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A SKETCH:OF A

PHYSICAL DESCRIPTION OF THE UNIVERSE

BY

ALEXANDER VON Selntarhate terse:
TRANSLATED BY E. C. OTT

Nature vero rerum vis atque majestas in omnibus momentis fide caret, si quis modo partes
ejus ac non totam complectatur animo.—Plin., Hzs¢. Naz. lib. vii. c. 1.

VOL. III.

LONDON:

GEORGE BELL & SONS, YORK ST., COVENT GARDEN,
AND NEW YORK.

1892.

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CONTENTS OF VOL. III. FART

—_——

INTRODUCTION.

Historical Review of the attempts made with the object. of con-
sidering the Phenomena of the Universe as a Whole ............ 1—23

SPECIAL RESULTS OF OBSERVATIONS IN THE
DOMAIN OF COSMICAL PHENOMENA.

A. URANoLoGICAL PorRTION of the physical description of the
world. a. AsTROGNOSY RRR et? Morac WOPPPY |! ate)

I. The realms of space, and conjectures regarding that which
appears to occupy the space intervening between the heavenly
bodies ......... 53—50

II. Natural and telescopic vision, 51—96; Scintillation of the stars,
99—111; Velocity of light, 111—119; Results of eet:
metry, 119—137 ...S1—13”
III. Number, distribution, ‘na colour e the fixed stars, 138—
188 ; Stellar masses (stellar swarms), 188—193; The Milky
Way interspersed with a few nebulous spots, 193—203 fduekvis 138—203

IV. New stars, and stars that have vanished, 204—-217 ; Variable
stars, whose recurring periods have been determined, 217—
240; Variations in the intensity of the light of stars whose
periodicity is as yet uninvestigated, 240—247 .........eceees 204—247

V. Proper motion of the fixed stars, 248—-252; Problematical
existence of dark cosmical bodies, 252—255; Parallax—
measured distances of some of the fixed stars, 255—264 ;
Doubts as to the assumption of a central body for the
whole sidereal heavens, 264—270 ..........ccccseseseccseccesesseseeecees 248—270

VI. Multiple, or double stars—Their number and reciprocal dis-
tances.—Period of revolution of two stars round a common

- centre of gravity 271—289
TABLES.

PHOCOMOUTIC Tables OF TtAIS...<..0svccsscensscssccocscnscccescoscccsosecccesscessedvecs 134- 137
Clusters of Stars ...........0.c00.00 SeRRNss VEbcicd tues wizcduaeu Genevieve 191—193
New Stars........ ee aS. EER Ot Se ARR” 2 en ae 209—217
I haces 233—240
Ee ete goalies Suan beers Naes'sbpbsess 262
“lements of Orbits of double eis SRE Se SERRE a ee a saath isis bald 28y

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SPECIAL RESULTS OF OBSERVATION

’ IN THE

DOMAIN OF COSMICAL PHENOMENA

INTRODUCTION.

In accordance with the object I have proposed to myself,
and which, as far as my own powers and the present state
of science permit, I have regarded as not unattainable, I
have, in the preceding volumes of Cosmos, considered Nature
in a twofold point of view. In the first place, I have
endeavoured to present her in the pure objectiveness of
external phenomena; and, secondly, as the reflection of
the image impressed by the senses upon the inner man, that
is, upon his ideas and feelings.

The external world of phenomena has been delineated under
the scientific form of a general picture of nature in her two
great spheres, the uranological and the telluric or terrestrial.
This delineation begins with the stars, which glimmer amidst
nebule in the remotest realms of space, and passing from our
planetary system to the vegetable covering of the earth,
descends to the minutest organisms which float in the atmo-
sphere, and are invisible to the naked eye. In order to give ‘lue
prominence t.» the consideration of the existence of ono
common bond encircling the whole organic world, of the control
of eterral laws, and of the causal connexion, as far as yet
known to us, of whole groups of phenomena, it was necessary
~ avoid the accumulation of isolated facts. This precaution

VoL, III. B

2 COSMOS.

seemed especially requisite where, in addition to the dynamic
action of noving forces, the powerful influence of a specific
difference of matter manifests itself in the terrestrial por-
tion of the universe. The problems presented to us in the
sidereal, or uranological, sphere of the Cosmos, are, consi-
dering their nature, in as far as they admit of being ob-
served, of extraordinary simplicity, and capable, by means
of the attractive force of matter and the quantity of its mass,
of being submitted to exact calculation in accordance with the
theory of motion. If, as I believe, we are justified in regard-
ing the revolving meteor-asteroids (aérolites) as portions of our
} janetary system, their fall upon the earth constitutes the sole
means by which we are brought in contact with cosmical sub-
stances of a recognisable heterogeneity.’ I here refer to the
cause which has hitherto rendered terrestrial phenomena
less amenable to the rules of mathematical deduction than
those mutually disturbing and re-adjusting movements of the
cosmical bodies, in which the fundamental force of homo-
geneous matter is alone manifested.

