Abstract

ABSTRACT During a visit to Europe in the autumn of 1882, Henry Augustus Rowland, Professor of Physics at Johns Hopkins University, displayed diffraction gratings produced on a ruling engine he had designed and built, which were bigger and much higher quality than any previously made. Some were of a novel type, ruled on concave surfaces, which he used in a simple but equally novel spectroscope that he had devised, to reveal spectral lines in great detail, and by means of photography to record spectral data much more rapidly than previously possible. Over about twenty years Rowland built three ruling engines, published photographic maps of the solar spectrum, compiled a catalogue of the wavelengths of lines in the solar spectrum correlated with laboratory-produced spectra of almost all the chemical elements, and produced and sold the diffraction gratings used by spectroscopists everywhere. For decades after his death Rowland’s ruling engines remained practically the only source of good-quality diffraction gratings. This paper describes and analyses this work of Rowland and of the other men, Theodore Schneider, John Brashear, and Lewis Jewell, who played major roles in it.