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Stars and Telescopes

Concerning the Sun, wrote Sir William Herschel
in the opening year of the 19th century, * The influ-
ence of this eminent body on the j^/ode we inhabit is so
great ant/ so wiiiely diffifseti that it becomes a/most a
duty to study the operations which are carried on upon
the solar surface,^

^Pulcfjra • jmnt • omnia • faciente • Ce • ft • ecce • Cu
tnenatrabtUter • pulcljrtor • qui • fcctsti • omnia •

— s. AlJRELl I AUGUS'l I N I Coftfessiones

Stars and Telescopes

A Hand-book of Popular Astronomy

Founded on the 9th Edition of
Lynn's Celestial Motions

DAVID P.TODD

Professor of Astronomy and Director of the Observatory ^ Amherst
College. Author of **A New Astronomy," etc., etc.

BOSTON
LITTLE, BROWN, AND COMPANY

1899

DEPARTMENT OF EDUOATION
LELAKD STAIiroiD JUliiO^ UiilVEESITY

AU rights reserved.

626J74

John Wilson and Son, Cambridge, U.S.A.

DEDICATED

M" D. WILLIS JAMES

PREFACE

J^TARS AND TELESCOPES is intended
to meet an American demand for a plain,
unrhetoricai statement of the astronomy of to-
day; and it has been based upon M' LVNN'S
Celestial Motions, because his little book had
already covered excel-
lently part of the ground,
and had passed through
nine English editions.
Permission for this use of
Celestial Motions was
most courteously granted
by its author, formerly
of the Royal Observa-
tory at Greenwich. In
accord with M' Lynn's
wish, I have indicated

which is his work and which my own, both in
situ, and on the page of contents. For the
greater part of Chapter xvi I am indebted to
the kindness of D' See,

With a single exception, the ample illustra-
tions are wholly new additions. For excellent

vi Preface

photographs I acknowledge gratefully my in-
debtedness —

To M" Henry Draper of New York,

To MM. LoEWY, Deslandres, and Henry of Paris,

To M' Christie, Astronomer Royal of Greenwich,

To D' Gill, H. M. Astronomer at the Cape,

To Sir Howard Grubb of Dublin,

To D' Roberts of Crowborough Hill, Sussex,

To Professor Young of Princeton University,

To Professor Langley, Secretary of the Smithsonian

Institution,
To Professor Rowland of the Johns Hopkins University,
To Professor Pickering, Director of Harvard College

Observatory,
To Commodore Phythian, U. S. Naval Observatory,
To Professor Hale, Director of the Yerkes Observatory,
To M' Brashear, Director Allegheny Observatory,
To Messrs Warner and Swasey of Cleveland.

For the use of illustrations in astronomical
periodicals also —

To the Editors of the Vicrteljahrsschrift der Astro-

nomischen Gesellschaft (Leipzig),
To the Editors oi Bulletin Astronomique (Paris),
To the Editor oi Nature (I^ndon),
To the Editors of The Observatory (London),
To M. Ftjvmmarion, Editor of D Astronomie^
To D' ScHWAHN, Editor of Himmel und Erde (Berlin) ,
To M' Maunder, Editor oi Knowledge (London),
To D' Chandler, Editor of Tlie Astronomical Journal^
To Professor Payne, Editor of Popular Astronomy^
To Professor Hale, Editor The Astrophysical JoumdL

Preface vii

For the courteous loan of engraved blocks
also —

To D' Barnard of the Yerkes Observatory,

To Professor Payne, Director North field Observatory,

To the American Book Company of New York,

To the Messrs D. Applet on & Company of New

York,
To the G. & C. Merriam Company of Springfield.

For the use of illustrations in printed volumes
likewise —

To MM. Gauthier Villars et Fils of Paris (Father

Secchi's Le Solcily and M. Flammarion's La Planete

Afars) ,
To W. Engelmann*s Verlag of Leipzig (D' Vogel*s

Populdre Astronomies and D' Scheiner's Die Pho-

tographie der Gestirne),
To Hartleben*s Verlag of Vienna (Baron v. Schweiger-

Lerchenfeld's Atias der Himmelskunde)^
To Messrs A. and C. Black of Edinburgh (D'

Dreyer's Tycho Brake) ^

To Messrs Taylor and Francis of London (M' Den-

ning's Telescopic Work for Starli'^ht Evenings) ,
To Edward Stanford of London (M' McClean's

Photographic Spectra of the Sun and Metals) y
To Messrs Houghton, Mifflin & Company of Boston

(M' Lowell's Annals ^ vol. i., and M'' Todd's Corona

and Coronet) y
To Messrs Longmans, Green & Company of New

York (M' Proctor's Old and Neiv Astronomy) ^
To Messrs Charles Scribner's Sons of New York

(JScribner^s Magazine) .

Many of the portraits of astronomers are taken
from the published volumes of their lives and

viii Preface

works, to the editors and publishers of which
due acknowledgment is here returned. To the
courtesy of M" ADAMS I am indebted for the ap-
propriate design of Adams'S Ex Libris. Other
portraits have been made available through the
kindness of relatives and executors.

Stars and Telescopes has advantaged greatly
from the criticism of several astronomers who
have examined chapters in proofs, though no
one will hold them responsible for any errors
that may have escaped notice : —

The late Professor Newton of Yale University, Me^

tears and Meteoric Bodies^
M. Charlois of Nice, The Sfnall Planets^
Professor Newcomb of Washington, The Planets^
Professor Young of Princeton, The Sun,
Professor Pickering of Cambridge, The Fixed Stars,
M' Lowell of Boston, The Ruddy Planet,
Professor Barnard of Williams Bay, The Comets.

To all I am glad to accord my obligation in
fullest measure.

DAVID P. TODD*

Observatory House,

Amherst: March 1899.

%• While this work is passing through the press, announce-
ment is made of an important discovery by Professor W. H.
Pickering at the Harvard Observatory, of a ninth moon of
Saturn (page 129), with a period of about 2\ years, and five
times more distant from Saturn than Japetus, the outermost
satellite hitherto known. The new moon has been named
Phoebe, and it is probably about 200 miles in diameter.—
29^^ March 1899.

CONTENTS

XIII.
XIV.
XV.
XVI.
XVII.
XVI II.

IK Pace

Introduction [Todd) ■

Outline of Astronomical Discovebv [Lynn) 9

The Earth [Lynn and Tald) 19

The Moon {Lynn and Todd) 36

The Calendar {Lynn and Todd) .... 34

The Astronomical Rklateons of Light

[Lyntiand Todd) 41

The Sun (Z_t"i'ii""/ r.*/-/) 48

More about the Sun — Solar Physics

[T^dd) 69

Total Solab Eclipses (Todd) 81

The Solar System (Lymi and Ttnld) ... 90

The PLA.NETS (Zj;H«,jB,/r^,/) 104

The Ruddv Planet (To.id) 155

fl0ViT\% {Lynn and Toiid) iSl

Meteoric Bodies {Lynn and Teddy .... 208

Meteoric Bodies — djniiauid {Todd) . . . 320

The Constellations {Lynn and Todd) . . 231

Thb Cosmogony {See] 842

The Fixed Stars ILynn and Todd) ... 255

Telescopes and Houses for them ( Todd) 316

Table of the Small Planets (Todd) . . 397
Index {Tudd) ^o^

LIST OF ILLUSTRATIONS

Pack
Seasonal changes on Mars (Lowell) . . . frontispiece in colors

Portrait of William Thynne Lynn v

Portrait of Nicholas Copernicus ii

Portrait of Galileo Galilei 12

Herschel's 40-foot reflector 13

Portrait of Sir William Herschel 14

Portrait of Joseph von Fraunhofer 17

Portrait of Jean Sylvain Bailly opposite 18

Portrait of Jean Joseph Delambre opposite 18

Position of the vernal equinox, B. c. 2170 22

Present position of the vernal equinox 22

Land hemisphere of the Earth 24

Water hemisphere of the Earth 24

Trajectory of the Earth's north pole (Chandler) . . opposite 24

Portrait of Peter Andreas Hansen opposite 26

Portrait of Charles Eugene Delau NAY .... opposite 26

A part of the Moon (photographed by Henry) . . . opposite 28

Surface of the Moon (photographed at the Lick Observatory) . 29

Jupiter in occultation (Denning) 30

The Moon (photographed by Loewy and Puiseux) . opposite 30

The Royal Observatory at Greenwich 39

The photo-tachometer (New COMB) 44

Portrait of Olaus Roemer 45

Portrait of James Bradley 46

Portrait of Jean Bernard L^on FoucAULT 47

Relative distance and size of Sun, Earth, and Moon .... 49

Portrait of Edmund Halley 50

A group of sunspots (Rutherfurd) 52

The Sun (photographed by Rutherfurd) 57

^unspot highly magnified (Secchi) 58

(unspot zones according to Proctor 59

12-inch equatorial at Potsdam, Germany 60

The Potsdam Astrophysical Observatory 61

The Sun's surface (photographed by Janssen) 62

xii List of Illustrations

Pacit

Great protuberance of iSS6 63

Eruptive protuberance (Trouvelot) 6j

' Great Horn * of the eclipse of 1S68 63

Sunspots and zones of faculas (Hale) 64.

Zones of solar faculx (Deslandres) opposite 64

Solar chromosphere (Deslandres) opposite 64

Great sunspot of September 1898 opposite 64

The Sun's chromosphere (Hale) 65

Latitudeof spots and protuberances 66

Spots and magnetic declination (Wolfer) 67

Portrait of Gust AVE Robert Kirchhoff ji

Ruling engine (Rowland) 72

Spectra of the Sun and metals (McClean) .... opposite *j2

Bolometer in water jacket (L AN GLEY) 72

Portrait of Hermann Ludwig Ferdinand von Helmholtz ']^

Diagrams of Eclipses (Ball) 83

Corona of 1882 (Wesley and Schuster) 86

Portrait of Theodor von Oppolzer opposite 86

Portrait of Stephen Joseph Perry opposite 86-

Corona of 1878 (Harkness) %^

Tracks of future eclipses (Todd) opposite 88

Corona of 1898 (Maunder) 89-

Portrait of Tycho Braii^ 91

Portrait of Johann Kepler 92-

Kepler's second law 93

Portrait of Sir Isaac Newton 93.

Relative size of Sun, planets and satellites 95

Portrait of Leonhard Euler 96-

Portrait of Joseph Louis La Grange 97

Portrait of Karl Friedrich Gauss 99<

The U. S. Naval Observatory, Washington lox

Portrait of Sir George Biddell Airy 102

Portrait of Pierre Gassendi 104

Mercury (after Schiaparelli) 105

Venus (NiESTEN and Stuyvaert) 107

Venus near inferior conjunction (Barnard) 108

Venus (after Trouvelot) 108-

Mercury (after Lowell) opposite 108

Venus (after Lowell) opposite 108

Mars (after Flammarion) iix

Orbits of satellites of Mars xi2

Portrait of Christian Henry Frederick Peters . . . . 113

Jupiter (after Keeler) xi8:

The Lick Observatory 122:

Jupiter (after Knobel) 123

J^ist of Illustrations

Xlll

Jupiter^s satellite in (Campbell and Schaeberle) . . .

Eye-end of the Lick telescope

The Lick 36-inch telescope

Saturn and his rings

The Imperial Observatory at Pulkowa

Portrait of Jean Dominique Cassini opposiie

The Pulkowa 30-inch telescope

Portrait of Benjamin Peirce

Uranus (after Henry)

Tlie Paris Observatory

Portrait of Urbain Jean Joseph Le Verrier

Portrait of John Couch Adams

Portrait of Felix Francois Tisserand

Portrait of Mary Somerville

Portrait of James Craig Watson

Portrait of Heinrich Wilhelm Matthias Olbers . . .

Birthplace of Newton

Portrait of Dominique Fran^'Ois Arago

Portrait of Friedrich Kaiser

North polar cap of Mars (Knobel)

Dwindling of south polar cap (Lowell) opposite

Mars (after Perrotin)

Detail of Martian canals

Soils Lacus region (Douglass)

Mars (after Brenner)

The Observatory at Nice (B ISC HOP fsheim)

Mars (after Cerulli)

Mars (after Pickering)

Mars in 12 presentations (Lowell) opposite

Halley's Comet (after Struve)

The Great Comet of 1861 (Williams)

Head of Great Comet of 1861 (Secchi)

Brooks's Comet (1886 V)

Pons-Brooks Comet (1883)

Pons-Brooks Comet (after Swift)

Portrait of Caroline Herschel

Portrait of Johann Franz Encke

Biela's double comet

Swift's Comet (Barnard)

The Great Comet of 1843

Gale's Comet (photographed by Barnard) . . . . opposite

Donati's Comet (Bond)

Portrait of Maria Mitchell

The head of Coggia's Comet (Brodie)

Portrait of Ernst Florens Friedrich Chladni ....

Pack

24
[24

[25
[27

[30-
[32

[36
141

143

146

50.

'l^
^53.
'54
155
IT
[60.
[6z
164
165
166.
[67
[69

;72-

[76^
182

'83

[83

[84
188

isa

[89
190
192

'94
199

200

203

204

205

20S

xiv List of Illustrations

Page

Portrait of Denison Olmsted 210

Apparent radiation of meteors (Denning) 211

Photographing meteor-trails (Elkin) 212

Portrait of Friedrich August Theodor Winnecke ofposite 212

Portrait of Hubert Anson Newton opposite 212

Path of the November meteors 213

Telescopic meteors (Brooks) 214

Meteor of 1888 (Denning) 214

Path of August meteors in space 215

Brooks Comet of 1890 (Barnard) 218

The Paris collection of meteorites 221

Meteoric iron from South Africa 223

Widmannstatian figures 225

Pseudo-meteoric iron of Ovifak 226

The Pleiades (naked-eye view) 236

The Pleiades (photographed by Henry) 237

The great nebula in Orion (Roberts) 238

Portrait of William Cranch Bond 240

The great nebula in Andromeda (Roberts) 243

Portrait of Immanuel Kant 245

Portrait of Pierre Simon La Place 246

Lord Rosse's 6-foot reflector 247

Portrait of Lord Rosse 248

Orbit of Alpha Centauri (See) 250

Double nebula in Virgo 251

The figure of Poincar6 252

Portrait of Eduard Heis 256

The Milky Way in Sagittarius (Barnard) 257

The meridian photometer (Pickering) 258

Photographic equatorial telescope (Grubb) 259

Portrait of Friedrich Wilhelm August Argelander . . 261

Portrait of Benjamin Apthorp Gould 262

The Bruce 24-inch telescope 264

Vicinity of Eta Carinas (Bailey) 265

Cluster Omega Centauri (Herschel) 269

Portrait of Eduard Schunfeld 270

Portrait of Friedrich Wilhelm Bessel 273

Portrait of Christian August Friedrich Peters . . . 274

Portrait of Franz Friedrich Ernst BrOnnow .... 275

Portrait of Hugo GyldiSn 276

Heliometer at Capetown (Gill) 277

Divided object-glass of heliometer 279

Distances of stars from the Sun 2S0

Typical double star systems 281

Portrait of Friedrich Georg Wilhelm Struvb .... 282

List of lUustratioHi

Portrait of WtLUAM KuTiEK Dawes jSj

OibiC of Gamma Viiginis 984

OlUt of the Conipanion o( Sirius 184

Portrait of AlvanGhaham Clark 185

Portrait of JoHANN Christian DoppLHH jiS6

Star spednMCope by Brashear jSS

Obsetvalory of D' Isaac Kouehts, F. K. S i^s

ao-iodi reflector (Grubbj , » . 191

Globular cluster la PeEasus (Roberts) 193

Speclrutn of Sirius and iion(VocEi,) 194

Portrait of PiETRO Angelii SeCChi 294

Types of stellar spectra (Secchi) 396

Cluster in Perseus (Koberts) 397

Portrait of Henry Draper 29S

The Dache telescope at Camlnidge 399

Harrard College Observatory jos

Spectrum of Capella (Deslan[>hes) 301

Portrait of Sir John Heeschel 30*

Distribution of nebulaeand clusters (Waters) 304

Portrait of KiCHARD AkTHoNv Proctor 30J

Portrait of Johanm von Lamont 30S

Ring nebula in Lyta (Roberts) 309

Spiral nebula in CanrsVenitici(KOBERTs) 310

Portrait of Christian Huvgens 317

iTlh century telescope (Heveuus) 318

A modem field-^lass (Bausch and LoMi.) 319

A modem reflector (Br*shear) 311

The Melbourne 4-ft. reflector (Grubu) 321

Portrait of Thomas Grubb 31J

Portrait of Arthur Cowper Ranyard 316

Course of rays through telescope 327

Portrait of John DoLLaND 318

Portrait of David Kittemhouse 329

Portrait of Obmsbv MacKnigiit Mitchel 33a

Triple object-glass (Taylor) 331

Vienna 27^nch equatorial (Grubb) 333

The Imperial Observatory at Vienna 334

Portrait of Alvak Clark 335

Portrait of GsaRoE Bassett Clare 336

Yerkes Observatory o( University of Chicago 337

40-inch telescope of the Verkes Observatory ..*>•>• 33S

EqnatorUlCoud*(LoEWY) J,vt

Micrometer (schematic) 34a

A modem micTometet 343

Portrait of Lewis Morris Ruthertukd 344

XVI

List of Illustrations

Pack

40-foot horizontal photo-heliograph 345

Plate-measuring engine (Repsold) 34S

Variable nebula surrounding Eta Carinas 350

^pcctro-heliograph (Brash ear) 352

Universal spectroscope (Brashear) 353

I>iscovery of a small planet by photography (Wolf) . . . . 355

Modem camera for stellar photography (Hey de) 337

Meteor-trail (photographed by Barnard) 339

The pneumatic commutator (Todd) 361

Automatic photography of the Corona (Tonr) 362

The electric commutator (Todd) 363

Flash-spectrum, eclipse of 1898 (Naegamvela) 364

IIevelius and his consort observing 366

The Repsold meridian circle of Carleton College . " . . , . 368

Automatic dividing-engine (S^cretan) 369

Portrait of Franz Xaver von Zach 370

The Almucantar (Chandler) 371

Portrait of John Harrison , 372

Portrait of Johann Tobias Mayer 373

Portrait of Nathaniel BovjrDiTCH 374

£mith College Observatory 375

Oxford University Observatory 376

Manora Observator>', Istria ^"jj

3-inch portable telescoj>e 377

Portrait of Thomas William Webb 378

Portrait of James Lick 380

Portrait of Uriah Atherton Boyden 3S1

The Boyden Observatory, Arequipa, Peru 382

Portrait of Elias Loomis 383

Portrait of John Couch Adams {cx libris) . 385

INTRODUCTION

A STRONOMY may be styled a very aristocrat
among the sciences ; but, while its cosmic
conceptions never fail to arouse the broadest
general interest, it is an interest that has by no
means led to a knowledge of this engrossing
science proportionately widespread.

Antecedent to the 19th century, astronomy
was purely a science of celestial motions. Its
mystical parent, astrology, had taught that
planetary places influence men's destinies : how
important then, to know the place of every
planet in the past, and to be able to divine their
conjunctions in the future. Astrology was utili-
tarian to this end, and her offspring was hardly
less so; for upon a knowledge of celestial mo-
tions, still farther refined and perfected, were
founded the indispensable and very practical
arts of conducting merchant ships from port to
port in safety, and of surveying accurately coast
lines and other national boundaries.

But with the beginning of the 19th century
came the brilliant and imaginative conceptions
of the elder Herschel, concerning the consti-
tution and physical peculiarities of the heavenly

2 Introduction

bodies, based upon his minute and painstaking
scrutiny ; for his thought was acute, as his ob-
servation was thorough. Still it did not so
much concern him where these bodies were as
wftat they were. Sir WiLLlAM Herschel, in-
deed, was the first to build monster telescopes of
modern excellence, and he vastly augmented
our knowledge of the heavens by faithfully using
them. Also he prepared the foundation upon
which the imposing edifice of physical astronomy
has been erected by his followers.

As the marvellous revelations of the heavens
have come to us mainly through the telescope
in the hands of highly skilful astronomers, men-
tion of their labors is associated with the tele-
scopes that made the researches possible. In-
evitably these are intimately related : we cannot
neglect the human element, though we may affect
to do so. Thereby may human interest lead to
wider diffusion of astronomical knowledge.

So the book is embellished also by a profusion
of portraits of astronomers, among those not liv-
ing, — of many whose important work was done
so unostentatiously that their names have long
since passed from merely popular recognition.
Noteworthy and impersonal achievement is
everywhere associated with the distinguished
lives that have passed in unselfish discovery of
astronomical truth — lives of unswerving devo-
tion, of persistent self-sacrifice, of unwearying
toil, and here and there of sad disappointment,
and even pathetic disaster.

Introduction J

Next in our abiding concern with astrono-
mers and their labors are the tools with which
their work is accomplished — telescopes not
only, but all those modern adjuncts introduced
by the physicist, and called photometers, spec-
troscopes, and bolometers, as well as the multi-
fold adaptations of the photographic camera
which have revolutionized nearly all departments
of the science, and afforded a welcome and
unquestioned service. Nor have I neglected
either the men who made the telescopes or the
buildings in which all such instruments are
housed.

Stars and Telescopes begins with a running
commentary or outline of astronomical discov-
ery, with a rigid exclusion of all detail. Second
and third chapters deal almost as briefly with
the Earth, and the Moon, our nearest celestial
neighbor in good and regular standing. Due
prominence is given that occult phenomenon of
recent discovery, called technically the variation
of latitude ; so persistently has research upon it
been prosecuted that the tiny oscillations of the
Earth's axis within the globe itself can be pre-
dicted for a decade to come. So signally has
photography aided in delineation of the surface
of our satellite that photographs, reproduced by
the best modern processes, have been made to
serve instead of word descriptions of lunar
scenery. Of less popular interest is the Calen-
dar. But a chapter on the astronomical relations
of light is intended to emphasize the prime sig-

4 Introduction

nificance of this phenomenon in all celestial
enquiry. Without it the heavens would be as a
book forever sealed.

The Sun, monarch of the planetary system,
and source of all our light and life, could not
be dismissed without the fuller treatment de-
manded by his importance. The ever new
problem of his distance from us, providing
as it does our foot-rule of the universe; the
continually changing appearances of his sur-
face ; the power of his light, and the intensity
and maintenance of his heat — all are set forth,

not only the most recent results, but the instru-
ments and methods by which in part they have
been derived.

Solar eclipses, too, are introduced, but only
in the most general fashion. Their prediction is,
however, exciting sufficiently wide interest to
warrant a table and chart of these engrossing
phenomena in the future.

The chapter embodying a general outline of
the solar system necessarily brings to the read-
er's attention the labors of the most celebrated
of all the early astronomers — TvCHO, KEPLER,
and Newton. But an account of the individual
planets of our system called for still farther ex-
pansion, if the present state of our knowledge of
those bodies was to be abundantly set forth.
Particularly have the most recent results been
presented, with a view of exhibiting in a popular
way the state of technical literature down to the
present day. Wherever the desired verification

Introduction 5

of theory or observation is still lacking, I have
been careful to say so.

In the summer of 1898 was discovered a new
planet, probably a genuinq member of the aster-
oidal group, although periodically it approaches
nearer to the Earth by one-half than Venus ever
does, thereby outclassing not only this planet
when in transit over the Sun's disk, but Mars
also at his close oppositions, as a medium for
finding the Sun's true distance from us. Fresh
interest attaching to the small planet group as
a whole, I have ^appended in tabular form a
•complete list of these tiny members of the solar
system, but without amplifying it to include
particularities of their paths round the Sun.

The chapter on Comets deals especially with
historic detail of these filmy voyagers ; and the
great meteoric showers of 1899 and 1900 must
be justification for extending the space allotted
to meteorites — the sole material messengers
from outer space ever known to come within
human reach.

Even more amplified is the chapter on the
fixed stars and nebulae, because the methods of
the new astronomy have achieved unparalleled
revelations in the stellar realm. So fertile are
the starry fields, and so persistently have they
been tilled by a band of tireless workers for the
last quarter of a century, that the compacting of
results into a single chapter was found impos-
sible. The cosmogony was therefore allotted a
chapter by itself, and due space accorded the '

6 Introduction

newest research in our knowledge of the building
and development of worlds.

Both to encourage and to gratify a desire ta
consult original sources, there is added to each
chapter a bibliographic note, never intended to
be complete, and with both popular and scientific
papers purposely intermingled.

But nearly equal in interest with the stars
themselves are the telescopes by which alone we
ascertain their distances, inconceivably vast, and
the spectroscopes that tell the tale of stellar
motion and constitution. So Stars and Telescopes
may be said to culminate in an account of the
famous instruments, their construction and mount-
ing and use. To the gradual development of
skill in the arts and to present-day perfection
of mechanical and photographic methods is the
progress of astronomy vastly indebted in all its
ramifications. Just as the precision of the ' old
astronomy' could never have been attained in-
dependently of the skill of workers in metals
who provided accurate clocks and meridian
circles, so the * new astronomy ' would have
been wholly handicapped in its development
but for the splendid prisms and perfect gratings
of the modern optician. Evolution, too, of the
process of making great lumps of glass has been
mainly mechanical, not to mention the methods
of fashioning disks into lens and prism. During
the first half of the 19th century, there was little
chance to forget the optician and telescope
builder, because the greatest instruments o£

Introduction 7

those days were constructed by the astronomers
themselves, who used them so successfully.
Too often, however, in our own day we omit to
mention the optician and instrument maker,
unaided by whose consummate skill original
research in physics and astronomy would have
made but slender progress. Not only in the
title of this book, therefore, are the significant
labors of the mechanician recognized, but its
last chapter is lengthened to a degree fitting a
highly mechanical age.

By the most conservative estimate, the thresh-
old of the edifice of stellar investigation is but
barely crossed ; its corridors have been sub-
jected to the merest reconnaissance; nothing
but the crudest plan of the intricate temple of
the stars can yet be sketched with confidence.
Here comes an insistent demand for more light
and greater telescopes still — more light, not for
the expected discovery of new bodies, but for
studying in greater detail the constitution of the
•component bodies of the stellar universe already
known, and for investigating with greater pre-
cision their motions relatively to our solar orb
and his tributary family of planetary globes.

Greater successes for the optician of the future
seem safely predicated upon the rapid advances
of the recent past. No step can, however, be
taken except at infinite pains and large expen-
<liture. Mechanician and optician are ready to
"do their faithful part, and opportunity to go
forward must not be too long denied them.

Ifttroduction

Continuity of effort will alone guarantee success ;
each generation must build upon the platform of
its immediate predecessor. Otherwise gaps oc-
cur. With the passing of the elder Herschel,
nearly a generation elapsed before Lord ROSSE'S
great telescope was finished ; and he could then
profit relatively but little by Herschel's un-
paralleled experience. Already the Clarks
have passed from earth, father and both sons.
But we have worthy successors, still in the prime
of brilliant achievement : they await to-day their
keenly coveted opportunity.

D. P. r.

Amherst, February 1899.

STARS AND TELESCOPES

CHAPTER I

OUTLINE HISTORY OF ASTRONOMICAL

DISCOVERY

T T is not proposed here to enter into any discussion
^ of the knowledge of astronomy possessed by the
ancient Egyptians, Babylonians, or other Eastern na-
tions. Among the Greeks, Eudoxus, born at Cnidus
in Caria about b. c. 409, is the first astronomer that
need be named. His works have not come down to
us ; but it is known that one of them was a description
of the constellations, which is versified in the Phai-
nomena of Aratus of Soli in Cilicia, and is the work
quoted by Paul in his speech before the Areopagus
at Athens.

The greatest of the ancient Greek astronomers was
HiPPARCHUS, who, though a native of Nicaea in Bithy-
nia, made most of his observations at Rhodes. He
was the first to form a systematic catalogue of stars,
induced to do so by the appearance of a new star in
the heavens, which is thought to be the same as one
recorded in the Chinese annals as having appeared ia
the constellation Scorpio in the year corresponding to
B. c. 134. The most probable date of the death of
HiPPARCHUS is B. c. 120. His catalogue is known ta

lo Stars and Telescopes

us only by its incorporation, with some modifications,
into the great work of the Alexandrian astronomer
Ptolemy, entitled 'H Ma^ij/xaTiK^ 2wraf»ff, which, after
the Arabians, is usually called The Almagest, Ptolemy,
principally known from the system of the world which
bears his name, died early in the reign of the Emperor
AuRELius, which commenced in a. d. i6i.

The greatest of Arabian astronomers was Albatenius
(so called from his birthplace, Baten, in Mesopotamia),
who flourished in the ninth century of our era. About
a century later the Persian astronomer Al-SOfi formed
a catalogue of stars from his own observations. An-
other catalogue was made by, or rather under the
auspices of, the Mongol prince Mirza Mohammed
Taraghai, or Ulugh Begh (as he is generally called),
grandson of the famous Timour, from observations at
Samarkand about a. d. 1433.

The labors of Peurbach and Muller (usually called
Regiomontanus), toward the end of the same century,
prepared the way for Copernicus, who showed the
simple explanation of the planetary motions which
resulted from supposing the Sun to be placed in the
centre of the system. His work, De Revolutionibus
Orbium Coelestium^ was published in 1543, in which
year the illustrious author died. The foundation of
the true theory of the solar system was thus laid, but
the time for its establishment liad not arrived. It was
rejected by the great Danish astronomer, Tycho
Brah6, in favor of a system called from him the
Tychonic, in which the Moon and Sun were supposed
to revolve round the Earth, and the planets round the
Sun. Tycho's observations, however, furnished the
means by which, less than 20 years after his death,
Kepler deduced the laws of planetary motion. It
was in 16 18 that he discovered his third and last

Outline History

law, which shows the mutual correspondence existing
between the motions and distances of all the planets,
and proves (though it was reserved for the genius of
Newton to demonstrate this consequence) that they
■obey the same law of force directed toward the Sun.

Meanwhile Gauleo GALitEi, equally famous, had
been discovering a system of moons revolving round
Jupiter as the planets do round the Sun, confirming
by that and by other discoveries the truth of the Coper-
nican system, and establishing the laws of motion,
without a knowledge of which farther progress in
astronomy as a science was impossible. Galileo died

12 Stars and Telescopes

in 164a ; and in the same year wag bom Newton,
the prince of philosophers, who discovered the law
of gravitation, and demonstrated its competency to
explain the most important of the lunar ami planeury
motions. This was made possible by the French
astronomer Picard's determination of the tnie size of
the Earth, and by Fiamsteed's observations of the
Moon, commenced at Greenwich in 1676, the year
after the founding of the
Royal Observatory there.
The I^ilosophia NaturaHs
I^neipia Mathematica,
Newton's great work, was
published in 1687.

Of the satellites of Sat-
urn, HuYGENS discovered
one, and Cassini four, in
the latter part of the 1 7th
century; and Hia'cens had
explained the ring-like na-
ture of the appendage to
GALILEO (1564-1642) Saturn, the existence of

which had been first no-
ticed by Gauleo. It was not until some time after the
death of Newton in 1727 that his theory was further
developed, and shown to be capable of explaining not
only the principal courses of the planets, but the
smaller deviations in their movements. This is due
to the labors of several eminent mathematicians, but
especially to Lagrange and Laplace. The Meeanique
Anaiytique of the former was published in 1787, and
the Mieanique Celeste of the latter was completed in.

Toward the end of the 1 8th century arose an astron-

Outline History ij

omer, Hanoverian by birth and English by adoption,
who, by the discovery of Uranus in 1781, not only

extended what had previously been supposed to be
the boundary of the solar system, but who, turning
upon the sidereal heavens with unwearied diligence
the powerful instruments constructed by himself.

Stars and Telescopes

acquired for mankind a knowledge of the distribu-
tion and motions of the stars, which inaugurated a
new era in the history of astronomy. Sir William
Hersckel, elected in 1820 the first president of the
Royal Astronomical Society, died two years subse-
quently. That Society published in 1837 a compiled

hebschel (1738-1822)

catalogue of stars, which was the standard work of
reference on the subject until superseded by the cata-
logue of the British Association containing 8,377 stars,
published in 1845.

Soon after this the boundary of the solar system
was still farther enlai^ed by the famous discovery of
Neptune in 1846; and the year following, Sir John
Herschel published the results of his observations at

Outline History 15

the Cape of Good Hope, where he had devoted some
years to diligent scrutiny of the stars and nebulae visi-
ble only in the southern hemisphere, — a research
similar to that in the northern heavens, initiated by
his father and extended by himself and others.

Early in the present century four new planets were
discovered, the first of a group of many hundred
revolving between the orbits of Mars and Jupiter,
and so much smaller than all the others that distinct
terms — planetoids or asteroids — were suggested for
them. But as they differ from the other planets
mainly in size, it is now more usual to call them
small or minor planets. They remained four in num-
ber until 1845, when a fifth was found. Since then,,
discovery has been so rapid that members of that
group are now approaching 500 in number, and prob-
ably there are hundreds more. The later discoveries
cannot be seen without a powerful telescope, and
nearly all the most recent were first recognized on
photographic plates by D' Max Wolf of Heidelberg
and M. Charlois of Nice. The number of known
bodies of the solar system has been farther increased
by the discovery in 1877 of two satellites revolving
round Mars, and of the fifth satellite of Jupiter in
1892.

Also, the accurate observations of the last half cen-
tury have enabled astronomers to determine the approx-
imate distances of some of the fixed stars ; a Centauri^
in the southern hemisphere of the sky, and about
275,000 times more distant than the Sun, being, so
far as is known, the nearest.

It is now a third of a century since a new branch
of astronomy was inaugurated by the analysis of
the light of celestial bodies with the spectroscope.

l6 Stars and Telescopes

This began with the investigations of Kirchhoff and
BuNSEN in 1859, which were brilliantly followed up by
D' HuGGiNS (at first in conjunction with Miller), and
subsequently by Secchi, Janssex, Young, Lockyer,
VoGEL, Draper, Pickering, Maunder, and many
others. Not only has the spectroscope enabled us
to learn much of the chemical constitution and con-
dition of celestial bodies both in and beyond the
solar system, but its later developments have revealed
motions of several of the stars in the line of sight (in
some cases approaching, in others receding), which
cannot be recognized in any other way. Likewise,
the same instrumental method has led to the impor
tant discovery that many stars, although appearing
single under direct scrutiny with the highest telescopic
powers, are really double. One very interesting dis-
covery of spectrum analysis is that the light of many
of the nebulae (the great nebula in Orion, for exam-
ple) does not proceed from multitudes of stars, as was
once supposed, but from incandescent or intensely
heated matter in a gaseous condition.

The first person who is known to have noticed
(though it is not unlikely Newton had done so
before) a few of the dark lines crossing the prismatic
spectrum at definite distances, was Woli-aston in 1802,
and he is known as their discoverer ; but as the accu-
rate positions of a large number of them were first
measured in 1815 by Fraunhofer, the celebrated
German optician, they are always called Fraunhofer
lines. The measurement of the positions and dis-
tances of these lines in the spectra of different celes-
tial objects, and the comparison of the spectra of the
heavenly bodies with the spectra of incandescent ter-
restrial substances, have led to the important discov-

Outline History

eries alluded to above. But the spectroscope is not
the only new engine of astronomical research intro-
duced in recent years. The application of photog-

FRAUNHOFER (1787-1826)

laphy to celestial observations, and the instruments
for making exact determination of the comparative
amounts of light from different heavenly bodies have
both inaugurated new fields of study which have borne,
and are bearing, the richest fruit.

s * T — 2

1 8 Stars and Telescopes

Jablonow, De Astronomic Ortu ac ProgressUfetc, (Rome 1763).
Lalande, Astronomic (Paris 1792).
La Place, Exposition du Systhne du Monde (Paris 1800).
MONTUCLA, Histoire des Mathimaiiques (Paris 1802).
Lalande, Bibliographie Astronomique avec PHistoire de

r Astronomic (Paris 1803).
Bailly, Histoire de P Astronomic Ancienne ct Modeme (1805).
Delambre, Histoire de l* Astronomic Ancienne (Paris 181 7).
Delambre, Histoire de r Astronomic du Moyen Age (Paris i8i9)»
Delambre, Histoire de P Astronomic Modeme (Paris 182 1).
Delambre, Histoire de P Astronomic du XVIII' Siec/e {iS2y),
La Place, Pr/cis de i* Histoire de r Astronomic (Paris 182 1).
Bentley, Hindu Astronomy (London 1825).
Rothmann, History of Astronomy ^ * Library of Useful Know-^

ledge' (London 1832).
Narrien, Ori}:^in and Progress of Astronomy (London 1833).
Jahn, Gcschichte der Astronomic (Leipzig 1S44).
Grant, History of Physical Astronomy (London 1852).
Main, History of Astronomy^ 8th edition of Encychpadia
Britannica, vol. iii. (1853) ; 9th ed. ii. (1875), 744 (Procior).
LOOMIS, Recent Progress of Astronomy (New York 1S56).
Lewis, Astronomy of the Ancients (London 1862).

BlOT, Etudes sur P Astronomic Indicnnc et Chi noise (Paris 1862),

Wolf, Gcschichte der Astronomic (Munich 1877).

HOUZEAU, Bibliographic Geniralc^ i. (1887), Introduction.

Young, * Ten Years* Progress/ Xature, xxxv. (18S7), 67, 86, 117.

Bertin, * Babylonian Astronomy,' Nature^ xl. (1S89), 237, 261,.
285, 360.

Epping and Strassmayer, Astronomisches aus Babylon (Frei-
burg 1889).

Wolf, Handbuch der Astronomic^ i. (Zurich 1890).

Clerke, History of Astronomy during the XlXth Century
(London 1893).

Tannery, Rccherchcs sur C Histoire ^c V Astronomic Ancienne
(Paris 1893).

Lockyer, The Dawn of Astronomy (New York 1S94).

Berry, Short History of Astronomy (New York 1899).
Excellent chronological tables of salient events arc in the

Annuairc ol Brussels Observatory (1877), p. 52, Chambers's

Astronomy^ vol. ii. p. 468, and in Miss Clerke's History^ p.

531. Consult, also, the extensive lists of Houzeau's Vcuie

Mecum de tAstronontCf ch. ii. pp. 34-147, a work of invaluable

assistance in all investigation of the origins of astronomy, and

its development down to modern times. — D. P, T,

("736-17931

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tuTHcndwilh iJit ^rtidrncr n/ Ikr M.,,ion,,l Assembly of \^*^aHdl)l^

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manji elnttrnlr Irraliiri. and krld Ikr kigh imor <•/ mrmbtrMf it Ikt

(■749-'S*^)

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lulroHsmical ■KT-.lm. Hurscmel's ditc-tVTy 0/ Uraiu, /■ ,;8i jf-./
laTV him o^firlnHily ftr JiiliHcti^ ijt cwlr.rlint IM„ ,/ Ik. nn,
flaitft mialim. Hi via cirlliltirraliiir nilk ^r«CHAI^ in Kteamrimf
an arc 0/ miridiam. nW nactrdtd Ljiuniie in iRo; al flu Callitr dr
Franc: DKLAMKi-B «^ «. „Jlc.r^/ Ihi Ughn «///*-«-!

CHAPTER II

THE EARTH

T^HE general shape of the Earth on which we live
^ is that of a sphere or globe. Although the irreg-
ularities of its surface present in places what appear,
to our eyes, enormous elevations, the altitude of the
highest mountain does not really amount to nearly
the thousandth part of the diameter of the Earth;
and the depth of the lowest sea-bottom is about the
same as the height of the highest mountain.

But while our powers of locomotion are thus con-
fined within so comparatively small a part of the
vast universe of creation, the wonderful sense of sight
has enabled us to acquire, through the agency of light,
some knowledge of other bodies around us. Many of
them are seen to be in motion, though it has been
discovered that these movements are not all real, but
in part apparent, produced by real motions of the
Earth itself. All our knowledge respecting these bod-
ies is embraced under the term astronomy ; and as
that science has taught us to consider the Earth itself
as one of the moving bodies of the universe (one of
the planets, in fact, revolving round the Sun, from
which they derive their light and heat), a knowledge
of its motions, as well as of its shape and size, forms
also an important part of astronomy.

The Earth's actual form is not spherical, but slightly
flattened at the poles, — the diameter taken anywhere

20 Stars and Telescopes

across the equator measuring 7,926.6 miles, and the
polar diameter, or that taken from pole to pole, 7,901.5
miles, 25 less than the equatorial.*

On the polar diameter as an axis the Earth rotates
from west to east, while revolving in the same direc-
tion in an orbit round the Sun. The axis of the Earth
is inclined to the plane of this orbit at an angle of 66°
32' 52".o (in 1900), and its rate of increase is nearly
o".5 annually. The true period of axial rotation is

1 The Clarke spheroid of 1878, generally adopted, gives
more exactly: —

(Equatorial semi-diameter == 20,926,202 feet = 6,378-
301 metres = 3,963.296 miles.
Polar semi-diameter = 20,854,895 feet = 6,356,515
metres = 3,950.738 miles,

the polar compression being ytAt7* This supposes that the
figure of our globe corresponds to an oblate spheroid, its equa-
tor being a circle. Hut it is found that all existing measures
of the Earth are better represented if the equator is regarded
as slightly elliptical ; in other words, the Earth is an ellipsoid
with three unequal axes. The greatest equatorial bulge lies
very nearly coincident with Liberia on one side and the Gilbert
Islands at its antipodes ; while the City of Mexico in the west-
ern hemisphere and Ceylon in the eastern mark the meridian
of least eccentricity. A good notion of the refinements in
modern geodetic work is conveyed by stating that this investi-
gation places Ceylon only 1,500 feet nearer the Earth's centre
than Liberia ; farther observations are, however, necessary to
establish this conclusion beyond dispute. But owing to the
irregular past action of forces operant in moulding the Earth's
crust, it is wholly unlikely that our planet has the general out-
line of any mathematical solid ; so that it becomes the business
of the geodesist to assume the most probable figure, and then
measure the deviations of the actual Earth or geoid tlierefrom
in every particular. It is to be expected that the extensive
series of pendulum observations now conducted by represen-
tative nations will tentatively determine, not only the Earth's
general figure, but all local deviations, with greater accuracy
than the processes of the ordinary geodesy. — D, P, 71

The Earth

called a sidereal day; it is dixdded into 24 sidereal
hours, and is equal to 23^ 56" 4'.09 of ordinary time.
But, the convenience of life rendering it necessary
to regulate our time by the Sun, the day of our ordi-
nary reckoning is a solar day, and this also is sub-
divided into 24 equal parts called solar hours. The
reason for the two kinds of day will be seen on reflect-
ing that the Earth's actual motion round the Sun (or,
what is in effect the same thing, the apparent motion
of the Sun among the stars) places it a little farther east
every day. Evidently, then, the Earth, rotating east-
ward also on its axis, and having completed an entire
rotation referred to the stars, must turn a little farther
to complete an entire rotation referred to the Sun.
The solar day, therefore, is longer than the sidereal
day ; and these apparent solar days were employed as
a measure of time in France until 18 16. But they are
inconvenient for this purpose because of their unequal
length, which is due partly to variations from day to
day in the Sun's apparent motion among the stars.
In practice, a mean or average day for the whole year
(called the mean solar day) is now used, and the dif-
ference between the mean and the apparent solar time
^t any instant is termed the equation of time.^ The

2 Coincidence of true Sun and mean Sun occurs four times
annually; that is, the equation of time is then zero, and Sun
and mean time clock agree. Following arc the approximate
days of each year when this takes place, also the dates when
the equation of time is a maximum, either positive (Sun slow),
or negative (Sun fast): —

12 February, Sun 14.5 slow.
15 April, 00

14 May, Sun 3.9 fast.

1 5 June, 0.0

Sun

6.2 slow.

25 July,

31 August, 0.0

I November, Sun 16.3 fast.
24 December, 0.0

Between these dates the equation of time is intermediate in

22 Siars and Telescopes

mean solar day is universally accepted as the clementat
unit of time in all other astronomical measurements of
duration, and for the purposes of civil life as well.

Of these mean solar days the Earth occupies
365.25636 (equal to 365^ 6'' 9"" g'.o) in revolving
lound the Sun, and this period is called the sidereal
year, because at the end of it the Earth is in the same
position with respect to the Sun and the stars. But,
just as the conveniences of life lead us to regard as
the day not the precise period of time in which the
Earth completes one ro-
tation on its axis rela-
tively to the stars, so do
they not allow us to
adopt as the year the
exact period of time in
which the Earth revolves
in its orbit round the
Sun. For what makes
the observance of the
year necessary to us is
the change produced by
the variations in the sea-
sons ; and in conse-
quence of a slow conical
movement of the Earth's
axis (occupying about ™ 'o? 'th" vi"»*L'MQummf '^ow
35,800 years to com- .i^" "vohd taubus ano

plete a whole round, and

called precession of the equinoxes, from the effect it
produces upon the equinoctial points), the tropical

value, and Tlu Efhtmerii, or Nauliad Almanae, fur the par-
ticular year must b« consulted to find Ihe preciM amount at
DooD each day. — Z>. P. T.

The Earth 23

year, in which all the changes of the seasons are
run through, is 20™ 23».5 shorter than the sidereal
year. In fact, the true length of the ordinary, or
tropical year, is 365*^.24219, or 365*1 5** 48™ 45».5.
It is now apparent that the Earth has three prin-
cipal motions : ( i ) a rotation of the globe round its
own axis, (2) a revolution round the Sun, during which
the axis remains nearly parallel to itself, and (3) a
slow conical motion of the axis so performed as to
retain nearly the same inclination to the plane of the
orbit throughout. But it should be mentioned that the
axis is subject to an oscillation, in a period of a little
less than 19 years, which alternately increases and
diminishes the inclination by a small amount. This
is called nutation, and was discovered in 1747 by
Bradley, the third Astronomer Royal.*

' Recent investigation has brought to light still another
motion of the Earth which causes a periodic variation in the
latitude of all places on its surface. An early research of
EuLER demonstrated that if a *free rigid oblate spheroid*
(then supposed to represent what was known about the Earth)
be set in rotation round an axis making a small angle with its
axis of figure, and be not acted on by any force, the position of
the axis of rotation within the spheroid will describe a circular
cone round the axis of figure with a uniform motion. This
principle applied to the Earth gave a theoretic period of about
306 days, and the eminent German astronomer, C. A. F. Peters,
was the first to discuss the question whether observations were
sufficient to reveal a corresponding variation in terrestrial lati-
tudes. Later the investigations of Nyr6n and others showed
that if an inequality of this period existed at all, its amplitude
could not exceed a few hundredths of a second — that is, a few
feet on the surface of the Earth. As, however, the Earth is
not a perfectly rigid spheroid, but is partly covered by a fluid
envelope, and has perhaps the elasticity of steel (to adopt the
conclusion of Lord Kelvin), Professor Newcomb finds the
theoretic period not 306, but 441 days — a remarkably good

24 Stars and Telescopes

The mean density of the Earth is about five and a
half limes that of water ; which shows that some por-
tion at least of the interior must be much denser than
that of the exterior craat. The entire surface area of
our planet is about 197,000,000 square miles. Of this
about three fourths, or 145,000,000 square miles, are
covered by water : and the feict that the area of water

in the southern hemisphere is larger than that in the
northern proves that the former portion of the Earth
is somewhat denser than the latter, enabling it to retain
the larger bulk of water. If the globe be divided into
two hemispheres such that the surface of one contains
the largest possible amount of land, and the other the

agreement with the period of 427 days determined from ob-
servation by M' Chandler in 189*. Professor Nrwcomb
regards this agreement as affording conclusive and independent
evidence of the rigidity of our globe; and we may, he says,
accept the conclusion that the pole of rotation of the Earth
describes a circle round its pole of figure in about 4:7 days,
and in a direciion from west toward east, as a result of d)'nanii-
cal theory. Observations still in progress (1S99) at Tokyo,
Kasan, Pulkowa, Prague, Potsdam, Lyons, Philadelphia, and
elsewhere, have revealed the exact nature of the polar oscilla-
tion since 1S90, as in the opposite diagram, and defined its mo-
tion in the future. The curve is mainly elliptical rather than
drcular.and the extent of fluctuation is About 60 feet. — D.P.T,

^iliiiii

ftliili

The Earth 25

largest possible amount of water, the pole of the
former portion will be very near the British Islands^
and the pole of the other very near New Zealand.

Form and Size

ToDHUNTER, History of the Mathematical Theories of Attraction

and the Figure of the Earth. 2 vols. (London 1873.)
Clarke, Geodesy {Oxioxd 1880).

Woodward, American JourncU Science^ cxxxviii. (1889), 337.
Preston, * Pendulums, Am. Jour. SciencCy cxli. (1891), 445.
Gore, J. H., Geodesy (Boston and New York 1891).
Fowler, * Measurement of Earth,' Ktwwledge^ xx. (1897), 148.

Invariability of Rotation and Variation ok Latitude

Newcomb, American Journal SciencCy cviii. (1874), 161.
Newcomb, Astron. Papers American Ephemeras, i. (1882), 461.
Glasenapp, Downing, The Observatory, ji\\.(i^()), 173, 210.
Chandler, The Astronomical Journal, xii., xiv. (1801-94).
Newcomb, Month, Not. Royal Astron. Society, lii. (1892), 336.
DOOLITTLE, Proc. Am. Assoc. Advancement Science, xlii. ( 1893).
Ball, * Wanderings of North Pole,* Smithsonian Report 1893.
Woodward, The Astronomical Journal, xv. (1895), 65.
Albrecht, Astronomische A'achrichten, cxlvi. (1898), 129.
Chandler, The Astronomical Journal, xix. (1898), 105.

Aurora Borealis, Terrestrial Physics, etc.

LOVERING, Afem. and Trans. Am. Acad. Arts and Sci., 1867-73.

Huxley, Physiography (London 1882).

Tromholt, Under the Rays 0/ Aurora Borealis (London 1885).

LemstrOm, VAurore Boriale (Paris 1886).

Bishop, *Sky glows,' Warner Observatory (Rochester 1887).

Symons, The Eruption of Krakatoa (London 1888).

Ball, * Krakatoa, /«5'/a/'rj' Realms (London 1892).

Wallace, *Our Molten Globe/ Fortn. Rev., Iviii. (1892), 572.

Mill, The Realm of Nature (New York 1892).

King, * Age of the Earth,* Smithsonian Report 1893, P* 335-

Becker, • Interior of Earth/ North Am. Rev., clvi. (1893), 439'

Bonney, The Story of our Planet (London 1893).

Kelvin, Popular Lectures and Addresses, ii. (New York 1894).

Dawson, Salient Points in Science of Earth (New York l8i94).

Angot, Les Aurores Polaires (Paris 1895).

For Earth's density, tides, etc., consult Harkness, Washing-
ton Observations 1885, App. iii. pp. i W and 161 ; and Gore,
* A bibliography of Geodesy,* Report U. S. Coast Survey 1887 ;
also Poole's Indexes, vols, i.-iv., and Astrophysical Journal^
i.-viiL (1895-98).—/?. P. T

CHAPTER III

THE MOON

IN its annual journey round the Sun, the Earth is
accompanied by a smaller body called the Moon ;
her movement relatively to the Earth being in the
nature of a motion in an elliptic orbit round the lat-
ter, she is considered as a satellite or secondary planet
thereto.

The Moon, then, being by far our nearest neigh-
bor among the heavenly bodies, much more has been
learned about her than about the others ; selenog-
raphy, in fact, has of recent years become almost
a science of itself. The great work of Beer and
Madler upon the Moon was published in the year
1837, that of M"^ Neison (now M' Nevill) in 1876.

On account of the Moon's proximity to us, an
exact knowledge of her apparent motion among the
stars is of the greatest practical use in navigation,
thereby enabling the mariner to find his longitude at
sea. The difficulty of this problem, which has exer-
cised the labors of many distinguished mathemati-
cians, arises from the perturbations to which the
Moon's elliptic motion round the Earth is subjected
through the gravitating action of the Sun and the
nearer or more massive planets.* By reason indeed

^ Foremost among these investigators in the last half-cen-
tury have been Hansen in Germany, Pont^coulant and

tsl malhimalical

.._ .^ Sun and Afam,

old, art am the batis of cat*.
r resulalid. and thi ships ^
ksHsrcd by tkt award a/ tkr.
at SMirly)

(1816-1S72)

<Chari.es EuntNH Dt.i.\vv \\wai pirhafi Hi griaitst of mi>der,.
French geni-diri. Ht succndtd Arago and Le Verrier at
director of the Paris Oburvalory. DelaunaVs masterpieu in
lillid 'La Thiorii du Mouvtment dt la Line • is pnbtiihed in two
fuarta voliinus of tht • Mimoirei de fAcadlmii des Scitncis di
rinslilul de France • (Paris 1S60-67)

The Moon 27

of the much greater mass of the Sun, he exerts a
more powerful attractive force upon the Moon than
the Earth does, although the latter is so much nearer.
The mathematician might, therefore, take exception
to calling the Moon a satellite of the Earth ; and she
is certainly not so, in the full sense that the moons
of Jupiter and Saturn are satellites of those planets.
Still, as we have said, the Moon's motion, relatively
to the Earth, is a motion round it ; she is connected
with our planet by an indissoluble tie, and, from her
great benefit to us, will always be called ' our satel-
lite,' exciting our gratitude and commanding our con-
stant attention.

The actual duration of the Moon's orbital motion
round the Earth is 27^ 7** 43"* ii*.545; but here
again convenience compels us to regard as a lunar
month or lunation not this, the time of her sidereal

Delaunay in France, Airy and Adams in England, and Pro-
fessor Newcomb and M' G. W. Hill in America. Hansen,
Delaunay, and Airy spent a goodly portion of their lives
upon the intricate mathematics of the ' lunar theory,* as it is
termed. However, the formation of final tables for predicting
the Moon's motions is a task so prodigious that only one of
these investigators (Hansen) arrived at this complete solution
of the problem; publishing in 1857 his Tables de la Lune con-
struiUs d*apris le principc N^wtonien de gravitation UniverselU.
These, in conjunction with Professor Newcomb's Corrections^
are now exclusively employed in calculating future positions of
the Moon ; and at the present time the error of prediction does
not often exceed 4", while its average is half that quantity, or
at>out xim P^'^^ ^f ^^^ Moon's breadth (that is to say, about
two miles in space). The story of the labors of mathematicians
in determining the 'secular acceleration of the Moon' (one out
of nearly a hundred perturbations which derange its motion
round the Earth) is told by Professor Newcomb in the intro-
duction to his masterful work entitled Researches on the Motion
cf the Moon (Washington Observations, 1875). — ^' ^' ^-

28 Stars and Telescopes

revolution, but the mean period between successive
conjunctions with the Sun. This period is some-
times called a synodic revolution, and amounts to
29^ i2*> 44" 2*.684 ; upon it of course depend the
Moon's phases as presented to the Earth, her illumi-
nation being due to the light of the Sun. The Moon
also receives solar light reflected from the Earth;
and when the illuminated part of our globe turned
toward her is the greatest (that is, near our New
Moon), this light is sufficiently strong to be reflected
back again, enabling us to see the other part of her
surface, as at Full Moon, only very faintly. This is
popularly called * the old Moon in the young Moon's
arms.'

In consequence of the comparative proximity of
our satellite, her distance and size can be determined
much more accurately than those of any other heav-
enly body. Her mean distance is 238,840 miles
(the mean horizontal parallax being 57' 2".3) ; but
her actual distance varies, in different parts of her
orbit, between 221,610 and 252,970 miles.* The
eccentricity of the Moon's orbit is 0.0549 : and its
inclination to the ecliptic, or Earth's orbit, varies
between 4° 57' and 5° 19', the mean value being
5° 8' 40".

* It is worthy of note that, while the Moon comes nearest
to the Earth of all the heavenly bodies, the meteors alone
excepted, its distance (about 60}), in terms of the radius of its
primary body, exceeds that of all other known satellites in the
solar system. Only Japetus, the outer satellite of Saturn^
approaches this maximum, its distance being 59.6 times the
equatorial diameter of that planet ; while the satellites nearest
their primary, when estimated in like manner, are Phobos, the
inner moon of Mars (2.8), and the newly-found satellite of Jupi-
ter (2.6). — Z>. -P. T.

* PART OF THE

IFmm a ftui^grafk hr rhi BrclHtn HrNUT al Pari,. ijrJ start* 1893. Aew t/tkt MMn.
} day, .f, hrxrt. Tlu Ikrn larf, craltn aitvr Ihl rnln nf tk, fitld an ThrntkUw
{Irani smt), Cyriaui.nHd Calkarina; amd iMi diamiltr 9/ tacK it aioul d^ tiiari\

B MOON, 1ST SEPTEMBER, 1890
I PitUgra^d mlilu Lick Oiiirvaitry)

30 Stars aud Telescopes

The diameter of the Moon is 3,163 iniles, or some-
what less than two sevenths that of the Earth; so
that the bulk of our planet is about 50 times as
great as that of the Moon. But her density being
little more than half that of our own globe, her mass
amounts to only about ^ that of the Earth.

The Moon rotates on her axis very much more
slowly than our Earth does. In fact, the duration of
her rotation is exactly the same as the period of her
revolution round the Earth, The consequence is
that we always see precisely the same face of the
Moon ; an entire half of her surface being always con-
cealed from us, excepting such small portions of it
near the visible half as come into view from libra-
tions (as they are called), mostly produced by the
varying velocity of her orbital motion and the incli-
nation of her orbit to that of the Earth.

That portion of the Moon's surface which we are able
to see and study presents an appearance very differ-
ent from that which any portion of the Earth's surface
would do if similarly scrutinized. All indications show
that there is no atmosphere surrounding the Moon ; •

* The adjoining picture will serve to illustrate one of the
critical indications referred to — (he
planet Jupiter in pari hidden behind
the limb o£ the Moon. No distortion
of the delicate details of the planet's
surface is apparent along Ihc Moon's
edge, as would be the case if the
Moon had an appreciable atmos-
phere. Planetary occultations are
now excellently photographed. Lu'
nar photography, begun by the elder
Draper in 1840, and continued by
his son Henry, and by Ruther-
fi;rd, in New York, has culminated in splendid series of

IFram a fAMefratk unik t

»ST QUARTER (LOEWV AND PUISEUX)

( ermi t^matrial Cndi ^ On Parit Ohtnrtlnj)

The Moon 3 1

or at least that if there be any, it must be of exces-
sive tenuity, and unable to hold clouds, or any ap-
preciable amount of aqueous vapor, in suspension.
Indeed, if there be any water on the surface of our
satellite, it can only be very trifling in amount, and
conflned to the lowest depressions. Yet there is
decisive evidence of the action of water on the lunar
surface in bygone ages, so that this has probably in
the course of time been all absorbed into the interior,
or has by degrees become chemically combined with
the solid material of the exterior.

The surface is diversified by a large number of
crateriform cavities (many of them containing a coni-
cal hill at the bottom), and extensive arid plains.
The latter retain the name of seas, given them when
selenography was in its infancy, and when it was erro-
neously thought that they were large bodies of water.
Markings of a very peculiar character have also been

negatives procured with the 13-inch Harvard telescope on
Mount Wilson, California, and with the 36-inch telescope of the
Uck Observatory. At the Columbian Exposition, Chicago,
1893, were exhibited many superb enlargements of portions of
the moon from both series, some of the Harvard prints being
on a scale corresponding to a lunar diameter of 14 feet. Many
of the Lick originals (of nearly six inches diameter) are tech-
nically perfect enough to bear enlargement to six feet : while
M. Prinz of the Royal Belgian Observatory has made photo-
graphic amplifications of the lunar crater Copernicus from
these negatives to a scale on which the Moon's diameter
would exceed 30 feet. The finest photographs rival the clas-
sic handiwork of Madler, Schmidt, and Ix>hrmann, but are
secondary in this, that the very small craters are sometimes
indistinctly registered by photography. Also the Lick nega-
tives of the Moon have been industriously studied by Professor
Weinek of Prague, who appears to have discovered new rills
and craters, and has elaborated a beautiful series of enlarged
drawings, which, reproduced by heliogravure, form very perfect
detail pictures of lunar scenery. — D, P. T,

32 Stars and Telescopes

noticed in comparatively recent times, consisting of
long whitish streaks running across other formations.
These are called rills, and are usually supposed to be
the results of crackings in the surface ; but it has been
suggested that they may be dried water- courses.'

7 The ordinary surface structure of the Moon, apparently
volcanic in the main, is best seen at or near the time of quad-
rature, under oblique illumination. But the lunar rills or
streaks, difficult to observe when the shadows of the mountains
are most conspicuous, and very prominent when these shadows
are imperceptible, demand a front illumination for their visibil-
ity. Theoretically, the material of the streak-surface must, as
pointed out by D' Copeland, be made up of multitudes of
surfaces more or less completely spherical, but either concave
or convex ; and he therefore regards the streaks as produced
by a material pitted with minute cavities of spherical figure, or
strewn with minute solid spheres. On critical investigation of
the rill systems (with a 13-inch telescope, at an elevation of
8,000 feet, at Arequipa, Peru), Professor W. H. Pickering
finds that the streaks of the system surrounding Tycho and other
craters radiate, not from the centre of the ring mountains, but
*£rom a multitude of craterlets upon their rims. Also there are
not, as heretofore supposed, any streaks hundreds or even thou-
sands of miles long; but their usual length varies from ten to
fifty miles, while they seldom exceed one quarter mile in breadth
at the crater. In the volcanic region surrounding Arequipa,
the roads are, in some places, partially covered with a white
pumice-like material, and its behavior under different inclina-
tions of the line of illumination to the line of vision has led
Professor Pickering to a conclusion quite identical with that
of D*" Copeland, that the general appearance of the streaks
is most readily explained by the hypothesis of a light-colored
powder extending away from the craterlets. The only farther
step necessary to a satisfactory explanation of these mysterious
markings is a reasonable elucidation of the process by which this
powder has come to be radially disposed. \Vi)RDEMANN*s the-
ory, cited by D' Gilbert in his address on ' The Moon's Face:
a Study of the Origin of its Features ' {Bulletin Philosophical
Society of Washington, xii. 285), is that meteorites, striking the
Moon with great force, have splashed whitish matter in various
directions, — which seems plausible. — D, P. T.

The Moon 33

GUILLEMIN and Mitchell, The Moon (New York 1873).
Proctor, The Moon ; her Motions ^ Aspects ^ etc. (London 1873).
RossE, Bakerian Lecture on ' Radiation of Heat from the

Moon,' in Philosophical Transactions for 1873, P- 5^7*
Nasmyth and Carpenter, The Moon (Ix)ndon 1874).
N EI SON, The Moon^ and . . . its Surface (London 1876).
LoHRMANN, Mottdcharle (Leipzig 1878).
Schmidt, Charte der Gebir^e des Mondes (Berlin 1878).
TTu Selenographical Journal (a London monthly, begun in 1878).
Opelt, Der Mond (Leipzig 1879).

Harrison, Telescopic Pictures of the Moon (New York 1882).
LangleYi 'Temperature of the Moon,' Mem. Nat. Acad.

Sciences^ iii. (1885) ; iv. (1889) with bibliography.
Struve, L., Total Lunar Eclipses, 1884 and 1888 (Dorpat 1889

and 1893), giving for the lunar semidiameter 15' 32" 65.
RossE and Boeddicker, 'Lunar Radiant Heat,' Sci. Trans.

Royal Dublin Society, iv. (1891).
Very, * Distribution of Moon's Heat, and its Variation with

Phase,' Utrecht Society of Arts and Sciences, 1891.
Webb and Espin, Celestial Objects (London 1893).
Weinek, Publications of the Lick Observatory, iii. (1894).
PRINZ, Agrandissements des Photoffraphies Lunaires (1894).
Pickering, W. H., Ann. Harv. Coll. Obs., xxxii. pt. i. (1895).
Elger, The Moon: description and map (London 1895).
LoE\VY, Puiseux, Atlas Photograph ique de la Lutie (Paris

1896-98).
HoLDEN, Lick Observatory Atlas of the Moon (1897).
Weinek, Photographischer Mond- Atlas (Prague 1897-98).
Schweiger-Lerchenfeld, Atlas der Himmelskunde (Vienna

1898).
Hkrz, Valentiner's Handworterbuch der Astronomic (1898).
Krieger, Mond- Atlas (Trieste 1898).
Very, * Range of temperature,' Astrophys. Jour. viii. ( 1898), 199-

So extensive is the popular literature of the Moon that
reference only can be made to the ample lists of Poole's
Index to Periodical Literature, vol. i. (1 802-1 881), pp. 865-866 ;
vol. ii. (1882-1886), p. 296 ; vol. iii. (1887-1891), pp. 286-287;
vol. iv. (1892-1896), p. 381.

The scientific literature of the Moon occupies sixty-five

pages of Houzeau and Lancaster's Bibliographic Ginerale de

r Astronomie, vol. ii. (Brussels 1882), cols. 1185-1317. Consult,

also chap. xiii. of Houzeau's Vade Mecum de VAstronome

(Brussels 1882) ; and the lists in The Astrophysical Journal,

1895-98.— /?./>. T,

SAT — 3

CHAPTER IV

THE CALENDAR

A LL those astronomical concepts which pertain to
•^^ the measurement of time having already been
given, the relations of this important element to the
concerns of ordinary life are now presented, as they
obtain in the construction of the calendar.

Originally the words almanac and calendar had the
same meaning ; but, as often happens in such cases,
usage has, in the course of time, given a slightly dif-
ferent meaning to each of them. Almanac, as now
understood, means an annual volume containing infor-
mation of various kinds specially useful in the year to
which it applies. Every almanac contains a calendar
which gives in tabulated form for the year (divided
into its months) the days of the week corresponding
to each day of the month, with the dates of the prin-
cipal anniversary days, and the times of the most
important celestial phenomena, such as the rising
and setting of the Sun and Moon, the Moon's changes,
etc. 'Almanac' comes to us from the Arabic, 'al'
being the definite article in that language, and * man-
akh ' signifying a calendar. The word calendar is from
the Latin caUnda^ by which name the Romans called
the first day of each month; and this is probably
derived from a word calare^ to call (cognate with the
Greek «zXfiv), because it was customary in very ancient

The Calendar 35

draes to summon people together at the beginning of
a month to make known the calendar arrangements
for that month.

Now it is evident that in distributing time its divis-
ions must be made to correspond to those periodical
celestial phenomena which regulate the coui^e and
ordinary actions of our lives. Most important of these
is the day, or period of time in which the Earth, by
revolving on its axis and turning successively toward
and from the sun, causes the alternations of light and
darkness. There is an unfortunate ambiguity in the
word day, as it sometimes means the whole length of
this revolution (arbitrarily divided into twenty-four
hours, as there aie no natural divisions except light
and darkness), and sometimes that portion of it
between sunrise and sunset. In all parts of the world,
except the equatorial regions, the length of this varies
considerably throughout the year.

Besides the day there are two longer periods of
time marked by celestial motions which are of great
importance in the concerns of life. First of these is
the year ; and the relation of the or<linary or tropical
year to the sidereal year has already been given in
Chapter 11. An astronomical year does not contain
any exact number of days ; and the year in question,
amounting to 365'' ^ 48" 4S'.5, is called the tropical
year. As it would be awkward to make a year con-
sist of a number of days and a fraction of a day, the
difficulty is got over by adopting in the calendar two
years of differing lengths : one called a common year,
consisting of 365 days, and an occasional one called
a bissextile or leap year, embracing 366 days. This
simple expedient keeps the designation of any part of
the year in closer correspondence to the same state

36 Stars and Telescopes

of the seasons. By the old Julian reckoning, which
erroneously supposed the year to contain 365 J days
exactly, each year which was divisible by four with-
out remainder was considered a leap year, the extra
day being added to the month of February. But by
the Gregorian or present reckoning, adopted in Eng-
land in 1752, the leap-year day is dropped at the end
of each century, unless the centurial year is divisible
by 400 without remainder — in which case the bissex-
tile day is retained. For example, the years 1800 and
1900 are not leap years, while the years 1600 and
2000 are.® This further adjustment is equivalent to
considering the year as consisting of 365.24250 days,
thus making it differ by only 0.00031 of a day (or
about 27*) from its true value, 365.24219 days. The
accumulation of this small difference will not amount
to an entire day for more than 3,000 years.

The other natural division of time (called a month)

8 Generally speaking, the number of days by which the Julian
calendar differs from the Gregorian is as follows: —

In the 15th century (1400-1500), 9 days.

i6th centurj' ( 1 500-1600), 10 days.
17th century (1600-1700), also 10 days, as 1600

was a bissextile year.

i8th century (1700-1800), ii days.

19th century (1800-1900), 12 days.

20th century (1900-2000), 13 days.

As the discovery of Columbus occurred in the 15th century,
the day of the year on which it took place (12th October, Julian
reckoning, or Old Style) falls nine days later in the Gregorian,
or present reckoning (that is, 21st October, New Style). Russia
still retains the Julian calendar ; and to avoid confusion, Russian
dates are customarily written in fractional form, with the Old
Style date as numerator : for example, 14th May (of any year in
the 19th century) would be written May — ; and 5th September
(Gregorian) becomes in Russia ^ ^^^* - — -D. P, T.

The Calendar 37

was suggested by the revolution of the Moon in its
orbit; and, as already pointed out, it corresponds, not
to the actual period of the Moon's revolution round
us referred to the stars, but to her revolution round
the Earth as seen from the Sun. Evidently then the
latter, called the synodic month, is the longer, because
the Earth has been moving through a considerable
portion of its orbit while the Moon has been going
round it. The length of the synodic or lunar month,
or a lunation simply, is zg*" i z^ 44" z'.684 ; so that
about izj lunations are completed in a year. But
as it is desirable to divide the year into nearly equal
portions, an integral number of which are completed
at the end of each year, the months adopted in our
calendar have no real relation to the period of the
Moon's revolution, but are purely artificial divisions,
each of which, excepting February, is a little longer
than a lunar month. Some nations, the Hebrew peo-
ples, for example, who attribute greater comparative
importance to the lunar month than we do, actually
employ it in their calendar, so that their year con-
sists sometimes of twelve and sometimes of thirteen
months.

The fact is said to have been first noticed by Meton,
a Greek astronomer, that 235 lunar months are very
nearly equal to 19 tropical years. The former, in fact,
contain 6,9391* •6'' 31""; the latter, 6,939'' 14'' 27™.
From this it results that during each 19th year of
our reckoning the position of the Moon with refer-
ence to the Sun will be very nearly the same on the
same day of the year. Owing to the importance of
this fact, the years were distributed into cycles of 19,
each of which is called a Metonic cycle, and the num-
ber of any year in this cycle is its Golden Number.

38 Stars and Telescopes

The year called by us b. c. i corresponded to the
number one, and a. d. i to the number two in this
cycle. As a cycle will be completed in 1899, the
golden number of 1894, for example, is 14 ; and that
of 1900 is I, in the next period or cycle.

The Sunday Letter, also termed the Dominical
Letter, primarily of use in determining the date of
Easter, is employed in ascertaining the day of the
week on which any day of the year falls. To
find the Sunday Letter of any common year, affix
the first seven letters of the alphabet in their usual
order to the first seven days of January ; then the
letter adjoining Sunday is the Dominical or Sunday
Letter of that year. If, for example, New Year's
Day falls on Sunday, the Dominical Letter of the year
is A ; if on Saturday, B ; if on Friday, C ; and so on.
Manifestly, now, if every year contained only 364 days
(364 = 52 X 7), all years would have the same Sun-
day Letter perpetually; that is to say, a given day
of any month would always fall on the same day of
the week. But as the common year contains 365
days, it must always end on the same day of the week
on which it began ; so that any year (whether common
or bissextile) immediately following a common year
must begin one day later in the week. Therefore its
Sunday Letter falls one letter earlier in the alphabetic
cycle. But the addition of the intercalary day at the
end of February, and not at the end of the year,
makes it usual to assign two Dominical Letters to
each bissextile year; the reason for which may be
illustrated by the following example: The year 1892
beginning on Friday, its Sunday Letter is C. But
the intercalary day, 29th February, disturbing the
regular periodic succession of the common year, the

Stars and Telescopes

ist March falls one day later in the week on that
account; so that the Dominical Letter for the re-
maining ten months of the bissextile year evidently
drops back one letter in the alphabetic cycle, — or
leaps ever one letter, whence the name ' leap year.' »

* Easier day is given in tlie following table, together wilh
the Golden Number, Dominical Letter, and the corresponding
yean of the Jewish and Atahotneian Kras, with (he day of the
month in each ordinary year when they begin : —

fclMM 'ij^'f^" '^■jji'""

0...I1 Lm

llih

nic...n E,j

^■■^ I'b.. 'll^He-iVur

^ B,=p„>

vl^

B,gii,.

.Sod

4!hil£^

I Is;

,,.,S.p,..J.j^

''IhA^^u^I

■itaiB

.7th April

.'itijuir"

■Sg]

id April
iSlhIlif.rch

G ;

lli

■ 89J

liUi April

iB^B

Sth April

■B*7

iSih Apnl

C i-:^

.olh April

B 5t.5g

lid Slly

>sw

,d April

A jAto

jlhSeplember|ill7

txh M>r

■ 9B>

iju. Arrii

G 1^

■■■""

Other chronological data sre printed each year in Tic- Ameri-
CiXH Ephtmetis and JVau/ieal Almaiiac. For farther information
on calendars and chronology, consult the articles on these sub-
jects in Tht EncyclBpaJia Britjnah-.i (9th edition). Ideler's
Handlntck dir HathematischtH tiiid Techmsiken C/ironologif,
CHAMliERS's.4jMi>ii>iR)'(4lhedition),vul.ii.bk.lo,and6CHKAM's
J/il/ilaJela fur Chrenidogu. Also. Mahler's Chroiiologische
Vtr^riihungs-b^llttt will be found helpful. More accessible
doubtless is HoU-a's/r,iiidyBpaip//iuleiandTabliSfir rii-lfy-
ing Dalei with the Christian Era. etc. { London 1869) ; also Dr
\^\'i\.KM.ii\3-^% AsStanemisihc C^rrino/iif/ir (Leipzig 1895} ; and
the article by the same author in Vale.ntiner's Hand-aprteT-
buth dcr Astronomic, i. (Breslau 1897), Lewis has a popular
paper on Almanaci in The Obicrfatary, ni. (1898). — DP. T.

CHAPTER V

THE ASTRONOMICAL RELATIONS OF LIGHT

T T is essential to make early reference to the means
by which the heavenly bodies become known to
us through the agency of light, and to the effects of
the motion of light upon their apparent places.

The undulations, or light waves, are transmitted
through a very rare but material substance, diffused
through all space, to which the name ether has been
given ; and to distinguish it from the chemical sub-
stance with the same name, it is called luminiferous
(that is, light-bearing) ether. The vibratory motions
of the particles of this ether, called waves of light,
when once originated by a luminous body acting as a
source of light, are transmitted through the atmos-
phere in its ordinary state, because it is permeated by
these particles, and through some other substances
called for this reason transparent. In passing from
one transparent medium into another of different
density, the rays of light, propagated originally in
straight lines, are bent or turned in a direction in-
clined to that previously followed. This bending is
called refraction, and is greater, the greater is the
difference of density of the different media through
which the light is successively transmitted. It also
varies according to the angle of inclination to the
surface of a medium at which a ray of light enters it ;

42 ■ Stars and Telescopes

the law being, that if the media be the same, the sine
of the angle of incidence (whatever that angle be) is
always in a constant ratio to the sine of the angle of
refraction. This law was discovered about 162 1 by
WiLLEBRORD Snell of Leyden. The ratio in any par-
ticular case can only be determined by experiment.

Rays of light coming to us from one of the heavenly
bodies suffer a constantly increasing refraction in
passing through the successive strata of the Earth*s
atmosphere, which are more and more dense the
lower down they are. The general result can only
be ascertained by astronomical observations, the celes-
tial object appearing in the direction in which the
ray of light proceeding from it enters the eye. The
law just mentioned shows that a body exactly over-
head, or in the zenith of any place, is seen in its true
position, its rays having undergone no refraction at
all ; and that the refraction is greater the farther the
object is from the zenith, or the nearer it is to the
horizon. Half-way between the two, or at an altitude
of 45°, the refraction amounts to nearly i'; at 20°
to 2W ', at 10° to 5J'; at 5° to 10'; close to the
horizon it is as much as 33' or 34', varying consid-
erably with the temperature and pressure of the
atmosphere. As this arc is a little more than the ap-
parent diameter of the Sun or Moon, it follows that
when either of those bodies seems to be just above
the horizon, it is really just below it, refraction always
making a heavenly body appear higher above the
horizon than it really is.

That the propagation of light, whether it be a sub-
stance, as was formerly supposed,^^ or an undulatory

1^ * It is possible,' says Clerk Maxwkll, ' to produce dark-
ness by the addition of two portions of light. If light is a sub-

The Astronomical Relations of Light 43

motion in a substance, as it is now known to be,
should occupy time, seems a priori what might be
expected. But so extremely rapid is this propaga-
tion that the ancients, having no means of recogniz-
ing it by astronomical observations, appear to have
thought that it was instantaneous, which it practically
is between places on the Earth's surface. The first
person to discover that the velocity of its transmission
is measurable was the illustrious Romer of Copen-
hagen in 1675, while discussing the obser\'ations of
Jupiter's first satellite made by himself, and at Paris
by Cassini. He found that the interv^als of time
between successive immersions of the satelUte into
the shadow of the planet and its emersions therefrom
were different according to whether the Earth in its
orbital motion was approaching Jupiter or receding
from it ; and he concluded that the cause of this
was the Earth's motion combined with that of light,
which was thus recognized to be a sensible and meas-
urable quantity. Romer's explanation of the differ-
ences observed was contested by Cassini ; but it
nevertheless gradually obtained general acceptance
among astronomers, and about 50 years after its
publication a most remarkable confirmation of its
truth was obtained by the discovery of the aberra-
tion of light. Romer's approximate determination of
the time required by light in passing from the Sun to
the Earth was rather more than eleven minutes ; but
it is now known that when the Sun is at its mean
distance, this interval is 498* (8"' 18*), the best
determinations of the velocity of light by the refined

stance, there cannot be another substance which, when added
to it, shall produce darkness. We are, therefore, compelled to
admit that light is not a substance/

MKASURING T

Vir,

,fr

mo*™-

{(Mr

thal/^f

0"t

«f w

«:ity <,/ ligkl /!r

-™

V.ilh«tK

Mnl

nn^lrd i

186.

*>■

CAU

A, rHm

HlFr

K* ^jr„„i/ (/

Fn/fatr MlCHIL50>, «™ o/ l*t UHhariilj, n/Ckicags, imfrmvd «foH Ail

tke grrttily trdarxed af/ntraiKj ititnn ifuwn^ /mit>djfiftg /arthtr important
tKcdificaUoHS. Tlu tfccd of lAt rivtlviwg mirrtr, c D — it rtclanentiir frilKt
i,/pelitludiliitiUvKti\iralut>qmm — v,as%'f>l'>rmmaitii,,id. TIk Ikm
fim tuftmrling tin italrumiat wrr. niml j/rrl apart : attd thl stationary
mirrtr rrjtnling Ihr rtttm my mu ntar/y i^ milrt tlltlaml. For dacriflioii
a/lki affaralus axd its HSt, and a /ml diUHStian of llu frohltm, s/i 'Aslrs-
KHMiiid Paprrs of Ihl AiMrrican E/ihrmeris.' vol. iHIVaslliHgtoi iSlt>i>. Also
CoBNii, 'Annalrs dt rOharvalfirt d4 Pari,; Mtmoirts, jm. {|S;M; \cassc.
and FOBMS ' Pkilosofhical TraiuactioHt.' iBgl. For bihliograpk}, contull
•irasAi«elo« Ohrmtliotu-yer iSSj. A//rf.dix Hi. p. .».)

