Henry Augustus Rowland

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(b. Honesdale, Pennsylvania, 27 November 1848; d. Baltimore, Maryland, 16 April 1901)


Rowland was the son of Harriette Heyer, the daughter of a New York merchant, and Henry Augustus Rowland, Sr., who, like his father and grandfather before him, had gone to Yale and entered the Protestant clergy. In the spring of 1865 Rowland’s mother (now a widow) enrolled him in the Phillips Academy at Andover, evidently as a first step toward Yale and the ministry; but Rowland had been an avid chemical and electrical experimenter as a boy, and he wanted to study engineering. In the fall of 1865 he went to the Rensselaer Polytechnic Institute, where, after developing a distaste for a career in the business world, he resolved to devote himself to science. In 1870 he graduated with a degree in civil engineering and then spent a year as a railroad surveyor and another year as a teacher at the College of Wooster in Ohio. In 1872 he returned to Rensselaer as an instructor of physics.

Rowland’s first major research was an investigation of the magnetic permeability of iron, steel, and nickel. In order to determine this quantity, he set up toroidal transformers made of each of the three metals in question, broke or reversed the direct current in the primary windings, and measured the charge that flowed in the secondary circuit. Plotting the permeability against what he thought was the induced magnetic field, B, for each of the metals, Rowland found that a general mathematical function could be fitted to all the curves; but by using the toroidal arrangement, he had actually measured ΔB rather than B. His data were distorted by effects of hysteresis unknown to him, and it is clear from modern theories of ferromagnetism that his mathematical function had no physical significance. Rowland had proved that—contrary to the assumption then common in the literature on ferromagnetism—magnetic permeability varied with the “magnetizing force,” H and, hence, with B. His work on the subject won the praise of Maxwell and established his reputation as one of the most promising young experimental physicists in the United States.

In 1875 Rowland accepted the chair in physics at the new Johns Hopkins University and went to Europe for a year to inspect various laboratories and purchase apparatus. He traveled widely, discussed contemporary physics with many leading practitioners of his discipline, including Maxwell, with whom he became good friends, and Helmholtz, in whose laboratory he spent four months. Rowland spent about $6,000 on apparatus for the Hopkins physics laboratory, emphasizing equipment suited for research rather than for teaching demonstrations. By the late 1870’s the Hopkins facility was far better equipped than any other American or even many European laboratories. In part because of his European trip, Rowland kept in touch all his life with developments in physics abroad, which was unusual for an American physicist of his day. He regarded himself as midway between an experimental and mathematical physicist and often tried to focus his experimental efforts on problems of theoretical import.

In 1868, stimulated by his study of Faraday’s Electrical Researches, Rowland conceived an experiment to test whether the magnetic effect produced by electric current was the direct result of charge moving through space or of some interaction between the current and the conducting body. Performing the experiment while in Helmholtz’ laboratory, Rowland used a charged vulcanite disc with an astatic needle suspended above it to register magnetic effects. He found no magnetic effects in the arrangement for the interactive case, in which the charge was held stationary while the disc was made to rotate. But he did detect magnetic effects when the charge was allowed to rotate with the disc, and the motion of the astatic needle correlated with the rotational sense of the current. Though not decisively in favor of one or another of the prevailing electrical theories, Rowland’s experiment was the first, as Helmholtz reported to the Berlin Academy of Science, to demonstrate that the motion of charged bodies produced magnetic effects.

Like his studies of permeability, Rowland’s subsequent work was characterized by meticulous attention to experimental detail and remarkable mechanical ingenuity. In the late 1870’s he established an authoritative figure for the absolute value of the ohm. At the opening of the 1880’s, he painstakingly redetermined the mechanical equivalent of heat and conclusively showed that the specific heat of water varied with temperature. Then Rowland turned to the work for which he is best known, the invention and ruling of the concave spectral grating.

The range, resolving power, and accuracy of a grating were determined respectively by the number, density, and regularity of its rulings. Lewis Rutherfurd, an amateur astronomer in New York City, had managed to rule up to two square inches of metal with thirty thousand lines per linear inch, but his gratings were inaccurate. Rowland recognized that to make a grating of highly uniform line-spacings, one needed an exceedingly regular drive screw in the ruling engine. He found that he could manufacture a nearly perfect drive screw from a roughly cut screw simply by grinding it in an eleven-inch-long nut which, split parallel to its axis, was clamped over the screw. With the problem of the screw overcome, Rowland could rule up to forty-three thousand lines per inch on more than twenty-five square inches of metal and, hence, construct gratings of unprecedented accuracy and resolving power.

Rowland saw numerous advantages in ruling his gratings on a spherically concave grating rather than on a flat surface. Since such gratings were self-focusing, they eliminated the need for lenses, in which the glass absorbed infrared and ultraviolet radiation. More important, the optical properties of a concave grating permitted a vast simplification in the observation of spectra. Consider a circle drawn tangent to the inner face of the grating with a radius equal to half its curvature. Wherever on the circle the source was placed, its spectrum would come to a normal focus at an eyepiece placed at the opposite end of a diameter from the grating. If the eyepiece was fixed at that point, the focus of the apparatus had to be set only once. By moving the source, one could quickly read off the wavelengths of numerous spectral lines from a scale on a chord of the circle, easily photograph the spectrum of one element superimposed on that of another element, or reliably determine line intensities even in the infrared region.

