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LVI. On the Thermoelectricity of Molten Metals. 
By F. Braun (Carlsruhe)*. 
ia Ye a circuit of metallic conductors a current produced by 
difference in temperature must be the equivalent of heat 
derived from an external source. If we assume (1) that the 
process is reversible, (2) that heat is absorbed only at the point 
of contact of higher temperature, and is given out only at the 
colder point of contact, then it follows that the thermo- 
electric force must be proportional to the difference in tem- 
perature of the junctions for intervals of any magnitude. If 
we assume a change in potential function at both junctions, 
the resuli may be expressed thus: that the change in poten- 
tial is proportional to the absolute temperature of the junc- 
tion. The electromotive force therefore, expressed as a 
function of the difference of temperature, ought to be a 
straight line. But experiment shows that in all the thermo- 
piles as yet examined this linear relationship does not hold 
good; in by far the majority of cases the curve is much 
nearer a parabola. This led Sir W. Thomson to the conclu- 
sion that even in the interior of one and the same metal 
unequally heated there must be produced, upon the passage 
of a current, a quantity of heat proportional to the first power 
of the current-strength (adopting Le Roux’s term, we may 
call this ‘“ the Thomson-effect ’’). 
In fact, if the thermopile works, not between two tempera- 
tures, but between an infinite number, it follows inversely 
that its electromotive force can no longer be expressed as a 
linear function of the greatest temperature-difference which 
occurs in it. Although, strictly speaking, nothing can be 
determined as to the locality of the electromotive force, yet 
we should be disposed to add to the changes in potential 
assumed to exist in the junctions (of which, however, no 
proof has yet been given that they occur there) other 
changes of potential occurring in the interior of the unequally 
heated metal. : 
Hitherto, so far as I know, only thermopiles have been 
examined in which at least one metal has been solid. The 
explanation is then obvious, that these internal thermo- 
electric forces are due to changes produced by the heat itself 
in the solid metal—hot and cold metal behaving like two 
different substances, or, as we may shortly express it, the 
heat produces structural changes. In fact, as shown by the 
* Translated from the Sttzwngsber. der kinigl. Akad. d. Wissensch, of 
Berlin, of April 9th, 1885. : 
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