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Monthly Archives: August 2013

Newton’s ‘Phenomena’

Kirsten Walsh writes…

On this blog, I have often argued that Newton’s Principia should be characterised as a work of experimental philosophy (for example, here, here and here).  To support this argument, I have tended to emphasise similarities between Newton’s work in optics and mechanics.  Recently, however, I have noted that some aspects of Newton’s methodology varied according to context.  For example, in the Opticks, Newton employed ‘experiments’, but in the Principia, he employed ‘phenomena’.  Given that experimental philosophy emphasises observation- and experiment-based knowledge, it is important for my project that I understand Newton’s use of phenomena, and its relationship to observation.  In this post, I’ll discuss the phenomena in Principia, and in my next, I’ll discuss the relationship between phenomena and experiments in more detail.

Firstly, let’s consider the origin of the phenomena of Principia.  In the first edition of Principia (1687), book 3 contained nine hypotheses.  But in the second edition (1713), Newton re-structured book 3 so that it contained only two hypotheses.  Five of the old hypotheses were re-labelled ‘phenomena’, and he added one more (phenomenon 2), to bring the total to six:

Phenomenon 1: The circumjovial planets, by radii drawn to the centre of Jupiter, describe areas proportional to the times, and their periodic times – the fixed stars being at rest – are as the 3/2 powers of their distances from that centre.

Phenomenon 2: The circumsaturnian planets, by radii drawn to the centre of Saturn, describe areas proportional to the times, and their periodic times – the fixed stars being at rest – are as the 3/2 powers of their distances from that centre.

Phenomenon 3: The orbits of the five primary planets – Mercury, Venus, Mars, Jupiter, and Saturn – encircle the sun.

Phenomenon 4: The periodic times of the five primary planets and of either the sun about the earth or the earth about the sun – the fixed stars being at rest – are as the 3/2 powers of their mean distances from the sun.

Phenomenon 5: The primary planets, by radii drawn to the earth, describe areas in no way proportional to the times but, by radii drawn to the sun, traverse areas proportional to the times.

Phenomenon 6: The moon, by a radius drawn to the centre of the earth, describes areas proportional to the times.

There are several things to notice about these phenomena.  Firstly, they are distinct from data, in that they describe general patterns of motion, rather than measurements of the positions of planetary bodies at particular times.  So, while the phenomena are detected and supported by astronomical observations, they are not observed or perceived directly.

Secondly, they are distinct from noumena (or the nature or essence of things), in that they are facts inferred from the observable, measurable properties of the world.  They describe the motions, sizes and locations of bodies, but not the substance or causes of these properties of bodies.

Thirdly, they describe relative motions of bodies.  That is, in each case, the orbit is described around a fixed point.  For example, phenomenon 1 describes the motions of the satellites of Jupiter around Jupiter, which is taken as a stationary body for the purposes of this proposition.  In phenomena 4 and 5, the motion of Jupiter is described around the sun, which is taken as stationary.

Fourthly, these phenomena do not prioritise the observer.  Rather, each motion is described from the ideal standpoint of the centre of the relevant system: the satellites of Jupiter and Saturn are described from the standpoints of Jupiter and Saturn respectively, the primary planets are described from the standpoint of the sun, and the moon is described from the standpoint of the Earth.  And because Newton doesn’t prioritise the observer, effects such the phases and retrograde motions of the planets are not phenomena but only evidence of phenomena.

The re-labelling of these propositions as ‘phenomena’ is somewhat puzzling.  The term ‘phenomenon’ has a variety of uses, such as:*

  1. A particular (kind of) fact, occurrence, or change, which is perceived or observed, the cause or explanation of which is in question;
  2. An immediate object of sensation or perception (often as distinguished from a real thing or substance); or
  3. An exceptional or unaccountable thing, fact or occurrence.

But, as we’ve seen, Newton’s ‘phenomena’ don’t properly fit any of these definitions.  Can any reader shed light on what Newton really meant by the term?


* Definitions (a) and (c) feature in both C18th and C21st dictionaries, but in the C21st, definition (b) has become more prominent, particularly in philosophy.


UPDATE: I have written a follow-up post.



