2ea9
Henry A. Rowland, Johns Hopkins University’s first physics professor, has been called the finest physicist of his day, a brilliant experimentalist who did seminal work on electricity and magnetism. However, he is best remembered for the invention and ruling of concave spectral grating, an instrument of unprecedented precision and ease of use.
Henry Augustus Rowland was born in Honesdale, Pennsylvania on November 27, 1848, the son of the Rev. Dr. Henry Augustus (a Protestant clergyman who was the latest in a long line of theologians) and Harriet (Heyer) Rowland; grandson of the Rev. Henry A. and Frances (Bliss) Rowland; great-grandson of the Rev. David Sherman and Mary (Spaulding) Rowland, and a descendant of Jonathan Edwards, and of the Rev. John Warham, first minister of Windsor, Conn.
Henry’s great-grandfather had used his pulpit to denounce foreign oppression with such zeal that he had to flee the city during the American Revolution, when a British fleet invaded Providence. Young Henry was expected to follow suit, attending Yale University and entering the ministry, but he rebelled against family expectations. He was an avid chemical and electrical experimenter and wished to study engineering. His family ultimately relented and he enrolled at Rensselaer Polytechnic Institute in the fall of 1865.
Rowland graduated with a degree in civil engineering in 1870, and worked as a railroad surveyor and as a teacher at the College of Wooster in Ohio before returning to Rensselaer in 1872 as an instructor of physics. Whatever time he could spare from teaching he spent in research on magnetic permeability. His report on his work was rejected by the American Journal of Science, so he sent it to James Maxwell in Britain; Maxwell, impressed, had it published in London in the Philosophical Magazine.
Few people in the United States noticed the paper. Rowland grew increasingly disgusted with his situation at Rensselaer and with the difficulties of physics research in America generally. Later, in 1883, he told a meeting of the American Association for the Advancement of Science, “I here assert that all can find time for scientific research if they desire it. But here, again, that curse of our country, mediocrity, is upon us. Our colleges and universities seldom call for first-class men of reputation, and I have even heard the trustee of a well-known college assert that no professor should engage in research because of the time wasted.”
Rowland’s quest for a place to do research ended suddenly in 1875 when he met Daniel Coit Gilman. Gilman was assembling a faculty for the newly endowed Johns Hopkins University, which was to be America’s first true research institution, complete with graduate students, on the German model. The founding of The Johns Hopkins University was made possible through a private endowment by Johns Hopkins, a Baltimore merchant. The original faculty consisted of six professors.
Rowland joined happily and was sent on a tour of Europe to study laboratories and buy instruments. At Helmoltz’s laboratory in Berlin, Rowland (like Michelson five years later) paused to perform a fundamental experiment which he had conceived earlier but had lacked the means to perform. This was a search for the magnetic effect of a charged rotating disc, a matter of considerable interest at a time when Maxwell’s equations were the subject of vigorous debate. The experiment was difficult in the extreme, demanding extensive mathematical calculations as well as measurements at the edge of detectability, but Rowland carried it off. The experimental setup consisted of a disk of hard rubber or an old phonograph record connected to shaft of an electric motor.
The disk is given an electrostatic charge by rubbing it with a piece of woollen cloth. The disk is then spun and a magnetic compass is bought in close to the spinning disk. The compass is deflected and the faster the spin the greater the deflection. It appears that a magnetic field is not only set up by a current moving through a wire but by a moving electrostatic field as well. Rowland’s work, the first demonstration that a charged body in motion produces a magnetic field, attracted much attention.
Rowland returned to Johns Hopkins with one of the finest collections of research instruments in the world. At the university he gave as little attention as possible to administration and teaching. To his students and colleagues he was often a forbidding figure, intolerant of mediocrity, so devoted to the truth that his frank criticism could be devastating. He spent most of the 1870’s and 1880’s in his laboratory turning out a remarkably varied and competent series of researches.
Although he was a capable mathematician and did some work on electromagnetic theory, Rowland’s true genius was for experiment. He determined authoritatively the absolute value of the Ohm, the ratio of electrical units, the mechanical equivalent of heat, and the variation (which he was the first to demonstrate) of the specific heat of water with temperature.
He also suggested and supervised the experiments which led Edwin Hall, one of his graduate students, to the discovery of the Hall effect. He invented in 1897 the multiplex printing telegraph, by means of which a telegram can be transmitted upon a typewriter and reproduced in typewritten format the receiving end; and he devised a means of making practical use of the force of Niagara for the generation of electricity.
But his greatest contribution to science was the construction of diffraction gratings, begun in 1882. Astronomers in the late 19th century had begun using reflective plates etched with thousands of fine lines to analyze the light from stars. The plates, or diffraction gratings, dispersed the light from the sun or other star into its component colors, or wavelengths.
