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Transcriber’s Notes

Obvious typographical errors have been silently corrected. Variations
in hyphenation have been standardised but all other spelling and
punctuation remains unchanged.

Footnotes are placed at the end of chapter.

Italics are represented thus _italic_, and superscripts thus ^.

The periods of the satellites of Uranus have been added to the table as
specified in a subsequent note.

The layout of several tables has been modified to maintain clarity
within wdth restrictions.




[Illustration:
LONDON STEREOSCOPIC CO.      PHOTOMEZZOTYPE.

STANMORE OBSERVATORY.

INSIDE VIEW.]




                            TELESCOPIC WORK

                                  FOR

                          STARLIGHT EVENINGS.

                                  BY

                     WILLIAM F. DENNING, F.R.A.S.
      (FORMERLY PRESIDENT OF THE LIVERPOOL ASTRONOMICAL SOCIETY).

  “To ask or search I blame thee not, for heaven
  Is as the book of God before thee set,
  Wherein to read his wondrous works.”
                                     MILTON.

                                LONDON:
           TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.
                                 1891.

                       [_All rights reserved._]


                    [Illustration: ALERE FLAMMAM.]

                    PRINTED BY TAYLOR AND FRANCIS,
                     RED LION COURT, FLEET STREET.




PREFACE.


It having been suggested by some kind friends that a series of articles
on “Telescopes and Telescopic Work,” which I wrote for the ‘Journal of
the Liverpool Astronomical Society’ in 1887-8, should be reprinted, I
have undertaken the revision and rearrangement of the papers alluded
to. Certain other contributions on “Large and Small Telescopes,”
“Planetary Observations,” and kindred subjects, which I furnished to
‘The Observatory’ and other scientific serials from time to time, have
also been included, and the material so much altered and extended that
it may be regarded as virtually new matter. The work has outgrown my
original intention, but it proved so engrossing that it was found
difficult to ensure greater brevity.

The combination of different papers has possibly had the effect of
rendering the book more popular in some parts than in others. This
is not altogether unintentional, for the aim has been to make the
work intelligible to general readers, while also containing facts
and figures useful to amateur astronomers. It is merely intended as a
contribution to popular astronomy, and asserts no rivalry with existing
works, many of which are essentially different in plan. If any excuse
were, however, needed for the issue of this volume it might be found
in the rapid progress of astronomy, which requires that new or revised
works should be published at short intervals in order to represent
existing knowledge.

The methods explained are approximate, and technical points have
been avoided with the view to engage the interest of beginners who
may find it the stepping-stone to more advanced works and to more
precise methods. The object will be realized if observers derive any
encouragement from its descriptions or value from its references,
and the author sincerely hopes that not a few of his readers will
experience the same degree of pleasure in observation as he has done
during many years.

No matter how humble the observer, or how paltry the telescope,
astronomy is capable of furnishing an endless store of delight to its
adherents. Its influences are elevating, and many of its features
possess the charms of novelty as well as mystery. Whoever contemplates
the heavens with the right spirit reaps both pleasure and profit, and
many amateurs find a welcome relaxation to the cares of business in
the companionship of their telescopes on “starlight evenings.”

The title chosen is not, perhaps, a comprehensive one, but it covers
most of the ground, and no apology need be offered for dealing with one
or two important objects not strictly within its scope.

For many of the illustrations I must express my indebtedness to the
Editors of the ‘Observatory’ to the Council of the R.A.S., to the
proprietors of ‘Nature,’ to Messrs. Browning, Calver, Cooke & Sons,
Elger, Gore, Horne Thornthwaite and Wood, Klein, and other friends.

The markings on Venus and Jupiter as represented on pages 150 and 180
have come out much darker than was intended, but these illustrations
may have some value as showing the position and form of the features
delineated. It is difficult to reproduce delicate planetary markings
in precisely the same characters as they are displayed in a good
telescope. The apparent orbits of the satellites of the planets,
delineated in figs. 41, 44, &c., are liable to changes depending on
their variable position relatively to the Earth, and the diagrams are
merely intended to give a good idea of these satellite systems.

  W. F. D.

  Bishopston, Bristol,
  1891.


Plates I. and II. are views of the Observatory and Instruments recently
erected by Mr. Klein at Stanmore, Middlesex, lat. 51° 36′ 57″ N.,
long. 0° 18′ 22″ W. The height above sea-level is 262 feet. The
telescope is a 20-inch reflector by Calver, of 92 inches focus; the
tube is, however, 152 inches long so as to cut off all extraneous
rays. It is mounted equatoreally, and is provided with a finder of
6 inches aperture—one of Tulley’s famous instruments a century ago.
The large telescope is fixed on a pillar of masonry 37 feet high, and
weighing 115 tons. Mr. Klein proposes to devote the resources of his
establishment to astronomical photography, and it has been provided
with all the best appliances for this purpose. The observatory is
connected by telephone with Mr. Klein’s private residence, and the
timepieces and recording instruments are all electrically connected
with a centre of observation in his study.




CONTENTS.


  CHAPTER I.
                                                                    Page

  THE TELESCOPE, ITS INTENTION AND THE DEVELOPMENT OF ITS POWERS       1


  CHAPTER II.

  RELATIVE MERITS OF LARGE AND SMALL TELESCOPES                       20


  CHAPTER III.

  NOTES ON TELESCOPES AND THEIR ACCESSORIES                           38


  CHAPTER IV.

  NOTES ON TELESCOPIC WORK                                            66


  CHAPTER V.

  THE SUN                                                             87


  CHAPTER VI.

  THE MOON                                                           113


  CHAPTER VII.

  MERCURY                                                            137


  CHAPTER VIII.

  VENUS                                                              145


  CHAPTER IX.

  MARS                                                               155


  CHAPTER X.

  THE PLANETOIDS                                                     167


  CHAPTER XI.

  JUPITER                                                            170


  CHAPTER XII.

  SATURN                                                             195


  CHAPTER XIII.

  URANUS AND NEPTUNE                                                 215


  CHAPTER XIV.

  COMETS AND COMET-SEEKING                                           227


  CHAPTER XV.

  METEORS AND METEORIC OBSERVATIONS                                  260


  CHAPTER XVI.

  THE STARS                                                          286


  CHAPTER XVII.

  NEBULÆ AND CLUSTERS OF STARS                                       324


  NOTES AND ADDITIONS                                                347

  INDEX                                                              353




ILLUSTRATIONS.


  PLATE I. Interior of Mr. Klein’s Observatory            _Frontispiece_

       II. View of Mr. Klein’s