THE many papers which have been written in recent years upon the above subject have dealt chiefly with the now well-known annual fluctuation (first noticed by Lord Kelvin nearly fifty years ago), by which the mean intertidal level of the sea stands on our North Sea and Baltic coasts something like 20 cm. higher in autumn than in spring. But while we still know too little about the details and the causes of this phenomenon, we know much less about the fluctuations of longer period, or even of the elementary facts of correspondence between different coasts in regard to the mean level in successive years.