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APR 29 1908

Astron.

COPYRIGHT, 1908

BY

CHARLES LANE POOR

The knickerbocker Press, New York

THI

PREFACE

'HIS work grew out of a series of lectures delivered at Columbia University. Intended for the general student, these were mainly historical and were used to supplement standard text-books and to guide the students in their reading. An attempt was made to present the subject in untechnical language and without the use of mathematics; to show by what steps the precise knowledge of to-day has been reached, and to explain the marvellous results of modern methods and modern observations.

The subject of the present volume, the Solar System, covers such a wide field that, in order to keep within reasonable bounds, many interesting subjects had to be omitted. To this may be attributed the rather scant mention of many important matters and the entire elimination of others. Eclipses of the sun, the most impressive of astronomical phenomena, have been passed over with but brief mention in connection with the study of solar physics. On the other hand considerable space has been devoted to the Tides and to Tidal Evolution, subjects but briefly treated in most astronomical works.

Mars has been given more space than the subject

really warrants. But so much has been written about the so-called Martian Canals and such attractive conclusions drawn from the observations, that a rather full discussion of even the most radical hypothesis does not seem to be entirely out of place in the present volume. Certain highly imaginative and exceedingly popular ideas in regard to this planet have attained such prominence and are supported with such a mass of apparently valid observations, that they cannot be dismissed with a word. Observations made and theories advanced in good faith deserve courteous and careful consideration.

The author is indebted to Professor Harold Jacoby and to Dr. S. Alfred Mitchell for valuable suggestions. Dr. Mitchell read the manuscript, revised the proof, and aided in the selection of the illustrations. To him are due most important criticisms, notes, and suggestions, especially in the treatment of the astrophysical problems. The author desires to express his sincere appreciation of this assistance.

October, 1907.

C. L. P.

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