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A SERIES OF FAMILIAR ESSAYS ON

THE MOON AND PLANETS, METEORS AND COMETS, THE

SUN AND COLOURED PAIRS OF SUNS.

BY

RICHARD A. PROCTOR, B. A. (CAMB.)

HONORARY SECRETARY OF THE ROYAL ASTRONOMICAL SOCIETY:

Author of The Sun,' Other Worlds than Ours,' 'Saturn and its System,'

'Essays on Astronomy,' 'Sun-Views of the Earth,'

PREFACE.

THIS VOLUME contains matter which, if space had permitted, I should have included in Other Worlds than Ours,' partly in the way of introduction or explanation, and partly to complete the information contained in the several chapters. It will be understood that to make this work complete in itself, I have admitted certain passages which contain information already given in Other Worlds than Ours ;' but such passages amount in all but to some ten or twelve pages; the rest of the work is strictly supplementary to that volume. In this respect the present volume differs essentially from my recently published

Essays on Astronomy.' Many of the essays in this last-named volume do, indeed, so far supplement 'Other Worlds than Ours' that they might have been added to the present volume. This remark applies for instance to the essays on Mars, Saturn, the Zodiacal Light, Meteors, Coloured Suns, News from Sirius, the Milky Way, and Nebulæ. But the volume of

essays was chiefly intended to present the nature and results of my original researches. It was on this

account that it was made uniform with Saturn and its System,' which it resembles in character.

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The paper on the Gamut of Light' presents the subject of spectroscopic analysis in a way which I have found effective with those readers who are not desirous of discussing the details of this mode of research. In the next two papers on Other Habitable Worlds' and 'Other Inhabited Worlds,' a sketch is given on the subject of the Plurality of Worlds. The fourth paper relates to the application of the Rosse Telescope to determine the heat of the lunar surface. Then follow papers on Venus, Mars, and Jupiter; two essays on Meteors, one relating to the past history and the other to the present condition of meteoric researches; a paper on Tyndall's Theory of Comets (a subject deserving close examination), and another on the general phenomena of comets and comets' tails. The three papers on the Solar Corona might have been added, almost as they stand, to my chapter on What we learn from the Sun,' in

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Other Worlds,' but for the

requirements of space. Lastly, there is a paper on the Colours of the Double Stars, a subject which the same cause compelled me to leave almost untouched in that work.

I have to return my thanks to the editors and