The Astronomical Relations of Light 45

and accurate methods of modem physicists and
astronomers {viiie opposite page) giving 186,330
miles a second. So that when, for example, we are
observing Neptune (a planet 30 times more distant
than the Sun), we see it by light which began its
journey earthward somewhat more than four hours
previously.*^

A few words in conclusion on the aberration of light.
In 1725-27, while making a number of careful obser-
vations of y Draconis (a
star which crosses the merid-
ian in the south of England
very near the zenith), in the
hope of determining its par-
allax and distance, Bradley
was surprised to notice a reg-
ular change in its apparent
position. Its period, like that
produced by a measurable
parallax, was exactly a year ;
but the amount was much
greater than he had exi>ected,
and the direction was the reverse of that whi
be caused by parallax. Speculating on the

" This quanlily

{i6j4-i

is technically termed the 'aberration-time,'
and is equal (in secDndsl to 498 limes the planet's distance from
(he Earth exiiressed in astronomical units. The mean value
of the abe nation -time (between Sun and Earth) is the constant
term in the 'equation of light.' Also there is an aberration of
the planets due to their orbital motions in space. Suppose our
globe to be at rest in its orbit ; the aberration of light would
then vanish. Bui as a planet is always seen from the Earth in
the direction where it actually was when light left i1, obviously
its absolute position at the time of observation must differ
troin the apparent position, because of (i) the aberration-
time, and (z) (he planet's orbital motion athwart the lirie of

Stars and Telescopes

this, it occurred to him that the Earth's motion round
the Sun would lead to an effect of this kind when
combined with the gradual propagation of light as
discovered by Romer. Calculation confirmed this
conjecture ; and the ab-
erration of light (as
this phenomenon is
called) affords one of
the methods by which
the velocity of light was
subsequently deter-

The nature of the
apparent change in a
star's place produced
by aberration depends
upon its position with
respect to the plane
of the ecliptic. If
that position be in the
plane of the Earth's orbit, the star will, in conse-
quence, appear to change its place in a straight line
only ; if it be nearly in the pole of the ecliptic, the
star will appear to describe a circle round its true
place ; while, if situate anywhere between the ecliptic
and its pole, the change of apparent place will form
an ellipse whose eccentricity is greater the nearer
the star is to the plane of the ecliptic. The angular

sight. This is called planetary aberration. A similar but very
small effect obtains for Ihe Moon, amounting to about o's.
the linear value of nhich. at the distance of our satellite, is
2,650 feel i that is lo say, while light is travelling from the
Moon to the Earth Inearlv fj). the Moon advances about
one-half mile easlmaiil in i'ts orbit. — Z>. P. T.

The Astronomical Relations of Light 47

semi-diameter of the circle in the former case, or the
serai-major axis of the ellipse in the latter case, is
practically a constant quantity, called the constant of
aberration ; for the only circumstance that can make
it vary b the change of the Earth's orbital velocity
at its different distances from the Sun, and the pro-
portion of this variation to the whole velocity is very
small. The best modem value of the constant of
aberration is 20",492, detemiined by M. NvRiN.

The Earth's ro-
tation on its axis,
combined with the
motion of light,
also causes a phe-
nomenon of a simi-
lar kind, called the
diurnal aberration.

Its

cording to the lati-
tude of the place
of observation, be-
ing greatest at the
equator, where the

Leon Foucault (iSi^iit68>

velocity produced
by the Earth's ro-
tation is greatest, and smaller the nearer the poles
are approached, at which points the diurnal aberra-
tion vanishes. At latitude 40°, the average for places
in the United States, the constant of diurnal aber-
ration (for an equatorial star at meridian passage)
amounts to o".24 ; the velocity of rotational transla-
tion at latitude 40° being about the eighty-fifth part
of the Earth's velocity in its orbit.

CHAPTER VI

THE SUN

ON the Sun*s distance depends our knowledge of
all absolute magnitudes in the solar system ; for
by Kepler's third law (page 93), the proportions of
the distances of all the bodies moving round the Sun
are known exactly from their periodic times of revo-
lution : so that if the Earth's distance from the Sun
be known, the distances of all the planets from the
Sun and from each other can be deduced by a very
simple piece of arithmetic. Also, the Sun*s distance
is of the first order of significance, because it is the
elemental unit in our measures of the distances of the
fixed stars." To measure the Sun*s parallax with pre-

12 The Sun, cosmically speaking, is simply a star, but the
nearest fixed star is 275,cxx) times more remote ; so that the
Sun V vastly greater brightness is, for the most part, due to mere
proximity. Still, the distance of the Sun is by no means easy
to conceive or illustrate. Recalling that the distance round the
Earth's equator is about 24,000 miles, ten times this gives the
distance of the Moon, which is practically inconceivable ; but
the Sun is 390 times more remote. As the two bodies are
about the same in apparent size, it follows that the Sun's actual
diameter is about 390 (accurately 400) times greater than the
Moon's. The diagram on the opposite page will not only con-
vey a true idea of the relative size of Sun, Earth, and Moon,
but by imagining spheres of the given proportions set at the
distances indicated, the actual relations of these bodies in
space may, in some sense, be comprehended. On the same

KELA TIVE SIZE OF SUN, EARTH &• MOON
(On scale of iS,ooa miles =- I iocb.)

THE EARTH

THE MOON
O

Mean Distance from the Earth,

i3i inches.

J At perigee, J in. nearer

I At apogee, \ in. fanher.

50 Stars and Telescopes

cision is difficult on account of the great distance of
that body compared with the size of the Earth ; a
small error in the measured parallax produces a large
error id the resulting distance.

From the time of Flamsteeo (Astronomer Royal
from 1675 to 1719) it has been known that the Suo's
parallax does not exceed 10". Hallev pointed out
the advantage that
might be gained by
observing transits of
Venus, those rare oc-
casions when she
passes at inferior con-
nction over the
Sun's disk. Accord-
ingly the transits of
1761 and 1769 were
observed by a large
number of parties
sent to different re-
gions of the world.

Edmund Hallev (1656-174:}

But the solution of

the problem in this
manner is encompassed by practical difficulties. Many
lestilts were obtained by calculation from the observa-
tions of the transits in those years ; but for a long time
it was agreed among astronomers that the value of the
Sun's parallax obtained by Encke in 1835, which
amounted to 8".57, was the best. More recently
many determinations, made by observing Mars at its
closer oppositions, and by other methods, have shown

reduced scale, the nearest (iiced star would be 16,000 miles
disiam. equal 10 a journey from New York westerly to Japan
and back. — Z'./', T.

The Sun 5 1

tiiat the Sun's parallax is greater by at least o".3
than ELncke's value. Moreover, M' E. J. Stone,
late of Oxford, pointed out that Encke's discussion
was affected by erroneous interpretations of some of
the observations, and that, when these are rightly
explained, they also give a value considerably larger.
The observations of the more recent transits in 1874
and i88a likewise prove to be most consistent with a
value of about 8".84 ; but the method is now some-
what discredited, as compared with other methods."
From bis skilful observations of Mars at Ascension

w The available methods of ascertaining ihc Sun's dis-
tance, more than a dozen in number, may be divided into three
classes; (i) b/ geometry or trigonometry; (j) by gravitational
effects o[ bun. Moon, and planets; (3) by the velocity of
transmission of light. The first includes transits of Venus,
and near approaches of the Earth to Mars, or to small planets
exterior thereto, — at which times the distances of these bodies
from the Karlh are not difficult lo measure. Adopting, with
Professor YouNC, the number 100 as indicating a method
which would insure absolute accuracy, this class of determi-
nations will range all the way from 20 to 90. I'he second class
of methods, too mathemalical for explanation here, depends on
the Earth's mass, and their present value may be expressed as
40 to 70: but (he peculiar nature of one of them (utilizing the
disturbances which the Earth produces in the motions of Venus
and Mars) offers an accuracy continually increasing, so that
two hundred years hence it alone will have settled the Hun's
distance with a precision entitled to the number 95, But the
best methods now available are embraced in the third class,
which employ the velocity of light (determined by actual physi-
cal experiment, as related in the last chapter) : and their present
worth is about 80 or go. The problem of the Sun's distance is
one of the noblest ever grappled by the mind of man ; and no
one of the numerous elements with which it is complexly inter-
woven can yet be said to have been determined with the highest
attainable precision. (Harkness, The Amrrinm Journal gf
Stiinee,ca.\\. (iSSi), 37S;Vou.NC, General Ailrenomy (Boston
(8981, chapter xvii.) — Z>. P. T.

'?«> #

•

iPhirltfraflird «r Ruth

The Sun

Island during that planet's favorable opposition in
1877, D' Gill obtained a solar parallax of 8".78,
which gives for the Sun's mean distance very nearly
93,000,000 miles, — quite certainly within a quarter
of a million miles of its true value."

** An admirable summary of investigation of the Sun's
distance is given by DrGiLL as an introduction to M" Gill's
Stx Months in Ascension {VxiXiiioxiy 1880), — an account of the
expedition to that island three years previously. The value
of the Sun's parallax, 8".848 ± o".oi3, determined by Professor
Newcomb {Washington Ohseriuitions^ 1865), and now become
classic, is adopted in all the national astronomical ephemer-
ides except the French, which uses Le Verrier's slightly
larger value. Independent determinations of this constant
here given show the measure of modern precision in this im-
portant field of research; and the relations of the values to
each other will be apparent on recalling that the addition
of o".oi to the Sun's parallax is equivalent to diminishing his
distance about 105,000 miles ; —

(1880)

Todd

Velocity of Light

8.808

r 0006

(fSSi)

PUISEUX

Contact and Micrometer Observa-
tions, Transit of Venus, 1S74

8.8

(I88I)

Todd

American Photographs, Transit of

Venus. i'<74

8.883

- 0.034

(l88r)

Newcomb

Velocity '^f Liglit

8,704

(1885)

Obrkcht

French Photographs, Transit of

Venus. 1S74

8.3i

± 0.06

(1887)

Cruls

Brazilian Observations, Transit of
Venus. 1882

8.8o3

(1887)

E. J. Stone

British Contact-Observations, Tran-

sit of Venus, 1882

8.S32

± 0.024

(1888)

Harknsss

American Photographs, Transit of

Venus, 1882

8S42

± 0.012

(1889)

Harknbss

Planetary Masses

8.795

t 0.016

(1890)

Battkrmanm

Lunar Occultations

8.794

± O.Olf)

(1890)

Newcumb

Transits of Venus, 1761 and 1769

8.79

± 0.034

(1891)

AUWERS

Transits of Venus, 1874 and 1882

8.896

.-^ O.U22

(189a)

Gill

j Opposition of 1 (") Victoria

8.S01

± 0.006

(1893)

Gill

I Small Planets j (^) Sappho

8.7^8

Tz 0.01 1

(1898)

Elkin

' ^ (7) Ins

8.812

i o.oo<)

A nearly complete list of the more important earlier papers
is given in Newcomb's Popular Astronomy (Appendix). The
newly discovered small planet 1898 DQ, at its near approach
to the earth in 1900, is expected to yield a value of the Sun's
distance far exceeding all others in precision (page 408).

54 Stars and Telescopes

It must be noted, that in consequence of the eccen-
tricity of the Earth's orbit (which amounts to 0.01677),
the Sun's actual distance varies between a million and
a half miles less, and a million and a half miles more
than this. It is least about ist January, when the Earth
is at that end of the major axis of its orbit which is
nearer the focus occupied by the Sun, and greatest
about I St July, when the Earth is at the opposite end
of that axis. These two points are called respec-
tively the perihelion and the aphelion of the Earth's
orbit.

Accepting, then, 93,000,000 miles as the Sun's mean
distance from us, it is easy to find, by observing his
apparent diameter, that his real diameter is 865,350
miles. This is nearly no times as great as the Earth's,
so that the Sun's volume is able to contain the Earth's
1,300,000 times over. But the comparative effects of
their attractive forces show that the Sun's mass is only
331,100 times as great as that of the Earth. Conse-
quently his density must amount to only about one

Professor Harkness published in 1891 a laborious paper
entitled The Solar Parallax and its Related Constants (Washing-
ton Observations, 1885), in which this quantity is treated, not
as an independent constant, but as 'entangled with the lunar
parallax, the constants of precession and nutation, the parallac-
tic inequality of the Moon, the lunar inequality of the Earth,
the masses of the Earth and Moon, the ratio of the solar and
lunar tides, the constant of aberration, the velocity of light,
and the light-equation.* Collating the great mass of astro-
nomical, geodetic, gravitational, and tidal results which have
been accumulating for the past two centuries, and applying the
mathematical process known as a 'least square adjustment,'
he derives the value 8".8o9 i o".oo6, giving for the mean dis-
tance between the centres of Sun and Earth 92,797,000 miles.
A valuable bibliography of the entire subject concludes Pro-
fessor Harkness's paper. — D. P T.

The Sun 55

fourth that of the Earth, or rather more than i^ times
the density of water.^*

The shape of the Sun appears to be that of a perfect

^ Possible changes of the Sun's diameter from time to time
have been critically investigated by D' Auwers of Berlin, and
Professor Newcomb, with negative results ; nor are the obser-
vations yet made sufficient to disclose any difference between
equatorial and polar diameters. The heliometer (p. 277) affords
the best means of measuring the Sun's apparent diameter,
or the angle subtended by its disk. The orbit of the Earth
being elliptical, this diameter changes in the inverse proportion
of the Earth's varying distance from the Sun ; at the beginning
of the year it is 32' 32", and 31' 28" early in July, the mean
value being 32' o". Supposing the form of the Earth's orbit
unknown, daily measures of the Sun's varying diameter would
alone, in the course of a year, enable the precise determination
of the figure of that orbit, so accurately can these measures
now be made. The linear equivalent of one second of arc at
the Sun is 450 miles. The present uncertainty in the solar
diameter does not much exceed 2"\ that is to say, about 900
miles, or approximately y^^ of the entire diameter. D' Au-
wers' recent value of the semi-diameter is 15' 59/'63.

A simple relation between the Sun's mass and its dimen-
sions relatively to the Earth enables us to determine that the
force of gravity at the Sun's surface is 27 J times greater than
it is here ; so that while a body on the Earth falls only 16.2 feet
in the first second of time, at the Sun its fall in the correspond-
ing interval would be no less than 444 feet. If a hall clock were
transported to the Sun, its leisurely pendulum would vibrate
more than five times in every second. So great is the Sun's mass
that a body falling freely toward it from a distance indefinitely
g^reat would, on reaching the Sun, have acquired' a velocity of
3S3 miles per second. The great Krupp gun exhibited at the
World's Fair in 1893, ^^ ^''^^ from Chamounix in the direction
of Mont Blanc, at an elevation of 44°, would propel its projec-
tile of 475 pounds in a curve meeting the earth at Pre-Saint-
Didier, 12^ miles from Chamounix, and whose highest point
would be more than a mile above the summit of Mont Blanc.
If we could suppose the same gun to be fired similarly on the
Sun, so great is the force of gravity there that the projectile
would be brought down to rest about half a mile from the
muzzle. — Z? P. T,

56 Stars and Telescopes

sphere. As soon as he was observed through a tele-
scope, it was seen that his surface is usually diversified
by a number of black spots of varying dimensions and
configurations. In 1 6 1 1 , John, son of David Fabricius,
of East Friesland, first noticed their apparent motions
across the disk, from which it became evident that
the Sun is endued with a stately rotation on his axis.
These motions are such as would carry an equatorial
spot from first appearing on the Sun's disk to appear-
ing there again (if persistent enough to do so) in
about 2 7 days ; hence, taking into account the simul-
taneous motion of the Earth in its orbit round the
Sun, it was inferred that the Sun turns on his axis in
about 25** 7**. It should be stated, however, that
recent observations have shown that the spots nearer
the Sun's equator move somewhat piore rapidly than
those farther from it. Spots are very seldom seen at
a greater distance from the Sun's equator than about
30° of solar latitude. These regions of the solar sur-
face take as much as 26 J days to make a complete
revolution.^*

!• From groups of the faculae (pages 57-58) D' Wilsing has
found that the Sun's equator revolves in 25*.23 ; but these
observations are exceedingly difficult, and a repetition of the
work is desirable. Professor Young and D' Crew have deter-
mined the period of rotation of the Sun's equator by means of
the spectroscope, utilizing that technicality called Doppler's
principle. This means that the spectra from opposite sides of
the Sun (the east side coming toward the Earth, and the west
receding from us) are brought into juxtaposition ; then, careful
measurement of the difference in position of a given line in
the two spectra forms the basis for calculating the rapidity of
rotation. M. Dun6r of Lund, Sweden, carrying this research
still farther, into high solar latitudes, finds for the equatorial
regions a period of sidereal rotation equal to 25"*.46. in close
correspondence with the determinations of Carrington and

Tk€ Sun

The periodicity of the sun spots was discovered by
ScHWABE of Dessau in 183S. The subject has since
attracted much attention, and the period, so far as
it is constant, has been pretty accurately determined
by Wolf of Zurich to be a httle more than eleven
years ; but the physical cause of the periodicity is not
yet satisfactorily explained. A recent epoch of maxi-
mum abundance and frequency, more than usually
protracted, was in 1883-84. The diminution being
generally less rapid than the increase, a minimum
followed in 1889; the next maximum passed during

THE SUN {from a phalograph by RuTHKrFURD)
(Facidat an iknm ii4jmtnl It Hu i^li luar Ih, S—'i limi

SpoeRer from the spots alone. The slowirj; down as th«
poles are approached is remarkably verified, his results giving,
for Ihe rotation period ai latitude 75', no less than 33^.54.
M. Di;n£r's observations were made near (be lime of mini-
mum spots, and it would be interesiing 10 repeal Ihe deterui^
lulion near the epoch of maximum spotledness. — D P. T.

Stan and Telescopes

the latter half ot 1894, and the next minimum may
be expected early in 1900.

The solar spots are thought to be produced by dis-
locations in portions of the photospherical envelopes
which surround the Sun, so that we see in them to a
depth below that of the ordinary surface." In their
immediate neighborhood there are often to be seen
patches of more than usual brightness (heapings up,
so to speak, of luminous matter), which are called
/actila, the Latin word for torches. Both phenomena
indicate activity and commotion in the outer part
(and to some unknown depth below) of the Sun's
surface.

" The Sun, as seen with telescopes 01 low magnifying power,
ii shown on the preceding page ; and page 52 illustrates admi'
rably the chanees taking place from day 10 day in an average

group of spots as they transit (he apparent face of the S;n.
Above is a chaiactcrisiic suo'spot, from a drawing with much
detail, by Secchi. Also, the opposite illuslralion indicates
the legionsoF gteate^il spotledness (where the zones are dark-

The Sun

Other manifestations of this have been recognized
in tremendous rushes of gaseous matter, moving with
enormous velocities, to great heights above the solar
surface. Modern instruments and methods of investi-
gation have enabled astronomers to trace the action
and course of these at any time when they are in prog-
ress; but the appearances afterward found to be due
to them were first perceived on the occurrence of total
eclipses of the Sun. These phenomena, now known
to be produced by glowing hydrogen, were long called

est), and the apparent positions of these zones at the different
seasons. The Sun's axis is inclined 83° to ihe plane oE the
Earth's orbit; and if prolonged northward to the celealial
■phere, that axis would intersect it near the third-magnitude

star S Draconis : so that in March the Sun's north pole is
turned (arihest from the Earth; in September 11 is inclined
7° toward us. Spectroscopic study of the liun-spots shows that
their inferior brilliance is due in part to a greater selective
absorption than obtains in the photosphere generally. Con-
tinuous and systematic records of the solar spots are now kept
■t Greenwich (in connection with Dehra Dun, Indial, at Pots-
dam near Berlin, at Chicago, and elsewhere. Excellent photo-
graphs of aun-spots and the solar surface have been obtained
« Potsdam {Nimmel H«ii Erdi,\\. (li^) 34; iv.4841. This

5o Stars and Telescopes

red flames, or lose-colored piotuberances, attention
having been first attiacted to them during the eclipse

(amous obiervaiory is iUusirated on the opposite page; alto
ils peculiarly mounlcd telescope below, wilK its oblong lube
and duplicate object-glass, which makes ii possible to keep the
instTument pointed with the greatest accuracy while exposures
are making with the photographic objective, mounted in a twin
tube. The advantages of the overhanging pier commend them-
selves at once to the practical observer.

Also at Meudon. Paris, M. Janssev has had extraordinary
success in photographing the .Sun's surface in detail ; it£ gran-
ulation, sharply defined in his originals, is somewhat blurred
in the reproduction on page 62. In viewing the Sun with a
telescope this granulalimi can be satisfactorily seen with a
magnifying power of about 400 or 300, under good atmospheric

While the 41 years' faithful work of Schwabe, as revised by
Wolf and collated with other and scatterinj; results, gives an

62 Stars and Telescopes

which was total in Switzerland in 1 706." It was long
contested whether they belonged to the Sun or to the

average sun^pot period of iij years, there are great irrregu-
lahties: the intervals between maxima h;xve varied from 8 10
I Si years, and between minima from 9 to 14 years. True inter-
pretation of this indicates n>ilh an approach to certainly that

Moon, the dark body of which concealed the Sun dur-
ing a total eclipse ) and it was then thought that she

{H„tkl.

miU,)

ubseived during total eclipses^

those of iS6S and 1SE6
while thai of 1891 was
•un-Ught, by means of a spect rnscope
adjusted delicately 011 the edge of the
Sun, this inaltument reducing tiic sl;y
glare, without dispersing very much the
light of the prominence itself. 'I his
method has now been in common use
more than a quarter-century. In Ucto-
ber, 1S78, Professor Young observed
the highest prominence ever recuided.
which reached an elevation of nearly
400,000 miles above the Sun's limb,
TACCHtNi and Ricco in Italy. Tbouvr-
LOT and Deslanohks of Taris. Maun-
der and SidgrIlaves in England, and
VON KoNKOLV and F^nvi in Hungary,
ue the most faithful Euiopcan obser-
vers of these wonderful phenomena.
By means of the spectro-hcliograph de-
vised by Professor Hale of ihe Uni-
versity of Chicago, the hindering effects Solas Pbci
of our atmosphere are in considerable 'Gkbst Hob
part evaded. In April, 1891, he obtained {Hugki, 10.
the tirst photograph of the spectrum of

64 Stars and Telescopes

might be surrounded by an atmosphere which occa-
sioned these phenomena. But the careful observa-
tions made during later eclipses (particularly in
Norway and Sweden in 1851 and in Spain in i860,

» prominence ever taken without an eclipse; and he is enabled
to secure on a single plate (with a single exposure) not only
the photosphere and sun-spota, but the chromosphere and pro-
tuberances. Also the same instrument (which utilizes mono-
chromatic light, or light of a single color only) has demonstrated

(Fr,>

Hali

that the faculx, which to the eye arc ordinarily seen only near
the Sun's limb, aelually extend all the way across its disk, in
approximately the regions of greatest spot-frequency. Hy the
courtesy of Professor Hale, both these results are here illus-
trated. The bright zcmes of faculx are related to the promi-
nences — perhaps identical with Iheni ; and Ihey indicate an
abundance of glowing calcium vapor. His progressive methods
of solar research will soon afiord large accumulations of facu-
lar observations, £rom which the laws of their appearance may

'""""

tft

.•

" -i

by AiRV, then Astronomer Royal, and by many other
astronomers) showed clearly, from the way in which

be finally detennined, and their connection wilh the formalion
of spots and prominences satisfacloril)' made out. A vast
advantage hai been secured through the recent erection of the
Maharajah Takhlaslngji Observatory at Poona, India, where a
spectro-heliograph simiiar to Che one at Williams Uav is already
in operation. Professor HaI.k's spectro-heliograph is illus-
trated on page 353.

(25lh July 1892)

Both Spots and prominen>:cs have a nell-recognized varia-
tion in heliographic, or solar l.iiitude ; the former has been in-
vestigated by Dr Spuerer of Potsdam, and the latter by
M, RiCCtj of Palermo. Just before the epoch of 3. minimum

66 Stan and Telescopes

they were first covered and then uncovered by the
Moon, that they were appendages of the Sun.

(iSSS, for example), the spots are aeen nearest the Sun's equa^
tor ; coincidently with the minimum, these circum-equalorial
spots cease, and a series breaks out afresh in high soUi lati-
tudes. Thenceforward to the time of the neit minimum, the
mean latitude oE the spots tends to decline continuously, as
shown in the adjacent diagram. This fluctuation is called ' the

1 ^

^..

'^'

-^N

...

~~<:;

-\ ™

■^-

-S

VARIATIONS i:

law of zones.' SrORER's careful research farther shows aa
occasional predominance of spots in the Sun'i southern hemi-
sphere not counterbalanced by a corresponding appearance in
the northern. Also, during the last half of the 17th century
and the early years of the 18th, there seems to have been a re-
markable interruption of the ordinary course of the spot cycle,
and the law of zones, too, was apparently in abeyance. M.
GuiLLAUMB of Lyons recorded in 1S96 two instances of small
and short-lived spots in solar latitude44° and 47". On approach
of the minimum, there is often a transient outburst of very large
■pots, as in September 1898, well exemplified in the photograpba

The Sun

opposite page 64. An unexplained disturbance of the magnetic
needle, often violent if the spots are large, takes place coinci-
dently with the appearance of spot areas; and there is a
fairly accurate correspondence between the number of spots
and the fluctuations of the needle, as exhibited in D' Woi.fer's
diagram below. Brilliant auroras, too, are to be expected.

IjO

•to

/ .-

Sl_

■^^

■ .— ^)^^

> -j^^Mi^

4.0

3i>

2.0

0.0

nST M 89 M 01 »a (3 M 95 9« 1097

VARIATIONS OF MAGNETIC DECLINATION AND NUMBER OF SPOTS

KCotH feared by Dr Wolfer of Z Uric h)

As the upper half of the opposite diagram shows, latitude
variations of prominences follow closely tluctuations of spots,
although exhibiting greater divergence l)eiween the two hemi-
spheres than the spots do. Professor Yoi.'Nc; has classified these
phenomena of the solar limb into eru))iive and quiescent promi-
nences. While the former are metallic and ihcir distribution
follows nearly the same law of zones as the spots, the latter are
apparently more cloud-like, and are found in all latitudes, even
about the solar poles. — D. P. T.

Sestini, 'Observations of Spots,' Washinj^ton Obs.^ 1S47.
Carrington, Ohsen'atious of Spots on t/ie Sun (1853-61) at

Redhill (London 1S63).
Tacchini and others, Mem.Soc. Spettroscopisti //a/iant {Fa]ermo

and Rome, since 1872).
SpOrer, Biod. dt'r Sonne nfieckett zu Anclatn (Leipzig 1874).
Secchi, Le Soldi (2 volumes and atlas), Paris 1875-77.
Proctor, The Sum KuUr, Fire^ Li^ht (London 1S76).

68 Stars and Telescopes

Newcomb, Popular Astronomy (New York 1877).
Fi^VEZ, Annuaire Obs. BmxelUs, 1879, 255- Bibliography.
ZoLLNER, Wissenschaftliche Abhandlutigen^ iv. (Leipzig 1881).
Dewar, McLeod and others. Reports Brit, Assoc. Adv. Set,

1881, p. 370 ; 1884, p. 323; 1889, p. 387 : 1894, p. 201.
Perry, * Solar Surface,' Proc. Roy. Institution, xii. { 1888), 498.
Langley, The New Astronomy (Boston 1888).
Unterweger, 'Lesser Spot-periods,' Denk. kais. Akad. Wis-

sense kaf ten IVien, Iviii. (1891 ).
Dun6r, Recherches sur la Rotation du Soleil (Upsala 1891).
F^NYI, • Prominences,' Publ. Haynald Obs. vi. (1892).
Maunder, ' Sunspots and their Influence,' Knowledge, xv.

(1892), 128; xxi. (1898), 228.
Ball. The Story of the Sun (New York 1893).
V. Oppolzer, E., * Sunspots,' Astron. and Astro- Phys. xii. ( 1893),

419. 736-
Sporer, • Sonnenflecken,* Publ. Obs, Potsdam, x. (1895).

Sampson, * Rotation and Mechanical State,* Mem. Roy. Astr,

Soe. li. (1895), 123.

Janssen, Ann. Obs. Astron. Physique Meudon, i. (Paris 1896).

Young, The Sun — newly revised edition (New York 1896).

Meyers R'onz>ersations-Lexikon,xvi. p. 95 (Leipzig 1897).

WOLFER, 'Oberflachc.' Publ. Stern. Polytech. (Ziirich 1897).

Very, * Heliographic Positions,' A.^trophvs. Jour, vi., vii.

(1897-98).
WiLCZYNSKi, Hydrodynamische Uiitersuchungen mit Anwen-

dungen auf die Sonnenrotation (Berlin 189S).
F0NTSER6 Y RiBA, Sobre /./ Rotacion del Sol (Barcelona 1898).

D' Alfred Tucker man's fndix to the Literature of the
Spectroscope (' Smithsonian Miscellaneous Collections,* No. 658,
Washington 1888), contains at pp. S8-132 an exceedingly full
bibliography, conveniently subdivided under sunspots, rotation,
protuberances, eruptions, chromosphere, corona, solar spec-
trum in general, solar atmosphere, etc.

CHAPTER VII

MORE ABOUT THE SUN— SOLAR PHYSICS

' TT is because the secrets of the Sun,' writes Sir Nokman
1 LocKYEB, 'include the cipher in which the light messages
from external Nature in all its vastiiess arc written, that those
interested In the "new learning," as the chemistry oE space
may certainly be considered, are so anxious lo get at and
possess Ihem." Hul even more significant lu us ate the heat
radiations of the Sun. because they are determinant in all
animal and vegetable life, and are the original source of nearly
every form of terrestrial energy recogniicd by mankind-
Through the action of the solar heat-rays the forests of palieo-
loic ages were enabled to wrest carbon from the atmosphere
and store it in forms afterward converted by Nature's chem-
istry into peat and coal ; ihrough processes incompletely under-
8lood. the varyinB forms of vegetable life arc empowered lo
conserve, from air and soil, nitrogen and other substances
suitable for and essential to the life-maintenance of animal
creatures. Itteezes operant in the production of rain and in
keeping the air from hurtful contamination; the energy of
water, in stream and dam and fall ; trade-winds facilitating
commerce between the continents; oceanic currents modifying
coast climates (and no less the tornado, the waterspout, the
typhoon, and other manifestations of natural forces, excepting
earthquakes, frequently destructive to the works of man), — alt
are traceable primarily to the heating power of the Sun's rays
acting upon those readily movable substances of which the
Earth's exterior is in part composed.

A* the Sun shines with inconceivably greater power than
any terrestrial source, an idea of its total light is difficult to
convey intelligibly in tenns of the ordinary standards of the

70 Stars and Telescopes

physicist. Its intrinsic brightness, or amount of light per square
unit of luminous surface, exceeds the glowing carbon of the
electric arc light about 3^ times, or the glowing lime of the
calcium light about 1 50 times. ' Even the darkest part of a sun
spot outshines the lime light' (Young). Some rude notion of
the total quantity of light received from the Sun is perhaps
obtainable on comparison with the average full Moon, whose
radiance the Sun exceeds 600,000 times. In consequence of
absorption of the Sun's light by its own atmosphere, the Earth
receives very much less than it otherwise would ; while if the
absorbing property of that atmosphere were entirely removed,
the Sun would (according- to Professor Langley) shine with
a color decidedly blue, resembling the electric arc. As a farther
effect of this absorption, the intrinsic brightness at the edge or
limb is J that of the centre of the disk (according to Professor
Pickering); and D' Vogel makes the actinic or photo-
graphic intensity only i for the same region. While this shad-
ing off toward the edge is at once apparent to the eye, when
the entire Sun is projected on a screen, the rapid actinic grada-
tion is more marked in photographs of the Sun, which strongly
show the effect of under-exposure near the limb, if the central
regions of the disk have been rightly timed.

KiRCHHOFF of Berlin (whose portrait is given on the fol-
lowing page) in 1S59 formulated the following principles of
spectrum analysis : ( i) Solid and liquid bodies (also gases under
high pressure) give, when incandescent, a continuous spectrum ;
(2) Gases under low pressure give a discontinuous but char-
acteristic bright-line spectrum; (3) When white light passes
through a gas, this medium absorbs rays of identical wave-
length with those composing its own bright-line spectrum.
These principles fully account for the discontinuous spectrum
of the Sun, crossed as it is by the multitude of Fraunhofer
lines. But it must be observed that the relative position of
these lines will vary with the nature of the spectroscope used:
with a prism spectroscope the relative dispersion in different
parts of the spectrum varies with the material of the prism ;
with a grating spectroscope (in which the dispersion is produced
by reflection from a gitter, or grating, ruled upon polished
speculum metal with many thousand lines to the inch), the
dispersion is wholly independent of the material of the gitter,
thereby giving the normal solar spectrum. Compared with
this a prismatic spectrum has the red end unduly compressed,
and the violet end as unduly expanded.

More about the Sun — Solar Physics 71

RirrHERFURD, assisted by Ckapma.n, tuled excellent gratings
mechanically; but the last degree of Euccess*has been aiiained
by Professor Rowland of Baltimore, whose ruling engine cov-
ers specular surfaces, eillier plane or concave, si* inches in
diameier with accurate lines, up to 20,000 to the inch. The

F (IS

!/)

y of the gratings v.istly simiilifies the accessories of
the spectroscope, for ^e^^eatcl)es in which they art; applicabl;.
So great is the dispeisiuu olilaiiiable that the siilar sptcttuiii,
as photographed by Rowland with one of these gratings and
enlarged three fold, U abuut forty feet in length. An illuMra-
tion of his ruling engine is given on p. ^2, and its snpcriurity
1 and pcrfcLt

72 Stars and Telescopes

mourning of the screw, which has lo threads to the inch, and is
a sulid cylinder uf meel, abuui ij inches long, and i^ inches in
diameter. (Article 'Screw,' hneydBpadia Bntanmca, gth edi-
tion.) The perfect gratings ruled with this engine are now
supplied to physicists all over the world.

By means of a spectroscope properly arranged with suitable
accessories, the Sun's s|>ectruiii has been both delineated and
photographed alongside of the spectra uf numerous tenestrial
substances. Foremost among recent investigators in this field,
and in mapping the solar spectrum, are Thollon in France,
LocKVBR and illGtis in England, Thal^k in Sweden, Skvtk

in Scotland, and in America Rowland, YyuNO, Trowbridg
and HuTCKiNS, Their research, together with that of previo
investigators, principally Kcrchkokf and ANCSTRtiM, VoGl
and FtEVEZ. has led to Che certain detection of at least 35 el
mental substances in the .Sun, among which are : —

<A1) Aluminium.(Ci)Chroniium.(MK| Magnesium, (Ag) Silver,
(Bi) Katium, ICo) Cobalt, (Mn) Manganese, (Na} Sodiun
(Cd) Cadmium, (Cu) Copper, (Nil Nickel, ITi) Titanini

(Cj> Calcium, (H) Hydrogen, (Scj Scandium, (V)Vanadiui
(C) Carbon, < Ft) Iron, (Sil Silicon, lZi.)Zinc.

More about tfte Sun — Solar Physics 73

Hydrogen, iron, nickel, lilanium, calcinm, and manganese are
ihe most strongly marked. Runge's researches in 1897 defi-
nitively eslablUhed the exislence of oxygen in the Sun. Chlo-
rine and nitrogen, so abundant on ihe Earth, and gold, mercury,
phosphorus, and sulphur, are as yet undiscovered- Also the
soiar spectrum appears lo indicate the existence of many metals
in the Sun not now recognized upon the Earth ; but it must
be remembered (hat oui globe is known only superficially, and
there is every reason for believing thai Ihe Earth, if healed to
incandescence, would afford a spectrum very like thai of the
Sun itself.

On the opposife page is a reproduction from one of M*
McClea^'s large charts of the Comftiratwe Pkelo^-nipbic
Spt<tra of Ihi Suit ,iHd Ih/ t\f(tals (IftnAon iSgt). The region
is at the violet end of the spectrum, near Ihe Fraunhofer lines
H and K, which ate due to calcium. The solar spectrum is
at the extreme top and bottom, with AngstrO.m's scale, and
next to it is the spectrum of iron ; mark the coincidence of the
bright lines of the latter with djrk lines of the former. In alt,

nized. The symbols of other chemical elements are given at
the left side, opposite their characteristic s)>oclra. The chemi-
cal spectra of many metallic elemciils freed from iniiiurilies are
not yet fully known, but these are in the process of (linrniigh
invesligalion by Rowland, and Kavser and Runi-.f. of Han-
over. On the completion of these researches a farther and more
searching comparison will be made with the solar spectrum,
hundreds of the dark lines in which are due to absorption by
Ihe Earth's atmosphere, and consequently called lelluric lines.
Especial studies of these have been made bv MM. Janssen,
TH0LI.0N and CoKNi;, Decker, and McCi.ean. M' lltr.cs,
studying (hos3 strikingly marked bands in the solar spectrum
due to aljsorption by the oxygen in our atmosphere, and known
as 'great B' and 'Krcal A.' finds that the double lines are in
rhythmic groups, in harmonious sequence capable of represen-
(alion by a simple geometric conslruction. Whether Ihe solar
spectrum is constant in character is not known ; with a view
10 the determination of this question ii
PiAZZi Smvtu conducted a series of observ
the absolute spcclrum in Ihe year 1884.

Regarding the solar spectrum (prismatic) as a band of color
merely, the maximum intensity of heat-rays falls just belon
the red (at some distance inferior lo Ihe dark Fraunhofer line

74 Stars and Telescopes

A); that of light falls in the yellow (between D and E);
and that of chemical or photographic activity, in the violet
(between G and H) ; but in the normal spectrum, these three
maxima are brought more closely together, approaching the
middle of the spectrum which nearly coincides with the yellow
D lines of sodium.

Beyond the red in the solar spectrum is a vast region wholly
invisible to the human eye ; but modern physicists have devised
methods for mapping it with certainty. Sir John Herschel,
J. W. Draper, and Becquerel were the pioneers in this re-
search, the last utilizing various phosphorescent substances
upon which an intense spectrum had been projected for a long
time. Direct photographic maps of the infra-red region are
very difficult, because the actinic intensity is exceedingly feeble ;
and Abney, by means of collodion plates specially prepared
with bromide of silver, has made an extended catalogue of the
invisible dark bands. But Professor Langlev has pushed the
mapping of the infra-red spectrum to an unexpected limit by
means of the bolometer, a marvellously sensitive energy-meas-
ured of his own invention. In order to understand in outline
the operation of the bolometer, or spectro-bolometer, it is neces-
sary to recall that, as the temperature of a metal rises, it be-
comes a poorer conductor of electricity ; as it falls, its conduc-
tivity increases, iron at 300° below centigrade zero being, as
Professor Dewar has shown, nearly as perfect an electrical
conductor as copper. The characteristic feature of the bolo-
meter is a minute strip of platinum leaf, looking much like an
exceedingly fine hair or a coarse spider web. It is about J inch
long, jjj inch broad, and so thin that a pile of 25,000 strips
would be only an inch high. This bolometer film, then, having
been connected into a galvanometer circuit, is placed in the
solar spectrum formed either by a grating or through the agency
of rock salt prisms ; and as it is carried along the region of the
infra-red, parallel to the Fraunhofer lines, the fluctuations of
the needle may be accurately recorded.

In this manner he first represented the Sun's invisible heat
spectrum in an energy-curve; but his recent application of an
ingenious automatic method, accessory to the bolometer, has
enabled him to photograph its indications in a form precisely
comparable with the normal spectrum, Holography is the
name given by Professor Langley to these processes which,
by the joint use of the bolometer and photography, have auto-
matically ])roduced a complete chart of the invisible heat spec-

More about the Sun — Solar Physics 75

trum equal iii length to ten times the entire lumtnoaa spectrum
of the Sun, though indicaiiuns of heat extend still farther. Be-
low, on this page, is an illusttation al this extraordinary instrU'
mcnt, reproduced from a photograph Itindly sent me by Pro-
fessor Langlev. It shows only the bolometer portion of ihe
entire apparatus, in its case and with the connections as in
actual use. The bolometer was built by Grunow oENew York,
and farms part □[ the equipinent of the astro-physical observa-
tory oE the Smillisonian Institution al Washington. So sensitive
is this delicate inatruinent that it is competent to delect a tera-

BOLOMETEl

peralure fluctuation as minute as the millionth part of a degree
centigrade. It is proper to add that the researches conducted
with such an instrument, often appearing remote'and meaning-
less 10 a l.iyman. are eminently practical in thcit bearing, as
thev pertain directiv tn the way in which the Sun affecl'i the
Earth, auil man in his relations to it, and to the method of dis-
tribution of solar hcnt, forming thus, among other things, a
Rcienlitic basis fnr meteomlony-

At the end of the solar siiectrum remote from the red is the
nltra-violet region, ordinarily invisible ; a portion of which mav,
honcver. lie Seen by receiving it upon nranium glass or other

^6 Stars and Telescopes

fluorescent substances. Glass being nearly opaque to the short
wave-lengths of violet and ultra-violet, the optical parts of in
struments for this research are made of quartz or calc-spar, or
the necessary dispersion is obtained by using the diffraction
grating. The superior intensity of the chemical or actinic rays
in this region renders photography of especial service; and
sensitive films stained with various dyes have been effectively
employed. The painstaking investigations of Rutherkukd,
CoRNU, H. Draper, Rowland, and Vogel have provided
splendid maps of the invisible ultra-violet spectrum, exceeding
many times the length of the visible spectrum. The farther
region of the ultra-violet is pretty abruptly cut off by the ab-
sorptive action of our atmosphere.

The constant of solar heat, first investigated by Herschel
and PouiLLET in 1837-38, was re-determined by Professor
Lang LEY in 1881. He adopts three calories (small) as the
solar constant, — which signifies that 'at the Earth's mean
distance, in the absence of its absorbing atmosphere, the solar
rays would raise one gram of water three degrees centigrade
per minute for each normally exposed square centimetre of
its surface. . . . Expressed in terms. of melting ice, it implies
a solar .^radiation capable of melting an ice-shell 5445 metres
deep annually over the whole surface of the Earth.* Professor
Langley's Researches on Solar Heat and its Absorption by the
Earth* s Atmosphere: A Report of the Mount Whitney Expedi-
tion^ form No, xv of the Professional Papers of the Signal Service
(Washington 1884). Scheiner (1898) adopts 3.75 calories.

To express the solar heat in terms of energy : When the Sun
is overhead, each square metre of the Earth's surface receives
(deducting for atmospheric absorption) an amount of heat
equivalent to \\ horse-power continuously. In solar engines
like those of Erfcsson and Mouchot, about } of this is vir-
tually wasted. Of heat-radiation emitted from the Sun and
passing alone: its radius, Professor Frost finds that about J
part is absorbed in the solar atmosphere, which, were it re-
moved, would allow the Earth to receive from the Sun 1.7
times the present amount. Imagine that hemisphere of our
globe turned toward the Sun to be covered with horses, ar-
ranged as closely together as possible, no horse standing in the
shadow of any other ; then cover the opposite hemisphere with
an equal number of horses • the solar energv intercepted by
the Earth is more than equivalent to the power of all these
animals exerting themselves to the utmost and continuously.

More about the Sun — Solar Physics 77

It is easy lo show that 'the amount of heal emitted in a
minure by a square metre of the Suii'a surface is about 46.000
limes as great a* that received by a square metre at the Earth,
■ . • that is, over 100.000 horse-power per square metre acting
continuously.' . . . (Yoi;nl;). If the Sun were solid coal, this
rate of expenditure would imply its entire combustion in about
5,000 years. The effective temperature of the Sun's surface is
difficult tu determine, and has been variously evaluated, from
the enormously high estimates u£ Secchi, Ehilsson, and
ZoLLNER. to the more moderate figures of Spoeheb and Lame,
who deduced temperatures
of 80,000" to so,oooo Fah-
renheit. According to Ros-
SETTl, it is not less than
18,000= Fahrenheit, an es-
timate probably not far
wrong. M, LeChatelier,
however, in 1S92. found the
[emperature at little short
of 14.000°, and Wilson and
Grav. about 12,0000, ur
Schetner's recent obser
vations upon the peculiar
behavior of two lines in the
spectrum of magnesium
confirm these lnwer values
in a remarkable way, ap-
parently showing that the
Sun's temperature lies be- voN 1
tween that of the electric
arc (about 6000°), and that of the ete
high as :o.ooo°).

The maintenance of this slupendou
is explainable on the theory advanced by v
in 1S56, who calculated that an anr
in the Sun's diameter will accou't f(
year, — a rate of .thrinkage so slon

elapse before it will become deteclalile with our t>est inslru
ments. Accepting this theory. Lord Kelvtn estimates that the
Earth cannot have been receiving (he Sun's light and heat
longer than 20,ooo,txjo years in the past ; and Professor New
COMB calculates that in 5,000,000 years the Sun will have con
traded to one half its present diameter, and i( is unlikely that

-iStM)
c spark (probably a*
outlay of solar energy

e radiation in a
ly centuries must

jS Stars and Telescopes

it can continue to radiate sufficient heat to maintain life of types
now present on the Earth longer than 10,000,000 years in the
future. Assuming that'solar heat is radiated uniformly in all
directions, a simple computation shows that all the known
planets receive almost a two-hundred-millionth part of the
entire heat given out by the Sun, the Earth's share being about
^^ of this. The vast remainder seems to us essentially wasted*
and its ultimate destination is unknown.

To epitomize Professor Young's statement of the theory
of the Sun*s constitution, generally accepted : —

(</) The Sun is made up of concentric layers or* shells, its
main body or nucleus being probably composed of gases, but
under conditions very unlike any laboratory state with which
we are acquainted, on account of the intense heat and the
extreme compression by the enormous force of solar gravity.
These gases would be denser than water, and viscous, in con-
sistency possibly resembling tar or pitch.

{b) Surrounding the main body of the Sun is a shell of incan-
descent clouds, formed by condensation of the vapors which
are exposed to the cold of space, and called the photosphere.
Telescopic scrutiny shows that the photosphere is composed of
myriad 'granules,' about 500 miles in diameter, excessively bril-
liant, and apparently floating in a darker medium.

(r) The shallow, vapor-laden atmosphere in which the pho-
tospheric clouds appear to float is called the ' reversing layer,'
because its selective absorption produces the Fraunhofer lines
in the solar spectrum. During the India cclii)se of 1S98 it was
shown to be about 700 miles in thickness (pp. 364-65). The
reversing layer contains a considerable quantity of tb.ose va-
pors which have given rise to the brilliant clouds of the
photosphere, just as air adjacent to clouds is itself saturated
with the vapor of water.

(d) The chromosphere and prominences are permanent gases,
mainly hydrogen and helium, mingled with the vapors of the
reversing layer, but rising to far greater elevations. Jets of
incandescent hydrogen appear to ascend between the photo-
spheric clouds, much like flames playing over a coal fire.
Calcium vapor is the most intensely marked, even more so
than that of iron, which has over 2.000 line-coincidences, while
calcium has only about 80. In 1S95 Professor Ramsay first
identified helium as an earthy element.

{e) Still above photosphere and prominences is the corona,
hitherto observable only during total eclipses, and extending

More about the Sun — Solar Physics 79

to elevations far greater than any truly solar atmosphere pos-
sibly could. The characteristic green line of its spectrum, due
to a substance called * coronium,' is brightest close to the Sun's
limb, and during the eclipse of ist January 1889 it was traced
outward by Professor Keeler to a distance of 325,000 miles.
Professor Nasini of Padua in 1898 announced that, in the
spectrum of volcanic gases of the Solfatara di Pozzuoli, he finds
a line corresponding in position with this coronium line, 1474 K
as it is often called. Coronium may therefore Le a terrestrial
substance, as well as solar. But much of the coronal light
originates in something other than coronium, because of the
dark lines in its spectrum. These indicate solar light, reflected
probably from small meteoric particles, possibly the debris of
comets circulating about the Sun in orbits of their own. Cal-
cium, hydrogen and helium do not appear in the corona.

Sir William Huggins and D^ Schuster maintain the
view that the coronal streamers are in part due to electric
discharges. The corona is a very complex phenomenon, by no
means fully understood ; and no theory has yet been shown com-
petent to undergo the ultimate test, — that of predicting the
general configuration of coronal streamers at future eclipses.

Among modern solar theories may be mentioned that of
Schmidt, an optical theory of the solar disk, making the
Sun wholly gaseous, in fact a planetary nebula; and that of
D' Brester of Delft, published in 1S92, a theory of the Sun
characterized by much novelty. Rejecting the hypothesis of
eruptional translation of solar matter, he conceives the Sun
to be a relatively tranquil gaseous body, of essentially the same
elementary composition as our Earth ; and he attempts ta
show, in accordance with well-known properties of matter,
that the same cause which would keep the mass in repose must
produce also * chemical luminescence,' as he terms it Great
material eruptions, then, are merely deceptive appearances,
being simply moving flashes in tranquil, incandescent gases.

The surface of the Sun (photosphere, spots, faculae, and
prominences) is now a subject of daily study at many observa-
tories, particularly at Potsdam, Meudon, Rome, and the Yerkes
Observatory of the University of Chicago ; and observations
are rapidly accumulating, the complete discussion of which
ought soon to settle many points in the solar theory, now dis-
puted. But as the Sun's corona is visible only a few hours in
a century, our knowledge of that object makes haste very slowly,
and must continue to do so, unless the photographic method

8o Stars and Telescopes

of Sir William Huggins (apparently successful in 1883,
though later not), shall make it possible to study the brighter
streamers of the corona without an eclipse. Recent results,
however, are not encouraging. Failing to detect even a trace
of the corona by its light, Professors Hale and Wadsworth
have attempted to chart its principal streamers by their heat
radiations, by means of the bolometer, though as yet without
success.

For sources of the early and historic papers on the solar
spectrum by Angstrom, Hrewster, the Herschels, father
and son, Kirchhoff, Mascart, Van der VVilligen and
many others, consult Houzeau and Lancaster, Bibliographie
GMraU, ii. (18S2), Soo.
CoRNU, ' Sur le spectre normal du Soleil,' Attn, de r£cole

A'ormaie^ iii. and ix. (Paris 1874 and 1882).
Tait, Recent Advances in Physical Science (London 1876).
Draper, J. \V., 'Distribution of Heat in the Spectrum,' in his

Scientific Memoirs (New York 1878), p. 383.
LangLEY, Proc. Am. Assoc, Adv. Science^ xxviii. (1879), 51.
Vogel, H. C, ' Sonnenspectrum,' Puhl. Obs. Potsdam^ i. (1879).
Peirce, ' The Cooling of the Earth and the Sun,' in his Ideality

in the Physical Sciences (Hoston 1881).
Haughton, * Sun-heat and Terrestrial Radiation,' Royal Irish

Academy (Dublin 1881 and 1886).
Smyth, Madeira Spectroscopic (Edinburgh 1882).
Kirchhoff, Gesammelte Abhandlumj^en (Leipzig 1882).
Fievez, 'litude du spectre solaire,' Annates de V Observatoire

Royiil, iv. and v. (Brussels 1882 and 1883).
Siemens, On the Conservation of Solar Energy (London 1883).
Siemens, * Solar Temperature,' Proc. Roy. Institution, x.

(1883), 315.
Langley, * Invisible Prismatic Spectrum,' Memoirs N'ational

Acad. Sciences, ii. (1883), 147,
Sparer, * Physikalische Beschaffenhcit,' Viertel. Astron. Gesell.

XX. (1885), 243.
LOCKYER, The Chemistry of the Sun (London 1887).
Kelvin, 'Sun's Heat,' Proc. Roy. Institntiofi, xii. (1887). i.
Trowbridge, ' Oxygen in Sun,' Proc. Am. Acad.xyS\\. (1888), i.
V. Fraunhofer, Gesammelte Schriften (Munich 1888).
WA'rrs, Index of Spectra (Manchester 1889).
Becker, * The Solar Spectrum at Medium and Low Altitudes,'

Trans. Royal Society Edinburgh^ xxxvi. ( 1890), 99.

More about the Sun — Solar Physics 8 1

Mkvuder, S/>^ctroscopic Astronomy fin Chambejls's Astrononiy,

vol. ii. (Oxford 1890), bk. viii.
McClean, Comparative Photographic Spectra of the High Sun

and the Low Sun (London 1S90).
Thollon, * Nouveau dessin du spectre sol aire,* Annates de

r Obsertfotoire de NicCy iii. (Paris 1890), with Atlas.
Schmidt, Die Strahlentn-echung au/der Sonne (Stuttgart 1891).
Young, • Solar Physics,' Sidereal Afessenger^ x. (1891), 312.
Rowland, y<?>4«j Hopkins University Circular ^ February 1891.
Kklvin, 'On the Age of the Sun's Heat,' and *On the Sun's

Heat,' Popular Lectures and Addresses^ i. (London 1891).
Brester, Thiorie du Soldi {\vc\.%\^x^2im 1892).
Le Chatelier, 'Temperature of the Sun,' Astronomy and

Astrophysics^ xi. (1892), 517.
Knopf, Die Schmidt' sche Souucntheorie (Jena 1893).
Gore, ♦ Fuel of the Sun,' The Visible Unri>ersc (New York 1893).
HlGCis, Photographic Atlas of the Normal Solar Spectrum^ in 3

series (Liverpool 1893).
Hale, * Corona without Eclipse,' -^j/;^?//. ^w^/ Astrophys. xiii.

(1894), 662.
Wilson and Gray, ' Temperature of Sun,' Astron. and Astro-
phys., xiii. (1894), 382; Phil. Trans, clxxxv. (A 1894), 361.
Sciieiner and Frost, Astronomical Spectroscopy (Woston 1894),

with bibliographies of numerous papers.
Langley, ' Infra-red Spectrum,' Nature^ li. (1894), 12; Report

Brit. Assoc. Ad'i'. Sci. 1 894, p. 465.
Ramsay, * Helium,' Proc. Roy. Soc. Iviii. (1895), 65, 81.
Young. ' Helium,' Pop. Sci. Mo. xlviii. (1896), 339.
LocKYER, * Helium,' Science Progress, v. (1896). 249.
Maunder, 'Helium,' Kuaiuledge, xix. (1896), 86, 284.
Rowland, Solar Spectrum Wa^'cdcngths (Chicago 1897).
Keeler, ' Astrophysics,' Astrophys. Jour. vi. (1897), 271.
Clerke, 'Coronium,' The Obsenuitory, xxi. (1898), 325.
Vo<;el. * Kirchhoff'schen Spectralapparat,' Sitz. Kon. Preuss.

A had. Wiss. Berlin 1898, 141.
SCHEINER, * Temperature of Sun,' Himmelund Erde, x. (1898),

433 ; Publ. Astron. Soc. Pacific^ x. (1898), 167.

For a nearly complete bibliography of recent literature, con-
sult Poole's Indexes under Sun, and Spectroscope (page 395 of
this book) ; Astronomy and Astro-Physics, xi.-xiii. (1892-94) ;
also The A strophysical Journal (i.-viii.) 1895-1898.

s *T — 6

CHAPTER VIII

TOTAL SOLAR ECLIPSES

T^OTAL eclipses of the Sun, the most impressive
^ of natural phenomena, and formerly serviceable
only to the mathematical astronomer in correcting the
tables of solar and lunar motions, and in the deter-
mination of longitudes, are now observed by the astro-
physicist chiefly, for the knowledge afforded as to the
Sun's constitution and radiations.

Nearly 70 of these phenomena happen every cen-
tury. In order that an eclipse may be total, the apex
of the conical lunar shadow must at least reach the
Earth. But when the Moon is near apogee, its shadow
does not extend to the Earth, and an eclipse happen-
ing at that time is of the more frequent type known
as annular, seven of which take place on the average
every eight years ; in some regions of our globe the
Sun may then be seen as a ring of light surrounding
the Moon's disk. Sir Robert Ball's diagram on the
opposite page makes clear the relations of Sun, Earth,
and Moon in eclipses of the various types.

On the occasion of a total eclipse, the Moon's orbi-
tal advance, 2,100 miles hourly, causes her narrow
shadow to trail easterly over the surface of the Earth.
Total obscuration is visible only within this trail, a

Total Solar Eclipses

region which may exceed 8,000 miles in length, but
whose average breadth near the equator is less than
100 miles. Obviously, then, a total eclipse at a given
place must be an exceedingly infrequent occurrence ;
indeed, every spot on the globe is likely to come
within the range of the Moon's shadow but once in
about three and one half centuries.

While the lunar shadow is sweeping over land and
sea from west to east, it is to be noted that the axial

(i) Moon's shadow cut off by earth (total solar eclipse)

(2) Moon's shadow does not reach earth (annular eclipse)

(3) Moon in earth's shadow (total lunar eclipse)

(4) Moon's shadow just reaches earth {total solar eclipse in

middle oj path^ but annular at both ends)

rotation of our globe is carrying the observer eastward
also, 1,040 miles hourly at the equator, so that the
Moon's shadow as it sweeps past him has a minimum
speed of 1,060 miles per hour (the difference of the
two velocities). Swift as this motion is, the lunar
shadow has repeatedly been seen advancing and re-
ceding with appalling speed. Total eclipse lasts only

84 Stars and Telescopes

while the observer remains within the Moon's shadow.
It is apparent, then, that the longest total eclipses
must take place near the equator, because the observer
located there is transported most rapidly in the same
general direction as the moving lunar shadow. Also,
the longest eclipses happen in summer, for the Earth
is then farther from the Sun, thus making its diameter
appear smaller, so that our satellite can cover it
longer. With the Moon near perigee, and other
necessary and favorable conditions, the calculation
has been made that it is possible for the Sun to be
totally obscured nearly eight minutes. Total eclipses
have every range of duration, from this limit down to
a single second ; but no totality is known to have been
observed longer than 5"^ 36* (1868, in India), while
the average duration is about three minutes.

Eclipses may be approximately predicted by means
of the Saros, a period of 18 years, 11 J days (or 18
years, 10^ days, if five leap years have intervened).
At the end of this cycle another and similar eclipse
will occur, only 1 20° of longitude farther west. The
eclipse of 1896, for example, is a return of the famous
ones of 1878, i860, and 1842 ; and there will be
other repetitions in 1914 and 1932. When, however,
three periods have passed, an eclipse may return to
the same general region on the Earth, but the dis-
placement in latitude will ordinarily amount to several
hundred miles; for example, the eclipse of 1842 was
total in Austria, but its third return in 1896 fell vis-
ible in Norway. By utilizing the mathematical data
of the Astronomical Ephemeris J published by the gov-
ernment three years in advance, a brief computation
will give the time of every phase of an eclipse, exact
to a small fraction of a second, for any place on the

Total Solar Eclipses 85

Earth where it may be visible. The subject of the
remarkable recurrence of eclipses, and the great pre-
cision with which they may be predicted, is treated
more fully in Number i of the * Columbian Knowl-
edge Series.*

To select a single salient result from each recent
eclipse whose observation has important bearing on
our knowledge of solar physics: i8th August 1868
(India), when M. Janssen, using a high-dispersion
spectroscope, succeeded for the first time in observ-
ing the solar prominences after (as well as during)
the eclipse; 7th August 1869 (Iowa, U. S.), when
Professor Young at Burlington obser\Td and accu-
rately identified the green hne (1474 on Kirchhoff*s
scale) in the spectrum of the Sun*s corona, which
is regarded as due to the vapor of a solar element
not yet found on the Earth, and hence called ' coro-
nium'; 22nd December 1870 (Spain), when, just
as totality was coming on. Professor Young obser\'ed
a multitude of the Fraunhofer lines in the Sun's spec-
trum instantly reversed into bright lines, — a phe-
nomenon repeatedly confirmed, and which indicates
the existence of a stratum in the Sun's atmosphere
known as the * reversing layer ' ; 12th December 1871
(India), when M. Janssen saw Fraunhofer lines super-
posed upon the faint continuous spectrum of the
corona; 29th July 1878 (Western United States),
when Professor Newcomb in Wyoming and Professor
Langlev on Pike's Peak, Colorado, observed a vast
ecliptic extension of the coronal streamers to a dis-
tance of eleven millions of miles, east and west of
the Sun; 17th May 1882 (Egypt), when D^ Schuster
photographed the spectrum of the corona for the first
time, getting no less than 30 measurable lines ; 6th

86 Stars and Telescopes

May 1883 (Caioline Island), when, with a la^e in-
crease of knowledge lelating to the prominences, the
coronal structure and its spectrum, the non-existence
of intramercurian planets was settled to the satisfac-
tion of most astronomers by MM. Trouvelot and
Palisa; agth August 1886 (Grenada), when D'
Schuster found the maximum actinic intensity in the
continuous spectrum of the corona displaced consid-

erably toward the red (in comparison with the spec-
trum of sunlight), proving that the scattering light
from small particles is feeble; ist January 1889
(California), when M' BARnARD at Bartlelt Springs
and Professor W. H. Pickering at Willows obtained
exceedingly fine detail photographs of the Sun's
corona; i6th April 1893 (Senegal), when M. Desian-
DRts, by photographs of the coronal spectrum on

lSj4 al S'trj^KtUa Iibttiit, and iKSi in A/aJaeaKar : alii four rilifsr
txptdiluria, in iHto, 1886, iB«7, o«rf IHi iKtml Mai 1*1, •.ralim «/ iS8q,
ri^ la,' i,.t him hit lift. Ht nnln Frllm, /•/ llu R^y^l Socitly. and

Total Solar Eclipses

both sides of the Sun, found evidence, on comparing
them, that the corona rotates on its axis bodily with
the Sun; 9th August 1896 (Nova Zembia), when
M' Shackleton verified the existence of the reveising
layer by photographing its spectrum ; 3 2d January 189S
(India) , when M" Maunder secured the first fine pho-
tographs of the outermost streamers of the corona.

A fact of much significance in solar research, and
now generally regarded as established, is the periodi-
cal fluctuation of the stteamere of the corona coinci-
demly, or nearly so, with the eleven year cycle of
the spots on the Sun. The total eclipse of 1882, on
the opposite page, shows the type of corona near the
times of maximum spots, — a corona rather fully de-
veloped all around the Sun, with an abundance of
relatively short, bright streamers, often complexly inter-
laced; while the eclipse of 1878, in the adjacent
figure, exhibits the type
occurring at the sun-
spot minimum, — a cor-
ona with uneven radi-
ance, but with a vast
extension of its stream-
ers east and west, and
beautifully developed in
delicately curving fila-
ments around the solar
poles. The physical cause underlying this cycle of
the corona is not yet made out ; and the investigation
of this problem, with a host of others arising in con-
nection with total eclipses, leads astronomers to an-
ticipate their occurrence with absorbing interest.

The total eclipses of the next quarter- century most
favorable for observation are (map opposite) 1 —

■i./rom flulotrafkil

Stars and Telescopes

DATK

1900, May 28

1 901, May 18
1905, August 30
1907, January 14
19 1 2, October 10
191 4, August 21
1 91 6, February 3

1918, June 8

191 9, May 29

1922, September 21

1923, September 10

1925, January 24

1926, January 14

REGIONS OF CKNEKAL VISIBILITY

Mexico, United States (from
New Orleans to Norfolk),
Spain, and Algeria.

Sumatra, Borneo, and Celebes.

Labrador, Spain, and Egypt.

Russia, Turkestan, and China.

Colombia and Brazil.

Norway, Sweden, and Russia

\. extremity of S. America.

U. S., from Oregon to Florida.

Urazil, Liberia, and Congo.

Northern Australia.

California to Texas.

Canada and Maine.

Africa, Sumatra, and Borneo.

DURA-

riON OF

TOTALITY

*%
**

The totality-path of the great ecUpse of 9th Sep-
tember 1904, and those of 3rd January 1908 and
28th April 191 1, unfortunately lie for the most part
over the unavailable wastes of the Pacific Ocean. No
total eclipse will be visible in New England or the
Middle States till 24th January 1925. On 20th June
1955 occurs the longest echpse for many centuries,
totality lasting more than seven minutes in the island
of Luzon, at or very near Manila.

A full list of popular articles on eclipses, and the researches
undertaken by eclipse expeditions to all parts of the world,
will be found in Poole's Index to Periodical Literature^ vol. i.
(1802-81), pp. 381-2; vol. ii. (1882-86), p. 129; vol. iii. (1887-
91), p. 127; vol. iv. (1892-96), p. 167. Also, Fletcher's In-
dex to General Literature (Boston 1893), P- QO-
Johnson, Eclipses^ Past and Future (London 1874).
Bessel, Analyse der Finsternisse (Leipzig 1876).
Ranyard, Memoirs Royal Astronomical Society^ xli. (1.S79).
Newcomb, On the Recurrence of Solar Fclipses^ with Tables of

Eclipses from B.C. 700 to A. D. 2300 (Washington 1879).
HUGCINS, * Corona,' /'r<7r. Royal Society, xxxix. (1884), 108.
Hastings, Memoirs A- ational Academy Sciences ^ ii. (1884), '07-

/ 1

;

• ^n-

/ '^

\ •

\ \^

Wj/U

>-.' ^

k-.^

t-i

-Xv,&

fe^

■^

^'4

l(f

^'\

■/

^S •

'■•'/^

'/^

'/J(

' 1 }

iiii

*— 1

'. /•] 1

h— -Pn

[V'

^ — 1

Total Solar Eclipses 89

V.OppoLzEr, T., Canon dtr Finsttmisse {\'KVTi3. iSS?).
WesleV. ill ChambiiRS' Aslrouimiy (Londun 1889), i. 311.
PROCTUR, Old and Ncvi Ailronomy (New York 1892).
CleRKe, Hiitory of Astronomy (London 1893).
Toiii), TbIjI Eihpits of the Sun QiofA<m 1894). Bibliography.
GiNZEL, ' Nfystische bo line 11 tins tern isse,' Ilimnul und Erdt,

vii. (1895), 167.
LVNN, Rtmarkablt Eclipses (London 189O).
LocKVER, Reient and Coming Edifsts (London 1897).
KoituLli, ValENTINER'S I/iiilduiiirtertuch der Astronamit, i.

(Ureslau 1S97).
ItL-RRARij, Edifse nzd January 1898, -a-ilh Charts of Erlifu

Families (Dehra Dun iSyM).

Fur the literature of current eclipses, consult also the recent
volumes of Knirailtdge, The Observali/ry, Pvfular Astranamy,
/•luriial Briliih Aitnmoniiiai Association, Puilicaliont Astro-
nomical SotUty Pacific ; and f Or teclinical reports, the Proceed-
ings and Transactions of the Royal Society. — D. P. T.

(Fram a /AnlKtrafJi it India i^

CHAPTER IX

THE SOLAR SYSTEM

nPHE Earth on which we hve is one of a large
-■■ number of bodies circulating in orbits round
the Sun, and attracted to him by a force called gravi-
tation, which, constant in itself, acts in such a way
that its effect diminishes as the square of the dis-
tance increases. The revolving bodies themselves are
endued with a similar attracting energy, but much
smaller than that of the Sun in consequence of the
much smaller amount of matter which they contain.
The Sun, the central body of this great system, ra-
diates light and heat to the whole with an intensity
diminishing, like the force of gravity, in the same pro-
portion as the square of the distance increases."

*• Independently of his light and heat, the Sun's supreme
right to rule his family of planets is at once apparent from his
superior size (see diagram on page 95), and from his vastly
greater mass. Relative weights of common things readily give
a notion sufficiently precise: let the ordinary bronze cent
represent the weight of the Earth ; Mercury and Mars, then,
the smallest planets, would, if merged in one, equal an old-
fashioned silver three-cent piece ; Venus, a silver dime ; Uranus,
a gold double-eagle and a silver half-dollar (or, what is about
the same thing in weight, a silver dollar, half dollar, and quarter
dollar taken together); Neptune, two silver dollars; Saturn,
eleven silver dollars; Jupiter, rather more than two pounds
avoirdupois (37 silver dollars) ; while the Sun, outweighing
nearly 750 times all the planets and their satellites taken to-
gether, would somewhat exceed the weight of the long ton. —
Z>. P T.

The Solar System 91

The bodies known to revolve round the Sun are
divided into three classes, — planets, comets, and
meteors. In their orbital revolutions, many of the

planets are attended by one or more companion bod-
ies CLilled moons or satellites. Also, some of the
comets are known to consist of double or multiple

Stars and Telescopes

portions. But the meteors mostly travel in vast shoals
together, along orbits similar to those of comets, with
which they seem to have a connection not yet fully
understood.

Kepler, by his laborious research upon the appar-
ent motions of Mars as obtained from the obser-

vations of TvcHO BrahS:, and by extending to the
other planets by analogy the conclusion derived there-
from, established three simple laws according to which
these lx)dies move in the same general direction
round the Sun. Kepler's laws are : ( i ) The planet-
ary orbits are ellipses, with the Sim in one focus: (2)
the planets move fastest when nearest the Sun, in such

The Solar System

a way that the radius vector describes equal areas of
the ellipse in equal times, as the figure shows ; (3) the
squares of the periodic times of the
planets' revolutions round the Sun
are proportional to the cubes of their .
mean distances from him.

The first two of these laws wi
shown by Newton to be necessary
consequences of the planets being
attracted by the Sun with a force '

the distance ; while the third proves

that the force of this attraction is the !
the actual intensity being, as in thi

upon each,
of each

separate planet, inversely proportional to the square
of the distance from him."

94 Stars and Telescopes

The planets vary very much in size, as is apparent
from the opposite illustration, the largest (Jupiter)
being more than 1,300 times greater than the Earth,
while many of the small planets are so minute as to
be visible only with the aid of powerful telescopes,
and it is impossible to measure their real sizes.
These small planets, however, form almost a class of
themselves. Their mean distances from the Sun are
all smaller than that of Jupiter, though greater than
that of Mars, with a single exception ; and their
faintness arises not so much from their great distance
as from their really small size.

All the planets revolve round the Sun in elliptical
orbits of small eccentricity, not differing greatly from
circles.^* These planetary paths are inclined at va-

with physical causes underlying those laws. Newton himself
says : * The cause of gravity is what I do not pretend to know.
. . . Gravity must be caused by an agent acting constantly ac-
cording to certain laws, but whether this agent be material or
immaterial, I have left to the consideration of my readers.*
Consult Professor Tait's Properties of Matter ^ pp. 131 -138,
Clerk Maxwell's article on 'Attraction' [Encyclopadia
Britannica^ 9th edition), and the admirable resume of kinetic
theories of gravitation by M' W. B. Taylor in the SmithsouLin
Report for 1876. Research upon the mechanism of gravity
belongs rather to the field of physics than astronomy, and the
cause of gravitation is yet undiscovered. — D. P. T.

^ In a subsequent chapter it will be shown how the law of
gravitation, regnant through untold ages in the remote past, has
brought about the evolution of the planetary system in its form
at the present day. But a century and a half ago, it was a mere
speculation what the future of such a system might be. Gravi-
tation, that definite and powerful bond, mutual and interacting
between the Sun and all his planets, maintaining each body in
its individual orbit, and preserving continual order and har-
mony, — might it not relax its hold with the lapse of time, leav-
ing all the planets, the Earth among them, to recede farther and
farther into the cold of space, thus bringing all organic life to

The Solar System

rious angles to
the ecliptic or

>nend? Ormight
not the very po-
tency of that same
force, through or-
bitil changes then
known to be going
on, eventually
bring down all the
planetary members
of the system, with

deed, EuLER, who
made the bat suc-
cessful auemiu tu
develo|> fully the
significant results
from the law of
gravitation, had
written a letter

17491

jWei

stating his conclu-

had been sensibly
accelerated in the
three (

previi

Hen

orally accounted
for this by the hy-
pothesis of a sub-
tile resisting me-
dium, causing all

travel round the
Sun in slowly

Stars and Telescopes

plane of the Earth's orbit, and the courses of a few
small planets are considerably more inclined to the

involving apirats, inth the rapidity o( their motioa augmented
at every revolution by increasing nearness to the Sun, Mani-
festly, then, the solar system could not last forever in its pres-
ent state. The eminent French aslronomers. La Grange
(whose portrait \i opposite| and La Place (page Z46I, attacked
this great problem of stability of the planetary system j and
by the application of mathematical tnethodt and expedients,
newly invented, solved it. The path in which each planet
travels has certain geometrical characteristics; its form, its
size, and its position relatively to the stars in space. Tech-
nically these are termed the datitnts of tht orbit, and every
orbit has six such elements. La Gkahce and La Place, pro-
ceeding on the hypothesis
that all the planets were rigid
bodies, proved that no inter-
action of gravity among them

Id .

within

icillate

which their
researches were competent
lo define So long, then, as
the iniierent force of gravity

system, in itself considered
and independently of ex-
terior influences, possesses
all the elements necessary to
absolute stability in taculo
toitdorum. The farther researches of PoissoN and Le Ver-
RiK.R in France, of Schubert in Germany, and of Stockwf.ll
in America, have contributed greatly to our accurate knowledge
of these important terms.

The eccentricity of the Earth's orbit, then, could not go
on increasing indefinitely in the future ; so that our globe is
t the possibility of retreating at one sea-
ntral luminarj- that all the waters ,if ihe

RULER (i707-t783)

forever insured ai

The Solar System 97

ecliptic than the orbits of the large planets are. Also,
the orbital eccentricities of the small planets present a
wider range.

(1736-1813)

Earth would freeic ; nor at ihe opposite season could it ever
approach so near the Sun thai all forms of life would become
extinct by tekson of the exccssitc heat. It is the path of our
own planet in which interest chiefly centres : it^ eccentricity,
already given in Chapter VI as 0.01677, ""ay vary between the
limits 0.0047 and 0.07^7. accoidiiig to Le Verrifr. It is di-
minishing at the present time ; that is, our yearly path round
the Sun IS now appioximating mnre and more nearly to the cir-
cular form, and its nearest approach will take place about
14,000 years hence ; after which the orbit will agiin grow more
and more elliptical. The relatively mmute fluctuations of an
orbit ate termed s/iiil,ir variaiimii: and Ihey may be crudely
represented by holding a flexible and nearly circular hoop
twtween the hands, now and then compressing it slightly, also

wobbling ; ■■ ■

I,A

t the

(ligations

. .il.y.i

98 Stars and Telescopes

But, whether large or small, the planetary bodies
are all alike in partaking of the same easterly motion
in their orbits round the Sun. Comets (at least those
which are permanent members of the solar system)
also move about the Sun in elliptic orbits ; but their
inclination and eccentricity are generally much greater
than those of the planetary orbits, and many which
travel in very elongated ellipses move in the reverse
direction from that of all the planets. Of the meteors,
those moving in regular orbits pursue paths like those
of many comets, swarms of them travelling in ellipses
nearly identical with known cometary orbits. Indeed,
it would seem not unlikely that many comets are com-
posed of clusters of meteors loosely kept near together
by the feeble bond of attraction of the separate parti-
cles, similar discrete bodies being scattered along the
whole or a part of the orbit, but more thickly congre-
gated in some portions than in others.

The large planets at present known are eight in
number: Mercury, Venus, the Earth, Mars, Jupiter,
Saturn, Uranus, and Neptune. The mean distances
of Mercury and Venus from the Sun, in proportion to
the Earth's, are 0.387 and 0.723, respectively; and
the mean distance of Mars from the Sun is 1.524, of

Cileste also led him to the discovery of the invariable plane of
the solar system, which passes through its centre of gravity,
and is determined by the dynamical principle that the sum of
the products of all the planetary masses by the projection of
the areas described by their radii vectores, in any given time, is
a maximum quantity. Relatively to the ecliptic, or ordinary
plane of reference, the invariable plane is defined as follows : —

Longitude of its ascending node, 106° 14' 6"
Its inclination to the ecliptic, i 35 19,

according to Stockwell, one of the latest investigators who
have calculated its position. — D. P. T,

The Solar System 99

Jupiler 5.303, of Saturn 9.539, of Uranus 19.183, and
of Neptune 30.055 times that of the Earth.**

» Recalling thai Ihe distance of our globe from the Sun is
93,000,000 miles, these numbers readily give the approximate
distances in miles of all the large planets from (he central
luminary. There has been devised no better illustration of
relative distances, magnitudes, and motions in ihe solar system
than the (allowing, from Sir John Herschel's Outline) of
Arlranemy : 'Choose any well leveled field or bowling-^reen.
On it place a globe, two feet in diameter ; this wilt represent
the Sun; Mercury will \k represented by a grain of mustard
seed, on the clrcumierence o£ a circle 164 feel in diameter for
its orbit ; Venus a pea. on a circle of 284 feet in diameter; the
Earth also a pea. on a circle of 430 feet ; Mars a rather large
pin's head, on a circle of 6j4 feet ; the asteroids, grains of Sand,
in orbits of from 1000 to 1300 feet ; Jupiter a mode rate-sized
orange, in a circle nearly half a mile across ; Saturn a small
orange, on a circle of four-fifths of a mile; Uianus a full
siied cherry or small plum, upon the circumference of a drcle
more than a mile and a half ; and Neptune a good sized plum,
on a circle about two miles and a half in diameter. As to
getting correct notions on Ibis subject by drawing circles on
paper, or, still worse, from the very childish toys called

To ii

e the n

the planets, in the above-mentioned
orbits, Mercury must describe its
owndiamcterin4i seconds; Venus,
in 4' 14' ; the Earth, in 7 minutes ;
Mars, in 4" 48*; Jupiler, in 2' 56- ;
Saturn, in 3' 13-; Uranus, in a»
16^1 and Neptune, in 3" 3CP.'

Among the great astronomers
who, at the beginning of the present
century, turned their attention to
the important problem of deter-
mining a planet's motion from ob-
servation, Gauss is pre-eminent,
and his finished work is embodied gauss (I777"'855t
in his ThiBriii Metus Cerporum

Caltsiium (1809), translated by Admiral Davis I1S57). The
large planets, with the exception of Uranus and Neptune, have

lOO Stars and Telescopes

It has often been surmised that there is a planet
(possibly several planets) nearer the Sun than Mer-

now been accarately observed so long a time, and the elements
of their motion are so thoroughly well ascertained, that it is
possible to predict their future positions with a precision which
is satisfactory for most purposes. This is done through the
instrumentality of 7a^//x of their motion, which extend ordinarily
a half century in advance of their date, and are capable of farther
extension indefinitely. From such tables is prepared each year,
by a tedious and complex arithmetical process. The Nautical
Almanac and Astronomical Ephcmeris^ which gives the data
required by navigators in conducting ships from port to port, and
by astronomers in carrying on the operations of observatories.
Some of these data are the accurate positions of all the planets
among the fixed stars ; and the degree of their precision de-
pends upon (i) the perfection of the mathematical theory of
their motion and (2) the accuracy with which the planets have
been observed, chiefly during the past two centuries. It is at
the great observatories maintained by the principal govern-
ments that such researches are systematically kept up: at
Greenwich, founded 1675 (already shown on page 39) ; Ber-
lin, founded in 1700; Paris, founded in 166S (on page 141);
Washington, founded in 1842 (page loi, an illustration of the
new Observatory, completed in 1893), ^"^ elsewhere. The ex-
pense of maintenance of each of these establishments averages
about $50,000 annually. Sir George Airy, seventh Astrono-
mer Royal at Greenwich (from 1835 '^ 1881), whose portrait
is on page 102, was the most eminent of the modern astronomers
who have devoted themselves to planetary observation. Since
the time of his early predecessor, Bradley, in the middle of
the i8th century, observations of the planets had been accumu-
lating in unavailable form, and Airy undertook and completed
the prodigious task of calculating, or reducing them, as the
technical expression is. This finished product of the observa-
tory formed the basis of Le Verrier's tables of all the princi-
pal planets of the solar system, completed in 1877, ^ind published
in the Annates de V Observatoire ImpSrial de Paris^ MSmoires.
An entirely new system of tables has now for many years
been in progress of construction under the immediate direc-
tion of Professor Newcomb, who gives in the Introduction to
volume i. Astronomical Papers of the American Ephemeris

102 Siars and Telescopes

cury ; but such objects must be very small, aad none
have yet been certainly discovered. The number of
sma]] planets now known is almost 450; many new
ones are discovered every year, and there probably
are more than 1000 in all. Whether there are planets
more distant than Neptune it is impossible at present

(1801-1892)

(Washington 1882). a brief »nd lucid review of a century's
progress in planetary tables. Also in his Elimints of Ihe Four
Inner Plantls and tkt Fumlamiiilii! Comlanls of AUrenemy
(Washington T895), he [ireseuts a general summary. — D.P. T.

