Of the general appearance of the Corona some idea may be obtained from Fig. 1 (see Frontispiece) which so far as it goes needs little or no verbal description. Stress must however be laid on the word “general” because every Corona may be said to differ from its immediate predecessor and successor, although, as we shall see presently, there is strong reason to believe that there is a periodicity in connection with Coronas as with so many other things in the world of Astronomy. A curious point may here be mentioned as apparently well established, namely, that when long rays are noticed in the Corona they do not seem to radiate from the Sun’s centre as the short rays more or less seem to do. Though the aggregate brilliancy of the Corona varies somewhat yet it may be taken to be much about equal on the whole to the Moon at its full. The Corona is quite unlike the Moon as regards heat for its radiant heat has been found to be very well marked. There is another thing connected with the Sun’s Corona which needs to be mentioned at the outset and which also furnishes a reason for treating it in a somewhat special manner. The usual practice in writing about science is to deal with it in the first instance descriptively, and then if any historical information is to be given to exhibit that separately and subsequently. But our knowledge of the Sun’s Corona has developed so entirely by steps from a small beginning that it is neither easy nor advantageous to keep the history separate or in the background and I shall therefore not attempt to do so.