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When David Hockney visited a 1999 exhibition at London's National Gallery of paintings by the early 19th-century French neoclassicist Jean-Auguste-Dominique Ingres, the uncanny accuracy of Ingres's portraits startled him. He began to wonder: Had Ingres used some sort of optical aid to render minute facial features so precisely? Hockney subsequently examined paintings by other masters and surmised that artists began using rudimentary forms of optical devices as early as the 15th century, nearly 200 years before Galileo and the emergence of the telescope.

In his new book, Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters, Hockney explores the revolutionary implications of his theory. The early use of optical aids by artists—earlier, even, than their use by scientists—could account for the sudden, dramatic improvements in the rendering of perspective and proportion and for the remarkable transformation in the realistic appearance of portraits that occurred at the beginning of the 15th century. Some art mavens have scoffed at the idea that the genius of some Renaissance masters may have been augmented by rudimentary optical technology. But Hockney has diligently amassed an impressive body of scientific, as well as historical, evidence to support his case.

To test his theory, Hockney solicited the help of physicist Charles Falco, a professor of optics at the University of Arizona, who systematically analyzed key measurable distortions in early paintings. "The images themselves are the evidence, if you know how to read them," says Falco. For instance, in Lorenzo Lotto's late Italian Renaissance painting Husband and Wife (circa 1543), the geometric pattern of the tablecloth loses focus as it recedes into the painting, and oddly, there are two vanishing points clearly visible in the detail of the fabric's border. "Had linear perspective been used, the pattern would have receded in a straight line, the single vanishing point corresponding to a single viewpoint," says Hockney. Instead, there is a kink in the pattern, which then continues in a slightly different direction. Hockney and Falco concluded that Lotto had used some sort of lens to project and trace the pattern of the cloth but then found he could not keep it all in focus at the same time; so he refocused the lens to complete the back portion of the cloth, changing the vanishing point, which he painted "out of focus" in an attempt to camouflage the process.

The earliest evidence of the use of optics that Hockney and Falco have discovered is in a 1431 sketch and portrait of Cardinal Niccolò Albergati by the Flemish artist Jan van Eyck. The subject's facial features are perfectly rendered. And although the finished painting is 41 percent larger than the sketch, when the latter is enlarged and laid over the painting, many key features line up exactly: forehead, right cheek, nose, mouth, eyes, and even laughter lines. Falco insists that to have scaled up the sketch so precisely, Van Eyck must have used an optical aid.

So what kind of optical devices did these early artists use? Later paintings offer some clues. The seemingly photographic manner in which the Dutch painter Jan Vermeer (1632-1675) recorded the soft play of daylight on various shapes and surfaces has prompted many art historians to speculate that he used a camera obscura. In its simplest form, this device is nothing more than a small hole in a shade or wall, through which light passes from a sunlit garden, for example, into a dark room, projecting an inverted image of the scene onto the wall opposite the hole. An artist could easily tack a piece of sketch paper to the wall and trace the key outlines of the subject, then complete the painting from life. Hockney suggests that Ingres (1780-1867) most likely used another innovation, the camera lucida, which consists of a prism mounted on a stick that can be attached to a drawing table. The camera lucida is more portable than the camera obscura and allows the artist to work in direct sunlight as opposed to a darkened room. However, it is notoriously difficult to use, since it doesn't actually project an image of the subject onto paper; the image seems to appear on the drawing surface only when the artist looks into the prism. A slight movement of the head will cause the image to move also, disrupting the accuracy of the tracing.

But neither the camera obscura nor the camera lucida existed until the late 16th century—after Lotto and Van Eyck had stopped painting. Hockney was at an impasse until Falco chanced to comment that a concave mirror has all the optical qualities of a lens and can also project an image onto a flat surface. Small pocket mirrors and spectacles first appeared at the end of the 13th century, and Hockney reasoned Van Eyck and his contemporaries most likely owned such "mirror lenses" and might have used them in their work.

To see whether this idea was plausible, Hockney created a small, makeshift window in his studio and asked a portrait subject to sit just outside in the bright sunlight. He then placed a small shaving mirror opposite the window and darkened the room to improve clarity. The result was an inverted image of his subject projected onto a sheet of sketching paper mounted next to the window, from which the outlines of the portrait could easily be traced.

In Hockney's view, the notion that some early painters used optical aids does not diminish their artistic achievement. The manipulation of devices like the camera lucida for tracing purposes requires a great deal of skill, he says, and did not produce impressive results in the hands of less skilled artists. Falco agrees. "In the end, optics are just a tool, the way a paintbrush and palette are tools," he says. "I always thought Van Eyck was a genius; I underestimated him."


Pride of the PequotsA Native American museum rises above a history of bad blood

Native Americans have had a contentious relationship over the years with archaeologists and anthropologists who have dug up Indian graves and collected sacred relics in the name of science. The triumph of the Mashantucket Pequot Museum and Research Center ( near Mystic, Connecticut, is that it transcends any lingering enmities between the guardians of tribal traditions and the scientific community. The $193 million museum was built by the Mashantucket Pequots using profits from the tribal-run Foxwoods Resorts Casino, and its exhibits are based on solid scientific research. "The archaeology that is being done here is sponsored by the tribe," says Jack Campisi, the director of the museum. "That brings a sense of cooperation."

