The difference between the magnetic diurnal variations on ordinary and quiet days at Kew Observatory

Abstract

§1. While investigating the nature of the diurnal inequality of the magnetic elements at Kew Observatory, I have discovered a somewhat remarkable relationship between the inequalities derived respectively from quiet days and from ordinary days ( i. e. all days expert those of large disturbance). The period whose records were employed consisted of the 11 years 1890 to 1900. During that period five days were selected for each month by the Astronomer Royal as typical of quiet conditions. An analysis of the diurnal inequalities at Kew on these days was given in an earlier paper. Use is also made of the diurnal inequalities derived from 209 disturbed days, being the days of principal disturbance from 1890 to 1900. The new material employed consists of diurnal inequalities based on all the days of the 11 years, excluding the 209 highly disturbed days but including the quiet days. The cost of measuring the curves was defrayed by a grand from the Government Grant Committee. The diurnal variation in the horizontal components of magnetic force is often advantageously studied by considering the vector which represents the force to whose action the departure from the mean value for the day may be ascribed.