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Posts Tagged ‘Newton’

Understanding Newton’s Experiments as Instances of Special Power

Monday, March 17th, 2014 | No Comments

Kirsten Walsh writes…

In my last few posts, I have been discussing the nature of observations and experiments in Newton’s Opticks.  In my first post on this topic, I argued that Newton’s distinction between observation and experiment turns on their function.  That is, the experiments introduced in book 1 offered individual, and crucial, support for particular propositions, whereas the observations introduced in books 2 and 3 only supported propositions collectively.  In my next post, I discussed the observations in more detail, arguing that they resemble Bacon’s ‘experientia literata’, the method by which natural histories were supposed to be generated.  At the end of that post, I suggested that, in contrast to the observations, Newton’s experiments look like Bacon’s ‘instances of special power’, which are particularly illuminating cases introduced to provide support for specific propositions.  Today I’ll develop this idea.

Note, before we continue, that there are two issues here that can be treated independently of one another.  One is establishing the extent of Bacon’s historical influence on Newton; the other is establishing the extent to which Bacon’s methodology can illuminate Newton’s.  In this post I am doing the latter – using Bacon’s view only as an interpretive tool.

Identifying ‘instances of special power’ (ISPs) was an important step in the construction of a Baconian natural history.  ISPs were experiments, procedures, and instruments that were held to be particularly informative or illuminative.  These served a variety of purposes.  Some functioned as ‘core experiments’, introduced at the very beginning of a natural history, and serving as the basis for further experiments.  Others played a role later in the process.  They included experiments that were supposed to be especially representative of a certain class of experiments, tools and experimental procedures that provided interesting shortcuts in the investigation, and model examples that came very close to providing theoretical generalisations.  In some cases, a collection of ISPs constituted a natural history.

The following features were typical of ISPs.  Firstly, they were considered to be particularly illuminating experiments, procedures or tools.  For example, a crucial instance, or a particularly clear or informative experiment, or experimental procedure.  Secondly, they were supposed to be replicated.  On Bacon’s view, replication was not merely an exercise for verifying evidence; it was an exercise for the mind, ensuring that one had truly grasped the phenomenon.  Thirdly, they were versatile, in that they could be used in several different ways.  As we shall see, the experiments of book 1 display these essential features.

In book 1 of the Opticks, Newton employed a method of ‘proof by experiments’ to support his propositions.  Each experiment was introduced to reveal a specific property of light, which in turn proved a particular proposition.  We know that Newton conducted many experiments in his optical investigations, so why did he present the experiments as he did, when he did?  When we consider Newton’s experiments alongside Bacon’s instances of special power, common features start to emerge.

Firstly, for each proposition he asserted, Newton introduced a small selection of experiments in support – those that he considered to be particularly illuminating or, in his own words, “necessary to the Argument”.  Unlike in his first paper, in the Opticks, Newton did not label any experiments experimentum crucis.  But his use of terms such as ‘necessary’ and ‘proof’ make it clear that these experiments were supposed to provide strong support: just like ISPs.

Secondly, Newton usually provided more than one experiment to support each proposition.  These were listed in order of increasing complexity and were carefully described and illustrated.  That Newton took this approach, as opposed to just reporting on their results, suggests that these experiments were supposed to be an exercise for the reader: they were about more than just proof or confirmation of the proposition.  The reader was supposed either to be able to replicate the experiment, or at least to understand its replicability.  Starting with the simplest experiment, Newton led his reader by the hand through the relevant properties of light, to ensure that they were properly grasped.  Like Bacon’s ISPs, then, Newton’s experiments were intended to be replicated.

Thirdly, Newton’s experiments were recycled in a variety of roles in the Opticks.  For example, the experiments he used to support proposition 2 part II were experiments 12 and 14 from part I.  Newton introduced and developed these experiments in several different contexts to illuminate and support different propositions.  Again, this is typical of Bacon’s ISPs.

And so, Newton’s experiments in the Opticks play a role analogous to Bacon’s instances of special power, and thinking of them as such explains why they are presented as they are.  They are particularly illuminating cases that are introduced to provide support for specific propositions.  Newton selected the experiments which best functioned as ISPs for inclusion in the Opticks.  Moreover, seen in this light, the seemingly disparate set of experiments start to look like a far more cohesive collection, or a natural history.

Many commentators have emphasised the ways that Newton deviated from Baconian method.  Through this sequence of posts, I have argued that the Opticks provides a striking example of conformity to the Baconian method of natural history.

