In this first paper of several on the design and production of diffraction gratings of high resolving power, an outline is given of the development and present status of mechanically controlled ruling engines. Gratings having notable performance are described, and problems involved in producing on a reflecting surface large numbers of parallel equidistant grooves of constant or controlled form, with position tolerances of one micro-inch or better, are analyzed. Distinctive features of the engines of Rowland, Michelson, Gale, Anderson, Babcock, Siegbahn, and others are discussed. It is pointed out that the low productivity of many ruling engines in the past should not discourage present-day experimenters, as improved surfaces for ruling, superior ruling tools, alloys less susceptible to wear, warpage, creep, and fatigue, better methods of lubrication, and servo-mechanisms capable or making a ruling engine self-correcting, are all now available. Much can be learned by studying the strong points and weaknesses of previous engine designs. A current trend in the use of gratings appears to be away from the concave and toward the plane form. Succeeding papers will deal with a suggested method for obtaining improved gratings having high resolving power, and with the modification and testing of a 14-inch ruling engine, originally designed and partially built at the University of Chicago by Gale and O’Donnell, and recently transferred to M.I.T.
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