The Solar System 103

to say; but such bodies would not be visible without
the aid of a powerful telescope, *•

■ Professor Todd in 1877 [from uneipliined deviaiioni of
Uranus), and Professor Fokbes in iSSa (from the aphelion
distances of a family of cornels thought to have Ixcn ca[iiured
by planetary bodies far exterior to the present boundary of the
(olar system), derived two independent positions for the trant-
neptunian planet which are in Kurprisingly good agreement;
but, although the suspected region among the itara has been
cirefutly searched, both opticziliy and photographically, thU
planet ii not yet visualiied. — D. P. T.

AlRV, Crmiitatien (London 1834).

Hansen, Allgcmcint Uibtrrickt Jts Senntniy!ltms, in Schd-
macuer's ' Jahrbuch,' IV. (1837).

Hind, Tht Solar Systtm (London and New York 1851).

Maedler, Dai Planetemystim dcr Sonnt ( Leipzig 1854).

Bkeen, Tht Plaiutary iVorldi (London 1854),

KiKKWOOD and Chase, Papers on planetary mechanics and
harmonies in Am, Jour. Stitncr, Prat. Am. Phil. Society,
Jour. FramM. /nslitule, and Prat. Am. Allot. Adv. Scitnce.

l.t.Vit.MKti, Ameritaii /.!ani,il 0/ Scifiiet, xXxW. (1861), 1».

K.\.t.ltl, Dai Sonneniytl/m (Brunswick 1871).

Kaisek, Measures of all the planets with double-image microm-
eter, Annalen dir Slertraiarte in Lfideii, iii. (Hague 1872I.

Stockwell, 'Secular Variations of Orbits of Principal Plan-
ets,' Smilkioniiin Coiilributions to KnmvUd^, jtviii. (1873).

Alexander, ' Harmonies of the Solar System,' Smi/Aionlan
CenlributioHi to A'liowledge, xxi. (1875).

Gladstone, 'Chemical Constituents of the Sular System,'
Philosophical Magatint, iv. (1877), 379,

LEiMiER, Tht Shu: Plantli and SattlUtes (London i83z|.

ScHEiNES, Frost, AUroHomical Sfettrosetfy (Boston 1894).

Bors, 'Newtonian Constant of Gravitation,' Naiun, \. (1894),
330, 366, 400; Phil. Trans, ciiixvi. (A 1895), I.

HlLL.'ProgressofMecanique Celeste,' 0*j/rt«wry,xii, (1896).

PoincarS. ' Stability of Solar System,' Naturt, Iviii, (1898), 183.

Seelider, ' Law of Gravitation,' Pcf. Astron. v. ( 1898), 474, 544.

CHAPTER X

THE PLANETS

'T^HE large planets of the solar system are classified
■*■ as inferior planets (Mercury and Venus), and
superior planets (Mare, Jupiter, Satum, Uranus, and
Neptune), As seen with a telescope, the inferior
planets pass through all the phases of the Moon. I'he
phases of Venus were first noticed by Galileo in 1610.
The orbits of Mercury and Venus lying wholly
within that of the Earth,
these planets can never
come into ajiparent op-
position to the Sun as
seen from the Earth.
But either body may
come from time to time
into line or conjunction
with the Sun, called in-
ferior conjunction when
it is between Sun and
Earth, and superim- con-
junction when beyond
the Sun. If one of them
when in inferior conjunction is near the node of its
orbit, where it crosses the plane of the Earth's, the
planet will be seen to pass like a round black spot
across the Sun, and this phenomenon is called a

(1592-1655)

The Planets 105

transit. The first time Mercury was ever seen on the
Sun's disk was by Gasskndi at Paris, 7th November
1631. The transit of 7th November 1677 was well
observed by Halley at Saint Helena. Dates of re-
cent transits are 9th May
1891, and loth November
1894.*'

Mercury can be seen with
the naked eye only when
near greatest elongation from
the Sun (which averages
about 23° and never exceeds
28°), a little before sunrise
or after sunset, as the case
may be. He ,e,olve. round l"™"^;;'„"^2"""™i
the Sun in 88 days at a " ' '"""j'vZ, ""•'"
mean distance ol 36 millions

of miles ; but, as the eccentricity of his orbit is con-
siderable, his actual distance from the Sun varies
between aSJ and 43^- millions. Mercury is too

* As the Earth passes Mercury's descending node about Tlh
May, and (he ascending node about 9lh November, transits are
possible near these dates only. Also this planet's path being
very eccentric, and al its least distance fiom the Sun near the
time a( its passing the November node, there are about twice
as many transits in November as in May, if long periods of time
are considered. And while the greatest length of a May transit
it 7' so". Mercury's swifter motion near perihelion reduces the
maximum duration of a November transit to ^ 24'. About 13
transits of Mercury lake place every century, the intervals being
either 31,7, 9I. or 13 years. A period of 46 years (exact to
about ^ day) rarely fails of a return of any given transit. Pro-
fessor Nkwcomb's researches on the motion of the Moon lead-
ing him to suspect that (he Earth's rotation on its axis might
be variable, he has investigated this question by means of the
independent time-measure furnished by Mercury's motion round

io6

Stars and Telescopes

near the Sun to allow us to see anything very dis-
tinctly on his surface. His diameter is about 3,000
miles. As shown on the preceding page, markings on
the surface of Mercury have been carefully observed
during several years by Professor Schiaparelli of
Milan, indicating that the planet has a rotation on
its axis equal in duration to its revolution round the
Sun. Mercury's mass is about one tenth that of the
Earth, and his density is therefore much greater than
that of our planet.^

the Sun; but his critical discussion of 21 transits of the planet
observed from 1677 to 1881, afforded no conclusive evidence
of change in the length of the day. {Astronotnical Papers of
the American Ephemeris, i. 465.) Following are the transits
during the half century, 187 5-1925: —

Date

Eastern Standard

Time of

Mid-transit

Duration
of Transit

Position of Transit-path
on the Sun's Disk

1878 May 6

2^ I- P. M.

7" 28-

Considerably north
of centre.

1881 Nov.;

7 57 PM.

5 17

Slightly south of
centre.

1891 May 9

9 24 P. M.

4 47

Near south limb.

1894 Nov. 10

I 34 P. M.

5 13

Slightly north of
centre.

1907 Nov. 14

7 7 A.M.

3 21

Near north limb.

1914 Nov. 7

7 5 A.M.

4 4

Near south limb.

1924 May 7

8 34 P. M.

7 47

Very nearly central.

Transits of Mercury are chiefly useful in physical observa-
tions of the planet, its distance from the Earth being generally
too great to allow its throwing any light on the problem of the
Sun's distance, although the May transits, when the planet
comes within 50,000,000 miles of the Earth, might advanta-
geously be photographed for this purpose. — D. P* T.

^ Recalling Professor Darwin's theory of tidal evolution
(vide Chapter XVI) it is important to observe that the near

The Planets

107

STUVVAEBTl

Venus moves in an orbit more nearly circular than
that of any other of the principal planets, and her dis-
tance from the Sun never varies much from 67^ mil-
lions of miles. She revolves round him in 335 daj-s.
The inclination of
her orbit to the
Earth's is greater
than that of any
other except Mer-
cury's, The great-
est elongation of
Venus from the Sun
amounts to about
45", so that she
may sometimes be seen for a very considerable part
of the night, before sunrise or after sunset. In very
ancient times she was called, when seen in the morn-
ing, Phosphorus, and when seen in the evening,
Hesperus.

The transit of Mercury in 1677 led Hallev to sug-
gest the observation of transits of Venus as the best
means of obtaining the distance of the Sun. Venus
had already been seen on the Sun by Horrox and

proximity of Mercury to the Sun, together with the small
surface-gravity of the plane), render it h priori eitiemely prob-
able that the periods oE axiil rotation and orbital revolution are
identical. Also, observations by M' Denning in [8S2, and in
1892 by Professor W. H. Pickering at Arequipa, Peru, appear
to confirm this view. Although Mercury seems to have no
atmosphere, or one of extreme rarity, the markings upon its
surface are exceedingly faint. Professor ScHtAPABELLi Gndi
(he axis of Mercury perpendicular to the path of its motion
round the Sun. One side of the planet, then, must be con-
stantly in full sunlight, the other remaining in total darkness;
but on account of the large tibration, the Sun is forever hidden
from only \ of the planet's surface. — D. P. T.

io8 Stars and Telescopes

CRABiitEE in 1639; but no other transit would take
place until 1761. The transit or that year, as well as
the following transit in 1 769, was extensively observed,
and so have been those of i874and 1882. The next
pair will occur in the years 2004 and 2012."

The diameter of Venus is 7,700 miles, not »iuite
equal to that of the Karth. Her mass, likewise smaller
than that of our planet, indicates that her density also
must be somewhat smaller. There is doubtless a
very considerable atmosphere surrounding Venus, and
loaded with clouds so dense as to render it very diffi-
cult to observe her surface distinctly, and to deier-

* As Venus revolves almost exactly 13 times round the Sun
while the Earlh is compleling eight revnlulioiis. the general law
of recurrence of transits of Venus is quile simple. In cen-
turies adjacent to ihe present, transits occur in pairs, eight
years elapsing between the two transits of each pair, and lh«
intervals between the midway points of the pairs Iwing alier-
naiely liji and 129! years. Usually, then, one pair will fall
in each calendar century, and a June pair in one century will
be followed by a December pair in the next, transits being pos-
sible only in the earlier days of these months, whtn the Earlh
is passing the planet's nodes. The rgth century pair having
taken place only recently, no transit of Venus will occur in the
20th century, and the pair belonging 10 the list will happen

ID^i^ ,S^-„. Ihr P

1.C.VAL L

OWBLL

at /

/ag.tatr, Ari«,Ma, W

Uafi^^

,i„^/pi-

™./.m

.Wrvwrr"' a'"* »''* *«

ikekcLf*!

Uieoft.

fii,firu T.

nil too.

tium.lkal

lu/^^«,-

<,:cM^d,

riUal ttriirdl arrllu a

ThrHo/M

LOW.LL

-r.t^

^l^ll^m.

laHid kiK It Jmm a ctmflitalij maf „/ lit fUnaCt ma

if,, a clu.

fiatnn rfwkUk

cluit CToti-llatlkiHr,

,xpUi<»dh

,ilk.^ c-

atki <"■ I

•TT„g«l

m oj n m>// ^ tiii' /i^iK

f«/,V- «"««//,»

tr.mdtf.nde.,ly

*-rf

miJfy Mat Ltoiii.KD

M' Dmw.

Fr-bM) Mtrc.ry-t

alm0,flurt.

niwKf p/

trtipra

€r^

i (LC

l-ELL)

(/n AKgnil-Oclniir iSgA, A/-- LnmLL. vmltd ir Mr Dhiw, tiirrvidiUH
at dUk ./ ^-Huu, andlktir m>rk u camfirmalory •/ Sch1*hii.h.i's, at
Itnimidmctcfaiiala^STbitalftriiidt. Tkrtt if M' XavnvCi drm-
ingt an kin tivtt, and Mil ckarl nf tkt plamf> atr/att niuiiuwll]/
tmtlntcltd VKa indtfmJntll]! cunfirmad tjt jV' DoucLIH in itrfi. tamr
rvirj' prKBHliait It fnrtnl lUcrflian, Tki ifoir-likt markintt nAuvi

ptrptndktdar to Hi or&il fbint. Notuiitkitandinf an rvidtnt atmwfktrt
,/ daalmg halrt. AT' LowiLLy(>U[r Ihi marking, imariaH, vuiNt :
Ikal ii, Ikr almai/iktrt is cimditu. PrvSnily Ikr Urmis^ri »/ Vttnu
al«ia,t lunud from tlu Smit it tiattdimglf ccld. and tkt nffnUitn
cfa ^ar lumitfktn vJoiUd ixptain tki ' ^ttkariKitKt .' Mo-callrd. rr-
fnUidl/ aiurfrd ea tkt prtftltiaU^ aaitinminrd nrimt nf Iki disk.
FrttidtiU tt imfpuralita ailk Ikt btdy of itlahtiiktd atlrimtmieal
fact, iktu laltntliag oittrBalioHt tf Ikt inftritr flaatll ftl await fall
coafirmalica tlifwktrr. Tkt Flagsla^ abitrvtrs iaiitt, aad rtattmably,
tkat an atmtifktrt of griat tran^aaiily, nut a Itltittft tf grtal fatatr,
il tkt frimt maiiiUfor vinalitiat dtlicalt flamttarj ftalant\

The Planets

109

mine with certainty the time of her axial rota-
tion. It was, indeed, thought that periodical changes
had been seen indicating a rotation in about
2jh 21™; but such conclusion is now regarded by
astronomers as very doubtful. As Professor New-
comb says, * The circumstance that the deduced times
of rotation in the cases both of Mercury and Venus
differ so little from that of the Earth is somewhat

ear]y in that century. The last pair of transits of Venus and
the next to occur are as follows : —

Date — Eastern Standard Time

Duration of
Transit

Limb of the
Sun

1874 December 8, 11'' P. M.
1882 December 6, noon.
2004 June 8, 4 A. M.
2012 June 5, 8 p. M.

3" 38-
6 20

North.
South.
South.
North.

Of any December pair of transits (ascending node), the
path of the earlier one always lies across the Sun*s northern
limb ; and of the later one, across the southern limb. For any
pair of June transits (descending node), the circumstances are
reversed, the earlier one always crossing the Sun's south limb,
and the later one the north limb. The shortest transit of Venus
ever observed was that of 1874. Several centuries hence, when
Venus passes centrally across the Sun, the maximum length of
transit, equal to 7^ 58"*, will be reached. As the inferior planets
are always retrograding, or moving westerly, at the time of
transit, it is important to notice that ingress always take place
on the Sun's east limb, just the opposite of the solar eclipse,
which always begins on the west side of the Sun.

Many observers in the 17th and i8th centuries thought they
had discovered a satellite of Venus ; but M. Stroobant has
satisfactorily disposed of nearly all these observations by other
hypotheses. As none of the great telescopes of the present
day reveal any such body, the existence of a satellite of Venus
is extremely improbable. — D. P. T,

■1

no Stars and Telescopes

suspicious, because if the appearance were due to any
optical illusion, or imperfection of the telescope, it
might repeat itself several days in succession, and
thus give rise to the belief that the time of rotation
was nearly one day.' Professor Schiaparelli's re-
cent observations would seem to show that Venus as
well as Mercury rotates in the same time in which she
revolves round the Sun; but M. Perrotin thinks
that the rotation of Venus, though very slow, is prob-
ably not quite so slow as this.*'

^ Among the famous astronomers who observed Venus in
the 17th and i8th centuries were Cassini at Paris. Bianchini
at Rome, Schroeter at Lilienthal, and Sir Wiliam Herschel
in England. The mountains supposed to have been seen by
Schroeter were not visible to Herschel, nor can they be
seen at the present day. Near the middle of the 19th century,
Maedler and De Vigo made careful studies of the planet, and
many astronomers have in recent years turned their attention
to Venus, but with slender avail. Among them M' Denning
made several fine sketches in the spring of 1S81 ; and MM.
NiESTEN and Stuvvaert, observing at Brussels 1881-1890,
saw a great deal of detail, as the illustration on page 107 shows,
embodying all their drawings into a chart of both hemispheres
of Venus. In the same year M. Trouvelot published a series
of observations made partly at Paris and partly at Cambridge,
U. S., and extending through fifteen years. A pair of narrow
white markings at the opposite edges of the disk were usually
visible when properly illuminated, and they are thought to be
snow caps at the planet's poles. Occasionally large gray spots
could be seen covering equatorial regions. The terminator,
sometimes seen as a wavy line, rather than straight or slightly
elliptical, has by its roughness in certain parts assisted in
affording an idea of elevations and depressions on Venus, and
in estimating the time of rotation. While this is to be regarded
as well determined, it is a little less than 24 hours, according
to M. Trouvelot. On page 108 is one of his sketches of the
planet, near the time of greatest elongation. The little double
drawing adjacent to it represents Venus as seen at times when
she is very nearly between the Earth and Sun ; her dense at-

The Planets 1 1 1

Mars is a much smaller planet than the Earth, his
mean diameter beii^ only 4,230 miles ; but the ellip-
ticity of his figure is greater, the difference between
his polar and equa-
torial diameters being
about a hundredth
part of the latter.
The mass of Mars
is about one ninth
that of the Earth,
and his density, less
than that of Venus,
is only about three
fifths that of our globe.
Mars revolves round hars, ist aucust is^i irLAUiiAmoii)
the Sun in 687 days,
at the mean distance of 141 J million miles.

The disk of this planet is well seen with our tele-
scopes at the favorable oppositions, and many maps
have been drawn of the surface, which exhibits in
many respects a striking analogy to that of the Earth,
It differs, however, in this, that on Mars the propor-
tion covered, or thought to be covered, by sea is con-
siderably smaller than that which is apparently diy

mosphere appearing like a very slender sickle or crescent of
silvery light, the Korns ii( which M' Harnard saw. 5th DecembcT,
1S90, nearly meeling together. A similar observation had been
made under more favorable circuiiis lances by Maedi-ea in 1849,
and in December 1S66, by Lvman, both of whom saw the delicate
atmospheric ring completely encircling the planet, and made
measures o( it which enabled them to calculate that the hoii-
lontal refraction in the atmosphere of Venus is 54'. As the
corresponding quantity foi the Earth is only 35'. the greater
density of the atmosphere surrounding Venus is readily
inferred. — D. P. T.

112 Stars and Telescopes

land. The duration of the axial rotation of Mi-rs is
>4'' 37" **"7. a constant now very accurately known.
The axis is inclined to the orbit at an angle of about
63°, somewhat less than in the case of the Earth ; so
that the inclination of his equator to the plane of
orbital motion is greater by 3 J" than it is on our
planet. Mais is surrounded by an atmosphere, prob-
ably of no great density.

In August 1877 Professor Hall discovered that
this planet is attended by two satellites, to which he
afterward gave the names Phobos and Deiinos,^ The

^ The illustralion on Ihe preceding page repiesenls Mats
as dtavFii by M, Flammariu.^ al Juvisy when the planet was
35,Soo,coo miles from the Earth, or very neat its mmimiim dis-
tance. The minute salelliles of Mais, so long in being discov-
ered, but su easy to see with large telescupes once thcit existence
became certain, have been glimpsed with instruments of very
moderate capacity, one of the smallest being the 7) inch Clark
glass of the Amherst College Ubservatory, with which, near the
opposition of iligz, I saw both satellites without great diDiculty.
Their apparent orbits are indicated in the above illustration.
At the favorable oppositions they are remarkably easy objects
in the Lick telescope; indeed, Professor Kkkler in liigo ob-
tained a few succe.<isful observations of eclipses of Phobos by
the shadow of the planet. With the exception of the minute

The Planets

'"3

inner of these (Phobos) is the brighter, and likely
somewhat the larger of the two ; but neither of them
probably exceeds ten miles in diameter. The period
of the inner satellite round Mars is 7'' 39" 1 5'. i ; that
of the outer, so*" 17" 54'-9- The distance of Phobos
from the centre of Mars is only about 6,000 miles, so
that its distance from the nearest point of the planet's
surface must be less than 4,000 miles. Deimos is
about two and a half tiroes as far from Mars as

Phobos, its distance from

the planet's centre being
approximately 15,000
miles.

Hundreds of small plan-
ets are now known to re-
volve round the Sun in
elliptic paths lying be-
tween Mars and Jupiter.
The smallest orbit is only
a very little less than that
of Mars, and the largest
is not much smaller than
iheorbit of Jupiter. While^thra (132) when at peri-
helion is actually nearer the Sun than Mars is at aphe-
lion, no small planet yet discovered ever recedes so
far from the sun as the perihelion distance of Jupiter.
(433) Eros(p. 40S) has the smallest mean distance

particles composing the dusky ring of Saturn, the inner satellite
of Mats is the only secondary body in the solar system known
to revolve round ils primary in less time than the planet takes
to turn round once on its axis, a seemingly strange relation
which is easily accounted for by the secular action of tidal
friction. So great interest attaches to Mars that 1 have thronn
the fuller additions on this planet into a separate chapter, fol-
lowing (he present one. — D. P. T.

(.SI3-I

114 Stars and Telescopes

(1.457 in terms of the Earth's mean distance) ; while
that of Thule (279) is the greatest, amounting to 4.247
on the same scale. The first four small planets were
discovered in the early years of the 19th century (the
first, Ceres, on the ist January 1801), and these are
probably the largest; but it is not likely that the
diameter of any one of them exceeds 300 miles.
After the discovery of the fourth (Vesta), in 1807,
no more were found until 1845, when Astraea was de-
tected.® Since then discovery has been nearly con-

* Peters (portrait on the preceding page), the most suc-
cessful American discoverer of small planets, calculated the
diameters of 40 of these bodies found by him, the mean of
vrhich is 43 miles. M^ Barnard in 1894 measured the largest
with the Lick telescope as follows : Ceres, 485 miles ; Pallas,
304 miles ; Vesta, 243 miles. Mr Roszel estimates the united
mass of the first 31 1 small planets at j^i^ that of the Earth.
In a general way the group of these bodies ranges through
} of the broad interval between Mars and Jupiter, or about 280
million miles. Their orbits, by no means concentric, also ex-
hibit wide divergence from a median plane. While the orbital
inclinations of six small planets exceed 25°, the mean inclina-
tion to the ecliptic for the entire group is only 8°, not much
more than that of Mercury. In general, orbits greatly inclined
are also very eccentric. The periodic times of the small plan-
ets vary between x.76 and 8.75 years. Regarding their cosmic
origin, the explosion hypothesis of Olbers was long ago aban-
doned, and it is now commonly considered that their discrete
existence is sufficiently explained by the proximity of the ex-
cessive mass of Jupiter, whose perturbative influence in this
region prevented the concentration of primordial planetary
material into a single body. Kirkwood in 1866 directed atten-
tion to the fact that in those portions of the small planet zone
where a simple relation of commensurability exists between
the appropriate period of revolution and the periodic time of
Jupiter, gaps are found, similar to those which separate the
rings of Saturn. Minute intercomparison of their orbital ele-
ments reveals numerous instances of a near identity of paths
about the Sun, or an apparent grouping, sometimes only in

The Planets 115

tinuous ; and of late years a large number have been
found by photography. The number at present known
is about 450.

pairs, but several times in families, one of which includes ii
members. Some of the outer members of the group suggest a
transition between small planets and periodic comets; the path
of Andromache (179). for example, being very like the orbit of
Tempel's comet. Minute and distant as these bodies are, the
careful observations of M' Parkhurst have established the
fact of a phase (peculiar to each minor planet), which cannot
be neglected in comparisons of brightness at different times.
Studies of the small planet group have been made by MoNCK,
TissERAND, NiESiKN, and others, among them KiRKWOOD,
whose researches are embodied in his monograph entitled The
Asteroids or Minor Planets (Philadelphia 1888). For complete
data respecting the orbits of these bodies, consult the most
recent issue 'of the Berliner Astronomisches Jahrbuch. The
simple facts of interest connected with their discovery are
given in a table at the end of this book.

The striking advantage of photography is shown in the ra-
pidity and thoroughness with which the sky is now searched
for new objects of this character; for example, M. Charlois
of Nice, the most successful of all discoverers, using a portrait
lens of 6 inches diameter, and 32 inches focus, obtains every
star to the 13th magnitude, on plates including more than 10°
square on a side; that is, an area covered by 400 full moons
arranged in a square, 20 on a side, with their disks just touch-
ing. Each plate is exposed 2\ hours, and its critical examina-
tion requires an equal amount of time; so that in five hours, a
given region of the sky can be more thoroughly searched than
in 90 hours by the old-fashioned method, at the eyepiece of a
telescope. New discoveries of small planets are now double-
lettered, provisionally, until observed at least five times ; then
a permanent number is assigned in the regular list. The first
small planet found in 1894 is lettered A Q^ and most of the
recent discoveries are still without names. There is a growing
recognition of the significance of the small planet group in the
cosmogony ; and it is hoped that an international agreement
may soon be reached, looking toward the more even distri-
bution of the vast labor of the calculations which the rapidly
increasing discoveries of these bodies now entail upon the pa-
tience of Ciermany almost unaided. — D. P. 'P.

Ii6 Stars and Telescopes

Exterior to the small planets are four bodies very
much larger than the four planets interior to this
group. Of these, the nearest to the Sun is the largest
planet of all, Jupiter, often called the * giant planet.'
His bulk is 1,309 times as great as that of our globe,
his mean diameter being 86,500 miles. But his mass
being only 316 times that of the Earth (or yg^^y that
of the Sun), his density is apparently less than a quar-
ter that of our planet. He revolves round the Sun at
a mean distance of 483 ^ millions of miles in a period
amounting to nearly twelve (11.86) years.**

^ Jupiter, always during its visibility a magnificent planet
among the stars, was first mentioned by Ptolemy, who re-
corded its near approach to the star 8 Cancri, 3d September,
B.C. 240. About ten times as bright as a Lyra and Capella,
many modern observers, knowing just where to look, have
found it visible in full daylight. Bright as Jui)itcr is, at times
almost sufficient to cast a shadow, it would require 6,500 such
stars to equal the lustre of the full Moon. I)*" Lohse, during
a conjunction of Mars and Jupiter in 1883, found from his pho-
tographs of these planets that the intensity of the actinic or
chemical rays reflected from Jupiter was 24 times stronger than
that of Mars, and that the two hemispheres of Jupiter were by
no means alike, the light from the southern hemisphere being
twice as effective as that from the northern. Not until 1630,
nearly a quarter-century after the invention of the telescope,
were its conspicuous belts discovered by ZiiccHi, at Rome.
The phase effect on Jupiter, though slight, is not difficult to
detect when the planet is near quadrature and can be seen at a
high altitude in twilight.

This giant planet, the most satisfactory of all celestial objects
for scrutiny with a small telescope, has already been depicted
on pages 30 and 95, as seen with instruments of moderate
capacity. As the edge or limb of the planet is approached,
not only the colors of the markings but their definiteness fades
out completely. Area for area, Jupiter receives but 2^7 the
heat from the Sun that the earth does, and its own intensely
heated condition must in large measure account for the exces-
sive cloud. Professor Nkwcomh's value of the mass of Jupiter

The Planets 1 17

The great ellipticity of Jupiter's figure attracts
attention the moment the planet is seen with a mod-
erately large telescope. This polar compression (or
fraction representing the difference between polar and
equatorial diameters divided by the latter) amounts
to ^Jg, according to the best measures (that of the
Earth is only 5^3)- The planet is surrounded by
a thick atmosphere, in which are dense masses of
cloud. The belts and spots on the apparent disk are
interesting objects of study ; and a large red spot,
first noticed in 1878, has attracted very special atten-
tion during the last few years, undergoing remarkable
changes in brightness, while retaining the same form
and size. Observations of the spots have given the
time of Jupiter's axial rotation with some approach to
accuracy. Being about g'' 56"", it is less than that of
any other planet whose rotation is known. The axis
being nearly perpendicular to the plane of the orbit,
the equator makes but a very small angle with the
latter."

adopted in his investigalions of planetary molion, Is tWttt
thai of the Sun. M- Barnard's recent measures with the Uck
telescope give foi the equatorial diameter of the planet 90,190,
■nd for the polar, 84.570 miles. These correspond 10 apparent
diameters 38".52 and 36".ii, respectively, for a distance of
Jupiter from ihe Earth equal 10 5.30 times that of ihe Earth
from the Sun. — £>./■. T.

*' Jupiler'ii ratalion on his axis, first determined byCASSINl
about 330 years ago, presents many points of resemblance to
that of (he Sun. The equatorial regions revolve most rapidly,
and blight spots on thai part of the planet have quite uniformly
given a rotation in about 9" 5oJ". Receding from the equator,
either north or south, Ihe atmospheric markings revolve in
longer periods, but the exact relation to Jovian latitude is not
yet established. Following are a few of the belter recent de-
terminations for regions other than equatorial : —

ll8 Stars and Telescopes

As soon as telescopes were directed to Jupiter, it
was seen that he had four attendant moons or satel-

1880. ScHMCDT , . ■ ■ 9 55 344

1885. Hough 9 55 37-4

1S86. Marth 9 55 4^-^

1887. Williams 9 SS 36.5

1898. Denning 9 55 37.7

The lasi depends upon jg years' observation of the great
red spot; and should this object eventually prove to be actually
permanent part of the body of (he planet. M' Denning's value
must be very near the truth. So rapid is this rolalion, and so
great the sije of Jupiter, that a point on its equator travel*
nearly eight miles a second.

These differing periods of rotation have suggested a theory,
now accepted by many astronomers, that entire zones of the
Jovian atmosphere, as well as indi-
vidual spots in it, may differ in ro-
tation period, the dense envelope
perhaps drifting in sections quite
independent of each other. The
great white etjuatorial belt is at
times nearly free from markings at
any kind, and it usuallv exceeds
all other features in brilliance, the
markings upon it being often ex-
niriTiR. mth Trtv iR^KEEii-ii) ceedingly faint, as shown in (he
AS SUN WITH TMH 16-ijnjH accompauying illustration. Small
LICK TELEscors spots of an intenser white, and

lEara^HiitsAmisca/i.ilusia al)out 1500 to 3500 miles across,
a/ a fin-titaJ) are Sometimes seen upon it, and

they are presumably at (he highest
level of all the cloud formations in Jupiter's atmosphere.
These bright spots going through a complete rotation in 5I
minutes less than that of the great red spot, must pass it at a
speed exceeding 250 miles per hour; and in six or seven weeks
they make a complete revolution round the planet, relatively
to that well-known marking. This vast whirling cloud mass,
banding the planet's equator, is about 20,000 miles in bread(h,
and has been termed the 'hurricane girdle.' Also, occasional
small white spots appear on the light strip south of the southern

The Planets 119

lites. Their discovery is generally attributed to
Galileo, who Doticed them first on 7th January 1610,

equalorial bell, which ia usually more active than the northern
one, its detailed configuration often changing rapidly. The
principal belts arc variable in color and intensity of tint, their
hue being sometimes brownish, coppery, ot purple. Usually
the darkest and most permanent regions ot these great belts
are their edges adjacent to the planet's equator. Lesser changes
in form and intensity are frequent, but long observation has es-
tablished the essential permanence of their general outlines.

The bells on Jupiter's tropics are not uniform in color in the
two hemispheres, the southern one having a strong reddish tint,
and the northern one shading into blue and gray. They seem
to be regions relatively little disturbed, and have no connection
with the rapidly whirling equatorial belt, eicept through the
oblique streamers, often seen trailing over them, as Professor
Kbeler's drawing shows. The extensive polar regions adja-
cent 10 both poles of the planet beyond these median belts are
sometimes seen banded nearly to the pole, and the prevailing
tint of the northern region is bluish.

It is not to be inferred that the very great dilferences of il-
lumination in the apparent disk of Jupiter indicate anything
more than fleeting cloud-configurations. Bui while this atmo-
spheric envelope may be said to resemble that encircling our
own globe, it is by no means identical with it ; in fact its metallic
*apors render it more nearly like a solar atmosphere than a
terrestrial one. The intense heat of the great globe, its activity
and its rapid rotation, all tend to complicate the atmospheric
movements and configurations, about which (here is much re-
maining unexplained, and which must continue so until the
variable markings have been more critically and persistently
studied. Members of the British Astronomical Association
have banded together for detailed research upon this planet's
surface, having made as many as JOO drawings in a single
year; and Mt Stanley Williams's painstaking investigation
of an excellent series of photographs of Jupiter is effecting
substantial advances.

Careful studies of Jupiter's spectrum by D" Huggins in
England, and D' Vogel in Germany, have revealed a dark
band in the red, which may indicate some substance in the
planet's atmosphere not present in our own. The fluctuations

I20 Stars and Telescopes

and gave in his Sidereus Nuncius an account of his
subsequent observations, proving them to be satel-

of long period in Jupiter's atmosphere are matched by detail
variations of intensity in the lines of its spectrum. Whether or
not Jupiter may be slightly self-luminous, is, according to D'
ScHEiNER, a question upon which the spectroscope furnishes
but little evidence.

The great red spot, excellently shown in Professor Keeler's
drawing on p. ii8, was probably first recorded in recent times
by Gledhill and Mayer in 1S69. Ten years later many
observers had noticed it, and there are indications that Cassini
at Paris observed it in 16S5. The gigantic size of Jupiter may
be imagined from the magnitude of this object, the superficial
area of the elliptical spot alone exceeding the surface area
of the whole Earth. About the middle of 1883 it nearly disap-
peared ; was so faint the year after as to be very difficult to
observe, and in 1885 a white cloud a])parcntly covered its cen-
tral portions, making it appear like a flattened ring. In this
year and the one following, the intensity of the spot was slightly
recovered; but onward from that time it grew gradually less
and less easy to see until 1891, when there was again a partial
return to its former visibility. So that fluctuations of this
familiar object are now well recognized. To Professor Wilson
in October 1891, and M*" W^illiams at the end of 1892, it ap-
peared quite pale in the middle regions, as if a bright elliptic
ring. Also it seemed to be very diffuse, as if covered in part
with a veil of dense mist. If this object is periodic, it must now
be near another minimum, as M"^ Barnard reports it as very
faint in the Lick telescope in 1894-95. Often this spot has been
observed to exercise a strikingly repellent effect upon cloud-
markings near it. The great red spot, and its variations of
form and visibility, have for years been studied, not only by
many foreign astronomers, but by Professor HouGii with the
18^ inch Chicago telescope, whose measures place this strange
marking at a considerable south latitude, and make its length
about 30,000 miles, and its width 8000 miles. Many astrono-
mers think that this persistent object is simply a vast fissure in
the outer atmospheric envelope of Jupiter, through which at
times are seen the dense red vapors of interior strata, if not the
actual surface of the planet ; but its slow drift in longitude, and
its slight shift in latitude are unwelcome obstacles to this

The Planets

121

Ikes. Simon Marius (or rather Mavr) claimed to
have discovered them a few weeks before Galileo ; but
this was contested, and at any rale he did not pub-
hsh his observations until later. Mavr's proposed
names for the satellites are not much used, lest per-
haps such acceptance should seem to imply recogni-
tion of his claim to the first discovery, Gauleo named
them jointly the Medicean stars, in honor of the
Grand Duke of Tuscany, and individually after mem-
bers of his family ; but these designations have been
dropped by general consent, as all were discovered at
the same time, and were called the First, Second,
Third, and Fourth Satellite respectively, reckoning
according to their distance from Jupiter outward, and
this nomenclature h.is been found quite sufficient.

THE SATELLITES OF JUI'lTER

Number

1 of Ji,pi«r \ b,lw«n Eclip«,

J, TOO ■ 0.™»1]1

j,S50 o<™o8B,

111
IV

Eu^p^

415."°

; 1 S9 3!8S|

A fifth satellite, probably not exceeding 100 miles
in diameter, was discovered by M' Barnard at the

theory. Proctor raainiained thai the real globe of Jupiicr lies
far within the globe we sec and measure, and that ihi: almos.
pheric envclo|>e 19 perhaps 10,000 miles in depth. Professor
Hough thinks that all the olraerved phenomena can be best
accountetl for by assuming thai Jupiter is slill in a gaseous
condition, — Z>. P T.

122 Stars and Telescopes

Uck Observatory, gth September 1892. Its distance
from the centre of Jupiter is only about 1 1 3,000 miles,

and it revolves around him in ii"" 57"" 22. '7,*'

Next beyond Jupiter, and next in size, is Saturn, the
equatorial diameter of which is about 73,000 miles,

•* The possession of one of the practical handbooks named
on page 396 will add greatlv to the interest of the young ob-
server; and the A'aiilical Almanac will be tcquisile in identify-
ing and following the ever changing configurations of the four
bright satellites, as they undergo tlieit frequent eclipses by
dropi.ing Into the planet's shadow, and pass allernately behind
the planet and in front of it, their little shadows dotting the
brilliant disk like a transit of Mercury or Venus in miniilure.
The opposite drawing represents such a phenomenon ; to an eye

so that its bulk is rather more than half that of the
giant planet, and would contain the Eanh's about

placed anywhere within the black spot, a total eclipse of the
Sun lakes place. It is no unusual thing for two such solar
eclipses to happen upon Jupiler at the
same tinie (though of course not at the
same place), caused by two dJfTerent
tnoons. During a Jovian year a specta-
tor on Jupiter who coiild transport him-
aelf anywhere at will on that planet
might observe S,3co eclipses of Sun and

From La Place's relation between jvnne. iSth Fbbbu-
the mean motions and longitudes of the aiv •S:4 (Khobel)
three inner satellites, it is impossible

that all of them can ever be eclipsed at the same lime, but
it sometimes happens thai while two of these satellites are
eclipsed the fourth is also undergoing eclipse; and the remain-
ing satellite, being of necessity on that side of the planet oppo-
site its shadow, may be projected upon the disk of Jupiter,
where it will usually be invisible. Also ihis interesting phe-
nomenon may happen from numerous other conditions of
configuration. Une o( the longcbl recorded instances when
this great planet was seemingly devoid of its wonted letinue of
satellites was that observed by Ihi: writer at Amherst College
Observatory, zist March 1S74, when no satellites could be
seen for nearly two hours.

Markings upon the satellites of Jupiter were repeatedly seen
by the earlier observers, Dawes, Lassell, and Skcchi, Ihefirst
of whom gives drawings of what he saw, in the Monthly Notice!
Royal Aslronemital Sociity.xi,. (1S60), p. 246; and in 1897 these
bodies were intently scrutinized with the fine 24-inch Clark
refractor in Ariiona, belonging to M' Lowell. From observa-
tions of their surfaces M' Douglass reports the disks of satel-
lites I and III striped with series of narrow bands, which he
has charted, and which have enabled him to ascertain the true
period of rotation of these satellites on their axes- He finds
the period of I to be iz" 24'°.o, and confirms Professor W. H.
Pickering's earlier observations (p. 125), assigning an equal-
ity between axial and revolution periods to both III and IV,
Also the little disks have been carefully observed with the

124 Stars and Telescopes

760 times. But its density is not much more than
half that of Jupiter, and the mass of the latter is equal

great Lick telescope, two drawings made wilh which are bcre
shown. M' Baknaro has made interesting studies of the first
iiellite which, having an

equatorial region relatively
bright, is somcliines seen very
much elongate, when pro-
jected on a dark bell of Jupi.
ter; while on a bright belt,
the saletlite's central region

jupitbk's t

A> drlwn indcue
{.Ir/D and Sl

ndcDlly by CAHfBBl-L

relatively dark polar regions

U.«'b., .8,.

of the satellite may give the
deceptive ap])earaiice of a

double body.

rrofessor W. H.

PccKKKCNG at Arcquipa. Peru,

in 1892, and

t the Lowell Ub=

crvaiorj in Arizona, 1894, has

{•krmint lit 6-iiK*jf«A.

to three or four times that of Saturn. Indeed, the
mass of Jupiter is more than double that of all the

seen surface detail upon all
the satellites except the sec-
ond. His observations in-
dicate that the equator of
the first satellite is appre-
ciably elliptical, not circular,

lion. Satellite t exhibits
many striking peculiarities
of form not easy
for. II is m
observe, and its axial period
is not known. The corre-
sponding periods of III
and IV are the same in
duration as their periods ot

e difficult

revolulii

Jupii

therefore resembling the

latior

Mor

) tin

Earth. A while

several times !^een near the

north pole ot IV,

M' Barnard's new fifth
satellite was discovered
with the telescope here
shown, the chief instrument
of the great observatory
founded by Jamks Lick in
1875 (p. 122). It has not yet
been seen with any telescope
oE less than i3| inches ap-
erture; and the eclipses of
this minute body, whose

would have SO great sig- (,
nificance in exact astrono-
my, appear to be beyond ibe optical reach of alt telescopes at
present in existence. M. Tisserand, applying the principles

124 Stars and Telescopes

760 times. But its density is not much more than
half that of Jupiter, and the mass of the latter is equal

great Lick telescope, two drawings made with which are here
shown. M' Uarnard has made iiiiereiiiing siudies □( ihe first
satellite which, having an
equatorial region relatively
btighl, is sometimes seen very
much elongate, when pro-
jected on a dark belt of Jupi.
ter; while on a bright belt,
the satellite's central regioi

witb \

deceptive appearance of a
double body. Trofessor W, H. PtCKFHCNfi at Arequipa, Peru,
in 1892, and at the Lowell Observatory in Arizona, 1S94, has

to three or four times that of Saturn. Indeed, the
mass of Jupiter is more than double that of all the

seen surface detail upon all
the satellites except the sec-
ond. His observations in-
dicate that the equator of
the first satellite is appre-
ciably elliptical, not circular,
and that it revolves on its
axi* in a retrograde direc-
tion. Satellite I exhibits
many striking peculiarities
of form not easy to account

for. n ii

difficult

observe, and its ajiial period

The

sponding pei

and IV are

duration as th

revolution round J p ter

therefore tesembl nglhe e

lation of our M. o to th

Earth. A white sp t

north pole of I V.

M' ItAR.SARD's new tiftl
satellite was d ^covered
with the lelesc | e he e
shown, the chief instrument
of the great obier ato
founded by James L k
l375(p.(l2). Ithasnotyet
been seen with any telescope
of Ums than i3| inches ap-
erture; and the eclipses of
this minute body, whose
successful observation ™'* <^* 7-j;;J^s« ""W. «"-
would have ao great sig- (Z.™ j//. « rf^-„(,r. 7-j.A- s7//.'™fJ
nilicance in exact a-strono-

my, appear to be beyond the optica] reach of all telescopes at
present in existence. M. Tisserand, applying the principles

126 Stars and Telescopes

other planets put together, while his volume is about
one and a half times as great as the aggregate of all
the rest. The compression of the figure of Saturn is
the greatest of all the planets, and amounts to as
much as one tenth. Saturn revolves round the Sun in
29 J years, at a mean distance from him equal to
886 millions of miles.

Belts are seen on Saturn similar to those on Jupiter,
but they are much fainter on account of the greater
distance from both Sun and Earth. Nevertheless, by
the aid of white spots in the equatorial belts in 1894,
M"" WrLLiAMs found the axial period of that region to
be 10*^ 12"™ 35^8. The axis of Saturn makes an angle
of about 62° with the plane of its orbit, so that the
planet's equator is inclined about 28° to that plane.'*

of celestial mechanics to the motion of this satellite, finds that
its short period, combined with the great equatorial protuber-
ance of Jupiter, produces a swift motion of the major axis of
the satellite's orbit, so ra])id, indeed, that the orbit makes a
complete revolution in about five months. — D. P. T.

^ Saturn, always shining as a dull reddish star of about the
first magnitude, is the farthest planet from the sun of those
which have been known from the remotest antiquity. Its
light as a whole is subject to some variation, owing to our
position relatively to the Saturnian rings : when the Earth is
near their plane, Saturn ap|>ears to be 2\ times less bright than
when our globe is at the greatest elevation of 26° above or
below the plane of the rings; therefore, its brightness will
slowly increase until 1899, and then as slowly diminish till
1907. The mass of Saturn is i^j^ that of the Sun, as deter-
mined by Professor A. Hall, jun', from observations with the
Yale heliometcr in 1885-7. So slight is the density of the planet
that it would float in water; probably, as surmised in the case
of Jupiter, the real Saturn is very much smaller than the ball
we measure, and surrounded by a gaseous envelope many hun-
dred miles in depth. The ball of Saturn has sometimes been
observed to assume an abnormal figure, very much flattened at

128 Stars and Telescopes

There are now known to be eight satellites revolv-
ing round Saturn. Owing to the confusion which
arose from the order of discovery being different from
that of distance from the planet, it became necessary
to give them names, and those proposed by Sir John
Herschel have been generally accepted. Of their
actual sizes, only very rough estimates are possible :
Titan, the largest, is probably about 3,500 miles in
diameter. Jape tus 2,000, and Rhea 1,500; while each

the poles, and very much bulged out at the four regions about
midway between poles and equator, giving it roughly the
shape of a square with rounded corners. This phenomenon,
first observed by Sir William Herschel in 1805, and several
times verified by other astronomers, is known as the * square-
shouldered aspect of Saturn ; ' but no satisfactory explanation
of so strange an anomaly has yet been advanced.

Careful studies of this planet were made by the Bonds at
Harvard College Observatory, 1848-51, and by Lassell with
his twenty-foot reflector at Malta in 1852-53; also by Dawes
in 1855-56, M. Trouvelot in 1872-75, M' Ranyard in 1883,
and M. Terby of Lou vain in 1887. In more recent years,
several astronomers at the Lick Observatory, among them
Professor Keeler and M*" Barnard, have employed the
36-inch telescope in observing this unique planet to the greatest
advantage, and the fine illustrations on page 127 embody sub-
stantially everything that can be certainly seen under the best
conditions. Excellent photographs of Saturn showing clearly
the belts on the planet and its system of rings have been taken
by Professor 1*ickering, the brothers Henry, and others.
The absorption at the edge of the ball, and the differing bright-
ness of the rings are well brought out; but, as in the case of
Mars and Jupiter, the photographs hitherto taken do not show
the minute details secured by close optical scrutiny of these
bodies directly with the telescope. No phase of Saturn's ball
is perceptible, even in the largest instruments. The spectrum
of the ball is difficult to delineate ; but according to Huggins,
Secchi, Vogel, and Janssen, the first of whom observed it
in 1864 3"d photographed it in 1889, '^^ lines are practically
identical with those of Jupiter. — D. P. T.

The Planets

129

THE SATELLITES OF SATURN

Distance

Name of

Date of

from

Sidereal Period

Satellite

Discoverer

Discovery

Centre of
Saturn

ot Revolution

Miles

d h m t

Mimas

W. Herschel

17 Sept. 1789

117,000

22 37 C.7

Enceladus

VV. Herschel

28 Aug. 1789

157,000 I 8 53 6.g|

Tethys

J. D. Cassini

21 Mar. 1684

186,000

I 21 18 25.6

Dione

J. D. Cassini

21 Mar. 1684

238,000

2 17 41 9.3

Rhea

J. D. Cassini

23 Dec. 1672

332,000

4 12 25 1 1.6

Titan

C. Huygens

25 Mar. 1655

771,000

15 22 41 23.2

Hyperion

VV. C. Hond

16 Sept. 184^^ 934,000

21 6 39 27.0

Japetus

J. D. Cassini

25 Oct. 167 1

2,225,000

79 7 54 171

of the four interior satellites, besides Hyperion, is
probably less than 1,000 miles in diameter.**

** The visibility of the Saturnian satellites corresponds to
the order of their discovery, a very small telescope sufficing to
show Titan, also Japetus in the western portion of its orbit,
where it is 4^ times as bright as on the other side of the planet.
Mimas and Hyperion, the satellites last discovered, are always
difficult objects, even in very large telescopes. The orbits of
the nve inner satellites are sensibly circular. At the great
Russian observatory shown on the following page, D' Her-
mann Struve, son of the late Director of the Observatory,
D' Orro Struve, has for many years been prosecuting a
thorough investigation of the Saturnian system, both mathe-
matically and by means of observations with the 30-inch
telescope (page 133). He has brought to light a sensible
acceleration in the motion of Mimas, the innermost satellite,
during the last few years. Also its orbit is inclined 1° 26' to
the equator of Saturn ; and as its nodes have a motion of
about 1° each day, the orbit returns to its previous position at
the end of every year. I)'' Struve's researches farther have
verified from observation the remarkable connection existing
between the orbits and motions of Mimas and Tethys, and of
Knceladus and Dione, previously developed from theory by
Professor Nkwcomb. Also the latter has investigated the
motion of Hyperion, the seventh satellite, the perisaturnium

s & r — 9

The Planets 131

Satum is unique among the planets in the posses-
sion of a ring, or rather system of concentric rings,
surrounding it within the orbits of all its satellites.
When Galileo first saw Saturn with a telescope, he
was astonished to see what he thought a small body
adhering to it on each side, which afterward disap-
peared, recalling to his mind the old myth about
Saturn devouring his own children. Huvgcns was
the first to explain the real nature of the appendage
and its varying ajipearance according to the posi-
tion of Saturn with reg.ird to Sun and Earth. This
he did in 1656, at the end of a pamphlet announc-
ing his discovery of the satellite Titan the year
before, which contains a Latin anagram, afterward

of whose orbit has an extraordinary reg re fiii on in a perioilof
about iS years. The peri sal urnium is that point in the path
of a salellite of Saturn which is nearest the planet; ami as
these points ordhiaiily partake of an advance motion, Ifyperion
has afforded a novelty in celestial mechanics, to which the
ordinary mathematic:i1 methuds were finind entirely inapplica-
ble. The cause of this anonialy was traced to the perturbative
action of Hyperion's massive inner neighbor. Titan, three
times the motion of which nearly equals four times that of
Hyperion. The miss of Titan is j%W that of .Saturn. The
orbit of Japctus, the outermost of all the satellites, is inclined
about ro° 10 the plane of Saturn's ring system. There is much
uncertainty about the size of all these bodies. PicKF.Rr No's pho-
tometric determinations in 1877-78 making them less than half
the diameters above given. Hyperion is the smallest satellite,
and is probably not over 500 miles in diameter, Mimas comes
next in size, its diameter being about \ greater than that of
Hyperion. Eclipses of some of the satellites, and transits,
particularly of Titan, Rhea, Tethys, and Uione, and of their
shadows across the ball of the planet, have occasionally been
observed, near the times (about 15 years apart) when the Earth
is passing the planes of their orbits; but these
require telescopes of exceptional power. — D. P.

132 Stars and Telescopes

interpreted to mean ' Annulo cingitur tenui piano
nusquam cohaerente, ad eclipticam inclinato.* (It
is surrounded by a thin, plane ring, nowhere adher-
ing to it, and inclined to the ecliptic.) The explana-
tion is given in his Systema Saturnium, published in
1659, in which he refers to the observations of
William Ball in England as confirming his own. In
1676 Cassini in France perceived that there was a
division in the ring. The inner ring of these two
is perceptibly brighter than the outer, and it ap-
pears that Campani at Rome, so early as 1664, had
noticed the greater brightness of the interior portion
of the ring, though he failed to recognize an actual
division between the two parts thus distinguished.
Other smaller divisions have been noticed since, par-
ticularly one in the outer ring by Encke in 1837.
But the most remarkable recent discovery in this
system of rings is that technically called the ' dusky
ring,* inside the two bright rings. This was first seen
in 1850 by the Bonds of Cambridge, U. S., though
there are several indications that a shading of the
inner bright ring toward the planet had been noticed
long before. Galle had in fact called especial atten-
tion to it under this description in 1838. Lassell
compared the dusky ring to ' something like a crape
veil covering a part of the sky within the inner ring * ;
and its transparency was afterward noticed.'*^ 'i'he

*» According to D' Otto Struve*s notation, adopted by
astronomers generally, the rings are called A^ B^ and 6', the last
being the dusky ring, and A the outermost one. The luminous
rings of Saturn differ greatly in brightness, the outer one being
much fainter; and having at times a very narrow, and proba-
bly non-permanent, division about midway in it. The inner
bright ring, area for area, is several times brighter than the
outer one; and the innermost, or dusky ring appears to be

mw.

't-

y\-

.-V ~ ^^Uo

<JB*K DOMINIOUE C*55rNI (1615-., 1)), „^,r ,ki,/ claim M duti-Klitn
rill, DH hit dUcmriii in Iki SalurninH syiUm. inri larlirr t-AM 4U a
ItudcHtalGiHri.iindafrnfiiiiir al Btirgna^wirr/ kis firti atlrtnami-
tat mirk iBa, a 4itcHili<M cf lit ctmrl ff 1651. C!>>$r ttun'Oiica v/m
JufiUr anJ Mar, tnniltd him In aarrlain lluir ftrinb ifralaliam n
1665. Ailrenirmiial rr/racli^H, Iki Jirta-Kf «/ Ikt S„n, litraliim t/tlu
MoiH, Ikr tivliaial ligkl, ami mnumrrmtnl e/ a mfrulian art vwn
amo^g Ikt ffrlUt nhjtttt of ki, invtitit;alion> Cas^^nTs ji'jv 4WfVd^
grandicH tatrt alie dirttlsr, /./ tkt Fori, Ohurvalory Ji-m, It ,Ui. o-^
Mil graitJ,aa /iimiiH wa, tMgaftd IK Iht purutit tf Kitnei, Iktmgkmmr
dirtOor. Cassini al,o COHilrtutid laili, c/ Ike mttiim 0/ Jufilir't
,aUUiUi. Allkt-gk a li/ihng tburrir. ki availid kimalj tf b-U ftm t/
Ikt iHlmminlaladvamc,, ul nn/,^ in ku da/)

134 Stars and Telescopes

S-iturnian ring system, which has in so many ways
been an enigma to astronomers, is now regarded as
consisting of an innumerable multitude of very small
satellites, so arranged as to present at a distance the
appearance of a thin flat ring, with several narrow
divisions in its breadth. Doubtless the peculiar

immediately joined to it, the interior bright ring generally
seeming to be darker on its inner edge, as if shading into the
dusky ring. Kirkwood has explained the existence of divi-
sions in the rings as due to perturbations in their substance
caused by satellite attraction exerted in narrow zones where
there would be a relation of simple commensurability with the
periods of certain satellites, chiefly Mimas ; these divisions
being analogous to the well-known gaps in the group of small
planets caused by the perturbative action of Jupiter.

The partial transparency of the dusky ring, so well shown
in the illustrations on page 127, where the outline of the ball
of Saturn is readily seen through this ' crape veil,* was excel-
lently demonstrated by observations made by M"" Harnard
with the 12-inch telescope of the Lick Observatory, 2d Novem-
ber 1889, during an eclipse of Japetus in the shadow of the
Saturnian system. As the satellite passed through the shadow
of the dusky ring, its light grew fainter and fainter on ap-
proaching the shadow of the bright ring, showing that the
particles of this semi-transparent veil are more thickly strewn
as the bright ring is approached. That the latter is fully as
opaque to the Sun's rays as the globe of Saturn itself was
convincingly shown by the complete disappearance of Japetus
immediately on entering the shadow of the bright ring. Also
the blackness of its shadow on the ball emphasizes the opacity
of the substance composing this ring. In the same year Pro
fessor Keeler examined the spectrum of the Saturnian rings
with the 36-inch telescope of the Lick Observatory, but found
no trace whatever of any such bands as are strongly marked in
the spectra of Jupiter and the ball of Saturn; so that there
can be no atmosphere about the ring. Also in 1895, by a neat
adaptation of Doppler's principle to an interpretation of the
distorted spectra of the planet and its ring-system, he demon-
strated anew the meteoric constitution of the rings ; for he
proved that their inner edges revolve more swiftly round the
planet than their outer edges do. — D. F. T.

The Planets 135

appearance of the dusky ring is due to the liny satel-
lites of which it is composed being much more scat-
tered than those forming the bright rings. The outer
diameter of the exterior ring amounts to 173,000
miles, and the breadth of this ring is somewhat more
than 1 0,000 miles. The outer diameter of the interior
bright ring is 145,000 miles, and its breadth is 16,500 '
miles. The distance of Mimas, the innermost satel-
lite, from the exterior ring is 31,000 miles, and an
interval of nearly 10,000 miles divides the dusky
ring from the ball of the planet. The rings and
satellites all revolve around Saturn in planes making
only small angles with the planet's equator."

* Salutn's ting is sometimes lolally invisible, except in very
large telescopes ; and then, even wilh these, it can be seen only
asdepicted in Ihc lower figure on page 127, This most interest-
ing ptienomenun takes place when ihe Earth reaches the plane
of the ting (for this object is so lliin that il docs not hll an
appreciable angle when seen edge on); when the plane of
the ring is direcleit toward the .Sun (for then its edge only is
illuminated, and the reflected light is vcty feeble) ; and when
Sun and Eatthateon opposite sides of the ring (for ilsunillumi-
nated side is then toward u«). As the plane of the ring always
remains parallel 10 itself, the epochs of disappearance are
nearly 15 years apart, this inletval being about one half the
periodic time of Satutn. The two disappearances of the tings
In 1861-62, many weeks in duration, wete excellently observed.
The subsequent recurrences, in 1S73 and 1891-92, were short,
and could not be well seen because Saturn was too near con-
junction with the Sun. But about the middle of 1907 will
occur the next disappcaiance, with a repetition in a general
way of the phenotnena of i36l-6;, and with Saturn very favor-
ably placed for observation.

Our present knowledge of the constitution of the Saturnian
rings has been attained through the researches of La Place,
who showed that the rings could not be solid, because even the
attractions oE the external satellites would be sufRcient to rup-
ture them; of Ihc late Professor Benjamin PEiRCEof Harvard
College, whose investigation ofihe dynamics of the rings led him

136

Stars and Telescopes

Beyond the orbit of Satum are two large planets,
Uranus and Neptune, the existence of which was not

Clerk Maxwell

1857 showed the incon-
clusiveneas of both pre-

potheses, and eslab-
iished on a firm basis
the present theory of a
vast shoal of clustering
meteors, all revolving
lound Saturn in orbits
oflheirown, as if actual
satellites. Panicles on
the inner edge of (he
dusky ring, (hen, must
revolve round the planet
BENJAMIN PKiRCE (iSoQ-iSSo) in 5*50"; whilc the pe-

riodic time of those
making up the outer edge of the outer ring is 12' 5". Probably
the rings are slightly eccentric about the ball. According to
H. Strove, the entire mass of the ring system cannot exceed j}j
that of the planet; Hessel had, in iSjc, estimated it as ^{j,
and M. Tissf.rand in 1877, as jjj.

The meteoric constitution of the rings is farther demonstrated
from what is technically termed ' Roche's limit,' equal (for
each planet) to 2.44 its radius; and Professor Darwin ha»
pointed out that no large satellite can circulate round a ]]lanet
inside this limit, because the known action of tide producing
forces would tear it into small fragments. As the Saturnian ring
system lies wholly inside this critical limit, even the periphery
of the outer ring lying about 3.500 miles within it, the conclu-
sion is justifiable that the rings are composed of particles too
small to be disrupted by planetary tides — of 'dust, rocks, and
fragments.' Secular changes in the ring syslem are doubtless
taking place 1 and the observations of (he middle of the 20th
century may, on comparison with those of the past, suffice to
disclose such slowly progressive variations : perhaps a ninth
satellite is in process of formation, — D. P. T.

The Planets 137

known to the ancients. Uranus was discovered by
Sir WnxiAM Herschel while observing at Bath, 1 3th
March 1781, and at first supposed by him to be a
slowly moving comet. Its planetary character was
established as soon as the nature of its orbit became
approximately known; and the principal credit of
pointing this out is due to Lexell, whose name is
more generally known by connection with the comet
of 1 7 70, the remarkable story of which is told in a
later chapter. Herschel proposed to name the new
planet Georgium Sidus, or the Georgian Star, in honor
of his royal patron, George the Third, while others
preferred to call it after the discoverer ; but when the
name Uranus was suggested, it soon obtained general
acceptance. This planet takes 84 of our years to
revolve round the Sun, from which it is distant about
1,782 millions of miles. It was seen several times
before Herschel's discovery, but always supposed to
be a fixed star ; the first of these observ^ations was by
Flamsteed in 1690. Its mean diameter is 32,000
miles.

Some recent observations made by Professor
ScHiAPARELLi at Milan and by Professor Young at
Princeton tend to confirm results obtained by Madler
at Dorpat in 1842-43, that the polar compression of
Uranus is about one twelfth, or greater than that of
any other planet except Saturn. Markings have been
noticed on its surface which indicate that Uranus has,
like Jupiter and Saturn, a rapid rotation, performed in
a period of about ten hours. This rotation, however,
takes place in a direction nearly perpendicular to the
plane of the planet's orbit. The density of Uranus is
a little less than that of Jupiter, and nearly one fourth
that of the Earth ; while its mass is rather less than
the twentieth part of that of the ' giant planet.'

■38

Stars and Telescopes

Early in 1787, Sir William Herschel discovered
two satellites revolving round Uranus; he afterward
thought he had discovered four more, but the exist-
ence of these has never been confirmed. Small
fixed stars near the planet were probably mistaken

THE SATELLITES OF IJRANUS

•Stmtif

_ DiK of 1 Cen'"'""ur°nu,

Sidtreil Pcr>«l of
Kivoiulioii

. [>i.M>l» JnA>c

Ariel

1 ! "

MSepl, 1S4? 1 110.000 ' 1J.S

h n. .

11 =9 i' I

Umbrid

8 Oct. 1847 ; T67.000 19.2

3 ^7 37-5

Titania

n Jail. 17S7 ■ 273,000 31.5

16 56 29.5

Obcion

I [Jan, 17S7 1 365.°°° :4=.i

.. 7 6.4

for sntellites. Hut two other satellites, additional to
Hekschel's first tivo, were discovered by Lassell
toward the end of 1851 ; and on
removing his telescope temporarily
to -Malta the following year in order
to ])rofit by its transjjarent sky, he
succeeded in determining their
periods with considerable accuracy.
URANUS m iSSj These two, which are interior to
(T-A, fl-vi*,,, hhnkvI Herschf.l's two, were named Ariel
«w»/,..wv/ff«r 'o-and Umbriel ; while the others
H. ftit »ffi>i<it jggg[^,gj (jjg designations Titania

and Oberon, It is not possible to measure accurately
the sizes of these distant and comparatively small ob-
jects, but Ariel and Umbriel are estimated to be about
500 tniies, and Titania and Oberon about 1,000 miles

The Planets 139

in diameter. Their motions are nearly perpendicular
to the plane of the planet's orbit, and are performed
in the reverse direction to that of all known planets,
and of the satellites of all the planets interior to
Uranus."

*< Uranus on dear, Tnoonless nights is bright enough to be
seen without a telescope; but one must know from the EfHc
mtrii just wheie to look, as 11 is not far from the limit of visi-
bility with the naked eye. Its stellar magnitude is Jj, and
does not vary greatly from opposition to conj unction. This
exceeding (aininess, relatively to Saturn, is partly due to the
remoteness oE Uranus, which is (he only planet whose distance
is more than double that of its next interior neighbor. The
inclination of the orbit of Uranus to that of the Earth is the
least uf all the planets, being only ]|°. ProlessoT Young, who
observed this distant member of the solar system in 1SS3, with
the ij.inch Princeton telescope, saw faint belts upon its disk,
and found iis ellipticity to be jf,. Professor Schtaparelli
the year before had found the degree of oblatencs.s expressed
by -f^; and both series of observations indicate that the
planet's equator coincides with the orbits of the satellites.
M. PEtROTiN, formerly of the Observatory at Nice, and his
assistant, the late M. Thoi.lon, discovered on Uranus in :gS4
a white spot, whose reapjiearances indicated a rotation of the
planet in about ten hours, a result needing confirmation.
Five years later, with the 30-incli refractor at Nice, the belts
seemed only a few degrees inclined to the plane of the satel-
lite orbits, and (he oblateness was not less than ^.

The paths of the satellites uf Uranus are sensibly perfect
circles ; and in particular the orbits of Oberon and Tilania
Professor Newcomb { iVashinglBH Ohitrvations iax 1873) found
to be more nearly circular than in the case of any of the large
planets of our system. Also these orbits have no discernible
mutual inclination. The motions of the satellites lead to a
mass of Uranus etjual to uigg that of the Sun. Professor
Pickering's determinations of the diameters of the outer satel-
lites from pholomelric measures in 1S78 gave, for Titania
59a miles, and for Oberon 54c miles. Indications ace that the
inner satellites, Ariel and Umbriel, have a diameter about half
as great; and probably the combined mauofthe satellites does

140 Stars and Telescopes

We now come to Neptune, the most distant known
planet of all. When Bouvard was forming his Tables
of planetary movements, about 40 years after the dis-
covery of Uranus, he found it impossible to reconcile
the observations of that planet since its discovery with
the earlier observations made at various times when it
was supposed to be a fixed star. Therefore, in forming
his Tables, he rejected the latter altogether, and made
use of the former only ; but stated in doing so that he
left it to future time to determine whether the diffi-
culty arose from inaccuracy in the older observations,
or whether it depended on some extraneous and un-
perceived influence which might have acted on the

not exceed Yshws ^^^t of the planet. At present the apparent
orbits of the satellites of Uranus are ellipses of small eccentri-
city, and large telescopes will now show these bodies at every
point of their paths about the planet. In 1903 the Earth will
be near the pole of these orbits, so that they will appear
almost perfectly circular. The outer, or Herschelian satellites-
have been seen under perfect atmospheric conditions with a
6-inch telescope ; but the inner ones, Ariel and Umbriel, require
for their certain observation the largest of telescopes and the
keenest of eyes. Variability in the light of Ariel is suspected.
The si>ectrum of Uranus has been critically surveyed by
D^ HuGGiNS with the assistance of photography, and by
D' VoGEL, Professor Keeler, and M' Taylor. Professor
Keeler's optical observations of the spectrum of Uranus with
the 36-inch Lick telescope give ten broad diffused bands, from
C to F, indicating strong absorption by a dense atmosphere
differing greatly from ours ; and the presence of these bands
accounts for the invariable sea-green tint of the planet. The
substance producing the absorption is not yet identified, and
the darkest band, about midway between C and D, is also
shown in exactly the same position in the spectra of Jupiter
and Saturn. So great is the light-gathering power of the Lick
glass that even the outer satellites of Uranus, faint as they are,
gave spectra which Professor Keeler could just recognize as
continuous. — D. P, T.

142 S/d/s aiij Tikscopes

Iil.uiei. Tlie qufstiiiii as to the nature of the cause
was soon settled by the rapidly increasing deviation of
Uranus from the course marked out for it by the Tables
based upon observations between 1781 and 1831;
HOT could it reasonably be doubted that the cause
was the perturbing attraction of a planet still farther
from the Sun, and never (so far as was known)
hitherto observed.

LE VERKIKR ([8n-i877)

But the problem of calculating the place of an
tmknoWD planet by simple knowledge of its infltience
npon another, staggered the few mathematical astron-
omers who were capable of attacking it, most of
whom were already deeply engaged in labors too

The Planets

143

essential and exacting to bear an intemiption of the
length which its solution would seemingly demand.
In 1843-45, however, it was taken up by two young
mathematicians, one in England the other in France,
whose names are now famous wherever astronomy
is studied. The fonner, John Coui;h Adams, for a
long time Professor of Astronomy al Cambridge, and

HSrg-iSgj)

Director of the Obser^-atory there, died aist Jamiary
i8gj; the other, Urbain Jeam Joseph Le Vkrrier,
was for many years Director of the National Observa-
tory at Paris, where he died i3rcl September 1877.
We cannot enter here into the history of their recon-
dite investigations ; the approximate place of the
unknown planet was carefully determined by botb

144 Stars and Telescopes

independently, and Challis at Cambridge began
searching for it by its motion, 29th July 1846.
During several weeks he mapped down all the stars
visible in a considerable tract of the heavens around
the place indicated by Adams, with the intention of
comparing afterward the places of all these stars and
ascertaining which of them had moved ; and he thus
obtained several positions of the planet. But before he
had completed his charts in this way, news arrived that
Galle at Berlin had discovered the planet, 23rd Sep-
tember 1846, on looking for it in the place pointed
out by Le Verrier, who had suggested that the planet
might be distinguished by its disk among the fixed
stars in the neighborhood of the calculated place. Its
appearance at once showed that it was the object of
search ; also it was wanting in a map (then recently
made by Bremiker) of the stars in that part of the
heavens, and which had just been received at the
Berlin Observatory. The next evening, 24th Septem-
ber, the alteration in its place put its planetary char-
acter beyond a doubt. Subsequently the name * Nep-
tune * (one of the names suggested for Uranus when a
designation for that planet was under discussion) was
by common consent adopted.

Neptune occupies 164! ^^ ^"^ years in revolving
round the Sun, at a distance of 2,792 millions of
miles, about 30 times that of the Earth. The eccen-
tricity of its orbit is the smallest of those of all the
principal planets, with the single exception of Venus.
The diameter of Neptune is about 34,800 miles, so that
its volume or bulk is 85 times that of the Earth, but
only about -^ that of Jupiter. Its density is nearly the
same as that of Uranus, and its mass is to that of the
Sun in about the proportion of i to 19,380. Being

The Planets 145

at so great a distance, it has not yet been found possi-
ble to perceive any spots or markings on the surface ;
so that its time of axial rotation is unknown to us.
Like the other large planets, it probably rotates much
more rapidly than the Earth.

Only one satellite of Neptune is known. This was
discovered by Lassell, loth October 1846, very soon
after the discovery of the planet itself. Being visible
at so great a distance, it is probably the largest satel-
lite in the solar system. Like the satellites of Uranus,
it moves in a reverse direction to that of the planetary
motions, and its orbit is very much inclined to those
of the planets (about 55° to that of Neptune itself).
Its distance from the centre of Neptune is 225,000
miles, and its time of revolution is ^^ ji'' i™ ^S'.p,
If this planet has other satellites, as is possible, they
must be much smaller, since none have hitherto been
detected with the powerful telescopes which have
been brought into use in recent years."

■■ So remote is Neptune thai ils disk, although more than
4} times the actuai diameter of the Earth, shrinks lo an angle
no greater than that which a nickel s-cenl piece would fill, if
held up a mile dialant. According to Professor Pickebing,
its stellar magnitude is 7.6J. so that it can never be visible
to the unaided eye.

Portraits of both the theoretical discoverers of Neptune
have been given on pages 14= and 14J. For the fullest ac-
count of their great discovery it is necessary to conaull the
original papers; bul D' GouLD has given a complete resumrf
in his Reperten the History of Ike Diic<n:ery of NtfliiHi (Wash-
ington 1850), As in the case of Uranus, so with Neplune, il
was soon found that the new planet had been accidentally
observed as a star (by Lalande in 1795), so that observations
of Neptune now extend through more than a century, or an
arc of about 22;° round the Sun as a centre. Among Ameri-
can astronomers who performed a zealous and important part
in the researches on Neptune's orbit, immediately after its dis-

1/^6

Stars and Telescopes

vritx^, most be mentioned Peirce and Walker ; and in iS66

were published Professor Newcomb's Tables ofNtptutv, which
provided a good reptesentalion of the planet's motion for about
15 years. In 1877, Le Verrier's Tablis appeared, founded
upon many years more obseivalions than the preceding; but
already, in leas tlian 25 years, the planet is beginning to deviate
widely from their prediction, and ttie theory of Neptune's mo-
tion 13 at the present time undergoing a second revision by
Professor Newcomd. Neptune's path round the Sun, like that
of jupitet, is but slightly removed from the invariable plane of
the solar system.

F. F. TISSERAND (1845-I896)

orbit plane to par-
take of a regressive motion round the pole of the planet in a
period exceeding 500 years. At the present time the path which
the satellite seems to describe about its primary is so o])cn that
this minute object is at no lime overpowered by the planet's
rays ; any good telescope above I2 inches of aperture will show
it. The diameter of Neptune's satellite, as determined by Pro-
fessor Pickeri.m; from photometric measures in 1878, is S26o
miles. Critical search for an additional satellite, both optically

and by means of photography, has shown that Ihcre is no such
body, unless its dimensions are very minute. Neptune's spec-
trum closely resembles that of Uranus, and probably the planet
is surrounded by a dense atmosphere. — D. F. T.

e popular literature of the planets can only be
indicated here by tabulated reference to the pages of Poole's
ftidixet to periodical lite

"ir

I'^'^^/ltl^'.r,

■'■'--'•' '■•^"l 1

^H"^'

^™Z.

1^7

■*«

A«c raids

ii.

'■"'si:
■■t:

is6

'■■s

p. ICH

A thorough study of Che planets will be greatly facilitated by
reference to the following important papers, for the most part
original sources. These lists need, however, to be supplemented
by reference to current numbers of TSi- Aslraphysi<al Jeurnal,
1895-1898; —

Le Verkier and Lescarbault, Cemplci Rtndus, iliji. and L
(1859-60). Also LeVehrier, Ibid., 1S76-78.

WoLK, Hatuibuch der Matktmatit, ii. (Ziirich 1872), 326.

Watson, Am.Jaur. Science and Am, cxvi. (1878), 130, 310.

Swirr, American Jeurail of Seitnce and Arti. cxvi. (1878), 313.

Peters, Astronomischi Naihrichlen, xciv. (1879), 321, 337.

Ledger, Ltctare on Inlramercurian Planets (Cambridge 1879).

TissHRAND, Anauairi du Bureau des Longitude! for 1882, p. 7*9.

Newcomb, Ailron, Papers of Am. Ephemerii.K. (1882), 474.

Hoi;ZBAU and Lancaster, Biiliograpkie Ginirale dt CAstrtK'
ontie. ii. (Bruxelles 18S2), 1090, contains nearly 150 titles.

Bauschinger, Brui/gung del Plamten Merkur (Munich 1SS4).

Chaubers, ' Vulcan,' Astronomy, i. (Oxford 1889), p. 75.

CORBIGAN, Popular Aitron. iv. (1897), 4:4; v. (1897).

148 Stars and Telescopes

Mercury

SCHROETER, Hermographische Fragmente (Gottingen 181 5-16).

Le Verrier, * Tables of its Motion/ Annates de V Observatoire di
Paris^ Mimoires v. (1859).

VoGEL, Bothkamp Beobachtungen^ ii. (1873), '33-

Harkness and others, * Transit 1878/ Wash. Obs. 1876, App. ii.

HoLDEN, Index of. . . Transits of Mercury (Cambridge 1878).

Todd, * Satellite,' Proc. A. A. A. S. xxviii. (1879), 74.

NiESTEN, ' Transits 1600-2000,* Annuaire de VObs. Roy. Brux-
elles, 188 1, p. 192.

Schiaparelli, Attideir Accad. dei Lined, v. ( 1889), ii. ; Pop. Set.
Monthly y xxxvii. (1890), 64 ; Astron. A'achr. cxxiii. (1890), 241.

Clerke, ' Rotation,' yi?//^. Brit. Astron. Assoc, i. (1890), 20.

Harzer, 'Motion perihelion,' Astron. A^achr.cxxxVx. (1891), 81.

Ambronn, 'Diameter,' Astron. Nachr. cxxvii. (1891), 157.

Trouvelot, Les Plauites Venus ct Mercnre {Vtux'xs 1892).

MtJLLER, 'Magnitudes,' Puhl. Obs. Potsdam, viii. (1893).

Newcomb, Elements of the Four Inner Planets and the Funda-
mental Constants of Astronomy (Washington 1895); 'Small
Planets between Mercury and Venus,' p. 116.

Lowelu The Atla7itic Monthly, Ixxix. (1897), 493-

Lowell, Popular Astronomy, iv. (1897), 360.

Lowell, ' New Observations,' Mem. Am. Acad. xii. ( 1898), 433.

Villiger, Ann. k. Sternwarte, iii. 301 (Munich 1898).

Venus

Schroeter, Aphroditographische Fragmente (Helmstedt 1796).
Le Verrier, * Tables of its Motion,' Annates de V Observatoire de

Paris, Mimoires, vi. (1861).
Lyman, C. S., Am. Jour. Sci. xliii. (1867), 129; ix. (1875). 47.
Kaiser, * Diameters of Planets,* Leyden Observations, iii. (1872).
SafaRIK, Report British Assoc. Adv. Sci., 1873, p. 404.
YoGEh, Bothkamp Beobachtungen, ii. (1873), 118.
Proctor, The Unrverse and the Coming Transits (London 1874).
Forbes, Transits of Venus (London 1874).
Schorr, Der Vcnusmond {VtWirss^'xcV. 1875).
Hartwig, Pubt. Astron. Gesetlschaft, xv. (Leipzig 1879).
Perrotin, Comptes Rendus, cxi. (1890), 587.
Terby, Bulletins Acad. Royate de Betgique, xx. (Brussels 1890).
Schiaparelli, Rend, del R. 1st. Lombardo, xxiii. (1890), ii.
Clerke, A. "^l.^four. Brit. Astron. Assocn. i. (1890), 20.

The Planets 149

Newcomb, 'Transits/ Ast. Papers Am, Eph, ii. (1890), 259.
AUWERS, 'Diameter/ Astron. Nachr, cxxviii. (1891), 361.
LoscHARDT, Sitz. k. Akad. IVi'ss.f c. (Vienna 1891), 537.
NiESTEN, Rotation de la Platihte Vinus (Brussels 1891).
Trouvelot, Nature^ xlvi. (1892), 468.
Clerke, E. Mm The Plafut Venus (London 1893).
Flammarion, Comptes Rendus, cxix. (1894), 670.
Brenner, Astronomische Nachrichten^ cxxxviii. (1895), '97'
SCHIAPARELLI, Astrononiische Nachrichten^ cxxxviii. ( 1895), 249-
Vogel, ' Planetary Spectra,' Astrophys.Jour. i. (1895), 196, 273
Lowell, Popular Astronomy ^ iv. (1896), 281.
Antoniadi, * Rotation,'y<7«r. Brit. Astr. Assoc, viii. (1897), 43.
Lowell, The Atlantic Monthly ^ Ixxix. (1897), 327.
Flammarion, Knowledge, xx. (1897), 234, 258.
Chandler, * Rotation,' Popular Astronomy, iv. (1897), 393.
Stoney, * Atmospheres,' A strophysical Journal , vii. (1898), 25.
Douglass, * Markings/ M. N. Roy. Astroti. Soc. Iviii. (1898), 382.

Mars
For the literature of this planet see page 178.

THE small planets

Gould, The American Journal o/Scienct', vi. (1848), 28.
d'Arrest, Ueder das System der kleinen Plancten (Leipzig 1851 ).
Newcomb, Mem. Am, Acad. Arts and Sciences, viii. (1861), 123.
Stone, E. J., M. A^. Royal Astron. Society, xxvii. (1867), 302.
Callandreau, Re7!ue Scientifique, xviii. (1880), 829.
"SlESTEii, A nnuaire de V Observatoire Royal de Bruxellesioi 1881.
SvedstrUP, Astronomische Nachrichten^ ex v. (1886), 49.
PaRKHURST, Annals Harvard College Observatory, xviii. (1888).
LlAlS and Cruls, Annates de VObs. de Riode Janeiro, iv. (1889).
Schmidt, R., Publ. Astron. Society Pacific, ii. (1890), 238.
TiSSERAND, Popular Science Monthly, xxxix. (1891), 195.
KiRKWOOD, Proc. Am, Phil. Society, xxx. (1892), 269.
BackLUND, Mim. Acad. Sci. St Piter sbourg, xxxviii. (1892).
ToDD, Astronomy and Astrophysics, xii. (1893), 313.
Callandreau, Comptes Rendus, cxviii. (1894), 751.
RoszEL,y. H, Univ. Circ. xiii. (1894), 67 : xiv. (1895), 23.
Charlois, Bulletin Astron. xi. (1894) ; xiii. (1896).
Zenger. Bulletin Sociiti Astronomique de France (1895), 243.
Mascart, ' Small Planets,' Bulletin Astron. xv. (18^), 235.
Crommelin, * Planet D Q,' Knowledge, xxi. (1898), 250.

ISO

Stars and Telescopes

JUPCTBR

:, Mrckanism aflhi //foveni {\janioa i83i|.
I, Tables £<lipti^uti Satetliiti {?».t\s 1836).
HcUigktitn-trhditaiist dcr Jufiittrslraianltn

Bothkiimp Beobachtangtn, i. (1872); ii. (1873). Also
Publ. Astraphys. Obierv. PaUdam,\. (1879); jii. (iSS;).

SOMI

De Uam(
Engelm/

(Lei

) Cwjvmwioei

(irSo-iS?:)

Glasenapp. Cpame»it HoAAtodaaa ',

lOnumepa (C.-Urmep6ijpn 18Ti).
DoiVNlNC, Abstract of foregoing, Oiirrvalory, lii. {1889), 173.
Rossn, A//'iiti/yAWKaffpya/AstrD»i>mi(a/Soi-iu-fy,xxx\v.(i&74).
HkKDlCHCN, Aii'i. de rObservaldre de Metceu. ii.-vl. (1875-80).
TuDn, CotiliiiHiition ef Dk Damoiseau's Tablet £chpliques to

1900 (Washington 1876).
Le \'ERRrER, 'Tables of its Motion.' Annates dt P Observateire

de Paris, Mlmoires. xii. (r876).

