Daily Variation of the Horizontal Magnetic Force at the Magnetic Equator

Abstract

IN a communication on the daily magnetic variation to the Edinburgh meeting, 1936, of the Association of Terrestrial Magnetism and Electricity, A. G. McNish1 states that the establishment of the magnetic observatory at Huancayo has led to the discovery of a daily variation of the horizontal force (H) "markedly different from those expected for such a region", the amplitude being more than twice the value found from the analysis of S. Chapman. McNish has based his investigation on the assumption that the daily variation depends on magnetic co-ordinates, and points out that the daily variation of the declination varies considerably in a very narrow region at mag. lat. 0. The great daily variation of H at Huancayo is explained as an augmentation of the normal varying field originating from special circumstances. For Huancayo this augmentation, which is increasing when the distance of the magnetic equator from the geographic equator is increasing, is great.