I have endeavoured, in my delineation of the earth, to arrange
natural phenomena in such a manner as to indicate their causal
connexion. In describing our terrestrial sphere, I have consi-
dered its form, mean density, electro-magnetic currents, the
processes of polar light, and the gradations according to which
heat increases with the increase of depth. The reaction of
the planet’s interior on its outer crust implies the existence of
volcanic activity ; of more or less contracted circles of waves of
commotion (earthquake waves), and their effects, which are not
always purely dynamic; and of the eruptions of gas, of mud,
and of thermal springs. The upheaval of fire-erupting moun-
tains must be regarded as the highest demonstration of the
inner terrestrial forces. We have therefore depicted volcanoes,
both central and chain formations, as generative no less than as

+ Cosmos, vol. i. pp. 45-47, 125. “

INTRODUCTION. S

destructive agents, and as constantly forming before our eyes
for the most part periodic rocks (rocks of eruption); we
have likewise shown in contrast with this formation how sedi-
mentary rocks are in the course of precipitation from fluids,
which hold their minutest particles in solution or suspension.
Such a comparison of matter still in the act of development
and solidification with that already consolidated in the form
of strata of the earth’s crust, leads us to the distinction of
geognostic epochs, and to a more certain determination of the
chronological succession of those formations in which lie
entombed extinct genera of animals and plants—the fauna
and flora of a former world, whose ages are revealed by the
order in which they occur. The origin, transformation,
and upheaval of terrestrial strata, exert, at certain epochs, an
alternating action on all the special characteristics of the
physical configuration of the earth’s surface; influencing
the distribution of fluids and solids, and the extension and
articulation of continental masses in a horizontal and vertical
direction. On these relations depend the thermal conditions
of oceanic currents, the meteorological processes in the aérial
investment of our planet, and the typical and geographical dis-
tribution of organic forms. Sucha reference to the arrangement
of telluric phenomena presented in the picture of nature,
will, I think, suffice to show that the juxtaposition of great,
and apparently complicated, results of observation, facilitates
our insight into their causal connection. Our impressions of
nature will, however, be essentially weakened, if the picture
fail in warmth of colour by the too great accumulation of
minor details.

In a carefully-sketched representation of the phenomena
of the material world, completeness in the enumeration of
individual features has not been deemed essential, neither
does it seem desirable in the delineation of the reflex
of external nature on the inner man. Here it was

Bz

4 COSMOS.

necessary to observe even stricter limits. The boundless
domain of the world of thought, enriched for thousands of
years by the vigorous force of intellectual activity, exhibits,
among different races of men, and in different stages of
civilization, sometimes a joyous, sometimes a melancholy tone
of mind ;? sometimes a delicate appreciation of the beautiful,
sometimes an apathetic insensibility. The mind of man is
first led to adore the forces of nature and certain objects of
the material world; at a later period it yields to religious
impulses of a higher and purely spiritual character.* The
inner reflex of the outer world exerts the most varied
influence on the mysterious process of the formation of
language,‘ in which the original corporeal tendencies, as well
as the impressions of surrounding nature, act as powerful
concurring elements. Man elaborates within himself the
materials presented to him by the senses, and the products
of this spiritual labour belong as essentially to the domain of
the Cosmos as do the phenomena of the external world.

As a reflected image of Nature, influenced by the crea-
tions of excited imagination, cannot retain its truthful purity,
there has arisen besides the actual and external world, an
ideal and internal world, full of fantastic, and partly sym-
bolical myths, heightened by the introduction of fabulous
animal forms, whose several parts are derived from the
organisms of the present world, and sometimes even from the
relics of extinct species. Marvellous flowers and trees spring
from this mythic soil, as the giant ash of the Edda-Songs,

* Cosmos, vol.1. pp. 8-5; vol. ii. pp. 376 and 456.

§ Itd., vol. ii. pp. 392-396, and 411-415.

‘ -Jbid., vol. i. pp. 8366-869; vol. ii. pp. 473-478.

* M. von Olfers Ueberreste vurweltlicher Riesenthere in
Besehung auf Ostasiatische Sagen in the Abh. der Berl. Akad.,
1832, s. 51. On the opinion advanced by Empedocles
regarding the cause of the extinction of the earliest anima]
forms, see Hegel’s Geschichte der Philosaphre, bd. ii. s. 344.

