- The Washington Times - Saturday, July 31, 2004

PENDULUM: LEON FOUCAULT AND THE TRIUMPH OF SCIENCE

By Amir D. Aczel

Atria Books, $25, 275 pages, illus.

REVIEWED BY RAYMOND PETERSEN

In “As The World Turns,” the vintage soap opera of the early era of TV, it was taken for granted that the world does indeed turn, or at least that the lives of the program’s characters turned, lurching from crisis to crisis, as they do in melodramas.

A little over a century before the soap opera debuted, the great French scientist Leon Foucault showed that Earth does turn — rotate — on its axis and that this rotation can be proved by the elegant, steady — and never lurching — swing of the pendulum.

How Foucault arrived at his amazing discovery is taken up in Amir Aczel’s book “Pendulum: Leon Foucault and the Triumph of Science.” Foucault’s story as told by the able Mr. Aczel is a mesmerizing tale of one individual’s faith in reason overcoming the narrow-mindedness of the many — in this instance, the august members of the French Academy of Sciences.

Foucault’s proving of Earth’s rotation on its axis took place in a Paris basement on the night of Jan. 6, 1851. The young scientist — Foucault was in his early 30s — released a free-moving pendulum. Unlike the familiar back-and-forth motion of a grandfather clock, the plane of swing of a free-moving pendulum is unrestricted; with every swing, the perceptive Foucault saw the world itself turn.

Why? As he watched, his pendulum glided back and forth, but its plane of swing changed gradually and incrementally in a clockwise direction, doing always a slow, majestic pirouette around a central point on that basement floor in Paris. What Foucault realized, in a moment of tremendous scientific insight, was that in reality it was not the pendulum’s plane of swing that was changing. Rather, it was he, the basement room, Paris, and indeed the whole world that were turning and turning relative to the plane of swing of the pendulum.

Foucault arrived at this conclusion through abstract reasoning and his knowledge of Newtonian physics. According to Newton, the motion and direction of motion of an object remain unchanged — “inert” — unless acted upon by some outside force. This is Newton’s First Law of Motion, the so-called principle of inertia.

If the motion and direction of motion of an object remain unchanged unless acted upon by an outside force, then, reasoned Foucault, the back-and-forth motion of his pendulum, once it has been released, and its plane of swing must remain unchanged. Ergo, what he was witnessing was Earth spinning on its axis.

It was a momentous discovery, but one that France’s leading mathematicians and physicists were reluctant to give him credit for. They didn’t, until near the end of Foucault’s short life (he died at 49), when he was inducted into the Academy of Sciences, one of the highest awards that can be bestowed on a French scientist.

Foucault had been born in 1819, the only child of a well-to-do family. His father ran a successful publishing house. After he had entered medical school, Foucault learned — as many before and after him have discovered — that he wasn’t intended for a medical career because he couldn’t stand the sight of blood. His lack of an advanced degree would plague him the rest of his life, and would be used by his detractors as a way of discrediting the value of his scientific discoveries.

But there were those who recognized Foucault’s talents and stood by him. One such person was Alfred Donne, who had taught the young man while he was still in medical school. Donne appointed Foucault his assistant — a position the budding scientist used to make significant advancements in the new art of photomicroscopy.

Donne was editor of the “science pages” in the Journal des Debats, where current issues in science were presented to the public. Later, Donne turned over the editorship of the science pages to his assistant, which gave Foucault the opportunity to keep abreast of what was happening in the scientific community — and to establish, as he soon did, a reputation as a brash but thoroughly knowledgeable editor.

It was while he was an editor at the Journal des Debats that Foucault demonstrated, through his observations of pendulum motion, that the earth moves. He also realized that pendulums placed at different latitudes on the earth take differing amounts of time to complete one entire cycle, and he worked out a simple mathematical algorithm for determining these different times.

At either pole — north or south — the cycle takes exactly 24 hours. At Paris, which is at 48 degrees 51 minutes north, it takes 32 hours. Whereas at the equator — 0 degrees — it takes an infinite amount of time (for the simple reason that it is aligned precisely with the direction of the rotation of the planet), it never changes its apparent plane of swing. South of the equator, rates are the same as for the corresponding northern latitudes but with a major change: The plane of the pendulum’s swing is counterclockwise.

But Mr. Aczel’s book is about more than a pendulum. One of the most interesting stories the author tells, for example, is Foucault’s relationship with Louis-Jacques Daguerre, who, in 1837, had invented the daguerreotype.

Soon after his invention had been announced to the world, Daguerre advertised free classes in photography: “Painting without need for talent” was what he promised those who signed up, and the 19-year-old Foucault did. How the young scientist used what he learned from Daguerre shows the richness of the young man’s mind, and his ability to turn what he discovered from others into material and knowledge very much his own.

Foucault applied Daguerre’s work to the nascent science of photomicroscopy. By 1845, he had developed a regulator for the very intense carbon-arc light needed to generate photomicrographic daguerreotype images. And along with his collaborator Armand Fizeau, Foucault went on to enhance greatly the light sensitivity of the unexposed daguerreotype plate.

In practical terms, this means that the exposure time required to generate a usable image was cut from a very long 20 minutes to a very short 20 seconds. Having done so, Foucault and Fizeau were able to generate not only the first photos of cells but the first portraits of people as well.

Foucault then adapted his regulated carbon-arc lamp to stage lighting, and dazzled Paris audiences by simulating the dawning sun in a Paris Opera production of Giacomo Meyerbeer’s “Le Prophete.” Mr. Aczel notes that Foucault’s exposure to mercury in his work on daguerreotypes was very likely the cause of his early death.

But before he died, Foucault made another contribution to science. He conceptualized the idea of the gyroscope and then, in 1855, had one built to his specifications. His remarkable device was pretty much ignored until 1896, when an Austrian engineer discovered that gyroscopes could be used to guide torpedoes to their targets.

Mr. Aczel’s book is not without its flaws. His condemnation of the Catholic Church for the suppression of science can only be described as overbearing. Surely such a complex subject as the church’s role in Western intellectual development could have been presented wihout a negative editorializing tone. Further, the author strongly implies that Ptolemy invented the concept of the epicycle when it would be more accurate to say that he borrowed the notion of epicycles from Apollonius of Perga.

But Mr. Aczel makes a greater error in describing Tycho Brahe, the great early modern Danish astronomer, as Johannes Kepler’s “mentor.” Brahe was hardly mentor to Kepler. Each man needed the other to complete his own work. The younger Kepler could not have done without Brahe’s then state-of-the-art and accurate observations and data, while Brahe needed Kepler’s syncretic genius to make sense of the observations he had made.

However, these are minor slips in a crisply written, intelligent biography of a great scientist whose significance isn’t appreciated as much as it should be. “Pendulum” will help set the record straight and give Foucault his due.

Raymond Petersen is a botanist and professor of biology at Howard University. He teaches a course in the history and philosophy of science.

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