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The decay of the amplitude of the free modes of the<br />Earth is a potential source of information on the mechanism of dissipation<br />of the elastic energy of the Earth.<br />However there are serious difficulties in the interpretation of the decay;<br />they are caused by several facts. One is the limited length of the significant<br />part of the record which prohibits to identify the splitting of all the modes<br />caused by the Earth rotation and also to follow the pattern in its rotation;<br />another reason is the coupling between modes, caused by the inhomogenities<br />and the flattening of the Earth, which can transfer energy from one mode<br />to another. The results available are therefore very few and of poor accuracy.<br />In order to seek new information on the mechanism of dissipation of<br />the elastic energy we solve a generalized form of the equation of elastodynamic<br />in which we have introduced some unspecified operators to represent<br />the dissipation of the elastic energy. By confronting these operators with<br />the observations we would hope to find informations on the mechanism<br />of dissipation. Unfortunately the laws of variation of Q with frequency,<br />found by various authors who were using different observations, are not in<br />agreement and are very uncertain. Therefore we can only estimate the<br />average values of the parameters of the supposed mechanisms of dissipation.<br />We analyze also the dissipation of energy due to viscous frictions at<br />the core mantle boundary. This dissipation would be negligible even for<br />viscosities of the core up to 1010 poise