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Workshop: Mathematics and methodology from Newton to Euler

Monday, March 3rd, 2014 | No Comments

University of Sydney

20 March, 2014

9:15-5:30

 

Program:

  • 9.15 Katherine Dunlop (Texas): ‘Christian Wolff on Newtonianism and Exact Science’
  • 10.45 Coffee
  • 11.00 Peter Anstey (Sydney): ‘From scientific syllogisms to mathematical certainty’
  • 12.30 Lunch
  • 2.00 Kirsten Walsh (Otago): ‘Newton’s method’
  • 3.30 Stephen Gaukroger (Sydney):  ‘D’Alembert, Euler and mid-18th century rational mechanics: what mechanics does not tell us about the world’
  • 5.00 Wind up

 

Location: Common Room 822, Level 8, Brennan MacCallum Building

Contact:    Prof Peter Anstey

Phone:       61 2 9351 2477

Email:       peter.anstey@sydney.edu.au

RSVP:      Here

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Observation and Experiment in the Opticks: A Baconian Interpretation

Monday, January 20th, 2014 | No Comments

Kirsten Walsh writes…

In a recent post, I considered Newton’s use of observation and experiment in the Opticks.  I suggested that there is a functional (rather than semantic) difference between Newton’s ‘experiments’ and ‘observations’.  Although both observations and experiments were reports of observations involving intervention on target systems and manipulation of independent variables, experiments offered individual, and crucial, support for particular propositions, whereas observations only supported propositions collectively.

At the end of the post, I suggested that, if we view them as complex, open ended series’ of experiments, the observations of books 2 and 3 look a lot like what Bacon called ‘experientia literata’, the method by which natural histories were supposed to be generated.  In this post, I’ll discuss this suggestion in more detail, following Dana Jalobeanu’s recent work on Bacon’s Latin natural histories and the art of ‘experientia literata’.

The ‘Latin natural histories’ were Bacon’s works of natural history, as opposed to his works about natural history.  A notable feature of Bacon’s Latin natural histories is that they were produced from relatively few ‘core experiments’.  By varying these core experiments, Bacon generated new cases, observations and facts.  The method by which this generation occurs is called the art of ‘experientia literata’.   Experientia literata (often referred to as ‘learned experience’) was a late addition to Bacon’s program, developed in De Augmentis scientiarum (1623).  It is a tool or technique for guiding the intellect.  By following this method, discoveries will be made, not by chance, but by moving from one experiment to the next in a guided, systematic way.

The following features were typical of the experientia literata:

  1. The series of observations was built around a few core experiments;
  2. New observations were generated by the systematic variation of experimental parameters;
  3. The variation could continue indefinitely, so the observation sequence was open-ended;
  4. The experimental process itself could reveal things about the phenomena, beyond what was revealed by a collection of facts;
  5. The trajectory of the experimental series was towards increasingly general facts about the phenomena; and
  6. The results of the observations were collated and presented as tables.  These constituted the ‘experimental facts’ to be explained.

Now let’s turn to Newton’s observations.  For the sake of brevity, my discussion will focus on the observations in book 2 part I of the Opticks, but most of these features are also found in the observations of book 2 part IV, and in book 3 part I.

Figure 1 (Opticks, book 2 part I)

The Opticks book 2 concerned the phenomenon now known as ‘Newton’s Rings’: the coloured rings produced by a thin film of air or water compressed between two glasses.  Part I consisted of twenty-four observations.  Observation 1 was relatively simple: Newton pressed together two prisms, and noticed that, at the point where the two prisms touched, there was a transparent spot.  The next couple of observations were variations on that first one: Newton rotated the prisms and noticed that coloured rings became visible when the incident rays hit the prisms at a particular angle.  Newton progressed, step-by-step, from prisms to convex lenses, and then to bubbles and thin plates of glass.  He varied the amount, colour and angle of the incident light, and the angle of observation.  The result was a detailed, but open ended, survey of the phenomena.  Part II consisted of tables that contained the results of part I.  These constituted the experimental facts to be explained in propositions in part III.  In part IV, Newton described a new set of observations, which built on the discussions of propositions from part III.

When we consider Newton’s observations alongside Bacon’s experientia literata, we notice some common features.

Firstly, the series of observations was built around the core experiment involving pressing together two prisms to observe the rings that appeared.

Secondly, new observations were generated by the variation of experimental parameters: i.e. new observations were generated, first by varying the obliquity of the incident rays, then by varying the glass instruments, then by varying the colour of the incident light, and so on.

Thirdly, the sequence of observations was open-ended.  Newton could have extended the sequence by varying the medium, or some other experimental parameter.  Moreover, at the end of the sequence, Newton noted further variations to be carried out by others, which might yield new or more precise observations.

