Henry Rowland (27.11.1848-16.04.1901) was an American physicist and a member of the National Academy of Sciences. Born in Honesdale. Graduated from the Rensselaer Polytechnic Institute, where he worked in 1872–75. From 1875 he was head of the department of physics at Johns Hopkins University.
His work was in the field of electrodynamics, optics, spectroscopy and heat. In 1876 he proved that the convection current of free charges in a moving conductor is identical in its magnetic action to a conduction current in a stationary one (the Rowland experiment). This experiment played an important part in confirming Maxwell's equations for moving media. In 1880 he determined the mechanical equivalent of heat with high accuracy, obtaining the value 426.2 kgf·m/kcal. He invented the concave diffraction grating (1882) and achieved great success in the technique of making such gratings, in particular making a grating with 800 lines per millimetre. He built a dividing engine for making concave diffraction gratings, which greatly widened the possibilities of spectroscopy. In 1893 he developed the theory of the diffraction grating. He compiled a photographic atlas of the solar spectrum (1886–89). He carried out new measurements of wavelengths.
A Fellow of the Royal Society (1889) and a member of the Paris Academy of Sciences (1893). The B. Rumford and H. Draper Medals.