Title: Successful Detection of a Preferred Frame Using Eclipses of Jupiter's Moon Io Subject: In this paper tests by Maxwell and Gift that search for a preferred frame or ether arising from movement through that frame using Jupiter's moon Io are reviewed and discussed. Unlike the Michelson-Morley second-order experiment which unsuccessfully attempted to detect the orbital motion of the Earth relative to the ether, these tests are both first-order and therefore are unaffected by the second-order effects of length contraction and clock retardation. The test by Maxwell utilizes the delay in the eclipse of Io as the Earth orbits the Sun in an attempt to detect ether drift resulting from the galactic movement of the Sun. This test requires a 6-year duration for its full execution and was never performed because of practical difficulties. The test first presented by Gift can be conducted over a few days and employs the observed variation of the period of Io as the Earth moves toward or away from Jupiter. The result is a positive detection of ether drift arising from the orbital motion of the Earth. The detected ether drift is evidence of a preferred frame which we argue corresponds to the solar system barycentric or sun-centered inertial (SCI) frame. Keywords: Ether Drift, Maxwell, Roemer, Jupiter, Io, Luminiferous Ether, Preferred Frame, Sun-Centered Inertial Frame Author: Stephan J. G. Gift Creator: Acrobat PDFMaker 11 Word Producer: Adobe PDF Library 11.0 CreationDate: Wed Feb 16 10:04:41 2022 ModDate: Wed Feb 16 10:04:43 2022 Tagged: no Form: none Pages: 11 Encrypted: no Page size: 595.32 x 807.96 pts (rotated 0 degrees) File size: 321775 bytes Optimized: no PDF version: 1.7