Samuel Pierpont Langley
(22 Aug 1834 - 27 Feb 1906)
Samuel Pierpont Langley
By William F. Magie
Professor of Physics in Princeton University
from Chautauquan (1906)
[p.237] THE life of the subject of this sketch, like the lives of most men of science, was marked rather by achievements than by events. In its main outline it may be briefly told. Samuel Pierpont Langley was born in Roxbury, Massachusetts, August 22, 1834. He was educated in the Boston Latin School and the Boston High School. He did not go to college but prepared himself for civil engineering and architecture, the two kindred professions to which he was led by the strongly marked features of his mind, scientific ability and artistic interest and taste. He practised these professions for several years in Chicago and St. Louis, but finally abandoned them to devote himself to science. After two years spent as assistant in the Harvard Observatory, and a year spent as assistant professor of mathematics and director of the observatory in the Naval Academy at Annapolis, he was called to the professorship of astronomy and physics in the Western University of Pennsylvania at Pittsburg and to the directorship of the Allegheny Observatory. There he remained until, twenty years later in 1886, he became assistant secretary of the Smithsonian Institution. In August, 1887, after the death of Professor Spencer Fullerton Baird, the second secretary of the Institution, he was appointed to succeed him in the secretaryship. In this post he remained until his death on February 27, 1906. The limits of this sketch forbid the notice of the minor [p.238] discoveries and inventions of Langley made during his long and active scientific career, and restrict us to the consideration of the main lines of work with which his name will always be associated. These are three in number: the study of the solar surface and of radiant energy; the development of the work of the Smithsonian Institution; and the study of the problem of aerial navigation.
Before entering upon these topics, mention should be made of the great practical service rendered by Langley in the introduction of a uniform system of time for the railroads of the country. When he went to the Allegheny Observatory he found there a fine telescope, but no accessory instruments or appliances to render it useful in scientific work. The observatory did not possess even a suitable clock. He conceived the idea of obtaining these necessary instruments by interesting the managers of the great railroads which converge in Pittsburg in the question of standard time. By his persuasive insistence he succeeded in accomplishing his purpose. The railroads adopted his plans for the dissemination of standard time by signals from his observatory, and furnished him the equipment by which these plans were realized. The splendid time service of our present railroads is thus in a large measure Langley’s creation.
The first few years of Langley’s life in Pittsburg were devoted to the careful study of the solar surface. In those days the modern methods of dry-plate photography had not been invented, and for various reasons it was difficult, if not impossible, to apply the old wet-plate process to recording astronomical phenomena. Records were made by careful drawing based on visual observations. In making these records, especially of such appearances as those presented by sunspots, there was needed not only great accuracy of vision and skill in delineation, but a high degree of scientific sagacity to enable the observer to discriminate between the occasional, or as they may be called, accidental [p.239] phenomena presented by the particular object under observation, and the typical or universal features of it. Langley possessed the necessary qualifications for this sort of work in the highest degree, and the diagrams of the typical sunspots which he prepared are now, and perhaps will long remain the best delineations of the essential characteristics of those mysterious appearances.
The energy which comes to us from the sun and which we recognize as the sun’s light and heat, is transmitted through space by waves in the luminiferous ether. Just as in the case of the sound waves coming through the air from an orchestra or from a piano, the waves which transmit the tones of different pitch differ in length, so in the case of the light and heat from the sun, the waves which transmit it differ in length. If a narrow beam of white light is received on a prism of glass or of some other transparent substance, some of these waves are absorbed in the substance of the prism, and the rest are variously deflected by it, so that after emergence the narrow incident beam is spread out into a long band of radiance, the visible part of which exhibits the well known colors of the spectrum. By far the largest part of the radiance, however, is transmitted by waves which lie outside the range of visibility for the human eye. It is a question of the highest scientific importance to determine the extent of this invisible part of the spectrum, and especially to measure the proportion of the solar energy which each portion of the spectrum transmits. Most of the years which Langley spent at the Allegheny Observatory were devoted to the study of this question. At the outset of the investigation, it became necessary to invent an instrument by which the requisite observations could be made. What is needed is a receiving instrument which can be placed in the spectrum, so narrow that it is affected by only a small group of waves of nearly equal length, and sufficiently sensitive to indicate and to measure the radiant energy which falls upon it. Langley supplied [p.240] this need by his invention of the bolometer. The receiving part of this instrument is a narrow straight strip of the thinnest sheet iron or of platinum foil, which is joined up with wires in an electric current in such a way that its electric resistance can be measured. As the spectrum is usually formed, the light from the source comes through a narrow vertical slit, and is spread out by the prism into a long horizontal band. The strip of metal of the bolometer is set vertically somewhere in this band, and being narrow, receives upon its surface only the radiance caused by a small group of wave lengths. It is coated with lamp black so as to absorb practically all the incident energy. It thus becomes warmed and its electric resistance changes. By measuring this change in electric resistance, the amount of energy absorbed by the bolometer strip is determined.
