Their motions are evidently of a two-fold nature; the Sun itself rotates on its axis, and the spots collectively participate in this movement of rotation; but over and above this it has been conclusively proved that sometimes a spot has a proper motion of translation of its own independently of the motion which it has in consequence of the Sun’s axial rotation. Curiously enough, spots are very rare immediately under the Sun’s equator. It is in the zone extending from 8° to 20° North or South, as the case may be, that they are most abundant; or, to be more precise still, their favourite latitude seems to be 17° or 18°. They are often more numerous and of a greater general size in the northern hemisphere, to which it may be added that the zone between 11° and 15° North is particularly noted for large and enduring spots. A gregarious tendency is often very obvious, and where the groups are very straggling an imaginary line joining the extreme ends of the group will generally be found more or less parallel to the solar equator; and not only so, but extending a long way, or sometimes almost entirely, across the whole of the visible disc. With respect to the foregoing matters Sir John Herschel remarked:—“These circumstances ... point evidently to physical peculiarities in certain parts of the Sun’s body more favourable than in others to the production of the spots, on the one hand; and on the other, to a general influence of its rotation on its axis as a determining cause in their distribution and arrangement, and would appear indicative of a system of movements in the fluids which constitute its luminous surface; bearing no remote analogy to our trade-winds—from whatever cause arising.” More often than not when a main spot has a train of minor spots as followers that train will be found extending eastwards from the east side of the spot, rather than in any other direction. Spots remain visible for very diverse lengths of time, from the extreme of a few minutes up to a few months; but a few days up to, say, one month, may, in a general way, be suggested as their ordinary limits of endurance. As the Sun rotates on its axis in 25¼ days, and as the spots may be said to be, practically speaking, fixed or nearly so with respect to the Sun’s body, no spot can remain continuously visible for more than about 12½ days, being half the duration of the Sun’s axial rotation.