This plan is likely to be most successful when the Sun is near its meridian passage; but it may be applied at any hour, if care is taken to adjust the eyepiece so that the Sun’s motion is precisely at right angles to the vertical wire. One other plan may be mentioned. Draw on cardboard, with compasses, a circle about 10 or 12 inches diameter, and divide this with 31 parallel lines. Subdivide each of the spaces into 5, less prominently marked. Then, during observation, keep both eyes open, and hold or fix the circular disk at a distance enabling it to coincide with the telescopic image of the Sun. By carefully noting how many divisions the group covers on the cardboard, its dimensions may be readily found, because one division will be equal to about 5410 miles. Of course these methods[10] are simply approximate, and only strictly applicable to objects not far removed from the central regions of the Sun, because the spots are portions of a sphere, and not angles subtended by a flat surface. When close to the E. or W. limbs, foreshortening is considerable, though the polar diameter of a spot is not affected by it then. Presuming an observer to have his 3-or 4-inch telescope duly fitted with a solar diagonal and tinted glass, he may naturally ask, after his curiosity has been satisfied by the contemplation of his first sun-spot, what he can do further: What special features is he to look for? What changes ought to be recorded? What are the doubtful points that require to be cleared up as regards the Sun’s physical appearance? In what way are new and novel facts likely to be glimpsed? In a word, he desires to know in what manner he may employ his eyes and instrument usefully for science, while also gaining pleasure for himself. Information like this is often needed by the young student, and sometimes indeed by men who have already gained a little experience, and who possess much larger instruments than we have intimated above. In endeavouring to offer suggestions in response to such inquiries, I would remark that the nature and direction of a research essentially depend upon several conditions, viz. the observer’s inclination, his instrumental equipment, his place of observation, and the amount of time he can devote to the pursuit of his object. There are very few men who, like Schwabe of Dessau, will confront the Sun on nearly every day for more than forty years in order to learn something of its secrets. Such extraordinary pertinacity is fortunately not required, except in special cases. Amateurs may effect much valuable work in the short intervals which many of them steal either from business or domestic ties and offer at the shrine of astronomy. There are quite a considerable number of attractive phenomena and features on which the solar observer will find ample employment, and to the principal of these it may be as well to make individual references.