Pequot warriors [A] were no match for the British, who methodically massacred the tribe in 1637.

During the 1640s, tribal leader Robin Cassacinamon [B] helped the Pequots restore their tribal identity.

In the game of hubbub [C], players scored when chips landed same side up.Photographs courtesy of Mashantucket Pequot Museum and Research Center

The centerpiece of the museum is a giant 22,000-square-foot re-creation of a 16th-century Pequot settlement along the Connecticut coast. Visitors wander beneath artificial trees and walk beside streams frozen in time, seeing, hearing, even smelling (thanks to wooden building materials and scent generators) a Pequot village rendered life-sized. The diorama's power lies in the accuracy of its details, gleaned from an extensive archaeological and historical record. Inside one of the wigwams, a black wolf's pelt lies draped over a bed; one of the few marks of rank among the Pequot, the fur signifies that the dwelling belonged to a sachem, or tribal leader. A returning fisherman seated in a canoe holds up his catch; the front of his head is plucked bare of hair—one of the elaborate hairstyles preferred by young Pequot men. Current tribal members modeled for the 51 plaster figures of villagers, lending an additional level of authenticity to the exhibit.

The museum has vigorously encouraged academic rigor and intellectual freedom among its scholars, with the unusual result that several exhibits offer multiple perspectives—drawn from a wide range of sources—about critical events in tribal history. In 1636, the murder of a trader sparked a bloody two-year war with the English that nearly drove the tribe to extinction. Yet the incident is recounted in three distinct versions—through the eyes of the Pequot, the English, and the Dutch, all of whose actions led to the devastating conflict.

After the war ended in 1638, most of the 1,500 surviving Pequots were divided as slaves among the English and two tribes allied with the Europeans—the Mohegan and the Narragansett—and were gradually assimilated into these cultures over the next three centuries. Dispersed throughout New England, they became farmers, soldiers, and whalers. A Pequot reservation was established near Mystic in 1666, but it was not until the 1970s that tribal members returned to fight for federal recognition as a sovereign Indian nation. Granted in 1983, this designation gave them the legal basis to operate the Foxwoods casino.

This most recent chapter in the tribe's 11,000-year history is exhibited in several rooms overlooking their ancestral lands. In one gallery sits a yellow house trailer similar to the ones occupied by the first returning Pequots as they resettled their land. Nearby is an old blue Smith-Corona typewriter used by former tribal chairman Richard Hayward to write letters and wage a legal battle against the U.S. government as the Pequots rebuilt their tribe one person at a time. It is an artifact as important to their story as any dug from ancient campsites. Louis Porter


Bidding Farewell to the Strange and WondrousA Gap in Nature: Discovering the world's extinct animals Tim Flannery and Peter Schouten Atlantic Monthly Press, $34.95.

Hang a bird feeder out a New York City window, and you'll get a pretty drab collection of pigeons, mourning doves, finches, and sparrows. But if you had hung one out 200 years ago, you might well have attracted droves of gorgeous parakeets, with dazzling green wings and red-and-yellow heads. The Carolina parakeet thrived throughout the eastern United States when Europeans first settled there. Looking at orchards filled with their flocks, John James Audubon wrote that they "present to the eye the same effect as if a brilliant coloured carpet had been thrown over them."

Those splendid carpets are gone. The forest homes of the parakeets were logged and fragmented, while hunters killed them as pests. By the early 1900s, their numbers had dwindled down to one—a male Carolina parakeet named Inca living in the Cincinnati Zoo. When Inca died in 1918, the species passed into extinction.

A Gap in Nature recalls to life—if only in the imagination—the Carolina parakeet and more than 100 other species known to have gone extinct at the hand of man. The book is a strangely guilty pleasure. The large-format paintings by Peter Schouten are elegant and inviting, and the text, written by the Australian biologist Tim Flannery, is full of so many delightful details that you might believe for a moment that you're reading a field guide to animals still among us. But A Gap in Nature is a field guide to the disappeared, including such fabled creatures as the Tasmanian wolf, Steller's sea cow, the dodo, and countless others.

The animals featured in A Gap in Nature are "the tip of the extinction iceberg," writes Flannery. He and Schouten limit their selection to extinct birds, mammals, and reptiles, even though frogs, fish, bivalves, insects, plants, and many other groups of species have suffered extinctions as well. Island species are particularly common in the book, for two reasons: Scientists can observe their decline closely and be very confident of their extinction. Even sadder, island species are particularly vulnerable because their habitat is small and easily disturbed by deforestation, hunting, and alien fauna introduced by humans.

Mainland species that are limited to small ranges have also suffered because of close proximity to humans. Gone are India's pink-headed duck, Australia's rat kangaroo, and South Africa's bluebuck. Scientists predict that many more mainland species will follow them to oblivion. Some estimate that half of all species will disappear in the next century. If a revised edition of A Gap in Nature appears in 2101, it will be a fearsomely huge book. Carl Zimmer

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For a detailed history of the Pequots, see Find a chronology of the Pequot war, complete with diagrams of the attacks, at ~rmccaugh/earlyAC/ lecture_notes/pequotle.html.

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