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 |
We see that the maxima and minima years of the two phenomena very nearly coincide. The accord is so evident that we may calculate the diurnal variation as proportional to the increase in the number of sun-spots. This is shown by the two last lines of the table.
The yearly variation is again exactly the same as that of polar lights, as the following table indicates, in which the disturbances of magnetic declination, horizontal intensity, and vertical intensity are compiled for Toronto, Canada; for comparison the means of these three magnitudes are added for Greenwich. The unit of this table is the average annual variation:
TORONTO
| Jan. | Feb. | Mar. | April | May | June | July | Aug. | Sept. | Oct. | Nov. | Dec. | |
| Declination | 0.57 | 0.84 | 1.11 | 1.42 | 0.98 | 0.53 | 0.94 | 1.16 | 1.62 | 1.31 | 0.78 | 0.76 |
| Horizontal | 0.56 | 0.94 | 0.94 | 1.50 | 0.90 | 0.36 | 0.61 | 0.75 | 1.71 | 1.48 | 0.98 | 0.58 |
| Vertical | 0.57 | 0.74 | 1.08 | 1.49 | 1.12 | 0.50 | 0.71 | 1.08 | 1.61 | 1.29 | 0.75 | 0.61 |