The Planets 151

Denning, Science for All, part xxx. (London 1880), 169.
SouiLLART, Memoirs A'oyal Astronomical Societyy xlv. (1880), I.
Trouvelot, Proc. Am. Acad. Arts and Sciences, viii. ( 1881 ), 299.
Kempf, * Mass,' Puhl. Astrophys. Observ. Potsdam, iii. (1882).
Denning, * Summary of Markmgs and Rotation-periods,'

Nature, xxxii. (1885), 31; Observatory, ix. (1886), 188; xi.

(1888), 88, 406; xiv. (1891), 329.
Williams, The Observatory, ix. (1886), 231.
Lamey, Comptes Kendus,c\\. (1887), 279, 613.
SouiLLART, Mem. Academic des Sciences, xxx. (Paris 1887).
Backlund, 'Satellites,' Bulletin Astronomique, iv. (1887), 321.
Barnard, Publ. Astron. Society Pacific, i. (1889), 89.
Landerer, Estudios j^eometricos sobre el sistema de los satHites,

(Barcelona 1889). Comptes Rendus, cxiv. (1892), 899.
Williams, Zeuoi^aphic Pragmcnts (1889).
VI wen, /our. Brit. Astron. Association, i. (1890).
Keeler, Publications Astron. Society Pacific, ii. (1890), 286.
IIiLL, * A New Theory of Jupiter and Saturn,' Astron. Papers

Am. Ephemeris, iv. (Washington 1890).
Schaeberle, Campbell, Pub. Ast. Soc. Pacific, iii. (1891), 359.
Clerke, E. 'S\., Jupiter and /lis System (London 1S92).
ScHUR, Astronomische A^achrichtcn, cxxix. (1S92), 9.
Tisserand, ' Fifth Satellite,* Comptes Rendus, cxvii. ( 1893), '024.
Pickering, W. II., Ast. and Astro-Phys. xii.-xiii. (1893-94).
Williams, Freeman, and others, Mem. Brit. Astron. Assoc, i.

(1893). 73; ii. (1894). 129.
Hough, ' Constitution of Jupiter,' Astronomy and Astro-P/iysicSf

xiii. (1894), 89; Popular Astronomy, ii. (1S04), 1 45.
Barnard, Astron. and Astrophysics, xiii. (1894).
Maunder, Green, Kuawledi^e, xix. (1896), 4, 5.
POTTIER, * .Satellites,' Bulletin Astronomique, xiii. ( 1896), 67, 107.
Flam MARION, Bulletin Soc. Astron. France, July 1896.
B^LoroLSKY, * Rotation,' Astron. jVach. cxxxix. (1896), 209.
DoU(;lass, * Satellite lli,' Pop. Astron. v. (1S97), 308.
Brenner, * Observations 1895-96,' Vienna Acad. Sci. 1897.
Denning, 'Red Spot,' Nature, Iviii. (1898), 331.
Williams, 'Rotation,' M. N. Roy. Ast. Soc. Iviii. (1S98), 10.
Denning, M. A\ Roy. Ast. Soc. Iviii. (1898), 480, 488.

Saturn

Bond, G. P., * Rings of Saturn,' Am. Jour, of Sci. Ixii (1851), 97.
Dawes, American Journal of Science ^ Ixxi. (1856), 158.

IS*

Stars and Telescopes

Watson, ' Ring,' ,)/fl. N^m. Ray. Ailr. Six.iyi. (1856), 152,

Maxwell, SlaMily of Saturn's Rings (Cambridge 1859).

Vv.ocn)t,, Saliirn and Us System (London 1865).

PeIkce, ' Saturnian Sysleni,' Mem. Nat. AcaJ. Siiitcet. i. (1S66).

HlRN, Anneaiix di Salnrni (Colmar 187:).

Bkssrl, AbhamilHn^m, i. (Leipzig 1875), pp. 110, 150, 319.

TroUVKlot, Prot/idiHg! Am. Acad. \\\. (1876), [7^.

Le Verrceh, 'Tables of its Uattan,' A iinalei di f Obiertiiloiri

de runs. Mfmoires, xii. (1876).
PrcKERTNC. K. C. Annah H-irvard Obstrt-attry, xi. {[879), 269.
Hall, 'Six inner Satellites.' Washington Obsmitlions 1S83.

Trouvelot, Bulletin Astrvn. i.

(.884), 527: ii. (1885), 15.
Batllaiii). bulletin Astrona-
mifue, i. (1884), l6[ ; ii.
(18851,118.
Meykr. Le Svslhne dt- Salume
(Geneva 1S84).

.^K±,

iillelin

<iSK5).
, MJm. dc rAcad,
Siiimes di Bavihe (Munich
r887).

I M E. J . K., Planrlarv and Stel-
- uUes ( l,on<)iin 18S8).
Monlh. X^ti^e! Keval
. Society, xlviii. ( [888).

Perrotin, ■ Rings,' Cemptts Rendns. cvi, (1S8S), 1716.
StbuVe, H., Obser-jaiions de Poulkava. SuppUmcnt. i. (iS88);ii.

(1892). Also .)/; N. Roy. Astren. Society, liv. ( 1894I , 452.
TisSKRANIN Atmalis de 'f Obstrfatoire dr Taiilouse. ii. (1889) ;

Bullelin Aslronomique. Vl. (1889), 383, 417-
Hall. A., jr.. Trans. Obs. Yale Univ. i. (1889), 107.
Darwin, ' Tiie Rings.' Harper's Ar„gazi».; Ixxix. (1S89), 66.
AndInc. Astranornischc Nachrichlen, cixi. (1SS9). i,
Ot'DKMANS. M. N. R. A. i-.ilix. {l339l. M ; Astron. N.irh.-^n^.
•s-TSiOMt\HT. BulleliHs de rAcadfmie Kayole Hel).-i'jH/,x\r.. [i^f».
Trouvelot, Bulletin Ailroncmii/ut, vii. (1890). 147. 185.
Newcomb, Aslran. Papers Am. Ephemeris. iii. | lS9[), 345.
Strl-ve. U., Bulletin Acad. Sci. St PitcrsbcHrg, ii. (1891).
KicnELiHEHCER.7».'/(rfri.«cm(V,(/y,™--™/,xi. (iSg;), 145.
Grekn, Freeman, Mem. Brit. Astron. Assoc, ii, (1893), i.

The Planets

153

Williams, Mtnlh. Not. Roy. Aiiron. Sscitly, liv. (1894), jg?.
Olbp.HS, ' Ring.' Srin UWh utid Seine Wcrkc (Berlin 1894).
Pkitcmett. Ueber Hit Verjinslerungen der Satamtrabanttn

(Munich 1S95}.
BucHHOLZ, ' Eclipse oE Japetus,' Ailroti. Naek. ciuvii. (1895).
Keeler, 'Ring Spectra,' Attrefhys.Jour.i. {1895), 416; ii. 63.

Witt, f/iminel Mid ErJe. n. (1896). 75, iii.

Barnard, Pof. Astro;, v. (1897). 285; //, N. R. A. S. Irf.
(.S96). 14; Iviii. (1898). J17.

Uranus

Newcomb. ' Orbit of Uranus,' Smithsonian Canlributiens to
Knowtedgt. t'iii- ( 1872).

Newcomb, 'The Uranian and Neptunian Systems,' Washing-
ton Observaliens ioT 1873, Appendix 1.

Le Verrier, 'Tables of its Motion,' Annai'ts di T Oisirvatoire
dt Pari!. Mimoires, ;iiv, (T877),

SCHlAPAREtLI, Astttnomisehe Nachriihten, cvi. {1883), 81.

154 Stan and Telescopes

YonNC, Aitrenomiicht Nachriehlen, cvii. { 1883), 9.
PBRROTtN, Complis Rendui, xcviii. (1SS4I, 718, 967.
Henry, Campus Kendus, xcviii. (1S84). 1419.
Gkbgory, ' Uranns,' Naturt, xl. (1889), 435.
LocKVKR, ' Spectrum,' Attran. Nack. cxxi. (18S9), 369.
HUGOINS, W. indM. I., Procttdingi Royal Satiety, tiv\. (1889),
231; alsO.V. N. Royal AitTBHomUal Sotiiiy, xlix. (1889), 404,
KlELER, Attmnetniichi Natkriehtin, cxxii. (18S9), 40T.
Taylor, ' Spectrum,' M. N. Royal Astren, Soc. xlix. ( 1889), 405.
Babnard, The AsttonomUal Journal, ivi. (1896).
Neptune

LOOMIS. 'History of its Discovery,' Wm. Jour. Sei. Iv. (1848),

187. Also RetiHt Progress 0/ Astronomy (New York 1850).
GOUUJ, History 0/ tit DiscBJiry (Washington l8;o).
Hbrschel. J- F. \V., ' Penurbalion of Uranus by Neptune,'

Outlines 0/ Astronomy (London 1865), p. 533.
Newcomb, ' Tables of its Motion,' SniithioniaH CoHlribulions te

Knimiledge. xv. (Washington 1867).
Lb Verrier, 'Tables of its Motion," Annales de FObservatnrt

dt Paris, Mimeirts, xiv. (1877).
^t.\1XX., Idtality in the Physital Seimiis i^oiXOn 1881), App. B.
TlssERAND, • .Satellite," Comflei Rendui, cxviii. (tS^i), 1372.
StruvE, H., ' Satcllile,' Af/m. de rAcad. Sciences, xlii, (St.

Petersburg 1894).
LlAIS, ' Historia 1 lescubrimiento,' Antmrio del Qbservatorio

AsttonSmiiO Nueioilal de Tiinibiiya farn el A no de 1895, p. 247,
Adams, Scientific Papers (tlambridge, Eng. 1896), i.

CHAPTER XI

THE KUDDY PLAAKT

MARS, the earliest observation of which, B. c. 356, is its
ciccuUatlon by the Moon recorded by Akistotle, was
first scruuiii/.ed with the telescope by Gaule^, who discovered
the planet's phases in 1610. The earliest sketch of ils sur-
face was made by Fontana, in 1636, though little or no detail
was made out until 1639, when Huyckns observed its markings
clearly enough to show him that the period ot rulalion of Mars
was about 1 he same as that of the iiarth. Seven \ears later

ivell-knt

id made the

first de term in

lalion of the a

xial

period, 24" 4(

i', now knoHi

1 10

be only 4

5 part m er

Among othe

ob-

servers of t

he .7th ceni

■ ury

were Rjccio

Lf, IIOOKK,

and

HEVELIUS; .

and in the .

BlANClIlNl.

and

SirWlLLtAM

Mkk:.ciiri..'u

■■ho.

begiTiniiig in

1777. first (iet

ed, in 17S3. the fluctuating

ili-

mensions of

the pol.it c

aps

with the Ma

de-

termined the

inclination of (lie

planet's axis

to its orbit,

and

measured th

e oblateness

Mars,

Early in the 19th century cai
and Arago who observed the planet for 36 years; and in
1S30-40, Beek and MaedLer, who drew the first map of Mars,
with the markings then known (among them Laciis Phaiiicis)
carefully set down in Arean longitude and latitude. Since their
day Martian investigations have ra[)idiy increased in fulness
and importance, the chief observers down 10 the very favorable

146

Stars and Telescopes

coveiy, must be mentioned Peirce a.nd Walker ; and in 1S66

were published Professor NewcoMB's Tailes BfNfptune, which
provided a good representation of the planet's motion for about
15 years. In 1877, Le Verriek's Tabtii appeared, founded
upon many years more observations than the preceding; but
already, in less than 25 years, the planet Is beginning 10 deviate
widely from their prediction, and [he theory of Neptune's mo-
tion is at the present time undergoing a second revision by
Professor NehCOmB, Neptune's path round the Sun, like that
of Jupiter, is but slightly removed from the invariable plane of

F. F. TISSERANU (184J-1S96)

orbit plane to par-
take of a regressive motion round the pole of the planet in a
period exceeding 500 years. At the present time the path which
the satellite seems to describe about its primary is so open that
this minute object is at no time overpowered by the ^ilanet's
rays: any good telescope above 12 inches of aperture will show
it. The diameter of Neptune's satellite, as determined by I'ro-
fessor PicKF.HENO from photometric measures in iS;8, is 2;6o
miles. Critical search for an additional satellite, both optically

and by means of photography, has shown that there is no such

body, unless its dimensions are very minute. Neptune's spec-
trum closely resembles that orUranus, and probably the planet
is surrounded by a dense atmosphere. — I}, J". T.

The extensive popular literature of the planets can only be
indicated here by tabulated reference to the pages of Poole's
Indtxii to periodical lit<

sub^c

I.HSup

Lm'^Z't,

.«!*

Plancu

PllJ

I- <('

p »]

,.,no

P .".

iHll™

N.pl.n,

9^1 3-9

A ihoiDugh study of Ihe planets will be greatly facilitated by
reference lo the following important papers, for the most part
original sources. These lists need, however, to be supplemented
by reference to current numbers of The Aslrophyska! Journal,
1895-1898:-

Le Verriek and Lescarbault, Compiis Rendus, xlix. and L
(1859-60), Also LeVerribr, Ibid., 1S76-78.

Wolf, NanJbucli der \falAfmatit, ii. (Zurich 1871), 3!&

Watson, Am. Jour. Siitnce and Arts, cxvi. (1878), J30, 310.

SwiiT. -4 mcwfl" y"'"-™^"/-^"""-"""/ '*'■'■'. cxvi. (1878), 313.

Peters, Astrononiiahe NaihrUktm, xciv. (1879), 321, 337.

Ledges, Lectun on Intramtreutian Planets (Cambridge 1879).

TiSSERAND, AniiuaiTi du Bureau del Longiludii for 1882, p. 719,

NewCOMB, Astron. Papers of Am. Epktmfria,\. (1882), 474,

Houzeau and Lancaster, Biktio^aphie Chiirali dt PAsiran-
omit, ii. (Bruxelles l882|, 1090, contains neatly 150 titles.

'ZKV^KWC'i.*., BeiBigung dcs Planettn Mtrkiir {i.\Ma\n\i 1884).

CkaUBERS, ' Vulcan,' Aslmnemy, i. (Oxford 1889), p. 75.

CORRIGAK, Popular Aslron. iv. (1897 ), 4I4; v. (1897).

148 Stars and Telescopes

Mercury

SCHROETER, Hermographische Fragmen/e (Gottingen 181 5-16).

Le Verrier, * Tables of its Motion/ AnnaUsde V Observatoire di
Paris y Mimoires v. (1859).

VoGEL, Bothkamp Beobiuhtungetty ii. (1873), ^33*

Harkness and others, * Transit 1878/ Wash. Obs. 1876, App. ii.

HoLDEN, Index of, . . Transits of Mercury (Cambridge 1878).

Todd, * Satellite/ Proc. A. A. A. S. xxviii. (1879), 74.

NiESTEN, ' Transits 1600-2000/ Annuaire de VObs. Roy. Brux-
elles, 188 1, p. 192.

SCHIAPARELLI, Atti deW Accad. dei Lined, v. (1889), ii. ; Pop. Set.
Monthly , xxxvii. (1890), 64 ; Astron. Xachr. cxxiii. (1890), 241.

Clerke, ' Rotation/ yi?//r. Brit. Astron, Assoc, i. (1890), 20.

Harzer, * Motion perihelion/ Astron. Nachr.zxxsW. (i89i),8i.

Ambronn, * Diameter/ Astron. A^achr, cxxvii. (1891), 157.

Trouvelot, Les Planhtes Venus et Mercure (Paris 1892).

MtJLLER, 'Magnitudes/ Publ. Obs. Potsdam, viii. (1893).

Newcomb, Elements of the Four Inner Planets and the Funda-
mental Constants of Astronomy (Washington 1895); 'Small
Planets between Mercury and Venus/ p. 116.

LrOWELU The Atlantic Monthly, Ixxix. (1897), 493.

Lowell, Poptdar Astronomy, iv. (1897), 360.

Lowell, * New Observations,' Mem. Am. Acad. xii. (1898), 433.

ViLLIGER, Ann. k. Sternwarte, iii. 301 (Munich 1898).

Venus

SCHROETRR, Aphroditographische Fragmentc (Helmstedt 1796).
Le Verrier, ' Tables of its Motion,* Annates de V Obsematoire de

PariSy Mimoires, vi. (1861).
Lyman, C. S., Am. Jour. Sci. xliii. (1867), 129; ix. (1875). 47.
Kaiser, * Diameters of Planets,' Leyden Observations, iii. ( 1872).
Safarik, Report British Assoc. Adv. Sci., 1873. P- 404-
YoGYX., Bothkamp Bcobachtungen^ ii. (1873), 118.
Proctor, The Universe and the Coming Transits (London 1874).
Forbes, Transits of Venus (London 1874).
Schorr, Der Venusmond {^^xy^xi'&^\z\i 1875).
HARTWir,, Publ. Astron. Gesellschaft^ xv. (Leipzig 1879).
Perrotin, Comptes Rendus, cxi. (1890), 587.
Terby, Bulletins Acad. Royale de Belgique, xx. (Brussels 1890).
Schiaparelli, Rend, del R, 1st. Lombardo, xxiii. (1890), ii.
Clerke, A. V^.^Jour. Brit. Astron. Assocn. \. (1890), 20.

Tlu Planets 1 49

KrWCOHB, ' Transits,' Ait. Paferi Am. Efh. \\. { 1890), 259.
AuwERS, 'Diaraeier.' AsItbh. Nachr. cxiviii. (1891), 361.
LosCHARDT, Sitt. k. Akad. Win., c. (Vienna 1891 ), 537.
NiESTEN. Rolatiot d< la Planili Vinu, (Brussels 1891).
TaoovELOT, Nature, ilvi. (tSgi), 468.
ClerKE. E. M., nt Plant! Vtnus (London 1893).
Flammarion, Comples Rendus, cxii. (1894). 670.
Brenner, Astranomiicht NaehrUhltit, cxxxviii. (1S95), 197.
SCHIAPABELLI, Ailreimmischi Nathrilhlm, cxxxviii. ( 1895), 249.
VoCEL, 'Planetary Spectra,' /<j/ro/*^i,_/our. i. (1895), 196, 273
Lowell, Popular Astroninay, iv. (1896I, 381.
Antomiadi, ' Rotation,'/™)-. Brit. Aslr. Aiiec. viii. ((897), 43,
Lowell, The Atlanlk AUnlily. Ixiix. (1897), 337.
Flammarion, A««oWiv, jcx. (1897), 234, 258.
Chandler. ' Rotation,' Papular Aslreiiomy. iv. (1897). 393.
StosHV, ' Atmospheres,' Asfrophyiical Journal, vii. (1898), 25.
DoucLASS, ' Markings,' M. N. Roy. Ait- on. Sm. Iviij. (189S), 382.

For the literature of this planet see page 178.

Could, TAe Ameriiau Ji-urnal ofSdince. vi. (1848!, s8.
d'Arrest, Ueber dai Syslcm dcrklihiin Ptanettn (Leipzig iSji).
NeWCoMB, i*/^™. Am. Aiad. Arts and Seienees,\\\\. (1861), I2J.
Stone, E. J., Af. A'. Royal Aslrt-n. Society, xxvii. (1867), 302.

tilt.slr.V.Anituaire deFObsfrtialoir/ Royaldr Bruxellesiot 18S1.
SVEDSTHVP, Astranomischt NachritbteH, cxv. ( 1886), 49.
PiRKHURST, A»n(Ui Harvard Cellfge Oburvatory. xviii, {1888).
LlAls inA Ctmis, AmiaUi de rOhi. de Riodt yaBeiro,\i. {i2ia^).
ScHMtDT, R., PuM. AitrOH. Soeitiy Paci/it. ii. (1890), 238.
TisSERAND, Popular Scif net Monthly, miiix. (i8gi), 195.
KiRKWooD, Prix. Am. PAH. Society, xxx. (189=), 269.
Backlund, Mim. Acad. Set. St Pitersbourg. juiviii. (1893).
Todd, Astronomy and Ait rophy sic s, xii. (1893), 313.
CallandreaU, Camples Rendus, cxviii. (1894), 751.
ROSZEL,/. H. Univ. Cire.xm. (18941,67: x\v, (1895), 23.
Cha&lois. Sulletjn Aslron. xi. (1894); xiii. ([S96).
Zenoer, Ballelin Si>eiM Aslranemique de Frame (1895), 243.
Mascart, ' Small Planets,' Bulletin Aslron. xv. (1898), 135.
Ckohmblin, * Planet D Q.' Knimledgt. »xi. (1898), J50.

Stars and Telescopes

JVPITBR

SoMERVILLE, Metkanism of the HaauBt (London 1831).
De DamoisbaU, Tablei £<lipliquis SatciliUt ( Paris 1836).
Engelmann, Htlligliiit^erhdllnitst dtr Jiipilcrslraianlcn

(Leipiig 1871).
LiiifSE, Bolhiiimp Beobachtungen, J. (1871); ii. (i873). Also

FuU. Astrophys. ObseTV, PoUdam, i. (1879) j iij. {1S82).

Gi.ASEKAPP, Cpaem»it HaSAiodetiiu 3amMibHi!t CnijmnuKoai

JOiiumepa (C.-IIeniepSypit 1874 J.
Downing, Abstract of foregoing, Obsen>atBry, lii. (1889), 173.
Vii}S%t., Monthly A'i}tictsKoyjiAslr,momicalSmU!y.x\x\v.(lZ7i).
BREDtCHiN, Ami. di rOhsenialoire dr Moicou. ii.-vi. (1875-80).
TuDi), CoulinH:ilion of Dk DaMOISEAU's Tabtis £c!iftignn tit

1900 (Washington 1876}.
Le Verrter, 'Tables of its Motion.' Aanaltt derOistrvaloire

dt Pari,, Mlmoirts. xii. (1876).

The Planets 151

Denning, Siientifor All, part xm. (London 1880), 169.
SouiLLART, Mcmoiri koyal Astreticmkal ScKiity. xlv. (1880), I.
Trouvelot, Free. Am. Aead. Arli and StUfKes, viii. ( i83i ), 199.
Kempf, ' Mass,' fubl. Attrephyi. Ot-icrv. Polsd.im, iii. (1882).
Denninu, ' Sum mar)' of Markings and Ratal lon-petiods,'

Naturt, xxiii. (18S5). 31; Ohsirvatory. U, (1SS6), 188 ; xi.

(I8SS),SS.406; xiv. ( 1891 ). 319.
Williams, Thr Ohim-alory, ix. {i8S6), 231.
\j>MWi,CoiHpiis KenJits.civ. (1SS7), 279,613.
SouiLLART, Mim. Afiii/mie dts Scien<tt, xxx. (Paris 1887).
Backlukd, ' Satellites,' Biilltlin Aslronnmigii^, iv. ( 18S7], 331.
Barnard, Puil. Aslron. SoeUly Pacific, i. (1889), 8g.
Landerer, EsliHiies fitamtlrKos iohrc tl lislcma di hs s-ilHiln.

(Barcelona 13S9). Comptii Rtmlus. cxiv. (1892), S99.
Williams, Zeno^-raphic /■>vifwi/ni'/ (18S9).
WauOH. yo«r. Brit. AslrcH. AiiBeiatu-i. i. (1S90).
KEEI.ER, PuilicatiOHt Asfrnii. Sa-it/y Pacific, ii, (1890), 286.
Hill, ■ A New Theory of Jupiter and Saturn,' Aihfii. Pupcrt

Am. lifkcmcri,. iv. ( Washing loii 1S90).

SCHAEKERLC, CAMPBELL, Pub. Alt. SiK. P,<llflC. Ui. (iSgil, 359.

CleRKE, E. J.l.,Jiipittr and Ais Srifrm (London 1X92).
SCHL-K, Astrarwmiichc N.iclirichl,ii, cxiix. (iSgs), 9.
TissERANri, ' Fiftii Sateilitt,' Co«/i'«A'^«i(i(j,c\vii, (1R93), 1024.
PlCKERINc, W. H., All. and Ailio-Phvi. xii.-xiii. ( 1X93-94).
Williams. Krkeman. .itid others, Al'.-m. Brii. Aslron. Asw. i.

(18931.73! ii-(iS94). i;*
Houim, ' Constitution of Jujiiter,' Aslrotipmyanil Ailre-Pbysici,

xiii. (1894), 8g: Psfniar A.<lr..ni'my. ii. (I^l-H). 145.
Bar^arh, Aslron. and Astrap/iy.iics. xiii, ( |8(J4).
MaITNDER, Gkken, A'nnwM^'4. xix. (1896I, 4. 5.
PotTlER,'SatellilC3,'/.W/<'//H^jfr,iHPmjy«,', xiii, (18961,67, 107.
Flammariun, BnltflinSBc. Aslron. Pran. c. }u.iy 1S96.
BftLOiiiLSKV, ' Kotation,' Aslron. A'acA. cxxxii. (i8c)6). 109.
Dooi;lass, ' Satellite Til.' /'p/t. AiUvn. v. ( 1.S97I, 308.
Brenner, ■ Observaiion,^ [895-96,' ricnna A,;r,/. Sci. 1897.
Denning, 'Red Spot.' ^Ti/wn'. Iviii. (1898), 331.
WlLLL\MS, ' Rotation,' .1/, A'. A'oi', Aii. So,. Iviii, f rRgS), 10.
De\MNC, a/. A\ Ri>y. Ast.Soc. Iviii, (1898), jfio. 4S8.

Sati'hn

Stars and Telescopes

I5»

Watson, 'R\r.g: ^U. Net. Roy. Aslr.S0i.T.v\. (:8s6). iji.

Maxwell, Sraiility ef Saturn's Ringi (Cambridge 1859).

VtxKny».. Saturn attiliti Syztrm (London 1865).

Pefrce, ■ Saturtiian Sj-slem," Mem. Nat. Acad. Sdeneei. i. ( 1866).

HlBN, Axneiux de Saturue (Colmar iS;2).

Bksskl, AbhandiuHsiH, \. (Leipzig 1875), pp. 110, 150, 319.

Trouvei.oT, PraiaJingi Am. Acad. iii. (1876), 174.

Le Verhieh, ' Tables of ils Molion,' Antialei de f Observatoire

di Riris. AUmoirei, xii. (1876).
Pickering, V. C. Ainuils Himard ObstrtHilory, xi. (1879), 569.
ILm.i., ' Sin inner Saiellites,' WasAiHglon Ob^crvath^u rSSi.

WATSON (1838-1880)

(:S8j), 527: ii. (1885), 15.

miijui. \
(i8Ss), 1

. (■SS4I.
18.
Syslimc d.

161
■ Sa

(Geneva'

OrNCARfi.

18X4),
B.dlitin

miqiu, ii.

(1SS5),

/., r Sli-di, 1 (Lonit.

362,

n.Society. J;lviii.(lS

PebROTIN, ' Rings,' Comptci Rendus.

Struve, H.. Obsenaitlem de Poulkafn. Supplimeal. i. (iSSS); ii.

(1891). M!.a M. N. Rpy. Astroa.SMiety.Wi. (1894), 452.
TlSSERANr-, Anmilc! dc rObsirvateirc dt Toulouse, ii. (1889);

BuUetirt Aslronomiqiie, vi. I1889), 383. 417.
Hall. A., jr., Tram. Obi. Yale L'uh: i. (1S89I, 107.
Darwin. * The Rings.' Harper's Ar.i);aihie, Ixxix. (1S89). 66.
ANDlNii, Ailronemische NacHrichleii. cini. (1SS9), 1.
OUDEMANS, .^/l ;V. ^. rf. J.xlix. (1889), 54;/*J/fo«. AW*.3074.
StrooHaNT, Bulletins de r Academic Royalt Iltl^-i./itc. xix. ( 1S90I.
TrouVElot, Bulletin Astrouomique, vii, (iSgo). 147, iSj,
Newcomf, -^J/ran. Papers Am. Ephemeris.m. (1891). 345.
Strove, n.,BiilleliH Acad.Sci. St Pitershours, ii. (iSgi).
}fAC\\V.'i.MV.f.a¥Jt.,The Astrancmical Ji'ur-ial.^x. (1892). [45.
Green. Freeman, Atem. Brit. Asiron. Assoc, ii. (1893), i.

The Planets

IS3

Williams, Mmfh. Not. Roy. Aslren. Society, liv. {1894), 197.
Ol.-BV.\i%^ Rin^.' S/i'i Ltbea UHd Seine IVerke (lierlin 1894).
Pkitchett, Utbtr die VerfinHeniHgen dir Sahimtrabanttn

(Munich 1895).
BUCHHOLZ, ' Eclipse of Japelus,' Aslron. Nach. cxxxvii, (1895).
KEELtK, 'RingSpeclia,' Astropkys.pur. \. (1895), 416; li. 63.

OLBERS (1758-1840)

Witt. Hitnsiel u„d Erdi, ix. (1896). 75. i^"-

Barnard, Pop. Aslr,m. v. {1S97), 285; Af. A'. R. A. S. Irf.

(.896), 14: Iviii. (:898), M7.

Uranus
Newcomb. 'Orbit of Uranus,' Smttksonian Contributions 10

A'«™/^a't^, xviii. (1873).
Newcomb. 'The Uranian and Neptunian Systems,' Washing-

ton Ofstrvatioiii foi 1873, Appendix r.
Le VerrIeR. ' Tables of its Molion,' Ani-aiei dt P Obieniateirt

de Firis. Mimoirti. ;;iv. (1877).
SCHIAPARELLI. Astronomiiiht Na<hri<hten, cvi, {1883), 81.

Stan and Telescopes

IS4

YoUHC, Aitranamiickt Nachrithltn, Cvii, (1883), 9.
PkrrotIN. Complts Hindus, nzvm. (1884). 718, 967.
Henrv, Complti Ktiidiit, xcviii. (1S84). 1419.
Gregory, ' Uranus,' Nature, jtl. (1889), 135.
LocKVSR, ' Spectrum,' Ailron. Nath. cxxi. (1889), 369.
HUGCINS, W. and M. \^. Proaaiin^s Rayal Socitly, xlvi. (1889),
131 ; also M. N. Royal Astronemiial Society, xlix, ( 1889), 404.
Keeler, Ailronoinitcht Naehrhhttn, cxxH. (1S89), 401.
Taylor, ' Spectrum,' M, N, Royal Ailren. Soc. xlix. ( 1889), 405.
Barnard, TAe Aitronomieal Jountal, xvi. 1:896).

NEPrUNE
LOOMIS, ' History of its Discovery,'^™. /our. Sd. Iv. (1848),

187. Also Kc<tnt Pro,^!Si of Astrotmmy (New York 1830).
Gould, History of the Disiireiry (Washington 1850).
Hekschel. J.F. W., 'Penurbalion of Uranus by Neptune,*

Oulli'iti ffAslrotwmy (London 1865), p. 533.
Newcomb. ' Tables of Its Motion,' Smithsonian Ceniribulioni ta

KtiowleJs'. xi. (Washington 1867I.
Le Verrier, 'Tables of its Motion,' Aiinalts di C Observaleirc

dt Paris, .W«iBirii,%\v. (lij'j).
Peirce, Ideality in thi Physical Scimcts (Boston 1S81 1, App. B.
TlssERANP, ' .Satellite,' Coml-les Kendus. cxviil. (1894), 1 J72.
Strove, H., 'Satellite,' Mlin. dt I' Acad. Siitncrs. xlii. (Si.

Petersburg 1894).
LlAIS, 'Historia nescubrimiento,' Anaario del Ohserv.Uorie

AstronSmico /C'icionai de Tatubaya pani el Ahf de 1S95, p. z^-j,
Adams, Scimtific Pafirs (llambridge, Eng. 189O), i.

CHAPTER XI

THE RUDDY PLAAET

f ARS, the earliest abservation of which, B. c, 356, is its
occultatinn by Ihe Moon recatded by AristuTlEi was
Grst scrminized with ihe ldescoi)e by (Jalileo, who discovered
the plaiiel's phages in [610, The earliest skclch of in sur-
face was made by Fontana, in i6jG, though little or no detail
was made out until [659, when Hu^
clearly enout;h lu show him that the period of rr
was about the same as that of the Karth, Se'
Cassinj discovered the B'ell-linc

period. 24' 40". now known 10
be only sjj part in error.
Among other [irominent ob-
servers of the 17th centurj-
were RlCCIol.r, Hooke. and
HEVF.t.[OS; ai..

Sir William IIkhscii:
beginning ill I777. first
ed, in 17S3. Ilie Huctii:
mensions of the poli
with the Martian seas
termincd Ihe inclinalio
planet's axis to it
measured the oblatene:
Mars.

Early in the 19th centurj' c.
and AiiAi'.o who observed the
1830-40, BtER and Maehlkr, who drew Ihe li
with ihe markings then known (among ihi'ni
carefully set down in Aican longitude and lati
day Martian investigations have rapidly inci
and importance, the chief observers down to the very favu

156 Stars and Telescopes

opposition of 1862 being Sir John Herschel, Kaiser, Secchi
who studied the colors of different regions, Lord RosSE, Las-
sell, and LocKYER whose fine sketches inaugurated the modem
standard of excellence. From that time onward, there have
been critical observations by Dawes, Knobel, Trouvelot,
Green, Terby, Niesten, Lohse, and others, culminating in
the classic labors of Schiaparelli, begun at the memorable
oppositions of the planet in 1S77 and 1S79. ^^ abundant and
careful have been the drawings of this planet in the past that
many excellent maps of its entire surface have been made, by
Kaiser (1864), Proctor (1867), Green (1877), Drever (1879),
and in particular by Schiaparelli (1888), supplanting all
others, from his elaborate sketches with the i8-inch Merz re-
fractor of the Brera Observatory at Milan. D' WiSLlCENUS
of Strassburg has done excellent service by applying the mi-
crometer to the more conspicuous markings, thereby establish-
ing their accurate positions ; and it is no exaggeration to say
that the areography of Mars is now better known than the
geography of immense tracts of our own planet.

Mars, although the nearest to the Earth of all the planets,
Venus alone excepted, is an object by no means easy to ob-
serve. To realize the extent of the difficultv, even under the
best imaginable conditions of instrument and atmosphere, let
any one with no previous knowledge of the Moon attempt to
settle precise markings, colors, and the nature of objects on
our satellite by simple scrutiny with an ordinary opera-glass.
Indeed, the Moon would, for many technical reasons, prove the
less perplexing, although the two cases would be quite parallel
in so far as mere geometry is concerned.

Sketches and Variations

Personal differences affect all sketches of Mars unduly, and
the delicate and changing local colors add much uncertainty.
Still, the leading features of the planet's surface are well made
out, and their stability leaves no room to doubt their reality as
permanent planetary crust. Here, unfortunately, the great ad-
vance in photographic application to astronomical requirements
has not yet helped much, although excellent plates have been
obtained by Professor Pickering, and at the Lick Observatory
as well : the texture of the sensitized film is too coarse, and the
image of the planet is too small and faint. The border of its disk
is brighter than the interior, as the Lick photographs show ;

The Ruddy Planet 1 57

but this brightness is far from uniform, and the variation is
probably caused by the suiface features of the planet. Also varia-
tions of color in the markings of Mars depend upon the diurnal
rotation of the planet and the angle of vision ; and changes oE
apparent brightness in certain regions ate as well established as
in the case of the Moon, Ar^re /.for example, first ol)served
by Dawes. In 1S52, has often been seen by Sihiapabf.lli to be
reddish yellow when near the central meridian, while again, after
the planet's rotation has carried
it round to the limb, it has :
peared so brilliant as to be n
taken at first fur a polar c.
This skilful observer has a
noticed similar changes, jirogt
sire in character, coveting e
Sive continental regions. A:
white spot, -Vij- AllanlUa,
observed by him in 1S77, then '
almost square, and mure
than any other ]iarl of th
became at subsequent op|

pearance am! brilliancy,

188S had entirely disappeared. ^^„^^ (,Ro3-i37=)

Mindful of these obstacles in ' '

why the early lelcscopists failed to discern very much ; .ill had
not only that ever-present foe of the astronomer, the atmos-
phere, to battle against, but the imperfections of iliiir inMru-
menls were a farther and most serious handicap. Formerly
observations of a near approach of Mars to the Kartli would be
made only from localities where observatories nete previously
established ; but the exceeding present interest in onr neighbor-
ing planet led to the building and maintenance of .in observatory
with a large and perfect telescope and a corps of astronomers
at a mountain elevation in a clear and steady atmosphere,
with the especial intent of a critical survey of the ruddy
planet, during its recent and very favorable presentation in
1894-95. Frequent allusion will be made in this chapter to the
excellent work of M' Pf.rcival I.owkll (at the observatory
bearing his name, and temporarily located at nagstaff. Arizona,
elevation 7250 i"^ above sea level), and of his coadjutors.
Professor W. H. PicKmiNC and M' Dovclasi.

158 Stars and Telescopes

General Topography

The most casual observer of Mars would not fail to notice
the striking difference between the brightness of the two hemi-
spheres — the northern chiefly bright, and the southern pro-
nouncedly dark. In fact, the light and dark regions are each
approximately a hemisphere in area. Allowing that the cosmic
conditions of Mars are still suitable for the existence of water
and an atmosphere, though of no great density, it is an easy
surmise, and perhaps the true one, that the lighter regions of
the planet's face disclosed by the telescope are land and the
darker water. The southern hemisphere of Mars, then, is
principally water, and the northern continental land, precisely
as in the case of the Earth (page 24) ; but while, on our globe,
the proportion of land and water is about four to eleven, the
surface of Mars shows water and land in very nearly equal
amounts, with a slight preponderance of the latter.

Mars, in its general topography, presents no analogy with
the present scattering of land and water on the Earth. Fully
one third its surface is the great Mare AustraU^ strewn
with many islands, and apparently intersecting the continents
by numerous divisions, narrowing northward and suggesting
gulfs. There seems little reason to doubt that the northern
regions, with their predominant orange tint, in some places a
dark red and in others fading to yellow and white, are really
continental ; and Professor Schiatarelli thinks that the Arean
continents appear red and yellow because they are so in fact,
atmospheric action having little or no influence upon their hue.
Different from the Earth, the lands of Mars are mostly massed
in a single vast continent, spotted with the great lakes Mare
Acidalium and Lacus Niliaais, the former of which is found to
be variable in area. Other extensive regions, for example, the
islands of Mare AnstraU and Mare Erythraeum, sometimes
appearing yellow like continents, and again dark brown, are
thought by Schiaparelli and Niesten to be vast marshes,
the varying depth of water causing the diversity of color.

The seas of Mars, generally brown mixed with gray, also
vary in intensity from light gray to deep black ; it seems prob-
able that only the darkest of dark regions may actually be deep
water. The true aquatic character of the suspected seas would
best be established by watching for the reflection of the solar
image from them; and M. Flammarion has calculated that
under favorable circumstances the Sun, thus reflected, ought to

The Ruddy Plana

■bine as a star of the third magnilude ; but nc
non has yet been ubserved. Professoi
servations incline him to the opinion Ihal ihe permanent
area u|io[i Mars, if il exists at all, is extremely limited-
Axis AND Polar Capj

The axis of Mars [lieices the
way between the two bright

iDeneb), and no precessional motion o( ihe pole is yet made
out. The waxing and waning of the polar caps, being largest
near Ihe end o( Ihe Martian winter and smallest near the end of
summer.are phenomena which have lung tieen well established.
A brilliant white, they are generally thought to be composed

argument for the reality of a Martian atmosphere, capable of
transporting and diffusing vapor.

The northern c.ip is centred on Ihc north pol« of ihe planel
almost exactly; and its gradual melting, observed by SCHIAPA-
RELLI in [S3z, 1S34, and 1SS6. appeared to create a temporary
tonal ocean, from which radiated many darkish streaks, con-
necting southward with numerous round patches, called 'lakes'
by him, and ' oases ' by M' Loweli, Our knowledge of Mars
has mainly been derived from a study of its surtace at the
very favorable oppositions, about IJ years apart, when the
planel was near its perihelion, and consequently near its least
distance of 34 million miles. Always at ihose limes the
inclination of Ihe planel's axis brings the south pole into
view, while the noilhern i« turned from us. At (he inter-
mediate oppositions, when the planet's north pole is best
visible. Mars is not far from aphelion, and least favorably situ-
ate, in point of distance ; there is, however, a compensation in
that the great telescopes of the world, located tor the most part
in northern latitudes, are better placed for observations of the
planet. But its apparent diameter being so much reduced. and
ihe difficul ties o( studying il5 surface so greatly augmented, rela-
tively few oliservers have made a study of so unpromising an
object as Mars on Ihese occasions, when its distance usually
exceeds 60 million miles ; and our knowledge of the norlhern
hemisphere is proportionally incomplete.

M'' Knohel, among others, undertook to obliterate this in-
equality during the opposition of 1834, and three of his sketches
during that period are reproduced here. No irregularity in

Stars and Telescopes

i6o

the polar spot wai detected. The next favorable oppoiitioni
fur observing its norlh polar regions will occur in 1S99, 1901,
and 190J, when, with the planet's pole tilted toward [he Katth,
it is especially desirable that the phenomena of the iiieliirg of
the northern poUr cap be closely watched by experienced ob-
servers with the most powerful telescopes.

Curiously, while the north polar snows cap the exact pole
quite concentrically, and as far as the S5th parallel of latitude
all around, the south circumpolar snows do not centre about
the pole, but round a point now nearly SCO miles removed from

the planet's tr
established var

cap from the true pole is unacennnteri for : it was as much as
V in the elder Hehscmel's time (1783), and even 30° as
measured by Ltnsser in 1863. but only 3° at the opposition in
1892, according to Professor Comstock, whose observations
»ery clearlv bring out not only the rapid shrinlimg of the snow-
Cap — its diameter diminishinp about fifteen miles daily — but x
prt^essive shiftinR of its centre, which would seem to show an
nnsyinmetrical shrinking. At the bepinninE of the Martian
iummer the polar cap reached down to latitude 70°. and its
diameter was lloo miles. In three months it had shrunk to
one seventh this diameter. Frobablv the north cap wac all the
while increasinK, but this pole was turned away from the Earth,
mnd consequently invisible.

The Ruddy Planet i6i

All the changing conditions of 1892 were most scrupulously
observed by Professor Pickering, then located at the Harvard
Observatory in the Andes of Peru (frontispiece), where, with
a 13-inch telescope he had much better opportunity than any
other astronomer for observing the planet at its nearest ap-
proach to the Earth. Mars was faithfully followed on every
night but one, from 13th July to 9th September, and the appar-
ent alterations in the polar cap, even from night to night, were
very marked. As the snow began to decrease, a long dark
line made its appearance near the middle of the cap, and grad-
ually grew until it cut the cap in two. This white polar area
(and probably also the northern one), with the progress of its
summer season becomes notched on its edge, dark interior
spots and fissures form, isolated patches separate from the
principal mass, and later seem to dissolve and disappear. It
is much as if one were located at the distance of Mars and
viewing with a telescope the effect of the advancing summer
season upon the ice and snow of circumpolar regions of a
nearly cloudless Earth.

Evidently the fluctuations of the polar caps are the key to
the physiographic situation on Mars, and at the opposition of
1894, as well as that of 1892, the southern one has been criti-
cally scrutinized. The south pole reached its maximum dip of
24° toward the Earth on 22d June 1894. The rate of its pro-
gressive diminution is by no means constant, and its area, some-
times increasing and again diminishing, is at other times
intersected by one or more dark narrow markings ; naturally
interpreted as heavy falls of snow in the one case, and in the
other as the melting of snow in the polar valleys. These fluctu-
ations were subjected to exact measurement by M. Flammarion
and others ; and the average rate of diminution was not very
different from that found by Professor Comstock in 1892. One
* great rift * of the polar cap, very conspicuous, M' Lowell com-
pared to the appearance of *a huge cart-track coming down to
one over the snow.' Its breadth he estimates at 220 miles, and
length 1,200. Surrounding this polar cap is a narrow, dark
line, nearly uniform in breadth, which is, M' Lowell surmises,
'clearly water at the edge of the melting snow — a polar sea, in
short.* Concerning the dark line dividing the polar cap, which
made its appearance in the same place at the corresponding
Martian season in 1894, he farther says: 'It started appar-
ently not far from the centre of the snow-cap, and increased in
width and length till it opened into the polar sea in longitude

SAT— II

€

1 62 Stars and Telescopes

i6o*^. Later its opposite end came out in longitude 330®.
Meanwhile it was spreading even faster in the middle. While
it was thus eating into the snow, some brilliant points, shining
like stars, were observed in the snow between it and the outer
edge of the cap on several successive mornings. They un-
doubtedly were the far-off glisten of snow-slopes. The subse-
quent behavior of the spots from which they came bore witness
to this. For the rift grew till it formed a large lake in the
midst of the snow not far from the geographical pole. Other
rifts also appeared and ate into the cap, but the spots that had
shone out so brilliantly still remained as snow islands, though
daily diminished in size. At last the smaller of the two chief
portions into which the cap had been split dwindled entirely
away, and the other became a tiny patch eccentrically placed.*
In consequence of the one-sided situation of the southern
cap, the planet's true pole is always uncovered at the height of
the summer season ; and until the opposition of 1894, the min-
imum size of this cap was that observed by Schiaparelli in
1879, when its diameter shrank to less than 150 miles. But
the observers at Flagstaff were treated to a genuine surprise,
when, in October 1894, M' Douglass witnessed the complete
disappearance of this polar cap, undoubtedly the first phenome-
non of this character ever recorded ; it was verified also by
Professor Wilson at Northfield, M. Bigourdan of Paris, and
others. The region formerly occupied by it became in no
respect different from the east and west limbs of the planet.

The Terminator

As Mars is the nearest of the outer planets, its phase at
times is very marked, being about like that of the Moon when
two days before or after full. (See the illustration on page
172). Its terminator, the line marking the limit of visibility on
the incomplete side of the disk, may therefore be well observed ;
and the phenomena of this region should tell us much about
the general character of the planet's surface.

Bright projections on the terminator of Mars were first ob-
served by M' Knobel, who, on several occasions in 1873,
described and delineated a white spot in this position, 'glisten-
ing as brightly as the polar ice.* In 1884, however, with Mars
at a corresponding phase, he could detect no bright spot in the
same areographic location. Similar markings were discerned
by M. Terby in 1890. Also, in August 1894, MM. Perrotin

iJhtfl.^,ftUc/r.

SOUTH POLAR CAP IN 1894 (LOWELL)

Hiim »/ llu mf ii itim-w. ai wtll J Iht
Aiig krtadlli if 1*1 dart itll Aal friagid

Tht Ruddy Planet 163

id Javellb, and M' Will

tion, ate probably' due to Martian mountains, or clouds, o:
combination oi boib. Certain gray region! oi lar^je area, as
walcbed by ProEeasoc PICKERING in pauing the iciminator,
weie noicbed Co difictenl depths, indicating hills and valleya,
and nut the surface of an ucean. At the lecenl op|>ositions,
irregularities of the Martian lerminaior have been carefully
looked for, particularly at the Lowell Ubservaiory, where, on
30Ih June 1894, M' Douglass delected local flaitenings in Ihis
line of demarcation, 20° to 40° in extent. M' LuwkLL finds
them almost invariably upon that pan ui the terminator where
the darker of the dark rcgiuna waa then passing out of sight.
These chuid-like Hatteninga arc atill uuaccuuiitcd for. Also
there were prujeccioiis and small imlcbes, similar to those on
the lunar terminator, though much less pronounced, and indi-
cating mountains of perhaps 3,000 to 4,000 feel elevation.
About two months later, I'rofessor Pickering sketched a
•eries of unusually marked elevations and depressions upon
the terminator (page 172). Eventually data of (his character
will suffice for a map oE approiimate contours, but great care
is necessary in distinguishing those projections which the
observations of 1896-97 indicate as perhaps due to cloud-
Evidently the most persistent scrutiny of this ever-changing
line ofsunrise and sunset can alone enlighten us ns to config-
orations of the Martian surface, which without doubt is rela-
tively flat in comparison with the present riigEed contour of
Earth and Moon. Only when the crowdinp enigmas of the
Moon have dissolved shall we be readv to pronounce upon
Martian appearances with certaintv. Particularly must the
marked chanECS of lunar objects with the direction of their
Illumination be critically interroeated as an auiiliarv key to the
aituation on Mars. The strjkinj; systems of lunar 'streaks'
Yanish utterly as our satellite recedes from the full: an .i this
simple fact shows the dancer of attach inp too peat significance

ihenomena of the Martian surface which may turn

■e phantom changes of illur "

The Lakes, or Oases

It is the vast orange-tint area of the norlhem hemisphere.
probably little diversified with hilts and valleys, which the

164

Stars and Telescopes

keen eye of Professor Pickesinc tirsl doited with numerotw
darkish regions of relatively snutl extent, and which are con-
nected together by the complex system of lanaii, iniersecting
the northern Martian continents, as if the lines of a huge sys-
tem of triangulation. If these dark spots are lakes, they are
not permanent reservoirs, like terrestrial ones, as someliroes
they wholly disappear. Also their apparent doubling, or gemi-
nation from time to

regarding them as
oases in the vast
Arcan deserts, and
their visibility as
due to the growth
of vegetation with
the advance of
spring. Onpp-176-
77 are twelve charts
of Mars, obtaJtted
by photographing
a globe on which all
the known features
of the planet had
been drawn by M'
Lowell, through
whose courtesy they arc here presented. They give compre-
hensively the important results of his recent studies of the
planet, and show the striking systetn of the spots admirably.

Lacui Fioeniiis, one of the southernmost, on very fine nights
with medium power, appears as a small spot, almost black and
nearly round, resembling a shadow of a Jovian satellite near
the middle of its transit. A little farther south is one of the
best known regions of the planet, also a dark, oval, isolated spot,
about 530 miles in its longest diameter, and formerly called veiy
appropriately the 'Oculus,' or eye of Mars. First obstrved by
MaEDler in 1830, charted as Trrby Sea on Green's map, it is
now known as Solii Lacui, after ScHlAPARELl.l. As early as
June 1S90 this keen observer saw it divided into two distinct
parts, and on 2d September 1894, the Lick telescope enabled
M' ScHAEBERLE to divide it into three regions, all separate

The Ruddy Planet i6$

and very dark. M' Douglass has still farther subdivided it
(page 166). ttcHiAPARELLl has often seen a large part of the
planet's disk, particular!)' near the polar regions, sprinkled with
minute white spots, for example, in January iSSl, the region be-
tween Gangei and Iris; and these phenomena, so important in
■todying the physical constitution of the planet, are often within
the reach of moderate telescopes. Dut the smallest of the true
' oases,' or dark spots, which are about 60 miles in diameter,
are even more difficult to see than their intersecting 'canals,'
and both oases and canals have been observed to fluctuate to-
gether in visibility, as if they were parts of one intimately con-
nected system.

The Martian 'Canals'

Although faint markings of this character were first indi-
cated on the map of liEtit and Maedler (1840), and Dawes
detected eight or ten of them in 1S64, they are generally regarded
as the original discovery of Schiapakelli during the remark-
able opposition of 1877, when he made the first extended tri-
angulalion of the Martian surface, and majiped most of the
canati known at the present time. Many observers fail utterly
to detect these delicate markings ; others, practised in ihe ob-
servalion oE them (M' WILLIAMS, for example, who verified
nearly all of them in 1894), would call the plainer ones con-
spicuous, and the average of them not difficult. Ijul at least
they require a steady atmosphere, and a perfect telescope with
a trained eye behind it. Not even then are they always visible.
Their appearance and degree of visibility are variable, often in

artificial

periods of only a few days' duration. Seemingly capricious
even the general law of this varialion is not yet fully understood.
Generally only a few of the raHo/i are visible at once. Owing to
the changing physical aspects, as to Mars's season and orbital
position with reference to the Earth, under which they may be

l66 Stars and Telescopes

presented, given markings of this type may for a long time r»>
main invisible ; but nearness of Che planet is not essential to Ehcir
visibility, for they were seen at the remote opposition of 1896-7.
If it is granted that the lanali have an artificial origin, and
were constructed for the very reasonable purpose of irrigation,
one would naturally expect their minute structure to be some-
what as shown schematically on the previous page ; straight and
relatively narrow channels through the middle, intersected, at
intervals more or less regular, by a multitude of short cross-
channels, throughout their entire length. Indeed, says SCHIA-
FAKELLI, they very often look like gray bands deepest in inten-
sity at the middle and shaded at the edges. Such a theory
would obviate the necessity of supposing that (be tanali ue
reallyas wide as they look; because at our great distance, the

MjifrotoB^ Douglass, 91A 0^li>irr iS^. SioJt, 1 itick= iioo mUti)

apparent width of a ' canal ' would simply be equal to the mean '
breadth of the system. Optically it is a question of resolva-
bility which ought not to be beyond the power of the largest
existing telescopes with a perfect atmosphere.

Straight in their course and rarely deviating from a great
circle, but very different in length (from 300 to 4,000 miles),
they join one another at various angles like spokes in the
hab of a wheel ; and intersect the great northern c

The Ruddy Planet

167

with a marvellous network of fine darkish stripes. M' Lowell
describes Iheir color as a bluish green, identical nilh that of
the seas with which they connect. While each canaU main-
tains its own width throughout its entire length, the breadth o(
these markings is by do means uniform ; perhaps 3o miles Tor
(be narrowest, and ten times that amount for the broadest, of
which the Nilaiyrtis is probably the easiest of all to see. But
although minor changes are suspected, and beginning to be
made out, the canali form a pemtanenl configuration of the
Martian surface ; and every etiiiaJr, as is apparent from M'
Lowell's charts, page 176, connects at its ends with another
marking of like character, or with darker ones, possibly seas.

Preferably, honever, they converge toward the small spots
named lakes, or oases ; for example, seven canali coit-
verge in Lacus Photnitis, eight in Trivium Charontis, six in
Lunar Lacus, and six in Isminius Larui. About 50 of these
dark spots, or lakes, are now known, including the recent addi-
tions of Pickering and Loweli. Often the canals open out
into an expanding Irumpet-shaped region — eg., mouth of
Nilesyrtis named Syrlis Major, an area which exhibits sea-
sonal changes, as if due to iregetation. Schiap*relh's criti-
cal studies of these markings, and their changes of width and
colors at the oppositions of Mars in iSS:, 1S84. and iS36, when
the planet's northern pole was turned toward us. have led him
(o the simple and natural interpre-
tation thai the ca'iali form a veritable
hydrographic system, for distributing

Whether 01

whole,

le detached portion of high de-
tail, as in the opposite sketch of the
Siriii Lacia region hy M' Douglass,
it is difficult to escape the conviction
thai the canali have, al least in part,
been designed and executed wiih a

definite end in view. "*"■ '1'^^^,°'." '^

A doien of the fonu/i became vis- ""v" . • ^t

ible to M- Lowell at Flagstaff in ^ t'til^'^l^ mZT^
■S94, ten week* preceding the sum- Mn-imn)
mer solstice of Mars's southern hem-

bphere ; and there were abundant verifications by many other
widely separate localities and with instruments

l68 Stars and Telescopes

of varying capacity, — Professor Wilson, Northfield, Minne-
sota, and the Mount Hamilton observers, 30 canali by Herr
Brenner in Istria, 40 by M. Antoniadi (who, at M. Flam-
marion's observatory at Juvisy, made numerous fine sketches
of Mars), and 50 by M*" Williams of Brighton, who saw nearly
all those marked on Schiaparelli's map, and a few new ones
in addition. But this record was far outstripped at the Lowell
Observatory, where some of the canals ap|)ear on more than
one hundred separate drawings, and 183 canals were seen in
all. M' Lowell has made out a progressive change in the tint
of the canali^ which he regards as seasonal, and probably due
to actual water, and vegetation fed by it. Naturally, extensive
irrigation and agricultural operations on a large scale would
seem the most likely explanation of the canali^ especially when
we reflect that upon Mars, doubtless a world farther advanced
in its life history than our own, in the first place, erosion may
have worn the continents down to a minimum elevation, making
■artificial water-ways easy to construct ; also with its vanishing
atmosphere and absence of rains, the necessity of water for
prolonging the support of animal and vegetable life could only
be met by conducting water from one part of the planet to
another in channels artificial or partly so.

In our present knowledge of the catiaii, this seems a plausible
explanation ; but many years of patient investigation are yet
required, especially with larger telescopes on perfect mountain
sites and by the most painstaking observers. Particularly
arc the best conditions for telescopic research paramount, be-
<:ause the catiali manifest themselves chiefly in the northern
hemisphere of Mars. To ascertain the true significance of the
<anaiit however, does not necessarily seem to be forever beyond
the power of man. The argument of the 'canals* is fully pre-
sented by M' Lowell in his interesting volume on Mars (Bos-
ton 1895) ! ^''^^ since its publication he has employed his 24-inch
Clark telescope in the study of Mars during its opposition in
1896-97. The north polar cap was first seen in August 1896,
practically central over the planet's north pole, and covering a
stretch of 50° in latitude, equivalent to 1800 miles.

Seasonal changes are well illustrated in the colored plate
(see Frontispiece), showing Hesperia central at three epochs
months apart : in early spring the polar cap has just begun to
shrink ; in early summer canals are beginning to develop from
south to north ; in late summer they are fully developed and
the polar cap has vanished.

I70 Stars and Telescopes

Doubling of the 'Canals'

Most striking of all the phenomena of Mars is the periodic
doubling of the canali, also discovered by Schiaparelli, who
first detected in 1879 ^^ gemination of Nilus. Two years later
this occurrence presented itself extensively, and he established it
as a characteristic feature of the Arean continents. At about the
Martian equinoxes, just before and after the apparent inunda-
tion of the northern continent, occurs this surprising phenom-
enon — never shown by all the canali simultaneously ; but under
the proper seasonal conditions, the gemination makes its appear-
ance irregularly and in isolated instances. A few of the canali
even have never been seen doubled, of which the iVilosyrtis is
one. The gemination takes place rapidly, in a few hours or
days at the most ; and the original and previously single mark-
ing becomes paralleled with precision by its duplicate, the dis-
tances between the faint parallel lines being as small as 25
miles in some cases, and ranging up to 350 miles in others.
Reference is again made to M"" Lowell's excellent charts,
pp. 176-77, on which Ganges and Nectar (chart No. 3) are typi-
cal instances of greatest and least distance between twin canals.
Ordinarily the two bands appear equal, as well as parallel, and
of the same color and intensity ; but the gemination of course
is not to be seen at all, except at suitable seasons, and even
then it is visible only with difficulty.

This strange transformation from single markings into double
ones, was many years doubted by astronomers generally ; but
having now been verified on many occasions, and independ-
ently, by M. Terby, M' Williams, the Lick astronomers, and
many other observers, it has been most reliably confirmed by
M. Perrotin, formerly director of the great observatory on
Mont Gros, depicted on page 169. One of his excellent
sketches has already been given on page 164. The gemina-
tions are found to vary at different recurrences, so that they
cannot be fixed formations on Mars, as the canali themselves
are. After some months of visibility, the twin marking fades
out, and is seen no more till the favorable epoch again recurs.
If Schiaparelli's theory is the true one, the duplication can
occur only between the spring and autumn equinox of the
northern hemisphere. A recent opportunity, thus, was in
1890, and a later one occurred in January and February 1895 «

Tin Ruddy PlamI

171

but already M' Lowell, from his lofty station in Aiiiona,
had on 19th November 1894 seen FAiivn and Euphratet
double, and M' Williams in the same season had recorded
(he gemination of Gangis, EutmlBs, Crrbrms and others.
Again Ibe geminalion duly put in an appearance in 1897, and
was depicted in many drawings by M< Lowell. The width
of each of Ihe double canals was 15 to 40 miles, and their dis-
tance apart 135 10 170 mites, from centre to centre. The
oases were about zoo miles in diameter, and nearly all of ihem
were seen 10 lie exactly between the twin canals. Among
others who saw the double canals at this opposition was M.
Cerulli, one of whose drawings 13 here given, showing the

Eu men ide$-0 reus plainly double. It is somewhat curious that
those observers who have seen the gemination best are most
puzzled as to the cause of it. In fact, no plausible explanation
of this wonderful phenomenon has yet been advanced, although
manycrude guesses have been hazarded. M. Antuniadi ha*
sought to account for il by maladjustment of focus. That it
cannot be due to optical illusion or double refraction seem*
quite certain; rather the twin canal appears to have in each

The sketch on page 172 shows a portion of Mar* not com-
monly drawn, which with ordinary seeing affords scarcely any
detail, except mere outlines. At the same time a number of
Ihe more interesting and difficult feature* are shown. Descrip-

Stars and Telescopes

ad Mn> Iki ,

mditi'm.

I th ProMicr W.

H. Pick

niNO, wM

«p., -a,

r«!>5''V/™"J'o)

thmtlm = ,<,\ mil.

■1. TlUliiuarvalii,

<«rl,^

Tki m.0 It/I land

'i.fci,',

:™«rtrrffr

tacimd

apart. T*^ /*aH ttf Marx

tiinraril.

Iht din

cunun

^.^au

luiir limi mirkini llu p-n

.i*™ .ftM.

- tr inUk /«Wr laf. vActt

dilfllUI

•mnl fivm

ly minxU itna «/ am if tin

««-■/,(

tnlnadmri

The Ruddy Planet 173

five of this drawing, Professor Pickering says, ' Syrtis Minor

has nearly reached Ihe middle ofihe disk, and JTyriiijl/.i/tfr has
jusl come around ihc limb. . . . The southern [upper] snow cap
is bounded by a uniform black line, of the widih shown in the
■kelch, and prcsumalily due lo water. Near it is a small iso-
lated patch of snow, probably located upon a mountain range.
. . . On the termiiiatot is noticed a projection which is unusually
high, and has unusually sleep ends. Near the cemre of (he disk
Bie seen six lakes and three canals. They are all difficult ob-
jects. The diameter of the lakes was about o."l [36 miles], and
the breadth of the canals o."05 [iS miles]. These canals are
rather blacker than they should have been, and the southern
lake is rather too conspicuous. In the northern hemisphere
arc seen the hazy, radiating surfaces which jirobably precede
the formation of the canals. South of Ihc northern cloud the
<lark regions were brownish, north of il, gray; while the Syriu
Major region was greenish gray. The northern hemisphere
and the limb were yellow, the radiiiting bands very faint gray,
and the extreme north bounded by the canal and the fine line,
light green.'

Still, great as is the amptitication in this drawing, it will help
to present in a forcible manner the difficulties with which
astronomers must contend, if it is remembered that the area of
the full Moon's apparent disk is ^ooo-fold Ihal of the little
disk of Mars at bis nearest.

Martian Atmosfhere
Likelihood of an atmosphere encircling Mars is inferred from
temporary obscurations of well-known and permanent mark-
ings of Ihe planet's surface, frequently obsen'ed and satisfac-
torily attributed to clouds. An important occunence of this
character was recorded by M' Douclass, 24th September 1S94,
when the western half of Elysium appeared as it veiled for a
time by a cloud, suluequently dissipated. Also M' WILLIAMS
saw Mare Cimmtrium itself occluded, with considerable varia-
tions in the extent of the cloud envelope from day to day. In
October 1S94, the same careful observer sawwhat he considered
to be cloud, or mist, affecting the visibility of the extensive
land region north of Marc Cimmcrima ; and be thinks these
atmospheric occlusions are common and extensive. Mars, how-
ever, seems never to be covered, as the Earth generally is, with
vast cloud area* obliterating it* contineDt* and oceanic features.

174 Start and Telescopes

but hi* ikie* appear to be nearly perpeCualty clear, in every
climate and cvecy zone. Now and tbeii a few whitish spots,
changing their form and position, though rarely extending over
a very wide area, frequent the islands of Afart Auslrale, and
Elysium and Ttm/it of the northern continents. Theit varia-
tion during the Martian day ia well known, and SchIapaielli
thinlis them a thin veil of fi:^ taiher than a true nimbus of the
type yielding terrestrial rains; or possibly a temporary conden-
sation of vapor as dew or hoar frost.

The apectroBCope, in the hands of Secchi, Huggins, RutH-
ESFURD, VooEL, and Maunder, has given certain evidence
of absorption tines in the spectrum of Mars not due to our own
atmosphere ; and the inference has always been irresistible that
the ruddy planet is flutrounded by a gaseous envelope. D*
Huggins in 1S67 detected lines in the spectrum due to the
presence of watery vapot ; also in the same year, enibracing aik
opportunity when Mars and the Moon were at the same altitude,
he found the spectra of the two bodies practically identical,
while, on applying photography in 1S79, no lines or modilica-
lions peculiar to the planet's spectrum made their appearaniie.
Professor Campbell, in July 1S94, when Mars and the Moon
were again neat together, repeated the observation o( D*
Huggins by making direct and critical comparison of their
spectra under improved conditions of drier atmosphere and
more powerful apparatus, with the identical result that the two
spectra were alihe in every particular. This may be interpreted
as meaning, of course, that Mats has no more atmosphere than
the Moon itself, long known to be devoid of such an envelope.

But the obstacles to such interpretation are by no means,
slight. For example, as the planet turns on its axis, carrying
the spots from centre to edge of the disk, they gradually mell
from view, just as they would if seen through a greater thick-
ness of atmosphere. The temporary obscurations of certain
parts of the disk, supposably by clouds, will have to lie other-
wise accounted for. The amount of water, loo, must be inap-
preciable, lei alone the difficulties of explaining that periodic
and well-established expansion and shrinking of the polar caps,
if there is no atmosphere to act as a medium in the formation
and deposition of snow. Frofessor Campbell does not con-
sider the spectroscopic observatfons as proving that Mars has
DO atmosphere whatever, similar to our own, but simply that
thej set a superior limit to its extent. In the latter part of
1894, both D' Hoggins and EH Vogel repeated thcii

The Ruddy Planet 175

tion of (he spectrum of Mars, resulting in essential verification
of their earlier researches ; and Professor Keeler, in the win-
ter of 1S96-97, obtained photographic tests at Allegheny wliich,
as far as they go, agree with the visual results of Professor
CaMpbeli. But judgment upon the spectroscopic evidence of
a Martian atmosphere mu-iC be suspended until the planet is
again very favorably placed for observation in 1907. Mean'
while, photometric observations by D' MQller show that the
behavior of Mars, as to its phases, distinctly indicates an
atmosphere comparable in density with that of the Earth. Also
M' Lowell, in discussing a fine series of observations of the
diameter of Mats, made at bis observatory by M' Douglass in
1894. finds an unmistakable twilight arc of 13°, — independent
evidence of an atmosphere. The dimensions of Mars are
41S4 miles for the jiolar diameter, and 4106 for the equatorial,
the polar compression of the planet being jj^. 1)' ScHUK,
however, in 1S96-7 finds it as great as -^ with the heliometer.

In considering the possibility of an atmospheric envelope
surrounding our neighbor planet, a few fundamental facts
ought to be kepi in clear and constant view. Mars is a planet
intermediate in size lietwecn Moon and Earth ; twice the diame-
ter of the Moon equals the diameter of Mars ; and twice the
diameter oE Mars a]iproiiraately equals the diameter of the
Earth. As to masses the Moon is ,^, and Mars about \, the
massof our globe. We have here an abundant atmosphere;
the Moon has none; so it would seem safe to Infer that
Mars may have an atmosphere of slight density, — not dense
enough for the B])ectrosco]ie to detect, but dense enough to ac-
count for the observed phenomena of the Martian disk, other-
wise hard to explain. Indeed, Mattieu Williams, from
considerations of the relative size and mass of the Earth and
Mars, calculated that the ruddy planet is entitled to ^g the
atmosphere that our globe has, and that the mercurial barome-
ter would stand at about 5I inches at the sea level on Mars.

The climate of Mars, then, would seem likely to resemble
that of a clear season on a very high terrestrial mountain, a
climate of extremes, with great changes of temperature from day
to night. But safe speculation regarding the possibility of or-
ganic life upon the ruddy planet really hinges upon the selective
absorption of the Martian atmosphere, and whether it aids the
planet, as our atmosphere docs, in storing heat by prevent-
ing its radiation. And until it has become known whether the
Earth's surface has >ct reached, or has passed, that maximum

176 Stars and Telescopes

of secular temperature, toward which it must tend so long as it
continues to receive more heat from the Sun than it radiates,
obviously there is little use in speculating whether some other
planet may or may not have passed that critical epoch. The
inequality of Martian seasons is such that in the northern
hemisphere, the cold season lasts 381 days, and the hot only
306. The polar caps attain their maxima three or four months
after the winter solstice, and their minima about the same time
after the summer solstice ; and this lagging affords a strong
argument for a Martian atmosphere with heat-storing properties
similar to the Earth's.

It should be observed that the existence of fluid water upon
Mars would imply that the temperature of Arean climates is
comparable with our own. The relations of the planet's axis
to its orbit are similar to ours; but the supply of direct solar
heat is about one-half as great per square mile as that of the
Earth. Owing to the eccentricity of Mars's path round the
Sun, the surface of the planet receives at perihelion about one-
half more of solar heat than at aphelion; so that the southern
summers must be much hotter and the winters colder than
those of the northern hemisphere. The length of summer,
twice that of the terrestrial season, may amply suffice lo melt
all the ice and snow, an unusual condition of things which
aaually took place in October 1894.

But the aspect of the entire situation is somewhat modified
by a recent paper (1898) by D' Johnstone Stoney of Dublin,
whose investigations of the phenomena of planetary atmos-
pheres began about 35 years ago. His method is based on
the kinetic theory of gas ; according to which, if free molecules
travel outward, as they often must, with velocities exceeding
the limit that a planet's gravity can control, they will effect a
permanent escape, forever after travelling in orbits of their own.
So D' Stoney succeeds in accounting for the practically entire
absence of atmosphere from the Moon, and of free hydrogen
and helium from the Earth's encircling medium. Applying
the same theory to Mars, he is led to the significant inference
that water cannot in any of its forms remain upon that planet.
Without water, there can of course be no vegetation such as
we know; and in its absence much free oxygen is unlikely.
Under these circumstances, analogy to the Earth suppests to
him that the atmosphere of Mars consists mainly of nitrogen,
argon and carbon dioxide.

It is part of the province of physical science not only to

{Al tvary jo° r>/ Martian taitgitudf. and
tartkwArd. Bglotu taeh prtitnl'tlien ii
lo£ttkrr teiih llu miHU a/ Ikr most firaiHIHtui

Tki Ruddy Planet

177

obaerre and record, but to explain, natural phenomena. How
Ihen shall we explain the observed and regular fluctuations of
polar caps, and the seasonal development of canals and oases }
As the hypothesis of water afibrds the leadiesl and most natu-
ral explanation, we are diiven to the important conclusion that
the secular dissipation of water on Mars, while constantly pro-
gressing through countless ages, is not yet complete, although
his original store of water already exhibits marked signs of
approaching exhaustion.

From the motions of Earth and Mars given in previous chap-
ters, it is easily found that the ruddy planet goes 1 7 times round
the Sun in 33 years, 01, more accurately, 25 limes in 47 years.
These relations then indicate when Mars may be best observed
in the future, as the following table shows, in addition to those
epochs of the past half century when this planet was excep-
tionally well placed for observation : —

Favorable Times

OR Observing Mars

l.^D,«,rc

.,f Mir^frcm

n II

Inmilci

ICF

Mk.

,n1i:'S?i

yHs

August iS

34,610,000

200S.

28*

July 22

36,370,000

August 4

37,660,000

1S77

August 21

Sept. 2

34,950,000

August 6

1SQ4

July 26

Oct. 13

40,000,000

1907

Sept. 24

S.'^

39.000,000

1909

August 13

36,000,000

4 s.

All delicate questions concerning the planet's surface, its
southern hemisphere in particular, must now be tabled for
many yeara. Meanwhile, the northern regions are being faith-
fully interrogated as they come more and more within reach ; and
the Intervening years will afford opportunity for thoroughly
discussing all the earlier drawings, and, in the light of large
and freshly garnered harvests, welding them together into a
homogeneous system, capable of consistent and reasonable
interpretation.

178 Stars and Telescopes

In additon to the references for this planet already given on
page 147, consult first of all Flammarion's comprehensive work
entitled La Planlte Mars etses conditions cT habitabiliti : synthase
gitUrale de ioutes les observations (Paris 1892). Also the follow-
ing, comprising the bulk of the more important Martian* liter-
ature, both popular and technical, chiefly since 1885 : —

Williams, *'M.citoro\og^* Fuel 0/ the Sun (London 1870).
Green, At Madeira in 1877, Mem. A\ A. S. xliv. (1879), 123.
Hartwig, ' Diameter,' Pubi. Astron. GtselL xv. (Leipzig 1879).
Young, * Diameter,' Am. Jour. Sci. cxix. (1880), 206.
ScHRciiKR, Areographische Beitrdge (Leiden 1881).
Maunder, The Sunday Magazine^ xi. (1882), 30, 102, 170.
Trouvelot, Comptes RendttSy xcviii. (1S84), 788 ; V Astronomic

iii. (1884), 321 ; Observatory^ vii. (1884), 369.
Bakhuyzen, ' Rotation,' Ann. Sternwarte Leiden, vii. (1885).
Green, * Northern hemisphere,' M. A\ A\ A. S. xlvi. (1886), 445.
Perrotin, ' Les Canaux,' Bidktin Astron. iii. (1886), 324.
Stanislas Meunier, Pop. Sci. Monthly, xxxi. (1887), 532.
FiZEAU, Janssen, Perrotin, Terby, Comp. Rend. cvi. (1888).
Flammarion, Perrotin, Comptes Rendus, cvii. (1888).
Maunder, 'Canals,' The Obsenuitory, xi. (18S8), 345.
Niesten, Bulletins Acad. Roy. Bcli^ique, xvi. (1888), Nr 7.
Flammarion, ' Variations,' Bull. Soc. Astron. de France (18S8).
Perrotin, 'Canals,' L"" Astronomic, vii. (1S88). 366.
Teruy, Cielct Terre, ix. (1888), 271, 289 ; xii. (1891) ; Mimoires

couronnis Acad. Bflgiquc (1888); Bull. Acad. Belgique^ xx.

(1890); C Astronomic, ix. (1890).
Wilson, ' Canals,' Sidereal Messenger, viii. (1889), 13.
Gerigny, ' Les Maries,' V Astronomic, vxW. (1889), 381.
Young, The Presbyterian RevintK x. (1889), 400.
Hall, Holden, The Astronomical Journal, viii. (1889), 79, 97.
Schiaparelli, V Astronomic, viii. (1889), 19, 42, 89, 124;

Himmel und Erdcy i. (1889), I, 85, 147.
Meisel, Astronomische Nachrichten, cxxi. (1889), 371.
Scheiner, ib. cxxii. (1889), 251.

WiSLiCENUS, ib. cxx. (1889), 241 ; cxxvii. (1891). 161.
Pickering, ' Photographs,' Sid. Mess. ix. (1890), 254, 369.
Ritchie, ib. ix. (1890), 450.
Williams, A. S., ' Canals and markings,' Joidr. Brit. Astron.

Association^ i. (1890), 82.

Flammarion, V Astronomic, th. (1891), xi. (1892).

LoHSE, Publ. Astrophys. Observatorium Potsdam, N"" 28 (1891).
y

The Ruddy Planet 179

LoHSE, Maunder, Niestkn, Jour. Brit. Astron. Asseiiation,

ii.(r892),4i7.4y. W-
TissERAND, ' Diameter,' Bulletin Astronomique, ix. (189;), 417.

FLANMARtON, PERROTIH, MEUNIER, Comp. Rind. CXV. (1893J.
LOCKVER, J. N., Naturi, xlvi. (1891)1443.

Barnard, Com STOCK, Pickering, Terbv, Wclson, Young,

Aslroiumy aad Ailra-Piyiia, xi. {1893).

Flamuarion, Lockver, Pickering, A'ature, xlvM. (iSgz).

Ball, In Starry Rialmi (London 1892), chapter xii.

Bai.L, The Fortnightly Revi..-vi, lii. (1892), z88 : In the High

Heavens (London 1893), chapter vi.
Peal, ' Distribution of land and water,' J9ur. Brit. Aitren.

^««/W/(i.H,iLL. (1893), 223-
CoMSTOCK, ' South I'olar Cap,' Aslraii. Jour. xiii. (1893), 41.
KeeLER, Memoirs A'eya! Astronomical Society, li. (1S93), 45.
Abetti, 'South Polar Spot,' ^rffOM. Nachr, cxxjtiii. (1893), 15.
MAUNDER,yi'H)-. Brit, Aslron. Associalioa. iv. (1894), 39?.
Douglass, Ixjwell, Pickehin(j, Schaeberle, Schiaparelli,

and others, Astronomy and Astro-Physics, xiii. ( 1S94),
Flammarion, L' a strom-mie, xiii. (1894), 447.
Lowell, Popular Astronomy, ii. (1S94).
Meyer, Die Physische Beschaffenheit (Herlin 1894).
Campbell, ' Atmosphere,' Publ. Astren, Society Pacific, vt.

(1894). JJ3, 273.
AWTOKIADI, Lowell, Nature, li. (1S94), 40, G4, 87, 259.
HuGOiNS, Knobel, Willtams, The Ohsen-atory, xvii. (1894).
Lockver, W. J,, Nature, 1. (1894), 476, 499
Young. ' Diameter,' The Astronomica! Journal, xiv. ( 1895), 163.
Brenner, Sketches 1894, Astron. Nackr. cxxxvii. (1895), 49.
Ellery, The Astrophysical Journal, i. ( 1895), 47.
IjawELL, Mars (Koston 1895).
SCHEAPARELLI, Osservatloni astronomiche e fisiche sulP cisse di

rolasione et lulla topografia del fiianeta Marte (Rome 1897),

Also 4 previous memoirs by same author.
Perrotin, -Zones,' The Obstrvatory, xx. (1897). 131.
Brenner. Ahhandl. KSn. Aiad. IViss. Berlin, 1897.
Lohse, Puil. Aitraphys. Obsen-ilorium Potsdam, xi. (1898).
Stonev. • Atmosphere.' Astrephys Jour. vii. (1898}, 44.
CkrULLI, Marie nel 1896-97 (Collurania 189S).
Lowell, Annals Lowell Observatory, i. (BoBlon 1898).

Bibliographic lists in the ' Smithsonian Report ' each year
comprise many additional titles. For papers since 1895 consult
the bibliographies in The A strophysitai Journal.

i8o Stars and Telescopes

The Plurality of Worlds, etc.

The absorbing popular interest of this subject, and the serious
attention accorded it by many eminent writers, render a brief
list of the better literature worthy of the space here given it.

HuYGENS, Cosmotheoros (Opera^ ii. p. 641) (1755).

FoNTENELLE, Etitretiens sur la Pluraliti des Mondes (Paris
1852) ; with notes by Proctor, Knowledge^ vi. (1884); vii.
(1885).

Whewell, The Plurality of Worlds (London 1853).

Brewster, More Worlds than Ofu (London 1855).

Smith, H. J. S., Oxford Essays (1855), 105.

Flammarion, La Plurality des Mondes habitis (Paris 1863).

Proctor, Otlur Worlds than Ours (London 1870).

Searle, G. M., The Catholic Worlds xxxvii. (1883), 49; Iv.
(1892), 860.

Miller, W., The Heavenly Bodies (London 1883).

Proctor, ' Life in Other Worlds,' Knowledi^e, vii. (1885).

Burr, * Are heavens inhabited ? ' Presby. Rev. vi. (1885), 257.

Porter, Our Celestial Home (New York 1888).

Searle, G. M., Pub. Astron. Society Pacific^ ii. (1890), 165.

Flammarion, V Astronomies x. (1891).

Guillemin, * Communication with the planets,' Popular Sci-
ence Monthly^ xl. (1892), 361.

Ball, *Life in other worlds/ The Fortnightly Review^ Ivi.
(1894), 718; McClure's Magazine, v. (1895), H7'

Flammarion, No. Am. Rev. clxii. (1896), 546.

Janssen, Popular Science Monthly^ 1. (1896), 812.

Serviss, ib. lii. (1897), 171.

For the periodical literature, much of it worthless, consult
under Worlds, the indexes of Poole and Fletcher, often
cited ; also, Matson's References for Literary Workers (Chicago
1892) contains, at pp. 410-412, abundant references to papers
on the plurality of worlds, an interminable subject.

