[Illustration: Fig. 42.—Curve of magnetic declination at Kew, near London, on November 15 and 16, 1905. The violent disturbance of November 15, 9 P.M., corresponds to the maximum intensity of the aurora. Compare the following figure] Celsius and Hiorter observed in 1741 that the polar lights exercise an influence on the magnetic needle. From this circumstance we have drawn the conclusion that the polar lights are in some way due to electric discharges which act upon the magnetic needle. These magnetic effects, the disturbances of the otherwise steady position of the magnetic needle, are not influenced by the light of the sun and moon, and can therefore be studied to greater advantage than auroras. We have already pointed out that it is only the aurora of the radial, streamer type which exerts this magnetic influence (compare Figs. 42 and 43). [Illustration: Fig. 43.—Curve of horizontal intensity at Kew on November 15 and 16, 1905. On November 15 a magnificent aurora was observed in Galicia, Germany, France, Norway, England, Ireland, and Nova Scotia, with a maximum at 9 P.M. The polar light was unusually brilliant as early as 6 P.M.] These magnetic variations show exactly the same periods as the northern lights and the sun-spots. As regards, first, the long period of 11.1 years, our observations prove that the so-called magnetic disturbances of the position of the magnetic needle faithfully reflect the variations in the sun-spots. This connection was discovered in 1852 by Sabine in England, by Wolf in Switzerland, and by Gautier in France. Even the more irregular diurnal variations in the magnetic elements are subjected to a solar period. The magnetic needle points in our districts with its north end towards the north—not exactly, though, being deflected towards the west. This western deviation or declination is greatest soon after noon, about one o’clock, and this diurnal change is greater in summer than in winter, and the fluctuation of the position of the magnetic needle greater in daytime than at night-time. It is, therefore, manifest that we have to deal with some solar effect. This becomes still more distinct when we study the change with reference to the daily variation in the number of sun-spots. In the subjoined table the variation in the declination has been compiled for Prague for the years 1856 to 1889. Only years with maxima and minima of sun-spots and of magnetic variations have been noticed in this table: 1856 1860 1867 1871 1879 1884 1889 Sun-spot number 4.3 95.7 7.3 139.1 3.4 63.7 6.3 DAILY VARIATIONS IN DECLINATION 1856 1859 1867 1871 1878 1883 1889 Observed 5.98 10.36 6.95 11.43 5.65 8.34 5.99 Calculated 6.08 10.20 6.22 12.15 6.04 8.76 6.17