No Actual Measurement was required…


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I’ve just put a preprint of my article, ‘No actual measurement … was required: Maxwell and Cavendish’s null method for the inverse square law of electrostatics’ on the Arxiv. It has grown and developed from my conference presentation last year – with thanks for great comments and stimulating discussions with Daniel Mitchell and the referees. It’s been accepted (hooray!), but still some minor corrections before the final published version.

Experimentalists in Maxwell’s Cavendish


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I was very excited recently to discover that a colleague was descended from Charles Heycock, who more or less founded Materials Science in Cambridge. However, Heycock’s significance for me is that he entered, and published from, Maxwell’s Cavendish Laboratory aged 17 while still at school. He exemplifies Maxwell’s open door policy at the Cavendish (provided you were male).

This prompted me to post up an analysis of those we know were doing experimental work in Maxwell’s Cavendish, plotted against their year(s) pre or post graduation and their subject. The results are remarkable and show very clearly the impact of the Cambridge system on experimenter numbers.


On the chart, zero represents their graduation year. Thus, -1, -2… etc are undergraduates at one, two, … etc years before graduation. 1, 2, … etc are postgraduates at one, two, … etc years after graduation.

The majority of postgraduates were mathematicians. They were hanging around Cambridge seeking research topics that would earn them a College fellowship in a year or two’s time. There was no such incentive for Natural Science postgraduates. In 1870 the University Reporter commented that some colleges would consider themselves ‘guilty of extravagance’ in appointing scientific fellows.

Conversely, the undergraduates were mostly studying Natural Sciences. From 1874 on a practical exam in physics had been included in the Natural Sciences course, providing an incentive for students to take an interest in experimental physics – though it is important to note that the students included in the chart here were doing research not a practical physics course. No mathematicians are recorded as doing experimental work while undergraduates. Although physical subjects had been added into the Maths Tripos in 1873, students very rapidly realised that there was so much choice in the question paper that they had no need to study physics in order to do well. Nor did they need practical work. Physics was removed again in 1882 to the postgraduate Part III of the Maths Tripos.

Thus the chart echoes George Bettany’s lament to Nature in 1874,

‘The great hindrance to the success of the Cavendish Laboratory at present is the system fostered by the Mathematical Tripos. The men who would most naturally be the practical workers in the laboratory are compelled to refrain from practical work if they would gain the best possible place in the Tripos list. Very few have courage so far to peril their place or to resign their hopes as to spend any valuable portion of their time on practical work… For a man to do practical work in physics at Cambridge implies considerable exercise of courage and self-sacrifice.’

And what of Charles Heycock? He is the “non-Cambridge” undergraduate at <-4. He was 17 when he worked in the Cavendish with Arthur Clayden (an undergraduate) on the spectrum of indium. He didn’t enter the University for another year, and subsequently read Natural Sciences, graduating with a first class degree in chemistry and physics. He became a FRS and founder of Cambridge’s Department of Materials Science.

No actual measurement was required


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I’ve just put up a copy of my presentation on Cavendish, Maxwell, and the inverse square law of electrostatic repulsion, given at the Making of Measurement Conference in Cambridge last week.

This poses the question of what Maxwell and his student Donald MacAlister, get out of repeating Cavendish’s null experiment on the inverse square law.  The abstract read,

Traditionally, the foundation of the theory of electrostatics has been taken to be Coulomb’s 1785 torsion balance experiments, reified as “Coulomb’s Law”. However, Coulomb’s results, and interpretation, were frequently challenged, notably by Volta and Simon and, as late as 1836, by William Snow Harris.

In the first edition of the Treatise on Electricity and Magnetism (1873), Maxwell acknowledges Coulomb’s experiments as establishing the inverse square law, merely to dismiss them again as demonstrating it only to a rough approximation. Instead he cites the observation that a charged body, touched to the inside of a conducting vessel, transfers all its charge to the outside surface of the vessel, as ‘far more conclusive than any measurements of electrical forces can be’ (#74). This assertion was based on mathematical proof that an exact inverse square law was a necessary condition for electricity to rest in equilibrium on the surface of a conductor.