Fourthly, the experimental process itself revealed things about the phenomenon, beyond what was revealed by a collection of facts.  For example, in observation 1, Newton noticed that increasing the pressure on the two prisms produced a transparent spot.  The process of varying the pressure, and hence the thickness of the film of air between the two prisms, suggested to Newton a way of learning more about the phenomenon of thin plates.  He realised he could quantify the phenomenon by introducing regularly curved object glasses, which would make the variation in thickness regular, and hence, calculable.

Fifthly, the trajectory of the experimental series was towards increasingly general facts about the phenomenon.  Newton began by simply counting the number of rings and describing the sequence of colours under specific experimental parameters.  But eventually he showed that the number of rings and their colours was a function of the thickness and density of the film.  Thus, he was able to give a much broader account of the phenomenon.

Finally, these general results were collated and presented as tables in part II.  Thus, the tables in part II constituted the facts to be explained by propositions in part III.

Many commentators have emphasised the ways that Newton deviated from Baconian method.  However, when viewed in this light, book 2 of the Opticks provides a striking example of conformity to the Baconian method of natural history: Newton led the reader from observations in part I, to tables of facts in part II, to propositions in part III.  Moreover, it ended with a further series of observations in part IV, emphasising the open-endedness of the art of experientia literata.

In contrast to the observations in book 2, Newton’s experiments in book 1 look like Bacon’s ‘instances of special power’, which are particularly illuminating cases introduced to provide support for specific propositions.  I’ll discuss this next time.  For now, I’d like to hear what our readers think of my Baconian interpretation of Newton’s observations.

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Observation, experiment and intervention in Newton’s Opticks

Monday, November 11th, 2013 | No Comments

Kirsten Walsh writes…

In my last post, my analysis of the phenomena in Principia revealed a continuity in Newton’s methodology.  I said:

    In the Opticks, Newton isolated his explanatory targets by making observations under controlled, experimental conditions.  In Principia, Newton isolated his explanatory targets mathematically: from astronomical data, he calculated the motions of bodies with respect to a central focus.  Viewed in this way, Newton’s phenomena and experiments are different ways of achieving the same thing: isolating explananda.

In this post, I’ll have a closer look at Newton’s method of isolating explananda in the Opticks.  It looks like Newton made a distinction between experiment and observation: book 1, contained ‘experiments’, but books 2 and 3, contained ‘observations’.  I’ll argue that the distinction in operation here was not the standard one, which turns on level of intervention.

In current philosophy of science, the distinction between experiment and observation concerns the level of intervention involved.  In scientific investigation, intervention has two related functions: isolating a target system, and creating novel scenarios.  On this view, experiment involves intervention on a target system, and manipulation of independent variables.  In contrast, the term ‘observation’ is usually applied to any empirical investigation that does not involve intervention or manipulation.  This distinction is fuzzy at best: usually level of intervention is seen as a continuum, with observation nearer to one end and experiment nearer to the other.

If Newton was working with this sort of distinction, then we should find that the experiments in book 1 involve a higher level of intervention than the observations in books 2 and 3.  That is, in contrast to the experiments in book 1, the observations should involve fewer prisms, lenses, isolated light rays, and artificially created scenarios.  However, this is not what we find.  Instead we find that, in every book of the Opticks, Newton employed instruments to create novel scenarios that allowed him to isolate and identify certain properties of light.  It is difficult to quantify the level of intervention involved, but it seems safe to conclude that Newton’s use of the terms ‘observation’ and ‘experiment’ doesn’t reflect this distinction.

To understand what kind of distinction Newton was making, we need to look at the experiments and observations more closely.  In Opticks book 1, Newton employed a method of ‘proof by experiments’ to support his propositions.  Each experiment was designed to reveal a specific property of light.  Consider for example, proposition 1, part I: Lights which differ in Colour, differ also in Degrees of Refrangibility.  Newton provided two experiments to support this proposition.  These experiments involved the use of prisms, lenses, candles, and red and blue coloured paper.  From these experiments, Newton concluded that blue light refracts to a greater degree than red light, and hence that blue light is more refrangible than red light.

Opticks, part I, figure 12.

In the scholium that followed, Newton pointed out that the red and blue light in these experiments was not strictly homogeneous.  Rather, both colours were, to some extent, heterogeneous mixtures of different colours.  So it’s not the case, when conducting these experiments, that all the blue light was more refrangible than all the red light.  And yet, these experiments demonstrate a general effect.  This highlights the fact that, in book 1, Newton was describing ideal experiments in which the target system had been perfectly isolated.

