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the Corona, which never appeared. During the time of preparation, however, he made several sketches of the instruments.

Page 251.—The Southern Cross. From a photograph taken with a 6-in. lens at the Sydney Observatory, on August 13, 1890. Exposure three hours.

Page 255.—The split nebula in Andromeda is from a photograph taken by W. S. Franks.

Page 256.—The Nebula in Cygnus is from a photograph kindly presented to the Observatory by the late Dr. Isaac Roberts. Exposed Oct. 27, 1896, for 2 hrs. 18 min.

Page 259.—The star cluster in Hercules (M 13), from G. W. Ritchey's beautiful photograph taken with the 40-in. Yerkes refractor, with a colour screen.

Page 273.—The coloured plate of spectra is the plate arranged by Professor Newall for his book on the Spectroscope. At the suggestion of the publishers, and with Professor Newall's kind permission, it is adopted here, to save the preparation of a special plate.

Page 281.—The flight of ducks. From the close resemblance of this picture to Fig. 91, representing star movements, it might be supposed that it was designed to fit. But the resemblance is purely accidental. Wandering one day among Mr. Newton's stacks of beautiful lantern slides, my eye fell on this picture, and I purchased it to illustrate stellar migrations, without realizing at the moment how closely it fitted the Taurus cluster. It is from a series which appeared originally in the Illustrated London News, and is reproduced by kind permission.

Page 286.—The billiard ball experiment. See note above on the illustrations for the cover.

Page 297.—The expanding nebula round Nova Persei is from the photographs by G. W. Ritchey, taken with the two-foot reflector of the Yerkes Observatory. See Astrophysical Journal, Vol. XIV. p. 293.