The Science of Weather and the Nature of Science

Apply for the Summer SchoolWe are very happy today to be able to publish this exclusive excerpt from Jessica Riskin’s new book, The Power of Life: The Invention of Biology and the Revolutionary Science of Jean-Baptiste Lamarck (Riverhead Books, March 2026). Jessica teaches history and philosophy of science at Stanford University. Many of us are in agreement that her previous book, The Restless Clock (Chicago, 2016) is among the best treatments of the natural-philosophical problem of life in early modern Europe ever written, and deserves to be considered a new classic. It is fitting that she should turn her attention next to Lamarck (1744-1829) — amply memorialized in statues and lecture halls in France and widely characterized here as the “founder of the theory of evolution”, even as his role in the history of science is mostly downplayed or dismissed in the Anglosphere. This dismissiveness is especially regrettable, given that some of Lamarck’s ideas have been positively reassessed in recent years by scientists working in such fields as epigenetics and developmental plasticity theory. It is to be hoped that Jessica’s book will help to bring about a deeper and more complete picture of this crucial figure. Jill Lepore has said of The Power of Life that it is a “truly remarkable achievement, at once a delightfully wry and wildly entertaining biography of Jean-Baptiste Lamarck and a riveting intellectual history.” Order your copy today. —The EditorsOrder The Power of Life!From THE POWER OF LIFE by Jessica Riskin. Published by arrangement with Riverhead Books, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2026 by Jessica Riskin.* From the garret window of the room where Jean-Baptiste Lamarck lived when he first moved to Paris in his mid-twenties, around 1770, he could see nothing but clouds and sky. The clouds therefore became his companions and source of entertainment. Watching them, he began to notice how they formed, gathered and dispersed. They didn’t behave randomly, he observed, but exhibited types and patterns. He began to watch more carefully, and in this way, he became the first person to classify the clouds, producing a veritable cloud atlas for his first presentation to the Academy of Sciences in 1777.

He divided clouds into five types: (1) veiled (en voile), (2) gathered (attroupés), (3) dappled (pommelés), (4) sweeping (en balayures), and (5) grouped (groupé). But Lamarck became busy, first with the study of botany and then with his new position at the National Museum of Natural History, created during the French Revolution, the wonderfully named Chair in Insects and Worms. He waited twenty-five years before actually publishing his classification of clouds, finally including it in his meteorological yearbook for Year Ten of the Revolution (1802) – the same year in which he coined the word “Biologie.”The following year, a young English chemist named Luke Howard introduced the basic categories of the current taxonomy: “cirrus” (made of parallel fibers, from the Latin word for a tendril of hair), “cumulus” (conical heaps, from the Latin word for a heap or pile), and “stratus” (horizontal sheets, from the Latin word for a “spread”). Lamarck and Howard apparently never heard of one another, which is a shame since they might have had a lot to talk about. On the other hand, they would probably have disagreed about some things too. For instance, Howard said he used Latin terms to name the types of clouds because he intended his system to be adopted by the “learned of different nations.” This strategy was successful: Howard’s terminology established itself internationally and is still in use today.Lamarck, on the other hand, used French terms, not because he wanted to speak only to French people – after all, he drew people from all over the world to his legendary classes on invertebrate zoology – but because he hoped to create a participatory community of meteorologists that would include the non- “learned.” Only an educated minority would have understood Latin terms; and Latin names would have indicated that meteorology was an elite, scholarly pursuit, which was exactly the opposite of what Lamarck intended. To be sure, when he named plants and invertebrates, he often used Latin roots, but in those cases, he was working within traditions that had existed for centuries before him. The clouds, in contrast, had no traditional nomenclature; no one had ever named them. Embarking on an entirely new science, Lamarck was free to define its terms as he liked.