Book 2 concerned the phenomenon now known as ‘Newton’s Rings’: the coloured rings produced by a thin film of air or water compressed between two glasses.  It had a different structure to book 1: Newton listed twenty-four observations in part I, then compiled the results in part II, explained them in propositions in part III, and described a new set of observations in part IV.  The observations in parts I and IV explored the phenomena of coloured rings in a sequence of increasingly sophisticated experiments.

Consider, for example, the observations in part I.  Observation 1 was relatively simple: Newton pressed together two prisms, and noticed that, at the point where the two prisms touched, there was a transparent spot.  The next couple of observations were variations on that first one: Newton rotated the prisms and noticed that coloured rings became visible when the incident rays hit the prisms at a particular angle.  But Newton steadily progressed, step-by-step, from prisms to convex lenses, and then to bubbles and thin plates of glass.  He varied the amount, colour and angle of the incident light, and the angle of observation.  The result was a detailed, but open ended, survey of the phenomena.

I have argued that Newton’s experiments and observations cannot be differentiated on the basis of intervention, but there are two other differences worth noting.  Firstly, whereas the experiments described in book 1 were ideal experiments, involving perfectly isolated explanatory targets, the observations in books 2 and 3 were not ideal.  Rather, through a complex sequence of observations, as the level of sophistication increased, the explanatory target was increasingly well isolated.  When viewed in this way, the phenomena of Principia seem to have more in common with the experiments of book 1 than the observations of books 2 and 3.

Secondly, the experiments of book 1 were employed to support particular propositions, and so, individually, they were held to be particularly relevant and informative.  In contrast, the observations of books 2 and 3 were only collectively relevant and informative.  Moreover, the sequence of observations was open ended: there were always more variations one could try.

What are we to make of these differences between observation and experiment in the Opticks?  I have previously argued that, while Newton never constructed Baconian natural histories, his work contained other features of the Baconian experimental philosophy, such as experiments, queries and an anti-hypothetical stance.  However, in viewing them as complex, open ended series’ of experiments, I now suggest that the observations of books 2 and 3 look a lot like what Bacon called experientia literata, the method by which natural histories are generated.  I’ll discuss this in my next post, but in the mean time, I’d like to hear what our readers think.

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Roger Cotes’ ‘Preface’ and the ESD

Monday, September 16th, 2013 | No Comments

Peter Anstey writes…

One of the main tasks of this blog over the last three years has been to provide evidence for our claim that from the 1660s the distinction between experimental and speculative philosophy is crucial for an understanding of early modern natural philosophy and even the philosophy of this period in general. More specifically, we have been furnishing evidence that the self-styled experimental philosophers both emphasized the importance of experiment and observation for the acquisition of knowledge, and decried the use of speculation and hypotheses that made little or no appeal to observation. We have also claimed that a prime example of a speculative philosophy that came under attack from experimental philosophers was the Cartesian vortex theory.

It may be surprising, therefore, that hitherto little has been said on this blog about Roger Cotes’ Preface to the second edition of Newton’s Principia published 300 years ago in 1713. For, Cotes’ Preface contains one of the most forthright and sustained defenses of experimental philosophy to be found in the early eighteenth century and it prefaces what can only be described as the most important contribution to natural philosophy in the early modern period.

Cotes begins his Preface with a tripartite distinction between ‘the whole of the Scholastic doctrine derived from Aristotle and the Peripatetics’, (The Principia, 1999, 385) ‘those who take the foundation of their speculations from hypotheses’ and ‘those whose natural philosophy is based upon experiment’. Needless to say, it is this latter method that is ‘incomparably [the] best way of philosophizing’ and ‘which our most celebrated author [Newton] thought should be justly embraced in preference to all others’. (386) The rest of the Preface is a justification of this method of experimental philosophy. First, he elaborates on the method in more detail. He then proceeds to show how Newton’s thesis of universal gravity was established according to this method. Next, he argues against the Cartesian vortex theory and plenist accounts of the universe and, finally, he brings it to a close claiming: ‘Therefore honest and fair judges will approve the best method of natural philosophy, which is based on experiments and observations’. (398).

In this post I shall outline one of the interesting features of Cotes’ critique of the Cartesian vortex theory. In my next post I’ll examine his view of the experimental philosophy in more detail. According to Cotes the speculators ‘are drifting off into dreams, … are merely putting together a romance, elegant perhaps and charming, but nevertheless a romance’ (386) One such romance is the Cartesian vortex theory.

