Leonardo and gravity

Mory Gharib an engineer from Caltech has published an article about his interpretation of some diagrams he discovered in one of the Leonardo manuscripts, which he claims are Leonardo’s attempts to determine the acceleration due to gravity. I’m not going to comment on Gharib’s work, which looks interesting, but rather on the article published in ARS TECHNICA by science writer Jennifer Ouellette describing Gharib’s work, which contains some, in my opinion, bizarre statements. 

It starts with Ouellette’s title: Leonardo noted link between gravity and acceleration centuries before Einstein! Equating an experiment of Leonardo’s, assuming Gharib is correct in his suppositions, with Einstein’s general theory of relativity is so far fetched it’s absurd. Just in case you think it’s just a hyperbolic title we get it repeated more emphatically at the end of the first paragraph:

Clip from article

Further investigation revealed that Leonardo was attempting to study the nature of gravity, and the little triangles were his attempt to draw an equivalence between gravity and acceleration—well before Isaac Newton came up with his laws of motion, and centuries before Albert Einstein would demonstrate the equivalence principle with his general theory of relativity.

Now we have Leonardo not just raised on a pedestal with Einstein, but with Newton too. I could point out that Newton didn’t come up with his laws of motion he collated them from the work of others. The comparison with Newton comes again in the next paragraph:

What makes this finding even more astonishing is that Leonardo did all this without a means of accurate timekeeping and without the benefit of calculus, which Newton invented in order to develop his laws of motion and universal gravitation in the 1660s.

Two things are wrong with this. Firstly, as I will explain shortly, lots of people investigated the acceleration due to gravity before and after Leonardo but before Newton without using calculus. Secondly, Newton did not invent calculus, he collated, and systemised the work of many other, as did Leibniz. He also didn’t do this to develop his laws of motion and universal gravitation, in fact, as I have explained once before, contrary to popular opinion, Newton did not use calculus to write the Principia, but good old fashioned Euclidian geometry. Just for the record Newton’s work in this area was done in the 1680s not 1660s. 

We get served up an old dubious claim:

Leonardo foresaw the possibility of constructing a telescope in his Codex Atlanticus (1490) when he wrote of “making glasses to see the moon enlarged”—a century before the instrument’s invention.  

Most expert on the history of the telescope follow Van Helden and don’t think Leonardo was here referring to any form of telescope but rather a single magnifying lens held at arm’s length. 

Moving on:

The concept of inertia wasn’t even known at the time; Leonardo’s earlier writings show that he accepted the Aristotelian notion that one needs a continuous force for any object to move. 

It is true that the theory of inertia wasn’t known at the time but around 1500 Leonardo almost certainly used the post-Aristotelian impulse theory.

As a historian of Renaissance mathematics, the following truly boggled my mind:

Leonardo went even further, Gharib et al. assert, and essentially tried to model the data from his experiment to find the gravitational constant using geometry—the best mathematical tool available at the time. “There was no concept of equations or math, but Leonardo had such an intuitive understanding of math in its non-equation form,” Roh told Ars. “I think that’s where he started using geometry to write out equations, in a way. 

“There was no concept of equations or math…”!!!!!!!! Just savour this statement for a moment, I can’t even begin… Leonardo’s maths teacher, Luca Pacioli, might have a few words to say about that.

To close, I wish to suggest a list of people in Europe, who in various ways investigated the acceleration of gravity, post Aristotle before Leonardo, contemporaneously with him or after him but before Newton and before the invention of calculus, with whom Ms Ouellette might have compared Leonardo’s interesting endeavours rather than Newton and Einstein. 

We start in the sixth century CE with John Philoponus. Moving on to the fourteenth century we have the Oxford Calculatores, who derived the mean speed theorem. Staying in the same century we have Nicole Oresme, who produced a geometrical representation of the mean speed theorem. Post Leonardo in the sixteenth century we have Tartaglia, and Benedetti. At the end of the sixteenth and beginning of the seventeenth centuries we have Simon Stevin and some guy called Galileo Galilei, you might have heard of him.  


Filed under History of Physics, Uncategorized

15 responses to “Leonardo and gravity

  1. This reminds me of the appendix to James Blish’s novel Doctor Mirabilis, where he claimed that Roger Bacon anticipated Einstein’s General Relativity because Bacon talks about a plenum.

  2. It’s fun that someone bigging up Leonardo gets Galileo tossed at her when he’s so often the subject of a piece that gets the HISTSCI_HULK treatment.

  3. Many people who should know better have been moving into click-bait territory recently, such as blogger Sabine Hossenfelder. Jennifer Oullette is married to Sean Carroll, who actually wrote a textbook on general relativity (and several other books and papers; he’s a professional academic physicist). I realize that not everyone has their spouse check over things before sending them off, but with a short piece like this, couldn’t he have just read it at breakfast or whatever and suggest some changes? Or maybe he did but didn’t?

