RT Journal Article SR Electronic T1 On a method of making the wavelength of sodium light the actual and practical standard of length JF American Journal of Science JO Am J Sci FD American Journal of Science SP 427 OP 430 DO 10.2475/ajs.s3-34.204.427 VO s3-34 IS 204 A1 Michelson, A. A. A1 Morley, E. W. YR 1887 UL http://www.ajsonline.org/content/s3-34/204/427.abstract AB