J 348 GALVANISM. 



$ Of f he theories proposed at this early period of the experimental inquiry to 

 / explain chemical decomposition by the Voltaic apparatus, that of Grotthus was 

 the earliest and most plausible. To simplify the view of this theory, we shall 

 take as an example of its application the decomposition of water. Each mo- 

 lecule of water being composed of a molecule of oxygen and a molecule of 

 hydrogen, their natural electricities are in equilibrium when not exposed to any 

 disturbing force, each possessing equal quantities of the positive and negative 

 fluids. The electricity of the positive wire acting by induction, on the natural 

 electricities of the contiguous molecule of water, attracts the negative and re- 

 pels the positive fluid. It is further assumed in this theory, that oxygen has a 

 natural attraction for negative, and hydrogen for positive electricity ; therefore 

 the positive wire in attracting the negative fluid of the contiguous molecule of 

 water, and repelling its positive fluid, attracts its constituent molecule of oxy- 

 gen, and repels its molecule of hydrogen. The particle of water, therefore, 

 places itself with its oxygen next the positive wire, and its hydrogen on the 

 opposite side. The positive electricity of the first particle of water thus accu- 

 mulated on its hydrogen molecule, produces the same action on the succeeding 

 molecule of water as the wire did upon the first molecule ; and a similar ar- 

 rangement of the second molecule of water is effected. This second molecule 

 acts in like manner on the third, and so on. All the particles of water between 

 the positive and negative wires thus assume a polar arrangement, and have 

 their natural electricities decomposed ; the negative poles and oxygen molecules 

 looking toward the positive wire, and the positive poles and hydrogen mole- 

 cules looking toward the negative wire. The attraction of the positive wire 

 now separates the oxygen molecule of the contiguous particle of water from 

 its hydrogen molecule, neutralizes its negative electricity, and either dismisses 

 it in the gaseous form, or combines with it, according to the degree of the af- 

 finity of the metal of the wire for oxygen. The hydrogen molecule thus liber- 

 ated effects in like manner the decomposition of the second particle of water, 

 combining with its oxygen, and thus again forming water and dismissing its 

 hydrogen. The latter acts in the same manner on the next particle of water, 

 and so on. Thus, a series of decompositions and recompositions are supposed 

 to be carried on through the fluid, until the process reaches the particle of wa- 

 ter contiguous to the negative wire, and the molecule of hydrogen there disen- 

 gaged gives up its positive electricity, by which an equal portion of negative 

 electricity proceeding from the wire is neutralized, and the molecule of hydro- 

 gen escapes in the gaseous form. It is equally compatible with this theory to 

 suppose the series of decompositions and recompositions to commence at the 

 negative and terminate at the positive wire, or to commence simultaneously at 

 both, and terminate at any intermediate point by the union of the last molecule 

 of oxygen disengaged in the one series with the last molecule of hydrogen 

 disengaged in the other. 



Grotthus illustrated this ingenious hypothesis by comparing the supposed 

 phenomena with the mechanical effects produced when a number of elastic 

 balls ivory balls for example being suspended so that their centres shall be in 

 the same straight line, and their surfaces mutually touch, either cf the extreme 

 balls of the series being raised and let fall against the adjacent ons. the effect 

 is propagated through the series, and the last ball alone recoils in consequence 

 of the impact ; and although the action and reaction are suffered by each ball 

 of the series, and each is ins'rumental in transmitting the effect, no visible 

 change takes place in any ball except the last, and the effect is continued by 

 the alternate action of the extreme balls until the motion is gradually stopped 

 by the resistance of the air, and other external causes. 



The experiments of Davy, which have been a'eriy r?;nticned, ve'-e 



