Astres Fictifs. Name given to hypothetical bodies/assumed to be responsible for component tides in harmonic analysis. More usually termed 'satellites' or 'constituents'. Fr. = 'False stars'.
Astrolabe. Probably oldest of navigational instruments. In its more advanced form consisted of a disc of metal, or wood, graduated in degrees and suspended from a ring representing the zenith. A movable bar, or alidade, pivoted at centre of dial, carried sight vanes that were aligned on observed body. Bar then indicated altitude. In all cases, vertical and horizontal planes were established by plumb line. 2. Optical instrument formerly used in surveying. Now superseded by theodolite.