IX. An analysis of the results from the Kew magnetographs on "quiet" days during the eleven years 1890 to 1900, a discussion of certain phenomena in the absolute observations

Abstract

I. In 1889 the then Kew Committee agreed to take part in a scheme which provided that at the end of each year the Astronomer Royal should select five magnetically quiet days for each month with a view to the tabulation of their records. The scheme has been in continuous operation since 1890, and the results from the selected quiet days have been published annually in the ‘Report’ made to the Royal Society. In 1895 I contributed to the British Association ‘Report’ an analysis of the declination and horizontal force records for the years 1890 to 1894, and described the previously unnoticed “non-cyclic effects” which appear to be characteristic of magnetically quiet days at Kew and elsewhere. In 1901 the development of electric traction in the West of London rendered it clear that no further records at Kew would be free from suspicion of artificial disturbances, and that it would be necessary in the near future to make arrangements for continuing the magnetic work elsewhere. Both contingencies pointed to the expediency of a complete discussion of the data obtained from 1890 to 1900, which I accordingly commenced. The delay in the execution of the scheme is largely due to the occurrence of various unforeseen difficulties, which have, however, I think been at last fairly satisfactorily surmounted. The object of the paper is not so much to put observations on record, as to make a critical use of them. The data used are mainly derived from old Kew ‘Reports,’ to which reference must be made for particulars.