CHAPTER XII

TTJHEN Kepler had shown that the planetaiy
* * orbits are ellipses, and Newixjn had proved
that this is a necessary consequence of their being
attracted toward the Sun with a force varying in-
versely as the square of the distance from him, it was
natural to surmise that comets also might be moving
round the Sun, in ellipses so much more eccentric
that these bodies would be visible only in those parts
of their elongated orbits which are nearest to the Sun
and Earth. As the law of equable description of areas
would of course hold good in their case, causing them
while in these nearer parts of their courses to move
much more rapidly than in any other part, the comets
would obviously be visible during only a small portion
of their whole orbital revolution.

Newton applied these principles to the splendid
comet of 1680 (visible a few years before the publi-
cation of the first edition of the Principia in 1687),
and found that it was moving in an ellipse of so
eccentric a character as to approach very nearly in
form to a parabola. It was thought by himself and
by Hallev that it might be identical with great
comets recorded as having been seen in b. c. 44, a. d.
531, and A. D. It 06, and that the period was about
S 75 years in length. Subsequent investigations have
not confirmed this particular conjecture, and it is

l82 Stars and Telescopes

probable that the actual period of that remarkable
comet (which made such an exceptionally close
approach to the Sun) amounts to, not hundreds, but
thousands of years ; so that any previous appearances
most likely took place before historic dates. But in
regard to a fine comet which appeared two years
later, in i68z, HaLLEV was able, after calculating the
elements of its orbit, to show that

I they were almost precisely the same
as those of comets observed in 1531
and 1607, so far at least as could be
decided by the observations accessible
to him. Hence in this case there was
ground for concluding that all these
appearances were one and the same
comet ; that its period was about 75
or 76 years in duration, and that it
would probably return in 1758 or
HALUv's coMtT 1759. ^^ '^^^ ^ fcturn, being first
IN i8js seen by Paloz-sch, near Dresden, on

(Struvi) Christmas Day, 1758; and it has

ever since been known by the name
of the illustrious astronomer who had so confidendy
predicted its return. It passed its perihelion at
appearance, 12th March 1759, and at the next re
i6lh November 1835. According to PoNTtcouLA>rr,
it will be due at perihelion again in 1910. The di
tanceof Halley's comet from the Sun varies between
0.58 and 35-3, in terms of the Earth's mean distance
that of Venus, expressed in the same way, being 0.7.
and of Neptune, 30.05.

A very large proportion of the known comets travel
in parabolas, or in ellipses of such great eccentricity
as to be undistinguishable from parabolas during the

Comets 183

time of visibility.* Following are a few particulars
about the most remarkable comets which are moving
in elliptical orbits of moderate eccentricity.

*i The trastvorChy records of cometary apparitions through
out all past time are about 1000 in number, and the increase i>
very rapid at the present day. because many skilful observers
with suitable telescopes are continually searching far comets.
Nearly one half of the entire number (rather more than 400)
have been subjected to mathematical calculation, and the paths
of their motion determined. It is only by the agreement among
the elements of these paths that the identity of two or more
comets can be proved ; for the physical appearance and charac-
teristics of a given cornel are generally very different at the
different returns. When a cornel is Rrsl discovered, if remote
from the Sun, its appearance will usually resemble that of the
Pons- Brooks comet (page tSS,/i/t); and a large proportion of
telescopic comets never develop beyond this simple stage. Bui,
if the comet is a great one, on approaching nearer a nucleus
will begin to aggregate in that part of the hazy mass on the
&rther side from the Sun ; from this centre the wonderful phe-
nomena of the coma, or head, soon manifest themselves, un-
folding in envelopes or sheaths, as in Cogcia's comet of 1874
(page 205), or more often opening toward the Sun, like the

1 84

Stars and Telescopes

Of the periodic comets, Halley's, by far the most
interesting, has been traced with high probabihty for

illustration of ihe head of the great comet of 1861. (A general
view of the entire object, as it appeared in the northern heav-
ens, is given above in miniature. This remarkable body, dis-
covered 13th May 1861 by M' Tebbutt of New South Wales,
had a tail which appeared to stretch one third the way round
the heavens. The Earth and Moon passed through the tail
of this body, joth June l36l, with no apparent effect save a
peculiar sky glare. According to Sir John Hbrschel, this
comet far eiceeded in brilliancy all other comets that he had
ever seen, even those of iSti and 1S53. It recedes from the
Sun to a distance nearly twice that of Neptune, in an elliptical
orbit, with a period of 410 years.) On the side of the nucleus
opposite the fan, and almost in-
variably directed away from the
J Sun, begins Ihe development of
the tall of the comet, usually the
" ing characteristic of a
1. Comelary tails some-
:s appear almost straight, and
• varying degrees of

net (1836 V|,
in the accompanying lllus-
Other comets (for ex-
ample, DoNATj'ii, the sixth comet
of 1858, shown oil page 203) have
tails both straight and curved.
When a comet has passed its
perihelion, the tail will, in nearly
s, be found to have swung
round and changed its apparent
position with respect (o thecomet't
motion ; so that it will still remain
"" "■" '™' true that the tail is directed from

the Sun, and the comet will move away from the Sun with its
head following the tail. The early astronomers described the
s position as the ' beard.' Generally the mediai

of the la
changes
Coggia';

il of a

irge c

s dark; though thii

n tbec

Comets i8j

nearly 1900 years. Dion Cassius tells us of a comet
seen in B.C. 12, about the time of the death of the

The taila of cornels appear to be made up from Ihe material
particles first projected toward the Sun from the nucleus in a
manner incompletely understood; afterward curving ovet and
forming the cup-shaped sheaths of the coma, and then repelled
by the Sun to form Ihe trains of various types, [t seems likely
that these Ulmy, evanescent objects exist as hollow cones in
space. BtssEL ill Germany, Norton in America, and in par-
ticular Bredichih in Russia, have contributed most lo estab-
lish a theory of comets' tails which accounts for nearly all the
facts of observation. Bkedichin's theory is that the straight
tails, like those of the comets of 1S5S and 1861, are ptobabljr
composed of hydrogen, Ihe Sun's aclion of repulsion upon
which would exceed twelve times the attraction of gravitation;
the moderately curved tails (the usual type) are hydrocarbons
in gaseous form;, with an action of repulsion slightly in excess
of gravity along Ihe inner edge of the tail, and increasing to z^
times that amount on the outer edge ; and a few comets exhibit
still a third type of tail, — short, sharply curved, probably doe
to the vapor of heavier substances (iron, chlorine, and sodium),
upon which the repulsive effect is relatively weak, varying be-
tween ^ and 1 thai of the Sun's gravilative action. In rare
instances a comet has been known to exhibit tails of all three
of these types. Probably ihe tail of a comet is formed by an
expenditure of the substances composing the nucleus, in sucb
a manner ihat the particles once leaving the nucleus are never
returned to it The larger comets, (hen, must grow smaller
and smaller at every return to perihelion. Undoubtedly this is
the true explanation of the faint and tailless condition of most
of the short period comets, whose encounters with solar dis-
rupting influences have been frequent.

The visibility of cornels chiefly depends upon two condi-
tions, — their intrinsic lustre, and their position in space rela-
tively to Sun and Earth. While some are seen for a few days
only, and ihe average visibility is about three months in dura-
tion, on rare occasions a comet can be observed throughout an
entire year, and the great comet of iSii was visible for 17
months. In nearly all cases, the curve traversed during visi-
bility is only a small part of Ihe entire path, so that a degree
of uncertainty exists in cometary orbits which does not obtain
in determining the paths of planets. — D. P. T.

1 86 Stars and Telescopes

great Roman general Agrippa, and the Chinese annals
also mention a comet seen at a date corresponding to
this. D' Hind has shown that this was probably the
first appearance of Halley*s comet. It is also prob-
ably referred to by Josephus as seen in a. d. 66, when
the Jewish rebellion broke out which led to the de-
struction of Jerusalem four years afterward by the
Roman army under Titus. The Chinese records also
speak of a comet seen at that time, as well as of
another in a. d. 141, which was probably the same.
In A. D. 218 it appears to have been noticed both in
China and Europe, being followed (according to Dion
Cassius) by the death of Opilius Macrinus, the Em-
peror, soon after his defeat at Irumae, near Antioch,
by Elagabalus. In the years 295 and 373 we are
also able to recognize with much probability Halley's
comet in accounts furnished by Chinese annalists;
and it can hardly be doubted that this comet was seen
in A. D. 451, not only in China, but also in Europe
(about the time of the great defeat of the Huns under
Attila near Chalons-sur-Marne by iExius and Theo-
DORic). In A. D. 530 or 531, during the reign of
Justinian, ' a very large and fearful comet ' was seen,
which (as already mentioned) Newton and H alley
thought to be an appearance of the comet of 1680.
The fuller observations of the Chinese have become
accessible to us since their time, and show that it
was more likely the comet of 1682.*^

♦0 ' Ugly monsters * that comets always were to the ancient
world, the mediaeval church perpetuated the misconception
with such vigor that even yet these gauzy, harmless visitors from
the interstellar spaces have a certain * wizard hold upon our
imagination.' This entertaining phase of the subject is invitingly
treated in President Andrew D. White's scholarly * History
of the Doctrine of Comets * {Papers of the American Historical

Comets 187

Like some previous appearances, the returns of
A. D. 608 and 6S4 were, so far as is known, recorded
only in the Chinese annals; but in a. d. 760 a re-
markable comet was chronicled, not only by their
annahsts but by a Byzantine historian in the reign
of CoNSTANTiNE CoPRO^fYM^ra, and D' Hind thinks it
little short of a certainty that this too was a return
of Hallev's comet. Also, appearances of it were
probably seen both in Europe and China in a. d, 837
and 913; likewise in a. d. 989, as related in the
Chinese records only. The next return was in the
year of the Norman Conquest, On the Bayeux
tapestry there is a representation of some people gaz-
ing at a comet which appeared soon after Easter
a. D, 1066, while England was threatened with two
invasions at once, — both taking place in succession,
but with very different terminations. This comet also
was doubtless Hallev's, and it was seen again in 1 145,
1223, 1301, 1378, and 1456. In the latter year it
seems to have been very conspicuous, making a great
sensation in Europe, where the Turks, who had taken
Constantinople only three years previously, were ad-
vancing into Hungary, when they were defeated and
repulsed at Belgrade by the famous Hunyadi. At the
succeeding return in 1531, the comet was apparently
less brilliant ; at any rate our knowledge of its path on
that occasion depends entirely upon the obsen'ations
of Peter Apian, or Bienf.witz. In 1607 this comet

AstocialioH, vol. il.); while for a very extensive collection o(
the literature of comets, both historical and scientific, reference
may be had to the CaMlogue of thi Crawferd Library of the
Royai Oisematory, Edinburgh (1890), pp. 89-142. The titles
of many other important papers and treatises on comets are
given at the end of this chapter. — D. p. T.

i88

Stars and Telescopes

was observed by the illustrious Kepler ; and it was by
a comparison of elements principally deduced from
his observations in that year, and Apian's in 1531, that
Hallev identified these comets with the one ob-
served by himself in 1682.

Two other comets have periods a little shorter than
Halley's, but their history cannot be traced farther
back than the apparitions preceding the last. One
of them, found at Marseilles, aoth July i8iz, by Pons,
the most successful of all discoverers of comets, be-
came visible for a few days to the naked eye, and

passed its perihelion on 15th September, the very day
on which the conflagration of Moscow broke out dur-
ing the French occupation of that city under Napo-
leon, Encke's calculations made its period 70^
years. Rediscovered by M' Brooks at Phelps, New
York, 1st September 1883, renewed observations
showed that the period was slightly longer, and that

Comets

189

h would arrive at perihelion in the. January following,
— which it did on the 25th of that month. The
next return will be due in 19SS- The other comet
was discovered by Olbers at Bremen, 6th March
1815, passed its perihelion 26th April, and was cal-
culated to have a period of about 7 2 years. It was
rediscovered by M" Brooks at Phelps, asth August
1887, and passed its perihelion 8th October; so
that its period is not quite 72^ years, and it may be
expected again early in i960.

All other comets of this class have much shorter
periods, and with one exception, they attain a dl»>
tance from the Sun which
never much exceeds that
of Jupiter. Encke's comet
is the most interesting.
First discovered by Mft-
CHAiN at Paris in 1786,
and again independently
by Caroune Herschel at
Slough in 179s, and liy
Thulis at Marseilles in
1805, it was each time
supposed to be a different
body. Pons, the first to
see it in November 1818,
also imagined that it was
a new comet; but at that (i7so-ig,B>

return Encke (who always

called it Pons's comet) showed that it was moving in
an orbit with a period of only about 3J years, and
that it was identical with those just mentioned. He
predicted another return in the spring of iSai, which
was observed in that year at Paramatta, New South

HERSCHEL

ipo Stars and Telescopes

Wales; and it has been seen at e\-ery subsequent
return, passing perihelion on the last occasion in May
1898. Its next return is due in the summer of 1901.
Of all the periodic comets, Enckf's approaches
nearest the Sun. When in perihelion, it is very near
the orbit of Mercury; and in 1835 it made a rather
close approach to the planet itself, affording the
means of determining the value of Mercury's mass.
Even in aphelion, Encke's comet does not recede so
far from the Sun as several of the small planets."

*' This small, though very important comet, the se»entli
diicoveied by Miss Herschel, one of Che most iiidefaligable
of the early searchers for comets, was formerly just visible
without the telescope, but at late returns it has been Taintet, so
thai il cannot Tiow be seen without optical aid. At no two
returns has its physical appearance been observed to be the
tame. As drawn by W. Struvf. in 13:8, it was almost struc-
tureless, being very like the typical telescopic comet shown o

e 188. In ■:

it had 11

a degree long,
pointing away from, and an-
other much smaller directed
toward, the Sun. In 1871
Enckk's comet eihibited
many freaks, — the nucleus at
one lime having the shape of
a star-fish, seen obliquely at
one side of the globular mas}
of Che comet, and later a sin-
gle straight lilament or tail
shot out a long distance from
the coma. At subsequent re-
turns no physical phenomena,
of especial interest have been
developed ; it has been grow-
ENCKE (1791-1865) ing irregularly fainter, and at

its last return in 1894-95, it
wa« first recorded, 31st October of the former year, on a pho-
tographic plate, by D' Max Wolf of Heidelberg, and during

Comets 191

Another very remarkable periodic comet is that
known as Bieia's, tlie periodicity of whicti was de-
tected at its return in 1826, when it was discovered

the neit few days ii was near the limit o( visibility with the
30-inch telescope at Nice.

At the return of ihis comet in 1S38, Ekcke, Che eminent Ger-
man astronomer, then director of the Observatory at Derlin,
was enabled to establish a remarkable progressive diminution
in its period, amounting to about z^ hours at each return to the
Sun, and this circumstance led to the immediate reneiral of
the old hypothesis of a resisting medium filling all space; not
dense enough to interfere with ihe motions of massive bodiei,
like the planets, but of such nature as might be conceived to
retard the motion of tenuous bodies like cornels. Subsequent
observations have fully confirmed this acceleration from a pe-
riod of 1212*79 in 17S9 to 1210^,44 in '85S, as ascertained by
EncKE in the latter year ; but there is no way of finding out
whether a resistance to the comet's motion takes place every-
where throughout its oibit, or only when near the Sun. Prob-
ably the latter is true. I'he resisting medium, however, is not
accepted by astronomers generally, because it is felt thai its
action upon other comets should be appreciable; but no such
effect upon any other cornel has ever been detected. (For the
literature of the resisting medium, consult Houzeau's ^/M>
grapkit Glnhaii, vol, ii. col. 6S0-6S6,) Enckk conimucd hia
computations upon this comet down lo his death in 1865; and
since that time his labors have been continued by vok Asten
and Backlund of Pulkowa. According to their researches,
the progressive shortening of the comet's period, although still
going on, was suddenly, about 1868, reduced to only half its
former rate; so that the theory of a resisting medium must
either be modified, or abandoned altogether. Professor YouNc:
has suggested a regularly recurring encounter with a cloud of
meteoric matter; and others have suggested a possible change
in the physical character of the comel. Especially marked in
the case of Encke's comet has been that apparent contraction
of bulk (as also exhibited in several other comets) on ap-
proaching the Sun, and the subsequent expansion when reced-
ing from perihelion; when in this region Encke's comet is
only ^ its visible diameter when it first comes into view. The
general eiplanation projiosed by Sir John IIerschel is that

192 Stars and Telescopes

by BiEiA at Josephstadt in Bohemia, First found,
however, in 1772 by Montaigne at Limoges, it was
also independently discovered (being supposed, as in
i8i6, to be a new comet) by Pons in 1805. The
period was detennined in 1826 to be about 6J years,
and the comet was accordingly observed again in 1831,
in 1S45— 46, and in 1853. At the second of these
appearances it was seen to have sep-

Iarated into two portions, the relative
brightness of which fluctuated consid-
erably, — the investigations of Hub-
bard, of Washington, afterward show-
ing that this disintegration probably
occurred in the autumn of 1844, Both
portions returned, but at a somewhat
greater distance from each other, in
1852. But since then the comet has
•I■LA'^i DOUBLE oi.MBr "ot bccn secR at all, — at any r:ite as
ixt^ Ftbriuiry \»i,t^ a comet, — though it is supposed that
a. shower of meteors sometimes seen
about the end of November, when the Earth passes
near the comet's orbit, may form part of its dispersed
material. (See page 219.)

Pons discovered another comet at Marseilles, 1 zth
June 1819, and Encke's investigations showed that it
was moving in a short ellipse with a period of about
5^ years. It was not, however, seen again until
1858, when it was rediscovered as a new comet by

near the Sun a large part of t)ie conictary substance 19 tendered
invisible by evapotalion, just as a cloud ot fog inighi be.

At the recent near approach of F.ncke's comet to llic planet
Mercury in 1891, D' BaCKlUNU determined anew the mass of
that planet, making it t?raiiAaa Ihat of the Sun, a value proba-
bly loo small. —Z>. /". T.

Comets 193

WiNNECKE at Bonn, who, after determining its orbit,
noticed its identity with the discovery made by Pons
nearly forty years previously. Hence it is generally
called Winnecke's comet. It was observed again in
1869 and 1875, but not in 1863 and 1880, when its
positions were very unfavorable. It was observed at
the return of 1886, and again in 1892, passing its
perihelion in June. The period having increased in
length, the next return came early in 1898.

A faint comet found by M. Faye at Paris in Novem-
ber 1843, with a period of about 7 J years, has been
observed at every subsequent return, the last in 1895,
when it was rediscovered by M. Javelle of Nice, 26th
September, about six months before perihelion passage.
It is next due in 1903.

Brorsen*s comet, discovered at Kiel in 1846 (period
about ^\ years), and not seen in 1851 and 1863, was
observed in 1857, 1868, 1873, ^^^ iS79* As it was
not seen in 1884 and 1890, some catastrophe has
perhaps overtaken it. M' Denning's comet of 1894
may be a portion of it.

In 1 85 1 D* Arrest at Leipzig discovered a small
comet. It was found to be moving in an ellipse with
a period of about (i\ years, and was observed again
(but only in the southern hemisphere at the Cape of
Good Hope) in the winter of 1857-58. In 1864 it
was invisible, being unfavorably placed; but it was
observed at the returns of 1870 and 1877, though not
in 1884. It was, however, seen again in 1890, and
last in the summer of 1897. The next return is due
in the autumn of 1903.

Another comet of more than double this period,
seen at several returns to perihelion, though not con-
secutive, is known as Tuttle's, from its discovery by

SAT — 13

194 Stars and Telescopes

M' H. P. TuTTLE at Cambridge, Massachusetts, in
January 1858, when its periodicity was detennined.
Previously discovered by MfecHAiri at Paris in 1 790,
its period is about 13I years, so that it had returned
four times without having been noticed. It was, how-
ever, observed in 1871, and again in 1885, when it
passed perihelion nth September. Another return
is due in the summer of 1899, Tuttle's comet is
near the Earth's orbit when in perihelion, and wanders
beyond the orbit of Saturn before reaching aphelion.

Two comets of short period were discovered at
Marseilles and Milan by Te.mpel. The first of these
(period about six years), found in r867, was observed
at the returns in 1873 and 1879, passing its perihelion
on both occasions in May ; but it has not since been
seen, and M. Gautier has shown that the period
has been lengthened by the perturbing action of
Jupiter. Tempel's second, discov-

Iered in 1873 (period about 5J
years), was observed in the autumn
of 1878, but esc.ipcd observation
during the subsequent returns in
1883 and i88g. It was, however,
re-detected near perihelion in May
1894, and the next return is due
in 1899. Tempel's third, found in
November 1869, was not recog-
nized as a periodic comet until
after it had been rediscovered in
swift's comet, sth 1880 by D' Swift, then of Roche s-
ACRiL 1S91 ter. Soil is usually called Swift's
{Frirm afkBisr-"^ h comct ; and the period being about
5 J years, an unoteerved return must
have taken place in 1875. The comet was due at

Comets 195

perihelion again in 1S86 and 1897 ; but, as in 1875,
it was unfavorably placed, and escaped observation on
both these occasions. The last observed return took
place in 1891, when the comet was detected on aSlh
September, and passed its perihelion in the middle of
November. Another return is due in 1902,

A bright comet discovered by D' Max Wolf at
Heidelberg, 17th September 1884, and moving in an
elliptic orbit (period nearly seven years), returned
according to prediction in the summer of 1891, and
was observed again in 1898.

M' FiNLAV at the Cape of Good Hope discovered
acomeC, 26th September 1886, which passed its peri-
helion on 22nd November following, and has been
calculated lo have a period of about b\ years. A
return duly took place in 1893 ; when the comet was
rediscovered by M' Finlay himself, 17th May, and
passed its perihelion i6th June.

A comet discovered by De Vico at Rome, sand
August 1844, and calculated to have a period of
about 5 J years, was thought to be identical with one
observed by La Hire at Paris in 1678, between which
time and 1 844 thirty periods would have elapsed. It
was not seen again for more than fifty years, except-
ing that GoiJ)SCHMiDT obtained a single observation
of a comet, i6th May 1855, which may have been
De Vico's, though the identity is not proved. A small
comet discovered by M' E. Swift on Echo Moun-
tain, California, 20th November 1894, moves in an
orbit very similar to that of De Vico's comet. D'
Schulhof's researches show clearly the identity of the
two bodies, with fluctuations in brightness ; also that
the last return was delayed by the attraction of Jupi-
ter, which was moving near the comet in 1885-86,
and still nearer in 1897.

196 Stars and Telescopes

M' Barnard discovered at Nashville, Tennessee,
July 1 884, a faint comet with a period of nearly 5 \ years.
It was not seen at the returns of 1889 and 1895.

A comet discovered by M' E. Holmes at Islington
6th November 1892, has a period of about 6| years,
and was just visible to the naked eye for a few days.
As it passed perihelion 20th June, nearly five months
before discovery, a return is due in 1899. Its orbit
is more nearly circular than that of any other comet.

Very remarkable seems to have been the career of
the comet of 1 7 70, commonly called Lexell*s, which
was a truly unfortunate body in the way its motions
were disturbed by the giant planet Jupiter. While very
near the Earth it was discovered by Messier, 14th June
1770 ; and a few days afterward it approached within
a distance of little more than seven times that of the
Moon. On calculating its orbit, Lexell found that it
was then moving in an ellipse with a period of about
5 J years; but that had not long been the case, for
in 1767 it had approached Jupiter within one sixtieth
part of the radius of his orbit, and the influence of his
attracting mass was so powerful that the comet's course
was completely changed. At the return of 1776, its
position was such that it could not become visible ;
and in 1779, before another return, it approached
Jupiter again, much closer even than before, coming
indeed within the distance of his fourth satellite. This
again completely changed the comet's orbit, and made
the period very much longer than Lexell's calcula-
tions had determined it to be in 1770. On 6th July
1889, M'^ Brooks, of Geneva, New York, discovered a
comet moving in an ellipse of short period. D'
Chandler showed that this body also made a very
near approach to Jupiter in 1886, and suggested its

Comets

197

identity with Lexell's comet of 1770; and the sub-
sequent investigations of D' Poor have corroborated
this idea. As the period of Brooks's comet is seven
years, it was visible again in 1896.

The above comprise all comets of short period
known to return.*^ One discovered by Rgott in No-

*2 For convenient reference, the returns of many periodic
comets are here tabulated, from 1898 onward: —

Returns of Periodic Comets

Date of
Return to

Periodic
Time

Name of Comet

Appantioos
Previously
Observed

Penheiion

•

Years

1898 April

5.818

Pons-Winnecke

1898 May

3303

Encke

1898 Tune
1898 June

8-534

Swift (1889V1)

6.821

Wolf (1884 III)

1898 September

6.507
8.687

TempeLi (1867 II)
Denninc; (1881 v)

1899 January

1899 March

33.178

TEMPEL4 (1866 I)

1899 April

6.309

IUrnard (1892 v)

1899 May

13.760

Tuttle (1858 I)

1899 May

b.909

Holmes (1892 in)

1899 July

5.211

TempeLj (1873 II)

1900 February

6.622

FiNLAY (1886 VII)

1900 July

5.800

De Vigo- Swift

1900 October

5-398

Barnard (1884 11)

1901 January

5456

BrORSEN (1846 III)

1901 August

7.480

Denning (1894 i)

1901 August

3303

Encke

1902 December

5-534

Tempel, Swiff

1903 September

7.566

Faye (1843 "0

1903 November

7-073

Brooks (1889 v)

1903 November

6.691

d'Arrest(i85i II)

1910 Tune
1955 March
1900 April

76.37

Halley

71.48

Pons-Brooks

72.63

Olbers- Brooks

,98s

123.0

SWItT(l862 III)

For the most part these are inconspicuous objects, and some
of them are never visible without the telescope. They can be

{

198 Stars and Telescopes

vember 1 783 was thought to be moving in an ellipse
with a period of about five years ; but this was un-
certain, some thinking the period ten years, and, at
any rate, the comet does not seem to have been ob-
served either before or since. Also, one that was dis-
covered by M' Denning of Bristol, 4th October 1881,
has a period of about nine years ; but the comet has
not been seen since, probably owing to perturbations,
as it approaches the paths of several planets.

Other remarkable comets, possibly seen at more
than one return, cannot yet be classed as periodic
bodies. Great similarity has been noticed between
the elements (so far as they could be determined from
descriptions of its course) of the splendid comet of
1264 and those of the fine comet observed in 1556,
about the time of the abdication of the Emperor
Charles the Fifth. This was first pointed out by
DuNTHORNE in 1 75 1, and attention was afterward spe-
cially called to it by Hind, who thought it extremely
probable that these were two consecutive appearances
of the same comet, and that it had returned after a
sojourn of about three hundred years in the depths of
space. The effect of planetary perturbation would
delay another return, which, on the whole, was thought
most likely to take place about i860. Neither then,
however, nor at any time since, has the comet put in
an appearance. The cause of this is as yet unknown ;

found by means of ephemerides, or tables of their positions
among the stars, published in advance in the technical jour-
nals. Generally one or more telescopic comets may be seen at
any time, and a telescope of ten inches aperture would have
shown no less than seven comets visible at one time in Novem-
ber 1892. The total number of comets always present in the
solar system has been estimated by Kleiber (on certain hypo-
thetical conditions) to be nearly 6,000. — D. P. T.

Comets 199

but it may be remarked that while the aphelion of
Hallev's comet is at about the distance of Neptune,
a comet with a period of three hundred years would
pass far beyond this outer planet of our system.

A comet obsen^ed by Tycho Bkah^ and others in
1596 appears to have elements similar to those of the
third comet of 1845 ; and the two may be identical,
with a period of about 25c years.

In the autumn of 1882 there was much discussion
of the question whether the great comet then visible
had any connection with the fine comets of 1843 ^""^
1880, or these with each other, or with any seen in
bygone centuries. It is an undoubted fact that all
the orbital elements of the comets of 1843, 1880,

200 Stars and Telescopes

and 1882, are very similar to each other; and it is
probable that the comet of 1668, though very imper-
fectly observed, had similar elements also. When at
perihelion, all these comets made remarkably close
approaches to the Sun, coming within a distance of
700,000 miles of his centre, or about 300,000 miles
of his surface. Hence it was suggested that the tre-
mendous attractive force exerted by the Sun at so
small a distance might greatly shorten the period at
each return, and lead before long to the comet's absorp-
tion into the Sun, producing an incalculable outburst
of solar heat. On the other hand, similarity of orbit
in two or more bodies does not prove identity of those
bodies, it being quite possible that two or more comets
may move along the same orbit at great distances from
each other. Moreover, the best determinations of the
orbit in which the comet of 1882 was actually moving
agree in assigning about 750 years as its period, and
it is probable that all these comets are travelling along
the same orbit, in about that same period.*' An addi-

*• This singular object, the most recent great comet on rec-
ord, was discovered early in September 18S2, by many observers
in the southern hemisphere. Also D^ Common at Ealing,
England, on the forenoon of the 17th, saw it as a bright object
near the Sun; and so brilliant was it that M' Finlav and D'
Elkin at the Cape of Good Hope actually followed it up to
the very limb of the Sun itself. Here it utterly vanished,
as if behind the solar disk ; but in fact it passed in transit
between the Earth and our central luminary, and became visible
on the opposite side of the Sun the following day. Although
it had passed within 300,000 miles of the solar surface, still
there was no appreciable acceleration due to a supposed resist-
ing medium ; and I)' Kreutz, who discussed the observations
of its position, found that it is moving in a very elliptic orbit,
with a period of between 800 and 1000 years. The extraordi-
nary brilliancy, and the long period of visibility of this comet,
permitted the successful application of photography to the de-

■, 3d M.y 1I94

Comets 20I

tional member of this comet family was discovered,
1 8th Januar}' 1887, which was conspicuous for a few
days in the southern hemisphere, though never visible

lineation, not only of the comet's features, but also of the lines
in its spectrum. At one time its tail was single and nearly
straight ; at another, there were two tails slightly curved. But
the most curious phenomena were those exhibited at its head,
which, during recession from the Sun, underwent a remarka>
ble subdivision into three or four, and. according to some ob-
servers, six or eight, distinct comctary masses. Stranger still
was the anomalous sunward extension of the coma, or sheath,
in a va.««t envelope 4,000,000 miles in diameter. All told, the
great comet of 1SS2 is perhaps the most remarkable on record,
and the continued eccentricities of its physical development
were, no doubt, the legitimate product of disturbances brought
about \i\ its near appoach to the Sun.

But even more vivid in memory, doubtless, is the great comet
of the year preceding, discovered by M' TEUKurr in New
South Wales, 22d May iSSi, and re;j;;irdcd by some observers
as a more striking object than Coggia's comet of 1S74. Mov.
ing rapidly northward, it shone as a brilliant object in the
northern heavens through the month of June, and was the
first comet satisfactorily recorded by i)hotography. — Draper
in New York, and Janssen in Paris securing successful pic-
tures almost simultaneously. I)' Mkver measured with great
care the positions of stars traversed by this object, and found
evidence of refraction of the stellar rays by the comet, although
in no instance was there any perceptible absorption of the star's
light. Celestial photography has been of the greatest service
in cometary astronomy, — the long exposures regulated to con-
formity with the comet's motion making it possible to secure
most of the physical features satisfactorily. When a comet's
own motion is rapid, and its exposure long, all the stars appear
as trails, instead of bright points, as shown in the photogra])h
of Gale's comet (opposite page). Also a comet has been first
discovered with the assistance of photography, by I)' Barnard
at the Lick Observatory, 12th October 1S92. His photographs
of Brooks's comet of IVS93 show rapid and violent changes in
the tail, as if shattered by an encounter with a swarm of
meteors. Also a comet was discovered by M'^ Chask of the
Yale Observatory, on several plates exposed for the Leonids
in November 1898. — /^./'. T.

202 Stars and Telescopes

in the northern. It should, however, be remembered
that the few and uncertain observations of the comet
of 1668 scarcely admit any decided conclusion with
regard to its path. The tail only was visible in Eu-
rope ; and our knowledge of the comet's orbit is
chiefly derived from a map of its course in the heavens,
laid down from some very rough observations made
in the East Indies, extending over an interval of less
than a fortnight. But they indicate that this object is
probably moving in the same orbit as the comets of
1843, 1880, 1882, and 1887 are.

In modern times comets which would otherwise
have eluded detection have been ' caught,' in passing
near the Sun while the latter was totally eclipsed. A
photograph of the eclipse of 17th May 1882, taken by
D^ ScHrsTER in Egypt, clearly depicted such a
stranger in the rays of the outer corona (shown in the
illustration on page 86). Its momentary detection
was due to the obscuration of the Sun's light by the
Moon when the photograph was taken. As this body
was not visible either before or afterward, nothing is
known of its orbit, and probably its motion was very
rapid. This comet was called * Tewfik,' after the
then Khedive of Egypt. Another, much fainter and
more difficult to recognize, was photographed in the
corona during the total eclipse of i6th April 1893,
by M' ScHAEBERLE in Chile, and by other expeditions
in South America and West Africa.**

*^ The earliest comet detected during a total eclipse of the
Sun was recorded by Seneca ; and during a similar obscura-
tion, probably total, slightly south of Constantinople, iQlh July,
A. D. 418, another ^¥as discovered. On a sketch of the corona
of i8th July 1S60, by Winnecke at Pobes, Spain {Mem. Acad.
Impirialc, St Pitersbourgy vii. S^rie, t. iv. i), is a curious struc-
ture, which, according to Ranvard, may have been due to a

or comets moving in elongated ellipses approaching
in form to ]>arabolas, many requite several thousand
years to complete a wKole
revolution, and they are
observable for so small a
proportion of their whole
course that its length can-
not be determined with
accuracy. The revolution
of the great comet of
1858 (known as Do-
NATi's) is accomplished
in about i,ooo years;
the splendid comet of
181 1 has a period of
more than 3,000 years ;
the fine comet discovered
by M. C(xx;iA at Mar-
seilles in 1S74 (the
sheaths of the coma of
which are illustraled on
page 105) has been coi
puted to be moving

comet; also, on Ihe Indlai
izlh Uecetnber iS/i.acomel
(Menlhiy Nalices Koyal Aslrtr,
a singular coincidence that Ihe four modern eclipses during
wliich comets were cither seen or suspected are separated by
intervals of about eleven years. Among other comets seen at one
apparition only. 1847 vi is interesting from the circumstances o£
its discovery, at Nantucket, isl October, by Miss MrTCHELl, to
whom a gold medal was awarded by Ckkistiak the F^iglith,
king of Denmaik. Madame RUmker also discovered it inde-
pendently at Hamburg ten days later. A recent discussion of
its motion by Miss Margaretta Palmer of the Vale Obser-
vatory assigns to it a hyperbolic orbit. — D. P. T.

in an orbit of :

than

204 Stars and Telescopes

10,000 years' period ; and others have orbits of even
greater duration. All the comets of short period
move round the Sun in the same direction as the
planets;** but many of those (including Hallev's)

** The chemical composition of comets has been invesligaled

by means o£ ihe » pec irosco pe, — this instrument having been

first used for this purpose in l364 by Donati, who applied it

toTEtiTEL's comet of

that year, diaciosing

(he fact that these

;:^

bodies ai

■t it

1 lai^e

part self-

HuGcr.vs

found the

WlN-

;t (186S

I[}tocoim

-ide with that

of olcliant g;

vacuum 1

ube;
ttiiil

but it
the ap-

of C

comet (IS

-4) 1

that the

full capab

5 of the

new method c

ould be

tested. This

bcillianl

object revealed the five
bands of the complete
MAKEA MiLciihi.i |itl - ■■91 hydrocarbon spccttum

tihading off on one
%\ie; but there w^s also a relatively faint continuous spec-
trum, showing that while the gaseous portions of tlie comet
were largely compoundetl of carbon and hydrogen, its light
was in part reflected from the Sun. Ke-iearches on conietary
Bpectra were continued bv Voi]ei,, Hasseijieri;, Vouno, and
others. The comet of iSSi, known as TBHiitirr's, or (iSSi in),
K3S the lirft one whose spectrum was pholt^raphed. by Pka-
PER in New Vntk, and HUGCINS in Ijindon, disclosing bands
in the violet due to carbon compounds, ami showing an iden-
tity with hydrocarbons burning in a Bunscn flame. Then came
the two comets of 1882. approaching very near the Sun. and
displaying the bright lines due to sodium, whose brightness
increased as the distance of the comets from the Sun dimin-

Ofmets

205

which travel in long elliptic orbits, and many whose
paths are parabolas, have retrograde motion, 'I'empel's
comet of 1866 (the comet of shortest known period
combined with retrograde motion) travels round the

Sun in rather more

Leonids, as will be
related in the next
chapter.

ishcd. Sear peiihelioii
the hydrocarbon
bands were verv faint
or wholly invisiWe;
and this behavior is
regarded by I>' ScKE[-

NER as proving that the intrinsic light of these comets had its
origin in disruptive HischarKes of an electric nalure in their
interior. .\lso D' Copeland, now AMronomcr Royal for
Scotland, delected in the speetrnm of the Sc|Hcmber comet of
iSS^ five other bright lines in the yellow and green, due to the
vapor of iron. No bright comet has since appeared. It ii
interesting to note, in the observalions just related. 3 partial
confirmation of the theories of D' Kredtchin. previously
staled, .iccording lo which the length and curvature of comets'
tails depend upon an clei;trical repulsion varying with the
molecular weigjil of Ihc repelled gases. The comets of iSSi
and iSSj. largely made up of hydrocarlwm compounds, pre-
sented ihe second ivpe of tail, as indicated bv theory. Whether
the long, straight tails of the first type are hydrogenous in
origin, and Ihe shortest busbv lails of the third tvpe are due to
the vapor of irnn and other heavy snbstanccs. can be decided
only when bright objects of these separate classes shall have
made their appearance in the future. — Z). P. T.

■y* 7.// 1874 (nRoom)

2o6 Stars and Telescopes

Bessel, Several papers in Astron. Nachrichten^ xiii. ( 1836).
Herschel, J. F. W., * Halley's Comet/ in Cape of Good Hope

Astrofiomicdl Observations (London 1847).
Hind, The Cornets: a descriptrne treatise (London 1852).
Watson, A Popular Treatise on Comets (Ann Arbor i860).
HoEK, • Comet Systems,' Recherches astron. de V Obscri'atoire

d' Utrecht (The Hague 1861-64).
Bond, G. P., *Donati's Comet,' Annals Harvard College Ob-

seri'atory, iii. (Cambridge, U. S. 1862).
Carl, Repertorium der Cometen-Astronomie (Munich 1S64).
Herschel, J. F. W., Familiar Lectures on Scieutific Subjects

(New York 1866), p. 91.
HUGGIN8, Philosophical Transactions^ clviii. (1868), 556.
Watson, Theoretical Astronomy (Philadelphia 1868), 536, 638.
Tait, Proceedings Royal Society Edinburgh y vi. ( 1869), 553.
V. Oppolzer, Bahnbestimniung, 2 vols. (Leipzig 1870-1880).
ZoLLNKR, Vber die Aatur der Contcten (Leipzig 1872).
V. Asten, Thcorie Encke'schen Cometen (St Petersburg 1872).
KlRKWOon, Contets and Meteors (Philadelphia 1873).
GyldI^N. Cahul des Perturbations dcs C^w^/t-j- (Stockholm 1877).
Gl'ILLEMIN, The World 0/ Comets {\jo\\<\on 1877).
HoiiZE.xr, Anuuiiire de rObseriKitoire Royal (Krussels 1877).
Bredichln, Annaies de VObsen^atoire de Afoscon, iii. (1877), et

seq. : Copernicus, i. (1881); ii. (1882); iii. (1884).
Norton, * Physical Theory,' Am. Jour. Science, cxv. (1878), 161.
Wilson, ' Comets of 1880-83,' Publ. Cincin. Obs.y Nos. 7 and 8.
WiNLOCK, W. C, * Comet of 1882/ IVash. Obs 1880, App. L
Peirce, Ideality in the Physical Sciences (Boston 1881).
CoPEL\ND and Lohse, Copernicus^ ii. (1882), 225.
Young, Boss, Wright, and others, 'Comet 1881 b,* American

Journal 0/ Science, cxxii. (1881).
Meyer, 'Comet of 1881,' Archives Sciences Gcnive, viii. (1S82).
Huggins, Proc. Royal Institution, ix. (1882); x. (18S3), i.
Backlund, ' Encke's Comet,' Mim. Acad. Impiriale Sciences

St Pitersbourg, xxxii. (1884) ; xxxiv. (1S86) ; xxxviii. (1892).
Gill, ' 1882,' Ann. Roy. Obs. Cape of Good Hope, ii. (18S5), pt. I.
Weiss, • Bericht,' Viertel. Astron. Gesell. xx. (1885), 287.
Newton. ' Biela'sComet,*^^^^. yi^wr. Science, c\xx\. (1886), 81.
Unterweger, Denk. Akad. der Wissenschaften Wieu (1887).
Proctor, Popular Science Monthly^ xxxi. (1887), 50.
Harkness, * Orbit Models,' Sidereal Messenger, vi. (1887), 329.
Thollon, Annaies de VObservatoire de Nice, ii. (1887).
Boss, * Comet Prize Essay,' Hist. Warner Obs. (Rochester 1887).

Comets 207

Langley, The New Astronomy (Boston 1S88).

Berberich and DeichmOller, * Brightness of Encke's Comet,'

Astronomische Nachrichtetty cxix. (1888); cxxxi. (1893).
Chambers, Descriptive Astronomy^ vol. i. (London 1889).
Hirn, Constitution de VEspace Celeste (Paris 1889).
Plummer, 'Comet Groups,* Observatory, xiii (1890), 263.
KiRKWOOD, * Age/ Publ, Ast. Soc, Pacific, ii. (1890), 214.
Peters, C. F. W., Himmel und Erde, ii. (1890), 316.
TiSSERAND, 'Origin,' Bulletin Astronomique, vii. (1890), 453.
Callandreau, Ann. Obs. Paris, Mimoires, xx. (1890).
Denning, * Comet-seeking,' Telescopic Work (London 1891).
Newton, * Capture of Comets by Jupiter,' Am. Jour. Science,

cxlii. ( 1891 ); Memoirs iVational Academy 0/ Sciences, vi. ( 1893).
Barnard, • Classification/ Astronomical Journal, xi. (1892), 46.
Clerke, History of Astronomy (London 1893), '09, 392, 417.
Wilson, * 1889 v,' Popular Astronomy, i. (1893), '5^-
Scheiner and Frost, * Spectra of Comets,' Astronomical

Spectroscopy (Boston 1894).
Galle, Verzeichniss der Elemente der bis her berechneten Cometen-

bahnen (Leipzig 1894).
Lynn, • History of Encke's Comet,' Nature, Ii. (1894), 108.
Olbers, Sein Leben und Seine Werke (Berlin 1894).
Spitaler, Deuk. Akad. Wissenschaften Wien, Ixi. (1894).
Plummer, y«?«r. Brit. Astr. Association, iv. (1894), 89.
HoLETSCHEK, Denk. Akad. Wissenschaften Wien, Ixiii. (1896).
MtJLLER, Photometric der Gestirne (Leipzig 1897).
Lynn, Remarkable Comets (London 1898).
Payne, * Comet Families,' Popular Astronomy, vi. (1898).

The keen popular interest in comets is responsible for a vast
literature which is excellently represented by the long lists of
titles in the Indexes of PooLK and Fletcher. The later vol-
umes of these invaluable indexes contain also many titles of
scientific papers ; but the fullest acquaintance with them will
be greatly facilitated by reference to Houzeac's Vade Mecum
de P Astronome, and his Bibliograpkie GMrale, ii. (Brussels
1882). Comet literature since that date is best summarized in
Bulletin Astronotnique, a Paris monthly, begun in 1884; also
the concise notes in the annual reports of the Smithsonian
Institution are helpful. Current information concerning comets
is given in the Annucure du Bureau des Longitudes, the astro-
nomical notes in Nature, and in Knowledge, The Observatory,
and Popular Astronomy, — D, P. T

CHAPTER XIII

METEOKIC BODIES

COMETS have been for about two hundred years
recognized as cosmical bodies, often travelling
in regular orbits round [he Sun ; but that swarms of
meteoric bodies move in a similar manner has been
known during only the last sixty years."

" The irue cosmic nalure o£ lu
been recognized a full century .

ninous metcora has, however,

earlier ihey were regarded

purely as phenomena

of the upper atmos-

Phef'

lifesl

While H ALLEY and
others seem ti> have
had a vague noiion of
the insulficicncy of this

gacions of the laws
sound, seems to ha
first expressed the ir
conception of n
matter, having pub-
lished in 1794 the view,
essentially unmodified
to-day, that interplane-
tary s]iace is tenanted
by shoals of moving
bodies, chiefly iron, ex-
ceedingly small in mass
s compared with the planets. Multitude* of
e bodies, then, collide with the Earth while it is

Meteoric Bodies 20g

The first definite establishment of the relation of
such a swarm to the solar system is principally due to
the labors of Professor Newton of Yale University, in
the case of the November meteors. The recurrence
of the shower as seen in the United States, 13th No-
vember 1833, on about the same day of the year that a
like shower had been witnessed by Humboldt and
BoNPLAND in South America 34 years earlier (12th
November 1799), led to a careful examination of pre-
vious accounts, and to the discover}' of evidence that
a shower radiates from the same point in the heavens
about that time every year.**' It happens later by

travelling through a shoal of them ; and by their impact with
the upper regions of our atmosphere, and by friction in passing
swiftly through it, are heated to incandescence, thus presenting
the luminous phenomena commonly known as shooting stars.
For the most part they are consumed or dissipated before
reaching the solid surface of our planet. The fact is deter-
mined from theory and well established from observation
that more meteors are seen during the morning hours (from
4 to 6 A. M.) than at any other nightly period of equal length,
because the sky is then nearly central around that general di-
rection in which the Earth is moving in its orbit about the Sun ;
and to the meteors which would fall upon the Earth if it were
at rest must be added those overtaken by reason of our own
motion. Also it is now recognized that from July to January,
while the Earth is passing from aphelion to perihelion, more
meteors are seen than during the first half of the year ; but
this seems to be chiefly because the rich shoals of August and
November are then encountered. — /). P. T,

*' This point is situate in the constellation Leo, and the
meteors of this shower are therefore known as I^onids. They
have fallen at 33-year intervals since A. D. 902. Their average
velocity on reaching the Earth is about 44 miles per second.
Meteors when encountered by our atmosphere are moving
through space in lines essentially parallel ; a fact of the first
order of significance, which Twining and Olmsted in 1834
were the earliest to recognize. Indeed, they actually suggested

SAT — 14

2IO Stars and Telescopes

about two days each century ; but it is especially
brilliant and conspicuous at the end of each interval

the cometary character of (he November shower. The appar-
ent phenomena of a great shower are well illustraied in the
opposite chati of a fall of August meteors, ot I'crseids, in which

DENISUN OLM5LKD ll79I-lSS9)

the apparent path of each meteor in the heavens is carefully
laid down, and ihe seeming radiation from a ceniral ]ioint,
wholly due to perspective effect, is made dear. These appar-
ent paths are the projected sections of otbi(3de<!cribed by the
meteors round the Sun. and intentccting our orbit. If a meteor
were met by the Earth head on, it would of course be charted a^
a mere point at the centre, or radiant ; those meteors nearest to
this position have their luminous courses most foreshortened, as

Meteoric Bodies

of 33 or 34 years. Professor Newton showed that
the bodies must move in one of five well defined

represented by the aliortest arrows; while those farlhesi from
the radiant are visible through the longest apparent course
among the stars. Accurate observation of the tracks of me-
teorsis very difficult ; »nd on every shower-chart will be found ■
iew arrows whose prolongation does not pass near the radiant.

fei lifwing' rkt PI
itU falkt/ tack milar aiiirwi. omd Iktir fr
ImfiUimi ivlnmrd Jtfiiiit th4 ^liltmt ^ li
radimi in Iht i^)

212 Stars and Telescopes

orbits to satisfy this delay ; but the investigation of
Adams, of Cambridge, Eogland, showed that one only
of these would explain all the circumstances of the

Smy or sporadic meleon are often th<u indicaled, as well as-
the effects of imperfect observation.

D' Max Wolp oE Heidelbei^, having exposed a plate aa
boDr for the stare of the Milk; Way, 7 th September 1891, found

APP

RATUS F

S OF METKO

M-,W

•uinrfola

«:,{, driven i.

Icctatrk, to

, M /b//™ /*

.1,. Ufon

M/JI

^./,)u,h.

7-**.. (*, f/»

l-i-K'

txf^n.

r..a„dil.

raUii imtniud

«.-, <*. .l«

• Hftnl/irfla

on development a line, dark, nearly uniform line crossing it, due
to a meteor of uneven brightness in ila flight; and this is the
first meteor trail ever photographed (see also page 359). Du-
ring tbe showEts of iil94. Professor Newtun and I}' Elkim
of New Haven brought into successful service at the Vale
Observatory the novel piece of apparatus pictured tii the ac-

Meteoric Bodies

2IJ

case. This true explanation is that the swaim of nie>
teorSy of which the November shooting-stars fonn a
portion, moves round the Sun in a regular elliptic
orbit, with a period of about
334 years ; and that the i>eri-
heUon of that path, where the
meteors are of course nearest
to the Sun,very nearly touches
the Earth's orbit, as indicated
by the accompanying dia-
gram.

The Earth, passing through
that point of its orbit in the
middle of November, encoun-
ters meteoric matter on every
such occasion; but the me-
teors being much more closely
aggregated in a certain por-
tion, called the * gem of the
ring,' the most abounding
showers occur only every

thirty-third year. As, however, the * gem * extends a
great distance along the line of the meteoric orbit
(about, in fact, ^ part of its whole length), fine
displays are generally seen on several years in succes-

PATH OP THS NOVCMBER MB*

TEORS AND OF TEMPSL*S

COMET (lS66 l)

{In rtlatioH to the planetmry
orbits^ to which it is imcitmeJ
in s/ace about ly^)

companying illustration ; and by means of it the trails of bright
meteors have been located among the stars impressed on pho-
tographic plates, with a precision wholly unattainable by the
purely optical methods of the past. These investigations are
conducted at the charge of a trust fund of the National Academy
of Sciences, provided by the late D' J. Lawrence Smith,
whose researches added very greatly to our knowledge of the
meteorites. The principal of this fund, about $8000, was
derived from the sale of D' Smith's splendid collection of
meteorites to Harvard University. — D. P. T.

314 Stars and Telescopes

sion. The orbital motion of these meteors, like that
of many comets, is in a reverse direction to that of
the planets ; and this of course greatly increases the
relative velocity with which a portion of them enter
the Earth's atmosphere, while the larger pari of the
mighty stream sweeps on nearly toward the part of
space which the Earth has left. The aphelion of
their path is a little beyond the orbit of Uranus. As
a result of these investigations, another grand display
of meteors was predicted for 14th November 1866 ;
ajid this was slriliingly verified."

o Like displays are expecteci, ^^^\y November 1899 and 1900.
Sometimes astriinomers when sweeping Ihe sky foi comets
encountet small meteoric bodies in
thetc search, A remarkable flight
of faint, telescopic meteors was thus
observed by I'rofessor IJROOKS, aSth
November 18S3. as depicted in ihe
accompanying illustration. They
were very small, and most of them
left a faint train, visible in the tele-
scope for one or two seconds. M'
Denning estimates that the tele-
scopic meteors are twenty-fold more
rucHT OF "Luscopii; MB- „umeroiis than tlie naked eye olj-

MOBS, iSlh Novembet iSSj . , ,. . ' ■

(Brooks! ]«='* "' "" "a'"'*- At rare inter-

vals telescopic views of very large

meteors, usually called fireballs, or aerolites, have been caught,

and all these physical phenomena arc doubtless of (he same

general character, although variously represented by the differ-

have been favored |

with the opportunity

of making such ob- 1

servations. Gener-

ally the individual

particles are seen to

be balloon-shaped.

Above is an excellent picture ot the disint^ation

loth
with

Meteoric Bodies

Not loDg afterward the meteors seen about
August were subjected to a similar examlDation,
the result that they too
move in an elliptic orbit
round the Sun in a re-
verse direction to that
of the Earth and plan-
ets; but their path is
much more eccentric
than that of the No-
vember meteors, and
though at perihelion it
meets the Earth's orbit,
at aphelion it stretches
far beyond Neptune.

These discoveries
were speedily followed
by another, priority in
which belongs to Pro-
fessor SCHIAPARELLI of
Milan. It is that each
of these meteoric orbits
is identical with that of
a comet, which bodies
must therefore be re-
garded as sustaining
very close and intimate
connecdoQ with the me-
teors. The orbit of the

movtnf! meleor in its aerial flight, a* drawn byM' Denning, of
Bristol, England, who Tinki among the foremost of living au-
thorities on meteoric attronomy. At the last phase the pear-
sh^>ed body spread into a wide stream of fine ashes and disap-
peared. Snch celettial displays are moit likely in April, Ka.-
got^ November, and December. ~D.P. T,

u rtfrtamUd by tin immII fi

mtml*i. Only Ou ttrOuliaii pt
^ Hh mftftrk path it iMffttm,

2l6

Stars and Telescopes

November meteors ^ has the same elements as that

^ So systematically have meteoric phenomena been watched
and recorded during the past quarter century, particularly by
the Italian astronomers, that nearly 300 distinct showers are
now recognized. Following is a selected list of those observed
in recent years by M^ Denning at Bristol : —

Position of

Radiant Point

Name of

Shower

Right

Declina-

Ascension

tion

Quadrantids
^ Cancrids

»5

ao
56

52 N.

16 N.

« Cygnids

53 N.

9 Coronids

31 N.

a Draconids

69 N.

a Serpentids

II N.

/i Leonids

10 N.

/i Ursids

58 N.

( Draconids

»7

62 N.

^ Serpentids

17 N.

Lynds

32 N.

i| Aqu.irids

2 S.

a Coronids

27 N.

ff Aquilids

»9

i\ Pegasids

27 N.

4 Cepheids

57 N-

Vulpeculids

24 N.

a Cygnids

4H N.

«-/3 PerseidH

43 N-

6 Aquarids

12 S.

A Andromcdes

51 N.

Perseids

57 N.

K Cygnids

53 ?*•

Draconids

«9

60 N.

c Perseids

37 N.

Y Pegasids
k Piscids

10 N.

1} Auri^ids

5»

42 N.

Lynads

43 N.

c Arietids

20 N.

Orionids

15 N.

i Geminids

23 N.

g Taurids

9 N.

Leonids

23 N.

Leo Minorids

40 N.

c Taurids

22 N.

Andromcdes

43 N.

Geminids

33 N.

a Geminids

29 N.

K Draconids

67 N.

Dates of Observation

January 2-3
anuary 2-4
anuary 14-20
{anuary 18-28
'ebruary 1-4
February 15-20
March 13-15
March 24
March 28
April 17-25
April 17-20
April 29-May 6
May 7-18
May 15

May 29-June 4
June 10-28

une 13-July 7

uly 11-19

uly 23- August 4
July 27-29
July 30-August II
'August 9-1 1
August 5-16
August 21-25
AuguKt 2i-September 21
August 25-September 22
September 3-8
September li-October a
September 21-25
October 11-24
October 17-ao
October
November a-3
November 13-14
November 13-28
November 20-28
November 26-27
December 1-14
December 7-12
December 18-29

* Probably, M*^ Denning says, the Perseids are observable
more than a month, during which period their radiant is con-

Meteoric Bodies 217

of a small comet discovered by Tempel at Mar-
seilles, 19th December 1865, which passed its peri-
helion, nth January 1866, and was found to have a
period of 33 J years. The Chinese observed a comet
in the year corresponding to a. d. 1366, which, it is
thought, was probably moving in an orbit identical
with Tempel's, seen just 500 years afterward (equal to
15 of its calculated periods). Farther, the orbit of
the meteors of loth August coincides with that of the
third comet of 1862 (discovered by Professor Swift,
iSth July, and visible to the naked eye during part of
August and September) , which has been calculated to
revolve round the Sun in about 120 years. The dis-
persion of meteoric particles along the cometary
orbit must be much more complete in the case of
the August than of the November meteors, since
the abundance of the former is far more nearly
uniform.*^

tinually shifting eastward and northerly among the stars.
Many of the showers in the above list are as yet incompletely
determined, and scattering observations by amateurs are well
worth recording. It will readily be inferred that there are few
clear, moonless nights when meteors can not be seen with a
little patient watching. — D. P. T.

^ A word concerning the origin of meteors. Many theories
have been advanced — that they came from the Sun, from the
Moon, from the Earth as a product of volcanic action, and so
on ; but the difficulties barring the acceptance of these and many
other hypotheses are very great. On the other hand, the theory
that all meteors were originally parts of cometary masses is one
that may be accepted without much hesitation. Comets in the
past have been known to disintegrate, — for example, that of
BiELA, already illustrated on page 192, in its double form ; and
its story has been admirably told by Professor Newton. Ap-
parently the process went on so rapidly that in 1885 farther
subdivision had taken place, and it is now exceedingly unlikely
that any part of the comet will ever be seen again, as a comet.

Stars and Telescopes

Another interesting (act bearing upon this subject
must be mentioned here. On ayth November the

During the shower of th« Btcia n

%, 37th November 1S85,
fell upon the Earth, at Maza-
pil, Mexico; and on subse-
quent occasions we may expect
capture still other fragments,

sthe B

r the a

BROOKS COMKT

jhere with a velocity of only
:n miles a second. The
range disintegration of the
iicleuB of the great comet of
^2 was watched and depicted
^ numerous reliable observ-
's ; and as it is a member of
a cometarv family, the comet*
of T84J, t88o, and 188; being
l/s /™«i 0/ dUiHUgralUm) fellow voyageia along the same

{BiiiNitKD) orbit through space, it is not

unreasonable loassume that all
four of these bodies may in past ages have been a single comet
of unparalleled proportions. Other comets, too, have beetk
recognized as fragmentary, but only a single additional instance
need be cited, — that of Hhooks's comet of 1890, the separate
nuclei of which are shown in the above illustration.

Many comets, then, having been known and seen to disin-
tegrate under the repeated action of solar forces, which force*
are exerted in greater or less degree upon all bodies of this
class, the theory of the secular disruption of all comets is
reached as an obvious conclusion. From several independent
lines of inquiry, it is known that the age of the solar system is
exceedingly great, probably many hundreds of millions of
years ; we should therefore expect to find almost the whole
mass of a few comets (perhaps the older ones upon which the
disrupting forces had been operant for indefinite ages) already
shattered into small pieces ; so that instead of the origin^
comet, we should have an orbital ting of opaque meteoric
bodies, travelling round the Sun in the original cometaiy path,
each body too small to reflect an appreciable amount of solar
light, and only visible as a meteor when in collision with our
atmosphere. Already the identity of four such comet-orbits

Meteoric Bodies 219

Earth crosses the orbit of Biela's comet, which body^
it will be remembered, has ceased to appear accord-
ing to calculation; and about that time showers of
meteors have been seen to radiate from a point in
Andromeda, from which a body moving in the orbit
of the comet would seem to approach. A very con-
spicuous display was seen on that date in 1872, when
the Earth crossed the comet's orbit about three
months after the body itself should have passed that
point; and it was even suspected that a portion of
Biela's comet was afterward seen receding in the
opposite direction to that of the radiant point of the
meteors. But this remains very uncertain, as it was
difficult to reconcile the motion of that body with the
theoretical motion of the comet. Another fine display
of meteors was seen 27th November 1885, when the
principal part of the comet was even nearer the Earth
than in 1872. Doubtless there is some connection
between these meteors and the comet, and the radiant
will continue to be watched with great interest. A
considerable shower of meteors was noticed to emanate
from this region of Andromeda, 23d November 1892^
somewhat earlier in the month than previous appear-
ances ; and it seems probable that this was a sporadic
group, also that a larger shower may be expected near
the end of November 1905.

and meteor streams has been established beyond a doubt, giv-
ing rise to the well-known showers of 20Ch April, loth August,
14th and 27th November ; and there no longer seems to be any
substantial reason for doubting a like origin for all other mete-
oric bodies. Meteors, then, belonged originally to comets, which
in the lapse of ages have trailed themselves out, so that discrete
particles of the primal mass are liable to be encountered any-
where along the original cometary paths. — D. P. T,

CHAPTER XIV

METEORIC BODIES {continued)

WITHIN very recent years, meteoric bodies have been seen
to fall upon our globe during periods of well known
showers ; and these objects, captured by the Earth and now in
relatively small numbers in our cabinets and laboratories, are to
be regarded as actual fragments of celestial bodies which were
originally comets, but which have become disintegrated by the
action of solar forces at their returns to perihelion. The recent
recognition of this connection between meteorites and the
showers of April, August, and November, breaks down the
last objection to the theory (toward which astronomers have
long been drifting, and which may now be accepted without
reserve) that all luminous meteors, heretofore classified and
subdivided as aerolites, meteoroids, shooting stars, bolides,
siderolites, fireballs, meteorites, and the like, belong to a single
class, and have a community of origin. Their points of differ-
ence relate only to size, and to composition, chemical and
physical.

Only two general terms, then, are necessary. All those ce-
lestial bodies colliding with the Earth and producing sudden
and characteristic luminous phenomena of the sky are (i) me-
tears. Sometimes they are very large, perhaps tons in weight ;
or their composition may be peculiar ; or their encounter with
the atmosphere may take place near a minimum velocity : for
those and other reasons, meteors which resist that intense dis-
ruptive action due to the friction of the atmosphere and the
heat due to atmospheric impact, and fall down upon the sur-
face of the Earth, are known as (2) meteorites. Of the last there
are many classes, representing in all about 400 different falls,
few of which were, however, actually seen to fall. The; most

Meteoric Bodies

celebrated collections of meteoriles >re at Vienna, (he BritUh
Muaeum, Paris (illustrated below), Harvard University (col-
lected by Lawrence Smith), Amherst College (collected bj
Shepakd), Yate University, and Berlin.

{.In Ou M-utnm tHi

tf DavbbAi)

Although the descent oi meteoric bodies from Iht sky was
generally discredited till the beginning of Ihe present century,
Gtill such falls have been recorded from the earliest times.
Usually regarded as prodigies or miracles, such siones have
commonly been objects of worship among the oriental peoples;
for example, the Phrygian stone, the ,' Diana of the Ephesians

222 Stars and Telescopes

which fell down from Jupiter/ the famous stone built into the
Kaaba at Mecca, and to-day revered by Mohammedans as a holy
relic. The earliest known meteoric fall is historically recorded
in the Parian Chronicle as having occurred in the island of Crete,
B. c. 1478. We must pass over the numerous falls of meteoric
bodies first brought together and discussed by Chladni
(chief among which was the Pallas or Krasnoiarsk iron, an
irregular mass weighing about f of a ton, found in 1772 by
the celebrated traveller Pallas near Krasnoiarsk, Siberia, and
the greater part of which is now preserved in the Imperial
Museum at Saint Petersburg), and devote a few words to a
* shower of stones * in the department of Orne, France, early in
the present century. BioT, the distinguished physicist and
academician, who was directed by the Minister of the Interior
to investigate the subject, reported that about i p. M. on Tues-
day, 26th April 1805, there had been a violent explosion in the
neighborhood of L'Aigle, heard for a distance of 75 miles
round, and lasting five or six minutes. A rapidly moving fire-
ball had been seen from several adjoining towns in a sky gener-
ally clear, and there was absolutely no doubt that on the
same day many stones fell in the neighborhood of L'Aigle.
They were scattered over an elliptical area 6^ miles long, and
2^ miles broad, and Biot estimated their number between two>
and three thousand. Thenceforward the descent of meteoric
matter upon the Earth from interplanetary space has been
recognized as an undoubted fact.

Many similar phenomena since investigated show (as would
be expected from their cosmic origin) that meteorites fall upon
our planet without reference to latitude, or season, or day and
night, or weather. Their temperature on entering our atmo-
sphere is probably not far from 200^ centigrade below zero, and
their velocities range from 10 to 45 miles a second. So great
is the atmospheric resistance to their flight that on traversing
the whole of this protecting envelope, their velocity is vastly
reduced, and very suddenly. On the basis of experiments by
Professor A. S. Herschel, it was found that the velocity (at
ground impact) of the meteorite which fell at Middlesborough,
Yorkshire, 14th March 1881, was only 412 feet a second; and
at Hessle, Sweden, ist January 1869, several stones fell on ice
only a few inches thick, and rebounded without either breaking
it or being themselves broken. The flight of a meteor through
the atmosphere is only a few seconds in duration, and owing to
the sudden reduction of velocity, it will continue to be lumin-

Meteoric Bodies

223

ons throt^hout the upper part of its courae only; on the airer-
age, visibility is loand to begin at an elevation o[ about 70
miles, and end at about half thai altitude. The work done by
the atmosphere in suddenly reducing the meieor's velocity ap-
pears in considerable part as heat, fusing its exterior to incan-
descence. But conduction of heat in stony meteoric masses
is slow ; and notwithstanding the excessively high temperature
o( the exterior, during luminous flight, there is good reason for
believing that all large meteorites, if they could be reached at
once on striking the Earth, would be found to be cold ; because
the smooth, black crust or varnish, which invariably encases
them as a result ol intense heal, is always thin.

■««. ivM

righl 116 lil.)

The Orange River meteorite of the Amherst College collec-
tion, here photographed, is an excellent typical specimen. Par-
ticularly aie the pittings or thumb-marks, generally covering
the exieriorofiron meteorites, well shown in this specimen; they
are due probably to the resistance and impact of the minute cot
omns of air which impede its progress, and to the unequal con-
ductton and fusibility of the surface material. Meteorites are
never regular in form or spherical ; and the Orange River
meteorite exhibits about average irregularities of exterior.
These indicate a fragmentary character and lack of uniform

224 Stars and Telescopes

structure in the original mass. Often there is an explosion,
which is in part accounted for by the sudden heat to which the
exterior is exposed, and the impact of the air column in front
of the swiftly moving meteor, which is so densely compressed
that it acts almost like a solid. Fragments are sometimes
found miles apart which fit perfectly together.

The surface of our Earth containing three times as much
water as land, a large proportion of all falling meteorites are
necessarily lost in the ocean. The processes of deep sea dredg-
ing have, indeed, in some instances brought to light an appre-
ciable amount of meteoric matter. Of meteorites which fall
without being seen, in regions where ordinary climatic condi-
tions prevail, by far the greater part soon disappear because of
atmospheric action, the irons gradually oxidizing, and the stones
rapidly disintegrating because of their porous structure. In
desert climates, however, their lifetime is greatly extended ; and
in such regions the search for meteorites is best rewarded.

Although meteorites are classified as metallic and stony^ the
division is far from abrupt. According to their structure and
composition, the metallic meteorites are subdivided into sider-
ites, siderolites containing 80 to 95 per cent of iron, and pallas-
ites, the first being homogeneous masses of iron and nickel com-
bined, while the last are spongy masses of iron filled with oli-
vine, or chrysolite. About eleven twelfths of the stony meteorites
(which are greatly in excess of the metallic ones) are termed
chondrites, by Rose, because their composite structure is that
of rounded grains (chondri), with nodules of iron generally
scattered through their mass. Professor Newton has carefully
investigated the history of about 265 observed falls, repre-
sented by specimens in existing collections, and he has found
that their motions about the Sun were direct, not retrograde.
He concludes also that the larger meteorites moving in the solar
system are allied much more closely to the group of short period
comets than to the comets whose orbits are nearly parabolic.

The largest fall actually heard or seen occurred in Emmett
County, Iowa, loth May 1879, in a shower of stones, the most
massive weighing 437 pounds. The largest meteoric stone
ever discovered weighs 647 pounds; it fell in Hungary, in
1866, and is now in the Vienna Museum. The iron meteorites
are often much larger, a famous one found in Tuczon, Arizona,
and now in the National Museum at Washington, being in the
shape of a ring weighing about 1000 pounds, and one found in
Texas, now in the Yale collection, weighing 1635 pounds.

Meteoric Bodies

225

There aie namerom othen in diSerent parti of the world, both
in collections and still in the field, whose meteoric character i*
perfectly established, the largest of which, more than six tons
in weight, is at BahJa, Braxil. The iron meteorites actually
seen to fall are, however, remarkably few, as the foUowiag
table shows. The largest is known as the Nedjed iron, and its
weight is 130 pounds.

Iron Meteor[tes skeh to Fall

Nime of pl«e

i™"*»«)*

Out ol FiU

Clurtolle
BrauDiu

VktarU Wat

Croalii, Hun-

r.S;Z»,.t;.s.

Bohemia
MJd^a^ Indil

i6tb May i;st

,«hbci. jSm

Spring. ,»(

iDih Adt. 1S76
ijih Nov. iWs
i;lh Mar. iS36

Bm A Vl^^

WIDMANNSTATTMH FIGUKES
(Mfltiritirm^Ttxai—ImfrtHioK lain/ram lit inn)

326 Stars and Telescopes

One of the first tests applied to a mass of iron suspected to
Ik meleoriiic is that known as the ' Widmannstattian figures,'
from VON WiDUANNSTATTEN of Vienna, who in i3o8 pol-
ished a piece of the Agram meteorite and etched it with acid.
These figures have a general resemblance in all meteoric irons,
well iUuHtrated on p. Z25, and they are sections of planes of
cleavage, along which chemical change of some sort has taken
place. Their form and relative posilion are determined by the
laws of crystallography. The test o£ the Widmannstattian fig-
ures is not, hovever, regarded by modern investigators as in-
fallible, because certain terrestrial substances exhibit them in
«ome degree, particularly the famous Ovifak masses discovered
by NoRDENSKiuLD on Disko Island. The largest of these dia~

{Lnglk, 6l/wii wv^, I

puted meteorites is shown in the annexed engraving. For a
long time these irons were thought to have had an extraterres-
trial origin, but the opposite opinion is now generally held,
^ue chiefly to the examinations of Lawrence Smith and

Chemical analysis of meteorites reveals the presence of atl

Meteoric Bodies

227

those elements most commonly recognized in the Earth's crusty
— iron, nickely sulphur, carbon, oxygen, calcium, with less of
hydrogen, nitrogen, chlorine, sodium, cobalt, manganese, cop-
per, and a trace of bromine, lead, and strontium. Iron is gen*
erally alloyed with nickel, and phosphorus nearly always
combined with both nickel and iron. Cobalt is very generally
associated with the nickel. Hydrogen and nitrogen are present
as occluded gases, and carbon usually appears as graphite, in
a few cases as diamond.

All investigations hitherto made of the question whether me*
teorites bear any testimony as to the existence of living organ*
isms in other worlds fail to show such existence. Chemical
compounds new to mineralogy have been brought to light, but
no new elemental substance has been discovered in analyzing
meteorites, and the study of these bodies has become a depart-
ment of mineralogy rather than astronomy.

The Zodiacal Light. — After twilight in the western sky
on clear moonless nights from January to April, may be seen
the zodiacal light, a faintly luminous and ill-defined triangular
area, expanding downward obliquely from the Pleiades to the
northwest horizon. The illumination of this region is not uni-
form, the central portions being the brightest and outshining
the white luminosity of the Milky Way with a slightly yellowish
tint First recognized by Childrey about the middle of the
17th century, Cassini observed it carefully from 1683 to
16S8, establishing its form and position so critically that no
observations at the present day would appear to indicate any
change. In the latter half of the present century this strange
object has been carefully observed by Schmidt, Heis, Max-
well Hall, Jones, Serpieri, and others; but there is still
much divergence of view as to what may be the cause of the
phenomenon. D*^ Wright, of Yale University, regards it as
due to the reflection of solar rays from innumerable small
interplanetary bodies, crowded more densely about the mean
plane of the solar system, and in parts extending outward from
the Sun far beyond the orbit of the Earth. It may be con-
ceived as a vast cloud of meteoric dust, approximately lens-
shaped in figure, still in slow process of formation from the
dibris of comets. That the zodiacal light is reflected sunlight
has been abundantly proved by the spectroscope in the hands
of LiAis, CoPELAND, and Smyth, who find a short continuous
spectrum similar to that of the Sun, possibly crossed by dark
Fraunhofer lines, but without a trace of bright ones ; and by the

228 Stars and Telescopes

polariscope deftly manipulated by D' Wright, who in 1873-74
found the light strongly polarized. This fact proves that it is
reflected ; and the especial manner in which it is polarized in-
dicates the Sun as its only source.

The Gegenschein. — In this connection should be mentioned
the zodiacal counterglow, or * gegenschein/ first described in
1854 by Brorsen, who gave it this name. A very faint and
evenly diffused nebulous light, it is seen almost exactly oppo-
site the Sun, and undergoes various changes of diameter (from
about 3*^ to 15°), and of shape (from circular to elliptical).
Even the proximity of bright stars or planets renders it quite
invisible ; and it can never be seen in June and December,
because it is then crossing the Milky Way. It is best seen in
September and October, in the constellations Sagittarius and
Pisces. M' Barnard, whose eye has the advantage of long
training upon comets and nebulae, has been very successful in
seeing this faint and difficult luminosity of the midnight sky, and
his observations with others show that it does not lie in the
ecliptic, though always close to it, being generally displaced
somewhat north. Apparently connected with the gegenschein
is often seen, especially in the autumn, a zodiacal band, six or
eight times the breadth of the Moon, lying along the ecliptic
and crossing the entire heavens. Whether the gegenschein is
due to abnormal refraction by our atmosphere, or to a zone of
small planets, or to cosmic conditions connected with meteoric
matter, is not yet satisfactorily made out.

Chladni, Ur sprung der von Pallas entdeckten Eisenmasse

(Leipzig 1794).
BlOT, Memoires de Vlnstitut National de Frame, vi. (1806), pt. I.
Chladni, Ueber Feuermeteore (Vienna 1819).
Olmsted, *Fall of i^ii^ American Journal Science, xxv. (1834),

363; xxvi. (1834), 132; xxix. (1836), 376.
Benzene ERG, Die Stemschnuppen (Hamburg 1839).
CoulvierGravier, Les Hoiles filantes (Paris 1847-54-59).
Heis, Die Periodischen Stemschnuppen (Cologne 1849).
Schmidt, /^esultate aus zehnjahrigen Beobachtungen ueber Stern'

schuuppen (Berlin 1852)
Smith, Numerous papers in American Journal Science (1855-

83), and Comptes Rendus (1873-81).
Jones, 'Zodiacal Light,' Report U, S. Japan Expedition^ iii.

(Washington 1856).

Meteoric Bodies 229

Greg, Hbrschel, Glaisher, and others, Reports British As-

socicUion Advancement Science ( i860 and onward).
BucHNER, Die Meteoriten in Sammlungen (Leipzig 1863).
Rose, Besckreibung und Eintheilung der Meteoriten (Berlin

1864).
Newton, * Shooting Stars/ American Journal Science^ IxxxviiL

(1864), *3SI Memoirs Nat, Acad. Sciences ^ i. (1866), 291.
ScHiAPARELLi, ' Orlgine probabile delle stelle meteoriche/

Bull. Met. deir Osservatorio del Collegia Romano^ v. (1866),

8, 10, II, 12.
Phipson, Meteors^ Aerolites, and Falling Stars (London 1867).
Y^iKKViOOH, Meteoric Astronomy (Philadelphia 1867).
Adams, * Orbit November Mtttors* Mon. Not, Royal A stron.

Society, xxvii. (1867), 247.
Graham, Proceedings Royal Society, xv. (1867), 502.
Daubr^e, 'Meteorites,* Smithsonian Report for 1868.
Rammelsberg, Die Chemische Natur der Meteoriten (Berlin

1870-79).
Maskelyne, * Meteorites,' Nature, xii. (1875), 485, 504, 520.
Tschermak, ' Die Bildung der Meteoriten', Sitz. kk. Akad*

Wissenschaften Wien, Ixxi. (1875), ^'*
Heis, Publ. Royal Observatory Munster, i. and ii. (1875-77).
Serpieri, *La Luce Zodiacale/ Mem. Soc. Spettr. Jtal., v.

(1876), Appendix.
V. KoNKOLY, Spectres de 140 itoiles filantes (Budapest 1877).
Newton, 'Relation of Meteorites to Comets,' Nature, xix.

(1879)* 3iS» 340.
Ball, ' Source of Meteorites,* Nature, xix. ( 1879), 493*
Lewis, 'Zodiacal light and Gegenschein,' American Joumai

Science, cxx. (1880), 437.
Herschel, * Meteor spectroscopy,* Nature, xxiv. (1881), 507.
Newton, 'Meteors,* Encyclopadia Britannica, 9th ed. xvi.(i883).
Lehmann-Filh^, Die Bestimmung von Meteorbahnen (Berlin

1883).
Tschermak, Die mikroskopische beschaffenheit der meteoriten

(Stuttgart 1883-85).
Meunier, * Meteorites,* Encycl. Chimique, tome ii. (Paris 1884).
Joule, * Shooting Stars,* Scientific Papers, i. (London 1884), 286.
Searle, a., * Zodiacal light,* Proc. Am. Academy Arts and Sep-

ences, xix. (1884), 146.
Brezina, Die Meteoritensammlung des kk. mineralogy ffo/kcM^

netesin Wien (i^s)'
Fletcher, Study of Meteorites (British Museum 1886).

230 Stars and Telescopes

Daubr^e, 'Origin and structure of Meteorites/ Popular SciefUi

Monthly , xxix. (1886), 374.
Newton, * Meteorites, Meteors, and Shooting Stars,* Proc. Am,

Assoc. Adv. Science^ xxxv. (1886), i.
Wendell, * Meteor Orbits,* Astron. A^achr.^ cxiv. (1886), 285.
SCHIAPARELLI, Le SttlU Cadcnti (Milan 1886).
Newton, * Biela Meteors,* American Journal of Science, cxxxi.

(1886), 409; 'Meteorite orbits,* cxxxvi. (1888), i; also,

cxlvii. (1894), 152.
Denning, ' Distribution of meteor streams,' Month. Not. Royal

Astron. Society, xlvii. (1887), 35.
Flight, A Chapter in the History of Meteorites (London 1887
Huntington, 'Catalogue of all recorded meteorites,' Pioe*

Am, Acad. Arts and Sciences, xxiii. (1888), 37.
Denning, * August Meteors,' iVa tu re jxxxym. (1888), 393.
Denning, In Chambers's Astrottomy, i. (London 1889), bk. v.
Wright, * Zodiacal Light,' The Forum, x. (1890), 226.
LOCKYER, The Meteoriiu Hypothesis (London 1890).
Denning, * Catalogue of 918 radiants,' Month. Not. Poyal

Astron. Society^ I. (1890), 410.
Plassmann, Verzeichniss von Meteor bahnen (Cologne 1891).
Denning, Telescopic Work for Starlight Evenings (London

1891).

Barnard, 'Gegenschein,* The Astronomical Journal^ xi. (1891)^
19; Popular Astrottomy, \. (1894), 337.

Ball, In Starry Realms (London 1892).

Bredichin, Melanges Math, et Astron. vii. (St Petersburg 1892).

KiRKWOOD, * Leonids and Perseids,' Astronomy and Astra-
Physics, xii. (1893), 385, 789; ' Andromedes,' xiii. (1894), 188.

Backhouse, Denning, and others, Memoirs British Astron,
Association, i. (1893), '7 J "*• (^894), i.

Denning, * How to Observe Shooting Stars,* Popular Astron-
omy, i. (1893-94).

Schulhof, Bulletin Astronomique, xi. (1894), 126, 225,324,406.

MoNCK, • Radiants,* ybwr. Brit, Astron, Assoc.y v. (1895), 253.

Ramsay, 'Argon and Helium,* Nature^ Hi. (1895), 224-

Farrington, Cat. 0/ Collection, Field Museum (Chicago 1895).

Harvey, Trans. Roy. Soc. Canada, 1896, § liL 91.

WuLFiNG, Meteoriten in Samml. u. Literatur (Tiibingen 1897).

MiERS, * Ancient and Modern Falls,' Sci. Progress^ vii. (1898), 349.

Wilson, 'November Shower,* Pop. Astron. vi. (1898), 502.

