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:
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.