Joule, Mayer, and Others: A Decade-and-a-Half-Long Debate over Priority in the Discovery of the Mechanical Equivalent of Heat

This article reviews the history of a debate over priority in the discovery of the mechanical equivalent of heat that was centered around J. P. Joule and J. R. von Mayer. The following two stages may be distinguished in this debate. During the first stage, those involved in it were Joule and Mayer themselves. While Mayer presented a numerical value for the mechanical equivalent of heat, which was based on the data from Gay-Lussac’s experiment, Joule determined the value of this coefficient in his own experiment although he did it later than Mayer (actually, Joule was unaware of Gay-Lussac’s experiment). This article shows that, in the end, Joule and William Thomson, who also participated in the debate, recognized (even though formally and with reservations) Mayer’s priority. During the second stage of the debate, its participants were British scientists who supported Mayer or Joule. Thus, Mayer’s priority was supported by Professor J. Tyndall of the Royal Institution in London and it was he who initiated the resumption of the discussion. Joule’s priority was advocated by Professor W. Thomson of the University of Glasgow and Professor P. Tait of the University of Edinburgh. It is noted that a personal animosity between Tyndall and Tait, as well as Tyndall’s competitive attitude towards Thomson, had a significant impact on the tone of the debate, and the examples of Tait’s provocative remarks and Tyndall’s reactions are provided. Joule’s involvement during the second stage of the debate that was mostly limited to private correspondence between himself, Tait, Thomson, and Tyndall, is discussed. Over the time elapsed after the first stage of the debate, the level of rejection of Mayer’s arguments by the scientific community had decreased significantly. The awarding of the Royal Society’s Copley Medal to Joule (1870) and Mayer (1871), both of them nominated by Tyndall, came as a symbolic conclusion of the debate.

Design of a mechanical knee joint for an exoskeleton

The main problem of designing a lower limb exoskeleton for healthy people is allowing unconstrained movement along with providing sufficient load carrying capability. It is not a simple task since most of the human body joints have more than one degree of freedom. A designed mechanical equivalent should imitate these movements being outside the human body. Due to this, the mechanical joints must provide shortening or elongation of the structure during load carrying. Authors present biomechanical analyzes of a knee joint and propose a design of a mechanical equivalent of this joint that can be applied in exoskeletons. Additionally, laboratory trials proved suitability of this solution.

When is enough enough? Accurate measurement and the integrity of scientific research

At a meeting of the Physical Society of London in 1925 participants expressed their concerns regarding a recent suggestion by the Australian physicist T. H. Laby for replicating the established value of the mechanical equivalent of heat. This rather controversial discussion about the value of redetermining this numerical fact brings to light different understandings of the moral economy of accuracy in scientific work; it signals a distinctive new stage in the historical understanding of accuracy and precision and the moral integrity in conducting research.

Julius Robert Mayer

Mayer built a conservation law that included heat based on his calculation for the mechanical equivalent of heat (MEH) involving the difference in heat capacity at constant pressure and that at constant volume.

Nineteenth Century

The Romantic Movement gave impetus to a process of unifying the forces of nature – an impetus that bore fruit in, especially, Oersted’s demonstraton of the magnetic effect of electrical currents (1820) and Maxwell’s theory of electromagnetism (1865). Also, during this period Sadi Carnot articulated the first version of the second law of thermodynamics (1836) while James Joule’s painstaking experimental demonstration of the mechanical equivalent of heat (1847) is an essential foundation of the first law of thermodynamics.