Figure 61: Pierre Duhem on the model craze of the English school

 

 

Pierre Duhem: L’Ecole anglaise et les Théories physiques. Revue des Questions Scientifiques 34, October 1893, 345-378;
engl.: The English School and Physical Theories: On a Recent Book by W. Thomson. In Pierre Duhem: Essays in History and Philosophy of Science. Translated and Edited, with introduction, by Roger Ariew and Peter Barker. Indianapolis: Hackett 1996, 50-74.

 

Additions in brackets [] by Roger Ariew and Peter Barker

 

pp. 52-55

 

I

 

If one examines with care the most salient features of English physics, which distinguish it most clearly from French or German science, one soon recognizes that all these features flow from a very deep, very pronounced aspect of the English mind, an aspect that relates some features to others and at the same time explains them.

 

To a degree one encounters in no other people of Europe, the English possess an imaginative faculty which permits them to represent to themselves a very complex set of concrete things, seeing each in its place, with its motion and its life. On reading a typical English novelist - Dickens, for example - who has not been struck by the abundance and minuteness of the details that overload the least description? To begin with, French readers feel their curiosity piqued by the vivid depiction of each object. But they are unable to see the whole, and the futile effort that they make to reconstruct the innumerable fragments of the picture, scattered before their eyes, soon causes a tiredness that often repels them. The English, however, see the arrangement of all these things without difficulty. Without difficulty their imagination puts each one back in its place, grasps the link that unites them, and finds charming what we find tiring.

 

This extraordinary power, this abnormal development of the faculty of imagining concrete objects, has its counterpart. Among the English, the faculty of creating abstract concepts, of analyzing them, of relating them by rigorously constructed arguments, seems not to have the strength or the sharpness that the same faculty acquires among Germanic peoples and in our Latin races. English philosophers are almost wholly concerned with applications of philosophy: psychology, ethics, social science. They have little liking for more abstract research and do it poorly. They proceed less by abstract argument than by the accumulation of examples. Instead of connecting deductions, they accumulate facts. Darwin and Spencer do not engage in the learned fencing of discussion with their adversaries; they crush them by stoning them.

This extraordinary power to visualize the concrete, an extreme weakness in grasping the abstract, appears to be the distinguishing feature of the English intellect. It excels at combining things and at creating [fictional] people. It can make the former move and the latter live. But it seems to be unable to give birth to an idea and to develop it. Such appears to be the genius that produced [a] Shakespeare but did not produce a metaphysician.

We wíll find these two essential traits, these two distinctive marks, again and again while analyzing the form in which the English school has conceived physics.

 

 

II

 

In treatises on physics published in England, one continually finds an element that astonishes French students to a high degree. This element, which almost invariably accompanies the presentation of a theory, is what British scientists call a model. Nothing more aptly captures the fashion, so different from our own, in which the English mind proceeds in the construction of science than this use of models.

 

Two electrified bodies are in evidence. French or German physicists, whether they are called Poisson or Gauss, conceive that, in the space outside these bodies, one places that abstraction called a material point, accompanied by that other abstraction called an electric charge. They then give formulae which permit the determination of the magnitude and direction of the force on this material point when placed at a given geometrical point in the space. Considered at the point in space, the direction of this force touches a certain line: the line of force. They demonstrate that the lines of force end at right angles to the surfaces of electrified conductors. They determine the force exerted on each element of such a surface.

This entire theory of electrostatics, formulated in the clear language of analysis and geometry, constitutes a set of ideas and abstract propositions related to one another by rigorous logical rules. This set fully satisfies the intellect of a French or German physicist.

Things go differently for the English. These abstract notions of potential function, equipotential surfaces, and trajectories at right angles to these surfaces fail to satisfy their need to imagine objects that are material, visible, and tangible. "But so long as we adhere to this mode of expression we cannot form a complete mental picture of the actually occurring operations." [1] It is to satisfy this need that they will create a model.

 

There, where the French or German physicist conceives a family of lines of force, they are going to imagine a bundle of elastic wires. These are stuck by their two extremities to various points on conducting surfaces and stretched; they seek at the same time to shorten themselves and to fatten themselves, to diminish in length and to increase in cross section. When two electrified bodies approach each other [the English] see them drawn together by these wires. Such is the celebrated model of electrostatic actions imagined by Faraday and admired as a work of genius by Maxwell and the entire English school.

