering decom- 

 position, and in accordance with this view he has given to the positive pole 

 _tho name of anode, or ascending way, and to the negative pole the name of 

 caViode, or descending way. 



At what point Thc manifestations of electricity will be most 

 is "eiecTricUy apparent at that point of the circuit where the 

 man^fcited? two currcnts of positive and negative electricity 

 meet. 



__ . . "When the two wires connecting the metal plates of a bat- 



When IS a cir- ° ^ 



cuit said to be tery are brought in contact, the galvanic circuit is said to be 



closed ? closed. No sign of electrical excitement is then visible ; the 



action, nevertheless, continues. The opposite electricities collected at the 



poles, in particular, neutralize each other perfectly on meeting ; every traco 



of electricity must therefore vanish, as when a Leyden jar is discharged, if a 



fresh quantity were not continually produced by the pairs of plates. If the 



wires which conduct the two electricities be shghtly disconnected, a spark 



will be observed at the point of interruption. 



„ . , In the formation of a galvanic circuit, by the employment 



Explain the „ , , ,. . , „ , . , .. , • , • 



theory of the of two metals and a liquid, the chemical action which gives 



production of pjgg ^q ^^le electricity takes place through a decomposition of 



galvanic elec- ■' ^ . i i r- 



trlcity. the liquid. It is, therefore, essential to the formation of an 



active galvanic circuit, that the liquid employed should be ca- 

 pable of being decomposed. Water is most conveniently applicable for this 

 purpose. When a plate of zinc and copper are immersed in water, the ele- 

 ments of the water, oxygen and hydrogen, are separated from each other, in 

 consequence of the greater attraction which the oxygen has for the zinc. The 

 oxygen, therefore, unites with the zinc, and by so doing produces an altera- 

 tion in the electrical condition of the metal. The zinc communicating its nat- 

 ural share of electricity to the liquid, becomes negatively electrified. The 