»

INTRODUCTION. 5

the world-tree, Yggdrasil, whose branches tower above the
heavens, while one of its triple roots penetrates to the
“foaming cauldron springs” of the lower world. Thus the
cloud-region of physical myths is filled with pleasing or
with fearful forms, according to the diversity of character
in nations and climates ;/and these forms are preserved for
centuries in the intellectual domain of successive generavions.

If the present work does not fully bear out its title, the
adoption of which I have myself designated as bold and
inconsiderate, the charge of incompleteness applies especially
to that portion of the Cosmos which treats of spiritual life;
that is, the image reflected by external nature on the inner
world of thought and feeling. In this portion of my work
I have contented myself with dwelling more especially upon
those objects which lie in the direction of long-cherished
studies; on the manifestation of a more or less lively appre-
ciation of nature in classical antiquity and in modern times ;
on the fragments of poetical descriptions of nature, the
colouring of which has been so essentially influenced by indi-
viduality of national character, and the religious monotheistic
view of creation; on the fascinating charm of landscape-
painting ; and on the history of the contemplation of the physi-
cal universe, that is, the history of the recognition of the uni-
verse as a whole, and of the unity of phenomena,—a reccgnition
gradually developed during the course of two thousand years.

In a work of so comprehensive a character, the object of
which is to give ascientific, and at the same time an animated
description of nature, a first imperfect attempt must rather
lay claim to the merit of inciting than to that of satisfying

* See, for the world-tree Yggdrasil, and the rushing (foam-
ing) cauldron-spring Hvergelmir, the Deutsche Mythologie
of Jacob Grimm, 1844, s. 530, 756; also Mallet’s Northern
Antiquities, (Bohn’s edition), 1847, pp. 410, 489, and 492
and frontispiece to ditto

G CUSMOS,

inquiry. .4 Book of Nature, worthy of its exalted title, can
never be accomplished until the physical sciences, notwith-
standing their inherent imperfectibility, shall, by their gradual
development and extension, have attained a higher degree of
advancement, and until we shall have gained a more extended
knowledge of the two grand divisions of the Cosmos,—the
external world, as made perceptible to us by the senses;
and the inner, reflected intellectual world.
IT think I have here sufficiently indicated the reasons
which determined me not to give greater extension to the
yeneral picture of nature. It remains for this third and last
volume of my Cosmos, to supply much that is wanting in the
previous portions of the work, and to present those results
of observation on which the present condition of scientifie
opinion is especially grounded. I shall here follow a similar
mode of arrangement to that previously adopted, for the
reasons which I have advanced, in the delineation of nature.
But before entering upon the individual facts on which special
departments of science are based, I would fain offer a few
more general explanatory observations. The unexpected
indulgence with which my undertaking has been received by
a large portion of the public, both at home and abroad,
renders it doubly imperative that I should once more define,
as distinctly as possible, the fundamental ideas on which the
whole work is based, and say something in regard to those
demands which I have not even attempted to satisfy, because,
according to my view of empirical—i. e., experimental—
science, they did not admit of being satisfied. These explana-
tory observations involuntarily associate themselves with his-
torical recollections of the earlier attempts made to discover
the one universal idea to which all phenomena, in their causak
connection, might be reduced, as to a sole principle.
The fundamental principle’ of my work on the Cosmos, a

7 Cosmos, vol. i. pp. 28-31, and 51-60.

‘

INTRODUCTION. 7

enunciated by me more than twenty years ago, in the French
and German lectures I gave at Paris and Berlin, compre-
hended the endeavour to combine all cosmical phenomena
in one sole picture of nature; to show in what manner the
common conditions, that is to say, the great laws, by which
individual groups of these phenomena are governed, have
been recognized; and what course has been pursued in ascend-
ing from these laws to the discovery of their causal con-
nexion. Such an attempt to comprehend the plan of the
universe—the order of nature—must begin with a genera~-
lization of particular facts, and a knowledge of the con-
ditions under which physical changes regularly and periodi-
cally manifest themselves; and must conduct to the thoughtful
consideration of the results yielded by empirical observation,
but not to “‘a contemplation of the universe based on specu-
lative deductions and development of thought alone, or to a
theory of absolute unity independent of experience.” Weare,
I here repeat, far distant from the period when it was thought
possible to concentrate all sensuous perceptions into the.
unity of one sole idea of nature. The true path was indicated
upwards of a century before Lord Bacon’s time, by Leonardo
da Vinci, in these few words: ‘“‘ Cominciare dall esperienza
e per mezzo di questa scoprirne la ragione .”*—‘‘ Commence
by experience, and by means of this discover the reason.” In
many groups of phenomena we must stil] content ourselves
with the recognition of empirical laws; but the highest and
more rarely attained aim of all natural inquiry must ever be
the discovery of their causal connexion.® ‘Lhe most satisfactory