Cometary motion through the vortices of Descartes

Cometary motion through the vortices of Descartes

In the first edition of the Principia (1687) Newton had advanced a number of arguments against the vortex theory at the end of Book Two, such as the claim that planets moving in a vortex would speed up at the point most distant from the sun when, in fact, the observational evidence and Kepler’s area law showed that they slowed down at this point. But apart from this, little mention is made of the theory. By contrast, in the second edition of the Principia the critique of the vortex theory is a prominent theme. In addition to the arguments at the end of Book Two, the new ‘General Scholium’ appended to the book begins ‘The hypothesis of vortices is beset with many difficulties’ (939) and there follows a whole paragraph on the problems with the theory. The final two sentences deal with the motion of comets, claiming that their regular motion ‘cannot be explained by vortices and that their eccentric motions can only be explained if ‘vortices are eliminated’. These are not claims that Newton makes in the Principia but are rather summaries of arguments that Cotes presents in his Preface.

About one quarter of the Preface is given over to a critique of vortices. In this section, Cotes develops the arguments from cometary motion that are alluded to in Newton’s Scholium. First he claims that bodies in a vortex must move in the same direction and with the same velocity as the surrounding fluid and must have the same density as the fluid that surrounds them. But comets and planets orbit the sun with different velocities and different directions even when they are in the same region of the heavens. Therefore, ‘those parts of the celestial fluid that are at the same distances from the sun revolve in the same time in different directions with different velocities’. But this cannot be accounted for by one vortex, so there will have to be more than one vortex ‘going through the same space surrounding the sun’. It must be asked then ‘how these same vortices keep their integrity without being in the least perturbed through so many centuries by the interactions of their matter’. (394 ) Moreover, because ‘the number of comets is huge’ and they obey the same laws as the planets going ‘everywhere into all parts of the heavens and pass very freely through the regions of the planets, often contrary to the order of the signs … [t]here will be no room at all for the motions of the comets unless that imaginary matter [of the vortices] is completely removed from the heavens’. (395)

What is striking about these arguments is that they are, in effect, the bookends of the Principia. They don’t appear in the body of the work, but are a kind of polemical after thought, and most importantly, they are set within the context of a defense of experimental philosophy. What is it that accounts for the extraordinary fact that Cotes introduced this material in the opening preface and that Newton should allude to it at the end when the arguments are absent from the book? This is not merely a rhetorical question. I would value any comments you may have.

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Newton’s ‘Phenomena’ continued…

Monday, September 2nd, 2013 | 1 Comment

Kirsten Walsh writes…

In my last post, I considered the phenomena in book 3 of Newton’s Principia.  Newton’s decision to label these propositions ‘phenomena’ is puzzling, as they do not seem to fit any standard definition of the term.  In this post, I’ll consider Bogen & Woodward’s (1988) distinction between data, phenomena and theories, and suggest that it sheds light both on Newton’s use of ‘phenomena’ and on the connection between his methodology in Opticks and Principia.

Bogen & Woodward (B&W) have argued for a 3-level picture of scientific theories in which:

  1. ‘Data’ are records produced by measurement and experiment that serve as evidence or features of phenomena.  E.g. bubble chamber photographs, and patterns of discharge in electronic particle detectors.
  2. ‘Phenomena’ are features of the world that in principle could recur under different contexts or conditions.  E.g. weak neutral currents, and the decay of a proton.
  3. ‘Theories’ are explanations of the phenomena.

B&W argue that theories explain phenomena, but not data.  Data usually reflect many causal influences besides the explanatory target, while phenomena typically reflect single, or small, manageable numbers of causal influences.  For example, General Relativity explains the phenomenon of bending light, but doesn’t explain the workings of the cameras, optical telescopes, etc. that causally influence the data.

Can we characterise Newton’s phenomena in terms of these three levels of theory?  Let’s consider 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.”

In his discussion of this phenomenon Newton explained, “This is established from astronomical observations.”  He provided the following table:

These observations are not data in the ‘pure’ sense that B&W discuss.  Rather, they are generalisations: average distances and calculated periods of orbit.  Moreover, the bottom row contains the average distances calculated from the period and the Harmonic rule (that the periods are as the 3/2 power of the semidiameters of their orbits).  These calculations illustrate the ‘fit’ between the expected distance and the observed distance.  Nevertheless, they provide a good example of how we might get from a set of data to a phenomenon.  So perhaps we can think of them as ‘data’ in a methodological sense: they are records from which phenomenal patterns can be drawn.

