NOMOS. 39 



tiguous copper element ; and the result is, that the 

 zinc molecule is decomposed, the positive element 

 tending to unite with the copper negative element, 

 and the negative zinc element uniting to form a new 

 molecule with the zinc positive element of that mole- 

 cule which had been decomposed by the chlorine, 

 and whose negative element had gone to form the 

 molecule of chloride of zinc, with whose formation 

 we started in our course round the circuit. And 

 thus we have travelled round the circuit to the point 

 from which we started. This, however, is not the 

 whole case. We have spoken of decompositions and 

 recombinations starting from the molecule of chloride 

 of zinc, and travelling in one direction around the 

 circuit to the same point ; but this is not all. On 

 the contrary, these decompositions and recombinations 

 travel in both directions. We have spoken of the 

 changes induced by the hydrogen, but we might, 

 with equal propriety, have pursued a contrary 

 course, and traced the changes induced by the po- 

 sitive zinc element which was liberated when the 

 molecule of chloride of zinc was formed. We might 

 have traced the element as acting upon the conti- 

 guous zinc molecule, decomposing it, forming a new 

 zinc molecule, and liberating another zinc positive 

 element. We might have traced this element setting 

 up corresponding changes, molecule after molecule, 

 first in the copper, then in the platinum, and last in 

 the hydrochloric acid, until we have travelled through 

 the whole circuit, and returned to the point from 

 which we started. So that, in fact, we may suppose 

 each molecule, as it were, to be acted upon at both 



D 4 



