Samuel Pierpont Langley was an American author, astronomer, physicist and inventor. He was a director of the Allegheny Observatory and professor of physics and astronomy in the Western University of Pennsylvania. He was also the third secretary of the Smithsonian Institution.
Background
Samuel Pierpont Langley was born in Roxbury, Massachussets. He was the son of Samuel and Mary Sumner (Williams) Langley. His ancestors were almost exclusively of English stock, with some slight admixture of Welsh. Some of them emigrated to Massachusetts in the early part of the seventeenth century and experienced the struggles of the times. Among his forebears were Richard, Increase, and Cotton Mather, and Rev. John Cotton, and many men prominent in the history of Massachusetts--members of the Phillips, Sprague, Sumner, Howell, Williams, Pierpont, and Langley families. Among his less known ancestors were mechanics and artisans skilled in various trades, and substantial farmers, men of rugged health and severely upright moral fiber and probity. His father was a wholesale merchant of Boston, but a man of liberal interests. He had a small telescope with which the young Samuel and his brother John Williams watched the building of Bunker Hill Monument. The boys constructed a complete telescope for themselves, grinding and polishing the mirror to an excellent optical figure, and making the entire mounting. With this instrument they made many amateur observations of the heavens. The family were omnivorous readers, and Samuel, as a boy, made frequent use of the excellent public libraries of Boston. As a man he surprised his intimates by his wide knowledge of the English, German, and French classics, his historical research, and his acquaintance with works on astronomical, physical, and mechanical science.
Education
His formal education comprised attendance at several private schools, the Boston Latin School, and the Boston High School, from which he was graduated in 1851; but he had no college or university training.
Career
Langley was engaged in engineering and architecture from 1851 to 1864. In 1864 and 1865 he traveled in Europe with his brother John, visiting observatories and learned societies. In 1866 he was appointed assistant professor of mathematics in charge of the small observatory of the Naval Academy at Annapolis, but in the following year became director of the Allegheny Observatory and professor of physics and astronomy in the Western University of Pennsylvania, where he remained twenty years.
Allegheny Observatory needed funds exceedingly when Langley assumed charge. He devised a method of regulating railroad time from the Observatory clock, and persuaded the Pennsylvania Railroad to contract with the Observatory for this service. This arrangement inaugurated a practice which later became universal, and was the Observatory's principal source of revenue during Langley's directorship.
In his earlier years he made the classic drawings of sunspots that became standard textbook illustrations. He observed the total solar eclipses of 1869, 1870, and 1878, and made valuable observations. He also made careful visual studies of the solar spectrum, and was much in demand as a popular lecturer and writer on astronomical subjects. He had always been more interested in the new astronomy of the physical characteristics of the heavenly bodies than in the older astronomy of position.
To measure the distribution of heat in the spectrum of the sun he invented the bolometer (1878). This is an electrical thermometer, the sensitive element of which is a thin, narrow, blackened metallic tape, adapted to absorb radiation in very narrow bands of the spectrum, and sensitive to a rise in temperature of the millionth of a degree. With the bolometer he began at Allegheny Observatory an epoch-making series of experiments on the distribution of radiation in the solar spectrum, the transparency of the atmosphere to the different solar rays, and the enhancement of their intensity at high altitudes and even outside the atmosphere altogether. He devised a new method of determining the "solar constant of radiation, " that fundamental quantity which is the measure of the intensity of solar heat at mean solar distance.
Because of the turbidity of the atmosphere at Allegheny, he organized in 1881 an expedition to the then wilderness of Mount Whitney, California, the highest mountain in the United States. This famous expedition was under the auspices of the War Department, but was aided by the Pennsylvania Railroad and by Langley's lifelong friend, William Thaw of Pittsburgh. In the clear atmosphere of Mount Whitney, Langley and his able assistant, James E. Keeler, measured the energy of solar radiation with the bolometer and carried the solar spectrum far beyond the then recognized limit in the dark regions beyond the red. Computations of the solar constant were made from the observations both at Lone Pine and Mountain Camp, and valuable new results on atmospheric transparency resulted. By an unfortunate error of theoretical deduction the value of the solar constant was stated as 3. 0 calories per square centimeter per minute, a value long quoted in textbooks, although the observations themselves, properly reduced, indicated approximately 2. 0 calories, which was very near the accepted value.
