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NATURE 



451 



attached, an arrangement is formed producing a quantity 

 current, the exponent of which will be measured by the 

 superficial area of the individual plates. Thus a current j 

 is produced of low tension but great quantity. 



If, contrariwise, the zinc and carbon plates of the series , 

 are connected together alternately, an intensity current 

 will be produced of high tension. It is thus seen that 

 quantity and intensity may be combined together accord- 

 ing to the disposition of the elements composing the 

 battery. For instance, the twelve cells may be arranged 



either as a quantity arrangement of six cells each, con- 

 nected together as two for intensity, or in groups of three 

 for quantity, connected as four in series as an intensity 

 current ; or again, as a series of four for quantity, con- 

 nected together into a group of three for intensity. It is 

 evident, therefore, that some ratio between quantity and 

 intensity must be determined to produce that character 

 of current which shall be best adapted to the work to be 

 performed. The effective force of every electric current 

 depends therefore on two conditions — the electro-motive 



Fig. II. — Naimc's machine, furnishing the two electridties. 



force or tension, and the resistance it has to overcome in 

 passing through the metallic conducting wire. The elec- 

 tro-motive force of a voltaic current varies with the num- 

 ber of the elements and the nature of the metals and 

 liquids which constitute each element, but is in no degree 

 influenced by the dimensions of any of the parts. Sub- 

 marine telegraphic circuits var>' in length, from one mile 

 across the Thames to 2,000 miles in a continuous stretch 

 across the Atlantic, and a current of electric force 



effective for the shorter distance would be absolutely 

 useless for the Atlantic circuit. 



The chemical power of the voltaic pile was discovered 

 in the year iSoo, and water was the first substance de- 

 composed. If water is made a part of the electric circuit, 

 so that a current of electricity passes through it, it is 

 decomposed, and yields up its elements oxygen and 

 hydrogen gases in obedience to certain laws. To decom- 

 pose acidulated water it may be confined in two glass 



,=d by : 



tubes (Fig. 13), sealed at one extremity, and made 

 part of the electrical circuit by being placed over 

 the two electrodes of the poles of the battery. Gas will 

 then be collected in each tube, but that in connection 

 with the positive pole of the battery will be about half 

 the volume of that in connection with the negative pole, 

 the former being oxygen and the latter hydrogen, as 

 o.xygen and hydrogen gases are to each other in water 

 exactly as two to one, by volume. 

 , It has already been stated that all substances, however 



well they may conduct electricity, offer some resistance to 

 the passage of the current ; thus, the copper conducting 

 wire offers more or less resistance according to its length. 

 If the resistance of a mile of the copper conducting wire 

 is ascertained, each successive mile, if the copper is of 

 equal purity, will have the same measure of resistance ; 

 therefore, the resistance of the copper conductor in a 

 cable 2,000 miles long will be 2,000 times the resist- 

 ance of one mile of the conductor ; in other words, the 

 resistance of the wire is in direct proportion to its length. 



