When several spots appear simultaneously, they describe in the same period of time similar paths which are sensibly parallel to one another although they may be in very different latitudes. The conclusion from this is inevitable, that spots are not bodies independent of the Sun, as satellites would be, but that they are connected with the Sun’s surface, and are affected by its movement of rotation. If we make every day for a few days in succession a drawing of the Sun’s disc with any spots that are visible duly marked thereon, we shall see that their apparent progress is rapid near the centre of the Sun, but slow near either limb. These differences, however, are apparent and not real, for their movement appears to us to take place along a plane surface, whilst in reality it takes place along a circle parallel to the solar equator. The spots in approaching the Sun’s W. limb, if they happen to seem somewhat circular in form when near the centre, first become oval, and then seem to contract almost into mere lines. These changes are simple effects of perspective, and are to be explained in the same manner as the apparent decrease in the size of many of the spots is often explicable. But this condition of things proves, however, that the spots belong to the actual surface of the Sun, for, on a contrary supposition, we should have to regard them as circular bodies greatly flattened like lozenges, and this would be contrary to all we know of the forms affected by the heavenly bodies. Of course besides the apparent changes of form just alluded to as the effect of perspective, it is abundantly certain that solar spots often undergo very real changes of form, not only from day to day, but in the course of a few hours. Several spots will often become amalgamated into one, and it was ephemeral changes of this character which hindered generally the early observers from determining with precision the duration of the Sun’s rotation.