There are few studies in astronomy more engrossing than the watch on the growth and changes of the solar spots. Their strange shapes, their rapid movements, and striking alterations afford an unfailing interest. For example, the amazing spectacle is continually being afforded of a spot, some two, three, or four hundred millions of square miles in area, moving over the solar surface at a speed of three hundred miles an hour, whilst other spots in the same group are remaining stationary. But a higher interest attaches to the behaviour of the sun as a whole than to the changes of any particular single spot; and the curious fact has been brought to light, that not only do the spots increase and diminish in a regular cycle of about eleven years in length, but they also affect different regions of the sun at different points of the cycle. At the time when spots are most numerous and largest, they are found occupying two broad belts, the one with its centre about 15° north of the equator, the other about as far south, the equator itself being very nearly free from them. But as the spots begin to diminish, so they appear continually in lower and lower latitudes, until instead of having two zones of spots there is only one, and this one lies along the equator. By this time the spots have become both few and small. The next stage is that a very few small spots are seen from time to time in one hemisphere or the other at a great distance from the equator, much farther than any were seen at the time of greatest activity. There are then for a little time three sun-spot belts, but the equatorial one soon dies out. The two belts in high latitude, on the other hand, continually increase; but as they increase, so do they move downwards in latitude, until at length they are again found in about latitude 15° north or south, when the spots have attained their greatest development. [Illustration: PHOTOGRAPH OF A GROUP OF SUN-SPOTS. (_From a photograph taken at the Royal Observatory, Greenwich, April, 1882, 20 d. 10 h. 6 m._)]