With this instrument Langley made a systematic study of the distribution of energy in the solar spectrum. He found, as a principal result of his inquiry, that by far the largest part of the solar energy, ninety-nine per cent, in fact, is transmitted by waves too long to be visible, and he was able to determine the relative amounts of energy transmitted by waves of different wave length. He traced the spectrum from the dark red at the end of the visible spectrum for which the wave length is about 0.7 thousandths of a millimeter, to the wave length of 5.3 thousandths of a millimeter. He further studied the effect of atmospheric absorption on the light from the sun. This robs the incident light of about 30 per cent, of its energy, when the sun is in the zenith, and of about 75 per cent, when the sun is on the horizon. The absorption is selective in character, and one of the curious facts about it is that, in the visible spectrum, the violet and blue rays are proportionately more absorbed than the yellow and red rays, so that, if it were not for the effect of the atmosphere, the color of the sun would appear distinctly bluish.
It would be impossible to describe in the limits of this [p.241] article, the various special researches to which Langley applied the bolometer. He advanced it to such a degree of sensitiveness that a change of temperature of one hundred millionth of a degree Fahrenheit could be detected. With this sensitive instrument he studied the radiation from the moon, from sunspots and other celestial sources, and mapped the spectrum of the heat radiated from a block of ice.
While in the full tide of success in these researches, Langley was called to the secretaryship of the Smithsonian Institution. His distinguished predecessor in that office, Joseph Henry, once said of himself, when he was asked to accept it, “If I go, I shall probably exchange permanent fame for transient reputation;” and Henry’s successors, each in turn, have been forced to face that issue. Langley’s sense of duty was too strong to allow him to decline the post which was offered him, but he could not bear to break off entirely from his purely scientific work, and so endeavored for awhile to maintain an active connection with the Allegheny Observatory. He soon found it impossible to do this, but by his success in obtaining a grant for the Astrophysical Observatory at Washington, he was enabled to push on, under more favorable conditions, the work which he had so much at heart. His principal task, however, from the assumption of his new office in August, 1887, was to conduct the activities of the Smithsonian Institution along the course already marked out by his predecessors, and also to enlarge those activities in other ways in harmony with its general plan of organization.
The Smithsonian Institution is one of the most notable agencies in the world devoted to the promotion of science. It “Was founded upon a bequest by James Smithson, an English gentleman, interested in science, who was an original contributor to the science of chemistry, and a member of the Royal Society. He bequeathed the whole of his estate to the United States to found at Washington, under the [p.242] name of the Smithsonian Institution, “an establishment for the increase and diffusion of knowledge among men.” This bequest, amounting to $500,000, was received by the United States in 1838. For the time, this was a really magnificent foundation. Harvard College was the only educational institution in the country which was so liberally endowed.
For several years Congress was occupied with the consideration of plans for the organization of the Institution. It was variously proposed to found a university, an agricultural school, an astronomical observatory, a library, course of public lectures, and other institutions more or less compatible with the expressed intent of the donor. The act which finally passed in 1846 fortunately left the details of administration somewhat indefinite, thus allowing the first secretary to interpret the phrases of Smithson’s will, declaring the purpose of the foundation, in the broadest and most liberal way. The “establishment” consists of the President of the United States, the Vice-President, the Chief Justice and the members of the Cabinet. Its business is conducted by a Board of Regents, consisting of the Vice-President, the Chief Justice, three Senators, three Representatives, and six citizens, two of whom must be residents of the city of Washington. The Regents appoint the Secretary, upon whom the administration of the affairs of the Institution practically falls. Their first appointment was a most fortunate one, and determined forever the lines along which the Institution has developed into a most beneficent organization for the support of scientific investigation and the dissemination of scientific knowledge.