The use of similar mechanical models, recalling the essential features of the theory they are trying to present through certain more or less crude analogies, is constant in English treatises on physics. Some, like Maxwell's electrical treatise, make only moderate use of them. Others, on the contrary, make a continuous appeal to these mechanical representations. Here is a book [2] intended to present modern theories of electricity and to outline a new theory. Here there is nothing but ropes running over pulleys, wrapping around drums, running across beads and carrying weights, tubes pumping water, others swelling and contracting themselves, cog-wheels engaging each other and forming pinions for racks.

 

It is far from the case that these models help French readers to understand a theory; on the contrary, in many cases the French must make a serious effort to understand the functioning of the apparatus that the author has described, which is sometimes very complicated. This effort is often much greater than that required to understand the abstract theory, which the model claims to embody in its pure form.

Yet the English find the use of a model so necessary for the study of physics that, for them, designing the model is mistaken for understanding the theory itself. It is amusing to see this confusion formally accepted by the very person who ís the highest expression of English genius today, W. Thomson [3].

 

It seems to me, he says, that the test of "Do we or not understand a particular subject in physics?" is, "Can we make a mechanical model of it?" I have an immense admiration for Maxwell's model of electromagnetic induction. He makes a model that does all the wonderful things that electricity does in inducing currents, etc., and there can be no doubt that a mechanical model of that kind is immensely instructive and is a step towards a definite mechanical theory of electromagnetism....

I never satisfy myself until I can make a mechanical model of a thing. If I can make a mechanical model I can understand it. As long as I cannot make a mechanical model all the way through, I cannot understand, and that is why I cannot get the electromagnetic theory. I firmly believe in an electromagnetic theory of light, and that when we understand electricity, magnetism and light, we shall see them all together as part of a whole. But I want to understand light as well as I can without introducing things that we understand even less of. This is why I address myself to pure dynamics. [4]

 

 

III

 

For physicists of the English school, understanding a physical phenomenon is the same thing as constructing a model that imitates the phenomenon. Consequently, understanding the nature of material things will be the same thing as imagining a mechanism that will represent or simulate the properties of bodies by its action. The English school has thus acceded entirely to purely mechanical explanations of physical phenomena.

This is not, to be sure, a characteristic that suffices to distinguish English doctrines from scientific traditions that flourish in other countries. Mechanical theories have resulted from French genius, the genius of Descartes. They have long reigned without dispute in France as in Germany. What distinguishes the English school is not the attempt to reduce matter to mechanism, it is the particular form of its attempts to reach this goal.

 

 

[1] Lodge, op. cit., p. 16 [Modern Views of Electricity (3rd ed., London: McMillan, 1907), art. 12].

 

[2] Lodge, op. cit.

 

[3] [Notes of Lectures on Molecular Dynamics and the Wave Theory of Light. Delivered at The Johns Hopkins University, Baltimore, by Sir William Thomson, Professor in the University of Glasgow. Stenographically Reported by A. S. Hathaway, Lately Fellow in Mathematics of The Johns Hopkins University. Baltimore: Johns Hopkíns, 1884. (Reproduced by the "papyrograph" process.) The passages quoted are from, respectively, p. 132 and pp. 270-271.]

 

[4] Pp. 270-271, emphasis added by Duhem. [The last sentence is a translation of Duhem's French. The English text (Thomson, Molecular Dynamics and the Wave Theory of Light, p. 271) reads, "That is why I take plain dynamics." Continuing, "I can get a model in plain dynamics, I cannot in electromagnetics." "Plain dynamics" here means dynamics limited to the fundamental concepts and relations of Newtonian mechanics, and not augmented by additional concepts or relations from electricity, magnetism, and so forth. Understood in this way, Duhem's translation of the final sentence makes good sense and provides a better ending.]

 

Note by Roland Müller:

It would have been fair if the editors of Duhem’s text of 1893 had pointed to the fact that in the years 1901-03 William Thomson (Lord Kelvin) had totally rewritten the lectures Nr. 16-20. Therefore the hardcover edition of the „Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light“ were published in 1904 without the sentences quoted above.