    • Jennifer Oullette has form for making totally ridiculous #histsci statements in her articles and that’s why I gave up reading them
      long ago. I read this one because the Leonardo research on which it is based interests me.

    • If I’ve learned anything from the HISTSCI_HULK, it’s that being a scientist (or other academic) does not mean someone knows history of science. So, Sean Carroll going over Jennifer Oullette’s work can’t be assumed to catch errors in history of science. For all we know, he could be the source of her errors.

    • What I’ve seen from Sabine Hossenfelder recently hasn’t been click-bait, but rather an exploration of some serious issues in fundamental physics presented in an accessible way. As she is herself a theoretical physicist, I don’t doubt that she has the background knowledge. Yes, the phone is a gimmick, but so what. If I wanted to be picky, I would say that her description of the Standard Model of particle physics is slightly misleading because in it neutrinos have zero rest mass, but she is quite right about theoretical physicists continually coming up with new particles and that apart from the Higgs boson the LHC has not detected any new particles beyond the Standard Model.

  4. Now that you’ve added the clip from the article, I’m struck by one thing: I can’t see any evidence of acceleration in the Leonardo sketch. It looks very much like a falling with constant speed.

    Misleadingly, the video immediately preceding, from CalTech, of course does show acceleration, noticable only near the very beginning. But just this initial fraction of a second is what appears (to my eyes) to be missing from the Leonardo sketch.

  5. I see that the phrasing of the Einstein mention has been changed slightly in the article:

    …the little triangles were his attempt to draw a link between gravity and acceleration—well before Isaac Newton came up with his laws of motion, and centuries before Albert Einstein would demonstrate the equivalence principle with his general theory of relativity. [Edited for clarity.]

    In this form, while the Einstein reference is technically correct, it’s pure clickbait.

    It’s as if someone wrote, “Lucretius wrote a long poem about basic particles, centuries before Gell-Mann proposed quarks…”

  6. And Leucippus & Democritus centuries befor Lucretius 🙃

  7. araybold

    Could this sort of thing be thought of as the Whig history of science, at least by analogy? In it, one takes something a historical figure wrote, inappropriately interpret it in the light of current knowledge, and, on the basis of that, ascribe to them concepts which would surely baffle them unless and until they were brought up-to-date with current knowledge.

    Now Caltech seems to be doing the same thing:

    • Back a decade or so ago, there was a lot of discussion about the term Whiggism; it has been used in many ways. Michael Bycroft’s excellent sci-hist blog Double Refraction (now dormant) had a long post detailing eight possible meanings.
      Different kinds of Whig history are wrong (or right) for different kinds of reasons

      With apologies in advance, I will now go off on a tangent. The late Steven Weinberg became a bête noire to many science historians for unabashedly championing three kinds of Whig history, Bycroft’s “Present-directed narrative”, “Comparisons to present-day beliefs”, and “Present-day criteria”. Here’s how Weinberg defended the last of these, the one most offensive to modern historiography:

      Of course, one has to try to understand the historical context of scientific discoveries. Beyond that, the task of a historian depends on what he or she is trying to accomplish. If the historian’s aim is only to re-create the past, to understand “how it actually was”, then it may not be helpful to judge a past scientist’s success by modern standards. But this sort of judgment is indispensable if what one wants is to understand how science progressed from its past to its present.

      This progress has been something objective, not just an evolution of fashion. Is it possible to doubt that Newton understood more about motion than Aristotle, or that we understand more than Newton? It never was fruitful to ask what motions are natural, or what is the purpose of this or that physical phenomenon.

      I agree with Lindberg that it would be unfair to conclude that Aristotle was stupid. My purpose here in judging the past by the standards of the present is to come to an understanding of how difficult it was for even very intelligent persons like Aristotle to learn how to learn about nature. Nothing about the practice of modern science is obvious to someone who has never seen it done.

      To return to Ouellette’s post: by the standards of the “Present directed narrative”, the question is: how much did Leonardo’s work contribute to the later development? As Thony details, not at all.

      • araybold

        Indeed, though there seem to be at least two separable issues here. The first one is whether the work Leonardo performed here and the views he actually held contributed to later developments, and the second being whether he actually held views that could, in any meaningful sense, be regarded as a version of something much more recent – in particular, the equivalence principle of general relativity. It is far from clear to me what the equivalence principle would even mean within Leonardo’s world-view, and, if I am not mistaken, your combined responses to this post seem to be offering a clear “no” to both of the above issues.

      • @araybold That’s right. That’s the cherry-picking aspect.

        A contrasting example, also involving Leonardo. The three “laws of dry friction” are conventionally named after Amontons and Coulomb. They were discovered hundreds of years earlier by Leonardo. This had no impact on the development of the subject, as they lay buried in his notebooks until historians starting digging up this work by Leonardo around 40 years ago.

        But “discovered the laws of dry friction” just doesn’t have the same pizzazz as “anticipated general relativity”.

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