Plasticity, Viscosity, Regelation \&Ndash; Remarks on the Bitter Forbes\&Ndash;Tyndall Controversy

Received: 10 July 2020 Accepted: 15 November 2020 DOI: 10.1002/pamm.202000158

Plasticity, Viscosity, Regelation – Remarks on the bitter Forbes–Tyndall Controversy

1, Dietmar Gross ∗ 1 TU Darmstadt, Division of Solid Mechanics, 64287 Darmstadt, Germany The paper highlights a few aspects of the so-called Great Glacier Controversy which started from questions regarding the viscosity of ice, which touched priority issues and which affected the just emerging thermodynamics and leading scientists.

1 Beginnings of Glacier Theory and Thermodynamics

In the context of geological research, glaciers became one hot topic of scientific interest in the early 19th century. From investigations of pioneers as e.g. J.J. Scheuchzer, J. Hugi or L. Agassiz it was known that glaciers may move and transport material. Later, the transport hypothesis of the so-called ‘erratics blocks’ led to the concept of ice ages. But the hidden mechanism behind the glacier movement and the nature of glacier ice as a material was not understood [1]. The first correct and clear concept was presented in 1840 by the canon and later bishop of Annecy, Louis Rendu. In his treatise ‘Théorie des Glaciers de la Savoie’ he stated that glaciers move like fluids and that glacier ice has ‘some sort of extensibility’ and ‘may behave like a soft dough’ [1]. Invited by Louis Agassiz, James Forbes (1809 - 1868) from Edinburgh visited him in 1841 during his displacement measurements at the Unteraar glacier. Here he got interested in glacier research and here he heard the first time about Rendu’s theory without having the opportunity to read it. One year later, in 1842, the physicist Forbes started his own, precise measurements at the Mer de Glace near Chamonix. Already in the same year, on basis of his observations and data, he set the cornerstones of his viscous or plastic theory of glaciers which he complemented by additional measurements in the following years until 1845 [2]. In his theory he stated that a glacier essentially is a viscous (plastic) ‘semirigid’ flowing mass containing a crack and vein-structure whose fluidity depends on parameters like temperature, water contents etc, [3]. In his numerous publications on glaciers he gave since 1843 credit also to Louis Rendu who, on request, had sent him his treatise.

b) c) Fig. 1: a) Glacier cross section, b) Flow pattern, c) ‘view of a model shewing the curves generated (experimentally) by the motion of a viscous ﬂuid’, all Figures and text in c) taken from Forbes [3]

Approximately at the same time the basic laws of thermodynamics have been found. Though Carnot’s principle of 1824 initially was ignored, its importance was recognized by William Thomson in conjunction with James Prescott Joule’s work on the mechanical equivalent of heat of 1850. In 1851 W. Thomson reconciled both principles, postulating the 1st and 2nd law of thermodynamics. It this context, a number of other scientists have to be mentioned, among them Robert Mayer, Rudolf Clausius and Hermann von Helmholtz. In fact, Thomson’s seminal paper starts with the phenomenon that two ice blocks consolidate into one after inducing surface melting by rubbing them together. From then on, melting or freezing of ice and the young thermodynamics were closely linked. Melting of ice under pressure and refreezing when pressure is reduced was later named by John Tyndall (1820 - 1893) as regelation; it was unknown to James Forbes until mid-1850.

∗ Corresponding author: e-mail [email protected] This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modiﬁcations or adaptations are made. PAMM Proc. Appl. Math. Mech. 2020;20:1 e202000158. www.gamm-proceedings.com 1 of 2 · https://doi.org/10.1002/pamm.202000158 © 2021 The Authors Proceedings in Applied Mathematics & Mechanics published by Wiley-VCH GmbH 2 of 2 Section 24: History of ﬂuid mechanics