8 Op. cit. vol. i. p. 661.

* In the Introductory Observations, in Cosmos, v. i. p. 30,
it should not have been generally stated that ‘“‘the ultimate
object of the experimental sciences is to discover laws, and to
trace their progressive generalization.” The clause ‘in
many kinds of phenomena,” should have been added. The
caution with which I have expressed myself in the 2nd

& cosifos,

and distinct evidence will always appear where the laws
of phenomena admit of being referred to mathematical prin-
ciples of explanation. Physical cosmography constitutes
merely in some of its parts a cosmology. The two expres-
sions cannot yet be regarded as identical. The great and
solemn spirit that pervades the intellectual labour, of which
the limits are here defined, arises from the sublime conscious-
ness of striving towards the infinite, and of grasping all that is
- revealed to us amid the boundless and inexhaustible fulness.
of creation, development, and being.

This active striving which has existed in all ages, must
frequently and under various forms, have deluded men into the
idea, that they had reached the goal, and discovered the prin-:
ciple which could explain all that is variable in the organic:

vol. of this work (p. 694), on the relation borne by Newton _
to Kepler, cannot, I think, leave a doubt that I clearly
distinguish between the discovery and interpretation of
natural laws, ¢. e., the explanation of phenomena. I there
said of Kepler: ‘The rich abundance of accurate observations
furnished by Tycho Brahe, the zealous opponent of the
Copernican system, laid the foundation for the discovery
of those eternal laws of the planetary movements which
prepared imperishable renown for the name of Kepler, and
which, interpreted by Newton, and proved to be theoretically
and necessarily true, have been transferred into the bright
and glorious domain of thought, as the intellectual recognition
of nature.’ Of Newton, I said (p. 736): ‘‘ We close it
(the great epoch of Galileo, Kepler, Newton, and Leibnitz, |
with the figure of the earth as it was then recognized from
theoretical conclusions. Newton was enabled to give an
explanation of the system of the universe, because he suc-
ceeded in discovering the force from whose action the laws
of Kepler necessarily result.” Compare on this subject (‘On
Laws and Causes”) the admirable remarks in Sir John Hers-
chel’s address at the fifteenth meeting of the British Associa-
tion at Cambridge, 1845, p. xlii.; and Edinb. Rev. vol. 87,
1848, pp. 180-183.

»

INTRODUCTION. 9

world, and all the phenomena revealed to us by sensuous
perception. After men had for a long time, in accordance
with the earliest ideas of the Hellenic people, venerated the
agency of spirits, embodied in human forms,” in the creative,
changing, and destructive processes of nature; the germ of a
scientific contemplation developed itself in the physiological
fancies of the Ionic school. The first principle of the origin
of things, the first principle of all phenomena, was referred
to two causes“—either to concrete material principles, the so-
called elements of Nature, or to processes of rarefaction and
condensation, sometimes in accordance with mechanical, some-
times with dynamic views. The hypothesis of four or five
materially differing elements, which was probably of Indian
origin, has continued from the era of the didactic poem of
Empedocles, down to the most recent times, to imbue all opi-
nions on natural philosophy—a primeval evidence and monu-
ment of the tendency of the human mind to seek a generaliza-
tion and simplification of ideas, not only with reference to
the forces, but also to the qualitative nature of matter.

In the latter period of the development of the Ionic phy-
siology, Anaxagoras of Clazomenz advanced from the pos-
tulate of simply dynamic forces of matter, to the idea, of a
spirit independent of all matter, uniting and distributing the

12 In the memorable passage (Metaph. xii. 8. p. 1074,
Bekker.) in which Aristotle speaks of “‘ the relics of an earlier |
acquired and subsequently lost wisdom,” he refers with extra-
ordinary freedom and significance to the veneration of phy-
sical forces, and of gods in human forms: “ much,” says
he, “has been mythically added for the persuasion of the
multitude, as also on account of the laws and for other useful
ends.”

1 The important difference in these philosophical direc-
tions rpémo, is clearly indicated in Arist. Phys. Auseult.
1. 4, p. 187, Bekk. (Compare Brandis in the Rhem, Museum
Sur Philologie, Jahrg. iii. s. 105.) '

10 COSMOS.

hemogeneous particles of which matter is composec ‘The
world-arranging Intelligence (vos) controls the continuously
progressing formation of the world, and is the primary source
of all motion, and therefore of all physical phenomena. Anax-
agoras explains the apparent movement of the heavenly bodies
from east to west by the assumption of a centrifugal force,
on the intermission of which, as we have already observed,
the fall of meteoric stones ensues. This hypothesis indicates
the origin of those theories of rotatory motion which more
than two thousand years afterwards attained consider-
able cosmical importance from the labours of Descartes,
Huygens, and Hooke. It would be foreign to the present
work, to discuss whether the world-arranging Intelligence of
the philosopher of Clazomenze indicates’ the godhead itself, or
the mere pantheistic notion of a spiritual principle animating
all nature.

