Our sun, therefore, viewed from the neighborhood of any of the stars, whence undoubtedly he would simply appear as one among many fixed stars, would be a “variable,” having a period of ten and a half years. And further, if an observer, viewing the sun from so enormous a distance, had the means of very accurately measuring its light, he would undoubtedly discover that, while the chief variation of the sun takes place in a period of ten and a half years, its light is subjected to minor variations having shorter periods.
The discovery that the periodic changes of the sun’s appearance are associated with the periodic changes in the character of the earth’s magnetism is the next that we have to consider.
It had long been noticed that, during the course of a single day, the magnetic needle exhibits a minute change of direction, taking place in an oscillatory manner. And, when the character of this vibration came to be carefully examined, it was found to correspond to a sort of effort on the needle’s part to turn toward the sun. For example, when the sun is on the magnetic meridian, the needle has its mean position. This happens twice in a day, once when the sun is above the horizon and once when he is below it. Again, when the sun is midway between these two positions—which also happens twice in the day—the needle has its mean position, because the northern and the southern ends make equal efforts (so to speak) to direct themselves toward the sun. Four times in the day, then, the needle has its mean position, or is directed toward the magnetic meridian. But, when the sun is not in one of the four positions considered, that end of the needle which is nearest to him is slightly turned away from its mean position toward him. The change of position is very minute, and only the exact modes of observation made use of in the present age would have sufficed to reveal it. There it is, however, and this minute and seemingly unimportant peculiarity has been found to be full of meaning.
The minute vibrations of the magnetic needle, thus carefully watched—day after day, month after month, year after year—were found to exhibit a yet more minute oscillatory change. They waxed and waned within narrow limits of variation, but yet in a manner there was no mistaking. The period of this oscillatory change was not to be determined, however, by the observations of a few years. Between the time when the diurnal vibration was least until it had reached its greatest extent, and thence returned to its first value, no less than ten and a half years elapsed, and a much longer time passed before the periodic character of the change was satisfactorily determined.
The reader will at once see what these observations tend to. The sun spots vary in frequency within a period of ten and a half years, and the magnetic diurnal vibrations vary within a period of the same duration. It might seem fanciful to associate the two periodic series of changes together, and doubtless when the idea first occurred to Lamont, it was not with any great expectation of finding it confirmed that he examined the evidence bearing on the point. Judging from known facts, we may see reasons for such an expectation in the correspondence of the needle’s diurnal vibration with the sun’s apparent motion, and the law which has been found to associate the annual variations of the magnet’s power with the sun’s distance. But undoubtedly when the idea occurred to Lamont it was an exceedingly bold one, and the ridicule with which the first announcement of the supposed law was received, even in scientific circles, suffices to show how unexpected that relation was which is now so thoroughly established. For a careful comparison between the two periods has demonstrated that they agree most perfectly, not merely in length, but maximum for maximum, and minimum for minimum. When the sun spots are most numerous, then the daily vibration of the magnet is most extensive, while, when the sun’s face is clear of spots, the needle vibrates over its smallest diurnal arc.
Then the intensity of the magnetic action has been found to depend upon solar influences. The vibrations by which the needle indicates the progress of those strange disturbances of the terrestrial magnetism which are known as magnetic storms have been found not merely to be most frequent when the sun’s face is most spotted, but to occur simultaneously with the appearance of signs of disturbance in the solar photosphere. For instance, during the autumn of 1859, the eminent solar observer, Carrington, noticed the apparition of a bright spot upon the sun’s surface. The light of this spot was so intense that he imagined the dark glass which protected his eye had been broken. By a fortunate coincidence, another observer, Mr. Hodgson, happened to be watching the sun at the same instant, and witnessed the same remarkable appearance. Now it was found that the self-registering magnetic instruments of the Kew Observatory had been sharply disturbed at the instant when the bright spot was seen. And afterward it was learned that the phenomena which indicate the progress of a magnetic storm had been observed in many places. Telegraphic communication was interrupted, and in some cases, telegraphic offices were set on fire; auroras appeared both in the Northern and Southern Hemisphere during the night which followed; and the whole frame of the earth seemed to thrill responsively to the disturbance which had affected the great central luminary of the Solar System.
Fig. 32.—Copernican System: Facsimile of the Drawing in the Volume by Copernicus Published in 1543
The reader will now see why I have discussed relations which hitherto he may perhaps have thought very little connected with my subject. He sees that there is a bond of sympathy between our earth and the sun; that no disturbance can affect the solar photosphere without affecting our earth to a greater or less degree. But if our earth, then also the other planets. Mercury and Venus, so much nearer the sun than we are, surely respond even more swiftly and more distinctly to the solar magnetic influences. But beyond our earth, and beyond the orbit of moonless Mars, the magnetic impulses speed with the velocity of light. The vast globe of Jupiter is thrilled from pole to pole as the magnetic wave rolls in upon it; then Saturn feels the shock, and then the vast distances beyond which lie Uranus and Neptune are swept by the ever-lessening yet ever-widening disturbance wave. Who shall say what outer planets it then seeks? or who, looking back upon the course over which it has traveled, shall say that planets alone have felt its effects? Meteoric and cometic systems have been visited by the great magnetic wave, and upon the dispersed members of the one and the subtle structure of the other effects even more important may have been produced than those striking phenomena which characterize the progress of the terrestrial or planetary magnetic storms.
When we remember that what is true of a relatively great solar disturbance, such as the one witnessed by Messrs. Carrington and Hodgson, is true also (however different in degree) of the magnetic influences which the sun is at every instant exerting, we see that a new and most important bond of union exists between the members of the solar family. The sun not only sways them by the vast attraction of his gravity, not only illumines them, not only warms them, but he pours forth on all his subtle yet powerful magnetic influences. A new analogy between the members of the Solar System is thus introduced to reinforce those other analogies which have been held so strikingly to indicate that the ends for which our earth has been created are not different from those which the Creator had in view when He planned the other members of the Solar System.