XV. CLUSTERS AND NEBULÆ 256 APPENDIX I.: LIST OF LUNAR FORMATIONS 273 APPENDIX II.: LIST OF OBJECTS FOR THE TELESCOPE 278 INDEX 285 LIST OF ILLUSTRATIONS PRINTED SEPARATELY FROM THE TEXT PLATE _To face page_ I. The 40-inch Refractor of the Yerkes Observatory [_Frontispiece_ II. Six-inch Photo-Visual Refractor, equatorially mounted 30 III. Twenty-inch Reflector, Stanmore Observatory 36 IV. Telescope House and 8-1/2-inch 'With' Reflector 38 V. The Sun, February 3, 1905. Royal Observatory, Greenwich 48 VI. Photograph of Bridged Sunspot (Janssen). _Knowledge_, February, 1890 50 VII. Solar Surface with Faculæ. Yerkes Observatory 60 VIII. Coronal Streamers: Eclipse of 1898. From Photographs by Mrs. Maunder 70 IX. The Chromosphere and Prominences, April 11, 1894. Photographed by M. H. Deslandres 74 X. Venus. H. MacEwen. Five-inch Refractor 94 XI. The Moon, April 5, 1900. Paris Observatory 102 XII. The Moon, November 13, 1902. Paris Observatory 108 XIII. The Moon, September 12, 1903. Paris Observatory 110 XIV. Region of Maginus: Overlapping Craters. Paris Observatory 112 XV. Clavius, Tycho, and Mare Nubium. Yerkes Observatory 114 XVI. Region of Theophilus and Altai Mountains. Yerkes Observatory 116 XVII. Apennines, Alps, and Caucasus. Paris Observatory 118 XVIII. Chart of the Moon. Nasmyth and Carpenter } } 124 XIX. Key to Chart of Moon. Nasmyth and Carpenter } XX. Mars: Drawing 1, January 30, 1899--12 hours. Drawing 2, April 22, 1903--10 hours 134 XXI. Chart of Mars. Memoirs of the British Astronomical Association, Vol. XI., Part III., Plate VI. 138 XXII. Jupiter, January 6, 1906--8 hours 20 minutes. Instrument, 9-1/4-inch Reflector 158 XXIII. Jupiter, February 17, 1906. J. Baikie, 18-inch Reflector 166 XXIV. Saturn, July 2, 1894. E. E. Barnard, 36-inch Equatorial 172