In striking contrast with these two divisions of the Ionic
school, is the mathematical symbolism of the Pythagoreans,
which in like manner embraced the whole universe. Here,
in the world of physical phenomena cognizable by the senses,
the attention is solely directed to that which is normal in
configuration (the five elementary forms), to the ideas of

% Cosmos, vol. i. pp. 122, 128, (note), and vol. ii. p. 690
(and note). Simplicius, in a remarkable passage, p. 491,
most distinctly contrasts the centripetal with the centrifugal
force. He there says, ‘‘ the heavenly bodies do not fall in
consequence of the centrifugal force being superior to the
inherent falling force of bodies and to their downward ten-
dency.”’ Hence, Plutarch in his work, De facie in orbe Lune,
p. 923, compares the moon, in consequence of its not falling
to the earth, to ‘‘a stone in asling.” For the actual signifi-
eation of the meptxopynots of Anaxagoras. compare Schaubach in
Anaxag. Clazom. Fragm. 1827, pp. 107-109. ie

% Schaubach, Op. cet. pp. 151-156, and 185-189. Plants
are likewise said to be animated by the intelligence, pots ;

tat. de Plant. i. p. 815, Bekk.

INTRODUCTION. Il

numbers, measure, harmony, and contrarieties. Things are
reflected in numbers which are, as it were, an imitative repre-
sentation (minnows) of them. The boundless capacity for repe-
tition, and ‘the illimitability of numbers, is typical of the cha-
racter of eternity and of the infinitude of nature. The essence
of things may be recognized in the form of numerical rela-
tions: their alterations and metamorphoses as numerical
combinations. Plato, in his Physics, attempted to refer the
nature of all substances in the universe, and their different
stages of metamorphosis, to corporeal forms, and these again
to the simplest triangular plane figures. But in reference
to ultimate principles (the elements, as it were, of the
elements), Plato exclaims, with modest diffidence, “God
alone, and those whom he loves among men, know what
they are.” Such a mathematical mode of treating physical
phenomena, together with the development of the atomic
theory, and the philosophy of measure and harmony, have
long obstructed the development of the physical sciences, and
misled fanciful inquirers into devious tracks, as is shown in
the history of the physical contemplation of the universe.
“There dwells a captivating charm, celebrated by all anti-
quity, in the simple relations of time and space, as manifested
in tones, numbers, and lines.’’®

The idea of the harmonious government of the universe
reveals itself in a distinct and exalted tone throughout the
writings of Aristotle. All the phenomena of nature are de-
picted in the Physical Lectures (Auscultationes Physica) as
moving, vital agents of one general cosmical force. Heaven and

-™ Compare on this portion of Plato’s mathematical physics,
Béckh De platonico syst. celestium globorum, 1810 et 1811;
Martin, Etudes sur le Timée, tom. ii. pp. 234-242; and
Brandis in the Geschichte der Griechisch-Romischen Philo-
sophie, Th. ii. Abth. i. 1844, § 375.

4’ Cosmos, vol. ii. p. 736, note; compare also Gruppe
Ueber die Fragmente des Archytas, 1840, s. 33.

12 COSMOS,

nature, (the telluric sphere of phenomena,) depend upon the
‘**unmoved motus of the universe.””"* The ‘ ordainer’”’ and the
ultimate cause of all sensuous changes must be regarded as
something non-sensuous and distinct from all matter." Unity
in the different expressions of material force is raised to the
rank of a main principle, and these expressions of force are
themselves always reduced to motions. Thus we find already
in “the book of the soul’’® the germ of the undulatory
theory of light. The sensation of sight is occasioned by a
vibration—a movement of the medium between the eye and
the object seen—and not by emissions from the object or
the eye.. Hearing is compared with sight, as sound is like-
wise a consequence of the vibration of the air.

Aristotle, while he teaches -men to investigate generalities
in the particulars of perceptible unities, by the force of
reflective reason, always includes the whole of nature, and

% Aristot. Polit. vii. 4, p. 1826, and. Metaph. xii. 7, p.
1072, 10 Bekk. and xii. 10, p. 1074-5. The pseudo-
Aristotelian work de Mundo, which Osann ascribed to Chry-
sippus (see Cosmos, vol. il. p. 380) also contains (cap. 6,
p- 397) a very eloquent passage on the world-orderer and
world-sustainer.

" The proofs are collected in Ritter, History of Philosophy
(Bohn, 1838-46), Vol. 3, p. 180 e¢ seg.

