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Johns Hopkins UniversityArts and Sciences Magazine

What the New World Brought to Science

Latitude is easy. Longitude is hard.

In the 16th century, Spanish cosmographers charged with charting the geography of the New World could easily rely on an astrolabe, an ancient astronomical instrument used to gauge the altitude of the sun and stars, to determine the latitude of a location. But longitude, which required a suitable timekeeper in an era 200 years before any existed, was much more difficult to determine.

While researching the work of early modern Spanish scientists for her dissertation, Maria Portuondo PhD '05 came across descriptions of a device—called the Instrument of the Indies—that helped provide a solution. Developed by Juan Lopez de Velasco, it was used from 1577 to 1588 in what is understood to be the first known large-scale systematic plan of astronomical observation. Velasco recognized that the eclipse is a global synchronizing event. And the portable, simply crafted wooden device worked like a sundial—except instead of measuring shadows cast by the sun, it measured shadows captured during lunar eclipses. These measurements were then calculated into longitude using spherical trigonometry and other mathematical methods.

"When I ran into this I was really astounded," says Portuondo, now an assistant professor in the Department of the History of Science and Technology and the author of Secret Science: Spanish Cosmography and the New World (University of Chicago Press, 2009). "It's very simple and yet it effectively solves the problem of determining the longitude of a particular place."

Some scholars might have stopped there, but not Portuondo. A former electrical engineer, she built her own Instrument of the Indies out of an old particleboard bookshelf and tested it in her Tuscany-Canterbury backyard during a lunar eclipse in October 2004. It worked. "My neighbors probably thought I was crazy but they knew I was a grad student, and they give you some leeway for that," says Portuondo, who observed the beginning of the eclipse with her neighbor, Ralph, and a bottle of Spanish sherry.

Portuondo was eager to know more. She wanted to see if the actual calculations the Spanish cosmographers derived made for an accurate reading of longitude. Using observations made in 1577, 1584, and 1588 between Madrid, Mexico City, and Puerto Rico that she found in the Archives of the Indies in Seville, Spain, Portuondo did the complex mathematical computations involved to determine longitude. She concluded that the Spanish cosmographers' calculations were correct. Results of her study were published in the August 2009 Journal for the History of Astronomy.

The Instrument of the Indies is just one of the advances made by early modern Spanish scientists that Portuondo examines in her book, which looks at how Spanish colonizers used cosmography, a humanistic science that became modern geography, to explain and understand the lands they discovered. "In the century following the discovery of the New World, the discipline of cosmography goes from a bookish, library-like way of describing the world to one that uses empirical, experimental, and observational methods we associate with the scientific revolution," Portuondo says. "This change provides a great example of what the New World brought to science."

During the 16th century, Spanish cosmographers developed entirely new methods for collecting geographical information—standardized navigation techniques, charts, maps, and detailed questionnaires that were used to survey inhabitants of faraway Spanish colonies. But because the information they collected was considered a state secret for much of the 16th century, many contributions went unpublished and largely unknown for centuries. "Spain does not feature prominently in the narrative of the scientific revolution, which is the defining moment of early modern science," says Portuondo. Instead, historical accounting focused on the achievements of scientists from Italy, France, and England.

Part of a small but growing group of historians who are looking at Iberian science during this period of history, Portuondo is working to place the contributions of early modern Spanish scientists into the narrative of the history of science. "This is not an argument that the scientific revolution started in Spain," she says. "I don't believe that it did. What this research shows is that you can set a preamble to that history."

Today, Portuondo's Instrument of the Indies sits on a top shelf in her faculty office on North Charles Street. "The last total lunar eclipse we had in February was cloudy," she says. "I'm waiting for the next one in 2010. I can't wait to use it again."

Samuel Iser

Maria Portuondo’s hand-constructed Instrument of the Indies has given her new insights into the work of 16th-century Spanish cosmographers.