156 CORRELATION OF PHYSICAL FORCES. 



yellow flame where combustion is at its maximum ; this latter 

 should be kept cool, to enable a thermo-electric current, which 

 is produced by the different temperature of the platinum 

 plates, to co-operate with the flame current ; wires attached 

 to the plates of platinum form the terminals or poles. By a 

 row of jets a flame battery may be formed, yielding increased 

 effects ; but in these experiments, though theoretically inter- 

 esting, so small a fraction of the power, actually at work in 

 the combustion, has been thrown into an electrical form, that 

 there is no immediate promise of a practical result. 



The quantity of the electrical current, as measured by the 

 quantity of matter it acts upon in its different phenomenal 

 effects, is proportionate to the quantity of chemical action 

 which generated it ; and its intensity, or power of overcoming 

 resistance, is also proportionate to the intensity of chemical 

 affinity when a single voltaic pair is employed, or to the num- 

 ber of reduplications when the well-known instrument called 

 the voltaic battery is used. 



The mode in which the voltaic current is increased in in- 

 tensity by these reduplications, is in itself a striking instance 

 of the mutual relations and dynamic analogies of different 

 forces. Let a plate of zinc or other metal possessing a strong 

 affinity for oxygen, and another of platinum or other metal 

 possessing little or no affinity for oxygen, be partially im- 

 mersed in a vessel, A, containing dilute nitric acid, but not 

 in contact with each other ; let platinum wires touching each 

 of these plates have their extremities immersed in another 

 vessel, B, containing also dilute nitric acid : as the acid in 

 vessel A is decomposed, by the chemical affinity of the zinc 

 for the oxygen of the acid, the acid in vessel B is also decom- 

 posed, oxygen appearing at the extremity of the wire which 

 is connected with the platinum : the chemical power is con- 

 veyed or transferred through the wires, and, abstracting cer- 

 tain local effects, for every unit of oxygen which combines 

 with the zinc in the one vessel, a unit of oxygen is evolved 