After his return from Mount Whitney, Langley employed the bolometer in studies of the deep infrared spectra of the sun and the moon, and of heated bodies. His work on the lunar spectrum led to determinations of the lunar temperature of the same order as, though somewhat lower than, those eventually preferred. In his later years at Allegheny, he did considerable popular lecturing and writing on astronomical subjects. Some of these lectures were published by the Century Magazine, and later collected in a book entitled The New Astronomy (1888), which passed through several editions and became a classic in astronomical literature. It is difficult to exaggerate its charm which culminates in a whimsical parable on the last page.
On January 12, 1887, Langley was appointed assistant secretary of the Smithsonian Institution in charge of library and international exchanges. When Secretary Spencer F. Baird died later in the same year, Langley was elected to succeed him (November 18, 1887), and retained the position until his death. Like his predecessors and those who came after him, he felt keenly the hampering poverty of this great institution. There was a misapprehension in the public mind that the Smithsonian was a government bureau liberally supported by public funds. This probably grew from the fact that the Institution administed eight important government bureaus, and fostered them in their early years from its private funds. In fact it was a private foundation under government guardianship. Its great mission, as stated by its founder, James Smithson, was "the increase and diffusion of knowledge among men. " Nothing could be broader in science than this object. The worldwide prestige of the Institution brought opportunities for accomplishments which the slenderness of its disposable income precluded.
The first considerable addition to Smithson's original foundation of $550, 000 occurred during Langley's administration. This was a bequest of $200, 000 from Thomas Hodgkins of Brooklyn. Among Langley's important administrative works were the establishment of the National Zoological Park and the Astrophysical Observatory. At this Observatory, which was founded in 1890 by private funds, he carried forward his studies of solar radiation. He introduced continuous photographic registration of the indications of his bolometer, and in this way he was able to feel out the positions of Fraunhofer and terrestrial absorption lines in the infrared solar spectrum. A map of this hitherto unknown dark region of spectrum was prepared under his direction, extending to a wavelength of 5. 3 microns, or ten times the wavelength of green light. The favorable total solar eclipse of May 1900 was observed by Langley and others of the Astrophysical Observatory at Wadesboro, North Carolina. On that occasion the bolometer was first used to measure the heat of the solar corona. Soon after, his attention was again turned to the solar constant of radiation.
Early results of 1903 indicated solar variability, and Langley cautiously announced these observations in the year 1904. This subject largely engrossed the Observatory after Langley's death. Expeditions have been sent to foreign lands, and much progress has been made towards realizing his vision. Shortly before leaving Allegheny Observatory, Langley commenced the series of investigations into the possibilities of flight in heavier-than-air machines which he continued with conspicuous results at Washington. The greatness of his contribution to aviation depends not only on his pioneering laboratory investigations and successful long-distance flights of large power-driven models, but on the very fact that a man of his reputation should have adventured it in a field at that time so much ridiculed. He devised and constructed novel instruments for measuring lift and drift of the moving plane surfaces which he carried at considerable speeds on long-armed whirling tables. In 1891 he published results of these investigations under the title "Experiments in Aerodynamics" (Smithsonian Contributions to Knowledge, vol. XXVII).
In "The Internal Work of the Wind", published in 1893, he suggested reasonable explanations of the source of power used in the flight of birds. He then proceeded to incorporate his established principles of flight in power-driven models of about fourteen feet span, built on the general plan of the four-wing dragonfly. He used curved supporting surfaces in all of his machines, though the experiments which led him to this improvement are unpublished. (Herring and others have claimed that Langley did not employ curved wings prior to 1895. The original notebooks, still at the Institution, show that Langley employed parabolic curvatures of 1 to 12 camber, alternately with planes, in his wing models as early as the spring of 1894. ) It was necessary to devise light engines as well as wing surfaces, and he constructed petrol-heated, flash-boiler steam engines of about five pounds weight per horsepower for this purpose. The light gasoline engine did not then exist.
On May 6, 1896, Langley's model No. 5, thus equipped, was catapulted from a houseboat at Quantico, on the Potomac, and flew with excellent stability for a distance of 3, 000 feet, resting quite uninjured on the water when the propellant was entirely exhausted. In November of the same year model No. 6 made the even longer successful flight of 4, 200 feet. These were the first sustained free flights of power-propelled heavier-than-air machines ever made. They attracted worldwide fame and enthusiasm. Nevertheless, he was persuaded to undertake the construction of a man-carrying airplane, for which the War Department Bureau of Ordnance appropriated $50, 000. Not only was the large machine built and equipped with a five-cylinder radial water-cooled gasoline engine developed by Langley's assistant, Charles M. Manly, but a quarter-size model of about the same dimension as Langley's steam-driven models was also prepared with a gasoline engine of similar design.
