The lunar diurnal variation as obtained at the Cheltenham Magnetic Observatory from a single complete lunation during February, 1903

The attempt, was made to determine how well the lunar diurnal variation of the magnetic elements,could be determined from simply one complete lunation, instead of using records extending over a period of a year or more. For this purpose the comparatively “magnetically calm” month of February, 1903, was selected and the photographic records obtained at the Cheltenham Magnetic Observatory of the Coast and Geodetic Survey with an Eschenhagen Magnetograph were utilized. The scale values used were: 1 mm. ordinate, declination = 1.014 minute, 1 mm. ” horizontal intensity = 0.00002 C. G. S. unit.