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Dapping Ducks and Drakes

That’s skipping stones to most of us. “To dap” is defined by the Oxford English Dictionary as “to rebound, bounce; to hop or skip (as a stone along the surface of water).” “Ducks and drakes” is the old English name for the pastime and can be referenced back to a 16th-century book written by humanist Hadrianus Junius. The age-old sport goes at least back to Homer of ancient Greece, who told of a shield-skipping challenge between Jason and Hercules.

Lichens on river stones, Iceland, South Coast. 1972 Mural of Thomas Jefferson in the Science and Business Reading Room, by Ezra Winter. 2007

Aside from the game’s storied past, what of the science? Haven’t you ever wondered how a stone skips across water? Spin, shape, speed and the “magic angle” are all crucial to success. Spin stabilizes the stone, which should be flat and round to work best. A minimum speed is required; otherwise the stone will hit the water and sink immediately. And, the “magic angle” between the spinning stone and the water should be around 20 degrees for maximum skip.

Of course, more detailed information can be found in applying concepts from physics, such as hydrodynamics, momentum and gravity. Rather than trying to explain it here, the Library’s Science, Technology and Business Division has skipping stone science featured as part of its Everyday Mysteries presentation. All of the questions presented on the site were asked by researchers and answered by librarians from the division’s Science Reference Services.

The Science, Technology & Business Division's primary responsibilities are to provide reference and bibliographic services and to develop the general collections of the Library in all areas of science, technology, business and economics. In addition, the division also maintains, services and develops its own specialized collections of technical reports, standards and international open-source materials in the same subject areas mentioned above. The scientific, business and technical materials for which the division has collection-development responsibility comprise roughly 40 percent of the Library's total book and journal collection.

Over the years, the division has produced more than 100 individual publications, ranging from indexes, chronologies, and definitive bibliographies on a particular subject, to interpretive written studies based on the Library's collections. These publications include the popular Science Tracer Bullet series, which are informal literature guides on topics of current interest, and “A Guide to Finding Business Information at the Library of Congress,” which is available from the Business Reference Services.

The institutional origins of the Science, Technology and Business Division can be found in this country's heightened awareness, following World War II, of the significant increase in the need for current, reliable, worldwide scientific and technical information. Established in June 1949 within what was then the Reference Department, the new Science Division provided a focal point for the acquisition and bibliographic control of the Library's rapidly growing international collections in science and technology. In 1998, the division's focus was dramatically expanded when the Science and Technology Division and the Business Reference Section (originally established as a part of the Library's Humanities and Social Sciences Division) were merged to form today's Science, Technology & Business Division.

However, science and business has been represented in the Library’s collections as far back as 1815, with the purchase of Thomas Jefferson’s personal library, which contained some 500 volumes in natural philosophy, agriculture, chemistry, zoology and technical arts, and an even larger number relating to economics and commerce. The collection was further enhanced with the Smithsonian Deposit of 1866—about 40,000 volumes of memoirs, transactions and periodicals of learned scientific societies, museums, exploring expeditions and observatories throughout the world—transferred from the Smithsonian Institution.

A. Lichens on river stones, Iceland, South Coast. 1972. Prints and Photographs Division. Reproduction Information: Reproduction No.: LC-USZC4-1972 (color film copy transparency); Call No.: PH - Porter (E.), no. 1-6 (Portfolio) [P&P]

B. Mural of Thomas Jefferson in the Science and Business Reading Room, by Ezra Winter. 2007. Prints and Photographs Division. Reproduction Information: Reproduction No.: LC-DIG-highsm-02752 (original digital file); Call No.: LOT 13907 [item] (ONLINE) [P&P]