This fourteen-foot model flew without pilot and with good stability on August 8, 1903, for approximately 1, 000 feet. The large machine was twice tried, on October 8 and December 8, 1903, catapulted from a large houseboat on the Potomac. On both occasions, according to the testimony of Manly and others, defects in the operation of the launching device brought disaster. On the first trial the front part of the machine apparently caught on a projecting pin, the front wings were deflected downwards, and despite all that could be done with the rudder, the machine plunged into the water 150 feet from the houseboat. On the second trial the rear wings collapsed, and the machine soared upwards, turned a complete somersault, and fell back near the houseboat. Newspaper ridicule and misunderstanding were added to failing health, exhausted funds, and vexatious administrative cares, and Langley failed to push forward by new trials to a successful issue.
Yet he said after the December trial: "Failure in the aerodrome itself or its engines there has been none; and it is believed that it is at the moment of success, and when the engineering problems have been solved, that a lack of means has prevented a continuance of the work" (Annual Report of the Board of Regents of the Smithsonian Institution, 1904, 1905, p. 125). This view has the great weight of the considered judgments expressed in written statements, public or private, by Manly, Chanute, Curtiss, Zahm, Ames, Taylor, and Durand. The large machine, restored, is now on exhibition with the earlier models in the United States National Museum. An exhaustive account of it is given by C. M. Manly in the "Langley Memoir on Mechanical Flight" (Smithsonian Contributions to Knowledge, vol. XXVII), published in 1911.
He was a member of the National Academy of Sciences, a correspondent of the Institute of France, foreign member of the Royal Society of London, of the Royal Society of Edinburgh, and of the Academia dei Lincei of Rome.
Of his many valuable publications perhaps the most important are: "Minute Structure of the Solar Photosphere" (American Journal of Science and Arts, February 1874); "The Bolometer and Radiant Energy" (Proceedings of the American Academy of Arts and Sciences, vol. XVI, 1881); "The Selective Absorption of Solar Energy" (American Journal of Science, March 1883); "Experimental Determination of Wavelengths in the Invisible Prismatic Spectrum" (Ibid. , March 1884); "Researches on Solar Heat and its Absorption by the Earth's Atmosphere: A Report of the Mount Whitney Expedition" (Professional Papers of the Signal Service, no. XV, 1884); "The New Astronomy" (Century Magazine, 1884 - 85); "On the Temperature of the Surface of the Moon" (Memoirs of the National Academy of Sciences, vol. III, pt. 1, 1885); "Observations on Invisible Heat Spectra and the Recognition of Hitherto Unmeasured Wavelengths" (Proceedings of the American Association for the Advancement of Science, 1885, and American Journal of Science and Arts, January 1886); "On Hitherto Unrecognized Wavelengths" (London, Edinburgh and Dublin Philosophical Magazine, and American Journal of Science and Arts, both August 1886); "The Temperature of the Moon" (Memoirs of the National Academy of Sciences, vol. IV, pt. 2, 1889); "Energy and Vision" (American Journal of Science and Arts, November 1888); Annals of the Astrophysical Observatory of the Smithsonian Institution, vol. I, 1900; "The Solar Constant and Related Problems" (Astrophysical Journal, March 1903).
His death occurred at Aiken, South Carolina, in his seventy-second year.
Views
Quotations:
Langley wrote about his childhood: "I cannot remember when I was not interested in astronomy. I remember reading books upon the subject as early as at nine, and when I was quite a boy I learned to make little telescopes, and studied the stars through them. . One of the most wonderful things to me was the sun, and as to how it heated the earth. . I asked many questions, and some of these childish questions have occupied many years of my later life in answering" (Goode, post, pp. 203-04. )
Personality
In mature life Langley was a large man of florid countenance, who concealed a deep-seated shyness by a front of dignity. Irascible, often giving offense, he yet revealed to his intimates a great charm of character. He was witty, apt of speech and quotation, warm-hearted, a lover of children, and impressed all who knew him as a man of large pioneering mind, ornamented with the graces of familiar intercourse. He had unusual facility in freehand and mechanical drawing. His writing was like copperplate, and his signature was a thing of beauty. He spoke fluent French, and was accustomed to make yearly trips abroad, where his reputation was justly very high in scientific circles.