Joseph Henry, first secretary, was professor of physics in Princeton. He was distinguished as an original investigator. The improvements which he had made in the earlier forms of electro-magnets, and his studies of the proper construction of such magnets to be used with effect in long circuits, made possible the practical establishment of telegraphy. His discoveries in connection with the induced current, while they did not attract the same notice as the contemporary [p.243] work of Faraday, were equally fundamental and important. He was a man of a lofty and unselfish nature and of a serene temper. He was besides profoundly convinced of the importance to mankind of the increase of scientific knowledge, even when its practical relations are not immediately apparent. Bearing in mind the two-fold purpose expressed by Smithson in his will, he proposed a plan of organization by which these purposes have ever since been carried out. He proposed to “increase knowledge” by stimulating men of talent to make original researches, by offering suitable rewards for memoirs containing new truths, and by appropriating a portion of the income for particular researches; and to “diffuse knowledge” by publishing a series of periodical reports on the progress of the different branches of knowledge, and also separate treatises on subjects of general interest. The publications which have been issued according to this plan, in the Smithsonian contributions to knowledge and the Smithsonian Miscellaneous Collections, consist of important original memoirs and admirable reports on the progress of science, made by recognized leaders in the respective branches of science. All branches of natural and physical science are sustained and assisted by the funds of the Institution. As was natural and proper, particular attention has been given to collecting and preserving everything of interest connected with the life of the aborigines on our continent, and the collections, made under the direction of the Institution or acquired by it for the National Museum, to illustrate the life and the past history of the American Indian are the most important in the world. The Institution also publishes memoirs and reports tinder grants from Congress in connection with the National Museum, the National Herbarium, the Bureau of Ethnology, and the Astrophysical Observatory. By a thoroughly organized system of exchange the memoirs of all important scientific societies the world over have been collected in the library of the Institution, now deposited in the Library of Congress.
[p.244] In fact, any scientific work or any publication which can be better undertaken by an endowed institution than by private effort comes within the province of the Smithsonian Institution and may be undertaken by it. Among these enterprises may be mentioned the inauguration, by Henry, of systematic and extensive observations of the weather for the purpose of weather prediction—the work now carried on by the weather bureau; the development, by Baird, of the National Museum; and the establishment, by Langley, of the National Zoological Park, and of the Astrophysical Observatory. The expense of these various undertakings is far greater than could be borne by the income of the original endowment, and is met by Congress by special appropriations.
The mere executive work demanded of the Secretary of the Smithsonian Institution is a sufficient burden for any man to carry; but Langley found time and energy to supervise the work done in the Astrophysical Observatory, and also to conduct important investigations in the field of aerial navigation. That a heavy body can be sustained in the air by the pressure of moving air against extended surfaces, is plain to anyone who has ever watched a hawk or buzzard soaring. The problem is to discover the conditions which make such flight possible, and to realize them with mechanism which can be constructed and controlled by man. Langley proceeded to investigate this problem in a thoroughly scientific way, by making elaborate experiments on the lifting force and resistance offered by plane surfaces of various shapes and set at various angles, when whirled rapidly through the air by means of a great whirling table. After ascertaining a number of facts and of general laws that are of importance to anyone attempting to secure artificial flight, Langley put them into application. He constructed four model “Aerodromes,” or flying machines, two of which made many successful flights. One of these was furnished with two pairs of broad planes as wings, [p.245] set outward from a central framework, somewhat as the wings of a soaring bird are set, and separated from each each other by a space in which was placed the motor and the propeller. The motor was a steam engine of wonderful lightness and efficiency. It gave between one and one and a half horse power and weighed only five pounds. When the machine was successfully launched, it sailed away in great curves, ascending higher and higher, until the motor stopped because of the exhaustion of fuel. It then settled down so gently that it was not in the least injured by the shock, but was ready at once for another trial. The distance covered in the longest flight was about 3,000 feet. After demonstrating in this way the possibility of artificial flight, Langley was content to consider his work done, and laid the subject aside; but he was induced to resume it again in 1898 at the request of the Board of Ordnance and Fortification of the United States Army. It was considered by that Board that a flying machine which could carry a man might be useful in time of war, and a grant of $50,000 was made for experiments directed toward the construction of such a machine. To this thankless and unremunerated task, Langley gave the last years of his life. The machine which was at last constructed, after many difficulties had been surmounted, failed to leave the launching platform properly, and was twice wrecked without really getting into flight at all. These failures, which were nothing more than the ordinary failures which occur in the course of the development of any complicated invention, were made the ground of adverse comment by the public and by speakers in Congress; and no further funds were supplied after the original grant had been expended. The experiments thus came to an end, but there is no good reason to doubt that, if they had been continued, the first self-propelling, man-carrying flying machine would have been due to Langley.