8 Compare Aristot. de Anima, il. 7 pag. 419. In this
passage the analogy with sound is most distinctly expressed ;
although in other portions of his writings Aristotle has greatly
modified his theory of vision. Thus in de Jnsomniis, cap. 2,
p- 459, Bekker., we find the following words :—* It is evident
that sight is no less an active than a passive agent, and that
vision not only experiences some action from the air (the me-
dium), but itself also acts upon the medium.” He adduces in
evidence of the truth of this proposition, that a new and very
pure metallic mirror will, under certain conditions, when
looked at by a woman, retain on its surface cloudy specks
that cannot be removed without difficulty. Compare also
Martin, Etudes sur le Timée de Platon. tom. ii. pp. 159-168.

s

INTRODUCTION. 13

the in‘e-nal connexion not ouly of forces, but also of organi¢
forms. In his book on the parts (organs) of animals, he clearly
intimates his belief that throughout all animate beings there
is a seale of gradation, in which they ascend from lower
to higher forms. Nature advances in an uninterrupted pro-
gressive course of develépment, from the inanimate or “ ele-
mentary” to plants and animals; and “lastly, to that which,
though not actually an animal, is yet so nearly allied to one,
that on the whole there is little difference between them.” ™
In the transition of formations, ‘‘the gradations are almost
imperceptible.”* The unity of nature was to the Stagirite
the great problem of the Cosmos. ‘In this unity,” he
observes, with singular animation of expression, ‘‘ there is
nothing unconnected or out of place, as in a bad tragedy.”

The endeavour to reduce all the phenomena of the universe
to one principle of explanation, is manifest throughout the
physical works of this profound philosopher and accurate ob-
server of nature; but the imperfect condition of science, and
ignorance of the mode of conducting experiments, ?.e., of calling
forth phenomena under definite conditions, prevented the com-
prehension of the causal connection of even small groups of phy-
sical processes. All things were reduced to the ever-recurring

1? Aristot de partibus Anim., lib. iv. cap. 5, pag. 681,
lin. 12. Bekker.

* Aristot. Hist. Anim., lib. ix., cap. 1, pag. 588, lin. 10-24.
Bekker. When any of the representatives of the four ele-
ments in the animal kingdom on our globe fail, as for instance
those which represent the element of the purest fire, the
intermediate stages may perhaps be found to occur in the
moon (Biese, Die Phil. des Aristoteles, bd. ii. s. 186). It is
singular enough, that the Stagirite should seek in another
planet those intermediate links of the chain of organised
beings which we find in the extinct animal and vegetable
forms of an earlier world.

* Aristot. Metaph. lib. xiii. cap. 3, pag. 1090, lin. 20,
Bekker.

14 COSMOS.

contrasts of heatand cold, moisture and dryness, primary density
and rarefaction—even to an evolution of alterations in the or-
ganic world by a species of inner division (antiperistasis) which
reminds us of the modern hypothesis of opposite polarities and
the contrasts presented by + and —.” The so-called solutions
of the problems only reproduce the same facts in a disguised
form, and the otherwise vigorous and concise style of the
Stagirite degenerates in his explanations of meteorological
or optical processes, into a self-complacent diffuseness and a
somewhat Hellenic verbosity. As Aristotle’s inquiries were
directed almost exclusively to motion, and seldom to differ-
ences.in matter, we find the fundamental idea, that all telluric
natural phenomena are to be ascribed to the impulse of the
movement of the heavens—the rotation of the celestial sphere
—constantly recurring, fondly cherished and fostered,*® but
never declared with absolute distinctness and certainty.

* The dvrurepioracis of Aristotle plays an important part in
all his explanations of meteorological processes ; so also in the
works de generatione et interitu, lib. ii. cap. 8, p. 380: in the
Meteorologicis, lib. i. cap. 12, and lib. iii. cap. 8, p. 8372, and
in the Probleme (lib. xiv. cap. 8, lib. viii, no. 9, p. 888, and
lib. xiv. no. 8, p. 909,) which are at all events based on
Aristotelian principles. In the ancient polarity hypothesis
kat ayvtimepioraow similar conditions attract each other, and
dissimilar ones (+ and —)-repel each another in opposite
directions. (Compare Ideler, Meteorol. veterum G'rec. et Rom.
1832, p. 10.) The opposite conditions instead of being
destroyed by combining together, rather increase the tension.
The Wvxpdr increases the @epydv; as inversely ‘in the for-
mation of hail the surrounding heat makes the cold body
still colder as the cloud sinks into warmer strata of air.”
Aristotle ‘explains by his antiperistatic process and the
polarity of heat, what modern physics have taught us to refer
to conduction, radiation, evaporation, and changes in the
capacity of heat. See the able observations of Paul Erman in
the dbhandl. der Berliner Akademie auf das Jahr. 1825,s8. 128.