The following year Maxwell acquired the hitherto unpublished electrical researches of Henry Cavendish, and found that around 1771 Cavendish had conducted a (fairly) rigorous test of the mathematically predicted null result concluding that the negative exponent in the force law could not differ from 2 by more than about 1/50. Maxwell and a research student, Donald McAlister, created their own version of Cavendish’s experiment, achieving a claimed sensitivity of 1/21600. By the second edition of the Treatise (1881) his previous, ‘…far more conclusive than any measurements…’ has become ‘… a far more accurate verification of the law of force [than Coulomb’s]’ (#74). In his draft for the Cambridge Philosophical Society, Maxwell wrote, ‘Cavendish thus established the law of electrical repulsion by an experiment in which the thing to be observed was the absence of charge on an insulated conductor. No actual measurement of force was required. No better method of testing the accuracy of the received law of force has ever been devised’ (my emphasis).

 More recently, Dorling (1974) has explored the sense in which it was rational for Cavendish and Maxwell to generate an entire law from a single (null) data point, while Laymon (1994) has pointed out the circularity of Maxwell’s argument and located the actual measurement in the testing of the sensitivity of the electrometer.

 Taking Laymon’s and Dorling’s critiques on board, and drawing on works and papers by Maxwell, Kelvin, Tait and Harris, this paper will examine how Maxwell and his contemporaries understood what Cavendish had done, what they thought the null method achieved, and the value to them of recreating the experiment.


Dorling, Jon. ‘Henry Cavendish’s Deduction of the Electrostatic Inverse Square Law from the Result of a Single Experiment’. Studies in History and Philosophy of Science Part A 4, (1974): 327–48.

Laymon, Ronald. ‘Demonstrative Induction, Old and New Evidence and the Accuracy of the Electrostatic Inverse Square Law’. Synthese 99, (1994): 23–58.

Editing Cavendish: Maxwell and The Electrical Researches of Henry Cavendish


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I’ve recently put the preprint on the arXiv of my conference presentation last September, on Maxwell’s edition of The Electrical Researches of Henry Cavendish.

Although, probably, Maxwell’s least significant contribution to science, I argue that we can learn a lot about his attitudes and preoccupations during the last five years of his life from the way he tackled this task.

Is crowdsourcing good for us?


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Last week I was listening in on a fascinating conversation between a group of research mathematicians about Polymath.  Polymath is a community of massively collaborative online mathematical projects which is achieving impressive results and is widely cited as an exemplar of the benefits of crowd sourcing.

Yet despite its apparent openness, my group felt excluded from Polymath – excluded by the pace of results production. There are, apparently, only a handful of mathematicians in the world clever enough to contribute effectively and the rest are left gasping behind. My group argued explicitly that what is important about mathematics is not getting results, but being engaged in the process, and Polymath does not allow this in practice even though it might in theory.

Their comments reminded me of James Clerk Maxwell’s remark to Arthur Schuster that, ‘The question whether a piece of work is worth publishing or not depends on the ratio of the ingenuity displayed in the work to the total ingenuity of the author.[1]. Like the mathematicians, he was arguing that engagement was the important thing, not results. For Maxwell there was an intensely moral imperative behind this view. Engagement in an abstract cause such as maths or physics helped one control baser desires. I’m not sure my mathematicians would have gone this far, but the value to society of participation is well worth thinking about.

Maxwell, of course, was one of the lucky ones. He was one of the handful that would have been able to keep up. And in fact he indulged in collaborative exchanges with William Thomson and Peter Guthrie Tait that bear many of the hallmarks of Polymath – all conducted on postcards through the Royal Mail [2]. These collaborations were thus less visible than Polymath. Were they less discouraging to contemporaries who might be engaging in their own collaborations at their own levels?

It seems that there is not much new in collaborative mathematics, but that being online and very visible may have downsides as well as benefits.

[1] Schuster, A. (1910) in A history of the Cavendish laboratory, 1871-1910, (Longmans, Green, London, 1910) p.32

[2] P. M. Harman ed. (1995-2002) The Scientific Letters and Papers of James Clerk Maxwell, vols I, II, III Cambridge University Press.

