as Bishop's ring. It is for the meteorologist to inquire whether a supply of dust sufficient in quantity and quality, appearing at the right time and enduring long enough, can he accounted for.
Kiessling, of Hamburg, already referred to, has done the best work on the corona as well as on the great sunsets with which it is evidently connected. His pamphlet, entitled "Die Dämmerungserscheinungen im Jahre 1883, und ihre physikalische Erklärung" (Hamburg, 1885), gives the most satisfactory account and explanation of the twilights that I have seen; and its value is largely increased by the experimental illustrations that the author has devised in imitation of the strange natural phenomena that he accounts for so well. A later paper, "Ueber die geographische Verbreitung des Bishop'schen Sonnenringes," in the May number of the little meteorological journal, "Das Wetter," and a short paper by Forel on "Le Cercle de Bishop," in the Geneva "Archives des Sciences" for June, are the most recent articles of consequence on the corona, and give important evidence as to the origin of its diffraction particles by showing its relation to the famous sunsets. The new corona was first noticed in Honolulu on the 5th of September, 1883, by the Rev. Sereno F. Bishop, who called attention to it by descriptions published at the time, and in letters to "Nature." Although seen so early in September in the Sandwich Islands, it was not recognized in this country till November 24th, when Professor Le Conte saw it at Berkeley, California; nor in Europe till the days directly following; but ever since then it has been continuously visible till now, in proper conditions of weather as already described. After rarely being seen in the summer, it has reappeared in the clearer days of the winter. Being always relatively inconspicuous, the date of its first visibility can not generally be determined with accuracy—alas for the neglect of so rare an opportunity of valuable observation!—but the agreement of the growth of the area in which it was noted and the spread of the great sunsets is placed beyond a doubt; and with them its origin must be referred to the explosive eruption of Krakatoa. Kiessling considers this relation of cause and effects to be firmly established, and even quotes approvingly the name given by Arcimis in Madrid, "corona solar krakatoense," although the name of "Bishop's ring" is undoubtedly the one that will come into general use.
The evident difficulties in the way of accepting the volcanic origin of the diffracting particles are the great quantity of material that would seem to be needed, the excessive fineness of its texture, and its long suspension in the thin upper air; but I believe that these difficulties are by no means fatal to the volcanic theory. The quantity needed is not absolutely so great, after all. Tyndall suggested that the minute, almost molecular particles, to which the blue color of the sky is usually referred, could all be contained in a snuff-box; and, while this need not be taken as in any way an accurate estimate of the
