493 



ItEI'ORT — 1SS4. 



A to B vid W, or vice vere&\ no work is done on the wliole. Quite true ; 

 but tlie conclusion that no work is done at the junction by no means 

 follows. Work rand be done at the junction in proportion to the force 

 there (by inspection of the diagram), and accordingly the existence or 

 non-existence of a Peltier effect has everything to do with the existence or 

 non-existence of a local E.M.F. This controverts the second form of the 

 argument. 



If the argument be now considered upset, are we to proceed to assert 

 that the difference of potential, or force, concerned in the Volta effect, and 

 the heat destruction or generation concerned in the Peltier effect, are 

 closely connected, and in fact different ways of observing the same thing ? 

 By no means. All we have proved is that the Peltier effect accurately 

 and necessarily represents and measures the true contact force at a junc- 

 tion. True, we have considered a difference of potential V— V as pro- 

 duced by this contact force in an incomplete circuit, and so it is ; but 

 nothing has been said to imply that this difference of potential has any- 

 thing to do with what is observed in electrostatic experiments as the 

 \ olta effect. So far from this I will assert that what is usually observed 

 when two metals are touched and separated is not primarily a difference 

 of potential between the metals at all. They are at different potentials 

 when separated, no doubt, because they are oppositely charged ; but 

 they may have been at the same potential until separated. The real 

 Volta effect is almost independent of the true contact force, and of the dif- 

 ference of potential which it produces. In other words, a good Volta 

 effect can be observed when there was no difference of potential whatever 

 between the metals when in contact. 



According to my view the Volta effect is produced, not by a contact 

 force at the junction of the two metals, but by a contact force at their 



Hydrostatic analogue of the Volta effect, or apparent difference of potential produced 

 by metallic contact, and of the opposite charges but uniform potential which it 

 maintains between tra in contact The vessels are covered by air-;. 



elastic bags differently stretched. 



free surfaces, between the metals and the air or other medium surround- 

 ing them. To represent this hypothesis by a hydrostatic model we shall 

 have to maintain the difference of level in the two connected vessels, 

 not by a force at the junction, but by a force at the surfaces ; say by using 

 closed vessels and compressed air, or more pictorially by differently 

 stretched elastic membranes or bladders tied over the tops of the vessels. 



