The relation between the Earth tide components and the forced nutations has been demonstrated in detail in previous publications (Melchior and Georis 1968, Melchior 1971,1973,1976,1977). We will therefore restrict the development to the essential formulae.

It is possible, in principle, to derive from astronomical observations both the tidal and nutational variations in the rotation of the Earth. However, in practice there are a number of difficulties. To detect the waves with periods of 18.6, 1.0 and 0.5 year one could use UT1-TAI. Unfortunately, this is impossible because of the lack of sufficiently long series of observations and because of significant non-periodic irregularities in the rate of the Earth's rotation. In addition, the annual wave consists of several harmonics of different natures which cannot be separated from one another. Investigation of short-period nutations is more promising, but it is also connected with specific difficulties.

We calculate corrections to the Love numbers resulting from the small frequency-dependent variations in the shear modulus, μ, arising from anelasticity in the Earth. The corrections are of the order of a percent, which in some cases exceeds the observational error. We point out the possibility of using these corrections to study the Earth's anelasticity at long (tidal) periods.

Analysis of astronomical observations recorded during the last 75 years by international services (ILS-IPMS, BIH) in charge of providing the coordinates of the instantaneous pole conclusively proves a persistent drift of the “mean pole” (≡barycenter of the wobble). A study was undertaken with the specific objective of investigating the possibility of a true secular motion of the barycenter, that is, an actual displacement of the Earth's pole of figure. Geophysical hypotheses available to explain the astronomically-observed drift of the “mean pole” suggest changes in the Earth's second-order inertia tensor as a plausible cause.

The purpose of this report is to summarize the discussions held on Friday, 1977 May 27, that preceded the adoption by IAU Symposium No. 78 of the four symposium resolutions concerning the theoretical and observational studies of nutation. It was the aim in the first half of the session to clarify the scientific problems and to obtain a broad concensus so that the resolutions committee could finish drafting the resolutions to be put to the symposium after the coffee-break. During the second half-session some new scientific points were made, but they have been incorporated in the report of the discussions during the first half-session; the report for the second half-session contains only a record of the voting and of the discussions on procedure and on the wording of the resolutions.

The Chairman apologized for the fact that the resolutions committee had been unable to submit the resolutions for prior consideration by the participants, but there had been insufficient time during the preceding days to resolve the differences of opinion about the form that the resolutions should take; the discussions before the coffee-break had, however, indicated that it was likely that agreement could be reached on the basis of the drafts that the committee had just prepared. English versions of the resolutions were displayed on the screen, and translations into Russian and French were made by Abalakin and Melchior.