I have another reason for considering these calculations ‘data’ in B&W’s sense of the term.  In his discussion of phenomenon 1, Newton indicated that these calculations reflect a number of causal influences besides gravity.  For instance, he explained that the length of the telescope affected the measurement of Jupiter’s diameter, because

    “the light of Jupiter is somewhat dilated by its nonuniform refrangibility, and this dilation has a smaller ratio to the diameter of Jupiter in longer and more perfect telescopes than in shorter and less perfect ones.”

This is a nice illustration of B&W’s notion of the shift from data to phenomena.  By attending to his theory about telescopes, Newton was able to manipulate the data to control for distortion.

Now let’s consider the role of phenomenon 1 in Principia.  Phenomenon 1 is employed (in conjunction with proposition 2 or 3, book 1, and corollary 6 to proposition 4, book 1) to support proposition 1, theorem 1, book 3:

    “The forces by which the circumjovial planets are continually drawn away from rectilinear motions and are maintained in their respective orbits are directed to the centre of Jupiter and are inversely as the squares of the distances of their places from that centre.”

This theorem doesn’t contain any information about the sizes or positions of the satellites of Jupiter, or about the workings of telescopes.  So, while it explains the phenomenon, it gives no direct explanation of the data.  This suggests that, in the Principia, data and phenomena are methodologically distinct.

B&W’s distinction between ‘data’ and ‘phenomena’ reveals two methodological features of Newton’s phenomena:

Firstly, Newton’s phenomena are explananda, but not appearances.  Traditionally, ‘phenomenon’ seems to have been synonymous with both ‘appearance’ and ‘explanandum’.  For example, the ancient Greeks were concerned to construct a system that explained and preserved the motions of the celestial bodies as they appeared to terrestrial observers.  2000 years later, Galileo and Cardinal Bellarmine argued over which system, heliocentric or geocentric, provided a better fit and explanation of these appearances.  This suggests that, traditionally, there was no real difference between phenomena and data.  For Newton, however, these come apart.  The six phenomena of Principia describe the motions of celestial bodies, but not as they appear to terrestrial observers.  In this sense, they are not appearances, but they do require an explanation.

Secondly, this reveals a continuity in Newton’s methodology.  The point of Newton’s articulation of ‘phenomena’ in Principia is the same as his experiments in Opticks.  Both identify and isolate a pattern or regularity.  In the Opticks, Newton isolated his explanatory targets by making observations under controlled, experimental conditions.  In Principia, Newton isolated his explanatory targets mathematically: from astronomical data, he calculated the motions of bodies with respect to a central focus.  Viewed in this way, Newton’s phenomena and experiments are different ways of achieving the same thing: isolating explananda.

These considerations are admittedly speculative, so I’m keen to hear what our readers think.  Does this look like a good way of characterising Newton’s phenomena?

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Newton’s ‘Phenomena’

Monday, August 19th, 2013 | 4 Comments

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.

 

 

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Borrowed Terms and Innovative Concepts in Newton’s Natural Philosophy

Monday, June 10th, 2013 | 1 Comment

Kirsten Walsh writes…

In my last two posts, I have discussed my alterations to the 20 theses of our project.  In this post, I’ll continue to discuss thesis 8.

In 2011, I claimed that:

    8.  The development of Newton’s method from 1672 to 1687 appears to display a shift in emphasis from experiment to mathematics.

But at the start of this year, I replaced this thesis with a new thesis 8:

    8.  In his early work, Newton’s use of the terms ‘hypothesis’ and ‘query’ are Baconian.  However, as Newton’s distinctive methodology develops, these terms take on different meanings.

In my last post, I told you that I decided to remove my original thesis 8 because the methodological differences between Newton’s early papers and Principia aren’t as great as I initially thought.  This isn’t to say that I now think that the methodology of the 1672 paper is precisely the same as the methodology displayed in Principia.  Rather, I don’t think my original thesis 8 captures what is important about these differences.

In today’s post, I’ll tell you about my new thesis 8.

On this blog, we have argued that the early members of the Royal Society adopted the new experimental philosophy in a Baconian form.  Newton initially encountered the experimental philosophy in the early- to mid-1660s through his reading of Boyle, Hooke and the Philosophical Transactions.  While he never adopted the Baconian method of natural history, other features of his early methodology resemble the Baconian approach.  For example, in Newton’s 1672 paper and the debate that followed, his use of experiment and queries, and his anti-hypothetical stance, were recognised and accepted by the Baconian experimental philosophers.  Moreover, his 1675 paper, in which he explored his hypothesis of the nature of light, was recognised by his contemporaries as an acceptable use of a hypothesis.

In Newton’s later work, however, hypotheses and queries look quite different.