PiCKERiNG,W.H.,*Leonids 1897,' /f//.//Jirz/.CV7/. C?^.xli. (1898), V.
Consult also Poole's Indexes^ under Meteors and Meteorites,

CHAPTER XV

THE CONSTELLATIONS

'X'HE distribution of the stars visible in the north-
-'" em hemisphere into groups, or (as they are
usually called) constellations, was made in very ancient
times, probably by the Babylonian star-gazers. Sev-
eral less important or conspicuous groups have been
added since ; and the principal constellations near the
south pole, visible only in the southern hemisphere,
were formed and named by the navigators of the i6th
century, especially Pierre Dircksz Keyser (sometimes
called Petrus Theodori) , chief pilot of a Dutch fleet
which sailed to the East Indies in 1595. Others were
added by Lacaille when observing at the Cape of
Good Hope in the middle of the i8th century.

About one hundred of the brighter stars have special
names (Sirius, Arcturus, etc.) given them by Greek
and Arabian astronomers or star-gazers ; but with these
exceptions, the only way of referring to any particular
star, .until comparatively modem times, was by means
of its place in the imaginary flgure or animal which
the constellation containing it was supposed to resem-
ble, — for example, the star in the head of Andromeda,
in the tip of the tail of Ursa Major, etc.

The suggestion to designate each star by a letter of
the alphabet placed before the name of the constel-
lation was first made by Alexander Piccolomini, an
Italian ecclesiastic and amateur astronomer, who pub-

232 Stars and Telescopes

lished at Venice in 1559 a small work on the fixed
starSy in which he gave some rough diagrams of the
principal constellations, with Roman letters affixed to
the most conspicuous stars in each. The suggestion,
however, was not generally adopted until John Bayer
of Augsburg pubHshed in 1603 his well-known series
of maps of the constellations, in which he designated
each star therein marked by one of the letters of the
Greek alphabet; and these have been universally
adopted, Roman letters being used when the Greek
alphabet is exhausted. Following the letter is the
name of the constellation in the genitive case ; for
example, a Ursae Majoris, /3 Cygni, etc. Numbers
also (following the lists in Flamsteed's catalogue) are
employed in the same manner, taken in the order of
right ascension of the stars in each constellation, —
being used exclusively for the fainter stars which have
no letters, and in addition to them for the brighter
stars which have."

^1 The tracing of constellations, fascinating as it is to the
popular mind, is of slender importance to the modern astrono-
mer, because he is accustomed to designate most of the stars
which he observes, not so much by their names as by their
numbers in standard catalogues of their positions relatively to-
the imaginary circles described in the next paragraphs. The
ability to recognize at sight about 100 of the principal stars of
the firmament, is, however, well worth the little exertion it
costs; and the helps to acquire this knowledge are abundant in
number and simple in use. Better for the beginner than the
star charts and atlases are the planispheres (p. 240), for reasons
which will become apparent on using them ; and Proctor's
Easy Star Lessons has an advantage over both, in reiterating
the asterisms in their varying seasonal relations to vertical
circles and the horizon. To the observer of luminous meteors
and of variable stars an intimate acquaintance with constellation
figures and stellar names is more important than in other lines
of astronomical inquiry. — D, P. T,

The Constellations 235

It should be noticed that in lettering the principal
stars Bayer did not (as some have supposed) make
the sequence of the letters follow throughout the
order of apparent brightness. The stars in each con.
stellation follow the old diNdsion into orders or classes
of magnitude, and the letters given to the stars in
each class were arranged rather according to the
form of the figure represented than the alphabetic
succession of the letters. This is clearly seen ia
the seven principal stars of Ursa Major, all rated of
the second magnitude. Of these, a and /3 form the
' pointers,' or two stars pointing toward the Pole Star ;
y, d, are the two other stars of the so-called * wain,*
and €, f, 17, are the three in the tail of the bear, or the •
three horses of the imaginary chariot ; but every one
must have noticed that, of these seven stars, 8 is much
the faintest, although taken like the others as of the
second magnitude. It should also be mentioned that,
from occasional touching or overlapping of the figures^
a given star has sometimes, in Bayer's original nomen-
clature, a name by a different letter in two constella-
tions : thus, /3 Tauri is the same star as y Aurigae ;
a Andromedae is identical with d Pegasi, etc. To
avoid confusion, astronomers have in each case dropped
the secondary and retained only the primary desig-
nation. Lacaille, in affixing letters jto the southern
stars, made their order correspond in most cases more
nearly to the successive gradations of brightness than
Bayer had done with the great mass of the constella*
tions lettered by him.

Full description of all the constellations would
require many maps ; but a few remarks may be made
upon some of the more noticeable stars and groups^
especially those in and around the zodiac.

234 Stars and Telescopes

The plane of the Earth's equator, extended to the
heavens, traces out a circle called the celestial equator
or equinoctial, ever5rwhere distant 90°, or a quarter
circumference from both celestial poles. The north
pole of the heavens is indicated in the sky by a star
of the second magnitude very near it, called from
this circumstance * [Stella] Polaris,' or the Pole Star.
Similar prolongation of the plane of the Earth's orbit
to the heavens traces out a circle called the ecliptic
which is inclined to the equinoctial 23® 28', or the
angle between the Earth's equator and its orbit.
These two great circles intersect at two opposite
points called the equinoxes, or equinoctial points.

A zone or band extending 8° on each side of the
ecliptic is called the zodiac ; within this the Moon
and all the large planets are always found, as the
inclinations of all their orbits to that of the earth are
less than 8°. The stars distributed along and around
this zone have been formed into 12 constellations,
proceeding eastward in the following order, — Aries,
Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio,
Sagittarius, Capricomus, Aquarius, Pisces ; and the line
of the ecliptic itself is divided into twelve signs (as
they are called), each having taken its name from the
constellation nearest to it. At the time of the earliest
astronomical writings, the equinoctial points were in
the constellations Aries and Libra, and they are still
said to be at the first or initial points of these signs ;
although in consequence of precession of the equi-
noxes (page 22) they are now in the constellations
Pisces and Virgo, and two thousand years hence will
be in Aquarius and Leo respectively.

As the vernal equinox (where the Sun crosses the
equator when moving northward) is situate in Pisces,

The Constellations

23S

it is evident that six constellations of the zodiac
(Pisces, Aries, Taurus, Gemini, Cancer, and Leo)
occupy a more northern position in the heavens
than the other six (Virgo, Libra, Scorpio, Sagittarius,
Capricomus, and Aquarius), so that the former are
visible more of the time from the northern hemi-
sphere of the Earth than the latter are.

The following considerations will show when these
constellations are above the horizon at night. Al-
though the Sun's light, diffused in our atmosphere,
generally renders the stars around him invisible during
the day, the place of the Sun in the heavens is always
in the ecliptic, and therefore in the middle of the
zodiac. On 20th March he reaches the vernal equi-
nox, so called because it is the one passed by the
Sun in the spring ; but, as previously mentioned, while
that point is still called the first point of the sign
Aries, as in ancient times, its present position is at
the beginning of the constellation Pisces. The Sun
is not therefore at the beginning of the group called
Aries till near the end of April, and he passes the
middle of it in May. Hence it follows that Libra,
at the opposite side of the zodiac, will at that season
be on the meridian, or due south at midnight, and
the rest in order ; so that the annexed table gives the
zodiacal constellation on or near the meridian at the
beginning of successive months : —

January .... Gemini.

February .... Cancer.

March Leo.

April Virgo.

May Libra.

June Scorpio.

July . . .

. SAOrTTARIUS.

August

. Capricornus.

September

. Aquarius.

October .

. Pisces.

November

. Aries.

December . . Taurus.

236 Stars and Telescopes

Before midnight each of these constellations will be
to the east, and after it to the west, of the meridian
during the mooth against which it is here placed.
llie winter Sun being south, and culminating low
down, the portions of the zodiac on the meridian at
night in winter are much higher in the heavens than
those which are similarly visible in summer ; just as it
is matter of common observation that the full MooD
in winter runs high and in summer low.

The most beautiful of the zodiacal constellations is

Taurus, which has several very bright stars (one of

the first magnitude called Aldebaran, or a Tauri) and

contains the splendid cluster known as the Pleiades,

also the more diffused cluster called

the Hyades, in which Aldebaran is

situate. Gemini is remarkable foE

two very bright stars near together,

named Castor and Pollux, — the

former being also designated a, and

THB rLDADi! t^c lattcr j9, Geminorum. Leo is a

iOrdiiuKy n-tkidrfi fine group, and has perhaps (what

koaI' ali"*!^^ ^^'^ have) a little resemblance to

grafku fiaitkavt the figufc indicated by the name.

™'^„™'*;^ The forepart of Leo has something

rtr/m, kuHdrtdi the shipc of a sickle, and contains

'itawi u tkTiK- * star of the first magnitude, a Leonis,

largnipiniicHat ©r Regulus. Virgo has only one

bright star, to which the name Spica

Virginis was attached by the ancients ; and it is now

known either as Spica or a Virginis, The only other

very remarkable star in the zodiac is the beautifiil red

' object known as Antares (Cor Scorpii), the brightest

star in the constellation Scorpio.

With regard to the other constellations, the most

THE PLEIADES —
IFrsm fluligraflu ^y llu Bmktri Hth

238 Stars and Telescopes

splendid is Orion, partly in the northern and panly in
the southern celestial hemisphere. The three bright
stars in a straight line above the middle of it (com-

NEBULA IN ORION

riii mMa it/amUji viiiUr In lAt mtkiJ fyr nrrimnia^ Ikr mit/iUr aar
mlkiSvitrd^CMni. Srt fta£t aba. A mnr likr mnii oui-iiifiit riirrtirrt
a/tUt magiii/icriU ttftcl, tr/urt IIU iltiytr/ Hi flirlstra^'e frrlrailim,ntn

Or Bniins [WiLLIlH ClONCH, jx^ iiianr.t: Philliv^. A'At'- ami m), IMC-
aairrfy Piricrt «/ lit Harvitrd Ohtrvalfrf. Tit tUlfr't Jnaninf rf
Iht Grral Nlbtila it imoirfmuiH

The Constellations- 239

monly called Orion''s beit, but by istrbnomcrs 9, t, (
Ononis) point in an easterly direction somewhat above
Krius, the principal star of Canis Major, which is the
brightest star of the entire heavens. Of the stellar
objects near the north pole, the seven which fonn
part of Ursa Major are best known. As already men-
tioned, a line prolonged through ^ and a points nearly
toward the pole star. Another (carried to a con-
siderably greater distance), through f, ij, passes very
near to Arcturus, the principal star in Bootes; and
one extended in the reverse direction through 8, a,
will similarly indicate the position of Capella, the prin-
cipal star in Auriga, and the brightest of the northern
hemisphere. It is thought that this object has some-
what increased in brightness of late year^, and that
Vega was formerly the brightest.

On the opposite side of the pole star from Urea
Major, and at about an equal distance from it, is the
fine group called Cassiopeia, which contains several
bright stars arranged somewhat in the shape of an
irregular W. Next in brightness to Capella is Vega,
the principal star of the small constellation Lyra, which,
at the average latitude of places in the United States,
passes very near the zenith at its upper culminatioD.
To the west of Lyra is the large and scattered group
known as Hercules ; to the east of it, AquiJa, the three
most conspicuous stars in which are near together and
almost in a straight line, the brightest of the three,
a Aquilae, being in the middle. Southward from Cas*'
siopeia is Andromeda, whose three principal stai»<
(with the three brightest in Pegasus at mi..- end and
the largest star in Perseus at the other) form w con-
figuration resembling the seven principal itars of Ursa
Major. That star in Andromeda (a) nearesi

240 Stars and Telescopes

was regarded by the ancients, and marked by Baver,

as belonging to both constellations ; and the square

formed by it and a,

ftyPegasi, is called
the ' square of Pe-
gasus.' Nearly be-
tween Aquila and
Pegasus is Cygnus,
resembling a Latin
cross ; while be-
tween Aquila and
the southern part
of Hercules is the
northern part of
Ophiuchus, a con-
stellaiion extend-

»-■■»" '■'^■»-' "^r^-

times called Serpentarius { serpent- holder ) , the same
in signification as Ophiuchus, the latter word being
derived from the Greek.

IDELER. Ursprun^ utid die BedfutuBg drr Stirnnamtn (Berlin

1 809).
HiGGiNs, Names o/Ihe Sl<Jri and Constillaliims {London 18S2).
GORK, An Astronomieal Glossary ( London 1893).
West, ' Pronunciation of Arabic Stit-names,' Popular Astrou-

omy, ii. (1895), 209.

WhitaLL, Megabit Plamsphere (Philadelphia).

Phili.tps, Planiiphtrt far iht LaiitHde of En^and (London).

GOLDTHWAITK, Plattisphrre for Latitudi 40° N. (New York).

\iKf.f.\KQ-lov,Pla«isphireforLalihtdeo/tlifU.S.(knah.i\iai).

Poole, Colas, CiUstial Planiiphtri (Chicago).

DuNKiN. The Midnight Sky {laxAiia \^).

The Constellations 241

Proctor, Half-hmtn vntk tht Start (London 187S).

Proctor, Easy Star Lessons (New Yoili i88a).

Colbert, The Fixed Stars (Chicago 1886).

Clakk and Sadler, The Star-guide (London 1SS6).

Jeans, Handbook far finding the Stars (London 1S88).

Young, ' Uranography,' in his Elements ef Astrunptny (Neir
York 1890).

Hill, R., The Stars and Conslellaliem (New York 1891 ).

Upton, ' Con slellal ion study,' Popular Astranomy, i. (1893-94).

Serviss, The Popular Stience Moiilhly, xlv.-xlvii. (1894-95).

Also the constellations aie accurately and aitistically figured
in The Century Dictionary (New York tSSg-gl).

Clarke, Haui te Find the Stars (Itosion 1893) ; for use in con-
nection wiib his convenient astronomical lantern. Also H*
ItAiLEV's 'Astral Lantern' will be found vetj bclpfui in
learning tlie stars and con 5 Id tat ions.

Argelander, Uranamel

Mjtcheu O. M., Atlai
edition of Burritt.

BURRITT, Geography 0/ the Heavens, with Alias (N. Y. lSj6).

Chacohnac, Atlas tiliplique (Paris i86i).

Ki.GV.X.t.-fm.i.. Atlas des mrd. C/slirnten Himmels {Gann 1863).

Hets, Atlas Caeleilis Novus (Cologne 1871).

Proctor, Nevi Star Atlas (London 1874).

NewcomH, Star maps in his Popular Astronomy (N. Y. 1878).

HOUZEAU, Uranomttrie Glnlrale (Brussels 1878).

Gould, Uranometria Argentina (Buenos Ayres 1879).

Peters, C. H. F„ Celestial Charts made at the Litchfirld Obser-
vatory (Clinton, N. Y. 1882).

Johnston, Grant, School Atlas of Astronomy (New York 1884).

EsplN, Elementary Star Atlas (London 1885),

ScHfiSFELO, Bonner Stemtarttn (Bonn lB36).

ScHURlG, Himmeli'Allai (Leipiig l886),

Messer, Stem-Alias fiir Himmtlsbeoixichtung (S\. Petersbui^
1888).

Klein, McClure, Star Atlas (London 1888).

Cottam, Charts of the Conslellalions (London 1889).

Peck, Handbook and Atlas of Astronomy {Hfw York 1891).

Weiss, Bilder-Atlai der Slernemivll (Esslingen 1891).

Ball, An Atlas of Astronomy (Mew York 1892),

RoiIRBACH, Sternkarlin in iptomon. Projection (Berli

Vf'roti, Star Atlas (Boston 1895).

Peck, Tit Oiierver's Alias i^ tie Hemens (LaaAonii
s^t — 16

CHAPTER XVI

THE COSMOGONY

npO inquire into the origin and development of the
•*• heavenly bodies is the object of the Cosmog-
ony, or the science of the formation of the world.

Have the planets, the Sun, and the stars always
existed, as they now appear in the sky ; or was there
a time when the present beauty and order of the
Cosmos was supplanted by a state of chaos? To
this question the cosmogony of the present time
answers that the heavenly bodies have been gradually
developed from a diffused or nebular condition, just
as animals and plants are developed on the earth;
but that it has taken countless ages for the Sun and
stars to attain their present state of evolution. It is
shown that in the beginning the nebular condition
prevailed, and the law of universal gravitation caused
the matter to gather into masses called nebulae.
The process then is the following : as these gaseous
masses condense, there arises a motion of rotation
around some centre, so that the nebula begins to
rotate on an axis. The particles of the nebula are
acted upon by two forces : ( i ) The gravitation of
the mass; (2) The centrifugal force of rotation.
As the mass condenses, the rotation becomes more
rapid, owing to the conservation of the moment of
momentum, and the contraction of the radius of

The Cosmogony 243

gyration ; so that at length the centrifugal force be-
comes equal to gravity, and the particles on the
equator of the mass cease to fall toward the centre.
Thus a ring (or lump) of nebulous matter is left

iPliMcgrafliid fy RoBU-n, 1SS8 — Exftturr, fnr kauri)

behind, revolving around the central mass in an
elliptic orbit, so well illustrated in the above engrav-
ii^ of the great nebula in Andromeda. The body
thus separated will in the course of ages condense
into a satellite or planet, 01 double star, as observed
in space.

244 Stars and Telescopes

Having stated this essential idea of celestial evo-
lution, the history of the subject will now be briefly
surveyed. Cosmogony has engaged the attention of
philosophers from time immemorial ; but it is only
in the last century and a half that substantial progress
has been rendered possible by the general advance
of all related sciences. Anaximander, Anaxagoras,
Democrftus and other ancient philosophers held that
the world had arisen from the falling together of
diffused matter in a state of chaos; and proceeding
on this supposition, they endeavored to predict its
future career and ultimate destiny. Some of the
Greek philosophers, Aristotle, for example, and
Ptolemy, while admitting the perishable character of
all terrestrial things, maintained that the world beyond
the orbit of the Moon is imperishable and eternal.
Other philosophers followed Anaxlmander and Anaxi-
MENES in maintaining that, as the world had arisen in
time, so it would in time pass away ; and thus the
universe had undergone and would continue to un-
dergo alternate renewals and destructions.

In like manner the still more ancient cosmogony
of Genesis declares that in the beginning the Earth
was * without form and void, ' and implies that the visi-
ble world has arisen by a process of gradual evolution.
These theories of the ancients are of course mere
speculations supported by broad analogies of nature,
but as they are in general accord with modem results,
they are of interest in the history of the cosmogony.

Cosmogonic speculation of a scientific character
began with Kant, who was the first of modem phi-
losophers to advance a definite mechanical explana-
tion of the formation of the heavenly bodies, and par-
ticularly of the bodies composing the solar system.

The Cosmogony 245

The views of Kant, however, do not seem to have
received much scientific recognition untL after Ia
Place's independent formulation of the nebular hy-

Ihmanuel Kant (1714-1804)

pothesis. La Place advanced the nebular hypothesis
as a result of his prolonged study of the mechanics
of our system, and the sound dynamical conceptions
underlying his explanation secured for it immediate
recognition. The work of Sir W[lliam Herschel
lent observational support to La Place's ideas, and
the observations of Sir John Herschel strengthened
the evidence gathered by his illustrious father.

But about 1850, when Lord Rosse's great reflector

346 Stan and Ttltscepa

La Plack {1749-1827)

showed the discontinuous nature of some of the objects
then classed as nebula:, the question arose whether
with sufficient power ail nebulas might not be re-
solved into discrete stars. Fortunately, the inven-
tion of the spectroscope by Kirchhoff about i860,
and D' Huggins's application of it to the heavenly
bodies at once answered this question in the negative,
by showing that many of the nebulx are masses of
glowing gas in the process of condensation. It then
became a matter of great scientific interest to inves-
tigate the formation of the heavenly bodies. The

The Cosmogony 247

principle of the conservation of energy and the me-
chanical theory of heat, which von Helmholtz was

the first to apply to the nebular contraction of the
Sun, and Lane's researches on condensing gaseous

24S

Stars and Telescopes

masses, together with the researches of Lord Kelvin
on the Sun's age and heat, have each marked im-
portant epochs in the development and confirmation
of the nebular hypothesis, as now maintained and
generally accepted by astronomers. The importance
of Lane's work consisted in showing that a gaseous
mass condensing under its own gravitation might rise
in temperature, and thus La Place's assumption of an
original high tempera-
ture became unneces-
sary, as the heat might
be developed by the fall-
ing together of cold
matter, I^ I'lace sup-
posed that the planets
and satellites resulted
from the condensation
of rings which were suc-
cessively shed by the
contracting nebula, but
to explain how a ring
would become a planet
has always been some-
what difficult. Yet prior
to the researches of Professor G. H. Darwtn, the ' ring-
theory' was never seriously questioned, at least in
regard to planetary evolution. But the course of
thought was greatly changed when he showed that the
Moon probably separated from the Earth not in the
annular form supposed by La Place, but in the form
of a globular mass, which had been driven away to its
present distance by the tidal reaction of the Earth.
The tides here alluded to are not surface oceanic tides,
but tides in the body of the molten globe, which were

(1800-1867)

The Cosmogony 249

especially high when the two bodies were close to-
gether. As the matter composing our planet is fric-
tional, the tides lag, and the tidal protuberance in
the E^rth therefore points in advance of the Moon,
and exerts on it a small force tending to accelerate
its motion, with the result that the distance increases ;
while the reaction of the Moon against the protube-
rance retards the rotation of our globe on its axis.

In this way Professor Darwin explains the expan-
sion of the Moon*s orbit from age to age, and shows
that the working of tidal friction would also render it
more and more eccentric. Also he sought to apply
this remarkable theory to the development of the
planetary system as a whole, but it was found that
elsewhere in our system the effects of tidal friction
had been comparatively unimportant.

The general result of Professor Darwin's work on
the cosmogony of the solar system is to leave La.
Place's theory without any material change except
in the system of Earth and Moon. If it were possi-
ble to overcome the mathematical difficulty of ex-
plaining how a ring could condense into a planet, the
regularity in the motions of the planets and satellites
and the circularity of their orbits might be explained.
The too rapid revolution of the satellite Phobos round
the planet Mars can be accounted for as a result of
tidal friction ; but it is difficult to explain in a satisfac-
tory manner the retrograde motion of the satellites
of Uranus and Neptune, though the suggestions of M.
Faye are ingenious and possibly of lasting value.

Recently D' T. J. J. See, of the University of Chi-
cago, has taken a farther and very important step in
the development of the theory of cosmical evolution,
and incidentally he has applied it to the planetary

250

Stars and Telescopes

system. In investigating the origin of double stars^
he found that their orbits are generally very eccen-
tric, as compared with the orbits of the planets and
satellites, and it occurred to him that the cause of
this remarkable phenomenon might be the secular
action of tidal fric-
tion. His orbit of
a Centauri shown
here is a typical bi-
nary with about the
average eccentri-
city.

It appears that
double stars have
arisen from the
breaking up of dou-
ble nebulae by a
process of division
resembling fission
among the proto-
zoans, and that their
orbits were origin-
ally nearly circular.
According to D'See
the average eccen-
tricity is about 0.45,
while in the plane-
tary system the ave-
rage eccentricity is
only 0.0389, or one twelfth of that found among bi-
nary stars. Another very important point in his
researches lies in the connection pointed out between
double nebulae and the dumb-bell-shaped figures of
equilibrium discovered by Darwin and PoiNCARfe.

ORBIT OF ALPHA CENTAURI
{CofHputed and protected by D'" Seh)

The Cosmogony

251

These eminent mathematicians have substantially
proved that it is possible for a rotating nebula to
break up, under its own contraction, into an hour-
glass figure exactly resembling the double nebulae ob-
served in space. On these pages are reproduced the
figure of PoiNCARi, and a typical double nebula, to
show the process of division.

The masses resulting from the figures of Darwin
and Poincar£ are much too large relatively to render
the results applicable
to our own system,
where the attendant
bodies are always
verysmall. Justsuch
masses, however, ex-
ist among double
nebujje and double
stars ; and D' See
therefore concludes
thai if such large rel-
ative masses are not
found in our system
they are found in
abundance elsewhere
in space. He points
out that the double scars are remarkable for two
fundamental facts; (i) The large mass- ratios of the
components, so that the masses are often nearly
equal and always comparable ; and (3) the high
eccentricities of their orbits.

Among all known systems, that of the Sun is re-
markable for the great number and small masses of
the attendant bodies, and for the near approach to
circularity in the orbits. Nearly all the mass of the

252 Stars and Telescopes

original solar nebula is embraced in the Sun, which
has 750 limes the mass of all the attendant planets

and satellites com-

bined. Our system is

essentially single — all
the mass in the Sun
— while in binary stars
the systems are essen-
tially double.

Applying the law of
binary evolution to
the planetary system, the figure of potNCAR*

D' See concludes that

the planets were separated not in the form of rings,
as La Place supposed, but in the form of lumps or
masses, which would easily condense into planets and
satellites. In this manner he escapes the necessity
of explaining how rings would condense into single
masses ; indeed, he maintains that rings would not
condense at all, but become swarms of small bodies,
like those which make up the rings of Saturn and
the small planets between Mars and Jupiter.

It is still too early to pronounce an opinion as to
the uhimate value of these later researches in cos-
mogony. The weak point in the older theories lies
in the deduction of all cosmical laws froni our own
system, whose formation appears to have been some-
what anomalous. But as D' See's theory of cosmical
evolution has been deduced from the study of other
systems in space, and is in harmony with the known
facts of Nature, it may fairly be regarded as the
most advanced step yet taken in the science of the
formation of the heavenly bodies.

The Cosfnogony 253

Kepler, Epitome Asironomiae Copemicatuu (Frankfort 1635).
SWEDENBORG, De Choo Universali Salts et Planetarum ( 1734,

and London 1845).
Wright, A New Hypothesis of the Universe (London 1750).
Kant, Naturgeschichte und Theorie des Himmels (Konigsberg

>755).
Lambert, Cosmologische Brief e die Einrichtung des Weltbaues

(Augsburg 1 761).
Herschel, ' Nature and Construction of Sun and Fixed Stars,'

Philosophical Transactions for 1 795.
La Place, Exposition du Systime du Monde (Paris 1796) ; and

Annuaire du Bureau des Longitudes for 1867.
COMTE, 'Cosmogonie Positive,' VInstttut, iii. (1835), 31.
Mayer, Dynamik des Himmels (Heilbron 1848).
Rankine, * Reconcentration of the Mechanical Energy of the

Universe,' Philosophical Magazine^ iv. (1852), 358.
Thomson, Mechanical Energies of the Solar System (Edinburgh

1854).
KiRKWOOD, *On the Nebular lly^oih^sxst Am. Jour. Science,

XXX. (i860), 161.
Trowbridge, * On the Nebular Hypothesis,' several papers in

American Journal of Science for 1864 and 1865.
Proctor, * La Place's Nebular Theory,' in his Saturn and its

System (London 1865), 201.
Roche, La Constitution et POrigine du Systhne Solaire (Mont-

pellier 1875).
Nyr6n, * Ueber die von Emanuel Swedenborg aufgestellte

Kosmogonie,* Vicrtel. Astron, Gcscll.y xiv. (1879), ^o*
Clifford, *The First and the Last Catastrophe,' in his Lec-
tures and Essays^ i. (London 1879).
Peirce, 'Cosmogony,' and 'From Nebula to Star,' in his

Ideality in the Physical Sciences (Boston 1881 ).
Darwin, Papers in Proceedings and Philosophical Transactions

Koyal Society, 1878-1881.
Helmholtz, *On the Origin of the Planetary System,' Popular

Lectures, 2d series (New York 1881).
Newcomb, * The Cosmogony,' in his Popular Astronomy (New

York 1885), 503.
Fa YE, Sur POrigine du Monde (Paris 188 5).
Faye, * Sur la Formation de TUnivers et du Monde Solaire,'

Annuaire du Bureau des Longitudes for 1885.
Wolf, Les Hypotheses Cosmogoniques (Paris 1886).

254 Stars and Telescopes

Parkes, Unfinished Worlds (New York 1887).

Braun, Ugbgr Cosmogonie vom Standpunkt Christlicher Wissen-
jr^//?(Munster 1887) ; Clkrke, AWwr^.xxxviii. (1888), 365.

Janssen, * L'Age des fitoiles,' Annuaire du Bureau des Longi-
tudes for 1888.

Coakley, 'On the Nebular Hypothesis of La Place/ Papers
American Astronomical Society (Brooklyn 1888).

Croll, Stellar Evolution (New York 1889).

Hirn, Constitution de PEspace Cileste (Paris 1889).

Ball, Time and Tide (London and New York 1889).

Lockyer, The Meteoritic Hypothesis (London 1890).

Green, The Birth and Growth of Worlds (London 1890).
Bibliography.

Tuckerman, ' References to Thermodynamics,' Smithson. Misc,
Collections^ No. 741 (1890).

Klein, Kosmolo^ische Brii'fe (Leipzig 1891).

Keeler, Astronomy and Asiro-PhysicSy xi. (1892), 567, 768.

Clerke, The System of the Stars (New York 1892).

Darwin, ' Cosmogonie Speculations founded on Tidal Fric-
tion,' Article ' Tides,' Encyclopcrdia Britannica (9th ed.), 1892.

Gore, The Visible Universe (London and New York 1893).

See, Die Ent7vickelung der Doppclstern-Systeme (Berlin 1893).

Ball, The Story of the Heavens, Chapter xxvii. (London 1893).

Stanley, Notes on the A-ebular Theory (London 1895).

Lockyer, Evolution of the Heavens and the Earth (London 1895).

Nolan, Satellite Evolution (Melbourne 1895).

See, Researches on the Evolution of Stellar Systems (Lynn 1896).

Gerlani), in Valentiner's Handworterbuch der Astronomic
(Breslau 1897).

See, The Atlantic Monthly, Ixxx. (1897), 484.

LiGOND^s, Formation Alicanique du Systime du Monde (Paris

1897).
Chamberlin, * Climatic Changes,'/<7i/r. of Geology , v. (1897), 653.

MoULTON, Popular Astronomy, v. (1898), 508.

La Fouge, Formation du Systtme Solaire (Chalons-sur-Mame

1898).
Darwin, The Tides and Kindred Phenomena in the Solar

System (Boston 1898).

Consult also under Nebulce^^ references in Poole's Indexes
cited on page 315 of this volume. Also in The Westminster
Review (July 1858) is an able discussion by Herbert Spencer.
Matson's References for Literary Workers (Chicago 1892) con-
tains at pp. 388-9 a bibliography of popular articles. — D. P. 71

CHAPTER XVII

THE FIXED STARS

TT remains to give a short account of the motions
-*• and distances of those far more remote heavenly
bodies which come under the general designation of
fixed stars, devoting also a few words to the investi-
gations concerning the probable motion of our own
system, as a whole, among them.

Those fixed stars which are bright enough to be
visible to the naked eye have been watched from the
most remote antiquity ; but, excepting the changes of
brightness to which a few are subject, and the occa-
sional appearance of a temporary star never seen
before, no other knowledge of the fixed stars than
that of their comparative brightness and apparent
distribution in the sky was obtained before the inven-
tion of the telescope, or indeed could be. With
regard to the temporary stars, it is not in all cases
€asy to say whether the accounts handed down to us
really refer to a new star or to a comet. The most
ancient record of such an object relates that in b. c.
134, a new star burst out with a brightness sufficient to
render it visible in the day-time, and attracted the
attention of Hn»PARCHUS, leading him to draw up a
catalogue of stars (the first ever made), with a view
of enabling future ages to trace with certainty any sub-
sequent appearances or disappearances. The Chi-
nese annals show that the astronomers of that country

256

Stars and Telescopes

also noticed this star, which seems to have been situate
in the southern hemisphere and in the consteUation
Scorpio. They also speak of one said to have been
seen in the constellation CenCaunis in a year coire-
L. D. 1 73."

^ Cataloguing the stars is the nii>sl tedious labor of the mod-
em practical astronomer. A high degree of accuracy in the
positions is demanded, and the latest catalr^ues embtace maiij
thousand faint stars, most of them invisible to the naked eye.
Stellar catalogues nearly always contain the magnitudes of the
stars, given according to an arbitrary scale of numbers exprets-
ing theit brightness. Twenty of the brightest stars of the fir-
mament, ten in the northern celestial hemisphere and ten ia
the southern, are rated oi the first magnitude. Then follow

63 of the second magnitude,
200 of the third,
500 of the fourth,
1400 of the fifth.

HEIS (1806-1877)

St being so faint that they
visible to a keen eye OD
lonless nights. The num-
reases rapidly with each
fainter magnitude, nearly in geo-
metric proportion; so that, if we
include stars of the tenth magni-
tude, the faintest included in cata-
logues, there are about a million in
all. Estimalcs of the uncounted
hosts of uncatalogued stars 'stilt
fainter and fainter, down to Che
17th magnitude, make the total
number far

Profea;

the

photograph opposite shows how thickly they :
many parts of the celestial vault. Until reci
magnitudes of the brighter stars were for the most part deter-
mined by mere eye estimates, and flEtS, Che Gei
mer, who spent many years observing paths of

(PielillT-a^d by PrB/il

258

Stars and Telescopes

Another star, as bright at one time as the planet
Venus, is said to have appeared in the year a. d. 389

an exceedingly accurate observer of stellar magnitudes as well-
But the most precise results have been obtained by means of
instruments called photometers, in which every star is re-
peatedly compared with a standard light of known intensity.

THE MERIDIAN

Stellar photometers are of varied designs. Pritchard as«d
a ao-called wedge photometer, in which a thin strip of colored
glass, with faces slightly divergent, waa attached to the e^e-
piece, and that position of the glass wedge was recorded at

Tlie Fixed Stars 259

(in the reign of the Emperor Theodosius) : but from
the accounts given by the ecclesiastical historians, it is

wliich ihe Slat's light was extinguished. Ptofessor PlCKBRlNO
has successfully employed a tyjie of his own devising, and
named ihe meridian pholomeiei, shown opposite, and Sa
called because each star, when near the meiidian, is ditectly
compared with Polatis. itself an invariable standard. The
ubltqu« minots enable this to be done, no uiatter what Ihe

PHOTOGRAPHIC EQUATOBTAL TELESCOPE
IBuill tf Sir Howaud Gauss >r /Ht R^ai ObiirvnUry m
Ca-^ r^vm- riu /irmiT l.i, i, Ihi tlalttnUac tiltMcafi,
mil* a l)-iPK* •iJtil-gLiii ; Iki nffrr «r ii an ^itj/ t,
tvidiae IfUKoft milk a g-iack aijnlim. TJu luSti an tl
flllltnt. Similar inilnimtnU hr Ikt lamt mak^,/sr Ih,
Inlt-tMitiml A ilrrfra/*it Siirvtf, art mimalfj al GrrtH-
mich, Oxfird, Mtltennu, SjiiIm^, and Ta.vtfa, ut Uixitt]

36o Stars and Telescopes

evident that a remarkable comet was seen at the time
to which this appearance is referred, so there can be

altiiude of the star. With this instrument, as tnounied at
Cambridge, Massachusetts, and later at Arequipa, I'etu, the
tuagnitudes of all the brighter stars of both iiurlheni and
southern hemisphetes have been deieimined with a degree of
accuracy unsurpassed. Attempts have been made in the hope
of increased precision in magnitude by means of photography,
but as yet without much encouragement. Photography, how-
ever, has already revolulioniied the construction of star cata-
logues, because the highly sensitive plate records in an hour
as many stars as an astronomer could observe the position of
in many weeks. Foremost in these highly significant re-
searches is D' Davtd Gll.L, the earliest to propose an interna-
tional congress of astronomers, which first met al Paris in 1SS7,
and undertook an asttographic survey and photographic map of
the entire heavens. This is now in progress, with 1 8 instruments
like the one on page 259, six of which ate located in the south-
ern hemisphere. Nearly all the great nations originally joined
in this im|>orfant work, including the observatories al Paris,
Algiers, Bordeaux, Toulouse; San Fernando (Spain), Catania,
and Rome (Vatican); I_t Plata, Rio de Janeiro, and San-
tiago, in South America: Helsingfors and Pot«lam in Ger-
many; in addition 10 the observatories named on the preceding
page, Some, however, have dropped out. from lack of funds.
The total number of plates exposed a( the conclusion of this
comprehensive survey will be more than 20.000, and the total
expense for all nations will aggregate not far from Jioo for
each plate. Then the plates must be carefully measured, and
the resulting data converted into arcs of the celestial sphere,
so that the right ascension and declination of every star may
be given as in catalogues constructed in the old-fashioned way
by means of the meridian circle (see page 36S). D' K.vptevn
of Groningen is foremost in the work of deriving star- positions
from photographs, and he has already measured and catalogued
rtcarly half a million stars from the Cape Town plates. At
Paris the work is progressing rapidly under the direction of
M°' Klumpke. But the degree of precision attainable by the
photographic method does not displace the necessitv for the
labors of the astronomer with the telescope alone. The long-
tested methods of slow observation with meridian instruments

The Fixed Stars 261

little doubt thai this report of a new star is simplj'
due lo a misunderstanding of the description of the

must still be employed when the last degree of precision is
soughl. The name o£ Aruelandeh, a pupil of the great
BKiSEL, stands out pie-«minently lor persistent faithfulness in

p. W. A. ARGELANDER (i799-'87S)

this clans of observation. His famous Durchmtaterung of the
northern heavens embraces no less than 324,198 a tars, set do vn
with some precision, both in catalogues and in a scries of stellar
charts, which are a prime essential in all working observatories.
In 1S65 the Atlranamuche Catllukaft of Germany undertook

262 Stars and Telescopes

comet, which moved in the heavens from near the
place where Venus then was to the constellation Ursa

a supplementary irork of vast magnitude, the re-observation of
about one third of Argblandkr's stars, with the highest tlegree
of accuracy attainable. These Gestllsehajt zones, observed at
13 observatoiies, European and American, are now nearly com-
plete. What Arcelanuek did for the nortbetii sky, Gould

BENJAMl

did tor the southern heavens, by residinj; for tifleen years at
Cordoba, Argentine Republic. Together with his assistants, he
observed nearly 75,000 stars, e^tlending to the <^ magnitude;
published in 1S79 the Uranemetriit Ari;inliva, an elaborate
series of charts of the southern heavens ; in t3S6 the Argentine
General Catalogue of 32,oooaiars; and in i8g;, shortly after his
lamented and accidental death, DrCHANm.FR brought out the
last great work of Gould, being a complete discussion of about
40 clusters of stars in the southern sky, with positions derived

The Fixed Stars 263

Major. A similar remark applies to new stars which
are said to have appeared in the northern heavens in
A.D. 945 and T164. In all probability both were
comets; in the latter year (that ofthe battle of Lewes)
a splendid comet is known to have been seen.

Bui it is quite certain that a very conspicuous and
remarkable new star t/itl appear near the constellation
Cassiopeia in 1572- It was noticed in other parts of
Europe several days before it was seen by Tycho
Brah£ ; but he made a series of careful observations
of the star, and left an elaborate account of it. He
first saw it while residing at his uncle's house in Scania
(then included in the kingdom of Denmark, but united
to the rest of Sweden in the following century), on nth
November 1572. Its brightness even then rivalling
Sinus, and increasing until it surpassed that of Jupiter,
the star was for a short time visible in broad daylight ;
but it soon began gradually to fade away, and by March
1574 had totally disappeared, after having been seen,
with more or less brilliancy, during a period of about
16 months.

from measure men Is upon photographs, which GouLi) began at
Cordoba in 1871 as the pioneer. In 1889 Miss CaTKERINB
W. Kruce of New Vork donated to Harvard College Obaer-
valory the Bum of (50,000 fur a great photographic telescope,
of S4 inches aperture. This has been constructed by Alvak
Clark 4 Sons, from designs by Professor Pickerikg, and it
is now mounted in Peru, where the more interesting regions of
the southern heavens are in process of permanent recotd. This
telescope and its unusual type of mounting are illustrated on
page 264, and opposite is a reproduction of a part of one of the
star charts taken with it. On the entire original glass, 14 X 17
inches square, were 400.000 stars by actual count. Probably
the Bruce telescope is the most powerful optical instrument in

stence. Certainly it can photograph the taint glimmer of

lusands of stars which no human eye can ever expect to see

iny telescope.— iJ./*. T.

ipi

iiiill

.jilL

* ■"■'-■■ ' . 'i' '

«- ■ -':

',"-N*

i^^:-'/

■m. •'^-. •

" ;'■

-j.i

»■ •- .; '

• ■■ ■'

■*" :'. ■ ! ■

' '"■'■.

^/^..s./.^

■ - ■■■

{P/ultcrafAtd ty Prtfixitr B*IL»y tuilk llu Bnut IlltKaft. Iipsniri
[EKtTiaiHi/ram Todd's ' Ntw Aitrtntm^; bf tftcial ftrmiai^ of llu A

266 Stars and Telescopes

Another temporary star appeared in the right foot
of the constellation Ophiuchus in the year 1604, and
was observed by Kepler and others. At one time as
bright as Venus, it continued visible for more than a
year, disappearing about the end of 1605. On 20th
June 1670 Father Anthelme, a French Carthusian of
Dijon, noticed another new star of the third magni-
tude, very near the head of Cygnus. Observed both
by Hevelius and by Cassini, it underwent several
remarkable changes in brightness during two years,
then completely disappeared, and has not since been
seen. Another star in the same constellation (now
known as 34 Cygni) underwent some remarkable
fluctuations of light in the i 7th century, but has re-
mained unchanged in brightness since, being just
visible to the naked eye.

Within the last fifty years several temporary stars
have appeared quite suddenly, whose previous exist-
ence is unrecorded. One of these was in 1848, when
Hind noticed, on 28th April, a star of the fifth mag-
nitude (easily visible to the naked eye), in a part
of the constellation Ophiuchus, where he was certain
that, so recently as the 5th of that month, no star so
bright as the ninth magnitude was visible ; nor is
there any record of a star having been observed there
at any previous time. From the date of its discovery
it began continuously to diminish in brightness, and it
is now visible only through very powerful telescopes.
A still more remarkable, as well as more recent case of
the appearance of a temporary star (temporary at least
as regards its visibility to the naked eye) is that of a
star in the constellation Corona Borealis, which seems
to have burst out quite suddenly, 1 2th May 1866, when
it was first noticed by Birmingham in Ireland. Of the

The Fixed Stars 267

second magnitude al the time of discovery, it dimin-
ished so rapidly as to be invisible to the naked eye
by the end of the month. In the autumn of the same
year it increased somewhat in brightness again, — but
not sufficiently to become visible without a telescope, —
and afterward sank down to what must be considered
its normal brightness. A third instance of the kind
occurred in 1876, when Schmidt, of Athens, noticed
on 24th November, a new star of the third magnitude
in the constellation Cygnus, which afterward gradually
faded away, ceasing to be visible to the naked eye in
about a month, and is now to be seen only with the
aid of a very powerful telescope. Toward the end of
August 1 885 another new star api>eareil in the midst of
the great nebula in Andromeda ; but it never became
bright enough to be visible to the naked eye. The
most recent case is that of a star in Auriga, which was
first noticed at the end of January 1892, but was after-
ward found to have been registered by photography
in the preceding December. It faded away in March
rSga, after having been for a few weeks visible to the
naked eye."

M Nova Aurigae has the most singular history of all the
temporary stars, D' ANor.RSON. an amateur of Edinburgh,
was its first discoveiei, his meagie equipment consisting of only
a star atlas and a pocket telescope magnifying ten times. But
examination of the Harvard stellar photographs at once
showed that the star had many times been recorded by its
own light on plates exposed between loth Dccetnlier 1891 and
3oth January 1S92. Measures of tliem showed that Nova
Aurigae had rapidly attained its maiimum brightness unob-
served on aoth December, when it was of the 4.4 magnitude,
and therefore plainly visible without a telescope. By the ist
of April the star had became invisible, except with a very
large telescope, but in August 1S9Z a temporary brightening
brought its magnitude up from the 13th lo the 10th. Through

268 Stars and Telescopes

The above are special cases, but the number of
stars which may be called regularly variable, being

1893 and 1894 it remained between the loth and nth magni-
tude, and Professor Barnard's observations with the 36-inch
Lick telescope from 1892 to 1895 show that Nova Aurigae had
become a small, bright nebula with a star-like nucleus. Pro-
fessor Campbell, D' von Gothard and others, who critically
examined the star's spectrum, showed that it was practically
identical with the sp>ectra of planetary nebulae. Parallax
observations, similar to those described later in this chapter,
showed that the star was as remote from the solar system as
the average of the stars whose distances are known. The
outburst which produced the sudden rise in its brightness
must, therefore, have taken place on a scale inconceivably
grand. Just what caused it cannot be said to be known ; but
the complex character of the star's spectrum in February 1892
indicates a probable collision, or at least a near approach, of
two vast gaseous bodies travelling through interstellar space,.
with a relative motion exceeding 500 miles a second.

A swarm of meteorites swiftly traversing a remote gaseous
nebula would account for most of the peculiarities of the
spectrum of Nova Aurigae. But a wholly satisfactory theory
is not likely until many other new stars appear in the sky, and
their constitutions are studied by means of spectra photo-
graphed at short intervals. That lynx-eyed watch of the whole
sky, both northern and southern, now kept by means of pho-
tography, enables us to say that new stars are not infrequent
objects, as formerly supposed. M" Fleming in 1893 found
one of the seventh magnitude in the southern constellation
Norma, with a spectrum practically identical with that of Nova
Aurigae (indicating hydrogen and calcium), and which is now
nebular also. And the same keen observer has since found
many other objects of this highly interesting character, the
most noticeable of which appeared in 1895 in Carina, a part
of the wide southern constellation Argo. Nova Carinae fell
in three months from the eighth magnitude to the nth, and
exhibited all the essential features of the new stars in Norma
and Auriga. Still another was found by her the same year
in Centaurus, which had a spectrum different from its prede-
cessors, but like them eventually became a gaseous nebula.
It is significant that nearly all the Novae have gleamed in or

The Fixed Stars

26(>

□ October

subject to regular changes in brightness of various
degrees, is at present known to b-e very large, and is
from time to time increased by fresh discoveries.
Usually these are subject only to smaller routatioas of
brightness. Of the few stars which undergo remark-
able irregularities of this kind, the two most interesting
cases are o Ceti and 7 Argfis. The former, sometimes
called Mira Ceti, was first noticed as being subject to
change in 1596, by David Fabricius, who saw it of the
third magnitude in August, and perceived
that it had ceased to be
visible. Baver saw it in
1603, and Phocylides in
1638, the latter noticing
(which Baver did not) that
it was the same star, thus
shown to be variable in
brightness. The observa-
tions of Hevelios between
1648 and 1663 established
its period, which is about

331 days in length; but the changes of brightness
during this interval are themselves of a very variable
kind, nor is the period quite constant in length. The
star is usually visible to the naked eye for about six
months, and invisible during the succeeding five.

Halley was the first to suspect changes of bright-
ness in that remarkable star in the southern hemi-
sphere, <7 ArgOs, which he had observed at Saint Helena

near the Milky Way ; and in the case of Nova Aurigae at leasl,
the striking display of 1891 must really have taken place u
long ago » the beginning of the 19th century. In the latter
part of i8g8, a «tar-tike condensation was reported in the centre
of the nebula in Andromeda. — D. P. T.

270 Stars and Telescopes

in 167715 of the fourth magnitude. Lacaille in 1751
saw it of the second ; and its changes from time to
time since have been exceedingly irregular. In 1838,
and again in 1843, it surpassed for a while all other
stars in brightness, excepling only Sinus. After the
latter date, it slowly but steadily diminisbed, and
ceased to be visible to the naked eye in 1867, and
it so remains, though its
brightness has slightly in-
creased in the last few
years.

Of the variable stars
of short period, the most
remarkable is Algol or fl
Persei. Its usual magni-
tude is about the second,
and as such it shines
constantly and regularly
for a period of about
two and a half days ; then
it fades gradually almost
schOnfeld (iSiS-iSgi) down to the fourth mag-

nitude, afterward recov-
ering its ordinary brightness by a similar gradual in-
crease. The whole amount of change takes place in
about nine hours, so that the complete length of a
period is not quite three days ; more accurately,
2* zo" 48"' 55'.4. Spectroscopic observations have
proved that these variations are caused by the regular
interposition of an opaque body revolving round Algol,
and cutting off at each revolution a portion of its light
in the manner of a partial eclipse.

The above are the most conspicuous and easily
detecled changes of brightness in the fixed stars ; but

The Fixed Stars

271

about 1 5 stars are now known to be variable, and the
application of photometry as an accurate means of
measuring the amount of light of a star is constantly
increasing this number. In many cases the variability
is confined within narrow limits ; in others, the stars,
even when at their greatest brightness, are scarcely, or
not at all, visible to the naked eye.**

•* So rapid has bten the recent progress in our knowledge
of (he variable star* that ihc total nuniber now known embracea
about 1,000. if we include the rather remarkable discoveries of
Professor Bailev, who, beginning in 1896, has found about
500 variables in the dense globular clusters photographed with
the Harvard telescopes. Their changes of magnitude are
marked within a few hours. In h Centauri alone (the cluster
shown on page 269) 125 variables were discovered. D' Chani>-
LER of Cambridge has published several cata1oguC!< of variables
in which about 500 of these obiects arc catcFuIly clasulied.
They are distributed all the way round the heavens, and for
the most part are included in a bell or zone tilled about lS° to
the celestial equator. Variables are best observed liy means
of Father Hackn's excellent Atlas. Following are a few of
the variable* :—

Variable Stars

.........

Pnilion for 1900.0

V«,.T„>K

R. A.

D«L

P«iod 1 Ring.

h IK

d 1

Omicron Cell

-3 ^6

3 Persei

i i

+20 43

+11 54

a Herculi*

-27 43

7 1 4 to 6

flLyrae

+33 '5

12I 1 3.4 to 4.5
si 1 3.7 to 4.9

21 IS

+57 54

Many of the newly discovered variables being faint *tar*,
they have no regular name except their number in some cata-
logue td poaitiofia. They are, therefore, designated by the

272 Stars and Telescopes

The determination of the parallaxes, and thereby
the distances of the fixed stars, constitutes a problem
which completely baffled astronomers until little more
than fifty years ago ; for so vast is the distance of
these bodies, that, although we use the diameter of
the Earth's orbit as a base, by comparing observations
made at opposite parts of the year, nevertheless the
angle at the star subtended by this diameter is gener-
ally so small as to be scarcely distinguishable from
inevitable errors of observation. The half of this angle
is the star's annual or heliocentric parallax.

Early in the present century Brinklev thought his
observations at Dublin indicated that he had found

letters R, S, T, and so on, in the constellation to which they
belong. The number of variables of the Algol type is now
about 20, two of the most pronounced being U Cephei and W
Delphini, and the total variation in the magnitude of each is
about 2.5. W Delphini is never visible to the naked eye, but
remains for about four clays at its full brightness of about the
9th magnitude, when in seven hours it falls to the 12th magni-
tude, so that a 5-inch telescope will barely show it. Algol, the
type star, is best visible in the northeastern heavens in the
evenings of early autuuin, and nearly overhead in winter.
The minima are given in many almanacs, and such astronomi-
cal journals as The Obxerratory and Popular Astronomy. Its
full decline takes place in rather more than four hours, and it
pauses at minimum brightness only 15 or 20 minutes. Vari-
ables are differently classified by various investigators, and
ScHONFELD of Bonn (page 270), a pupil of Argelander, de-
voted much time to these puzzling bodies in his best years.
Many variables are quite anomalous in their fluctuations,
having no regular period, and still others present several
mutations of brightness in every complete period ; as, for in-
stance, /3 Lyrae, whose complex spectrum shows a wealth of
helium bands and hydrogen lines not yet unravelled. The
shortest known variable is » Centauri 91, whose period is
6'' II"; and other variables 'in this interesting cluster exhibit
many exceptional peculiarities. — Z>. P. T.

The Fixed Stars

27i

parallaxes amounting to 2" or 3" for several of the
brighter stars ; but Pond (who succeeded Maskelyne
as Astronomer Royal in 1811) showed by more accu-
rate Greenwich observations that these conclusions
were untenable. The first really satisfactory determj-

PKIEDRICH WILHELM

(1784-1846)

nation was made long afterward by Bessel, in the case
of a star only just visible to the naked eye, known as
61 Cygni. Attention was directed to it as being prob-
ably much nearer us than others, in consequence of
its unusually large proper motion in the heavens, which

274 Stars and Telescopes

carries it though an arc of about 5" every year. 61
Cygni is itself double ; and taking advantage of the
circumstance that there are two other small stars ia
its close neighborhood (which, not sharing in this
motion, are probably much farther off), Bessel, in
1837, began observations at Konigsberg, with the
view of determining the parallax of this star relatively
to the small objects in the

• same field. As their paral-
lax might fairly be consid-
ered insensible, the result
would practically be the
parallax of 61 Cygni, or of
the two stars composing il.
In 1840 he was able to
announce that this quantity
was measurable, amounting
to about o".35, a value
which later observations by
other astronomers have es-
sentially confirmed. There-
c. A. ,. p.™. i,So(^,88o) ^^j,|,,g j|^,,„^^ ^f jj pj.^j

from the solar system is
over 50,000,000,000,000 of miles. Beginning with
those of Hexdkrsi>n (made about the same time as
Bessel's of 61 Cygni), obser\-ations of a bright star in
the southern hemisphere, a Centauri, show that its
parallax is the greatest of all the fixed stars yet meas-
ured ; and the best determination, made by D' Gill
and D' Elkin at the Cape of (lood Hope in 1881-
83, amounts too". 75, indicating a distance equal to
about 25,000,000,000,000 of miles. Several other
stellar parallaxes have since been measured : that of
Siriiis is o".38 ; one small star in Lalande's catalogue

The Fixed Stars

2;s

(No. 91,185) ^^ yielded a parallax of about o".5,
and that of another (No. 31,258) is about o".3. Also
many, smaller in amount, have been determined. Only
by the rapid propagation of light is it possible to
express the distances of the
enormously remote fixed
stats in small figures. In
a year light travels nearly
6,000,000,000,000 of
miles ; and this inconceiv-
able distance, now gener-
ally adopted as the unit of
length in expressing stellar
distances, is termed a ' light
year.' Of a Centauri, for
example, it is customary
to say that its distance is
about 4^ light years, and in
of 61 Cygni is about seve

BBtlNNOW (181I

I like manner the distance
light years.**

ulmosi the skill and patience

*^ Stellar distances t^
oE the practical a
be measured and calculated that finding a star's distance zray
be likened to the problem which would confront a prisoner
vrhu possessed instruments of the utmost precision, and
was told to measure the distance of a mountain twenty miles
away, but was given liberty only to observe the mountain from
the window of his cell. In this case, the orbit of (he Earth,
186,000,000 miles across, would be represented by the largest
hoop he could place in the window; while oar globe iuelf,
on the same scale, would shrink to a speck requiring a micro-
scope to render it visible. The steadiest atmosphere, instra-
ments of perfect type and construction, and observers of
consummate training can alone cope with the obstacles
encountered at every step. Following Bessel came the
painstaking Peters, who, about the middle of the 19th cen-
tury, attempted the more difficult undertaking of ascertaining,
not the relative, tiut the absolute parallaiei of certain fixed

276 Stars and Telescopes

In speaking of 61 Cygni, the expression 'double
star ' was used, and it is essential to distinguish between

■tare, among them Polaris. Capella, Arctunia, and Vega. Hi«
method employed the meridian circle (page 36S) by which ha
was skilful enough to detect very delicate changes in the ap-
parent direction of these stars with the change of •ea«aii.
About 1S70 BrUnnow, then Astronomer Royal for Ireland.

iftN |i84i-[S96)

began to devote his altonlion to these critical researches, de-
terminiiig many stellar parallaxes with high precision, and hit
work was al>Iy continued at Dunsink for several years by Sir
RoKEKT Ball. I'heir measures were made with the microme-
ter (pa£e 343), and the mathematical formula; requisite in
calculating such observations are presented in elegant form
by BKftNNOW in his Haii/ibffBk ef Sphirical Aslronomy (Lon-
don, 1865). Also GvLDfiN (from 1871 to 1896 Director of
tb« Royal Observatory at Stockholm), and D< A<;wElts. of

V gill's heliumeter a

o ,•/ //amh,rf IH ^mi. a«J itit^^ miJ,K OtUr.
iH4trtimrMti fff tkii Ij/f* in Ikt kanM 0/ traiittd

{

278

Stars and Telescopes

the two classes of stars which come under that desig-
nation. A stellar object which appears single to the
naked eye, but when viewed with a telescope is seen

Berlin, and D' Otto Struve, late Director at Pulkowa (pp.
130 and 133), have greatly advanced our knowledge of the dis-
tances of the stars. But the favorite method at the present day
is that originally employed by Bessel — measures by the heli-
ometer, which is a telescope of medium size, mounted equatori-
ally, as shown on page 277, and provided with a variety of
intricate appliances for facilitating the astronomer's use of the
instrument, and enhancing the accuracy of his measures with
it. But the cardinal peculiarity of the heliometer is its divided
object-glass, as in the opposite figure, one half of the glass
being mounted in a sliding frame, which enables the observer
to move it by a definite amount relatively to the stationary half.
As each portion makes a perfect image in the field of view, any
lateral displacement of the half-objective will produce a double
image. In the case of the sun, the two images of his disk
are then brought just tangent to each other; and so his diame-
ter has been most accurately measured (heliometer meaning
sun-measurer). The Yale Observatory possesses the only
instrument of this type in America, mounted in 1882, and it
has been successfully employed by D"" Elkin in determining
stellar parallaxes. Following is a table including many of the
stars whose distances are best known : —

Distances

OF Fixed Stars

Position for looo.o

Distance in —

Star's Name

(In order of

Distance)

Mafi^ni-
tude

Paral-
lax

Propci
motion

Ded.

Light-
years

Trillions
of miles

a Centauri

— ci

- 60 25

0.7s

»5

3.67

61 Cygni

5-«

+38 15

0.45

5.16

Sinus

— '•4

4»

—16 35

0.38

»-3i

Procyon

0.5

4- 5 29

0.27

7«

1.25

Altair

0.9

»9

+ 8 36

0.20

0.65

0' Eridani

4-4

- 7 7

0.19

100

4.05

Groomb. 1830

6.5

-38 32

0.13

158

7.65

Veea
Aldebaran

0.2

-38 41

0.12

0.36

-16 18

0. 10

191

0.19

Capella
Polaris

0.1

-45 54

O.IO

191

0.43

a.i

-88 46

0.07

276

0.05

Arcturus

0.2

|-X9 4»

0.02

160

950

3.00

The Fixed Stars

279

to consist of two so near as not to be separated by the
unaided vision, is naturaUy called a double star. But
the fact that there are two stars apparently in such
close proximity does not of itself prove any connectioD
between them ; they may, indeed, be merely optically
double, that is, appearing double only because the
individual stars happen to be nearly in the same line
of sigiit, without reference to their actual distance.
But Sir William Herschel's persevering survey of the
heavens revealed to him so large a number of these
apparently double stars that there was in many cases
great probability of physical connection between the

Of all the slais whose distances have been measured, per-
haps 50 are regarded as satisfactorily known, atid man^ of
them arc shown approximately in the diagram on page 280,
adapted from calculations by Ranvakd and Gregorv, in
which the solar system is at the centre and Ihe Concentric
circles are drawn at intervals of five light-years. Any star just
outside the otiter circle would have a parallax of a", i. Within
recent years photography has rendered great assistance iti find-
ing stellar parallaxes, chiefly because plates once exposed can
be critically measured and re-meaaured at any lime. The pho-
tographs of PRITCHAKD and KtJTHERFURD havc Contributed
conspicuously to this desirable end. GVLDfix, from an inves-
tigation of the parallaxes and proper motions of about half o(
the first magnitude stars, finds their average distance repre-
sented by 40 light-year* or 2jo trillions of miles, a result ct>n-
firmed by D'' Elkin's careful researches. — D. P. T.

28o Stars and Telescopes

compoDeots, as suggested several years before by
MiCHELL in the Phiioscphieal Transactions for 1767.
Herschel, in 1782, began the practice of carefully
observing and recording the relative positions and

KNOWN DIST,

^NCES OF STARS FROM THE SUH

IN LIGHT-VRAKS

(/y*M Todd'i

1 •Nrai Ailramnmj; by tftcial flyTiiium

,,/A,A<.»ricaM

distances of the stars which he had noticed as being
apparently closely double ; and when, after an inter-
val of some years, these values were determined again,
he at once discovered that in many cases the compo-

The Fixed Stars

281

nents of a double star have a distinct motion with ref-
erence to each other,
• In Herschel's first paper on the subject, contained
in the Philosophical Transactions for 1803, he remarks
that his obsetvations distributed over a period of twenty-
five years, and there recounted, prove that many of
the stars whose mutual positions and distances had
been measured by him, 'are not merely double in
appearance, but must be allowed to be real binary

combinations of two stars, intimately held together by
the bond of mutual attraction.' These, then, are called
binary stars, to distinguish them from such as are only
optically double ; and the discoveries of binary sys-
tems, or stars physically double, is constantly increas-
ing. The high interest attaching to this subject has
led many skilful astronomers to devote much attention
to it since Herschel's time. The elder Struve was
one of the first: and a catalogue of no fewer than

282 Stars and Telescopes

3,134 double stars was published at Saint Petersburg
iu 1837, containing the results of his observations at
Dorpat and Pulkowa. Many of the binary stars have ■
aregularorbital revolution,
the most interesting cases
being { Herculis, f Ursse
Majoris, and 70 Ophiuchi,
whose periodsof revolution
havebeendeterminedquite
accuratelyto be 34,61, and
94 years respectively. The
shortest known, those of k
Pegasi and S Equulei, are

(.793-1864) °"'y ^^""^^ ^i"^" ^*^«

half years. Much longer
than any of these, and therefore less precise, are the
periods of those interesting and long-known double
stars, y Virginis, y Leonis, and Castor, the first of
which amounts to nearly 200, the second to about
400, and the third to nearly 1,000 years.

Accurate investigation of the proper motions of the .
larger stars has disclosed, by means of irregularities
in these motions, more than one instance of the dis-
turbance of a star by an unseen companion ; so that
the binary character of the star was only discovered
in this way. Such was the case with the brightest of
all the hxed stars, Sirius ; and the disturbing compan-
ion was afterward detected as a small star near it,
visible only with a powerful telescope. Procyon, the
principal star in Canis Minor, is also subject to a simi-
lar irregularity of proper motion, and one which would
seem to result from orbital motion round a companion
possessing so feeble a luminosity that it was long si^-
posed to be opaque ; and its probable perception has

The Fixed Stars

283

been quite recent. The period of revolution in this
case is about 40 years.**

•• More than i
and catalogued, :
■Utm of many \^
Struves, father and son,
Dawes, Professor Schiapa-
RELU, Baron Dembowski,
and Professor Uurnham.
Few stellar objects will better
repay the amateur than ' dou-
bles.' Even a small tele-
scope will show many of
the wider and brighter pairs,
a lew of which, illustrated on
page 281, are readily located
by ordinary star charts. The
easiest is perhaps 7 Virgliiis,
discovered by Br.

double stars are now known, measured,

iber only reached by the faithful enthu-

chief among them the

(1799-1868)

ary;

c that

s period is pretty well established. The diagram on the next
page eKhibits the orbit and the observations upon which it ia
based. The real orbit has a high eccentricity, surpassing that of
every other known binary. Of yet greater interest is Sirius. Ihe
orbit of whose companion, a star of the tenth magnilude, ia
also shown. The existence of this companion was first pre-
dicted by D' AUWEKS, and verified independently in 1S62 by
Alvan Graham Clark, the distinguished optician, on the
completion of the iS^-inch telescope now belonging lo the
Dearborn Observatory at Kvanslon. The accompanying dia-
gram of the companion's orbit is by Professor lU'RNiiAM.from
observations between 1S62 and 1S96, There were no observa-
tions between i8go and 1896, because the companion was then
so near the blazing centred star as to be lost in its rays, and
wholly invisible even with the Lick 36-inch telescope, fl is
now visible again, and will remain so till cg^:, when it will
disappear once more. The full period of the companion of
Sirius is 51.8 years and its mass equals that of the Sun itself.
The nearest known fixed star, a Centauri, is also a binary

284 Stars and Telescopes

When stellar positions observed at considerable
intervals of time are compared, nearly all the stars

system with a period of Si years (page 250). The component
stars, very nearly equal, have each about the mass of the Sun.
When at their nearest [feriailr^H) they are about as far apart
as Saturn is from the Sun, and at their farlhesl {apailron) their
distance fiom each other is equal to 36 astronomical units, or
one fifth greater than Neptune's distance from the Sun, About
200 binary systems are now known, of which D' See regards
40 as well ascertained. The longest known binary is (

Aquarii, with a period not less than 1,500 years; and among
the very short ones not already mentioned are 8z Ceti (16
years), and 3 883 (Lalande 9091). the shortest of all, with a
period of 5} years.

A great gap still exists between even these short periods, and
the times of revolution of companion stars recently discovered by
means of the spectroscope, and therefore called spectroscopic
binaries; for their periods are not reckoned in years, bat in

Tke Fixtd Stars

28s

aie found to be endowed with regular though slow
changes of place in the heavens, called theii proper

diya, or eren hoara. If the orbit of a close binary Is teen
edg« on. twice in eveiy Tcvolalion the light of the two stars
will coalesce ; half wajr between which the two Mara will be
moving, one toward and the other from the Earlh, also twice.
Now pbolognph the star's spectrum at each of these four

GkAHAM CLARK (1831-1897)

critical points : in the first pair, the lines appear sharply
single ; in the second pair, they are found to be double. This
singular phenomenon is readily explained by DorPLER's im-
portant and most useful principle (page 56), according to
which the lines in the spectrum of a star receding from as are
displaced toward the red, while if the star is coming toward
ns, tbe spectral lines are displaced toward the vjolel. At c<m>

286 Stars and TeUscopts

motions. Presently we shall consider whether these
are in all cases wholly due to actual motioa of the

junction, then, u the two stais are passing athwart each other
the lines in their combined spectrum will be single, but doabl*
a[ (he quadratures, or intermediate between the conjunctionB.
Mizar (f Ursae Majoris) was the first discovered spectroscopic
binary, by Professor Edward C. Pickering in 18S9. Tbi*
moderately bright star in the middle of the Dipper's handle
has a mass exceeding that of the Sun forty-fold, and the period

JOHANN CHRISTIAN DOPPLER (1803-1853)

of its invisible companion is 52 days. 3 Aurigx is another,
with a much smaller mass and a period of four days. Also,
o' Geminorum, the larger of the two stars composing the bril-
liant double star Castor, proves to be a rapid binary with a period
of only three days. But the case of fi' Scorpii is the most
remarkable of all, with the c:(ceeditigly short period of 34' 41"
30", On the same photographic plate, side by side, are the
spectra of fi- and its companion /i', the lines of the latter

The Fixed Stars 287

■tars in space; but cerUunly a considerable part of
the proper motions which are exceptionally large
must be so. It has already been mentioned that tii
Cygni was thought to be probably nearer us than most
of the fixed stars, on account of its very large proper
motion of about 5" in a year. Two small stars, one
in the northern, the other in the southern hemisphere,
having no designation but numbers in star catalogues
(1,830 Groombridge, and 9,352 Lacaille), have
proper motions even larger than this, being each 7" in
amount, or nearly so ; but these stars do not, like 6r
Cygni, appear to be much nearer the solar system than
others. Only a few stars are known to have proper
motions between 4" and 5" in amount, and the proper
motions of the great mass of stars are much smaller,
and only to be recognized by comparing accurate
observations widely separate in time.

When the proper motions of several stars had been
tolerably well determined, the idea was soon suggested
that they might be due in part, not to actual motions
of these stars in space, but lo translation of the solar
system among them. Such movement would produce
an apparent motion in the stars in the opposite direc-
tion to that of the solar motion, or a tendency on the
whole to recede radially from the point in the heavens

alvays single and sharply defined. Those of fi', on the other
hand, arc now single and again doable, thus leaving no room
for doubting ihis most modem contribution of the spectroacope
to stellar astronomy, and marvellously confirming Ihc brilliant
Bbssel's prophecy of 'the astronomy of the invisible.' By
repeating these spectrum photographs and making compara-
tive measurements upon them, the period of levolulion and
other data can be found for binary stars so close togelher as
lo be forever beyond the separating poirer of the largest
telescopes. —D. P. T.

288 Stars and Telescopes

toward which the Sun was journeying. Approximate
determinations of this point were simultaneously made
in 1783 by Sir William Herscmel and by Pi£rr£
Prevost, of Geneva, both coming to the conclusion
that it was situate in the constellation Hercules, In
1S05 Herschel made a similar investigation, founded

on proper motions determined by Maskelyne; and
in later times others were made by different astrono-
mers, all of whom agree in placing the apex of the
Sun's motion in the same region of the heavens, either

Th* Fixed Stars

289

in Lyra or in the adjacent constellation Cygnus, and
therefore not lar from Hercules."

" Stellar proper motions were first made out by Hallbv in
1718. M. BossEKT.of the Paris Observatory, in 1896 published
a catalogue of all the well-ascertained proper motions of ttut,
over 3,6ca in number, in which the motion exceeds o*<oi in
right ascension and o".! in declination. An orange yellow
star of the eighth magnitude in Pictor has a proper moiian of
nearly 9", the largest known. Sir William Hucgiks was the
first to make, in l36S. that most important application of the
spectroscope to sidereal astronomy, by which a star's light
reveals unerringly its motion toward the Karth or from it, in
accordance with Doppler's principle. Thus was demonstrated
beyond a shadow ol doubt the fact that the swaims of the
stellar universe are in constant motion through space, not only
athwart the line of vision as their proper motions had long dis-
closed, but some swiftly toward our solar system and other*
as swiftly from it. So the term 'fixed stars' appeared to be
A double misnomer. Research of (bis character has also been
vigorously piosecuted by U' Vocel of Potsdam, near lierlin
(page 61), at the Lick Obaenratory by Professol CAMPBELL
with the fine spectroscope shown above, and by M' Maunder
at Greenwich (page 39), where the high significance of Ihi*
work led the Astronomer Royal many years ago to direct its
inclusion in the programme of observational routine. Follow-
ing are a few determinations of

Motion in t

HE Line op Sight

Mdiidi

Stw-sNime

■geco

Towml

Rilh.A«„ui™

In.Mil«

a Arieli*

2 "

+« 59

-11,7

Aldebaran

+32

Betelgeux

+ 17-6

+ 28

y Leon is

Id 14

+20 21

-SS.I

-40

Spica

13 20

-10 38

—106

-17

+*7 3
+ 8 36

i|5

19 46

-239

290 Stars and Telescopes

Attempts have been made to extend the theory fiu-
ther, and to ascertain the region round which the

The Bign minus means that the star is coming toward ns,
tnd -f that it is receding. It Is to be remembered that these
are simply motions in the line of sight, relative to the solar
Sfstem as a wbole, for the effect of the Earth's motion round

g^% ^^^.

(Slarfiild, CrnAoroM^ HiU. SiaKX, En^atnl)

the Sun has been eliminaied. To lind ihe actual motionl of
these stars through space, it is necessary lo combine the above
data with their distances and proper motions, a geometric
operation which ttill usually increase the sight-line motions
very considerably. Part of the research regularly pursued
with the 40-inch Yerkes telescope (page 338) it work of this

The Fixed Stars 291

solar motion is carrying the Earth and all the bodies
that move obediently to the Sun. Such attempts^
however, are yet premature, and can only be regarded
as tentative. Madler, about sixty years ago, consid-
ered it probable that the point in the heavens in ques-
tion was situate in or near the cluster of stars (see
next paragraph) known as the Pleiades. But it would
seem that the stellar motions noticed by him were
rather due to special cases of star-drift \ and M' Max-
well Hall, as the result of an investigation founded
on the proper motions of a few stars whose parallax
and distance are approximately known, has indicated
a point in the constellation Pisces as that around which
the solar motion is probably performed. In the pres-
ent State of our knowledge, the period of this great
revolution can be little more than matter of conjec-
ture ; and as a rough approximation, it is put down
by M' Hall at about 13,000,000 years.

Many of the fixed stars are arranged in groups or
constellations which imagination has likened to the
forms of animals and other objects, — some of these
in strings of various twists suggesting the idea of ser-
pents or dragons. While these groups are spread out
over regions of the sky many degrees in extent, casual
inspection of the heavens shows here and there a
group of stars arranged close (sometimes very close)
to each other, so as to form a cluster. Of these, the
most remarkable is a loose cluster called the Pleiades,

character, in charge of Professor Frost ; and photography \% a
most helpful adjunct, because the plates accumulated in periods
of clear and steady atmosphere may thereafter \x measured, and
the necessary results derived at leisure and with that high degree
of patience and painstaking which alone retider such investjga-
liotis of any value. — D. P. T.

agz Stars and TtUscopes

in Tauras (pages 236-237). It is easy to perceive
six stars in this well-known group, and some peisoDS
with unusually acute vision can detect seveial more ;
but while HvciNus and Ovid say there are only six,
there is evidence that as many as thirteen were seen
before the invention of the telescope. With a moder-

ately good instrument at least a hundred become visi-
ble, while very large telescopes reveal the existence of
more than a thousand. Near the Pleiades and in the
same constellation is a more scattered group called
the Hyades, resembling a letter V. Still another,
called PrEsepe, is visible to the naked eye as a faintly

The Fixed Stars

293

luminous spot or nebula in the constellation Cancel,
and is not well seen unless the night be clear and
moonless. The telescope, while showing that this and
many other nebulous or cloudy- looking masses are
composed of veiy distant or very minute stars, brings
into view multitudes more not visible to the naked

«ye at alt. The close clusters are excellently illus-
trated by the reproduction above, from photographs
by D' Isaac Roberts, of a typical globular cluster in
Pegasus, and the magnificent double cluster in Perseus
(page 297) ; and on pages 290 and 292 are D' Rob-

294 Stars and Telescopes

eric's observatory, and the ingenious arrangement of tel-
escopes with which he took these classic photographs.**

** And this is practically all that even the most powerful
telescope, if unaided, can .ivail. With it can be found the
star's exact position in the Armament, not only with reference
to neighboring stars, but its distance from us also. The
telescope solved the problem of ■aihcrt, but was utterly baffled
by the question -wkai, until supplemented by the spectroscope,
with observations interpreted by Kibchhoff's laws (page 69).

I II

II I

Here again Sir William Hicr.iNs was the pioneer, and

Betelgeux and Aldebatan were the iitst stars whose chemical

constitution was revealed to the eye of man. Many of these

distant twinkling luminaries

Owete at once found 10 contain
calcium, hydrogen, iron, mag-
nesium, sodium and other met-
als nhose cTisteiice in the Sun
had been demonstrated. What,
for example, could be better
proof of the fact of iron in Sinus.
than a spectrum like the one
adjacent, in which are repeated
coincidences of the dark (nega-
tive) iron bands (above and
below) with the intermediate-
bright lines of the spectrum
of the star itself? Only a year
intervened before the spectra
of stars had been examined in
niTKoANGiLosEtcHi (1818-1878! nuoibcrs sufficient to permit
their classification. This was
first satisfactorily done by Father Seclhi of Rome. wboM
comprehensive scheme embraced four distinct types t«sed oa
optical observations solely : —

The Fixed Stars 295

Stretching across the sky in clear nights is seen a
band or zone of luminous matter, which was a great

Type I is chief); characterized by the breadth and intensity
of dark hydrogen lines ; also a decided faintness or cntiic lack
of metallic lines (see next page). Stai^ of this type are veiy
abundant, and are blue or wbite. Sinus, Vega, Altair and
rumerous other bright stars belong to this type, often called
'Sirian stars,' a class embracing perhaps more than half of all
the stars.

Type II is characterized by a multitude of fine dark, metallic
lines, closely resembling the solar spectrum. They are yellow-
ish, like the Sun. Capella (page 301) and Arcturus illustrate
this type, oEten called 'solar stars,' and they are rather less
numerous than the Sirians. According to recent results of
Professor Kaptbvn, absolute luminous power of first type stars
exceeds that of second type stars sevenfold. Stars nearest to
the solar system are mostly of the second type-
Type III is characterized by many dark bands, well de&ned
on the side toward the blue, and shading off toward the red —
a'colonnaded spectrum,' as Miss Ci-KRKE very aptly terms it
(see the next page). Orange and reddish stars and a majority
of the variables fall into this citegoiy, of which a Herculia,
Aniares and Mira are examples.

Type IV is characterized by dark bands, often technically
called flulings, similar to those of the previous type, but
reversed as to shading : they are well dctined on the side
toward the red. and fade out toward the blue. Stars of this
type are few, perhaps 50 in number, faint, and nearly all blood-
red in tint. Their atmospheres contain carbon.

Type V has been added to Sklchi's classification ly Pro-
fessor FiCKBRiMC, and is characterized by bright lines. They
are al>oul 70 in number, and are all found near the middle ci
the Galaxy. From two French astronomers who first investi-
gated objects of this class, they ate usually known as Wou-
Ravet stars. They are a type of objects quite apart from the
rest of the stellar universe, and many objects termed planetary
nebulz yield a like spectrum.

A classification by D' Vocel combines Secchi's types III
and IV into a single type, and several other classifications
have been proposed since the inauguration of stellar spectrum
photography. The Harvard classification embodies at>oui ;o

The Fixed Stars 297

enigma to the ancients, and received the name of the
Galaxy, or Milky Way. As soon as Galileo applied

5 roups. Whether these differences of spectra arc due to
ifferent stages of stellar development, or whether they indi-
cate real differences of constitution, is not yet known. Prob-
ablv they are due to a combination of these causes. According
to M' EspiN, stars having the most bands io their spectra
present the greatest differences between their visual and photo-
graphic magnitude. As in the Sun, so in the stars, the girdling
atmosphere must be held responsible for numerous dark lines.

In the case of a Aquilx, M. Dejlandres, the able spectro-
scopist of Paris, has discovered fa\e double bright lines
traversing the middle of the dark hydrogen lines, also through
the iron lines and the K-\me of calcium; and he traces their
origin to a chromosphere similar to that enveloping our Sun.

The first star whose spectrum was successfully photographed
is Vega, by Henry Draper in 1S72. and our detailed knowl-
edge of stellar spectra is in great part consequent upon his
initiative. At the time of his lamented death, research upon
the constitution of the stars was still in the experimental stage ;
but the ample funds of the Henry Draper Memorial, generously

298 Stars and Telescopes

his telescope to the heavens, he saw that this appear-
ance is produced by millions of stars apparently scat-

inainUined by M" DitAPite, have enabled Pro(e»»or Pickewng
and his efficient corps to prosecute an unparalleled line of id-
vestigacions embracing the stars of bolh hemispheres. These
researches were at first conducted with the Bache telescope,
illustrated opposite, whose chief peculiarities are a large object
glass of short focal length, and a mounting with a forked polar

(■8j7-'8

axis. For the furtherance of this work M" Draper provided
an exact duplicate of this instrument. Also, both are equipped
with great prisms (not shown), mounted in front of the objec-
tives, thereby spreading out the stellar images into lines on the
photographic plate, instead of the mere points that appear on
chart plates. Suiuble adjustment of the prism and the dock-
motion causes the broken spectral line to trail over the plate
latitudinally, so that every star down to the eighth magnitude

The Fixed Stars 299

tered like dust along the black ground of the sky.
Analogy led many to suppose that the nebulae or

records its turn spectrum, sometimes many hundred on a single
plate. The advantages of this fortunate artangemenl are
obvious : peculiarities of spectra are continually leading Co the
detection of i-arUble stats that would otherwise pass unob-
served ; several new or temporaty stars have been discovered ;
and the spectra of about 50 stars in (he Pleiades exhibit at a
glance their close identity of chemical constitution. In 1S90

lAt Ban aid lilir iftrira- ff^rai
FfTM. and in mt <./«• Ilu imlAtm ,1

/i# Aw UltKPtl, ptgS J64)

The Fixed Stars

smaller patches of lumi-
nous matter brought into

was published the ' Draper
Catalogue of Stellar Spectra,'
including more than ia,Mo
■tars ; and the larger and
more powerful Bruce tele-
scope (page 164) is now con-
tinuing these researches to
Etara of fainter magnitudes.
If a star's spectrum is re-
quired with a high degree of
dispersion, the ordinary slit
spectroscope ia employed,

which s

I the s

light tliat targe objC'
come necessary. D' Vogel
and D' SCKEINER at Tots-
dam, and Sir Norman
LoCKVER at South Kensing-
ton have likewise been suc-
cessful in detailed photo-
graphy of especially

ding n

ihou

sand lines in highly luminous
objects of type II. Capella's
Spectrum adjacent, from a
fine photograph kindly sent
me by M. Deslandres of
Paris, exhibits not only the
wealth of lines, many of which

e to i

n,calcit

I. he-

lium and magnesium, but by
displacement of bright lines
in the lerreslrial spectrum,
shows the swift recession of
Capella from our solar sys-
tem. The door is now wide
opened to a study of the
constitution of at least the
brighter stars in every detail
of their chemical composi-
tion ; attd *dvuice along these

f -

III

tli

ill

1 1

302

Stars and Telescopes

view by telescopes aje also masses of stars, resembling,
on account of their greater distances, portions of the
Milky Way as seen by the naked eye, — and, indeed,
many of these were resolved into stars by more power-
ful telescopes ; but (as just stated with regard to the
great nebula in Orion) it is now known, from modem

HERSCHEL (1 791-187 1)

observations with the spectroscope, that many of the
nebulae are wholly or in part irresolvable. The improb-
ability of the older view had been shown by Sir John
Herschel's observations of those remarkable celestial
objects in the southern hemisphere which, from hav-
ing been first noticed by Magelhacns in the earliest

lines cannot much longer be checked by the seemingljr endless
magnitude of the task. — ZJ. P. T.