* « By the movement of the heavenly sphere, all that is

>

INTRODUCTION. 18

The impulse to which I refer, indicates only the com-
munication of motion as the cause of all terrestrial phe-
nomena. Pantheistic views are excluded; the Godhead
is considered as the highest ‘‘ ordering unity, manifested
in all parts of the universe, defining and determining the
nature of all formations, and holding together all things as an
absolute power.” The main idea and these teleological
views are not applied to the subordinate processes of inor-
ganic or elementary nature, but refer specially to the higher
organizations * of the aninral and vegetable world. It is
worthy of notice, that in these theories, the Godhead is
attended by a number of astral spirits, who (as if acquainted
with perturbations and the distribution of masses) main-
tain the planets in their eternal orbits.* The stars here

unstable in natural bodies, and all terrestrial phenomena are
produced.”’ Aristot. Meteor. i. 2, p. 339, and de gener. et
corrupt. 11.10, p. 336.

* Aristot. de Celo, lib. i. c. 9, p. 279, lib. ii. c. 3, p. 286;
lib. ii. c. 18, p. 292. Bekker. (Compare Biese, bd. i. s.352-1,
357.)

*® Aristot. Phys. Auscult. lib. ii. c. 8, p. 199; de Anima,
lib. iii. ec. 12, p. 484; de Animal. generat. lib. v. c. 1, p. 778.
Bekker.

* See the passage in Aristot. Meteor. xii. 8, p. 1074, of
which there is a remarkable elucidation in the Commentary of
Alexander Aphrodisiensis. The stars are not inanimate bodies
but must be regarded as active and living beings. (Aristot.
de Celo, lib. ii. cap. 12, p. 292.) They are the most
divine of created things; Ta Oedrepa rév havepov. Aristot.
de Celo, lib. i. cap. 9, p. 278, and lib. ii. cap. 1, p. 284.) In the
small pseudo-Aristotelian work, de Mundo, which frequently
breathes a religious spirit in relation to the preserving
almightiness of God, (cap. 6, p. 400,) the high sether is also
called divine, (cap. 2, p. 8392). That which the imaginative
Kepler calls moving spirits (anime motrices) in his work,
Mysterium cosmographicum (cap. 20, p. 71) is the distorted idea
of a force (vrtus), whose main seat is in the sun (anima

16 COSMOS,

reveal the image of the divinity in the visible world.
We do not here refer, as its title might lead to suppose, te
the little pseudo-Aristotelian work, entitled the ‘‘ Cosmos,”
undoubtedly a Stoic production. Although it describes the
heavens and the earth, and oceanic and aerial currents, with
much truthfulness, and frequently with rhetorical animation
and picturesque colouring, it shows no tendency to refer
cosmical phenomena to general physical principles sare on
the properties of matter.

I have purposely dwelt at length on the most brilliant
period of the Cosmical views of antiquity, in order to contrast
the earliest efforts made towards the generalization of ideas,
with the efforts of modern times. In the intellectual movement
of centuries, whose influence on the extension of Cosmical
contemplation has been defined in another portion of the
present work,” the close of the thirteenth and the beginning
of the fourteenth century were specially distinguished; but
the Opus majus of Roger Bacon, the Mirror of Nature
of Vincenzo de Beauvais, the Physical Geography (Liber
cosmographicus) of Albertus Magnus, the Picture of the
World (Imago Mundt) of Cardinal Petrus d’Alliaco (Pierre
d’Ailly) are works, which, however powerfully they may
have influenced the age in which thev were written, do not
fulfil by their contents the promise of their titles. Among
the Italian opponents of Aristotle’s physics, Bernardino
Telesio of Cosenza is designated the founder of a rational
science of nature. Allthe phenomena of inert matter are con-
sidered by him as the effects of two incorporeal principles (agen-
cies or forces) —heata»d cold. All forms of organic life—*‘ani-

mundi), and which is decreased by distance, in accordance
with the laws of light, and impels the planets in elliptic orbits
(Compare Apelt, Hpochen der Gesch. der easter: bd, 1
8. 274. )