Firstly, consider Newton’s Opticks.  When the Opticks was published in 1704, it contained no hypotheses, and the introduction explicitly stated that:

    “My Design in this Book is not to explain the Properties of Light by Hypotheses, but to propose and prove them by Reason and Experiments.”

Book III ended with a series of queries, which provided directions for further research, in the style of Baconian queries.  E.g.:

    “Query 2. Do not the Rays which differ in Refrangibility differ also in Flexibility…?”

However, in the 1706 and 1718 editions, Newton introduced new queries, which explore the nature of light.  E.g.:

    “Qu. 29. Are not the Rays of Light very small Bodies emitted from shining Substances?”

Like the earlier queries, these ones set out a new research program.  But they are much more speculative than was acceptable according to the Baconian method.

Now consider Newton’s Principia.  There are hypotheses in every edition of Principia, but they look nothing like Newton’s 1675 hypothesis.  In particular, they do not explore the nature of things.  For example:

    “Hypothesis 1. The centre of the system of the world is at rest.”

I have argued that the hypotheses in Principia provide a specific supportive role to theories.  These propositions are temporarily assumed in order to draw out the observational consequences of Newton’s theory of gravitation.  They are simplifying assumptions; not assumptions about the nature of gravity.

Previously, I have argued that Newton’s methodology should be seen as a three-way epistemic distinction between theories, hypotheses and queries.  I call this an ‘epistemic triad’.  I claim that Newton took these, already familiar, terms and massaged them to fit his own three-way epistemic distinction.  It is important to recognise, therefore, that the triad is a three-way epistemic division, rather than the juxtaposition of three terms of reference.  The terms ‘theory’, ‘hypothesis’ and ‘query’ are simply labels for these epistemic categories.

In fact, this is a feature of many of Newton’s innovative concepts.  He borrowed familiar terms and massaged them to fit his own needs.  I have shown that he did this with his key methodological terms: ‘theory’, ‘hypothesis’ and ‘query’.  Steffen Ducheyne has argued that Newton did this in other aspects of his methodology, such as his dual-methods of analysis and synthesis.  This suggests that Newton’s labeling and naming of things was very much post hoc.  It seems that, when discussing Newton’s methodology, we should emphasize divisions and functions over definitions.

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Newton on Experiment and Mathematics

Monday, April 15th, 2013 | 3 Comments

Kirsten Walsh writes…

In my last post, I discussed our 20 revised theses and why I altered thesis 5.  In this post, I’ll discuss why I replaced thesis 8.

In 2011, I claimed that:

    8.  The development of Newton’s method from 1672 to 1687 appears to display a shift in emphasis from experiment to mathematics.

But at the start of this year, I replaced this thesis with a new thesis 8:

    8.  In his early work, Newton’s use of the terms ‘hypothesis’ and ‘query’ are Baconian.  However, as Newton’s distinctive methodology develops, these terms take on different meanings.

Since my new thesis is a replacement of the original thesis, rather than a modification, two explanations are required.  So in today’s post, I’ll tell you why I decided to remove my original thesis 8, and in my next post, I’ll tell you about my new thesis 8.

I originally included thesis 8 because there are some obvious differences in the styles of Newton’s early work on optics and his Principia.  In Newton’s first paper on optics (1672), there is a strong emphasis on experiment.  Experiment drives his research and guides his rejection of various possible explanations of the phenomena under consideration.  Ultimately, he presents an Experimentum Crucis as proof for the certainty of his proposition that white light is heterogeneous.  In contrast, the Principia (1687) displays a strong emphasis on mathematics.  The full title of the work, the Author’s Preface to the Reader, and the fact that Book I opens with 11 lemmas outlining the mathematical framework of the work are just a few features that make it clear that Principia is primarily a mathematical treatise.

I now think that my original thesis 8 is misleading.

Firstly, as I have emphasised on this blog, Newton’s early work had a mathematical style that made it unique among his contemporaries.  While they recognised him as an experimental philosopher, his claims of obtaining certainty via geometrical proofs set him apart from the Baconian-experimental philosophers.  Moreover, his methodological statements show evidence of a tension between experiment and mathematical certainty.  For example, he says that the science of colours,

    “depend[s] as well on Physicall Principles as on Mathematicall Demonstrations: And the absolute certainty of a Science cannot exceed the certainty of its Principles.  Now the evidence by wch I asserted the Propositions of colours is in the next words expressed to be from Experiments & so but Physicall: Whence the Propositions themselves can be esteemed no more then Physicall Principles of a Science.”

Secondly, Newton continued to identify as an experimental philosopher until the end of his life.  For example, in the General Scholium at the end of Principia, he says:

    “and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy.”

