On periodical laws discoverable in the mean effects of the larger magnetic disturbances

Abstract

Abstract In a discussion of the two-hourly observations of the magnetic declination, made in 1841 and 1842 at the observatories of Toronto and Hobarton, published in 1843 and 1845, the author expressed an opinion that themagneticdisturbances,of largeamountand apparently irregular occurrence, commonly called magnetic storms or shocks, would be found, when studied in their mean effects on the magnetic direction and force extending over a sufficient period of time, to be subject to periodical laws, connecting them with the seasons of the year and the hours of the day at the particular stations. In preparing for the press the hourly observations of the declination in the years 1843, 1844 and 1845, at the same two stations, the author found his previous opinions strongly confirmed; and believing that the evidence thus obtained of periodical laws is far too systematic, and rests on a series of too long duration to make it probable that it will be otherwise than confirmed by the continuation of the observations in subsequent years, he has been induced to make it the subject of a communication to the Royal Society; although it is probable that the exact periods, and the mean numerical values of the effects produced, or their proportions to each other in the different seasons and at the different hours, may hereafter receive modifications.