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Newton and Galileo

‘Is a degree in Physics a necessary prerequisite to argue that an anecdote in history is not well documented (or perhaps even to write history of science)?’

This question was asked in a paper written a few years ago, by a historian who obviously expected the answer ‘NO’. But was that the right answer?

Certainly it would have been the right answer to the first part of the question and even, in a restricted sense, to the second, because Physics is not the whole of science and there have been many good scientists with no degrees of any sort. But, as a scientist who has turned in retirement to writing history, I am finding myself increasingly unhappy with histories of science that have been written by people with no scientific background at all.

I am currently writing about the voyage of the French corvette Uranie, which in 1817 was sent on a scientific circumnavigation of the world. It was arguably the first of all the voyages in which science rather than straightforward exploration was the primary aim, but it has two other claims to fame. The first is that the Uranie never returned to France, but was wrecked in the Falklands, on the last leg of a journey that had already taken two and a half years, and the second is that among the castaways was the captain’s wife, Rose de Freycinet. Unlike the Uranie, she did return to France and in doing so became only the second woman known to have gone around the world (and the first to write a diary about it). Unsurprisingly, the people who have written about the voyage have concentrated on Rose, but they could not avoid all mention of the science, because that was the purpose of the voyage. Every account and commentary I have read seems to have accepted without question the glowing report on the expedition’s scientific achievements written by the savants of the French Academy of Sciences, without noting that this was a necessary verdict. The first major overseas mission by the French Navy after its long humiliation at the hands of Great Britain during the Napoleonic wars had to be presented as a success. Whether it actually was is much less clear. In many respects it was a failure, which is why it is now so little remembered, even in France.

However, the quotation at the head of this blog is taken from Volume 20 of Studies in the History Philosophy Science, and it was not made in relation to the Uranie voyage. Its author, Michael Segre, was writing about Galileo and the Leaning Tower of Pisa, and was supporting what seems now to be the majority view among historians that Galileo never did climb that tower and drop from it weights of different sizes. I was reading, or rather, re-reading it because a few years ago I wrote a book, The Hunt for Earth Gravity, about the history of the study of the gravity field of the Earth, and the often certifiably insane people involved. I wrote about Galileo, probably the most rational of all of them, and about Newton, who was almost beyond the limits of the autism spectrum, and it was while pruning my files for that book that I came again on Segre’s paper. He wrote that:

Yet the leaning tower demonstration has often been regarded as a turning-point in the history of science, and many authors who believe that Galileo’s science was mainly empirical have produced it as a classical example of the superiority of empirical science over a priori science. This is so despite the fact that the leaning tower story, unlike the story of Newton’s apple — which is reported to have been narrated by Newton himself — is never mentioned in any of Galileo’s writings, nor is there any evidence that he ever narrated it. It was reported 12 years after his death by one of his closest pupils and collaborators, Vincenzio Viviani (1622—1703) as part of a biography of Galileo written in 1654 and published posthumously for the first time in 1717.

There is very little in this paragraph that stands up to close inspection, and the most remarkable word in it is ‘unlike’, because what Segre is actually revealing is that the lines of evidence for Galileo being on top of the tower and Newton being underneath the apple tree are exactly the same. Both were reported by people who admired the person directly involved, as having been told to them by him. Whether or not either story is actually true is unknowable and indeed not very important, but interesting none the less as a study in probability and the personalities of scientists. Whatever else they may or not have been, or have done, Newton and Galileo were both scientists, and the driving forces in both their lives were simple curiosity and the more complex desire to see their own brilliance acknowledged by their fellows.

Newton conformed to this pattern exactly, and he was not a nice man. He was quite happy to send men (and women) to the gallows. He conducted vicious campaigns against both Hooke and Leibniz to assert his priority, and in the case of Hooke the argument was all about gravity. The apple story was not just about an event but also about a time – a time when plague had forced Newton to flee Cambridge and take refuge on the family farm. The timing was ammunition, because if the story was true it showed that he had been thinking about gravity long before there was any other evidence for him having done so. Segre’s paragraph thus contains a second error, and an odd one for any historian to make. Even if some historical figure can be proven to have said that something happened, it does not mean that it did happen.

What of Galileo, and what he said, or what his biographer Viviani said that he said? Here is Segre’s translation.

And then, to the dismay of all the philosophers, very many of the conclusions of Aristotle were by him proved false through experiments and solid demonstrations and discourses, conclusions which up to then had been held absolutely clear and indubitable; as, among others, that the velocity of moving bodies of the same material, of unequal weight, moving in the same medium, did not mutually preserve the proportion of their weight as taught by Aristotle, but all moved at the same speed, demonstrating this with repeated experiments from the height of the Campanile of Pisa in the presence of the other teachers and philosophers, and the whole assembly of students.

That is all, and, just as with Newton, Galileo is pictured as recounting an event that had happened years before. But, unlike Newton, he had no strong motive for talking about it, if it had not been true. He was old, he was virtually blind and he was, by papal decree, confined to his house. The story was not going to advance his cause, or his reputation, which was going to rest on the book (Two New Sciences) that detailed the results obtained in many meticulous experiments. As even Segre admitted, the Pisa demonstration ….

…. had no impact on Galileo’s thought; if it occurred, it was only a public performance and Galileo would not have climbed to the top of the tower without knowing the result beforehand. ……. After all, it was a social event, not an organic part of his scientific work.

That would seem to be the perfect answer to any of the multitude of later historians whose only real grounds for suggesting that it never happened has been that Galileo himself never wrote about it. But why should he? He was a scientist, and this was not an experiment, it was a demonstration. Just the sort of thing an old man might have recalled as a bit of a joke, many years afterwards, when talking to a friend.

However (and as trainee geologists have banged into their heads at an early age), ‘absence of evidence is not evidence of absence’. Surely the historians who rejected the Pisa story had more than absence of evidence to go on? Segre did present one piece of evidence as having been influential on those who had come before him. He wrote that:

On one occasion Galileo even says that he dropped two different bodies, one of lead and one of wood, from the top of a high tower: “the lead moves far out in front. This is something I have often tested”

Why this is thought to serve as evidence against the Pisa story is beyond me. Galileo knew all about air resistance, and in later life he wrote extensively about the resistance of various media to motion through them. During his time in Pisa, and quite possibly to the end of his life, he believed that, because of that resistance, it was the density of the body that determined how fast it fell, not its mass. As far as the Pisa demonstration is concerned, it is surely sufficient to point out that Viviani specifically refers to the two bodies being made of the same material. If anything, this quotation, which comes from the collection of Galileo’s early writings known as ‘De Motu’, is evidence in favour of the story, because it shows him talking about dropping objects from ‘a high tower’. Segre reaches a fairly high level of absurdity when, later, he argues that the demonstration might have been done from some other tower, because ‘there are several leaning towers in Pisa’.

Galileo was clearly a nicer man than Newton, but he must still have been an irritating colleague. He was a showman who loved to show off, and he was surrounded by people who still believed Aristotle. He would have chosen the most prominent tower he could find, and he would have made very sure before he made his demonstration in front of his critics, that it was going to work. I cannot know for certain that he did confront them with such a demonstration, but I find it hard to believe that, with such a perfect setting available for proving them wrong, he did not take advantage of it.

To write history of science, a science degree is certainly not essential. But it is at least necessary to get inside the minds of scientists, and understand how they work.