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electro-motive force of the two plates of a Daniell's element 

 into 100 parts, from 60 to 70 of those parts are required to 

 reduce the zinc half ring and the copper half ring to such 

 a state that the moveable bar remains at rest whether it is 

 electrified vitreously or resinously. 



'•' If the copper half ring is oxydised by heat, the amount 

 of electro-motive force then required to neutralise the two 

 halves is much increased. If, after oxydising the copper one 

 day by heat, I leave the apparatus till the next day, the effect 

 is generally diminished, though something of it still remains. 

 After again heating the copper by laying it for some time on 

 a redhot iron heater and alloAving it to cool, I found the effect 

 almost exactly 100 parts. I have no doubt that by making 

 the coat of oxyde very complete and thick enough, and by 

 cleaning the zinc perfectly, I shall be able to get considerably 

 above the electro -motive force of a single Daniell's element. 

 I remembered perfectly Avhat you told me a long time ago 

 about heating the coppers of a battery and getting a strong 

 effect, for some time equal to that of the Daniell's cell, when 

 I tried the effect of oxydising the copper plate by heat. 



'^I believe there are also electrical effects of heat itself; so 

 that if one half of a ring of one metal is hot and the other is 

 cold, the needle will show a difference according as it is 

 charged positively or negatively. 



^^ For nearly two years I have felt quite sure that the proper 

 explanation of voltaic action in the common voltaic arrange- 

 ment is very near Volta's, which fell into discredit because 

 Volta or his followers neglected the principle of conservation 

 of force. I now think it quite certain that two metals dipped 

 in one electrolytic liquid will (when polarisation is done away 

 with) reduce two dry pieces of the same metals, when con- 

 nected each to each by metallic arcs, to the same potential. 



" There cannot be a doubt that the whole thing is simply 

 chemical action at a distance. Zinc and copper connected 

 by a metallic arc attract one another from any distance. 



