The problem of measuring the velocity of light by signals sent in one direction, instead of the usual method, by signals sent out and back, is studied. This requires two clocks, and the necessary steps to set the two clocks are discussed. It is found desirable to distinguish between “velocity” in its elementary and traditional sense, and the “rod-clock-quotient” directly obtained by measurement with rods and clocks experiencing the Fitzgerald-Larmor-Lorentz contractions. The precise formula derived for the one-way measurement of the velocity of light involves two rod-clock-quotients. The use of one-way light signal measurements in the Lorentz transformations and the Special Theory of Relativity is discussed.
HERBERT E. IVES, "The Measurement of the Velocity of Light by Signals Sent in One Direction," J. Opt. Soc. Am. 38, 879-884 (1948)