2 Tyndall’s criticism of Forbes’s work and the formation of parties In 1853, John Tyndall, just returned from Germany, started to work at the Royal Institution in London under the mentoship of Michael Faraday. First he tried to repeat former experiments of Forbes on musical rockers and found them to be completely wrong. From then on, in lectures and papers, Tyndall never missed an opportunity to make Forbes seem incompetent. The second attack on Forbes was in 1855, regarding a work on cleavage of clay which Tyndall called as ‘not proven’. Because of the similar structure of cracks in clay and of cracks or veins in glacier ice, encouraged by his friend the biologist Thomas Huxley, Tyndall started working on ice and glaciers. In the laboratory he observed the deformability of ice under pressure, crack formation, fracture and regelation. In addition, during a short visit to the Alps in 1856, which in subsequent years was followed by longer stays, he made his own impression of glaciers. This was enough for him to attack Forbes again in early 1857 and to completely put in question his viscous glacier theory [4]. A main issue of the attack was the term ‘viscous’ which never was clearly defined by Forbes. For Tyndall this term described the property of a fluid that could permanently be stretched under tension without fracture what was obviously not the case for glaciers. Contrary, he explained the ‘apparent quasi-viscous’ behavior through continuous cleavage and refreezing, i.e. through regelation. From today’s perspective, both properties, viscous flow, micro and macro-cracking combined with regelation contribute to the movement of a glacier, where viscous flow is clearly the dominating mechanism. At that time, however, the harsh attack did not lead to an objective scientific debate, but to a controversy between two parties, which was partly led by inexpert means and aroused public interest due to its heat. Forbes was a recognized scientist and his long established viscous glacier theory had many supporters as e.g. Stokes, Airy and Thomson. On the other hand, Tyndall’s arguments seemed to be in line with thermodynamics, and consequently found also many supporters. However, his own measurements on the Mer de Glace and other glaciers had not brought any substantially new findings, but rather confirmed those of Forbes.

a) b) c) Fig. 2: a) James David Forbes, b) John Tyndall, c) Louis Rendu

Now other aspects have gained the upper hand in the controversy. The Tyndall party implicitly accused Forbes of plagiarism because he did not adequately and correctly give credit to Rendu. This happened just at the time when Forbes was discussed as the most promising candidate for receiving the Royal Society’s Copley Medal in 1859 for his Viscous Glacier Theory. In this situation, the Royal Society decided not to award Forbes, but gave the medal to the German physicist Wilhelm Weber. Replies from Forbes were followed by further hidden allegations that led to the republication of some Forbes papers, which were supposed to prove the unsustainability of the attacks [2]. Another aspect was the visible opposition or competition between the English (London, Cambridge) and the Scottish party (Edinburgh, Glasgow). In a way, the Scottish scientists felt ignored or dominated by London. This became also apparent, among others, in the late appreciation of Scottish contributions to the development of thermodynamics. Despite a short peace period in 1867 on initiative of Thomson, the controversy ﬂared up again and again and continued even after Forbes’ death in 1868. In Tyndall’s popular book ‘The Forms of Water’, published in 1872, Rendu and Agassiz were recognized as the actual founders of glacier theory, whereas Forbes is only mentioned by the way. In return, P.G. Tait, in Forbes’ biography of 1873 gave credit for the discovery of glacial movement entirely to Forbes. In parallel, Tyndall’s account led 1874 to a counterstatement and to the English translation of Rendus Treatise by the son of Forbes. The different views of Tait and Tyndall erupted in a series of acrimonious letters to Nature until the editor stopped the unscientiﬁc dispute. It should be noted that Bishop Louis Rendu never commented on the heated debate and probably hardly took note of it.

Acknowledgements Open access funding enabled and organized by Projekt DEAL.

References [1] K. Hutter and D. Gross, A Historical Tour of Glacier Ice on Earth and its Role in Climate Dynamics, J. Earth Env. Sci. 7, 174, 2019. [2] J.S. Rowlinson, The Theory of Glaciers, Notes and Records of the Royal Society of London, 26, 189-202, 1971. [3] J.D. Forbes, An attempt to Explain the leading Phenomena of Glaciers, Edinburgh New Phil. J., 35, 221-252, 1843. [4] J. Tyndall and T.H. Huxley, On the Structure and Motion of Glaciers, Phil. Trans. R. Soc. Lond., 147, 327-346, 1857.