New Procedure at American Magnetic Observatories

Abstract

IN accordance with the usual practice of the United States Coast and Geodetic Survey, two years, 1915 and 1916, are dealt with in the Results of Observations at the magnetic observatories at Sitka and Honolulu, which have recently been published. In previous years the curves were read unsmoothed exactly at the hour local mean time. Commencing with 1915, the hourly value represents the mean ordinate for sixty minutes ending with the hour of the I35th meridian at Sitka (135° 20.1′ W.), and of the 165th meridian at Honolulu (158° 3.8′ W.). The value entered, for instance, under 2h. really belongs to 1.5h. Diurnal inequalities continue to be given, as in the past, only for 10q (quiet) days a month chosen locally, and for the 5q (international quiet) days, but hourly means are given for all days. The adoption of mean ordinates instead of instantaneous readings is in accordance with what is now probably the usual practice. Unless it is followed, all-day diurnal inequalities for disturbed months are apt to be very ragged. But the adoption of means for sixty minutes ending at the hour, instead of sixty minutes centring at the hour, is a practice not generally followed except in German. Even if the procedure had distinct advantages over the ordinary one, its spasmodic adoption by individual observatories or in individual countries has the serious drawback of introducing diversity where uniformity is desirable. This is especially true of the international quiet days, the special object of which is to supply exactly corresponding data from different observatories.