The Fixed Stars

303

voyage ever made to the Pacific Ocean, are called the
Magellanic clouds. These consist of two large and
nearly circular masses of nebulous light, — one larger
than the other, — which are conspicuous to the naked
eye, and look not unlike portions of the Milky Way.
The larger remains visible even in strong moonlight,
which obliterates the smaller. When viewed through
large telescopes these objects are seen Co contain mul-
titudes of stars, and hundreds of nebulae which cannot
be resolved into stars, all wedged together in such a
way as to suggest some close and immediate connec-
tion between them, quite inconsistent with the idea
that any portions are at very much greater distances
from us than others."

** Sir William Herschel, the goal of whose researches
was a knowledge of the construclion of the heavens, undaunt-
edly essayed a tedious series of 'gauges' or counts of the stars
visible in diSecenI parts of ihc sky in the lietd of his 30-foot
reflector. Twice the breadth of Ihe field reached across the
Moon's diameter ; and the field itself contained about ti^.mv
part of the area of Ihe whole celestial sphere. Herschrl
actually counted the stars in nearly 3.500 such fields, and the
number therein ranged all the way from o to nearly 600, These
gauges were distributed ail around Ihe sky, along a galactic
meridian inclined about 35° to the celestial equator, Sir John
Hersoiel continuing his father's work at the Cape of Good
Hope, The average number of stars in a field was as
follows : —

In the Galaxy itself

In galactic latitude 15°

30=

45°

7S°

906

From this very rapid increa

se in the number of the stellar

hosts, a

s we approach nearei

r and neai

rer the Milky Way,

304 Stars and Telescopes

The labors of the two Herschels greatly increased
the number of known nebulas, and many more have

^^%5^^ ^.i***^

,VENS (WATERS)

iMOi, Wa^ according It Bo.DBICKBI.. (A, d^, i. il m^tiHg ,1a

rclua^-.. Ti^dH,

ai./»m,l^(M^t

here enter into; but we may summarize as follows our knowl-
edge o£ this recondite subject down to the year 1890 : —

The component bodies of our sidereal universe are scattered.
without regard to uniformity, throughout a vast system having
in general the shape of a watch, whose thickness is, perhaps,

The Fixed Stars 305

been discovered since their time. About 10,000 are
now caulogucd, and their distribution over the celes-

one-tcntb of iu diameter. On either side of this, and cloitered
about the poles of the sidereal system, are the regions of
nebulae, thus making the entire visible universe sphert^dat in
general shape. The plane of the Milky Way passes through
the middle of Ibis stellar aggregation, and near its centre are
our Sun and his attendant worlds. In large part, the stars are
clustered irregularly, in various and sometimes fantastic forms,
but without any approach to sys-
tematic order. Often there are
streams of stars ; and elsewhere
aggregations leaf-like or tree-like
in apparent stniclure; also,' star-
sprays,' as Proctor termed
them. This painstaking investi-
gator laboriously charted all the
stars of Argklandf.r's Durih-
muileriing, nearly 315,000 in
number, and bate inspection of
his comprehensive map affords
the best notion of the seeming
capriciousness of stellar distri-
bution. But he proved clearly
the detailed connection between
the distribution of the stars and
the complci branching and d

John Herschel remarked many well-delined offshoots from
the Milky Way, each tipped at its eilremily with a fairly bright
star; and the physical connection between the two may be
regarded as certain. That is, the fainter stars of the Galaxy
thai give the effect of nebulous light are at practically the
same distance as the brigbtei stars. Proctor, too, directed
attention to the fact that the luminous streamers in the irregn-
tar nebutx often coincide with streams of small stars in the
same field i and in the case of Orion, spectroscopic analysis by
Sir William and Lady Ht;GG[Ns has proved the connection
between wisps of the nebulous light and the stars adjacent,
thus leaving little room for doubt as to the distance of the
nebulie. See also the nebulous streamers of the Pleiades
(page 237). Upon such inference, in fact, oar slender knowl-

R (1S37-1888)
:r portions of the Galaxy.

3o6 Stars and Telescopes

tial vault — by no means uniform — manifests a marked
tendency to avoid the zone of the Milky Way, and to

edge of the distance of the nebulae depends ; for the parallax
of a nebula, although attempted, has never been measured
directly.

Since 1890 the spectroscope has come to the assistance of
the telescope in solving the intricate problem of stellar distri.
bution. Professor Pickering had noticed that most of the
brighter stars of the Galaxy yield spectra of the first or Sirian
type ; and Professor Kapieyn, by combining the well -ascer-
tained proper motions of certain stars with their classification in
the ' Draper catalogue of stellar spectra,* concludes that, as stars
having very small proper motions show a condensation toward
the Galaxy, the stars composing this girdle are in great part of
the Sirian type and lie at vast distances from the solar system.
If a star is near to us, its proper motion will ordinarily be large ;
and in the case of stars of the second or solar type, the larger
the proper motion the greater their number. So it would ap-
pear that the solar stars are aggregated round the Sun himself ;
a conclusion greatly strengthened by the fact that of stars
whose distance and spectral type are both ascertained, seven
of the eight nearest to us are solar stars.

From Professor Kapteyn's further research he concludes
that our solar system lies, not at the centre, but slightly to the
north of the Galaxy. Returning then to the Sirian stars, he
reaches the conclusion that if we compare stars of equal bright-
ness, those of the Sirian type average nearly three times more
distant from the Sun than do those of the solar type. The
Sirian stars may therefore be legitimately regarded as far ex-
ceeding the solar stars in intrinsic brightness. Gould's theory
of a solar cluster receives remarkable confirmation, though the
evidence as to the figure of this cluster is far from complete ;
indeed, it may be ring-shaped. But Professor Kapteyn's con-
clusion seems hard to escape, that the Galaxy itself has no
connection with our solar system ; and is composed of a vast
encircling annulus of stars, far exceeding in number those of
the solar aggregation, and everywhere more remote than the
stars composing it, as well as differing from them in physical
type. So it is the mere element of distance that reduces their
individual glow and seemingly crowds them thickly together
into that gauzy girdle which we call the Galaxy. — D. P. T.

The Fixed Stars 307

aggregate north and south of it, near the poles of the
galactic circle, as illustrated on page 304. This is addi-
tional proof that the nebulae are connected with the
general system of the stars, and do not form other
systems, as was formerly thought, at immense dis-
tances beyond it. Sir John Herschel noticed that
one third of the nebulae catalogued by him, chiefly
from his father's and his own observations, are con-
gregated in a portion of the heavens occupying about
one eighth of the celestial sphere, extending from
Ursa Major in the north to Virgo in the south. If the
irresolvable nebulae are not placed at distances from us
immensely greater than are those that have been re-
solved into clusters of stars, what is the alternative ?
Simply that the irresolvability of the former arises, not
from the greater distance of the stars comprising
them, but from their actually smaller size, which pre-
vents their being seen separate, even under the high-
est telescopic power.

We conclude with a few words respecting three of
the most interesting of the nebulae. The most re-
markable of all surrounds B Orion is and is in that part
of the constellation Orion called * the sword.* Only
barely visible to the naked eye, it appears to have
been first seen by Cvsat, a Swiss astronomer, in 16 18.
It was first drawn and described by Huygens (who
was apparently unaware of Cysat's perception) thirty-
seven years afterward. Although this gigantic object
contains a large number of telescopic stars, spectral
analysis has shown that a portion of the light received
from it, and from some other nebulae as well, is due
to glowing gas (page 238).

The great nebula in Andromeda (page 243) is just
visible to the naked eye, and was noticed before the

308 Stars and Telescopes

invention of the telescope, there being evidence that
Al-SOfi, the Persian astronomer, saw it in the tenth
century of our era. Simon Mayr first examined it
telescopically and described it in 1612. A very in-
teresting nebula in the southern hemisphere and invisi-
ble in our northern latitudes, surrounds the remarkable
variable star yj Argils. The first to describe this object
seems to have been the French astronomer Lacaili^,
in the course of his observations, in 1750-53, at the
Cape of Good Hope, when Sir John Hf.rschel in the
following century drew an elaborate representation of
it, which still serves as a standard of comparison.*"

"> Regarding the nebuli as
worlds are fashioned from, our
Struclion of Ihe heavens rests
upon (1) the discovery and
classification of thousands of
nebulx, {2) the accurate detcr-
tnination of their positions
among the stats (rejieatcd at
long intervals), (3I ihestudy of I
their physical apiiearance
the telescope and by mean
photography, (4) their moti
in space and chemical const
tion by the spectroscope, (5) I
determinations of their dista
by the stars lo which they
found to be related. About I
8,000 nebula are now recorded |
in our catalogues, the ir
complete of which is that by I
D' Hrkver of the Armagh Ob-
servatory in Ireland. The keen-
eyed D' Swift, now work-
ing in the clear skies of Southern California, is
adding new discoveries. Following theHERSCHKL
MOKT of Munich and D'Arrest of Copenhagen, who devoted
many faithful j'cars to observation of the nebulx. Large tele-

(1805-1879)

The Fixed Stars

309

■copes are now requisite for continuing (hit Important work,

such as the 26-inch refractor of the University of Virginia, em-

ployed to good advantage in this field by Professor Stohb.

The Oiion nebula was the first one ever photographed, by

Henry Drapek in iSSo, and nebular photography has been

sucCTssfully followed up by D' vom Gothakd in Hungary ;

by Professor Barnard who has discovered extensii

of dillused nebulosity outside

the Pleiades, and an optically

invisible nebula of vast extent

in Scorpius ; by Professor

W. H. Pickering, whose

plates reveal spiral filaments

outlyin)! the nebula of Orion ;

and by Di Isaac; Kobekts.

whose fine photographs of

star clusters, the Orion nebula

(page 23S) and the Lj Placian

ting nebula in Andromeda

(page 243) have already been

shown. The spectrum of the

latter shows that it is not

gaseous, still no telescope has

yet resolved it. Two other _ ___

products of his remarkable iiliKs/ti)
skill and patience here follow

— the ring nebula in Lyra (not a good reproduction of his original
negative), and the marvellous spiral nebula in Canes Venatici,
the characteristic whorls of which, as drawn by Lord RossE, had
been doubted by many astronomers till this photograph revealed
them convincingly. Here we seem to sec a multiple star ia
process of actual evolution, much as the double stars are
thought to have originated from the double nebulae (page 251 ].
Following in the footsteps of Sir JuilN Hersci[EL, I)' Gll.L at
the Cape, M' Russell, Government Astronomer at Sydney,
and Professor Da[LEY at Arequipa, have continued the highly
important task of photographing the southern nebula; and
clusters with eminent success. In iSg? Bailey photographed
a fine spiral nebula in llydia. Wide lones of the southern
sky, however, remain yet unexplored, e.icept the mere rccon-
Evidences of variability have been sought in dif-
it regions of several of the larger nebulx ; but only a single
nee of change is satisfactorily made out — in the great

(PicUfrafiiJ fy R

\t ^fftejrra^, ii art txsttdmfty

310

Stars and Telescopes

incgulir nebula cDveloping q Argfls (page 165), a conipicaoot
pari of which, recorded near Ihc ccnire of Herschkl's draw-
ing, is wholly absent from M' Russell's photograph of 1890,
in which ihe same ipace ii occupied by a great dark oral.
The facts of highest significance concerning nebula recentljr
brought to light depend upon obsemtiona with the spectroscope
by Professor Keklek, now
director of the Licit Obser-
vatory. Sir William
MtJGCtNS in 1864 firat
found bright lines in tbeir
spectra, evidencing a com-
munity of chemical compo-

glowing

gas, mostly hydrogen. Re-
cently helium has been
added, and still other lines
are due to substances a»
yet unrecognized on the
Earth. The character of
the tines indicales exceed-
ingly high temperatures,
or a slate of strong electric
excitement. Temperature
n and pressure both increase
!„,„ toward the nucleus. Not
SK^. alt the nebulae yield bright
'ktd lines ; and this may be dae
to gas under extreme pres-
sure, or to aggregations of
stellar bodies. There are about forty lines in the photographic
Bpeclta of nebuli, the chief line, according to Professor
Keelkr, failing of identity with the magnesium fluting. Hi»
careful measurements upon the spectra of the Orion nebula.
are perhaps the most significant of all, fur they prove that
the distance between the nebula and our solar system is in-
creasing at the rate of eleven miles in every second of time.
However, neither this nor any other nebula has been discovered
to partake of proper motion, although the bright nebula in
Draco is coming toward us at the rate of forty miles per sec-
ond. All the evidence so far seems to show that the nebalse
are in motion through interstellar space with velocities com.
parable with those of the atars themselves. —D. P. T.

iNa. 51 in Mes^ieb'e Cal^Jog-
irafhtd if Rqbedts, 19/A /
Exffimri. 4 Hfri- Tlumi
^llu ifiml tuinlat)

Thi Fixed Stars 311

Stbute, W, Sttllarum Cempoiilanmt Mtnairat Siieromttritai

(Saint Petetsburg, 1837). See also Dun Eekt Oitrrvatery

Ptilitatiom, i. (Aberdeen, 1S76).
Stkuvb, W., Atudes SAstranomU Sttllaire (Saint Petetsburgi

1847).
Smyth, W. H, ' Colora of Multiple S\.i.n' Sidtnal CAremaiiet,

(London, 1S64).
HuGGiNS, 'Motion in Sight-line,' Preettdirtgi Rayal Society

x«i, (.866), 382.
D'Arrest, SiH/rum NtbiUaiBrHm Obttroatienti Havnitmii

(Copenhagen, 1867).
Wolf, Ravet, ' Bright-line Stars,' Cmnf. Rtttd. Ixv. (1867), 19*,
HuoGiNS, ' K^sumd oE Spectrum Analysis,' Report Brititk At-

taciatien, 1S68, pp. 140-165.
MotrriCNY, ' Scintillation,' Bulletin] de tAeadimie dt Bet-

gijiie, l863, el teq.
pROCroR, Univiruand Coming Traniili (London, 1874),
Knobel,' Bibliography of Slars and Nebula,' J/i>hi4. Ate. Rcy.

Aitr. Sec. xxxvi. (1876), 365. •
Newcomb, Pefular Ailnmom}' (New York, 1877).
Knuhel. 'Chronology of Star Catalogues,' Mtm. Rcy. Aitr.

i'nc.xliii. (1877), :.
Hall, M., ' Sidereal System,' Mrmoirt Reyal Ailrerunnitiit

Society. X\\\\.{1%71).\ SI ■
Hall, A., ' Double Stars,' ll'itihinfflon Ofit. 1877, App. vi.
H01.DKN, ' Nebula of Orion.' fVaihiitgtB; Ob,. 1878, App. i.
Secciii, Les EloiUs ( Paris, 1879).
Crossley, GLEnHiLL, Wilson, Handbeek of Dauile Start

(London 1879), Notes, etc. (1880). Kibliog rap hies.
RossR, ' Observaiions of Nebulx and Clusters, 1848-78,' lyam.

Roy. Soc. Dub/in, ii. (iSSo).
Pickering, ' Dimensions of Stars,' Rmt. Am. Acad. Arte and

i'rwBw, viii. (1881), 1.
Plummer, 'Sidereal System,' C<'/^f^ii-<«,ii. (i88i), 45.
Newcomb, 'Catalogue of Standard Stars,' Astr. PaperiAm.

Bpkemerii,\. ([882), 147.
VoGEL. MUller, ' Stellar Spectroscopy,' PuM. Astraphys. Obi.

Petsdam, iii. (:883).
Pluuher, * Sun's Motion in Space,' Mem. Ray. Atlran. S^

ciely. alvii. (1883). 317.
Grant, 'Catalogue of 6415 Stars,' Glasgow Univ. Obi. (1
Gill, Elkin, ' Parallaxes in So. Hemisphere,' Mem. Roy, Aitr,

Sac. ilviii. (1884), I.

312 Stars and Telescopes

Yarnall, Frisby, * Catalogue of 10,964 Stars/ Washington

Observations y 1884, Appendix i.
Draper, ' Stellar Spectrum Photograohy/ /V^. Am, Acad. xi.

(1884), 231.
Gill, • Future Problems in Sidereal Astronomy,' Proc, Roy,

Institution t xi. (1884), 91.
Pritchard, Uranometria Nova Oxoniensis (Oxford, 1885).
Pickering, * Harvard Photometry,* Annals Harv. Coll, Obs,

xiv. (1885); xxiv. (1890). Bailey, xxxiv. (1895).
Pickering, * Photographic Photometry,' Ann. Harv. Coll. Obs.

xviii. 1888, No. VII.
Gore, J. E., Planetary and Stellar Studies (London, 1888).
LOCKYER, * Classification,' Proc. Roy. Society^ xliv. (1888), i.
Dreyer, * Catalogue of Nebulae and Clusters,' Mem. Roy. Ast.

Soc. xlix. (1888), I ; li. (1895), 185.
Pickering, 'Index to Observations of Variables,' Annals

Harvard College Observatory, xviii. (1889), No. Vlll.
Chandler, ' General relations of variables,' The Astronomical

Journaly ix. (1889), I.
Pritchard, Researches in Stellar Parallax by the Aid of

Photography (Oxford, 1889-92). History, iv. (1892).
Chambers, Descriptive Astronomy^ iii. (Oxford, 1890).
Clerke, The System of the Stars (New York, 1890).
Boss, * Solar Motion,' The Astronomical Journal /\x. (1890), 161.
Pickering, * Draper Catalogue of Spectra,* Ann. Harv. Coll.

Obs., xxvii. (1890) : Maury, xxviii. (1897).
Russell, Description of the Star Camera (Sydney 1891).
SCHEINER, * Photographic Photometry,' Astronomische Ncuh"

r«V^/^«, cxxviii. (1891), 113.
Huggins, 'Celestial Spectroscopy,* iViz/wr^, xliv. (1891), 372.
Rambaut, * Binary Orbits by Spectroscope,' Month. Not. Roy.

Astron. Society, li. (1891), 316.
BoEDDiCKER, The Milky Way (London and New York, 1892).
Proctor, Ranyard, Old and New Astronomy (London, 1892).
VoGEL, Nevvcomb-Engelmann's Populdre Astronomic {\jt\^

zig, 1892).
Vogel, ' Motion in Sight-line,* Astronomy and Astrophysics^

xi. (1892), 203.
Porter, ' Proper Motions,' Publ. Cincinnati Obs. xii. (1892).
Ball, The Story of the Heavens (London, 1893). '
Gore, J. E., * Sun's Motion in Space/ The Visible Universe^

p. 193 (New York, 1893).
Easton, La Voie Lactic (Paris, 1893).

The Fixed Stars

3ii

"BiQVKKlt, Phal^raphs ef Stars emd Nebttla (Ij^m^iya, 1893).
BfiLOPOLSKY, 'jSLylle,' Meni, Sfettrascofiili Hal. uii. (l893>.
Clerke, Hillary of Aitronemy during the XlXth Cenlurf.

(London, 1893).
LocKVER, ' Spectra of the brighler BUra,' Phil. Tram, clxxxiv.

('893). 675-
Bau,. 'Solar tiorXon.' In tAi High Haanits (London 1893).
VocEL, '^Lyri/^iii. Akad. fViit. Btrlin 1894 (j), 115.
Janssen, ' Photographic Photometry,' SMilhiffHiaH Xtfiort 18^4^

p. 191,
SCHEtNER, Frost, As/ranomical 6'^^f/nufi^ (Boston and Lon-
don, 1894). Bibliography.
Campbell, ' Wolf-Rayet Stars,' Ailrenomy and Aitrophytiet,

xiii. {1894), 448.
GoBE, J. E., Thi Worlds of Space (London. [S94).
MOller, Kempf, ' Photometry,' Fiibl. Obs. Potsdam, ii. (1894).
Flammarion, Gore, Popular Asironomy (New York 1894).
Madler, Burnham, ' Double Stars,' Mimmrl u»d Erdt, vu.

(1894), 4'-
BURNHAU, ' Double Stars.' Publ. Lick Obsen-alory, ii. (1894).
Keeler, 'Spectra of Nebuli,' Pukl. Lick Oil. iii. (1894);

Astron. and Aslraphys. xin. (1894), 476.
GlBEBNE, Padianl Suas (New York, 1894)-
ChaMBERS, Tit S/oryo/ /At Stars (New York, 1895),
D'Engelhardt, ' Nebula and Clusters,' Oiiervatinni Aitr»-

nomiquts (Dre»deii, 1895).
Samtbr, ' Milchstrasse,' Himmtlund Erdt, vii. (1895), 508, 544.
VaLentInER, Handtobrttrbuch dtr Aslron. (Breslau 1895-98).
Chandler, ' Catalogue of Variables,' The Astronomical Jsur-

iuil.-E.yK. (1896), us,
RasaU, ' Solar Motion,' Bulletin AslroH. xiii. (1896), 169.
Everett, ' Poles of Binary Orbits,' M. N. Key. Aslr. Soc. 1ti".

(1896), 4&a-

SSE, Ifcscarthti on tit EtH^utiono/SMlarSy Items (Lynn, 1896).
Cekaski, 'Variables,' Annalti Oil. Moicau, iii. (1896); livr. ii.
Chase, 'Cluster in Coma Berenice*,' Tram, yo/^ Oij. i. ( 1896).
MouLTON, ' Spectroscopic Binaries,' Pop. Astr. iii. ( 1896), 337,
Clarke, H. L, • Life-history of Star Systenis,' Pop. Astr. liL

(1896), 489.
Russell, ' Southern Circumpolars,' Fop. Aslr. iv. (1896), 6t.
BiiRHHAM, ' Binary Systems,' Popular Astr. iv. (1896I, 169.
Gill, Kaptevn, ' Photographic Durchmustening,' Anmalt

Cape Observatory, iii (i^)i iv. <i897).

314 Stars and Telescopes

Ykndell, * Variable Stars/ Popular A str. iii.-v. (1896-97).
SCHIAPARELLI, ' Color of Sirius,* Rubra Canicula (1S97).
LoCKYER, * Celestial Eddies/ Nature, Iv. (1897), 249.
Fowler, 'Chemistry of the Stars/ Knowledge^ xx. (1897), 77.
MoNCK, ' Spectra of Binaries/ The Observatory , xx. (1897), 3891
Clerke, */3 Lyrae/ TAe Observatory^ xx. (1897), 410.
ScHEiNERf Die PhotographU der Gestirne (Leipzig, 1897).

Atlas and bibliography.
Gould, * Clusters/ Cordoba Photographs (Lynn, 1897).
Whitney, * Solar Motion/ Popular Astronomy , v. (1897), 309.
Wilson, *Ring nebula in Lyra/ Popular Astr. v. (1897), 337.
Clerke, * New Class of Variables/ Observatory, xx. (1897), 52.
MOller, Die Photometrie der Gestirne (Leipzig, 1897). Biblio-
graphy.
Hall, M., * Sidereal system revised,* M. N. Roy. Astr. Soc, IviL

(i897)>357;lviii. (1898), 473.
Pannekoek, •/3 Lyrx,* Kon. Akad. IVetenschap. Amsterdam,

V. (1897).
HUGGINS, ' Celestial Spectroscopy,' The Nineteenth Century^

xli. (1897), 907.
LOCKVER, The Sun's Place in A^ature (London, 1897).
Pannekoek, * Galaxy//(V/r. Brit. Ast. Assoc, viii. (1S97-98).
Gore, J. E., ' Sidereal Heavens,' Concise Knowledge Library

(New York, 189S).
Duner, SCHEiNER, 'Stellar Evolution,' Popular Astr. vi.

(1898), 85.
Myers, * System of /3 Lyric/ lite Astrophysical Journal, vii.

(1898), I ; Popular Astronomy, vi. (1898), 268.
Keeler, • Physiological Phenomena, and Spectra of Nebulae/

Publ. Astron. Society Pacific y x. (1898), 141.
Kapteyn, * Solar Motion/ Astron. A^achr. cxlvi. (1898), 97.
Easton, 'Theory of Universe (Proctor),' Knowledge, xxi.

(1898), 12.
Easton, * New Theory of Galaxy,' Knowledge, xxi. (1898), 57.
Maunder, McClean, * Photographs of Stellar Spectra,' Ob-
servatory, xxi. (1898), 163.
Schweiger-Lerciienfeld, Atlas der Himmelskunde (Vienna,

1898).
Deslandres, * Motion in Sight-line,' Bulletin Sae. Astron.

France, September 1898.
McClean, * Stellar Spectroscopy,' Proc. Roy. Soe. Ixiv. (1898).
Douglass, * Stellar Bands in Zodiac,' Pop. Astr. v. (1898), 511.
Eastman, Catalogue 0/ ^,1^1 Stars (Washington 1898).

The Fixed Stars 315

DiSLANDRBS, 'Motion in Sight-line,' BullttiH Aitren. xv.

(189SI, 49.
Young, Gtntral AttrBnomy, Ttvised edition (Boston. 1S9S).
Hagbn, Ailai Sitllarum V^riJiiUuin (Berlin, 1898}.

References to the p>opular literature of the itaia and nebulK
ait 10 be found in the volumes of Poole's Indti, on the
pages indicated below : —

Volun..ofln<l«,iindVa™

r»=

Rct^nncH
10 Sun

I (1800-81)

II <iS82-86)

III iTS,S7-9il

IV (iSgi-t^)

Annual Literary Index. 1S97
Index to General Literature, 1893

306
S9
^03

P- '243

417
407

54S
274

Most of (he earlier and more important scientific papers are
classified and titled in Sir Robert Ball's EUme'iis of Aslron-
jmy, pp. 427-40 (New York, iSSo), In vol.xxxii. [1SS3) of the
PrKtiHings Amtrican Association Aihanuminl of Scitnet,
W. A. Rogers has given a full prcsenlaiion of the German
survey of the northern heavens. The occasional bulletins oE
the Paris aslrographic conference contain important researches
relating to stellar photography and allied subjects. Recent
volumes of Kunuilidgc contain numerous papers on the stars
and nebula, by M' Maunder and others, with fine reproduc-
tions of astronomical photographs, especially those of I)'
Roberts. In \t\e Jimraal of the Britiih Ailronomital Aiiociatian
are found very useful lists and abstracts of papers. Occasional
bibliographic list) are given in BulUlin Aitrotiomiqiu, i.-xv.
( iS84~9S). Recent scientific literature is exhaustively dted in
the frequent lists of the Astmpkysical Jaumal, vols. i.-vUi.
(1895-98). -i?./-. 7:

CHAPTER XVIII

TELESCOPES AND HOUSES FOR THEM

ly^NOWLEDGE of the Sun, Moon and stars gained
^^ from the preceding chapters leads naturally^
to a brief story of the instrument by which astrono-
mers have mainly acquired that knowledge; fo»
before the invention of the telescope, it was impos-
sible that mankind should know very much about the
heavenly bodies. The working of a telescope is
much affected by its location and the construction of
the building in which it is sheltered : a few para-
graphs are therefore devoted to these important
considerations.

Gauleo (page 12), while not perhaps the original
inventor of the telescope, was still undeniably the
first to construct one and apply it to the higher pur-
pose of astronomical ol^servation, and he was richly-
rewarded by the supreme discovery of the satellites of
Jupiter. Before his day, not only were no bodies
attendant upon the planets known, save our Moon^
but many of the planets were themselves unknown ;
nor was it possible to ascertain the dimensions of
those that were known. The accepted truth of the
Copemican system had led to the prediction of phases
of the planets nearest the Earth and Sun ; but final
corroboration was lacking till the first telescope
achieved this significant revelation. Several cata-

Telescopes and Houses for Them 317

logues of the stars and Tycho's observations of the
planets among them were possible, before the days of
telescopes j but so crude were they that their value at
the present time is due solely to their antiquity.
Although invented early iti the 17th century, the
telescope was chiefly used as a gazing instrument for a
half century;
and it was not till
1668 that the
mechanical ge-
nius of Jean

PlCARD (1620-

1681) saw how
greatly the tele-
scope might en-
hance the pre-
cision of all
astronomical
measures of po
sition, if only it
were attached to
a circle to impart
deliniteness of
alignment Al- christian huvcens (1629-1695)
though R uMER

(page 45) had invented the transit instrument, Pic-
ard's invention produced the meridian circle, a mod-
ern type of which is shown on page 368 ; with It may
be found the exact place of any heavenly body on
the celestial vault with the utmost ease and celerity.
However, even the transit or the meridian circle
would be greatly restricted in use but for the astro-
nomical clock, the principles governing the pendulum
of which had been formulated by Galileo. But here

3l8 Stars and Telescopes

was a delay of nearly a half centuiy, for it was not till
1657 that HuYGENS, famous for his great telescopes
and the observations made with them (especially of
the planet Saturn) , constructed an accurate time-piece
by controlling its train with a pendulum.

In the telescopes of Galileo and Huygens and all
their followers for about a century, the image of a
remote object was formed by a single lens of double
convexity. The glass was full of imperfections ; but
besides this, the bafRing obstacle of the prismatic
spectrum surrounded all bright objects with highly

Telescopes and Houses for Them 3 19

colored fringes, so that a limit to the effective size of
the telescope seemed to be set by the laws of nature
herselfl But it was soon found that the disturbing
color effects were minimlxed, if the lens was ground
very flat. This, however, necessitated great focal
length, and many telescopes were built in the lytb
century with but little variation in model from the
famous instrument of Hevelius (1611-1687) illus-
trated above; in which ob-
ject-glass and eye-piece were
so far apart that no tube con-
nected them, and they were
kept in line by an open
framework, strongly trussed.
HiTVGENS built an aerial tele-
scope, with objectiveand eye-
piece wholly unconnected,
the former being mounted in
a small swivel tube on top of (By b>l>ch & I^m*. a mj tj
a high pole, and directed '^^.''"^'Zi^i'XZ',^
toward the eye-piece by a /nr utxn nftrud in frumi
cordorwirepulledtautbythe 'J'jt^^'CTV'J,^ '^' "'*'
observer. Definition was ex-
ceedingly imperfect except at the centre of the field
of view, wind precluded the use of the telescope, and
except for a moment at a time it was practically im-
possible to maintain the object in the field with that
steadiness requisite for critical observation. Never-
theless, the long telescope had its day, and one 600
feet in length is said to have been made in Italy, though
never successfully used.

Galileo's original telescope had but two lenses : a
double convex to form an image, and a double con-
cave to examine it with ; and this form of telescope

320 Stars and Telescopes

is preserved in the common opera-glass and field-glass
of the present day, if only slight magnifying power is
desired. Great improvement in optical power has,
however, been recently obtained by adjusting two
right-angled prisms, properly constructed, in the path
of the rays between objective and eye- pieces, whereby
the necessary compactness of a hand-glass is secured,
and with it the advantages of greater focal length and
a larger image at the focus. At the same time the
prisms effect that reinversion which is requisite for
terrestrial purposes. A magnification of 1 5 diameters
and more is easy.

Sir Isaac Newton (page 93), who was no less a
physicist than astronomer, after devoting many years
to a study of the imperfections of refracting tele-
scopes, expressed a definitive opinion that a f>erfect
glass of high power was a physical impossibihty ; and
this conclusion, coupled with the unwieldy propor-
tions of the most powerful instruments of that day,
forestalled farther attempts to improve the refractor
or dioptric telescope. But the genius of Newton led
the way by modifications of the reflector, or catoptric
telescope, already invented by James Gregory (1638—
1675), which forms the image of a distant object by
convergence of the rays on reflection from a concave
surface of suitable curvature and high polish. In the
refractor, the object-glass assembles rays of different
colors at different focal points, the violet nearest the
glass and the red farthest from it ; but in the reflec-
tor all rays are focussed at a single point, no matter
what their color. Still, as the image is formed directly
in front of the mirror itself, the head of the observer,
if placed in the ordinary position, would intercept
nearly all rays from the object. Gregory had dodged

Telescopes and Houses for Them 3 2 1

this difficulty by mounting a small secondary concave
mirror in the path of the rays, thus throving them
back upon the primaiy mirror. This be perforated
at the centre to allow the doubly reflected rays to
reach the eye-piece, which was then screwed into the

RFFLECTOR

back of the large reflector. Newton improved upon
this arrangement and preserved the principal mirror
intact by interposing a small diagonal reflector in the
path of the rays just before they come to a focus,
thereby diverting them to the side of the tube, where

322

Stars ami T^tscopis

the eye-piece is set peipendicubr to it. The obser-
ver then looks into the tube, not at one end, but at
one side, at right angles to the direction of its point-
ing. The Newtonian is the favorite type of construc-
tion for the reflector at the present day, especially if
moderate in size, as in the preceding illustration of a
Newtonian by if John
A. Brashear of Alle-
gheny, who, of all Am-
erican opticians, has
achieved the greatest
success in constructing
reflectors. A farther
improvement of the
Newtonian form, by
substituting a small to-
tally reflecting prisra
I for the secondary mir-
was carried into
;ct by Henry
Dhaper.
1 During the past cen-
tury five builders of re-
flecting telescopes have stood out pre-eminently : Sir
William Hf.rschel, whose 4-foot reflector is illustrated
on page 13, and who long served a self- apprenticeship
by constructing nearly zoo mirrors, one of them 34
inches in diameter which was nearly equal in per-
formance with the 4-foot, and with which his son, Sir
JOHX, continued the elder Herschel's researches;
Lord RossE, whose ' Leviathan,' or 6-foot reflector
illustrated on page 247, remains yet unsurpassed in
size; William Lassell (1799-1880), an eminent
English astronomer, who built two reflectors, dupli-

at tx Thomas

Telescopes and Houses for Them 323

cates in size of Hekschel's largest instruments, which
be used on the island of Malta, 1853-65; Thomas
Grubb, who in 1867 built a 4-foot Gregorian with a
sUver-on- glass speculum for the government observa-
tory at Melbourne, Australia, and who has a worthy
successor in his son, Sir Howard, the builder of the

ao-inch reflector illustrated on page 292, with which
D" Roberts has produced photographs of unusual ex-
cellence ; and D' A. A. Common, of Ealing, England,
whose iirst great reflector of 3-foot aperture is now
owned by the Lick Observatory, by gift of M'
Edward Crosslev, and who built in 1889 a 5 -foot
silver-on-glass reflector, employed to good advjniage
in photographing the nebulae. An instrument of like

324 Stars and Telescopes

dimensions is now building at the Yerkes Observatory
of the University of Chicago.

It will be noticed that all the great reflectors pre-
viously mentioned were constructed in Great Britain,
and that they achieved extraordinary success in the
hands of their builders. A great reflector is, indeed, a
delicate instrument, requiring much skill and patience
in adjusting, and more than ordinary care in preser-
vation of the specular surfaces from deterioration on
exposure to the atmosphere; but by M' Brashear's
formula, a new film of silver is readily deposited upon
the glass chemically. Besides this, the great reflector
is exceedingly massive, and unwieldy in proportion ;
and its performance is much influenced by disturbing
air-currents, while flexure or sagging of the mirror is
a most serious drawback. This is most successfully
overcome by making the thickness of the mirror not
less than one-sixth its diameter. A few reflectors of
great diameter have been built in France : a 4- foot
silvered glass reflector at the observatory of Paris by
Martin, a 39 -inch recently completed by the Brothers
Henry for Meudon, and two of 32 inches* diameter
at the observatories of Marseilles and Toulouse by
FoucAULT (page 47). Before his time all reflectors
were made of speculum metal, an alloy often composed
of 126 parts of copper to 59 of tin.

Amasa Holcomb, a land surveyor of Southwick,
Massachusetts, appears to have been the earliest
maker of telescopes in America, having begun in
1826. Although his first instruments were refractors
of small size, he afterward made specula as large as
10 inches in diameter, about 30 in all. His favorite
mounting was that known as the Herschelian t>-pe, in
which the speculum is tilted slightiy, throwing the

Telescopes and Houses for Them 325:

image at the side of the tube, instead of centrally^
All the light is thereby saved, but a disastrous distor-
tion is introduced. Holcomb devised a steady and
effective mounting, which received the award of a
Franklin Institute medal in 1835. M' E. P. Mason
of Yale College, aided by his classmate Professor H>
L. Smith of Hobart College, built in 1838 a reflector
of 13 inches aperture, then the largest telescope in
America; and it was used conjointly by them in
accurate delineation of a few prominent nebulas.

The signal success of Sir Wiluam Herschel's great
telescopes, and the giant reflectors of Lord Rosse in-
spired many private individuals in America as well as
other countries to build instruments of similar design.
Among them we mention Josiah Lvuan, of Lenox,
Massachusetts, whose 9j-inch speculum, with a system
of supporting levers to preserve its figure when pointed
upon stare in all altitudes, was exhibited before the
.American Association for the Advancement of Science
at the Albany meeting, 1851 ; and who subsequently
figured a 12-inch speculum, now the property of
Amherst College Observatory, by gift of his son, the
Rev. D' LvMAN of Brooklyn. As early as 1858,
Henry Draper (page 298), returning from a visit to
Lord RossE at Parsoostown, constructed a 15-inch
specalum, the perfected result of which was a splendid
photc^raph of the Moon, over 4 feet in diameter.
Professor Brooks, now of Geneva, New York, has
built a 9-inch reflector and used it to good advantage
in comet work, and M' Edcecomb of Mystic, Con-
necticut, has turned out many excellent reflectors.
Also we must include an 18-inch mirror ground and
figured by Professor Schaeberle, which he used in
planetary photography. It was an adapted Casse-

326

Stars and Telescopes

grain, or type similar to the Gregorian, except that
the secondary mirror is convex instead of concave,
thereby producing a larger focal image. Finally, in
1871, \y Draper completed the largest reflector, of
38 inches' diameter, yet constructed in America,

which is now part of

the equipment of Har-
vard Observatory.

Still another type of
reflector, revived of
late in Germany and
by D' Common in Eng-
land, is known as the
' brachy- telescope,' or
' oblique Cassegrain,'
a composite of Her-
schelian and Casse-
grain types. The tube
is exceptionally short,
and the figure of the
secondary mirror can
be made to neutrahze
the distortion inevi-
tably produced by tilting the speculum. Ranvard
devised a very ingenious type of mounting, completed
by Professor Wadsworth and adaptable to any form
of reflector, whereby the advantages of a stationary
eyepiece are assured, in all possible pointings of the
telescope.

Next in order we outline the development of the
refracting telescope from the beginning of the 18th
century onward. Although Newton's experiments
had satisfied him that a lens of short focal length
could never be made to yield an optically perfect

iRD (l845-'S94)

Telescopes and Houses for Tketn 327

image, Euler (page 96) doubted the accuracy of
this conclusion, and suggested that a combination of
lenses of glass and water, of suitable curvatures, might
produce a composite lens practically free from defects
of color — that is, an achromatic objective. In 1733
Chester More Hall in England was the first to
make and use such an objective, by combining a con-

(«>«/

»?/■«»,■«(

cave lens of flint glass with the original convex lens
of crown glass. Flint glass contains much oxide
of le:id and \i very dense, and its power of dispersing
a beam of white light is about double that of an
equal prism of crown glass, although the mere re-
fractive powers of equal prisms of the two kinds of
glass are the same. If, therefore, a double convex
lens of crown glass is capped by a plano-concive or
double concave lens of flint-glass, there is a residuum
of refraction with the harmful dispersion effectively
neutralized. The litde diagram above shows in
schematic fashion the passage of parallel rays from left
to right through such a double objective, also conver-
gence to the focal plane, and subsequent magnifica-
tion of the image by a small eye-lens, with emergence
in parallel pencils suited to human vision.

It was not Hall, however, who obtained the credit
for this signal improvement of the telescope, but John

328

Stars and Telescopes

DoLLOND, another English optician, who secured a
patent for the invention and reaped most of the
benefits therefrom. No limit to the size of refractors
now appeared to be set, save the difficulty of obtain-
ling large disks of glass of the requisite optical purity.
This embraces not only high transparency, and free-
dom from air bubbles and sand-holes, but absolute
Absence of strisc and waves of irregular density. So
nearly insurmountable
werethe obstacles in manu-
facturing flint glass that an
achromatic of high excel-
lence as large as 6 inches
in diameter was unknown
at the beginning of the 19th
century,

GUIN-AND (1745-1825).

a Swiss watchmaker, by
patient CKperiment finally
discovered how to prevent
the heavy lead oxide from
settling in the molten flint
glass; and his methods,
in some essentials secret,
have been communicated to his successors, MM.
Rosette & Feil of Paris, followed by M. Mantois,
who, with Chance Brothers of Birmingham, have
made the disks for nearly all the great refractors of
the present day. Guinand for many years before his
death was associated with Fraunhofer (page 17) in
' the manufacture of telescopes at Munich, and to-
gether they produced about 1824 an achromatic re-
fractor of nearly 10 inches aperture, with which the
elder Struve made at Dorpat a celebrated series of

DOLLOND (1706-I761)

Telescopes and Houses for Them 329

observations of double stars. So critical was Fraun-
HOfER in his optical nork, and so consummate a
mechanician was he that a knowledge of the success
of this great telescope finally penetrated to America,
where at that rime a permanent observatory had
scarcely been projected. Fraunhofer, too, made
great improvements in the equatorial telescope, by
modifying the old parallactic stand Into the Germaa
mounting now univer-
sally met with, and
only improved upon
by the Potsdam
mounting (page 60).
Ahhough David
RiTTEN HOUSE had es-
tablished a temporary
observatory at Norri-
ton near Philadelphia
for observing the
transit of Venus in
1769, and the elder
Bond (page 240) had
in 1825 a modest pri-
vate observatory at

Dorchester, Massachusetts, and Vale College had in
1832 a 5-inch porUble telescope of Fraunhofer's
make, the first American observatory, intended for per-
manent occupation as such, was erected at Chapel Hill,
North Carolina, in the years 1831-32. Few observa-
tions were, however, made there ; it was soon after
dismantled, and accidentally destroyed by fire about
1838. Olmsted (page 210) was for a brief period
professor at Chapel Hill. General Mitchel in 1841
visited Europe in the interest of the astronomical

(1732-1796)

330

Stars and Telescopes

society of CinciiiQati and ordered from Mbrz and
Mahler, of Munich, the successors of Fraunhofer,
a iz-inch refractor. By his successful touts as a
popular lecturer Mitchel aroused great enthusiasm
for astronomical knowledge, and to his forceful and
energetic personality may be traced the origin of many
American observatories. The great comet of 1843
led directly to the founding of Harvard College OIk
servatory (page 300),
andits equipment with
a telescope, colossal
for that period, of 15
inches aperture,
which, with its twin
companion at Pulkowa
in Russia, formed the
culminating labor of
the celebrated optical
house of Munich.

American telescope
builders have always
been obliged to order
the rough glass for
their objectives from
foreign makers, and
must still do so, the few experiments in optical glass
making outside of Europe having proved in the main
failures. But in that line and skilful fashioning of the
crude lump into a perfect lens, our countrymen have
for the last half century led the world. Frrz of New
York made about 30 refractors, between 6 and 13
inches aperture, many of which were subsequently
improved by Alvan Clark ; Spencer of Canastota,
New York, whose chief success was with microscope

liSo9-:S()2)

Telescopes and Houses for Them 33 1

objectives, undertook telescopes also and completed
a i3i-inch glass which the late \y Peters of Hamiltoa
College (page 113) made famous by his discovery of
48 small planets ; also Cucey of Boston and Byrne
of New York deserve more than passing meotion, not
to say many other skilful American opticians who have
turned out a host of telescopes of lesser dimension
and veiy satisfactory performance.

Nor have opticians of a high order been lacking
in European countries. Cauchoix, and the Brothers
Henry in France j Steinheil and Schroeder in Ger-
many ; and Cooke & Sons in England — all have
built refracting telescopes of large aperture and excel-
lent definition. The Hf.nrvs have constructed ten
of the photographic objectives engaged in the astro-
graphic survey (page 260), their mountings being by
GAiniER; also a 30-inch at M. Bischoffshk.im's
Splendid observatory on Mont Ores (pige 169), and
one slightly larger for the observatory at Meudon,
Paris. S'lKiNHK.iL's greatest achievement is in object-
glass of 31^ inches diameter for the astrophysical
observatory at Potsdam, and Cookf s a 25 inch
refractor now mounted at
Cambridge, England
Within recent years, Cooke
has been offering a new
photo- visual objective, a
triple glass said to be free

from the troublesome sec- {pkttefmtiucamivtniai/ixi.
ondary spectrum of the or- •dnwa/)

dinary double objective, and

lo converge visual and photographic rays to an iden-
tical focus. The curves are the work of M' H. D.
Taylor, and the glass employed is known as the new

E OBffCTIVE (T/

332 Stars and Telescopes

Jena glass, made from the formulse of Professor Abbe
of the University of Jena, who conducted a course
of experiments under the auspices of the German
government.

The secondary spectrum gives rise to an effect
which becomes especially harmful in very large
objectives, surrounding all bright stars and planets
with a brilliant bluish luminosity, greatly interfering
with the observation of faint adjacent objects like
-satellites and companion stars. This difficulty is in-
herent in the glass itself, because dispersion or de-
composition by the crown glass cannot be exactly
neutralized by the recomposition of the ordinary
flint. With the Jena glass, however, D' Hastings of
Yale University has succeeded in producing a double
objective practically free from secondary spectrum
effect, by careful investigation of the theoretical cur-
vatures, and placing the flint lens on the outside of
the combination, so that the light passes through it
before reaching the crown.

The curves of the lenses in achromatic objectives
have occasioned much research in theoretical optics,
and many different constructions have been evolved,
among them that of LnrRow, with the crown double
•convex and the flint plano-concave. Gauss (page 99)
devised a form in which the crown is plano-convex
and the flint concavo-convex. In the type of objec-
tive preferred by Clark, the crown is double convex,
and the flint double concave, the two lenses being
mounted in a long cell with a space between them
equalling about ^ their diameter. This construction
adds to the weight of the mounted objective, but
affords better correction of the aberration, permits
easy cleaning of the inner faces, and allows free circu-

Telesales and Houses for Thtm 333

la6on of air between flint and crown. In all these
types the light reaches the crown lens fitst.

Before passing to a consideration of the remarkable -
series of telescopes built by the Clarks, the excellent
work of Sir Howard Grubb must be further specified.

embracing a 37-inch telescope complete (illustrated
above), and mounted at the Imperial Observatory of
Vienna, one of the best equipped establishments of
Europe. Also he has constructed a j6-inch visual and
a j8-inch photographic objective for the Royal Obser-
vatoiy at Greenwich, as well as numerous glasses of
flmaller aperture ; and his mountings are especially
commended for rigidity. A type of clock-motion

334 Stars and Telescopes

with electric control devised by Grubb permits the
close following of a star in its diurnal motion, witli
that degree of accuracy necessary to secure circular
star-images on a phott^raphic plate during long
exposures.

Of all makers of telescopes Alvan Clark attained
the greatest celebrity. A portrait painter in Boston

in 1844, accident drew his attention to the construc-
tion of a small reflector, the success of which led to
his making refractors. Two years later he was estab-
lished in the business of telescope construction with
his two sons, Alvan Graham (page 285) and George
Bassett, Clark's first refractors were introduced to
astronomers by Dawes (page 283) who purchased

Telescopes and Houses for Them 335

five of them, and subjected them to the most critical
tests. Above the aperture of 6 inches, the Ciakks
made in all about 75 objectives, with mountings for
the most of them. Their objectives are optically
more perfect than the
atmosphereinwhichthey
■can generally be used,
bearmg a hundred di
. ameters of magnifymg
power for each inch of
aperture and separatmg
the components of close
double stars up to the
hmit set by Daw es b em
piric formula. Clark
telescopes have not only
a world-wide fame but a
world-wide distribution.
Between i860 and 1892
the C LARKS were iive
times called upon to

construct ' a telescope more powerful than any now
in existence ' ; and each time the advance was from
■one to six inches in excess of the aperture of the then
greatest glass. These were, in order, the i Scinch now
at Evanston ; the z6-inch at Washington, a duplicate
of which was built by them for the University of Vir-
^nia; the 30-inch for the Imperial Observatory at
Pulkowa, near Saint Petersburg; the 36-inch for the
ILick Observatory ; and the 40-inch, still the largest
refracting telescope in the world, for the Yerkes Obser-
■vatory of the University of Chicago. Among other
^eat refractors of their construction arc a 23-inch for
Professor Yotmc at Princeton, and a 34-inch for M'

336

Stars and Telescopes

Perctvai. Lowell, now mounted in his private obser^
vatory at FlagsUiT, Arizona. This gkss and theVerkes
objective were the last work of Alvan Graham Clark,
his constant co-worker bein^ M' Carl Lundin, an
able optidan who has served a quarter-century ap-
prenticeship under all the Clarks, and now continues
the work of the firm at Cambridgeport.

GEORGE B. CLARK (1827-189I

The Lick 36-mch lenses are mounted in a cast-
iron cell faced with inlaid silver where the glasses
rest against it. The weight of the objective in it*
cell is about 700 pounds, and its cost was ^55,000.
An additional lens, or photographic corrector of jj
inches aperture, was provided at a cost of ^13,000.
The focal length of the visual object-giass is 56 feet;

Telescopes and Houses for Them 337

48 feet when the photographic corrector is applied.
I'he Verkes objective weighs about half a ton, and its-
crown lens is three ioches thick at the centre. The
total cost of this telescope, inclusive of its mountings
was about f 125,000.

Alvan Clark was in 1867 awarded the Rumford
medal of the American Academy of Arts and Sciences
for the perfection of his optical surfaces. The com-
pletion of the 30-inch Russian object-glass brought the

THE UNIVERSITY C
■H l/u liart 0/ Laki GfMtoa, WUliami Bay. U
iMilding, aiuiroilaimt tyr^exa, llufifl oj M' Cl

Ci-ARKS the signal honor of the golden medal of the
Empire, conferred for the first time by Alexander
the Third.

Second in importance only to the objective of a
telescope are the mounting by which it is pointed to-
ward the heavenly bodies, and the eyepieces with
which the images formed by it are examined. The
mountings made by the Repsolds of Hamburg
are imsurpassed, their largest having been con-
structed for the 3o-inch Clark glass at Pulkowa
(page 133).

40-INCH TELESCOPE
idvi h M.KT015. ^inUvtby Alvan Cl
WxBHBi h SwAsitv ifClmland. Tin /.
imgfaru »/ Hii r"" I'tfica^ ttiif* w.
M«, /Ar^gJi iimlrnUftrvrralwlKlHcmn
/aUllipfl, m l/ufln- BTighv^dbf Sir
ia iBtMll ftlilioH. Tki dtwa it 9o/«< !■

THE VERKES OBSI

.*BK *• Sem, nf CnmMdtfftrl, imnmiimg i
•it il at<ml 6s fi" /•-r ; rtW. alHumfk iht mit
ar/j- ij /ow, tie lekoli i, nuify mitmofwd *» *■

lUBa Tki fluttrrafA liunt il ntt

Telescopes and Houses for Them 339

Refsold has many foreign rivals who have cod-
stnicted mountings for smaller instruments. Especially
may be mentioned S^cretan of Paris, Bamberg of
Berlin, Heyde of Dresden, and Salsioiraghi in Italy.
In America, Saegmuller has made fine mountings,
one of his largest for a 30-inch glass at Manila.
Warner & Swasey of Cleveland have met with marked
success in the larger mountings. Among their im-
provements are devices for all necessary manipulations
of the telescope from the eye end ; incandescent
lamps for illuminating the circles ; wheels and circles
for ' setting ' in both co-ordinates from the dome*
floor; and the adoption of ball-bearings to give ease
of motion to the massive steel axes which, in their
mountings for the Lick and Yerkes objectives, weigh
from I to 3^ tons each. The Lick mounting cost
/4a,ooo, and the Yerkes about S6o,ooo. The tatter
is provided with an elaborate system of electric
motors, which do the work of clamping and give quick
motion to the telescope on either axis as required.
Abo the dome is turned in either direction, and the
floor of the dome elevated or depressed by electric

The modern American mountings provoke little
unfavorable criticism. In some classes of observation
difficulties arise from their lack of rigidity, both as to
the axes themselves and the iron-work supporting
their bearings. Too great care cannot be expended
upon the founding and construction of the pier upon
which the mounting rests. In general, our moiuuings
are surpassed in rigidity by those of hke dimension
from the best English and Irish shops. But if the
American telescope is compared with those of foreign
makers, in point of subsidiary apparatus for its con-

340 Stars and Telescopes

venient working, we find a constantly growing dispo-
sition ou the part of the instrument builder to consalt
the wants of the astronomeT and to profit by hU
suggestions.

A convenient form of mounting known as the
equatorial coud^, or ' elbow equatorial,' was invented
in 1882 by M. Loewy, now director of the Paris Ob-
servatory. As the illustration shows, the instrument

E EQUATORTAL COUDfi (DESIGNED BY LOEWt)

rr sill in a ccm/arlablt nnm, iii Itltliafl iliut HUHMlitl in iMr

itself is mounted in the open air, while the observer,
as if working with a microscope, sits always in a fixed
position, no matter what the direction of the object he
may be observing. He may therefore avail himself
of comfortable temperatures. Easy and rapid hand-
ling, too, are very advantageous, as well as the attach-
ment of cameras and spectroscopes. There are dis-
advantages, of course, chiefly the loss of light by

Telescopes and Houses for Tkem 341

reflection irom two plane mirrors set parallel at an
angle of 45° to the declination and polar axes. The
objective is mounted in one side of the upper cube
which, with its mirror also, turns round on the decli-
nation axis. The long oblique tube is itself the polar
axis, at the upper end of which the observer sits, and
a powerful clock carries the instrument slowly round
to follow the stars in their diurnal motion. First cost
of the equatorial coud^ exceeds thai of the ordinary
equatorial, but the expense of a dome is mostly saved,
as the coud^ is housed under 3 light rolling structure.
This type of instrument, although not yet represented
in America, has many examples in the observatories of
France, With the larger one at the Paris observatory,
built by the brothers Henrv, was taken a remarkable
series of lunar photographs, now combined into a
complete atlas of the Moon. Two of these are well
reproduced in Chapter 111 (pages 29 and 31.) Defi-
nition in the coudS is excellent, and surface deteriora-
tion of the silvered mirrors is not troublesome.

Quality of the ocular or eyepiece is a factor of
great importance in the performance of an objective.
The character, field of view, and power oi eyepieces
should be carefully suited to the nature of the tele-
scopic work. The ordinary forms are the positive or
Ramsden eyepiece (used for micrometers and all
kinds of astronomical instruments requiring a reticle),
and the negative or Huygenian eyepiece (usually em-
ployed for gazing work merely). It is essential that
the eyepiece should be achromatic as well as the ob-
jective. The Steinheil monocentric eyepiece is a
triple glass, achromatic, and composed of two flint
menisci of different thicknesses capping a double con-
vex crown on both sides. The perfotmance of this

34^ Stars and Teltscepts

ocular is especially gctod on stars and planets. Direct
observation of the sun requires a polarizing eyepiece
or helioscope, best made in this country by Brashear.
It reduces the intense solar light and heat to a degree
not harmful to the delicate tissues of the eye.

The micrometer is an accessory of the telescope
used in the measurement of small arcs or angles. It
is attached in place of the ordinary
eyepiece by means of an 'adapter,'
or draw-tube. In the field of view
are at least three wires, or threads,
or spider-lines, as in the illustration
adjacent. By turning the microme-
ter screw the two parallel threads
are separated until the space to be
measured, as the diameter of a
planet, is just embraced between
limaiy ^(rr,imi.j these two lines. The divided head
•waOvroj T't-^uiwfv of '"^ micrometer screw and a
wkich an nnd/rsm jcalc adjacent record the number
%dii,\' ' of whole revolutions and fractional

parts i and this is readily converted
into arc, because the arc value of one revolution is
easily ascertained by observations upon stars. At
night the micrometer lines are rendered luminous by
light from a small electric lamp (at the left in the
opposite illustration) , or an adjustable oil lamp shown
below it. A micrometer will usually be provided with
a separate equipment or battery of eyepieces, ranging
in power from about 9 to 90 for each inch of aperture
of the object glass with which they are used. The
illustration represents the micrometer of the 36-inch
Lick telescope, constructed by Saegmuller. For
about ten years it has been kept in nearly constant

Telescopes and Homes fm' Them 345,

use, notably by Professor Busnham in the discoveiy
and observation of very faint or close double stars^
A similar instrument of unusual propoitioos was.
built by Warner & Swasey for the 40-inch Yerke&
telescope.

In considerable part the observations, particularljr
of larger arcs, formerly made with the micrometer, are
now supplanted by the greater accuracy attainable

with the heliomcter (page 277) ; but more especially
the photographic plate and measuring engines are re-
placing both. As early as 18^0 the younger Bond
obtained with the 15-inch H:irviird
photographic impressions of Vega,
double star Castor, showing an elongate disk.
the beginning of stellar photography. Barti
West Point, and Caupbell, in New York,
good pictures of the annular eclipse of »6lh !

344

Stars and Telescopes

1854, the first celestial phenomenon photographically^
observed. By measuring his plates of Mizar, Bond
in 1857 proved photography capable of results equally
precise with direct observation of stellar images. The
year following, RuTHERfURD of New York undertook
celestial photography at his private observatoty with >
an objective of iij
inches aperture fig-
ured by hiniselfl
Plates prepared by
the old wet collodioD
process were used, and
exfwsures of 5 to 10
seconds brought oat
e belts of Jupiter,
d even Saturn's ring.

In 1863, RUTHERFURD

began the construction
of the first objective .
figured solely for pho-
tographic rays, and he
obtained the required
actinic correction by
means of his neat
adaptation of the spectroscope in examining the chro-
matic condition of an objective. So great was the
improvement that an exposure of one second gave an
image of Castor, which required ten seconds in the un-
corrected telescope, RutherI'URd later demonstrated
the feasibility of converting any visual objective into
a nearly equivalent photographic telescope by mount-
ing in front of it a meniscus of flint glass. In 1869
he constructed the first instrument of this character,
13 inches in aperture, and with it were taken, in

(1816-1S92)

Telescopes and Houses for Them 345

August, 1871, the first photographs of the sun, show-
ing the minute granulations of its surface. Hia pictures
of sunspots have not yet been surpassed (page 52),
and his lunar photographs compare favorably with
recent work at Paris and Mount Hamilton.

■^u ilatian u JafoH, 188;)

The transits of Venus, in 1874 and 1882, offered
exceptional opportunities for the application of pho-
tography, and a type of instrument known as a 'hori-
zontal photo- heliograph,' originated by the elder
WiNLOCK in 1869, was brought into service by the

346 Stars and Telescopes

American Commission, whose work was directed in
the main by Professor Newcomb. The Clarks built
eleven of these instruments, eight for the Government,
and one each for the Princeton, Harvard, and Lick
observatories. They have photographically corrected
objectives 5 inches in diameter, and of 40 feet focal
length ; are mounted in the meridian, and the sun*s
rays are thrown constantly through the objective by
7-inch plane mirrors, suitably mounted and driven by
clock-work. In 1888, Brashear built a similar in-
strument for the Imperial Observatory of Japan at
Tokyo. Besides the large scale of the original image,
the sun appearing about 4^ inches in diameter on the
plate, the stationary image and plate-holder allow the
photographer to avail himself of any required number
of assistants, all of whom work within the dark room,
which thus replaces the moving camera as ordinarily
employed in celestial photography. The preceding
illustration represents one of the American photo-
heliographs as mounted by the writer at Shirakawa,
Japan, for the total eclipse of 1887. On the right are
mirror and objective, and in the background the
photographic house, the 40-foot tube between them
being housed from the direct rays of the sun. With
similar instruments Professor Schaeberle in 1893, in
Chili, and Professor Campbell in 1898, in India, ob-
tained very fine pictures of the sun*s corona, — not,
however, by using the mirror, but by rigidly fixing the
objective high in the air, and following the sun's mo-
tion with a slowly-moving plate- holder.

As it is not our present purpose to trace the history
of astronomical photography, but only to outline salient
departures, we mention but a few additional develop-
ments. Most interesting of all is the train of cir-

Ttlescopes and Houses for Them 347

cumsUnces leading up to our modem methods of
deteiraining star places by photographic means.

On the early morning of the 8th September, 188a,
M' FiNLAY, first assistant at the Observatory of the
Cape of Good Hope, discovered and first observed
a bright comet in Hydra (page 200). Several photo-
graphers in South Africa obtained photographic im-
pressions of the new comet within a month following,
by the use of ordinary apparatus only ; and on re-
porting this fact to D' Gill, he at once began to take
photographs of the comet, with the assistance of M'
At-us of Mowbray, whose only suitable lens was a Ross
doublet, but 2\ inches in diameter, and of 1 1 inches
focal length. They not only succeeded in taking fine
pictures of the comet, but their plates on develop-
ment showed hundreds of stars, well defined over an
area so large as to suggest at once the practicability
of employing similar and more powerful means for
the construction of star maps. Admiral Mouchez,
late director of the Paris Observatory, endorsed the
views of D' GiLL, and his encouragement of the
Brothers Henry led them to devote their attention to
the construction of suitable lenses. As D' Gill well
says, ' The brilliant results which Messrs. Henry soon
attained are still fresh in the minds of astronomers, and
mark an epoch in the history of astronomy in the
nineteenth century.' One of these is the remarkable
photograph of the Pleiades, already shown on page
237. Meanwhile D'Gill himself went zealously for-
ward with the work of star charting by means of a
6-inch Dallmeyer lens, the photographic work being
done by M' Woods at the charges of the Government
Grant Fund of the Royal Society.

The plates have all been measured by Professor

348

Stars and Telescopes

Kaptevn with a parallactic apparatus of his own de-
vising, dependent upon the following principle : hold
up against the slcy a photographic negative of the

{Dtsigtud and huill ij

«ame region, taking care to keep it perpendicular to
the line of vision through the center of the plate;
then if it be removed from the eye to a distance
■equal to the focal length of the lens, every star can be

Telescopes and Houses for Them 349

exactly covered by its dark image on the negative.
Then by substituting for the eye an instrument suit-
able for measuring stellar positions in the sky, their
positions are quickly read off from the plate itself. This
ingenious apparatus is quite different from the ordi-
nary plate- measuring engine, shown opposite, with
which stellar photographs are usually converted into
catalogue positions. This instrument measures merely
plane co-ordinates, while that of Professor Kapteyn
measures spherical co-ordinates, as the geometer des-
ignates them. The completed catalogue of stars of
the southern firmament, the joint research of D' Gill
and Professor Kaftevn, a work of enormous magni-
tude, is now appearing in the Annals of the Cape
Obiervatory. As a result of D' Gill's initiative came
also the Astrographic Congress (p. 260), with its
■comprehensive plans, and more than a dozen photo-
graphic telescopes at work for years in both hemi-
spheres — all as a direct issue from one comet and a
few nearly accidental photographs of it taken in re-
motest Africa.

Meanwhile, but quite independently, stellar photo-
graphy had been making rapid progress in America.
Professor Pickering, employing at first very small
photographic instruments of the ordinary type, ex-
tended his researches by means of an 8-inch Voigt-
lander lens, refigured by Clark, and since known as
the Bache telescope (page 299). The star charts
taken with this instrument in Cambridge and Peru,
and with its duplicate, the Draper telescope, have
yielded results of high importance ; not only in the
determination of stellar magnitudes, but, by affording
the means of studying certain regions of the sky at
many different epochs, they have brought to light

Stars and Telescopes

many new stars. But their use as spectroscopes has
secured the greatest contribution to stellar astronomy

ETA CARINAS (ARCbs)
Btjnltn Ultica^)

(pages 197-301). By mounting prisms in front <A
tfie objectives, on the plan first tried by FKAUNHomt

Telescopes and Houses for Them 3 5 1

in 1823, all stars in the field impress their spectra,
sometimes as many as i^ooo, on a single plate.

The requisite width of spectrum is given by mount-
ing the prism with its edge east and west, and suitably
varying the clock-motion from the true sidereal rate,
according to the degree of dispersion employed, as well
as the color and magnitude of the stars in the photo-
graphic field. These researches have culminated in
the construction and use of the Bruce telescope, al-
ready described and illustrated (pages 263-265), and
which has fully met the successes predicted for it.
Its enormous power is readily inferred from the fact
that on a single plate 14 x 17 inches were counted no
less than 400,000 stars. This extraordinary result is
a necessary consequence of the great aperture of the
lens with a relatively short focal length, a combination
which photographers designate by the term 'quick-
acting.' The rapidity of lenses of the doublet type
may be inferred on comparison of the 8-inch Bache
telescope of 44 inches focal length with the standard
13-inch astrographic telescope of 134 inches focus;
the former requires but an hour's exposure to record
a star of the 14.7 magnitude, while the latter consumes
three hours in impressing the same image.

During the progress of this work Professor Picker-
ing devised a novel form of double objective which is
equally efficient for both photographic and optical
work. This long-sought result is obtained by figuring
the two faces of the crown lens very different in cur\'a-
ture, and modifying the cell so that the flint lens may
be moved toward the focal plane when desired. For
visual observations the two lenses are in contact, the
more convex surface of the crown lying next to the
concave face of the flint. By reversing the crown lens

Telescopes and Houses for Them 353

and separating the flint three inches from it, the com-
bination becomes an objective perfectly corrected for
the actinic rays ~ or nearly so. The fact, however,
seems to be that there is a trifling sacrifice of quality,
in both the optical and the photographic combination,
for the sake of this convenient and inexpensive union

U/l, fatstt Ihrm^ Ou friiim or it rrfirclid /ram Iki r'-'ltn/T '" "ir
^l-lof^d hoi at lAl rigil, nxj cemii la tkr lyt vikkk ii flurd at llu

til liOr and fiMrMdt'.vAkll art oiiililHltd a*tH ifitira ,srr Is bt
f/laliirra^di

[By ificialfrrmiaum n/llu jlnuriraH SkA Ctr^f.iny',

of two objectives in one. A 1 3-inch telescope of this
pattern was made by the Clarks, with which the fine
photograph of 17 Carina: was taken (page 350), and a
construction practically identical was independently

354 Stars and Telescopes

invented by Sir George Stokes. The 28-inch Green-
wich lens figured by Sir Howard Grubb is an example
of this type.

The reflectors built by M' Brashear have been de-
scribed earlier in ihis chapter. But his mechanical skill
and untiring energy have enabled him to play a most
important r61e in the recent progress of physical as-
tronomy. His optical surfaces exhibit the last order
of precision and finish ; and many are the physicists
and astronomers whose work has been facilitated by
his deft constructions. I'rincipally by spectroscopes
(page 353) has his reputation been enhanced, and he
has buih the brgest instruments of this character ever
constructed, among them the Lick spectroscope (page
288), and one for the Verkes telescope. Also Pro-
fessor Hank's lesser spectro-hehograph, illustrated on
P^ge 352, is M' Bkaskeah's workmanship, and the
work atconijilished with it has already been described
on pages 63-65,

Likewise, M' Hra^hjur has achieved great success
in figuring objectives, both optical and photographic.
His largest object-glass is of 18 inches aperture, and
it acquired instant fame from its use by M' Percivai.
Lowell and his assistants in observing Mars, at Flag-
staff, Arizona, during the opposition of 1894. This
glass is now mounted at the Flower Observatory of
the University of Pennsylvania. Photographic ob-
jectives of all sizes have come from M' Brashear's
competent hands — the 6-inch Willard lens (ordi-
nary portrait), re-figured for Professor Barnard, with
which, at the Lick Observatory, he obtained his un-
surpassed photographs of the Milky Way ; an 8-inch
for Professor Terao, of Tokyo; a lo-inch for the
Yerkes Observatory; and a pair of 16-incb doublets

Telescopes and Houses for Them 355

for D' Wolf, of Heidelbei^, used to excellent advan-
tage in the photographic discoveiy of small planets
(p^e lis). Th* adjacent illustration is reproduced
from that part of a photographic plate on which was
discovered a small planet ; it shows as a faint elongate
trail, indicating the amount of
its motion during the exposure
of two hours. Perhaps the best
form of mounting for short-
focus cameras of this descrip-
tion is that shown in the
reproduction on p. 35 7, from a
design by Heyde of Dresden,
for the observatory at Moscow.
It readily admits of the neces-
sarily long exposures without
reversal from one side of the
pier to the other.

As the telescope and its
accessories become very lai^e
and massive, the disadvan-
tages of the Fraunhofer or Ger-
man mounting become more
and more pronounced, on ac-
count of the overhang of the
declination axis, and its flexure,
as well as the hindrance of the pier itself, preventing
very long exposures or periods of observation, except
by reversal of the telescope to the opposite side of
the pier. So there is a present tendency to revert to
the old type of parallactic stand first invented by
RoMER and now universally known as the English
mounting, in which the polar axis is supported at its
upper end by a second bearing and pier, and the axis

356 Stars and Telescopes

itself is a double fork with the telescope swung between
its prongs. Of this type is the old equatorial mount-
ing at Greenwich devised by Sir George Airy. The
chief disadvantage is that the sky close around the pole
and underneath it is inaccessible ; but this is more than
counterbalanced by the cardinal advantage of having
the entire space beneath the polar axis free and clear,
so that a celestial body can be followed from one
horizon to the other without reversal of the instrument.
Several of the astrographic telescopes were mounted
in this fashion; also in 1898 the reflector of one
metre aperture at the obser\-atory at Meudon, The
clock-motion is imparted with great steadiness, and
the general design of the P^nglish mounting permits a
very satisfactory solution of the engineering problems
that arise in the construction of great telescopes.
This type of mounting received the mature approval
of At.vax GRAHA^^ Clark.

With M' Brashear is associated D' Hastings of
Yale University, who calculated the curvatures of all
the objectives fashioned by the former in recent years.
I)' Hastings is himself a practical optician as well as
theoretical physicist, having made many objectives
with his own hands. The largest has an aperture of
9.4 inches, and is mounted at the Johns Hopkins Obser-
vatory. Contrary to the usual practice of opticians, no
examination of the quality of image formed by the
lens was made until the work upon it was finished ; and
on first trial the objective was found so nearly satis-
factory that only twenty minutes were required to ren-
der it sensibly perfect. In this achromatic glass, with
the flint lens in advance of the crown, with a space
of o'".i between them, a variation of this latter dis-
tance will effectively correct the objective for changes

Telescopes and Houses for Than 357

of temperature. The curves o£ M' Brashear's ob-
jectives being based on the formulae of D' Hastikcs
there is a close agreement of the actual focal length

{tyiSk t^wit^rial mouHliHg Jjiigttid by Hav

with the calcubtcd value, which is often a marked
advantage.

The effect of focal length upon the performance
a lens is excellently shown by the wonderful photo-

arked ^m

ice ^^

ihoto- ^^L

3S8 Stars and TeUscopes

graphs of the Milky Way recently obtained by Pro-
fessor Baknard with a. magic-lantern lens of i } incbes
diameter, and 5^ inches focus. In a few minates*

exposure it photographs what the ordinary quick-
acting portrait lens requires several hours to show.
The scale is of course very small, and the cloud-forms
of the Galaxy are so compressed that they act, not
as an aggregation of individual stars, but as a surface.
The earth-lit portion of the Moon was well depicted
by exposure of a single second; the brighter cloud-
forms of the Milky Way appeared in ten to iifteeii
minutes; and a great wing-like nebula involving
V Scorpii was discovered by Professor Barnard witb
this simple lantern !ens.

The recent application of photography to thfr
trails of meteors is very suggestive. Lenses of short
focus and a large field of view are best Professor
Barnard, on the 13th November 1893, obtained the
opposite photograph of a meteor which shot across
the field while he was making an exposure more than
two hours in duration in order to secure the faint
comet below (comet iv, 1893). But a still more
remarkable delineation has been secured; on the iSth
June 1897, when the Bache telescope at Arequipa.
was photographing spectra of the stars in the con-
stellation Telescopium, a bright meteor flashed across
the field, and the lines of its spectrum were there-
fore registered upon the plate — the first spectrum
of a meteor ever recorded by photography. There
were six lines, and their intensity varied in different
parts of the photograph, showing a change in char-
acter of the meteor's light as its image trailed across
the plate. The lines were mostly due to hydrogen,
resembling stars that have bright line spectra. Thus

360 Stars and Telescopes

the chance spectrum of this meteor will, Professor
Pickering hopes, aid in ascertaining the conditions
of temperature and pressure in such stars. The ex-
pected mid-November meteoric showers of 1899 ^'^
1900 will undoubtedly yield further and similar re-
sults. These, with trails from D' Elkin's multiple
cameras (page 212) will probably provide data for a
more accurate orbit of the Leonids. More than thirty
were photographed in November 1898.

An arrangement of multiple cameras for observa-
tion of total solar eclipses was first worked out by
the writer in 1889, for the eclipse of the 2 2d De-
cember in West Africa. In all, 23 instruments, chiefly
pliotographic, were attached to a massive pK>lar
axis, and pointed parallel to each other, following
accurately on the eclipsed Sun. The engraving oppo-
site illustrates many of them ; also in the foreground
are the pneumatic contrivances by which exposing
shutters, plate-holders, and all other moving devices
for eclipse obsen-ation were operated automatically.
The control was effected by a perforated strip of
paper, similar to the music sheets now commonly
used in automatic organs. Each perforation in the
eclipse, sheet represented, not a musical note, but a
mechanical movement of some particular device.
By the liberality of M' D. Willis James of New York,
a trustee of Amherst College, a similar battery of
instruments was duly installed in Yezo by the Am-
herst Eclipse Expedition in 1896. One of the nu-
merous devices was constructed with reference to
securing on a single plate the imprint of a few coro-
nal streamers complete in their entire length. This
had never been done, because exposure long enough
to give the outer corona bums out the film where the

THE PNEUMATIC C

U mmmt^at Ctift LtJ», A/rica./f Of fM ntitm <t Dt

1^
11

Telescopes and Houses for TJum 363

bright inner corona would otherwise be. In the de-
vice illustrated opposite, three concentric rings and a
central disk are removed from the photographic field
successively, pennitting long exposure for the outer
2nd short for the inner corona.

Instead of pneumatic operation, the necessary
ments, about 500 in all, were secured at the critical
instants by the control of an electric commutator

364

Stars and TiUicopts

(pieceding page). The pQcumatic and electric vj^
terns both worked perfectly ; but clouds at both sta-
tions unfortunately ob-
scured the corona.
The ease with which a
number of delicate
pieces of photographic
apparatus can be or*
ranged, the certainty
with which they can be
operated ; the largenum-
ber of photographs ob-
tainable by this means
for subsequent study, the
dispensing with manual
movements during total-
ity when every nerve is
at high tensioD — all
point to the desirability
of repeating the experi-
ment during the coming
eclipses of 1900 and
1901. Also the novel
device of M' Burckhai^
TER, for obtaining the
bright inner and (aint
outer corona on the same
plate by means of a suit-
ably shaped and swiftly
whirling vane, revolving*
in the photographic field
duringexposure, was suc-
cessful during the India-
eclipse of 1898, and i&
worthy of permanent

•

\ '

?tl

s .1

Telescopes and Houses for Them 365

adoption in eclipse programmes of the future. But
even more important is the ptiotogiaphy of the flash
spectrum, near beginning and end of the total phase.
The unobscured limb of the Sun is then a very slen-
der crescent; and by using the objective prism, or
prismatic camera, the developed image on the plate
comes out as in the opposite photograph — not a
single crescent, but a succession of crescents whose
position and size enables us to say to what substances
the light owes its origin, and to study the depth of
the reversing layer all around the Sun's edge. The
total eclipses of 1896 and 1898 indicate that the
depth of this stratum is about 700 miles.

The advances of astronomy by the aid of pho-
tography are too numerous for further treatment
here. In 1840 the Moon was first photographed,
in 1850 a star, in 1854 a solar eclipse, in 1872 the
spectrum of a star, in 18S0 a nebula, in 188 1 a comet,
in 1897 the spectrum of a meteor, and in 1898 a
stellar occultation by the Moon. -MI these epoch-
making photographs were made in America, Nearly
every branch of astronomical science has been ad-
vanced by the instrumentality of photography, so
univei^l are its applications, and so persistently have
they been put to the successful test.

Before passing to the construction of observatories
and suitable sites for them, one or two paragraphs
will be devoted to the instruments of the old astron-
omy, or astronomy of precision, as it is often termed.
Most important of all is the meridian circle, the joint
invention of Romer and Picard, before whose day the
position of a star or planet on the celestial sphere wa&
observed by means of a quadrant. Hevelius con-
ducted a long and valuable series of observations with

36S

Stars and Telesc(^

an instrument of this sort, illustrated adjacent; but
they were unfortunately destroyed by fire at Dantztg,
the scene of his labors. Two persons were neces-

sary to make a complete observation, and the star's
direction was fixed, not by the telescope, but by sights
or pinnies. A surprising degree of accuracy was
reached by carefully repeated measures.

Telescopes and Houses for Them 367

From the middle of the 1 7th century onward, we
must omit the intervening forms of arc- measuring
instruments, down to the end of the 19 th century,
when we find astronomers almost universally employ-
ing the meridian circle. An excellent type by the
best modem maker is shown on the following page,
by courtesy of Professor Payne, editor of Popular As-
tronomy^ an American monthly that provides much
information about all kinds of astronomical apparatus,
including telescopes, their manufacture, and use. As
its name implies, the meridian circle revolves in a verti-
cal plane north and south ; and its construction de-
mands a house with a sliding or removable roof, with
shutters opening below it, as at the extreme left in
the illustration. A clear strip of sky is thereby ac-
cessible for observation in every part, and unobstruct-
edly free from the zenith down to the north and
south horizons. The exterior of a meridian room is
shown in the left-hand wing of D' Roberts's observa-
tory, page 290.

