RT Journal Article SR Electronic T1 Ruling concave gratings JF American Journal of Science JO Am J Sci FD American Journal of Science SP 49 OP 53 DO 10.2475/ajs.s4-15.85.49 VO s4-15 IS 85 A1 Rollins, W. YR 1903 UL http://www.ajsonline.org/content/s4-15/85/49.abstract AB