The annual review of the “Caractère magnétique de chaque jour” for 1927 has been drawn up in the same manner as the preceding years; moreover it contains a review of the collaboration of the observatories during the years 1917–1927. In 1927, 43 observatories contributed to the quarterly reviews; 41 of them sent complete data. Table II of the annual review, containing the mean character of each day and each month, the lists of calm days and of disturbed days and the days, recommended for reproduction, are reprinted here. (It will be recalled that at the meeting of the Commission for Terrestrial Magnetism and Atmospheric Electricity of the International Meteorological Committee at Zürich, September 17, 1926, it was agreed that certain days included amongst the five most disturbed days of the month, should not be included amongst the days selected for the calculation of the diurnal irregularities. Days of character 2.0 should be excluded and other highly disturbed days, on which loss of trace has occurred.)