The strange case of Dr. Petit and Mr. Dulong

The Dulong-Petit limiting law for the specific heats of solids, one of the first general results in thermodynamics, has provided Mendeleev with a powerful tool for devising the periodic table and gave an important support to Boltzmann's statistical mechanics. Even its failure at low temperature, accounted for by Einstein, paved the way to the the quantum mechanical theory of solids. These impressive consequences are even more surprising if we bear in mind that, when this law was announced, thermal phenomena were still explained using Lavoisier's concept of caloric and Dalton's atomic theory was in its infancy. Recently, however, bitter criticisms charging Dulong and Petit of `data fabrication' and fraud, have been raised. This work is an attempt to restore a more balanced view of the work performed by these two great scientists and to give them back the place they deserve in the framework of the development of modern science.