Joule's 1840 manuscript on the production of heat by voltaic electricity

In 1840, James Prescott Joule submitted to the Royal Society a paper describing experimental research on the heat produced by electric currents in metallic conductors, and inferring that the effect was proportional to the resistance of the conductors and to the square of the intensity of the current. Only an abstract of this paper was published in the Proceedings of the Royal Society , although a full paper with a similar title was printed in the Philosophical Magazine in 1841. Several authors have assumed that the content of the 1841 publication was the same as the rejected 1840 paper; however, the unpublished manuscript has been found within the archives of the Royal Society and is published here for the first time, along with a detailed analysis and comparison with the 1841 paper. The unpublished version is much shorter, and is different in certain respects from the published article. A detailed comparison throws light on several shortcomings of the unpublished version. The present work also studies the assessment of Joule's paper by the Royal Society, and elucidates the roles of Peter Roget and Samuel Christie in this connection.