Samuel Pierpont Langley

American astronomer, physicist, and aeronautical engineer

• Born: August 22, 1834
• Birthplace: Roxbury, Massachusetts
• Died: February 27, 1906
• Place of death: Aiken, South Carolina

Through pioneering research, Langley discovered new portions of the infrared spectrum, and his invention of the bolometer aided in spectral measurements of solar and lunar radiation. He also established the principles of flight and demonstrated the practicability of mechanical flight with self-propelled, heavier-than-air machines.

Early Life

Samuel Pierpont Langley was the son of Samuel Langley, a Boston merchant of English descent, and Mary Sumner Williams. The family background included intellectuals as well as skilled mechanics and artisans. As a boy, Langley played with his father’s telescope and, with his brother John, built a new telescope and made astronomical observations. In addition to astronomy, the flight of birds fascinated the young boy. Langley read extensively throughout his life and studied science, literature, and history. He was well read in the classics in several languages, including English, French, and German. Langley attended the Boston Latin School and Boston High School. He had a gift for drawing and an interest in mathematics, so, upon graduation in 1851, he turned his attention to civil engineering and architecture.

Rather than attending a university, Langley went to work for an architectural firm in Boston. In 1857 he moved west and worked as an architect and civil engineer for several years in both Chicago, Illinois, and St. Louis, Missouri. In 1864 he returned to New England, where he built a larger telescope with his brother from the ground up. He and his brother also went to Europe for one year and visited observatories, museums, and art galleries.

With this varied background and without university training, Langley began a career as a self-taught astronomer. Upon his return to the United States in 1865, the director of the Harvard College Observatory asked Langley to become an assistant. In 1866 Langley became an assistant professor of mathematics at the Naval Academy in Annapolis, Maryland, although his primary responsibility was as director of the observatory. In 1867 he became a professor of astronomy and physics at Western University in Pittsburgh, Pennsylvania, where for twenty years he taught and was the director of the Allegheny Observatory.

Life’s Work

Langley did most of his original scientific investigations during his years in Pittsburgh. To get funding for the Allegheny Observatory, he tried to make astronomy practical and profitable. He convinced the Pennsylvania Railroad Company that he could produce an accurate time-keeping system for its train personnel. At that time, these personnel had to change time every forty or fifty miles along the railroad lines. The observatory sent out a signal two times per day based on astronomical observations that gave the accurate time to all Pennsylvania Railroad stations. This arrangement provided complete funding for the Allegheny Observatory for many years and established a practice of standard time that later became universal.

During his tenure at Allegheny Observatory, Langley determined that current measuring instruments were not precise enough for his astronomical work. From 1879 to 1881 he developed and invented the bolometer, an instrument that accurately measures heat in small increments and enables astronomers to study the infrared region of the solar spectrum. The bolometer is basically an electrical thermometer. The sensitive element is a thin, blackened metallic tape adapted to absorb radiation in very narrow bands of the spectrum and with precision to one ten-millionth of a degree centigrade.

Langley undertook many survey expeditions and investigated eclipses, sunspots, and other astronomical phenomena. He also studied the solar spectrum. One of his most important expeditions was to Mount Whitney in California, the highest point in the United States at that time (1881). His team measured the energy of solar radiation with the bolometer and discovered infrared areas of the solar spectrum that were far beyond the spectral limit that was recognized at that time.

Langley’s research at the Allegheny Observatory also encompassed many fields: the distribution of radiation over the sun’s surface and in sunspots, the solar energy spectrum and its extension into the infrared, the lunar energy spectrum, spectra of terrestrial sources and determination of unmeasured wavelengths, absorption of the radiation of the sun by the earth’s atmosphere, and the determination of the solar constant of radiation. This research contributed to what was originally known as the “new astronomy” and is now called astrophysics. Rather than investigating the existence and position of astronomical bodies, Langley studied their physical characteristics—heat, light, and radiant energy.

In 1887 Langley also began research into aerodynamics. He formulated Langley’s law, which states that the faster a body travels through the air, the less energy is required to keep it aloft. Langley’s experiments showed that the work of the wind aids soaring flight, just as buoyancy aids swimming. He discovered principles of lift and resistance for rapidly moving surfaces in air.

In January, 1887, Langley joined the staff of the Smithsonian Institution as assistant secretary in charge of exchanges, publications, and the library. This position interested Langley because he had been somewhat isolated in western Pennsylvania. His move to the Smithsonian brought him to the center of the scientific community in the United States. By November, 1887, Langley had become the third secretary of the Smithsonian, a position he held until his death in 1906. Under his leadership, the Smithsonian expanded its areas of research with the National Zoological Park in 1890 and the National Gallery of Art in 1904. The museum also added a “children’s room” for science education. Langley’s key contribution to the Smithsonian as an institution was the founding of the Smithsonian Astrophysical Observatory in 1890, where he continued his work on solar radiation during the 1890’s.

Aerodynamics also continued to fascinate Langley. He built what he called an “aerodrome”—an unmanned flying machine with wide-spreading wings to sustain its flight while it was driven along by a gasoline-fueled, steam-powered engine. It had a wingspan of about 14 feet patterned after a four-winged dragonfly. On May 6, 1896, Langley sent up aerodrome model number 5, which landed safely after flying over one-half mile (3,000 feet) for about 90 seconds. On November 28 of the same year, a larger model traveled about three-quarters of a mile (4,000 feet). The two flights proved the practicability of mechanical flight and were the first sustained free flights of power-propelled, heavier-than-air machines.

