An Open Book on Leonardo the Scientist

Step briskly past the diorama of a Komodo dragon and his prey at the American Museum of Natural History. Don't be waylaid by the stuffed leather-back sea turtle laying 100 yellow eggs the size of apples. What awaits you in the next room - Leonardo da Vinci's Water World - is just as illuminating a stage set of natural history as the museum's famous dinosaurs.

Everyone knows Leonardo as the artist who painted the two most famous paintings in the Western world, "Mona Lisa" and "The Last Supper." What's not so widely known are the artist's scientific breakthroughs and engineering genius.

Yes, Leonardo was a painter, sculptor, and architect. But he was also a mathematician, astronomer, inventor, and all-round student of nature. Brilliant and omni-competent, he combined the aesthetic dexterity of Martha Stewart with the smarts of Einstein. Leonardo was one for whom the term "Renaissance man" might just be an understatement.

An exhibit called "Leonardo's Codex Leicester: A Masterpiece of Science" is on display through Jan. 1, 1997. Eighteen double-sided sheets of Leonardo's notebook demonstrate many facets of the maestro's scientific thought. The manuscript, composed between 1506 and 1510, is the only one in the United States and the only one in private hands. It is on loan from Bill Gates, the Microsoft billionaire who paid $30.8 million for the notebook in 1994 when it was auctioned from the Armand Hammer estate. The "Leicester" part of the title comes from Thomas Coke, the first earl of Leicester in England, who owned the manuscript from 1717 to 1980.

Recorded in reddish ink on creamy linen paper in Leonardo's left-handed reverse (or "mirror") script, the fragile sheets are only sporadically illuminated to protect them from deterioration. They contain 360 pen-and-ink sketches accompanying Leonardo's far-ranging ruminations and theories on geology, paleontology, astronomy, and - above all - hydrology. The manuscript's focus on water is appropriate, since ideas gushed out of Leonardo's quicksilver mind in a constant stream.

In these pages, Leonardo draws delicate eddies around stones and speculates on how to shift a river's current to prevent erosion of its banks. He designs a pile-driving machine, devises an accurate wave theory, and gives advice on how to escape a whirlpool or "empty a swamp that flows into the sea."

At a time when North America was a blank on world maps, Leonardo explained the astral phenomenon called "the old moon in the new moon's arms," in which the bright crescent moon at twilight emits a hazy glow across its unilluminated parts. In the first correct account of the phenomenon, Leonardo deduced that sunlight reflected from the earth's oceans, or "earthshine," bathes the unlit portion of the moon in ashen light.

But it was not until 1604, when German astronomer Johannes Kepler published an account, that the scientific world had an explanation of the ashen-light phenomenon. Since printing was in its infancy and Leonardo's restless curiosity drove him from one idea to the next, he never published his theories, and they had no influence on scientific progress during the Renaissance.

"The desire to know is natural to good men," this incessantly inquisitive explorer wrote. Leonardo's great strength as a thinker was his willingness to abandon conventional dogma and proceed from untrammeled observation.

At the time, others explained the existence of marine fossils on mountaintops either as evidence of a Biblical deluge or by the prevailing notion that fossils "grew" in rocks like crystals. Not so, Leonardo concluded. Examining the deposited stone relics taught him that an ancient sea once covered the peaks.

The exhibition encourages experimentation, which Leonardo obviously relished, by offering opportunities for water play. In a demonstration room, viewers can drop objects like glass cubes or marbles into a stream of water to see how different shapes create distinctive currents. A transparent tube shows how bubbles billow upward in a spiral, another of Leonardo's observations in the Codex.

Since it is difficult to study the manuscript in dim light, banks of computer workstations allow the visitor to investigate the folio in detail on CD-ROM. With a trackball, you can click on any portion to magnify the sketches, read an English translation, or view the original backward script. Translations into modern Italian or Leonardo's Renaissance Italian appear at a point-and-click command.

In one section, Leonardo gives pointers, like Mark Twain in "Life on the Mississippi," on how to read the depths of a river from its surface. Fortunately for us, the Codex allows a similar window into the profundity of an extraordinary mind. As Ellen Futter, museum president, says, the Codex shows that "science and art emanate from a common spring, namely, the search for truth."

*A companion text to the exhibit, 'Leonardo da Vinci, Codex Leicester: A Masterpiece of Science' ($49.95), published by the American Museum of Natural History, reproduces the Codex with synopses translated into English. 'Leonardo da Vinci,' a CD-ROM produced by Corbis Corp. ($50), focuses on the relationship of nature and science to art.