Highlights of the OER4Adults SWOT survey |


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Highlights of the OER4Adults SWOT survey | These are the draft highlights of the OER4Adults project I have been working on, together with Lou McGill, Allison Littlejohn, and Eleni Boursinou, for the past 8 months. OER4Adults takes an overarching view of Open Educational Resources in adult and lifelong learning across Europe. Still a lot more analysis we could do, but the initial results are interesting. We conclude that open educational resources, and the practices associated with these resources, are an immensely powerful idea that potentially make a significant difference to education systems, but under-estimating the degree of cultural change needed to optimise their value, and the power of vested interests endangers realising this potential and the visions for lifelong learning 2030

New light on J J Thomson’s appointment as Cavendish Professor


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J J Thomson, nobel prize-winner and widely credited with discovering the electron, caused a degree of consternation in Cambridge in 1884 when he was appointed to succeed Lord Rayleigh as Professor of Experimental Physics at the Cavendish Laboratory in Cambridge. Thomson was only 28 and known more as a theoretical than an experimental physicist; he was not the obvious candidate.

I have recently found evidence showing that before putting himself forward, Thomson actually spearheaded a campaign to attract another candidate to the post. This candidate was Sir William Thomson (no relation to J J), the most eminent physicist of the day.  Sir William had been asked to fill this post twice before and had refused each time: once when the Laboratory was founded in 1871 ( Clerk Maxwell was appointed instead), and again in 1879 on Maxwell’s death. 

The Cambridge University Registry Guard Book for physics (a sort of scrapbook archive of documents relating to the physics laboratory) contains a copy of a memorial addressed to Sir William, urging him to take the chair. The campaign was led by J J and all members of the university who supported it were urged to contact him[1].

The case may have seemed hopeless, and J J had, so far, managed significantly fewer signatures on his memorial (24) than the equivalent petition to Lord Rayleigh five years earlier in 1879 (around 100) [2]. But it is interesting in showing that J J was already asserting his leadership within the Cambridge physics community – and raising his profile in this way clearly did him no harm when he came to apply for the post himself.

[1] Cambridge University Library, University Registry Guard Book, CUR 39.33, item 66

[2] Cambridge University Library, University Registry Guard Book, CUR 39.33, item 56

James Clerk Maxwell: Building the Cavendish and time at Cambridge


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Just sent off the final (I hope) version of my chapter James Clerk Maxwell: Building the Cavendish and time at Cambridge, to appear in Raymond Flood, Mark McCartney and Andrew Whitaker (eds), James Clerk Maxwell (1831-1879) to be published by Oxford University Press.

It’s been a fascinating exercise, re-examining the evidence (and finding some new) on a topic that has already been extensively covered.

Using Ngrams to test the prominence of the Cavendish Laboratory


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I was asked recently about the rise to prominence in British physics of the Cavendish Laboratory at Cambridge.

Certainly the Cavendish received a very good press from its alumni, former pupils and co-workers of its first professor, James Clerk Maxwell, and his successors Rayleigh, J J Thomson, and Rutherford, which ensured its prominence in history.  But is this a historical reconstruction? Or was the laboratory prominent from the time of its foundation in 1874, and if so, why?

I’ve been playing about with examining this using google’s Ngram viewer as a contribution to my forthcoming book chapter on Maxwell and the Cavendish. The Ngram measures the yearly count of a phrase, normalised by the number of phrases published in the year, in a corpus of over 5.2M books digitised by google up to 2009.[i]  It thus, potentially, gives a measure of how prominent a phrase (or institution) was in the public consciousness of the time. It is a very useful tool for tracking the frequency of certain types of phrases (and entirely useless for others).

Of course, the frequency of the phrase “Cavendish Laboratory” in absolute terms tells us little about the lab’s prominence – it needs to be compared to other laboratories.  The other obvious laboratory for comparison would be Sir William Thomson’s in Glasgow, or one of the London Colleges, but they lacked unique and distinctive names in the 1870s and hence could not be reliably tracked by Ngrams (I tried).  Oxford, however, had recently established a physical laboratory, the “Clarendon Laboratory”, and this served as a comparator.