This resembles Newton’s earlier emphasis on grounding propositions on empirical evidence, rather than on speculative conjectures.

Thirdly, in Principia, Newton appears to be negotiating a similar tension between experiment and mathematical certainty that we saw in his early work.  For example, in the Scholium to the Laws of Motion he asserts the certainty of his Laws, while at the same time, acknowledging their experimental basis:

    “The principles I have set forth are accepted by mathematicians and confirmed by experiments of many kinds.”

And:

    “By these examples [i.e. the experiments mentioned above] I wished only to show the wide range and the certainty of the third law of motion.”

From these three points, we can see that the methodological differences between Newton’s early papers and Principia aren’t as great as they first appear.  But I did not remove my original thesis 8 because I think that the methodology of the 1672 paper is precisely the same as the methodology displayed in Principia.  Rather, I don’t think my original thesis 8 captures what is important about these differences.

As I have explained here, my project is to distinguish between those features of Newton’s methodology that changed, and those that stayed the same.  Some aspects of Newton’s methodology developed over time.  For example, he came to value geometrical synthesis over algebraic analysis.  Other aspects of his methodology varied according to context.  For example, in Opticks, he employs ‘experiments’ and ‘observations’, but in Principia, he employs ‘phenomena’.  But this triumvirate of methodological ideas – experiment, mathematics and certainty – should be considered an enduring feature of Newton’s methodology.

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Teaching Experimental Philosophy III: the case of Francis Hauksbee the Elder

Monday, March 4th, 2013 | Comments Off

Peter Anstey writes …

In two previous posts I examined an early teacher of experimental philosophy, John Theophilus Desaguliers and a later one, George Adams. In this post I turn to a third teacher of experimental philosophy, Francis Hauksbee the Elder (1660–1713). (He was called ‘the Elder’ to differentiate him from his nephew of the same name who also taught experimental philosophy.) Hauksbee was one of the two most important first-generation pedagogues. (We will examine the other, John Keill, in my next post.)

He was a gifted instrument maker who not only developed a new much improved design of Robert Boyle’s air-pump, but also conducted a series of very important new experiments using this instrument. Many of these were published in the Philosophical Transactions. As a result of his proficiency with experimental apparatus he became a kind of de facto curator of experiments at the Royal Society in c. 1704 after Robert Hooke’s death. In addition he seconded James Hodgson FRS to carry out public lectures on experimental philosophy in London while he acted as the demonstrator.

By 1709 he himself was lecturing on experimental philosophy and continued this until his death in 1713. In 1709 he published a compilation volume of his air-pump experiments entitled Physico-Mechanical Experiments … touching Light and Electricity. This volume, in many ways, mimicked Boyle’s ground-breaking New Experiments Physico-mechanical touching the Spring of the Air (1660). (Even the titles are similar.) Hauksbee clearly saw himself as working in a tradition of experimental natural philosophy that extended back to Boyle.

The work gives us an interesting insight into how he viewed natural philosophy. He begins by telling us that:

The Learned World is now almost generally convinc’d, that instead of amusing themselves with Vain Hypotheses, which seem to differ little from Romances, there’s no other way of Improving Natural Philosophy, but by Demonstrations and Conclusions founded upon Experiments judiciously and accurately made. (Preface)

By now our readers should recognize the standard tropes of the experimental philosopher: the decrying of hypotheses; the likening of them to romances; the appeal to the necessity of experiment for the improving of natural philosophy.

Hauksbee goes on in the Preface to mention ‘The Honourable and most Excellent Mr. Boyle’ and ‘the … Incomparable Sir Isaac Newton’ implying that he himself is engaged in the same natural philosophical project. It is interesting to note, however, that there is no mention of the method of natural history as practised and promoted by Boyle in the Preface or in Hauksbee’s work. Hauksbee’s experimental practice was a natural extension of Boyle’s work, but at the same time methodologically discontinuous with it.

Hauksbee was also much quicker than Boyle to draw natural philosophical conclusions from his experiments. He did not, however, apply mathematics to his discoveries and he was later criticized by Desaguliers in his Course of Experimental Philosophy (1734) in so far as his experiments

were only shewn and explain’d as so many curious Phaenomena, and not made Use of as Mediums to prove a Series of philosophical Propositions in a mathematical Order, they laid no such Foundation for true Philosophy. (vol. 1, Preface)

Hauksbee may not have had developed views on the methodology of natural philosophy or much aptitude in mathematics, but he was a gifted experimenter and a keen promoter of experimental philosophy.

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