The basis of this comparison was the declination values scaled from the charts for some 2,900 stations, distributed over the entire Earth. These stations are ports for which the tidal constants are given by the tidal division of the United States Coast and Geodetic Survey. For the sake of general information it has been customary to give in the annual “Tide Tables,” published by the Survey, the approximate magnetic declination. The preparation of this data for the 1901 tables gave a splendid opportunity for comparing the most recent charts. The isogonic chart of the British Admiralty, being for the year 1895, was only made use of occasionally.