II. On a supposed periodicity in the elements of terrestrial magnetism, with a period of 26 1/3 days

In a paper published in the ‘Proceedings of the Imperial Academy of Sciences of Vienna,’ vol. lxiv., Dr. Karl Hornstein has exhibited the results of a series of observations which appeared to show that the earths magnetism undergoes a periodical change in successive periods of 26 1/3 days, which might with great plausibility be referred to the rotation of the sun. It appeared to me that the deductions from the magnetic observations made at the Royal Observatory of Greenwich, and which are printed annually in the Greenwich Observations,’ or in the detached copies of ‘Results of Magnetical and Meteorological Observations made at the Royal Observatory of Greenwich, would afford good materials for testing the accuracy of this law, as applicable to a series of years. The mew results of the measured hourly ordinates of the terrestrial magnetic elements are given for every day, and it is certain that there has been no change of adjustments of the declination and horizontal-force instruments in the course of each year. For the horizontal-force instrument the temperature of the room has been maintained in a generally equable state, and in later years it has been remarkably uniform.