216 THE ELECTRIC TELEGRAPH. 



attracts the negative or white components (the oxygen) of 

 the atoms of water immediately in contact with it, repelling 

 the black component (the hydrogen) which is positively 

 electrified. The black, or positive component of atom No. 1, 

 in its turn, attracts the white side and repels the black side 

 of atom No. 2, and so on through the whole mass of the 

 liquid. 



Let us now suppose another plate of a different metal, 

 a good conductor, but a less powerful electro-motor than 

 zinc, say copper, similarly immersed in the liquid at a 

 little distance from the first plate. 



On entering the liquid its natural tendency is to polarise 

 the atoms of water between itself and the zinc in the 

 reverse direction to that done by the latter ; and it would 

 do so if it were as strong an electro-motor as zinc, and 

 would depolarise all the atoms already polarised by the 



Fig. 116. Fig. 117. 



zinc. But not being so powerful an electro-motor, the 

 feebler polarisation which it takes itself and tends to 

 communicate to the atoms of water is overpowered by the 

 stronger polarisation of the zinc, and they retain nearly 

 the position given them by the latter. The black or 

 negative sides of the atoms all face the copper plate, and 

 induce a negative state in the part below the surface, 

 while the natural electricity of the copper, being decom- 

 posed, its positive component takes refuge in that part 

 which is above the surface of the liquid. An electrometer 

 of sufficient delicacy, brought to the upper end of a, would 

 indicate a negative tension, and in contact with b would show 

 a state of positive tension. This is what is called the open 



