Conservation and Innovation : Helmholtz's Struggle with Energy ...

important in his view: "to what extent can heat correspond to a force
equivalent"? 168
Here force equivalents should not be confused with mechanical equivalents: the
firsts are theoretically identifiable "energy terms"; the second are numerical
conversion factors.
The caloric theory was discussed in explicit reference to the interpretation of
Carnot and Clapeyron 169, for whom the force equivalent is the work produced in
the passage of a certain amount of caloric from a higher to a lower temperature.
Helmholtz criticised 170 W.Henry's and Berthollet's interpretation of the heat
produced by friction as displacement of caloric and asserted that results from the
field of electricity showed that the total amount of the heat of a body can be
actually increased. Helmholtz recalled experimental evidence, entirely based on
research in electricity, against the caloric theory of heat and in favour of the
mechanical one. While frictional and voltaic electricity did not give
unquestionable evidence, because the heat produced could be interpreted as
caloric displaced, "we still have to explain in a purely mechanical way the
production of electrical tensions in two processes, in which any quantity of heat
that can be assumed as transferred never appears" 171 : electrical (not
electromagnetic) induction and movements of magnets. Helmholtz gave the
example of an electrophorus used to charge a Leyden jar for the first, and for the
second the example of electromagnetic machines where "heat can be developed
ad infinitum" 172. It is only at this stage that Helmholtz recalled Joule's experiments
of 1843 173 and asserted that Joule "endeavoured to show directly" that the
electromagnetic current produced heat and not cold even in that part which is
under the actual action of the magnet (no displacement of caloric is thus
conceivable in the electrical circuit). Again the minor role that Joule's results
play in the exposition of Helmholtz's ideas must be noted .
For Helmholtz thus the caloric theory must be rejected, because heat can be
produced indefinitely through mechanical and electrical forces, and the
mechanical theory must take its place. As seen in the previous section, this result
168 Helmholtz Erhaltung P. 27.
169 Helmholtz Erhaltung P.28.
170 Helmholtz Erhaltung P.28
171 Helmholtz Erhaltung P. 29.
172 Helmholtz Erhaltung P.30.
173 Helmholtz Erhaltung P.30 ( Joule's rezsults were wrongly dated 1844)