1. A statistical method for determining the amplitude and period of certain harmonic or wave components in a set of data with the aid of Fourier series. Harmonic analysis has been used in meteorology, for example, to determine periodicities in climatic data (Conrad 1950); to determine the wavelengths most strongly represented in general circulation flow patterns; and to determine the spectrum of turbulent eddies (Sutton 1953). 2. The representation of tidal variations as the sum of several harmonics, each of different period, amplitude, and phase. The periods fall into three tidal species: long period, diurnal, and semidiurnal. Each tidal species contains groups of harmonics that can be separated by analysis of a month of observations. In turn, each group contains constituents that can be separated by analysis of a year of observations. In shallow water, harmonics are also generated in the third-diurnal, fourth-diurnal, and higher species. These constituents can be used for harmonic prediction of tides.