ruling-engine

Century Dictionary and Cyclopedia

1. n. A machine for ruling diffraction gratings. The ruling is performed by a fine diamond-point, the spacing of the lines being accomplished by the most refined micrometer-screw mechanism. (See grating, 2, and micrometer.) The new ruling-engine at Johns Hopkins University has produced gratings ruled with from 10,000 to 20,000 lines per inch, 6 inches in diameter, with faces formed on a radius of more than 21 feet, and having better definition than any ever before made. Such engines must be placed in as nearly equable a temperature as can be attained, as any sensible expansion or contraction during their operation defeats their purpose.