Although Langley showed the scientific feasibility of mechanical flight, he wished to leave further development to commercial applications. However, under pressure from the U.S. government, he pursued experimentation on a model large enough to carry a human. In 1898 the U.S. War Department, with the Spanish-American War looming, allotted $50,000 to Langley to develop, construct, and test a large aerodrome. The Smithsonian added another $20,000 to the project. Langley intended simply to build a larger version of the models already flown and add a different engine. He eventually used an engine based on a design by Stephen Balzer and modified by Charles Manly, who had been working with Langley over the previous few years. Manly tested the manned machine himself.

On August 8, 1903, a 14-foot model flew without a pilot for about 1,000 feet. However, two tests of the full-sized, manned machine failed on October 7 and December 8 of 1903. In both cases, failure occurred during the launch rather than during flight. In scaling up the models, Langley had not accounted for the fact that the drag would increase exponentially. Langley’s last trial preceded the successful flight of the Wright brothers by only nine days. Langley’s tests were well publicized in newspapers, unlike those of the Wright brothers, and the reporters called the machines “Langley’s Folly.” Less than two years after the failed tests, in November, 1905, Langley had a stroke. For rest and convalescence, he traveled to South Carolina in early February, 1906. He suffered a second stroke there and died on February 27, 1906.

Significance

Samuel Pierpont Langley’s work in aerodynamics followed a different technical path from that of the Wright brothers, but his work was key to aviation development. The notion of heavier-than-air flight by humans had been ridiculed, but Langley’s research provided a scientific basis for experimentation in mechanical flight. Coming from a prominent member of the scientific community, Langley’s beliefs carried weight. In addition, Manly’s improvements to Langley’s engine turned it into the world’s first radial engine designed for flight, and it was the same basic engine used in aircraft through World War II.

Langley’s primary contributions were in the field of astrophysics, where he developed new apparatus and techniques for the measurement of radiation. With his invention of the bolometer, it became possible not only to identify radiant energy but also to measure it. Langley used the instrument to discover and explore new portions of the solar spectrum and measure the heat of sunspots, various parts of the sun’s disk, and the temperature of the moon. His experiments aided in determining the distribution of radiation in the solar spectrum, the transparency of the atmosphere to different solar rays, and the enhancement of their intensity at high altitudes. In 1947 his name was given to a new unit of measurement: The “langley” is defined as a unit of illumination used to measure temperature, equal to one gram calorie per square centimeter of irradiated surface.

Langley also contributed to the institutionalization and popularization of American science, particularly astronomy. His administration at the Smithsonian Institution also expanded the exchange and distribution programs for scientific research. Langley gave many public lectures and wrote essays on astronomical subjects in popular magazines of his day, including Popular Science Monthly, Atlantic Monthly, Century Magazine, and McClure’s. He also wrote a book called The New Astronomy (1888). Langley not only advanced science but also diffused and distributed new scientific knowledge to both specialists and the public.

Bibliography

Berliner, Don. Aviation: Reaching for the Sky. Minneapolis: Oliver Press, 1997. Contains a chapter on Langley and the aerodrome, while chapters on other aviation pioneers provide context for his aeronautical research. Includes illustrations, a glossary, and a chronology of aviation advances.

Crouch, Tom D. A Dream of Wings: Americans and the Airplane, 1875-1905. New York: W. W. Norton, 1981. Covers developments in American aviation, including several chapters on Langley. This work is the most complete research on Langley’s aeronautical contributions and includes an extensive bibliography.

‗‗‗‗‗‗‗. A History of Aviation from Kites to the Space Age. Washington, D.C.: Smithsonian National Air and Space Museum, 2003. One of numerous aviation histories published during the celebration of the centennial of flight. Includes information about Langley’s aerodrome and his other contributions to aeronautics.

Eddy, John A. “Founding the Astrophysical Observatory: The Langley Years.” Journal for the History of Astronomy 21 (February, 1990): 111-120. Contains a short, general biography of Langley with major emphasis on his astronomical research and administrative duties at the Smithsonian.

Hallion, Richard P. Taking Flight: Inventing the Aerial Age from Antiquity Through the First World War. New York: Oxford University Press, 2003. This aviation history book contains information about Langley’s research on and development of the aerodrome and other contributions to aeronautics.

Jones, Bessie Zuban. The Golden Age of Science: Thirty Portraits of the Giants of Nineteenth-Century Science. New York: Simon & Schuster, 1966. Contains a chapter on Langley and provides context for his research.

Meadows, A. J. Early Solar Physics. Elmsford, N.Y.: Pergamon Press, 1970. Contains an overview of the development of the new astronomy from 1850 to 1900, including Langley’s accomplishments. Also includes the writings of contemporary astrophysicists and a reference list with technical and scientific details.

Oehser, Paul Henry. Sons of Science: The Story of the Smithsonian Institution and Its Leaders. New York: Schuman, 1949. Includes a chapter on Langley that contains information on all of his various activities and accomplishments. Includes a selected bibliography.

Vaeth, J. Gordon. Langley: Man of Science and Flight. New York: Ronald Press Company, 1966. Short but complete biography of Langley written for nonspecialists. Includes a short bibliographical essay on sources.