Then, to test the hypothesis that the initial prominence of the laboratories might be linked with the prominence of their first directors, I threw “Clerk Maxwell” (professor at Cambridge) and “Robert Clifton” (professor at Oxford) into the mix. The caveat here is that there may be noise from other, non-related, Clerk Maxwells or Robert Cliftons (another reason for not trying to compare with William Thomson which is a much more common name).

Thus, the chart shows the Ngram comparing the phrases ‘Clerk Maxwell’, ‘Cavendish Laboratory’, ‘Robert Clifton’ and ‘Clarendon Laboratory’.


The Ngram shows how Maxwell’s public profile rose through the 1860s and 70s, until his death in 1879 and was followed by the profile of the Cavendish Laboratory after its foundation. However, Maxwell was much more in the public eye than was the Cavendish. Clifton, and the Clarendon, were much less prominent in the literature of the time, but there is less discrepancy between the lab and its professor.

It appears that the Cavendish Laboratory was prominent – at least compared to Oxford’s lab – from the time of its foundation, and its fame probably had a lot to do with the fame of Clerk Maxwell.

[i] J-B. Michel, Y. K. Shen, A. P. Aiden, A. Veres, M. K. Gray, W. Brockman, The Google Books Team, J. P. Pickett, D. Hoiberg, D. Clancy, P. Norvig, J. Orwant, S. Pinker, M. A. Nowak, and E.L. Aiden.’ Quantitative Analysis of Culture Using Millions of Digitized Books’. Science (Published online ahead of print: 12/16/2010)

Do adult learners need open licenses?


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It is difficult to discuss OER without reference to the means by which content might be shared (typically online), or about the licensing that facilitates that openness – writes my colleague Ronald Macintyre

A question raised by the JISC-funded UKOER Delores project, that was working both with teaching staff and directly with learners, is, “is licensing really an issue for learners?”  What matters for learners, they claim – after focus groups with the learners – is that the resources are freely available and accessible to them.  They are not likely to want to re-use or repurpose them, so the license does not matter.

Whilst students might in many situations benefit from the unrestricted use of material – allowing them to borrow and re-use in the manner of the teacher – as learners, often all they need is ‘read-only’ access to the material from which they can then draw new knowledge. Even the most restrictive licence would not prevent their entirely legitimate use of the resource as study material and so, it follows, that, for the purposes of an individual learner OER provision, non-restrictive licences should not be a prerequisite. Material which carries no licence at all and which has clear, and restrictive, copyright may for the student at least be of equal value to that carrying the least restrictive of licences (Delores final report).

This claim foregrounds a tension that seems to me to be developing in practices around OER, especially in the sphere of adult and lifelong learning that our OER4Adults project focuses on  – that the expectations of practice that arise from the historical development of the “OER movement” and the motivation underlying much of the funding for OER initiatives, may not match the way they are being used in practice in adult and lifelong learning.  OER have a twin history in the development of open source software and that of reusable learning objects.  In both cases, development was within a community of practitioners (software developers or teachers) to whom collaboration, reuse and repurposing was a fundamental basis for effective and efficient development.

That use is also within such a community may (but only may) be a valid assumption within formal education, where much resource use by learners is filtered by and through the teacher.  As learners become increasingly self-directed, though, there is, by definition, less and less filtering.  In adult education and lifelong learning, where much learning is non formal, we have to think very carefully, probably on a case-by-case basis, about where we can assume that the users of resources belong to the developer/reuser community.

However, and equally, we cannot assume that learners – formal or non formal – are not reusing and repurposing resources.  Increasingly (perhaps) learners are in the habit of contributing back the outputs of their learning, in blog posts, Wikipedia articles, posts to forums, etc.  As with any work of knowledge creation, sometimes their outputs are sufficiently re-worked that, provided proper references are given, licensing should not be an issue.  Sometimes not. Where learners contribute online, we have evidence that they do so – but we have no/little idea of the numbers of those who do not do so.  Is the proportion of the iceberg that is submerged changing?  Is the openness of OER instrumental in changing learner practices with resources?  In what contexts, or for what types of learner, does it matter to learners whether resources are openly licensed or not?