René Réaumur and Charles Dufay on Experimental Natural Philosophy

A guest post by Michael Bycroft, a PhD Student at Cambridge.

Michael Bycroft writes…

René Réaumur

In a recent post Peter Anstey asked: “When did the French embrace experimental philosophy?” In this post I want to do two things. One is to draw attention to two Frenchmen who practised experimental natural philosophy (ENP) well before Jean-Antoine Nollet began teaching this method in the mid-late 1730s. These men were René Réaumur and Charles Dufay. My other task is to try to explain why these men, who did so much to practice ENP, did so little to explicitly define or defend their practice.

René Réaumur (1683-1757) was arguably the most active and influential member of the Académie des Sciences in the first half of the eighteenth century. Nowadays he is known for his research on insects, steel-making, and thermometry, but his interests were truly encyclopaedic. Charles Dufay (1698-1739) is known to historians of physics as a student of electricity, but his research interests were nearly as broad as those of Réaumur, his patron and collaborator.

There is no doubt that these two men practiced ENP. It is true that they were Cartesians, in the sense that their chief theoretical resources were vortices and subtle fluids. But they wore their theory lightly, and they saw themselves primarily as experimenters rather than as system-builders. This pair was at least as committed to ENP, and in some cases more so, than their French colleague Nollet or their English counterparts Francis Hauksbee the Elder and John Desaguliers.

Yet it is hard to find clear, succinct, accessible endorsements of the key tenets of ENP in the writings of Dufay and Réaumur. Such endorsements do exist, but they are invariably buried in the middle of one or other of the many papers they published in the Académie’s journal, the Mémoires de l’Académie Royale des Sciences. Here is an example from one of Réaumur’s first papers, on the growth of shells, published in the 1709 volume of the Mémoires:

    But conjectures such as these [ie. the ones Réaumur had just advanced in the first part his paper] are not enough in true natural philosophy. Experiments performed on the matters at hand are the only sound basis for our reasoning…It is to experiments that I shall turn to decide whether I have correctly described the manner in which nature behaves, or whether [instead] everything I have said is merely a trick of the imagination.
    Mais de pareilles conjectures ne suffisent point en bonne Physique. Les seules expériences faites sur les choses dont il est question, y doivent servir de bases à nos raisonnemens. … C’est aux experiences que je vais rapporter à faire voir, si j’ai véritablement décrit la maniere dont la Nature agit, ou si l’on doit regarder tout ce qu’on vient d’avancer comme un simple jeu d’imagination.

Charles Dufay

This statement is clearly in the spirit of ENP, and similar statements can be found elsewhere in Réaumur’s papers, and in Dufay’s. But they are fleeting asides rather than stand-alone manifestos. Why were these men so reticent?

An important part of the answer is that the stand-alone manifestos of Nollet, Hauksbee and Desaguliers appear in the prefaces of their natural philosophy textbooks, and Dufay and Réaumur did not write textbooks. They did not need to. They were independently wealthy, drew sizeable pensions from the Academy, and were well-rewarded by the state for their research on French industries such as steel and textiles.

Perhaps it is also relevant that Bernard le Bovier de Fontenelle, the Perpetual Secretary of the Academy, did much to define and defend the Academy’s activities on behalf of its members.

Another factor may be that Dufay and Réaumur were more concerned to defend the application of natural philosophy to industry (against skeptical artisans and ministers) than they were to defend the application of experiment to natural philosophy (against speculative philosophers). At any rate, the former concern dominated the preface to Réaumur’s first book, L’art de convertir le fer en acier (1722).

Finally, as we have seen, Dufay and Réaumur dispensed methodological advice in the course of the papers they published in the Academy. Perhaps they considered this the best forum for expressing their views on ENP, even though this choice makes their views harder for the historian to identify than if they had written textbooks or dictionary entries instead.

This is not to say that Dufay and Réaumur had no connections with earlier and later textbook writers on ENP in France. On the contrary. They both learned much of their physics from Jacques Rohault’s Traité de physique, and in their turn they taught Nollet much of what he knew about experimentation (Nollet assisted both Dufay and Réaumur in their laboratories in the early 1730s). These connections reinforce the broader lesson of this post, which is that the leading practitioners of ENP were not always its most explicit promoters.