In this paper the lig-ht curves of long period M-type stars were analysed. The method used was that of the autocorrelation and supse- quent power spectrum analysis. Applying this method we obtain the ampli- tudes of the overtones espressed in that of the fundamental as unit. The relation betweeD log P and the relative intensity of the first overtone A (1) was studied. slope of the Some indication who curve obtained that foı the Pop 1 stars the log P — A (I) nıay be different from the one valid with the Pop II stars, but as yet the evidence is not conciusive.