The concave grating reduced the work of days to a few hours, and Rowland sold over 100 of them at cost to physicists throughout the world. In the 1880’s Rowland remapped the solar spectrum; his wavelength tables, which were ten times more accurate than their best predecessors, became the standard for over a generation. At the Paris Exposition of 1890 his gratings and map of the solar spectrum received a gold medal and a grand prize. Rowland’s numerous other professional honors included appointment as a delegate of the United States government to various international congresses on the determination of electrical units. He became a foreign member of the Royal Society of London and the French Academy of Sciences and was elected to the National Academy of Sciences, which awarded him its Rumford and Draper medals. He was a founder and also the first president of the American Physical Society.

In 1883, as vice-president of the American Association for the Advancement of Science, Rowland delivered a celebrated address, “A Plea for Pure Science,” in which he disparaged technological invention and called upon his fellow countrymen to do more to foster basic research. But near the end of his life Rowland became an inventor himself. In 1890 he married Henrietta Troup Harrison. Not long afterward it was discovered that he had diabetes, and, eager to assure the future of his family, he worked on the development of a multiplex telegraph. Although technically successful, the system had not proved to be feasible commercially by the time of his death. In accordance with his express wish, Rowland’s ashes were interred in the wall of the basement laboratory, where the engine with which he ruled his gratings was housed.


A sizable collection of Rowland’s personal papers and scientific notebooks (1868–1901) is at the Johns Hopkins University, and he left about 100 letters (1865–1884) with his daughter, Harriette H. Rowland. Numerous letters from Rowland exist in the papers of his good friend, Edward C. Pickering, in the archives of Harvard University.

Rowland’s published writings and addresses are in The Physical Papers of Henry Augustus Rowland (Baltimore, 1902), which includes a biographical introduction by Thomas Corwin Mendenhall. John David Miller, “Rowland and the Nature of Electrical Currents,” in Isis, 63 (1972), is indispensable. Other useful treatments of Rowland include J. S. Ames, “Henry Augustus Rowland,” in Dictionary of American Biography, 8 (1935), 198–199; and Samuel Rezneck, “The Education of an American Scientist: H. A. Rowland, 1848–1901,” in American Journal of Physics, 28 (1960), 155–162, and “An American Physicist’s Year in Europe: Henry Rowland, 1875–1876,” ibid., 30 (1962), 877–886.

Daniel J. kevles

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Henry Augustus Rowland

The American physicist Henry Augustus Rowland (1848-1901) made fundamental contributions to magnetism and to celestial physics.

Henry Augustus Rowland was born on Nov. 27, 1848, in Honesdale, Pa., the descendant of a long line of clergymen. He studied at Phillips Academy, Andover, Mass., and then graduated from the Rensselaer Polytechnic Institute with a degree in civil engineering. During the next 2 years he did some work in his profession and taught natural science at Wooster University, Ohio. In the spring of 1872 he returned to Rensselaer as instructor in physics. While at Rensselaer he published an important paper on magnetism which brought him favorable attention from the English physicist James Clerk Maxwell and an appointment as professor of physics at the newly established Johns Hopkins University, designed to be the model of a graduate school. This early paper brought lasting fame to Rowland, for it proved to be the starting point for all calculations for the design of dynamos and transformers.

One of Rowland's first actions upon arrival at Johns Hopkins was the development of a workshop in which the apparatus for fundamental research could be produced; the machines that he himself devised were among his most valuable contributions to science. Becoming interested, for example, in the spectrum of the sun and the spectra of the elements, he designed a ruling machine to produce gratings for spectrum analysis more accurate than any previously known. Dissatisfied with the results obtained with the plane gratings of Joseph von Fraunhofer and Ernest Rutherford, he combined the principle of the grating with that of the concave mirror, eventually producing concave gratings of about 100,000 lines of 6 inches in length. With these superb diffraction gratings which split light into its components, he mapped the solar spectrum more thoroughly than anyone before him had done. Making possible the direct photography and higher resolution of spectra of the heavenly bodies, this work started a new era in spectroscopy.

In the field of measurements, in addition to his work on spectra, Rowland obtained long-accepted values for the mechanical equivalent of heat, the ohm, and the ratio of the electric units and the wavelengths of various spectra. In most cases, he designed his own measuring instruments.

Although Rowland had an engineer's training and always remained interested in practical applications—among his inventions was a printing telegraph and several other commercial instruments—he was primarily known as an ardent campaigner for the importance of basic research, and from his post at Johns Hopkins he trained many students who were imbued with this viewpoint. He was the first president of the American Physical Society. Rowland was married to Henrietta Troup Harrison of Baltimore in 1890. He died of diabetes on April 16, 1901.

Further Reading

The only biographical account of Rowland is Thomas C.Mendenhall's memoir, which appears in Mendenhall's edition of The Physical Papers of Henry Augustus Rowland (1902), in the Biographical Memoirsof the National Academy of Sciences, vol. 5 (1905), and is reprinted in Bessie Zaban Jones, ed., The Golden Age of Science: Thirty Portraits of the Giants of 19th-Century Science by Their Scientific Contemporaries (1966). A profile of Rowland and an interesting selection of documents and letters are in Nathan Reingold, ed., Science in Nineteenth-century America: A Documentary History (1964). □

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Henry Augustus Rowland


American physicist who designed precise scientific instruments. A civil engineering graduate of Rensselaer Polytechnic Institute, Rowland researched the magnetic behavior of metal. As Johns Hopkins University's first physics professor, he demonstrated that electric charges in motion display magnetism. He refined values for units of electrical resistance and mechanical heat. The ruling engines and concave diffraction gratings he invented enabled scientists to assess an object's physical characteristics more accurately. Rowland won awards for the solar spectrum maps his apparatuses made possible.