And, just as he boasted that he could turn any passerby in the Garden of Plants into a botanist, he also meant to turn everyone in France, and beyond, into a meteorologist. He addressed his readers fondly and familiarly as “friends of nature.”In September 1799, two months before Napoleon declared himself First Consul of France in a coup d’état, Lamarck published the first in his decade-long series of meteorological yearbooks, offering forecasts for the year 1800, the first year of the nineteenth century. In this inaugural yearbook, he issued a special “invitation to amateurs of meteorology” encouraging readers to annotate their copies of the book by recording their own observations in them, and to send him their annotated yearbooks at the end of the year. He offered careful instructions for how to make these annotations.In order to understand how you’d have annotated your yearbook if you’d been one of Lamarck’s participatory readers at the turn of the nineteenth century, you first have to know that each book includes a calendar arranged in columns. From left to right, there’s a column for the day; then the month; then for “natural periods useful to observe” such as the migratory arrivals and departures of certain birds, the blooming of particular plants, and the fall of leaves from various species of tree. Next comes the most important column, which is somewhat mysteriously labeled “epochs of changes of constitution.” This column in fact contains the positions of the moon: its apogees, perigees, and the northern and southern extremes of its orbit. In the course of a lunar month, the moon’s orbit carries it not only around the earth, but also north and south, above and below the equator. Lamarck explained that when the moon was traveling through the six northern signs of the zodiac, he called this period the moon’s “boreal constitution”; and when it was traveling through the six southern signs, he called it the moon’s “austral constitution.”The column containing the moon’s constitutions is the crucial one because Lamarck’s central meteorological principle was that the moon imposes cyclical effects upon the weather by exerting a gravitational pull on the earth’s atmosphere: pulling to the north, causing south winds to prevail, or to the south, bringing north winds. (

Lamarck’s essential idea remains present in current meteorological science; today, meteorologists refer to the effects of the moon’s gravitational pull on the earth’s atmosphere as “atmospheric tides.”)1After the column of lunar constitutions comes one for the “meteorological season,” and here Lamarck divides each of the four regular seasons into two parts: the winter and summer into “solstitial” and “median” phases, and the spring and fall into “equinoctial” and “median” phases. Next comes a column for the time of the moon’s passage over the meridian line through Paris, where Lamarck was conducting his observations; and finally, one for its declination (its angular distance above or below the equator) at noon. A second calendar, arranged in paragraphs rather than columns, describes what the weather will probably be like for each successive “constitution” of the moon. According to Lamarck’s theory, boreal constitutions, pulling to the north, bring south winds and therefore warmer temperatures, lower pressures, humidity, rain, storms and tempests; in contrast, austral constitutions, pulling to the south, bring north winds and therefore colder temperatures, higher pressures, and clear, dry weather.In his invitation to his readers, Lamarck explains how to record their observations of the weather day by day in the column containing lunar constitutions. He also offers detailed instructions for “how to judge the state of the atmosphere.” First, he says, you have to examine whether the weather is “simple” or “mixed.” Simple weather is either calm or has wind blowing only in one direction; mixed weather has upper and lower winds blowing in different directions. The lower winds are the familiar ones that turn weathervanes and windmills and fill the sails of ships; the upper winds are those we can see through gaps in the lower clouds as they blow around the upper clouds. Sometimes, even when the sky is heavily overcast and you can’t see its upper regions, you can still discern that the weather is mixed. For instance, if a south wind is blowing the clouds northward, and yet the barometer is steady or rising, there must be a cold north wind up above bringing the higher pressures; and if it’s rainy even though a north wind is driving the lower clouds southward, you can be sure there’s a warm south wind up above.

Having explained how to observe the atmosphere and how to annotate the yearbooks, Lamarck encouraged his readers to send him their marked up books at year’s end and said he’d be especially grateful to hear from any whose observations differed significantly from the probabilities he described. He also included a thorough explanation of the new metric system of weights and measures that the National Convention had introduced in April 1795, even though the system had no immediate use for annotating the yearbooks. The metric system was provoking widespread exasperation and resentment, but Lamarck believed in it; here was a further expression of his purpose to spread scientific literacy and a participatory feeling among his readers.* * *True to Lamarck’s romantic nature, he really loved storms. The participatory feeling wasn’t all about measurement systems, charts and tables: he wanted his readers to pay attention to the weather not only by recording it but also by relishing it. Storms, he said, were “the most imposing and the most beautiful” of meteorological phenomena. One summer while he was up at Beauregard, his country house in Héricourt, he observed a hurricane, which he described rapturously in the following yearbook in a special section entitled “Observations on the Hurricane of July 31, 1808, and on a large rotating cloud.” The storm’s great diversity of cloud shapes and colors had fascinated him, their rapid dance across the sky so “magnificent” that “I couldn’t tire of admiring the beautiful spectacle before my eyes.”Science and the appreciation of beauty were inseparable, since it was while he stood rapt in the midst of the storm, watching the drama unfold, that Lamarck made a surprising observation: “suddenly I perceived in a large cloud placed to the southwest, a singular movement that I had never noticed.” The cloud in question took up much of the horizon and was oddly shaped, resembling “an enormous pyramid” with its summit pointing downward toward the earth. “Soon the sides of this pyramid were torn into shreds” while its base took on “a gyratory movement,” turning on its axis “with great slowness.” This stately, circular motion was portentous: “a most violent wind” and squall soon followed, so powerful that Lamarck was obliged to flee back to the shelter of Beauregard and “abandon my observations.