Summary A small error in the computations of Cartwright & Tayler has been corrected, resulting in improved tables of the time harmonics of the principal terms in the tide‐generating potential. The correction removes certain previously anomalous features, and otherwise affects the amplitudes in their 5th decimal places.

A time-harmonic expansion of the gravitational tide potential is computed using an ephemeris of high precision for the Moon and the Sun and the latest I.A.U. astronomical constants. The results, which are computed for three different epochs and by novel methods, are compared with Doodson's classic expansion. The chief differences are due to secular trends in large terms and to revised constants which reduce all the solar terms. A new expansion is also given for the radiational tide potential. Notation t f T 0, A Ti, Ti' 6 t' L , L'

Direct tidal analysis of the altimetry from the Geosat Exact Repeat Mission's first year is used to derive estimates of the diurnal and semidiurnal oceanic tides. The geoid is removed by collinear differences at 34.1-day separation, and the orbit error is reduced by subtracting a slowly modulated 1 cycle/revolution term. A sequence of independent analyses at grid areas of 1 ø latitude x 1.5 ø longitude using "orthotide" functions ensures complete definition of the diurnal and semidiurnal species. Global admittance maps for M2 and S2 within the latitudes 58øN and 59øS compare well with ground truth at 66 open-ocean sites. Maps of differences between Geosat and the Naval Surface Weapons Center model show important areas of the order of 10-15 cm. The integral for the global power input from the moon gives 2.5! TW (M2), 0.44 TW (S2), lower than many previous estimates, but in agreement with figures deduced from a recent analysis of satellite orbits. Schwiderski, 1990], but we shall be ,concerned with the simpler situation provided by an orbit whose Earth track repeats itself almost exactly every T days, where in the present case of the ERM, T = 17.0505.With a repeating orbit, (1) may be applied to every point along the Earth track with a time lead r = nT, n being any small integer. Such a scheme is particularly suitable to tidal variations because a harmonic element a cos wt in g(0, it, t) is merely transformed in A•'(0, it, t) to 3069

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