GALVANISM. 403 



copper attracting the same electricity from the liquid, becomes positively 

 electrified, ; at the same time the hydrogen, which is the other element of 

 the water, is also attracted to the copper, and appears in minute bubbles upon 

 its surface. If the two metal plat€s be now connected with metallic wires, 

 positive electricity wLU flow from the copper and negative electricity from the 

 zinc, and by the union of these two an electric current will be formed.* 



"With water alone and two metals, the quantity of electricity excited is very 

 small, but by the addition of a small quantity of some acid, the excitement ia 

 greatly increased. 



What is th Although two metal plates are employed in the awangement 



necessity of two described, only one of them is actis'e in the excitement of elec- 

 yLnTj cireuiT?' ^'^^^^7^ ^^^ Other plate serving merely as a conductor to collect 

 the force generated. A metal plate is generally used for this 

 purpose, because metals conduct electricity much better than other substances 

 exposing an equal surface to the fluids in which they are immersed ; but other 

 conductors may be used, and when a proportionately larger surface is ex- 

 posed to compensate for inferior conducting power, they answer as well, and 

 in some instances better, than metal plates. Thus charcoal is very ofl;en em- 

 ployed in the place of copper, and a very hard material obtained from the ul- 

 terior of gas retorts, called graphite, is considered one of the best conductors. 



Two metals are not absolutely essential to the formation of a simple gal- 

 vanic circuit. A current may be obtained from one metal and two hquids, 

 provided the liquids are such that a stronger chemical action takes place on 

 one side of the metal plate than on the other. 



In some electric batteries also, two metals and two dissimilar liquids are 

 employed. 



„ . 775. The electricity developed by a simple 



How may gnl- , . . . , . 



vanic action be galvaiiic circuit, wlietlier it be composed of 



increased? " i t • ^ i 



two metals and a liquid, or any other combin- 

 ation, is exceedingly feeble. Its power can, however, be 

 increased to any extent by a repetition of the simple com- 

 binations. 



* The terms " electric fluid" and " electric current," which are frequently employed in 

 describing electrical phenomena, are calculated to mislead the student into the supposi. 

 tion that electricity is known to bo a fluid, and that it flows in a rapid stream along the 

 wires. Such terms, it should be understood, are founded merely on an assumed analogy 

 of the electric force to fluid bodies. The nature of that force is unknown, and whether its 

 transmission be in the form of a current, or by vibrations, or by any other means, is un- 

 determined. 



In a discussion which took place some years since at a meeting of the British Associa- 

 tion for the Advancement of Science, respecting the nature of electricity, Professor Fara- 

 day expressed his opinion as follows : — " There was a time when I thought I knew some- 

 thing about the matter ; but the longer I live, and the more carefully I study the subject, 

 the more convinced I am of my total ignorance of the nature of electricity." 



"After such an avowal as this," says Mr. Bakewell, "from the most eminent electrician 

 of the age, it is almost useless to say that any terms which seem to designate the forib of 

 electricity are merely to be considered as convenient conventional eipressiona," 