Within a meridian room the telescope, whether a
transit instrument or a meridian circle, surmounts two
stable piers, between which it turns 'round on bear-
ings called Y's. Circles adjacent to the telescope^
and on either side of it are rigidly attached to the
horizontal axis ; and they, with both telescope and axis
turn round as a unit, the axis of the telescope describ-
ing the plane of the meridian. The circles enable
any known star to be found, by means of its distance
from the zenith. Then the time of its passing the
wires in the reticle is observed by a clock or chronom-
eter, usually with the aid of a chronograph which
electrically records the precise instants at which the
transits take place. If a star's position on the celes-

Telescopes and Homes for Tkem 369

tial vault is already known, one complete meridian
observation provides the means of finding the latitude
of the observatory, and the local time ; or conversely,
if these elements have previously been found, a com-
plete observation enables us to assign the star's exact
geometric position on the celestial sphere ; in other
words, we determine its right ascension and declina-

iFfr gTudtialiMt circlts. Built ^StcstTAH cf Parii)

tion, as technically called. Meridian instruments of
high precision and excellent workmanship are con-
structed in America as well as in Europe. BoyF &
Berger of Boston, SAECMinj-ER of Washington, and
Warner & Swasev of Cleveland, are the chief mak-
ers. Accurate division of their circles is the chief
difGcnlty of construction, but this end is now attained

SftT — 14

3/0 Stars and Telescopes

with all necessary precision by means of giaduadng
engines, similar to the one in the last illustration.
Errors of a whole second of arc in the position of a
line on the face of a silver circle are now uncomnon
in the best niodem instruments. This means that of
all the lines automatically engraved on a fine circle 30
inches in diameter, one is rarely misplaced by so much
as the half of ^i^os of ^^ '^'^^■

ZACH [1754-1831)

But few observers are able to assign the absolute
time when a star is actually crossing a line in the field
of view : most will record the instant after the star
crosses, while a few will always set down the instant
before that event. Any difference between the abso>
lute and observed times is termed personal equation ;
and the value of it is susceptible of exact ascertain-
ment in several ways. The best observer is not one
whose personal equation is least, but the one whose

Telescopes and Houses for Them 371

equatioD remains most nearly constant. Avoidance
of the effect of personal equation is practically at-
tained by the photo-chronograph, an instrument de-
vised by Father Farcb of Georgetown College for
recording transits photographically. The telescope is
set upon the star as if for an ordinary visual observa-
tion ; but the eye-piece is removed and a tiny sensi-
tive plate inserted in its stead. In front of it is a
little strip of metal, or occulting bar, upon which the
star's image trails in crossing the field ; and this bar
is connected with an armature, a circuit through which
is sent by the clock at the beginning of every second,
as for the ordinary chronograph. This throws the
bar aside for an instant, so that the developed plate
shows a succession of black dots, or instantaneous
and equidistant impressions of
the star. Holding a lantern for •
a few seconds in front of the
objective will impress the transit
lines upon the plate, in their
correct relation to the stellar
dots ; and the fraction of a sec-
ond when the star was crossing
a wire can then be found by
measurement, practically free
from personal equation.

The first astronomer who dis-

, , . , , ., (/VuiJfJ */ Chandlm)

cussed the mherentand unavoid-
able deficiencies of instruments and their effects upon
observations was the versatile von Zacm, in his Corre-
spottdafue Ailronomique in 1819. In our day a de-
termination of ihe errors of an instniment gives vastly
more trouble than the subsequent observations and the
reduction or calculation of them. In the almucantar

372

Stars and Telescopes

as used by D' Chandler, many of the troublesome
errors of the meridian circle are skilfully eluded. The
flotage principle is adopted for the supports of the
telescope ; and while the small errora of the meridian
circle must be found from observations on less than
half its circle of reference, the almucantar has the
great advantage of permanent visibility of its entire
circle of reference, which is the small circle parallel
to the horizon and passing through the north pole of
the heavens, often called an almucantar.

So perfect is the constmction of the marine chro-
nometer at the present day that all observatories now
use this convenient in-
stniment in recording
and carrying on the time.
lis portability, and ease
of regulation to a rate
nearly invariable with
changes of temperature,
enforce its use on expe-
ditions where astronomi-
cal clocks would be im-
practicable. The chro-
nometer has received but
few cardinal modifica-
tions of design since the
days of John Harrison,
who early in the i8th
century began his great invention, in competition for
a prize of Sioo,ooo offered by the British govemmcDt
in 1 7 1 4, for the ' discovery of a method of finding the
longitude at sea within 30 miles.' Harrison's chro-
nometer was taken twice to Jamaica, and on other

(1693-.776)

Telescopes mid Houses for Them 373

voyages, actually finding the longitude with a precision
even greater than the mai^n stipulated, and in 1765
he was paid the reward, — but only half of it, because
the prize was divided between him and the brilliant
Tobias Maver, of Gottingen, another competitor, who
had succeeded in bringing the lunar tables to such a
state of perfection that the longitude of a ship could

(I7J3-I76I)

be found from observations of the Moon as accurately
as by the chronometric method. Mavi:r invented
also the principle of the repeating circle, for eliminat-
ing the effect of errors of division by repeating the
measure of an angle on different parts of the graduated
circle. Harrisoh's chronometer was in the latter
part of the century improved by both Arnoid and
Earnshaw ; and is to-day essentially in the form in
which they left it. It b out our purpose here to enter

- 374 Stars and Telescopes

upon an explanation of the method of using the chro-
Dometer at sea. That will be found exemplified to the
fullest detail in the Am-
Practical I^cmi-
gatoroii^ATHANiEL Bow-
DITCH, whose fame rests
also upon his admirable
translation of the Mica-
nique Celeste of La Place
(page 246), which he
supplemented by useful
annotations. It is suffi-
cient to remark here that
the chronometer simply
carries Greenwich time ;
the difference between
which and the ship's local
time gives the longitude.

The observatories amply illustrated in the preced-
ing chapters embody many excellent features, a]so
some constructive faults. Aslruiiomers a half century
and more in the past were accustomed to build their
observatories high up from the ground, a constructioD
far from desirable an<l always to be avoided if pos-
sible. Better is it to choose an original site as elevated
as convenient, and then build the observatory upon it
only a single story high. Architectural effect must
often be sacrificed to scientific utility. An attempt to
combine both met with some measure of success in
the instructional observatory on the following page,
built from the writer's specifications in 1886. The
instruments possess great stability, and all practical
observers appreciate the absence of long stairways

Telescopes and Houses for Them 375

"between dome and transit room. A better form of
dome wall is shown in D' Roberts's observatory (page
ago), the corners of the square dome-room affording
a welcome convenience for observing-chairs and other
accessories. This is the form adopted at Cambridge
(page 300), which exemplifies the proper construc-
tion of a great observatory, in marked contrast to the
main building of the Naval Observatory at Washing-

ton (page loi). Telescopes mounted in individual
domes, surrounded by low trees and heavy turf, meet
with minimum interference from the radiating heat
of early evening. A quiet atmosphere must be se-
cured at any sacrifice. Massive walls of brick and
stone are far from conducing to this end ; and the
observer whose instrument is mounted therein must
frequently wait several hours for them to cool down
before beginning his work on summer evenings. The
best type of observatory construction is that which
I of material, so that very little

376 Stars and Telescopes

solar heat can be stored in its walls during the day.
Local disturbance of the air in early evening is then
but slight. Louvers, as employed by Ey GuJ. in his
heliometer house at the Cape, or belter still, ivy-
grown walls, as in the observatory at Oxford University,
shown below, contribute effectively to this desirable
end.

Often circumstances enforce the building of an ob-
servatory surmounting a dwelling house, or a large

school building. M' Brenner's observatory oppo-
site is an example of this construction ; and the
observatories built on top of the new high schools at
Springfield and Northampton, Massachusetts, accord-
ing to plans furnished by the writer, show the best
that can be done under restricted conditions. It is
often difficult to get a telescope so mounted to per-
form its best : violent tremors of whatever sort, com-
municated directly to it, are fatal to delicate observa-

Telescopes and Houses for Them 377

tioD. Also high winds are very unfavorable ; and the
effect of warmer air from the building below, not to

(Mr LbO

say from adjacent chimneys, is often troublesome.
This is best avoided by entering the dome, not by a
stairway from underneath, but
from an exterior gallery in the
open air, usually easy to arrange,
if specified in due season. But
if the telescope is small, a port-
able mounting carried out and
in as required, and used upon
a firm foundation, will usually
yield the most satisfactory vis-
ion, and at very httle expense
or inconvenience. At the end
of this chapter will be found a ^
list of manuals for the use and

378

Stars and Telesc4>pes

care of such instniments. The earliest and most suc-
cessful of these is by the Rev. T. W. Webb, late Pre-
bendary of Hereford Cathedral, and entitled Celestial
Objects for Common Telescopes, which in 1893 passed
to a fifth edition under the able revision of the Rev.
M' EspiN. Its closely slocked pages comprise a handy
book for the practical observer which few professional
astronomers can afford to despise.

S WtLLUM

{1S07-18E5)

No less important than optical perfection of a tele-
scope is excellence of the site where it is to be located
and used. The greater freedom from cloud the bet-
ter ; the horizon should be unobstructed, especially to
the south and west ; and gravel foundations for the
instruments are north seeking for. But in addition to

Telescopes and Houses for Them 379

all this, optical quietude and transparency of the at-
mosphere is of the utmost significance. That a per-
fect telescope may perform perfectly, it must be located
in a perfect atmosphere. Currents of warm air are
continually rising from the earth, and colder air is
coming down to take its place, fiy removing the
eye-piece of the telescope these atmospheric waves
become plainly visible ; and when examining a star
or planet, their effect appears as blurring, distortion
or quivering of the image as seen through these shifting
air strata of variant temperatures and consequently
variant densities. At M' Lowell's observatory in
Arizona, his careful assisWnts have made a thor-
ough study of these atmospheric waves, and their
influence upon the conditions of telescopic vision.
If the air is much disturbed, only the lower magni-
iying powers can be used, and much of the expected
advantage of a great telescope is unavailable.

All hindrances of atmosphere are found best
avoided in arid regions of our globe, at elevations
of 3,000 to 10,000 feet above sea level. A dry
atmosphere is a prime essential for steady vision. On
the American continent several observatories are now
maintained at mountain elevation : the Boyden Ob-
servatory, Arequipa, Peru (page 382), at 8,000
feel ; the Lowell Observatory, Flagstaff, Arizona, at
7,000 feet; and the Lick Observatorj', Mount Ham-
ilton, California (page i2z),at 4.000 feet. Higher
mountains have as yet been but partially investigated,
the personal infelicities of occupying them seeming to
counterbalance the gain afforded by greater elevation.
But it is an easy assertion that the great telescope of
the future, if it is to do the work for which it is best
adapted, must be located at a mountain elevation of

380

Stars and Telescopes

10,000 to 15,000 feet, in a region where steaduiev
of atmosphere has previously been assured by critical
and protracted exploration with that sole condition in
view. Whether on the lofty table-lands of Asia, or
those of South America, is yet undecided.

Of the three greatest benefactors of American
astronomy, now deceased, two bequeathed their for-
tune largely to provide
for great telescopes
at mountain elevation.
Both scientific trusts
have been so adminis-
tered as to assure very
great scientific good.
James Lick, in 1874,
by a deed of trust, left
the sum of about
S7 00,000 forthe build*
ing of a telescope more
powerful than any then
in existence, and fw
equippiag and main-
taining an observatoiy-
in conjunction with it.
Fourteen years were
consumed in preliminaries, and in building the obser-
vatory, completing and installing the instruments.
The subsequent history of the Lick Observatory is
more widely known than that of any other scientific
institution in the world. Could M' Lick have known
the advantages to science and the general dillusioii of
astronomical knowledge accruing from this bequest,
he would probably have endowed this ^gle object
with his entire estate, exceeding ^4,000,000.

JAMRS LICK ([796-18

Telescopes and Houses for Them 381

Uriah A. Bovdln, who acquired a snug fortune of
about $330,000 from his inventioos and improvements
in turbine water-wheels, bequeathed it all to three
trustees to 'establish and maintain, in conjunctiott
with others, an astronomical observatory cm some
mountain peak.' Harvard College Observatory hav-
ing received an unrestricted bequest of Sioo,ooo from
Robert 'Ireat Paine, the two were consolidated in

(:804-i879)

1886, and the search for a suiLible peak began. In
our own country, lofty elevations in Colorado and
California were investigated, with unsatisfactory con-
clusions, after which the field of search was trans-
ferred to South America. The Chilean desert of Ata-
cama was tested, and later a temporary station was

Telescopes and Houses for Them 383

eatablished at Chosica in Peru, followed by the per-
manent observatory nov maintained at Arequipa in
the same country. Two photographic telescopes are
constantly in use at this remote station, and a pow-
erfol refractor could advanUgeously be added to the
workiiig equipment.

A third great benefactor of astronomy died in
New Haven in 1889 — Elias Loomis, whose fortune.

exceeding ^300,000, he left to Yale Observatory,
reserving its income exclusively for the employment of
astronomers who should make observalions and calcu-
late them, and for their subsequent publication.
Professor Loomis was widely known, not only as a
lecturer and teacher at Yale, but as a writer of highly

384 Stars and Telescopes

successful text-books on mathematics and astronciinj.
Also he was a keen investigator in meteorology and
terrestrial physics, his magnetic charts of the United
States being the first publbhed.

Most of the great telescopes of the world have in
their turn signalized their extraordinary power by some
important astronomical discovery — or at least some
significant piece of research which could not have
been dune so well with a lesser instrument. To
specify in part: Herscuel's reflector first revealed
the plautt Uranus; Ix>rd Rosse's 'Leviathan,' the
spiral nebula; ; the 15-inch Cambridge telescope,
Saturn's dusky ring ; the 18^-inch Chicago refractor,
the comjimiion of Sirius; the Washington 26-iDch
refractor the sntclliti's of Mars; the 30-inch Russian
objective, tlic nebulosities of the Pleiades; and, last
of all, the 36-inch Lick telescope brought to light a
fifth satellite of Jupiter, At the time of these dis-
coveries, each of the great telescopes was almost the
only instrument pon-erful enoujjh to have made the
discovery. With such a record, nre we not safe in
predicting further advances with larger telescopes still?
Two American opticians of wide experience and high
competency stand ready to undertake them, if only the
funds are forthcoming ; and as yet there is no indication
that a refracting telescope of five, or even six, feet aper-
ture would fail of a gratifying success to its projector.

According to Alvav Graham Clark, a six-foot
objective would not necessitate a combined thickness
of more than six inches ; and he also says, • Who
knows how soon glass still more transparent may be
at hand, considering the steady improvement made in
this line, and the fact that the present disks are infi-
nitely superior to the early ones ? ' The obstacles to

Telescopes and Houses for Them 385

overcoroe in mounting and using such a glass dis-
appear when we reflect that as yet the astronomer
has but just begun to invoke the fertile resources of
the modern engineer. The younger Clark further
wrote, in 1893, this remarkable union of fact and
prophecy; 'The increase in size of even our present
great refractors is not a possibility but a fact, and
with this will come large acquisitions to our present
stock of knowledge. The new astronomy, as well as
the old, demands more power. Problems wait for
their solution, and theories to be substantiated or dis-
proved. The horizon of science has been greatly
broadened within the last few years, but out upon the
border-land I see the glimmer of new lights that wait
for their interpretation, and the great telescopes of
the future must be their interpreters.'

JOHANNIS COVCH AEXAMS

Stars and Telescopes

Telescopes (History, Mouktino, and Use)

Grant, History of PhytUat Aslronamy (London 1852).
Grubb. T., • Mournings.' iftpi>rl Brit. Aisoc. Adv. Set. 1857,

p. 195.
llERsciiEL, J. F. W., Article ' Telescope,* 8lhed.£nov/<y«^^

Brilan»Ua, vol. xii. (i860). 117.
Woi.F, R., Gischichtt der Asironemit {^■a-axsAi 1877).
PoGCENDORFP, Gtschichit diT PHysH [Leipiig 1S79).
Knight, E. H., •'[t:\<:iCOpt,' AmtrUnH MeckanicaiDicHimary,

vol. iii. (Uoston iSSi].
Pickering. 'Large Telescope*,' Prx. Am. Acad. Arts and Sci-

««j,xvi. ([88i),364.
BtiRNiiAM, IJhNMNc, YouNC, 'Small vs. Large Telescopes,'

Sid. M,^s!.\v. (iSSs), 193. 2S9i V. (1886), I.
SeRVUS, Dit G,sdii<ktt dci Ftmrohrs (Berlin 18S6). Bibliog.
HOLDEN, ' I.ick Telescope,' PhU. Lick Oh. i. (18S7).
YoL'NG. ' Great Tdescopes,' T/ii Forum, iv. (1887), 78.
Gll.l., ' Telescope.' Emyclopadia Britannica, 9 ed. xiiii. (Edin-
burgh 1SS8).
Tuuu, ' Telescopic Work in U. S,,' Earyclapirdia Britannica,

xxiii. <PhilH(lelphia i8S3).
Common, 'Telescopes," A'.i/«r^ xlii. (1890), 183.
CnwiViLHS. nisaiptive and Pracli,:il Astmirom}' {Oxloid 1890).
Plummer, ' Pulkowa Rcfraclor,' A'alure, ilii. (1S90), 204.
W'QLV, R., HandbiKh der AslraimmU, ihnr GiichUhte untl

/.jterii/wr (Zurich 1890-92).
Swift, 'Telescopes,' Appleton's .innual Cyclopadia (1890-

1S98).
Ranvard, 'Penetrating Power,' KnmiiUdse, xiv. (189I), 154.
Hastings, ' History o£ Telescope,' Tht Siderral Mistrngtr, x.

('8911, 33S-
Knigh r, \V. IL, • Telescopes in the U. S.,' rAe Sidcreai Me^.

seager.x. (1891), 393.
VootL, Newcomb-Engelm ANN'S Pojruldrf AstrBtumie (Leip>

lig 1S92).
Clark. ' Possibilities of the Telescope,' I/orlA Amcricati Rf

vitw, clvi. (1893), 48.
Clark, 'Future Great Telescopes,' Aitronemy and Astra-

/ij-rifj. xii. {t893),673.
Warner, ' Engineering Problems of Large Refractors,' At-

troiiomy and AitrBfkysies,i\i. (i893),695.

Telescopes and Houses for Them 387

Grubs, H„ ' Great Telescope*,' Ktunohdge, xvii, (:894), 98,
Baknaro, ' Great Telescopes,' Pfff. Astron. ii. ( 1895), 245,
Nbwcomb, ' Telescopes,' Johnson's Umi. Cyct. viii. ( 1895).
Denning, ' Great Telescopes,' Naturt, lii. (1895}, 232.
GekLanD, VaLeNTIHEK's //andtaiirlirbuch der Aslrmomi^

(BiesUu 1895-98).
Barnard, ' Large and Small Telescopes,' M. N. Roy. Astron.

Jw.lvi. {1896). 163.
HALE,'Yerkes Telescope,' ^JCri'/Vi-y™''- ^i- (1897), 37.
Lewis, HoLLIS, ' Large Refractors,' The Oisertnilory, xii.

(1S9S), 239, 270.
Fowler, ' Concise Knowledge Library,' Aslronomy, part ii.

(New York 189S).

Glass, Oujectives, and Testing
RuTKKRKURD, ' Specltoscope in Testing Object

177.

ic Object i

.-es,' AUr. iWi

re,-l Mciscnt^'e.
i. (iSSj), 1
■ti.,1 Mi,s.

-/r:,' Am. /our.

Ir. xci.(i878).
:7r..ii.(i882),
i. (1883), 239.

No, 19,
Smith, H. L, ' Short-focus,' i"n/fr*
Gruuk, II., T'„,.!. A'oy. DiM. S«.
Hastin.;s, -Figurine Lenses,' SU

39(iSS3-.Si).
PE.NDLEmtMV, Lfnsts and Systems 0/ I.,-n
GhUUb, H.. 'Objectives and Mirror

ina.' Proc. Roy. /-isl. xj. (tSSG). 41;
VoL'Ni;, ' Lick Objective,' I!ost,mJoi.
Hastinos. 'Achromatic Objective,' Am. Jour. O^J, cxxxviL

(18S9I, 29r.
CONROY. 'Reflection and Transmission of Light by Glass,'

Phil. Tram, clxxx, (1889), 245.

' Lick Objective,' Piibl. Aitren. Soe. Paeifte, ii. ( 1890).

; rrcparatioii and Test-
r. (October 1S86).

160.
Coke. On lie Adjuslmertt and Tei

(Vorkl890.
FOWI.ER, ' Testing Objectives,' Nat
MAi;NDEfi,' Adjustment,' /,.ur. Br.

■«^ 0/ TeletcopU Otjativ,
re. xlv. {l8Q2),a04.

^88 Stars and Telescopes

Brashear, 'Optical Glass,' Pep. Aitron. t. (1894), 33t, 241,

391, 447.
Brashbar, ' Adjustment and Care of Objectives,' /V^. Atlrom,

ii- (1894), 9. 57.
VocEL, 'Absorption by Objeclivc'^rf/w/iy/./oKr.v. (1897), 75,
BraSHEAR, 'Glass Manu^cture,' Pepuiar Aitrort. vt. (1898),

104.

Replectdks and their Mountings

HerSCHEL, W„ ' 40-ft. Reflector,' Phil. Trans, for 1795, 347.
RossE, ' 6-tl. Reflector,' Philoiofhical Transacliimi 1840, P.S03 ;

alsocli, (t36t),68i.
Mason, Smith, ■ ii in. Reflector," Tram. Am. PHI, Soe. viL

(.S41), 165-
1,ASSELL, ' I'olUhing Specula,' Hfitn. Ray. Astr. Sat. xvtil.

(1850), I.
Drafek, ' Construction of Reflector,' Smitltion, Contr. Kntnel,

»iv,(i86s).
Lassell, '4-ft. Reflector,' ,)/,■«. ^nj'. Ast. Soc.7i\T.y\. ((867).
GrUbB, T., ' Melbourne Reflector,' Phil. Tratis. Roy. Soc. clii.

(1S69), 127.
THoKNTifWAiTK, Hint! on Rcfltcliiig and Rtfracting TeUscopei

(London TS77).
Common, ■ MinintLug for 3-ft. Reflector,' Mrm. Roy. Aitr. Soc.

xM.(iSSi). I7J.
Brashear, ' Silvetiiig a Rellector,' Brit. Jour. Photo. Aim. 1888.
JON£S,G..S.,' Figuring a Mirror,' Sid. ,V«r. ix. (iSgo). 353,
Common, 'j-ft. Kefleclor,'.I/fwi. i?of. ,4j/riw..S'm-. I. (18^), 11;^
Common, 'Mounting for Reflector,' M. N. Roy. Astron. Sot.

liii. (1893), 19.
ClerKf,, Thi JfersJifls and Modfrn AitnmmiyihoaAon 1895).
Calver, Hints on SiivereJ-glasi Rtfle<ti«g TeliKopis (London

1895).
ScHAEBEBLE, ' Cassegraln,' Pub. Ail. Soe. Pacific, vli. (1S95),

185.
Stonky, ' Supporting Large Specula,' M. Jf. Rey. Astren. Sat.

Ivi. (.896). 454.
Hale, 'Reflectors vs. Refractors," Aitrophysicid JattnuU, v.

(.897), .19.
Wadswortii, ' Coude Reflectors,' Astrephysital Journal, v.

<.897). T3^.
Gaittibr, ' Sid^rostat it lunette de 60™ de foyer et t'.aj d'on-

verture,' Annuaire Bur. Lang. 1899.

Telescopes and Houses for Them 389

Spectroscopy a«d Spectroscopes
Schuster, 'Modern Spectroicopy,' Proc. Kay. /nil.a. (iSSi),

493-
LocKYF.R, ' Spectroscopic Apparatus and Methods,' The Chem-

iitry of the Sua (London and N. Y. 1887).
Maunueh, in Chambers's Diicriptivt Ailmnomy.vi. (Oxford

1890).
Keeler, 'Elementary Principles of Spectroacopea,' The Sid-
ereal Messiiiger, x. (189c), 433.
DESLANDRES, Complis Rerfdus, cilii. {iSgif. 308; Cliv. (1892),

276,
Frost, ' Potsdam Spectrograph,' Aslrouomy and Aitra-Pkyiia,

xii. (1893), 'SO.
Hale, ' Speciroheliograph,' Astrontimy and Asiro-Physks, xii.

(1893), 241 ■
Keeler, ' Sjiectroscope,' Pop. Aslreu. i., ii. (1893-94).
Frost, SCHKINER, Tre,iliiC on Aslrononticat Sp/clrostopy {lir>^

ton and London 1894). Bibliography.
Reed, 'Spectroscope,' Pop. Astron. ii. (1895).
Young, ' Spectroscope and Adjustments," The Sun, p. 351

(New York 1896) ; Pop. Aslron. v. ( [897). 318.
Wadsworth, ' Resolving Power,' Astro. Jour, vi, (1897I, 27.
MlCHELSON, 'Echelon Spectroscope," Astrophyi. Jour. viij.

<i89S). 37.
Campbell, 'New Spectrograph,' Asirophyi. Jour. viii. (1S98),

123.
Poor, ' Concave Grating,' M. jV. Roy. Astron. Soc. Iviii. (1S98),

291.

The books and papers on celestial spectroscopy are exhaus-
dvety cited in D' ALFRED Tockerman's ' Index to the Liter-
ature of the .'Spectroscope.' Smithsonian AfiscMimoni CotUctiom,
No. 658 (1S88), pp. 8, 66.

Hansen, Die Themie dit Aequatorealt (Leipzig 1853).

Shadwell, Management 0/ Chronemelers (London 1861).

Karl, Principien der Astronsmisihen Instrumentenkunde {Leip-
zig 1863).

Newcomb, ' Theory of Meridian Circle," Washington Observa-
Uoiti 1865, Appendix i.

390 Stars and Telescopes

Kaiser, ' Double-image Mici
Davis, C. H., ' Ratings of Chro

lifHi 1875, App. iii.
Gill, • Heliomeler,' Dun Echt Oil. PuUUaliims, ii. (1877).
Sbbligkr, TA^jrie drs N^liometeri (Leipzig 1877).
LoCKVEK, Stargazing 1 Pait and Pmcnt (London 1878).
GoiiFRAV, A Trtatisi en Aslrenomy (London 1880).
Todd, ' Orbil-s weeper,' Prac. Am. Acad. xv. (1880), J70.
Harkness, 'Flexure of Meridian Instruments,' fVasA. Obi.

;8Sj, App. iii.
Clark, 1... Tnalise 011 lAt Traniit Iiistrumint (London 18S2).
V. KoNKoLY, Pniktiscke Anititung ntr AHsltiluHg Astron.

BtohichluHgen (Itrunswick iS8j).
Harrington, ' Tools of the Astronomer,' Sidereal Mtsietigtr,

ii. (.883-84).
Bkasiieak, 'Oplicril Surfaces,' Proc. Am. Assoc. Adv. Set.

xxxiii.(rSS4),iSS-
LoKWV, • liquatorial Coiidc,' Bulletin Ailron. 1. {1884), 265.
Radac;, ' lltliostats,' Ilullelin Atlron. 1. (1SS4), 153.
H^WCiMTS, /Accent /•npnremciits iu Aslron. lustrumtn/t (Vfaah-

inelon 1884).
ll.,ii,;[i, ' Printing rhrOTiograph.' SiAre,,! A/.-ss. v. (.886), l6t.
CHANDI.KR, ' Almucaiitar," Auai/s //an: Coll. Obi. xvii. {1887),
Gruuii, iL, 'ElcctricCoMr(il,M/..V.A'. ^.Xxlviii. {i888),3S».
Chandler, 'Square liar Micrometer,' Mem. Am. Aead. iL

(iSBS), isS.
LAMJi-f.Y, Yoo.Nc, PiCKERiNU, 'Wedge Photometer,' Sfem.

Am.Acid.xl (1S8S), 301.
SaNKiiRH, 'Personal Y.qi.X3,\\on' Am./our. J^ycAalogy,]L{\SS9\

3, 271, 403. Uibliography.
MiCHBLSON, ' Interference Methods,' Phil, Afag. xxx.fiSQO), i,
Roger,?. J. A., ' Correction of Sextants,' Smithsonian Atiie. Colt.

No. 7O4 (tSgo),
Hagen, The Pholochronografh (Georgetown Coll. Obs. 1891),
Clerkk, ' Instruments and Methods,' Hist, of Astren. dmring

X/X Ctntury (London 1893).
HucGiNS, M. I.., ' Astrolabe,' yo/' ^strou. ii. {1895), '99-
Becker, E., Herk, ' Micrometer, Personal Equation, Tras^t

Instrument,' Valentini!K's l/aiidworterbucA dtr Astronomit

(Breslau 189S-.9S).
Stonev, 'Sidetostat,'^. N. R. Ast.S<n.\\\. (18961,456,
Hamv, * Temperature Effect," Bull. Aitr. xiii. ( 1896I, 178.
Turner, 'Ccelostat,' M. N. R. A. S. Ivi. (1896), 408.

Telescopes and Houses for Tkem 391

MOller, Die Phoiomnrii dir Gistime (Leipzig 1897). Biblt

ography,
Updzgraff, ' Flexure,' TVans. Acad. Sd. St iMiis iii. (1897),

Todd, A Neat Atlronimy, Chapier ii. (New York 1897).
LIFPKANN, ■ Calostat,' BalUlia Astrmemiqur, liv, ( 1897), 369.
The literalure of astronomical instrumeiils by the a^te miters
x>l \\i& E'uyclBpadia Brilannica is summariied in Baldwin's
Syiltmalk headings in E. B.. p. 94 (Chicago and New York),
1897. Many novel devices of service to astronomer and astro-
physicist are described and figuied in the Herlin monthly begun
in iSSl, entitled Zij/K*rj///Hr hislrumeiiUnhundi.

Obsehvatohiks

Strove. F, G. W., Desctitlion di COburvaloiri de Poulieva (St

Petersburg 1845).
Main, EHcycl. Brii. 8th ed. iii. (1853), 816.
LooMls, Recent Progreis of Aitrenomy. ispedally in U. S. (New

York 1856)-
AndbS, Ravet, Anijot, L'Astronomie Pratique et let Otser'

vatoires en Europe et en Amirique ( Talis 1874-78),
Pebrotin, Visile^ di-.rr, Obsirvatoirts d'Europe (Paris iSSl).
NewcomBi No. Am. Rru. cxxxiii. (1881J, 196; Nature, xxvi.

(18S2), 326.
Drever, ' Observatories,' Eniyil. .ffriV., 9 cd.xvii. (1884), 708-
PerroTIN, Ann.,Us de f Obs/rvaloire de Xite, \. { Paris 1885).
WiNTERicALTER, ' European Observatories,' Washingtoa Oht.

1885, App. i.
Todd, ' Observatories in Ann
Young, ' European Observa

(1S88), 8r.

Love, 'First College Obs. in U. S.,' Sid. Afeti. vii. (1888), 417.
Clerkb, ' Cape Observatory,' Caatemp. Review, Iv. ( 1889), 380.
Lancaster, Z/,t// GiiUraiides Ohen-atairei.tic. (Smssela 1890).
CHAMBEtis, DeicriptmeaHdPraelieai^itronamy (Oxford li
Swift, 'New Observatories,' Apple

(1890-98}.
Gill, ' Work in Modem Obsemtory," Proc. Rtiyal /«i

(1891), 402.
Upton, ' Ancient and Modern Observatories,'

^Wiw^ir^n-.x. (1891), 481.

392 Stars and Telescopes

Proctor, Ranyard, Old and Nna Aitroaemy (London and

New York 1892).
AlcuS, ' Observatory at Manila," Aslron. and Aslra-Phyi. xiiL

(:894).8S-
Payne, ' Free Public Observatories,' Aitren. and Aitrv-Phys.

xiii. (1894), no.
Lynn, ' Observatories a Century K'ga! Kairalidsc,x\\a. (1895),

86.
Nkwcomb, ' Observatories,' Johnson's Uhw. Cytt. vi. (T895).
Valen riNER's Haudwiirltrbuch der /fjfruKom/f (Breslau 1895

-18991.

Stonev, Wadsworth,' Astrophysical observatory,' ^j/nSft^^VJ.

Jtmr. iv. {[S9f,), 23.S.
Janssen, ' AnuLiUs dt rObsematoire d'Astronamu Physiqur,' i,

(Paris 139O).
JACOHY, 'Caiie Observatory.' Pop. Astitni. \i\. (1S96), 217.
Stonky, ' Future Astrophys. Observatory,' .)/. jV. Kty. Astnm,

So,. Ivi. (1S96), 452.
Halk, • Yerkes Observatory,' Astrophys. Jour, v., vi. (1897).
Hale, ' Aim o£ the Yerkes Ubscrvator)',' Astrefkys. Jour. vi.

(1897). J.o,
Payne, 'Yerkes Observatory,' Pop. Astren. v. (1897), It 5.
Newcomii, ' Aspects of American Astronomy,' Paf. Aslron. v.

(1S97). 35'.
Mkyeks KoiiviTsalions-Lexikeii, Bd. xvi., p. 418 (Leipzig and

Vienna 1897)-
Witt, 'Meudon Observatory,' llimmel and Erde, i, (1898),

529.
Colin, 'End of Tananarivo Observatory,' The Obitrvatery,

xxi. (18981,305.
Mevek, Das Wdlgebdudc (Leipiig and Vienna 1898).

For detailed descriptions of observatories, and instruments
and ttic work done with them, consult the volumes of their
annals, especially Pulkoira, Greenvrich, Paris, Washington,
Cambridge (U. S.), Nice, Mount Hamilton (Lick), Dunsink,
and Leyden. For reports of observatories, refer lo the Monthly
Notids Jfeya! AilroHoraUal Sociify for F'ebruary each year, and
to the ViirtelJahTiichrift der Aslrenamlsihen Crsellichaft, pub-
lished at l^ipzig. The publications of observatories of all
countries' are excellently summarized by D' Cofeland, in the
elaborate Catalogue of tie Crawford Library of Iht Rgyai
Obieraaloty, pp. 315-45 (Edinburgh 1890).

Telescopes and Houses for Them 393;

Cblestial Photography
BoMD, G. P., ' Stellar Photograpliy,' Aslroii. NiKhricilen, xlvii.

England,' Kefort Brit:

(1858); jlviLi. ([SsS); xlii. (1859).
De la Kue, ' Celeslial Photography

Asioc, Adv. Sci. 1859. p. 130.
Draper, ' Reflector for Photogtaphy,' Smiths

xiv. (.86s).
RUTHEBFURD, ' Aslr. Photography,' Am. Jour. Sa. U.

(1865), 304.
Newcomb, ■ Photography of Precision,' P.iferi U. S. Tr

of Villus Commission, i. (Washington 1373).
Harkness, ' Pholoheliograph,' Memoirs Kay. Aslr. Sue.

(1877), 119-
GotJLii, ' Celestial Photography,' The Of-itn;ilBry . ii. (1879),
J, ' Photography of

Sac-.

xlvii. (iS

copes for Astr. Photog.,' j\'i/Krf, xxx
O Asltonomy,' Fro

(■884-5),

38, 270.
Common, ' Photography as

j/.?»rf,>«,jci. (:S3sl,307.
WlNTERHALTER, ' AslrophotogTiphic Congrcss,' Washingleit

Ois. (18S5, App. i.).
Henry, ' Astr. Photography,' A-.Uurt. xxxiv. (iSSO), 35.
Stri'Ve, ()., ' Die Photograpliie ini Uionsle ilir Astronomie,'

Bui/. AeaJ. Sd.St JV/.rsi.wrf;,xxK. iiS^b). S' .1.
RaVeT. 'History,' BuHelin Aslrowmi./ue, iv. (1887), 165.
Common, ' Astron. I'liotography,' JVineteenl/i Centurv. xxi.

(iS87).227.
MoucHKZ, ' Astrographic Survey,' Annuaire Bur. Leug. 1SS7.
MoL'CHE/, La rhala^ra/'hie Ailroiiomi,ji,e {V3.t'is 1SS7).
Gill, 'Applications of Photography in Astronomy,' Pref.Kttyal

di. (18

V, KONKOLY, Brailiiehe Anleilung tH,

(Halle 1887).
, ' Astr. Photography,' Siil. Met

Editdrurgh tonnes; clsvii. (1S8S), 23.
PlCKERrNG, E. C, ■ SlHIar Photograph'

<lS8S). 179.
Chambers, ' Astron. Photography,* Deseripth-t Ai

(Oxford 1890).
ScHOOLtNC, Westminster Rrvirw. cnjixn (iSgi), 303.
RussBLL, ThtStar Camera (Sydney iBgr).

Him melsph ologreiphU

vii.dssa). .38,18.5

' Mem. Am. Aead. xi.

394 Stars and Telescopes

BruTHEKs, Photography: its Nittmy, Proctsut, Affaraau.anJ

Maltrmh <Loiidun Itkjj).
PftAissiNET, 'J'atis Astrogiaphic Obscrvalorjr,' La MUure,

■893-
Taylor, ' I'hoiographic Objectives,' M. N. Roy, AslroH. Soc.

liii. t'SgsJ. 359-
TuRNKR, I.KWi^i, ' Aslrographic Chart,' The Obttrvatary, ivi.

(1893), jo;; Anion, ami Aslia-pkys. xiii. ((894), 20.
RoiiERTS, ' I'rogress in Photography,' Proe. Am. PAH. Sae.

™ii. <.894}. Ol-
RussKl.L, ' I'Dyress,' /".'/. Astron. [i. (1894-95).
riLKKRlNi., W. H., 'Astr. rholog.,' Atin. Han: Cell. Obi.

«Rii.{iS95).
Barnard, ■ A,.lroivmiicaI Photography,' Tht PhetographU

7>m«,xxvLi. (1S95), 6s-
KOBERTS, ' Rttkclor and Portrait Lens," _/oHr. Brit. Aitr. Aitac.

vi. (.Sg6),33:.
CtLu KAPTKV-i, ' Stellar Photography,' Annals Cape Oiiema-

f.-rr.iii. (L0.11I01, iSyC).
SCHAEHEKLK, * I'laiietan- Photography,' Pap. Astren. iii. (1S96).

2S0,
Tl-rner, ' I'liolo. Tr.^iisil Circle,' .1/. A'. Roy. As/ran. Sir. IviL

('S97). 349.
Wai.sworth, ■I'lanelan' Photography," Tie Obstrvalary, tol.

(1897).
Pickering, K. C, ' Bruce Photographic Telescope,' Pap. Astron.

iv. (1897), 53'-
DesLaNDres, Sphimtns di Phata^aphies Astr'anamt^uei{Paris

1897).
SCHEIMEE, /)id Photographic da- Geslimt ([^ipiig 1897), Bib-
liography.
LoEwv, PrisEux, ' Lunar Photography,' Annuaire Bur. Long.

1898. A.
ScHWEiGER-LzRCHENFELD, AlLis dtr Himmilsiandt (Vienntt

1S9S).
Barnard, 'Development of Photography,' Prec. Am. Aiioe.

AJv. Sciericr. xlvii. (Salem 1898) ; Pop. Asl. vi. (1898), 415.

In IIou^EAU's Vadc-AfteutH dt rAstronomt, p. 339 (Brussela
l88i), the earlier scientific papers on aiitronomical photography
are catalogued. All the preceding bibliographies need to be
su])plemenled by the classified lists of TAe AstrophyHcal /our-
Jlo/, i.-jt (1895-99).

Telescopes and Houses for Them 395

Mountain Observatories

Smvtk, C. P, ' Teneriffe,' Phil. Tram. Roy. Soc. cxlviii. ( 1858),

465.
Smvth, C. p., Teneriffe, an Astronomer's Experiment (I/mdon

1858).
Lanuley, ' Aetna,' Am, Jour. Scitnee, xvii, ('879), 159; %x.

(iSSof. 33.
Lanolev, ' Mouni Whitney Expedition,' Nalarc. xxvi. (1882),

• , ' Mountain Observatories,' EJinbiirgh Rei'iem, clx.

{iS84),3Si: />../>.&/. .l/™rt/r. xxvi. (1885).^.
Toor., ' Lick 01.se rvaior}-,' .V.-<>««, vi. <r8Ss), 181, i36.
H01.DEN, IlaiidhMk of ihi Lick Obsfi-:ito<y (San Francisco

188S).
Ranyard, Knowli.!^.: xii. (1.SS9). 135.
jANSSEN.'Ml. i;iaiie()bsfivator>-,'.4rm«Hr><-fl(ir. Z™^-.(i894-

1899). Also Kepi. SmilAsoiii.iii Iiisliliilion 1S94. p- 137.
HoLDEN. ■ Mountain Observatories,' Umilhieniai- MiK. Col-

UclioHs, 1035 (1S96). llibliography.
DouoTjVSS, ' Almosiiherc, Tclcsfope, and Observer,' Pop. Alt.

v.(.S97l.64.
See, -Air Waves and Currents,' /".'/m/iir/lj/rriii. v. (1898), 479.
Ske. ■ Mountain Obacrva lories.' P.'piihir A-'lron. vi. (1898), 65.
DofCLASS, ' Scales of .Seeing,' r,puljr .-Ulron. v\. (1898), 193.

Popular literature of the telescope, celi'Slial photograph)-, and
the spectroscope has experienced an enormous RrOB-lhi par-
ticularly in recent years. A nearly complete bibliography of
titles may be found on reference to Toole's Indexes, at the
pages given below ; supplemented, of course, by the annual
volumes for 1897, [S98: —

V.„.,<.,^„ 0.«.v.,™

Phmoftiaph y Spccirmcnptt

T„e™,«

I. (.800-Br) p. 936

II. (1881-86) 319
111.(1887-911 309

IV. (1892-96) 4'0

p. 1003

340
330
440

P- '^33

4'3

403
540

p. 1 291

433
4^3
567

396 Stars and Telescopes

Practical Astkonomv and Making Observations

Pea KsoH. Introduction to Pnutical Astronomy ( London 1 824—

!9). Wiih Appendix and Plaies.
Mason, Introduction to Fraciii.tl Astronomy (New York i34t).
LooMis, Introduction to Practical Astronomy (New York 1855).
Chauvenet, Manual ef Spherical and Fraclical Astronomy

(Philadelphia 1363).
Proctor, Half-hours iviih Ike Teltscope (New York 1873).
SawitscH, PkTERS,^*™i der Praktischta Astrenomii ( Leipzig.

1879).
Smyth, Chambers./* Cycle of Celestial Objctti {O-hIotA 1881).
SOUCHON. -rr-iiti d- Astronomic Prali^uc {¥it\s 1883).
DOOLIITLE, 'J'realisi on Practical Astronomy as affiled to-

Geodesy and Xavif;ation (New York 1885).
Noble, Ho,irs loith a Three-inch Telescope (New York 1887).
Serviss, Astronomy -^ith .,n Opera Class (New York 188S).
Oliver, ^jfj-eJiumj'/i'r/Ini.ii'iHri (London and New York 188S).
Densino, Telescopic Work f^r Starlight Ez-enings (London-

■S91).
Cam PUELL, UanJhook of Practical Astronomy (Ann Arbor 1891).
Greene, Introduction to Sfhtrical and Practical Aitrenamjr-

(Jioston 1891).
Colas, Celatiai Handbook (ChLcago 1S92).
Webb, Ksi'in, Celestial Objects for Common Telescopes (London.

'893-94)-
Gibson, The Amateur Telescopist's Handbook (New York 1894).
CoMSTOcK, * Practical Astronomy,' Bull. Univ. Wiscontin, i.

(1895). No. 3.
Fowler, Popniar Telescopic Astronomy (Ijindon 1896).
Mee, Obscnalional Astronomy (Cardiff and London 1897).
Brenner. Handbuch far Amateur Aslronomen (Leipiig 1898),

Siipplemeniary to the foregoing handbooks are the annual'
' Companion' to T&e Observatory; also the monthly notes in
Popular Astronomy, and in the Publications of the Astronomical
Society of the /'j^yfc, together with ephemetides in the AnnutUrt-
du Bureau dcs Longiludei.

Small Plantts between Mars and Jupiter 397

jDpnra

HUH

DATB OF ' DISCOVHBH KKV,

PLACI OP

"*"■

D1>CUV..V 1 HIS NUMBH

i,i«m«v

Ceres

I Ian. iSoi Hiazzi
38 Mar. iSo; Olbers i

Palermo

Pallas

JSremcn

Vesta

I Sept. 1.S04 Harding

Lilitnlhal

29 M.ir. 1N07 (Jlbcis,

Hrenien

Astraia

S Dec, 1N45 Henckc i

Uiies,scn

Hebe

1 Julv 1847 ' Hcnckc,

Dries-^n

Iris

11 Aug. 1S47 Hind,

London

Flora

iSOci. I-S4- Hind 5

London

Mclis

;5.\pr. iSjS Craham

Markree

Hygda

12 Apr, 1S49 DeGaspiriS[

Naples

Tatthenopc

11 Mav ISSO DeGasparisj

Naples

Victoria

13 Sept. I.S50 Hind,

London

Egeria

2 N.,v, lS;o I)e{;asparisj

Naples

Irene

19 Mav iS^l Hind,

•5

Eunomia

29july [S51 DcG.ispatis,

Naples

Psyche

17 Mar, 1S52 He Ga^jiari,-^ s

Naples

Thetis

17 Apt. 185; I.uiher,

Melpomene

i4 Tune iSs; llindj

Fortuna

22 Auk, .852 "''"l«

l^mdon

Ma&^alia

1986111.1852 DeGaspatisg

NaplL'S

I.utctia

16 Nov, [Ss= Hind,

Paris

Calliope

l/)n.!on

»3

Thalia

ijDee. .852 1 Hindi

l...mi"n

Themis

SApr. .SS3 DeGa^parU,
6 Apr. 185J 1 Chacurnac i

Naples

Phocaia

Marseilles

Proserpine

5 May 1853 ' Luther ,
g\ov. rsiji Hind,

Kilk

»7

Katerpe

l^ndon

Bellona

I Mar. 1S54 l.uthet,

Hilk

Amphilrile

1 Mar. 1S54 ' Marth

London

Urania

»July iS^t

Hind ,0

London

. Sept. 1854

Ferguson ,

Wichingtoit

Pomona

16 Oct. :8s4

Goldschmidt ,

Paris

Polyhymni*

iSOct. 1854

Chacotnaca

Paris

Circe

6 Apr. 1855

Paris

Leucothei

19 Apr. 1855

Luther 4

Kilk

Stars and Telescopes

«™-

DAT«Or

DliCOVIUIt ANB

ftACB OW

BIII

"*"■

DISCOVBRY

HIS HUHBII

AtalanCa

5 Oct. 1855

Coldschmidt ,

Paris

Fides

5 Oct. i8s|
(J Jan. .856
Si'eb. 1856

Luther ^

Bilk

Leda

Paris

Lititia

Chacomacj

Goldschmidi,

Paris

Harmonia

31 Mar. 1856

Paris

Daphne

22 May :856

Goldschmidl ,

Paris

23 May 1S56

Pogson ]

Oxford

Ariadne

[5 Apr. 1857

Pogson ,

Oxford

4; Nvsa

27 May ,857

Goidschmidt,

Paris

4S . Eugenia

27 June 1857

Goldschmidt ,

Paris

46 Heatia

16 Ang, 1857

Pogson

Oxford

47 Aglaia

ijSepi, i,S57

I.uther,

Bilk

48 , ntris

igScpi. rS57

Goldschmidt,

Paris

Pales

19 Sept. 1S57

Guldschtnldt ,

Paris

Virginia

4 Oct. 1M57

Ferguson j

Washington

Ncmausa

22 Jan, ..S5S

Laurent

Nismes

5S 1 Kuropa

4 Feb. 185N, Goldschmidi ,0

Paris

SJ 1 CalyjLo

4 Apr, iKsS 1 l.ulliel,

Itilk

Alexandra

10 .Sept. 1S5S ' Ciildschmidt ,1

Paris

Pandora

.oSepl.rSsS S.arle

Albany

Mekie

9 Sept. 1857 . Goldschmidl ,j

Paris

Mnemosyne

22 Sept. 1850 I.inhcr,

liiik

S«

tloncordia

24 Mar. 1S60 I.uther,

Bilk

gC"'"

i2Sept. t86o' Chacornac,

Paris

15 Sept.lSCo 1 Ferguson,

Washington

Danae

9 Sept. i860 1 Goldschmidt 1.

Chatillon

Erato

14 Sept. i860 FofnlfrS LfMtr

10 Feb. l36i 1 DeGaspatisg

Berlin

Ausonia

Naples

Angelina

4 Mar. 1861

Marseille*

Maximitiana

8 Mar, 1861

Tempel,

Marseilles

MaU

9 Apr. isai

Tuttle ,

C«.tai<%r.U.S.

Asia

17 Apr. 1861

Pogson ,

Madru

61i

Leto

29 Apr, 1861

Luther 10

Bttk

Hespcria

29 Apr- 1861

Schiaparelli

Milan

Pan5;«a

5 May 1861

Goldschmidt „

Paris

Niobe

13 Aug. 1861

Luther „

Bilk

FeronU

29 May 1861

P=tn.,&&.abrd

Clinton

ClytU

7 Apr. 1861

Tuttle .

Galatea

29 Aug. 1862

Tempel,

Marseillet

Eorydice

it Sept. 1862

Peteraj

Clinton

Small Planets between Mars and yupiter 399

nUH-

DAT. OF

1>IK0V.I..« AND

PL.C. OF

■u

HAUI

HIS HUHBIII

Freia

21 Oct. 1862

U' Arrest

Copenhagen

Frigga

12 Nov. 1861

Peters,

Clinton

Diana

15 Mar- 1863

Luther 1,

Bilk

Eurynome

14 Sept 1863

Watson 1

Ann Arbor

Sappho

2 May :864

Pogson (

Madras

Terpsichore

30 Sept. 1S64

Tempel ,

Marseilles

Alcmene

=7 Nov. 1864

Luther „

Kilk

Beatrix

a6 Apr. iH6s

DeGaspariss

Naples

Clio

25 Aug. i,S65 1 Lulhcr u

Hilk

It) Sept. 1865 Peters,

Clinton

Semele

4 tan. 1866 Tietjen

Berlin

Sylvia

16 May t866 I'ogson ,

Madras

Thisbe

1: June 1866 I'elLTSs
6 Aug. iSeC) Slophan

Clinton

Julia

Marseilles

1 Oct. 1S66 1 Luther ^

Bilk

*gina

4 Nov. \Wi> liorrelly ,

Marseilles

9»

Undina

7 July 1S67 Peters a

Clinton

Minerva

24 Aug. i8ti7 Watson 3

Ann Arbor

6 Sept. i8<l7

\V.1t-OH ,

Ann Arbor

Arcthusa

2 J Nov. 1*37

Luther IB

Bilk

.4-:slc

17 Feb. 1868

Coggia 1

Marseilles

floiho

17 Feb. 1S68

Marseilles

lanthe

18 Apr. 1S6K

Peturs ,

Clinton

Dike

28 May 1S68

H.irrelly ^

Marseilles

Hecate

11 July 1S6S

Watson 4

Ann Arbor

lot

Helena

15 Aug. l363

Watson I

Ann Arbor

Miriam

22 Aug. 1S68

Peters ,

Clinton

103

Hera

7 Sept. i8i«

Watson e

Ann Arbor

104

Clymene

iTSept.iSOS
16 Sept. 1S6S

Watson,

'OS

Watson B

Ann Arbor

106

Dionc

10 Oct. 1S6S

Watson,

Ann Arbor

107

Cimilla

17 Nov. t868

Pogson,

Madras

Hecuba

2 Apr. 1869

Luther 1,

Kilk

109

Feiicitas

9 Oct. 1869

Peters,

Clinton

Lydia

ig Apr. 1870

Borrclly g

Marseilles

III

Ate

14 Aug. 1870

Peters ,n

Clinton

19 Sept. 1H70 Peters ..

Clinton

Amallhea

12 Mar. 1S71 1 Luther u

Bilk

114

Cassandra

23 July 1871 Peters,,

Clinton

Thyta

^iu^,l87.

Watson lo

Ann Arbor

Stars and Telescopes

DAT. OF 1 DlKOV.«. *»D

fiAOior

BII

"*"'

mwcotmi

)i6

Sirona

SSept. 1S71 1 Peters,,

Clinton

i'7

Lomia

i2Sept.iS7i Borrelly,

Marseilles

i>^

Peilho

IS Mar. 1872 , Luther ,0

Bilk

119

Althzca

3 Apr, .872 i Watson,!

Ann Arbor

Lachesis

10 Apr. 1872 , Borrelly c

Marseillea

121

Hcrmione

12 May 1872 Watson 1,

Ann Arbor

Gerda

31 Jiilv 1S73 Pciei*]j
31 July 1872 1 Peters „

Clinton

123

Jirunhilda

Clinton

IJ4

Alceste

23 Aug 1872 ' Peters ,(

|] Sept. 1872 ' Pros. Henry 1

Clinton

Libcrairix

Paris

126

Vclleda

S Nov. 1872 Paul Henry,

Paris

127

Johanna

S Nov. 1S73 1 Pros. Henry,

Paris

128

25 Nov. 1872 1 Watson,,

Ann Arbor

129

S Vi\i. 1873- Peters,,

Clinton

.30 ; K.«„

i7Kcb. 1S73; Peters „

Clinton

131 Vala

24 May 1873 ' Peters „

Clinton

132 A'Aiiii

13 June [S73 : Watson,,

Ann Arbor

133 Cyrene

16 Aug. 1S71 Watson u

Ann Arbor

'34

SophiDsyne

27Stpl. 1S73 LuihetM

Bilk

'35

Hc'rlha

18 Feb, 1874' Peters 20

Clinton

136

Austria

18 Mar, 1874 ' Palisa ,

PoU

137 1 Melibcea

21 Apr. 1874', Palisaj

Pola

138 1 Tolosa

ig May 1874

Perrotin ,

Toulouse

^29

Jnewa

10 Oct' .874

Watson ,(

Pekin

140

Siwa

13 Oci. 1874

Pilisa ,

PoU

141

Lumen

13 an. 1875
ti an. 1875

Paul Henry J

Paris

14Z

p'olana

Palisa ,

Pola

•43

Adtia

!3Feb. 1875

Palisa ,

Pola

144

Vibilia

3 one 1875

Peters,,

.Clinton

145

Adeona

3 ""e '87s

Peters ^

Clinton

146

Lucina

8 June 1875

Borrelly ,

147

Ftotogeneia

lojuly .875

Schulhof

Vienna

iili

Gallia

7 Aug. 1875

Pros. Henry.

Paris

149

Medusa

li Sep., .875

Perrotin,

Toulouse

ISO

Nuwa

18 Oct, l87i

Watson 1,

Ann Arbor

^5'

Abundantia

1 Nov, .875

Palisa .

PoU

152

Atala

2 Nov. T875

Paul Ilenry,

Pari.

'S3

Hilda

2 Nov. 1875

Palisa ,
Pros. Henry,

PoU

'54

Bertha

4 Nov. .875

Paris

ScylU

8 Nov. 1875

Palita,

PoU

Small Planets between Mars and yiipiter 401

KUH-

DUTR

DI-iCOVlMk ASO

rLACE or

■m

HAHI

IHbCOV

»y

■k«hu«m»

Di«:ovt«v

156

Xanlippe

22 Nov

1875

Palisa,

Poll

'57

Dcjanira

1 Dec.

■875

Borrelly ,

MarseiUe*

'58

Coronis

4 tan.

1876

Knorre,

Berlin

vEmili*

=6 Jan.

1876

Paul Henry t

I'aris

Una

JO Feb.

1876

Peters „

Clinton

161

Aihor

(9 Apr.

■ 876

Watson „

Ann Arbor.

161

Laurentia

31 Apr.

1876

Pros. Henry (

'63

Kiigone

36 Apr.

1S76

Perrolin ,

164

Eva

12 July

1K7O

I'aulHenrvj

P.-iris

'6s

Loieley

9 Aug

1876

Pelera „

Clinton

166

RhodopE

IS Aug
28 Aug

1S76

Peters ;;

Clinton

Urda

1876

I'cters sc.

Sibylla

27 Sep.

.S7r.

Watson „

Ann Atbor

.'69

Zclfi

28 Sept

■876

I'ros. Henry,

Paris

170

Maria

,0 Jan.

■ 877

Perrotin ,

Toulouse

'71

Ophelia

I3j>n-

1S77

Borrcllv,

Marwillel

«7S

Baucis

i Feb.

1S77

BurrcUi-,

MarKcillei

"73

Ino

' Aug

1S77

Horrcllv,,,

Mar-scillcs

•74

Phxtira

3 Sept

'S77

Watson ,„

Ann Arbor

'75

Andrumache

1 Oct.

1877

Watson .,

Ann Arbor

'70

Idunna

14 Oct.

■S77

Peters ~

Clinton

'77

Irma

SXov

6 Nor

.877

Paul Uenty^

Psria

178

Bclisana

.877

Paiisaio "

iVla

'79

Clytcmncsua

M Nov

1S77

Ann Arbor

180

Garumna

=9 Jan.

,878

Pe?tut"n^

'i'Duliiuse

iSi

Eucharis

2 Feb.

1878

Gotten ot

Marseilles

■ 82

EUa

7 Feb.

.878

Paiisa,,

Pola

I83

Islria

8 Feb.

.878

Palisi. ,.

Pola

.84

Ddopeia

28 Feb.

187S

Palisa „

Pola

'85

Eunice '

I Mar.

1878

Peters „

tS6

Celuta

6 Apr.

1878

Pros. Henry,

Paris

187

L.imberta

is '^fne

1873

Coggiij

Marseilles

\?A

Mcnip|>e

9 Sept

1873

PetlTs j

Clinton

1S9

Phthia

1878

Peters „

Clinton

190

Ismcnc

S2 Sept ,878

Petere „

Clinton

191

KolB*

fM.

.S78

Peters „

Clinton

192

Nausicaa

1879

Palisa ,7

Pola

•93

Ambrosia

jS Feb.

18J9

Coggia.

Marseilles

I9i

Procne

31 Mar,

1879

Peters tt

Clinton

'9J

Euryidcia

=3 Apr.

-879

Paliuu

Pola

Stars and Telescopes

"bhT '""

»«7™ "s-::;;.".""

w=^^

196 Philomela

14 May 1879 Peters „

Clinton

197 Arele

21 May 1B79 Palisa,,

Pola

19S Ampella

13 June 1S79

Borrelly n

Marseilles

199 I Byblis

9 July t«79

Peters u,

Clinton

200 Dynamcne

=7j"iy 1879

Peters „

Clitilon

101 Penelope

7 Aug, 1879

Palisa ,,

Pola

Z02 ■ Chryseis

1 [ Sept. l»79 Peters „

Clinton

203 Pfimiieia

25 Sept. 1879 1 Pelers„
8 Ucl. :S79 Palisa „

Clinton

J04 Callisto

Pola

20 s Man ha

13 Oct. 1879 Palisi„

Pola

206 ' Hersilia,

13 Oct. 1879 I'etL-rs-

Clinton

207 1 lledda

17 Oct. 1S79 PiHsa"

208 , Laclirymosa

21 Oct. .S79ll'alisa,,

Pola

209 1 Uidn

22 Oct. 1870 1 Peters ,„

Clinton

210 1 Isabella

.2N0V..879 l'alisa„

Pola

211 [solda

10 Due. 1S79' Palisao,

Pola

2\2 . Mc-dca

6 1--cb. iSSo, l'alisa.';j

Pola

iC Feb. [SSo Peters,,

Clinton

2(4 Aschcra

2f, Feb. iSSo 1 Palisa .,,

Pola

215 , (Knonc

7 Apr. 1S80 ' Kiiorre-

Berlin

ai6 Cleopatra

10 Apr. 1880; l'nli»a,js

Pola

2r7 , Eiidora

30 Auk- iSSo.CoBgiai

Marseilles

21S Bianca

4 Sept. 1880 , Palisa ~,

Pola

219 ' Thusnelda

30 Sept. 18S0 : Palisa «

Pola

220 Sleiihaiiia

19 May iSai

Palisa „

Vienna

221 ' E03

18 Tan. 1882

Palisa an

Vienna

222 ; l.ucia

9 Feb. 1S.S2

Palisa ,.

Vienna

223 Kosa

9 Mar. 18S2

Palisa „

Vienna

224 Oceana

3^ Mar. .882

Vienna

225 , Henrietta

19 Apr. 1S82

l^alisaH

Vienna

220 ! Wetingia

19 July 1SS2

Palisa.

Vienna

227 Philosonhia

12 Ang. 1882 1 i'aul Henry,

Paris

22S ■ Agalhe

19 Aug. 1S82 1 Palisa„

229 ' Adelinda

22 Aug. 1882

Palisa „

Vienna

2JO 1 Athamanlis

3 Sept. .882

Dc Ball

Bolhkamp

231 1 Vindobona

10 Sept. 1882

Palisa »

Vienna

232 1 Russia

31 Jan. 1883
1. ilay 1883

Palisa S

Vienna

S33 1 Asterope

Borrelly „

Maneilln

134 1 Barbara

12 Aug. 1883

Peters „

Clinton

335 1 Carolina

28 Nov. 18S3

Palisa M

Vienna

Small Planets between Mars and Jtipiter 40J

236

v,«

ws't^;

"■^s

r„"»".;r

d'^^rv

Honoria

16 Apr.

1884

Palis

»«

Vienna

237

Ccekstma

S7 June

1884

I'alis

Vienna

238

HypalU

ij.ly

1H84

Knu

Berlin

339

Adrsslea

[8 Aug.

1SS4

Palis

Vienna

140

Vanadis

27 Aug.

1884 ; liurt

iiy„

MarsL-illes

241 1 GErmania

12 Sept

1S.S4 Luther,,

Diiiseldoif

242 Kriemhild

22 Sept

1884 l-ali

Vienna

243 Ida

29 Sept

18S4 I'ali

Viennn

244

Sita

14 Oct,

1884 , P:ili

Vienna

245

Vera

Ftb.

1SS5 . l'„B

on,

Madras

246

Asporiiia

6 Mar

iKS; Hot

fUv n

Marseilles

247

Kukrale

mM^.

1MN5 ' l.UI

1 hi^seldorl

248 l-amda

Sjunc

..ss's I'.li

249 ll^e

[(. Aui;

iSSs ■ !Vlc

2SO i iiet.ina

3 ^cpt

iSKj I'ali

■148

Vienna

25'

Sopliia
Clementina

40c,.

1.SS5
r.SNi;

I'ali

•v»

Vienna
Mte

256

Walpiirga

3 Apr.

issr.

Talis.! t3

257

Silesia

S Apr.

18N6

Tali.-a (,

2I8
259

Tvche
Allheia

,3S

18H6
iSSf.

Lutlier,,,
Peters,,

2&1

Huljerta

3 t'ci.

1SS6

Palisa M

=0:

I'nmno

3. Oct.

I,SS(,

Teter<,(

26-

VaUla

3 Nov

tS86

I'alisa.-

263

3 Nov

i,s8r.

Talisa „

264

Lilmssa

17 Pec.

1SS6

Peters „

26S

Anna

IS Feb.

ISM7

I'alisas,

266

Aline

17 May

ISS7

Palisa ,„

Jfi?

Tirw

27 M.-1V

ISS7

Cl.arli.iB

2(>S

Adorea

9 June

1887

Horrelly

269

21 Sept

1S87

270

Anahita

8 Oct.

18S7

Peters„

271

Penthesilea

13 Oct.

IS87

Knorre ,

272

X Feb.

iKNS

Charlois

273

8 Mar

18SS

P.ilisa„,

274

PhilagoHa

3 Apr.

18S8

Palisa „

*75

Sapientia

15 Apr.

i83S

Paliuci

Stars and Teltscopes

HUW-

DAT.

DlSCOVB.n ANU

P..AC110F

l<»

"*""

"'* "<"""

DISCOVMT

=76

Adelheid

17 Apr.

1B8S

Palisau

Vienna

377

Elvira

3 May

iSS^

Nice

=78

Paulina

16 May

Palisa,^

Vienna

=79

Thule

25 Oct.

Palisa M

Vienna

380

PhilU

29 Oct.

i33S

Palisis,

Vienna

rfl

Luctetii

31 Oct

iSSS

Palisa „
CharloFs,

Vienna

2%1

Clnrindi

zSJati.

Nice

aSj

Emmi

8 Feb.

.339

Charlois.

Nice

284

Ami'lia

29 May

.88?

Charlois,

Nice

^8s

R=eini

3Au|

Charlois,

Nice

:lgG

Idea

3 Aug

i8S9

Palisa „

Vienna

287

Ntphthvs

=5 Aug

if«9

Peters „

Clinton

388

Gl.uca

zo Feb.

.3.^

Lulhcr „

Diisaeldorf

a89

NcnEtu

[O Mar.

1890 1 Charlois,

Nice

390

Uruna

:o Mar.

1890, Talis* TO

Vienna

291

Alice

25 Apr.

1S90 Palisa,!

Vietina

=92

35 Apr.

1S90 Palisa-j

Vienna

*)3

Brasilia

=□ May

.S90 Charlois,

Nice

294

Fulicia

<s July

[890' Charlois ,„

Nice

29s

Thcresia

17 Aug

.8901 l'alisa„

Vienna

396

Phaethusi

19 Aug

1S90I Charlois n

Nice

=97

Cecilia

9 Sept

1S90 Charlois,,

Nice

BaplisliM

gSept

.S6o

Charlois „

Nice

299

Thora

6 Oct.

.890

Palisa.,
Chailois 1,

Vienna

3«J

Geraldina

3 Oct.

.890

Nice

301

navaiia

16 Nov

1890

Palisa ^s

Vienna

303

Clarissa

UNov

iS^

Nice

3°J

Josephini

12 Feb.

iS^

Rome

3°4

Olgi

14 Feb.

:85.

Palisa -

Vienna

Gordonia

16 Feb.

.15.

Charlois „

Nice

Unitas

I Mar.

1891

Millosevich,

Rome

307

Nike

(Mar.

rS^i

Charlois „

Nice

30S

I'olyxo

3? Mar.

1891

Borrelly 1,

MarseillM

3°9

Fratemitas

6 Apr.

.891

Palisa'

Vienna

310

Margarila

16 May

.891

Charlois „

Nice

Claudia

1 1 Tune

1891

Charlois ,,

Nice

rierrctta

2g Aug

iS^.

Charlois M

Nice

3'3

Chaldxa

30 Aug

.g^t

Palisa-
Charlois,,

Vienna

3'4

Roaalia

■'i Sep.

.8^1

Nice

3'S

Cotwtanlia

4 Sept

.85<

Palisa „

Vieiuia

Small Planets between Mars and Jupiter 405

WUM-

D*TB or

DBCOVBRK A -in

fL*CR HP

KAUI

DIICUVHV

HIS HUHBIli

DiM.-(IV¥llV

3"6

Goberta

8 Sept. 1891

Charlois „

Nice

3'?
3'8

Koxana

n Sep.. ,891

CSarloisa

Nice

Magdalena

24 Sept. 1891

Charioi,^*

Nice

319

Leon a

8 Oct. 1S91

Charlois .(

Nice

320

Kathaiina

11 Oct. 1891

P-ilisajo

Vienna

311

Flore mi na

IS Oct. 1891

Palisa s,

Vienna

3*1

Phaeo

27 No«. |S9T

llorrtllv „

Mats<.-illes

3*3

lirucia

20 Dec. iSoi ' Wolf. ■ "■

Heidelberg

3*4'

Bamberga

25 Feb. i.Sgji Palisa,j

Vienna

3*5

Heidclberga

4 Mar. iS^' Wolf 3

Heidelberg

326

Tamara

i9Mnr. i8q2 l'al!sa„

Vienna

327

Columbia

22 M,ir. 1.S92 CharloisM

3^8

Cudrun

iNM.ir. iS.;3 W.ilf,

irdddlwrg

329

Svca

21 M;ii. ],S.,2 Wolf,

ireiddberg

330

Adalbena

iS Mar. 1S92 Wolfj

llcidclbelg

3JI

Ethcridgca

1 Apr. iS.j2 Charlois™,

Nice

li-

Siri

i9M,ir. i.Syj Wolf,

Heidelberg

333

Badenia

22..^. ,,S....lWolf,

[leidcllietg

334

Chicaeo

ijAog. iS,p Wolf,

Heidelberg

335

Roberta

1 Su|.1. 1^92 ■ Staos ,

lleiddberg

336

I-acadiera

19 Sept. 1S92 fhatlois a

Nice

337

Dcv.isa

22 Sept. iSi)2 CliarloisT,

Nice

333

25 .Sept. iSyi Charlois „

Nice

339

Dorothea

25 .Sept. 1892

Wolf,

lleiddberg

340

Eduarda

25 Sept. 189:

Wolf ,0

Mddell^rg

34'

California

25 Se].t. 189!

Wolf ,1

HeidellMrg

343

t'oc't. 1S93

Wolf 15

lleiddberg

343

Oslara

■ S Nov. .89=

Wolf ,,

Heidelberg

344

1 )ciidcrala

15 Nov. 1892

Charlois j,

Nice

345

Tercidina

jj Nov. 1892

Charlois „

Nice

346

Hcrmentaria

15 Nov. 1892

Charlois „

Nice

347

Patiana

aS Nov. 1S92

Charlois „

Nice

348

May

28 Nov. 1892

Charlois u

349

Dembowska

Dec. 1892

Charlois ^

Nice

35°

14 Dec, 18^2

Charlois „

Nice

35'

Yrsa

16 Dec. 1S9Z

Wolf 1,

Heidelberg

35*

Giaela

t2 a.,. .893

Wolf 1,

Hddelberg

353

.893 /■

.6 at.. .8^3

Wolf „
Charloii .

Heiddberg

354

Eleonor^

17 an. 1893

Nice

355

1893 £

ao at.. 1893

Charlois „

Nice

re b«a mad* pbotecnphiciDii

4o6

Stars and Telescopes

«""

NAM*

xi;.".;

"i^r".*'^'"'

D^"^

3S«

1893(7

2. Jan. 1893
II teb. 1893
8 Mar. 1893

10 Mar. 1893

11 Mar. 1893

Chatio s „
Charlo s „
Charlo s ,3
Charlo s «,
Charlois „

Nice
Nice
Nice
Nice
Nice

3<H
365

1893 Z'

:89J^
1893 -S'
'893 7-
1893 r

11 Mar. .893

12 Mar. Ihy3
17 Mar. T8.J3
19 Mar. 1N03
21 Mar. iS^3

Charlois ,j
Charlois «
Chailois „
Charlois „
CharloU 1,

Nice
Nice
Nice

Nice
Nice

366

369
370

■893 "-

i.S9_, AA
lK9jW/f
Aiiria
1893 WC

21 Mar. I.'<<J3
njMav iS.)j
T9 May iS.,)3

4 July '893

14 July 1893

Charlois ^
Charlois i,
Charlois ^
HorreUy i,
Charlois la

Nice
Nice
Nice
MaTseU1e»

Nice

371

373
374
375

1893 Ai>

1893^7
1S93 AK
1893 ,(/.

16 July 1893 Charlois J,
19 Aug. r.'i(i3 ' CharloU B5
14 Sept. 1S93 Charloiijg
18.SCIH, iS-n' CharloiSj,
18 Sq.l. 1893 Charlois „

Nice
Nice
Nice
Nice
Nice

376

1893 ^.v

1893^ A'
.893 AP

.894 -*c

.894 ^iV

■8 Sept. 1893
20 Sci)l. |8.>3
fyUec. 1893
8 Jan. 1894
8 Jan. 1894

Charlo s„
Charlo S((.
(.harlo s „,
Charlo s „
Charlois „

Nice
Nice
Nice
Nice
Nice

1
384
38s

1894 -i-s"
1894^7-

\%^^AU
Burdigala
llmaut

10 Jan. 1894
29 Jan. 1894
jgjan 1894

11 Feb, :894
1 Mar. 1894

Charlois „
Charlois ii»
Charlois „

Wolf [/

Nice
Nice
Nice
Bordeaux

386
387
38a
389
390

1894 .4 K
:S94 AZ

1894^5
18945c

I Mar. 1894
5 Mar. 1S94

7 Mar, 1894

8 Mar. 1894
24 Mar. 1894

Wolf -a
Courty ]
Charlois „
Charlois (,
Bigouidan 1

Heidelberg

Itordeaiix

Nice

Paris

39'

393
394
395

.S94 5C
1894^*-^
1894 5^

I Nov. 1S94
4 Nov. 1894
4 Nov. 1894
19 Nov. 1894
30 Nov. 1894

Wolf „
Wolf a,
Wolfji
Borrclly „
Charlois n

Heidelberg
Heidelberg
Heidelberg
Marseilles

Nica

Small Planets between Mars and Jupiter 407

"«;

-.-.

w".7v

"r^'j-'L-r"

iTl^OVMV

396

.894^/.

I Dec.

1S94

Charlois „

Nice

397

1S94 5,1/

10 I>ec.
2SUCC.

1894

Charlois „

Nice

398

18?;^^

.864

Charlois -

Nice

399

.895 /;p

23 Feb.

189s

\Volf„

Heidelberg

400

1895 ^£^

IS Mar.

189s

Ch»rlois „

Nice

401

Ottilia

16 Mar.

■895

Wolf .,

402

1S95 B \V

21 Mar

1895

Charlois ,,

Nice

40J

iS95 RX

18 May

1895

Charloia -.

Nice

404

1895 /T

aojun,:

■89s

Cliarlois L

Nice

405

1895 BZ

23 Joiy

1895

Charlois „

Nice

406

1S95 CB

13 .Aug. 1S9;

Charlois ..

Nice

407

:S95 CC

13 Oct,

1.S9S

Wolf.,, '

Heidelbeig

40S

1S9S CD

13 Oct.

,89

Wolf ...

Heidelberg

409

TS91 c/-:

tSgO CJf

9 Dec.

1S95

Chariuis .,

Nice

410

7 J^ii-

Charlois ;„

Nice

411

i!i-)6cy

- Jin

iS^

Charlois ,,

Nice

4' 3

EMsaLclh.!

J J.'".

iSyG

Wolf „

lleidell>erg

413

EdUuiKa

7hn.

1896

Wolf-

Heidelberg

414

1.S96 C.V

16 |.-.n.

i.S</,

Charlois...

Nice

4' 5

1896 CO

7 hb.

.Sy6

Wolf .^

Heidelberg

4>6

Vatican:.

4 May

.S96

Charlois „

Nice

t\l

1S96 cr

G Mav

1896

Wolf.,

lleiacllM;rg

,^jf,<T

3 ■'^e|it

1896

Wolf la

Hei<tell>erg

4'9

1896 Clf

3 -■''■!"

.&,'.

Wolf,,

llciddl>erg

420

Bertholda

3 Sept

1896

Wolf ,5

Heidelberg

421

ZahriiKia

1S96

Wolf „

Heidelberg

422

iSi/,

Wilt ,

Jlerlin

4*3

iS.* n/i

7 Dec.

t.S96

Charlois,,

Nice

■1=4

iR.X> /)f

31 1>CC.

1896

Charlois „

Nice

4=5

189O DC

:8 Dec

1S96

t:harl«is „

Nice

426

1897 /)//■

=5 Aug.

1S97

Charlois „

Nice

427

27 Aug.

1S97

Charlois „

Nice

42S

18 Nov

1897

Viiliger,

Munich

429

1897 ^z-

ii Nov.

1897

Charlois'

Nice

430

1S97 n.if

iSDcC

1897

Charlois „

43'

1S97/W

i8 Dec.

1S97

Charlois „

Nice

431

1S97 iJO

18 Dec.

18^

Charlois „

Nice

433

E.OS

13 Aug.

■898

Witt,

lietiin

434

Hungari.

11 Sept

.8^

Wolf,,

• Woifis^

Heidelberg

435

iS^JJS

»Se^

1S98

Heidelberg

Stars attd Telescopes

■UM-

"*""

DATE or

DISCOVFS.K *«D

,^„OF

D1SCOVBBY

HIi NUHBIR

BISCDVBBV

436

T&^DT

13 Sept. .89S
8 Nov. 1898

■ Woff & S „

437

i^Dcr

Charlois„

Nice

438

:898i>r

6 Nov. 1898

Wolf & S -
•\Volf&r„

Kontgstuhl

439

isoszjir

6 Nov. 1898

Kiinii^tuhl

440

iS^DX

6 Nov. 1S98

Wolf & V „

Konigstuhl

441

iSfSnr

13 Nov. 1893

Wolf & V ,„

Kiinigstuhl

442

1893 nz

[9 Nov. 1S98

Wolf & V ,,

Kiinigslubl

443

1898 £A

,9 Nov. >S98

Wolf & S (2

Konigstuhl

444

1898 /■:/i

13 Oct. 1S98

Coddinglon ,

MiHi«.ili«>

445

1898 iC

.400.. 18^

Coddington ,

«6

iSgS£D

8 Ilcc. 1898

Chariois „

Nice

447

1S99 i A'

:S Feb. 1S99

Wolf & S .J

Konigstuhf

44S

.899 £/■

.7Kcb. .899

Wolf&S „

Kbnigstuhl

449
450

Plme

UziiJ.

«po»«.

t\ enceplionil inun

'n betauH nf ihg large tccen-

(rieilyo

can <ii<tinn of oiil;

■ .46. iha

ofMarabeins..^.

btthtpjlhofEnu

allying

withixhaloTMin,

hiK of t

i> Willi

nllunoiMMi: but

lie !■ Ih

Bbit Ih;.

il ippriMChes »iil

n 14 mil

onmiloorourown

IHtbtO

n near the lima of

perihelion, »i>iu!

Uhivibe

■n tl,. ciu m .BM,

UltElb

n.aKuiiadeli about

the 7lh.

naliecl^FC viubiKly

or PicnaitiHG ud

Mr. Fu

mm-, h

V* ti-diK

:o.<»d Ihe p1>«l

onabau

.0 Hamird plUe.

op»«d

neai Ihli

ime, grti

iheorbilcalcuUtod

byD'C

. N«u

til i9>i doH » f..

11 oppoution iBiiii

win De

Kmber.9

r»i<v,m>ppr<.«:h

iwilhii.

. .nlUion milea, or

mbDut fo

Thia opp«>iion will

e«and

rile value o{ the n

»r pjia

ai. beca™ of the

pncision

•nth w

ich > dLkl™ objea n( this

Dppa.iliOD of I9>

ide a value ol the

Sun', di

»nce lar uceediug

available.

Probably Era i%

luxha

»>nil<

in diini

ler, .nd its elOM apprauh t

the E«1h every jo

« penur

n of gte

litional

Miiumn ij jreara in

journey

rwind ih

uremta of diauna

INDEX

HMind»iiiia(iii)4o
liblberu Ijio] MS
Wunt'riii.iJ.Oiw/
I4).3S5i '44, IH

Udbnd (iT6)"4<>4
Ldel>i>daCiH|)«n

bniUa<iu) 4Bi
nil (369} 4t*

Aluite(ii4) 400
*■ — iie(S>))W

Al™nd,a{H)j,8

Allpihenx OIh. n

Al-SOfi ID, vi
Alihu(iijy4«

n.a]ll.w(..j JM

ArgtUnder ifcrir.') »

mb.or,. ..S

ArpOi, , 165, 169, jso

Mclia|iS.)t°4

An>dn=U3)J9*

m. Book t;o. TO, :rfis.

lHo

nhcruCollMeu]

Am'SS)7)"''**

mhem Ed. Kip. ]6]

d-Atrut 149. 191. •<

Andromache U7s) ''S-
Aiidconicda nebula 14]
AtiRelim (fiO ^

AXfrtsUo]"'

Aiequipi, Peni 164. iM
Amc Oot) *•'

Ai<e'rISd.7«/^

AMronomy, pnclinil yfi

Aulidsj"™"' '''

AUlinU (36) ]^
AtropM(i7j) 40 J

uwr* S3, Si, '49. »
Bachi telcKope 199, J49,.

Backlund ■}!>. 149, iSi

Sliley, I'. H. 141 I S. ]

Bailbudiji
B»ilJyi»,(>rtr.)«jV. .

Uarbata (114) 4°i
BuiuTcl viL, viii,

Bjuuch amTLDmbiEg

B^lawluk:

BifflVa, II.' 1^
Biminghjin 36b
Bischobhelni r69, 331

J. J. 4=1 W. C. ..8.
.1* ijJ, «38, iftrlt.)

Bunplnnd JOQ

34J,H6,JW J,]S8,390
Itraaiiia (393) 404
liraun iM
ltr«li..'bLn ijo, iSs, »5.

British Museum 111, IIS
Hmntl 184, 18K-9, 196-?,

Buchholll 133
Buchnn nv
BufF aiul BaiEf 1^
BtiUtlitt Ailriit. vi. lo;
Buii«n ■«

BurdigAll (384) 406
Bumhani 183-4, J 'J- 3«>

C»Lciuii,flM64,7»
Calendiir 34
CalifoTDia (34r) 409
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Callixo 111 ; (»I4) fu
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MagdaleDi (jiS) 40;
Uuneiic dccl. 6;

Aimosphere 17J-6

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phi.Inpiphir 156

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Nice ObL 169
Kicbolu I. 13a
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Full text of "Stars and telescopes; a hand-book of popular astronomy, founded on the 9th ed. of Lynn's Celestial motions"

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