By analyzing a star’s spectrum, astronomers could figure out many things about the star, such as its chemical composition and temperature. When Rowland, at age 27, began his tenure at Hopkins in 1876, spectroscopy had serious limitations. Diffraction gratings were relatively imprecise, yielding spectra that contained ghostlike false signals among the true spectral readings.
The problem, Rowland concluded, was the lead screw in the ruling engines that were used to etch the fine lines on diffraction gratings. The screw moved the grating a small amount after each line was ruled. “But the screws could never be perfect,” explains Hopkins astronomer Alan Uomoto, who is a spectroscopist on the Sloan Digital Sky Survey, an ambitious effort to map the stars. During each turn of the screw, the amount the grating moved varied slightly.
Rowland invented the ruling machine that made possible the creation of diffraction gratings. A diffraction grating simulates the effect of a prism by creating a spectrum. It was a scientifically important invention because spectra display what are called absorption or Fraunhofer lines, allowing a scientist to study the chemical properties of the material emitting the light. Thus Rowland was the inventor of a machine that made possible a new way of understanding matter, upon which most of modern physics and chemistry are based. Rowland’s gratings were more than an order of magnitude larger and more accurate than any previous ones.
Rowland gratings
Rowland’s genius was to engineer a ruling engine containing a screw of nearly flawless pitch. He also used spherically curved plates for his diffraction gratings, where his predecessors had been using flat plates. The result of his innovations was diffraction gratings that produced spectra of superb resolution and accuracy. Rowland used his gratings to produce a map of the spectrum of the sun that was 10 times more accurate than any other.
His “Photographic Map of the Normal Solar Spectrum” (1888) was a spectrogram more than 35 feet (11 m) long, and his table of solar spectrum wavelengths (Astrophysical Journal, vol. 1-6, 1895-97) contained tens of thousands of solar lines and was a standard reference for many years. He also began supplying gratings at cost to spectroscopists around the world, and soon his concave gratings were standard issue in labs in Europe and America. To this day, astronomers continue to use Rowland-style gratings.
Rowland received the honorary degrees, Ph.D. from Johns Hopkins in 1880, and LL.D. from Yale in 1883 and from Princeton in 1896; was made a chevalier of the Legion of Honor for his services at the Electrical congress at Paris in 1881, and in 1896 was advanced to the grade of officer, and later made a corresponding member of the British Association for the Advancement of Science.
He was one of twelve foreigners to be admitted to membership in the Physical Society of London. He was elected to membership in the Natioanl Academy of Sciences in 1881, and in 1884 received for his researches in light and heat the Rumford medal from the American Academy of Arts and Sciences, of which he was an associate, and in 1897 the Matteucci medal. Rowland received a gold medal and grand prize for his gratings at the 1890 Paris Exposition.
Other professional honors included appointment as a delegate of the U.S. government to various international congresses on the determination of electrical units. Rowland was a lifelong avid proponent of basic research, even disparaging technological invention in favor of “pure science” in a celebrated 1883 address as vice president for the American Association for the Advancement of Science. Yet even he was ultimately forced to acknowledge the economic necessity of technological innovation.
Henry Rowland wrote many pamphlets and monographs, among which are: On Concave Gratings for Optical Purposes (1883); On the Relative Wave Lengths at the Lines of the Solar Spectrum (1886); On the Mechanical Equivalent of Heat (1880), and Photographs of the Normal Solar Spectrum.
Once when Henry Rowland was involved in a lawsuit, the court noted the fact that he was “the highest known authority in this country upon the subject of the laws and principles of electricity. . . ” From this incident there grew a legend that Rowland had declared under oath that he was the world’s greatest physicist.
Like many apocryphal tales about scientists, this one symbolizes a truth: some American physicists were growing self-confident as the nineteenth century ended. After long struggle they had finally won to a high level of excellence. None struggled harder than Rowland. Henry Rowland was pronounced “the foremost scientist America has yet produced” by the president of the National Academy of Sciences in 1924.
Professor Rowland was married June 4, 1890, to Henrietta, daughter of George Law and Helen (Davidge) Harrison, of Baltimore, Md. and soon after learned that he was dying of diabetes. Eager to assure the future financial security of his family, he worked on the development of a multiplex telegraph, which, while technically successful, did not succeed commercially before his death in 1901. He wished to leave something for physics, too, and towards his death he was one of the principal founders and first president of The American Physical Society. He was also elected a foreign member of the Royal Society of London in 1899.
Henry Rowland died on April 16, 1901, in Baltimore. His ashes were interred in the wall of his basement laboratory in accordance with his wishes.
A former unit of wavelength measurement, equal to 999.81/999.94 A was named “rowland” after Henry Rowland.
680