Pendulum: Leon Foucault and the triumph of science

Pendulum is a fascinating journey through the mind and findings of one of the most important and lesser-known characters in the history of science. Through careful research and lively anecdotes, world-renowned author Amir D. Aczel reveals the astonishing range and breadth of Foucault's discoveries. For, in addition to offering the first unequivocal proof of Earth's rotation, Foucault gave us the modern electric compass and microscope, was a pioneer in photographic technology, and made remarkable deductions about color theory, heat waves, and the speed of light.

At its heart, Pendulum is a story about the illustrious period in France during the Second Empire; the crucial triumph of science over religion; and, most compelling, the life of a struggling, self-made man whose pursuit of knowledge continues to inform our notions about the universe today.

To add insult to injury Aczel writes:

"On January 6, 1680, Hooke wrote to Newton:"

"'In the mean time I must acquaint you that I have (with as much care as I could) made 3 tryalls of the experiment of the falling body, in every of which the ball fell towards the south-east of the perpendicular, and that very considerably, the last being above a quarter of an inch, but because they were not all the same I know not which was true.'"

"Hooke's experiments with falling objects thus revealed not only the correct deviation east, but also a smaller deviation to the south, now known to be spurious. These results were seen as inconclusive."

But the result is not spurious. At the moment of its release, the object would no longer be forced to rotate in a due east direction, which is a small-circle parallel the equator, but like a ball from a whirled sling it would begin to fall in the plane of a great-circle tangent to the small-circle through the point of release and centered on the center of the earth. As a result, in England, the falling object would fall south of east of the vertical through the point of release. This is what careful Hooke observed and, although the savants of the day may not have been convinced by three trials, the free fall of an object is the only simple-to-understand method to give proof of the earth's rotation. The complex behavior of the Foucault pendulum anywhere but precisely at the north or south pole provides for no clear proof. And that demonstration has never been done. The supposed mathematical "QED" explanation of the motion of the Foucault pendulum (at a latitude other than 90 degrees north or south) offered at the end of the book by Aczel is so nonsensical that it should be seen as laughable but not everyone will have the math to get the joke.

Save your sanity and your money and wait for someone to write a better and more informed book...

Aczel recounts how Foucault, an outsider to the world of the French academy, without the benefit of rigorous university training in mathematics and science, devised his demonstration, proved a surprising relationship between the behavior of the pendulum and the lattitude of the location of the pendulum, and finally overcame systematic discrimination by the reigning authorities of the French academy and was finally recognized for his achievements.

Foucault enjoyed the support of the emperor Louis Napoleon, who himself had dabbled with science during his time in prison, years before. Louis Napoleon arranged for a public viewing of Foucault's elegant pendulum demonstration in the Pantheon in Paris, which provided a great forum for the Parisian public to see science in action and history in the making.

Aczel is a master of relating episodes in the history of science and mathematics to a general audience. As in his earlier books, Aczel deftly sketches relevant biographical detail of the major dramatis personae and the historical context of the story. His explanations of the underlying scientific and mathematical principles are notably clear and jargon-free. "Pendulum" weaves Church history, French political and social history, biography, and science into a cohesive narrative that highlights, above all else, the human drama of scientific discovery. This is the history of science at its best.

Aczel rightly gives a history of the idea that the Earth turned, an idea that was at one time dangerous to hold because of religious implications. But the only thing the heliocentric model really had going for it was that the mathematical calculations for understanding and predicting celestial motion were simpler. That made it a good model, but still, you could sit on a hill and night and watch as the heavens moved, and feel no spin of the Earth. Foucault enabled us to see and feel a bit more accurately. He was a brilliant engineer, and an even better tinkerer with gadgets at his disposal. He had worked with electric lighting, microscopy, and photography, and turned his attention to the movement of the Earth. Mathematicians and physicists had said that such motion could never be observed, but Foucault worked in his cellar for months, perfecting his experiment, which seems so very simple in retrospect. He designed a series of larger pendulums. A pendulum swings in its own plane; on a moving Earth, the pendulum seems to shift around, depending on where the pendulum is located. People loved the huge pendulums and the clear demonstration.

Foucault was thereafter a celebrity, a status that he enjoyed. But it did not help him with the members of the Academy of Sciences. They were angry. He was not a trained scientist. He was not a trained mathematician. He had scooped them all with a simple experiment that had a universal appeal. It was not until three years before his death in 1865 that he was elected a member of the Academy, although he had gained many honors by that time. One of his further inventions was the gyroscope, which he invented specifically to see in another way the turning of the Earth (his word for it, "gyroscope", means literally "turn see"). Once again, he demonstrated the truth that the calculations had shown, but in a physical way. Aczel's book clearly shows how Foucault's ideas fit into the progression of our better understanding (and acceptance) of celestial movements. There are clear explanations here as well of how Coriolis force, a force Foucault knew nothing about, acts on pendulums, cannonballs, and storms, as well as how Foucault and his idea fit into the religious and political times. This is a readable tribute to a remarkable thinker. Come see the Earth turn.