THE TELESCOPE
McGraw-Hill Book Co. Inc.
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(Bull. de la Soc. Astron. de France.)
THE TELESCOPE
BY
LOUIS BELL, Ph.D.
CONSULTING ENGINEER; FELLOW, AMERICAN ACADEMY OF ARTS & SCIENCES; PAST-PRESIDENT,
THE ILLUMINATING ENGINEERING SOCIETY; MEMBER,
AMERICAN ASTRONOMICAL SOCIETY
First Edition
McGRAW-HILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE
LONDON: 6 & 8 BOUVERIE ST., E. C. 4
1922
Copyright, 1922, by the
McGraw-Hill Book Company, Inc.
THE MAPLE PRESS YORK PA
PREFACE
This book is written for the many observers, who use telescopesfor study or pleasure and desire more information abouttheir construction and properties. Not being a “handbook” intwo or more thick quartos, it attempts neither exhaustive technicalitiesnor popular descriptions of great observatories and theirwork. It deals primarily with principles and their application tosuch instruments as are likely to come into the possession, orwithin reach, of students and others for whom the Heavens havea compelling call.
Much has been written of telescopes, first and last, but it is forthe most part scattered through papers in three or four languages,and quite inaccessible to the ordinary reader. For his benefit thereferences are, so far as is practicable, to English sources, anddimensions are given, regretfully, in English units. Certainbranches of the subject are not here discussed for lack of spaceor because there is recent literature at hand to which referencecan be made. Such topics are telescopes notable chiefly for theirdimensions, and photographic apparatus on which special treatisesare available.
Celestial photography is a branch of astronomy which standson its own feet, and although many telescopes are successfullyused for photography through the help of color screens, thephotographic telescope proper and its use belongs to a fieldsomewhat apart, requiring a technique quite its own.
It is many years, however, since any book has dealt with thetelescope itself, apart from the often repeated accounts of themarvels it discloses. The present volume contains neither picturesof nebulæ nor speculations as to the habitibility of theplanets; it merely attempts to bring the facts regarding theastronomer’s chief instrument of research somewhere withingrasp and up to the present time.
The author cordially acknowledges his obligations to theimportant astronomical journals, particularly the Astro-physicalJ