Page:Science vol. 5.djvu/231

13, 1885 eclipse is doubtless entitled to interest the average observer but little; however, it is quite possible that the rapid development of the means of eclipse research may in time lead to the utilization of annular eclipses with quite the same regularity that total eclipses are at the present day observed. In so far as we have learned, astronomers have made no preparations for observing this eclipse within the belt where the annular phase is visible.

The notion that an annular eclipse is an indifferent species of occurrence has certainly been helped along by the deceptive way in which these eclipses are almost always represented in astronomical treatises, where the ratio of the semi-diameters of the sun and the moon are unnecessarily out of proportion; and frequently that of the moon is drawn only three-quarters that of the sun, thus giving the impression that a very large proportion of the total light of the sun is unextinguished at the time and place of central eclipse. In point of fact, the greatest breadth the annulus can have, under the most favorable circumstances, is only about a minute and a half of arc, or less than one-tenth the semi-diameter of the sun at the time; while not infrequently—as is the case with the annular eclipse which occurs on Monday next, when the moon's semi-diameter is only one-thirtieth part less than the sun's—the eclipse which is put down in the almanacs as annular, only barely escapes being total. It seems very possible that a strongly developed corona might be observed on such occasions: indeed, the experience of many observers who have followed the corona after the total phase, makes it quite probable. To be sure, the duration of the annulus at such times is very short; but, if the corona could be observed on these occasions, we should be able to halve the intervals of an observation as conducted by the present methods at the times of total eclipses only.

We have in America two classes of summer schools of natural history,—one in which only original investigators are allowed to study (Professor Agasaiz's laboratory at Newport, the Fish-commission laboratory at Wood's Holl, and the Johns Hopkins laboratory at Beaufort, being examples); the other where students of