Now, although during the two centuries preceding the invention of the spectroscope and the initiation of the solar physical researches now in progress, observations of eclipses were not very carefully conducted, yet we have some records of the appearance of the corona on different occasions, which, combined with the known law of sun-spot periodicity, may enable us to generalise more safely than we could from observations during the present spot-period, though these observations have been far more exact than the older ones. I propose to examine some of these. Necessarily I must make some selection. I need hardly say that even if there were no such relation as that which seems to be indicated by recent observations, and if my purpose were simply to prove, either that such a relation exists or that it does not, I could very readily bring before the reader of these pages what would seem like the most satisfactory evidence that the relation is real. I must ask him to believe, however, that my purpose is to ascertain where the truth lies. I shall neither introduce any observation of the corona because it seems specially favourable to the theory that the corona sympathises with the photosphere, nor omit any, because it seems definitely opposed to that theory. To prevent any possibility of being unconsciously prejudiced, I shall take a series of coronal observations collected together by myself, on account of their intrinsic interest, several years ago, when I had not in my thoughts any theory respecting periodic changes in the corona--the series, namely, which is included in the sixth chapter of my treatise on the sun. Each of these observations I shall consider in connection with the known condition of the sun as to spots, and those results which seem to bear _clearly_, whether favourably or unfavourably, on the theory we are enquiring into, I shall bring before the reader.