The spots on the sun are not always the same in number. Sometimes they are many, sometimes they are few. Long and close watching has made it clear that they pass through a regular _order_ of changes: some years of many spots being followed by other years of less and less spots; then some years of very few spots being followed by other years of more and more spots,--decrease and increase being seemingly regular and alternate. This turn or _cycle_ of changes--from more to less, and then from less to more again--is found to run its course about once in every eleven years, with some variations. Now, it has long been known that the magnetic-needle goes through curious variations. Though we speak of it as pointing always north, yet it does not always so point exactly. Every day the needle is found to make certain tiny, delicate motions, as if faintly struggling to follow the daily movements of the sun--just a little towards the east, or just a little towards the west. These tiny motions, having been long watched and measured, were found to go through a regular course of changes--some years more, and some years less, waxing and waning by turns. It was discovered that the course of changes from more to less, and from less to more again, took place in about eleven years. These two things, you see, were quite independent of one another. Those who watched the sun-spots were not thinking of the magnets, and those who watched the magnets were not thinking of the sun-spots. But somebody did at last happen to think of both together. He was laughed at, yet he took the trouble carefully to compare the two. And, strange to say, he found that these two periods in the main agreed--the eleven years of alternate changes in the number of sun-spots, and the eleven years of alternate changes in the movements of the magnetic-needle. When the spots are most, the needle moves most. When the spots are least, the needle moves least. So much we know. But to explain the why and the wherefore is beyond our power.