THEORY OF GALVANISM. 137 



be expected that the effect will be increased 

 when the extremities of the pile are united ; for 

 in this case the electricity will be powerfully at- 

 tracted towards one end of the apparatus, in order 

 to produce an equilibrium with the other end, 

 which is relatively negative. The chemical hypo- 

 thesis is not encumbered with the necessity of a 

 current of electricity from one end of the pile to 

 the other ; it only supposes the passage of the elec- 

 tricity across the interposed fluid in each individual 

 pair of metals. The chemical differs frc-m the elec- 

 trical hypothesis in the material circumstance of the 

 former pointing out a source for the liberation or 

 evolution of electricity, in consequence of a change 

 in the nature of one of these substances, which 

 diminishes its capacity for it, and therefore ren- 

 ders it less disposed than before to retain it. The 

 electrical hypothesis only contemplates an inter- 

 change of electricity between the different parts of. 

 the apparatus, one part merely acquiring what it 

 attracts from the other part, a process by which 

 there can be no absolute production of it. 



The chemical differs very essentially from the Relative 

 electrical hypothesis with respect to the supposed metals/ * 

 state of the contiguous metals ; the electrical sup- 

 poses that they can have different states of electri- 

 city while they are in contact; the chemical takes it 

 for gran ted, that, while they are in contact, their elec- 

 trical states must be similar. The chemical hypo- 

 thesis satisfactorily explains all the facts that have 

 been observed, respecting the necessity of oxygen for 



