1. It was discovered half a century ago by Sabine, Lamont and Wolf that a relation exists between sunspots and the daily range of magnetic declination. If the regular diurnal inequality of declination be determined for the year as a whole, then it has been shown that corresponding to equal increments of sunspot frequency, as determined by Wolf and Wolfer, of Zurich, there are at least approximately equal increments in the range. In some instances the range taken has been not that of an inequality derived from all hours of the day, but one derived from daily measurements at two fixed hours, approaching more or less closely to the average times at which the needle has its extreme easterly and westerly positions. The range thus derived is unlikely to bear an absolutely invariable ratio to the range of the diurnal inequality, but for the present purpose the comparison may be regarded as made with the range of the diurnal inequality, but of minor accuracy. The relation refers, it should be noticed, to corresponding data from the year as a whole. It may be expressed by the equation R = a (l + m S ) ,..........(1) where B denotes the range of the diurnal inequality of declination, S the sunspot frequency, while a and m are constants for the particular station concerned.