The New International Encyclopædia/Rowland, Henry Augustus

ROWLAND, rô'land, Henry Augustus (1848-1901). An American physicist, born at Honesdale, Pa. He studied civil engineering at Rensselaer Polytechnic Institute, Troy, where he graduated in 1870. He became instructor at Wooster University, Ohio, and then instructor and afterwards assistant professor at Rensselaer Institute. He became (1876) professor of physics at Johns Hopkins University, a chair he occupied at the time of his death. Professor Rowland was one of the greatest physicists of the nineteenth century and had an international reputation. His determination of the mechanical equivalent of heat was one of his most important investigations. His determination of the ohm was likewise of great value; and his study of the magnetic properties of iron led to entirely new conceptions of magnetism. His interest in spectroscopy led him to the discovery of the principle of the concave grating, and to the construction of a dividing engine provided with a screw of extreme accuracy and uniformity of pitch, by which gratings were prepared under his direction. Rowland not only made an eye study of the spectrum, but also applied photographic methods. He investigated the solar spectrum and the arc spectra of various elements, and carried on many researches in allied fields. His work on alternating currents and their application has also been of importance. One of his last investigations resulted in the development of a system of multiplex telegraphy based on the use of synchronous motors, for which he received a gold medal from the Paris Exhibition. Perhaps his most important discovery was that of the magnetic effect of electric convection, which has a wide-spread theoretical bearing upon electrical phenomena. At the time of his death Professor Rowland was the president of the American Physical Society, of which he was one of the founders. Some of his important researches are the following: On Magnetic Permeability (1873); On the Magnetic Permeability and Maximum Magnetisation of Nickel and Cobalt (1874); Studies on Magnetic Distribution (1875); On a Magnetic Effect of Electric Connection (1876); Research on the Absolute Unit of Electrical Resistance (1878); On the Mechanical Equivalent of Heat (1880); On Concave Gratings for Optical Purposes (1883); and On the Relative Wave Lengths at the Lines of the Solar Spectrum (1886). His collected physical papers were published by the Johns Hopkins Press, 1902. To this collection there is prefixed a biographical sketch by Professor T. C. Mendenhall.