Apparent effect of magnetic activity upon secular variation of the vertical component of the Earth's magnetic field
In a previous paper (Trans. Amer. Geophys. Union, fourteenth annual meeting, pp. 139-144, 1933) a definite negative correlation was reported between the second differences of the mean annual values of world-wide magnetic activity and magnetic horizontal force at several widely-separated observatories. This correlation demonstrated that during years of high magnetic activity the horizontal force tends to be lower than during inactive years. No correlation was found between the second differences of the horizontal force and the first differences of magnetic activity, indicating that no appreciable carry-over effect of the activity exists.