Page:Popular Science Monthly Volume 12.djvu/380

366 that have been disclosed between the variations of solar activity and resulting terrestrial phenomena:

1. The first coincidence observed was in the field of terrestrial magnetism. "A freely-suspended magnet, although it points in one direction, is nevertheless, within small limits, always in motion. Certain of these motions depend, as is well known, upon the hour of the day; but the magnet is also liable to irregular, abrupt fluctuations, which cannot be connected with the diurnal oscillations. While Hofrath Schwabe was engaged in delineating the sun-spots, Sir Edward Sabine was conducting a series of observations with regard to these spasmodic affections of the needle, and he found that such fluctuations are most frequent in years of high sun-spot activity." Nearly a hundred years ago, Van Swinden had suggested a periodicity in these irregular magnetic movements. Gauss, Arago, Lamont, and Gautier, pursued the research, and established the existence of a cycle of magnetic variation having an eleven year period, the maxima and minima agreeing with the maxima and minima of sun-spot activity. Schiaparelli and Broun have confirmed these results, and the latter observer concludes that, while the sun-spot activity is not an exact measure of magnetic action, "each is a distinct result due to the same cause." This disturbance is so great that, in years of maximum sun-spots, the working of the telegraph has been powerfully interfered with.

2. Connected with these effects there have been observed corresponding disturbances of electrical activity. A magnetic storm never rages without various accompanying signs of electrical excitement. These are seen in auroral displays that in their varying intensities conform to the magnetic cycles. Prof. Loomis, of Yale College, after a critical study of the subject, "concluded that the auroras observed in Europe and America exhibit a true periodicity closely following the magnetic periods, but not perfectly identical with them;" and Mr. Charles V. Walker, telegraphic superintendent, holds as an established fact that "earth-currents, disturbed magnetometers, and aurora, are parts of the same phenomenon."

3. There is evidence of thermometric variations, or fluctuations of temperature, in periods coinciding with the sunspot cycles. The observations in this case are, however, much complicated and obscured by the agency of the atmosphere, which acts as a screen upon the earths surface, disturbing the radiations that would affect our thermometers. But a large number of observers, among whom are Baxendell, Blandford, Stewart, Roscoe, Piazzi Smyth, Stone, and Köppen, have accumulated numerous observations both in the temperate zones and in the tropics, showing that "the calorific intensity of the sun's rays is subject to periodical changes, the maxima and minima of which correspond respectively with those of sunspot frequency."

4. The wind-disturbances of the earth's atmosphere follow the same law; there being a coincidence between the frequency of cyclones and sun-spots. Observations on opposite sides of the world, and in the tropics where wind disturbances are most violent, lead to the conclusion, as stated by Mr. Meldrum, that "the whole question of cyclones is a question of solar activity; and that, if we write down in one column the number of cyclones in any given year, there will be a strict relation between them—many sun spots, many hurricanes; few sun-spots, few hurricanes."

5. Confirmatory evidence of this is found in the records of shipping-disasters. From the returns of marine casualties posted on Lloyd's loss-book it was found that they disclose "a cycle closely corresponding with the sun-spot period. The percentage of casualties on