71 Cosmos, vol. il. p. 615-628.

_

INTRODUCTION, 17

mated” plants and animals—are the effect of these two vver
divided forces, of which the one, heat, specially appertuins to
the celestial. and tae other, cold, to the terrestriai sphere.
With yet more unbridled fancy, but with a profound spirit of
enquiry, Giordano Bruno of Nola attempted to comprehend
the whole universe, in three works,™ entitled, De la causa
Principio e Uno; Contemplationi circa lo Infinito, Universo
—¢ Mondi innumerabili; and De Minimo et Maximo. In the
‘natural philosophy of Telesio, a contemporary of Coperni-
cus, we recognise at all events the tendency to reduce the
changes of matter to two of its fundamental forces, which,
although “‘ supposed to act from without,” yet resemble the
fundamental forces of attraction and repulsion in the dyna-
mic theory of nature of Boscovich and Kant. The cosmical
views of the philosopher of Nola are purely metaphysical, and
do not seek the causes of sensuous phenomena in matter
itself, but treat of “the infinity of space, filled with self-illu-
mined worlds, of the animated condition of those worlds, and
of tne relations of the highest intelligence—God—to the
universe.”
Scantily endowed with mathematical knowledge, Giordano
Bruno continued nevertheless to the period of his fearful mar-
tyrdom™ an enthusiastic admirer of Copernicus, Tycho Brahe,

*® Compare the acute and learned commentary on the works
of the Philosopher of Nola in the treatise, Jurdano Bruno par
Christian Bartholméss, tom. ii. 1847, pp. 129, 149, and 201.

” He was burnt at Rome on the 17th of February, 1600,

‘pursuant to the sentence “ut quam clementissime et
citra sanguinis effusionem puniretur.’’ Bruno was imprisoned
six years in the Piomdi, at Venice, and two years in the In-
quisition at Rome. When the sentence of death was an-
nounced to him, Bruno, calm and unmoved, gave utterance to

the following noble expression, ‘‘ Majori forsitan cum timore
sententiam in me fertis quam ego accipiam.’’ When a fugitive
from Italy, in 1580, he taught at Geneva, J.yons, Toulouse,

VOL. III. fe)

iy

18 COSMOS,

ani Kepler. He was contemporary with Galileo, but did
not live to see the invention of the telescope by Hans Lipper-
srey and Zacharias Jansen, and did not therefore witness
the discovery of the “lesser Jupiter world,” the phases of
Venus, and the nebule. With bold confidence in what he
terms the lume interno, ragione naturale, altezza dell’ intelletto
(foree of intellect), he indulged in happy conjectures re-
garding the movement of the fixed stars, the planetary
nature of comets, and the deviation from the spherical form
observed in the figure of the earth. Greek antiquity is
also replete with uranological presentiments of this nature,
which were realised in later times.

In the development of thought on cosmical relations, of which
the main forms and epochs have been already enumerated, Kep-
ler approached the nearest to a mathematical application of the
theory of gravitation, more than seventy-eight years before the
appearance of Newton’s immortal work, Principia Philosophia
Naturalis. For while the eclectic Simplicius only expressed in
general terms “‘ that the heavenly bodies were sustained from fall-
ing in consequence of the centrifugal force being superior to the
inherent falling force of bodies and to the downward traction ;”
while Joannes Philoponus, a disciple of Ammonius Hermeas,

—_ Se

Paris, Oxford, Marburg, Wittenberg (which he calls the
Athens of Germany), Prague, and Helmstedt, where, in 1589,
‘xe completed the scientific instruction of Duke Henry Julius
of Brunswick-Wolfenbiittel. Bartholméss, tom. i. pp. 167
-178. He also taught at Padua subsequently to 1592.

* Bartholméss, tom. ii. pp. 219, 232, 870. Bruno carefully
collected all the separate observations made on the celestial
phenomenon of the sudden appearance, in 1572, of a new star
in Cassiopeia. Much discussion has been directed in modern
times to the relation existing between Bruno, his two
Calabrian fellow-countrymen, Bernardino Telesio and Thomas
Campanella. and the platonic cardinal, Nicolaus Nrebs of
Cusa; see Cosmos, p. 691, note.

INTRODUCTION. 19

ascribed the movement of the celestial bodies to “a primitive
impulse, and the continued tendency to fall;” and while,
as we have already observed, Copernicus defined only the
general idea of gravitation, as it acts in the sun, as the centre of
the planetary world, in the earth and in the moon, using these
memorable words, ‘‘Gravitatem non aliud esse quam appe-
tentiam quandam naturalem partibus inditam a divina provi-
dentia opificis universorum, ut in unitatem integritatemque
suam sese conferant, in formam globi coéuntes;’’ Kepler in
his introduction to the book, De Stella Marits,™ was the first
who gave numerical calculations of the forces of attraction
reciprocally exercised upon each other, according to their rela-
tive masses, by the earth and moon. He distinctly adduces the
tides as evidence * that the attractive force of the moon /virtus

# «Si duo lapides in aliquo loco Mundi collocarentur pro-
pinqui invicem, extra orbem virtutis tertii cognati corporis ;
ili lapides ad similitadinem duorum Magneticorum corporum
coirent loco intermedio, quilibet accedens ad alterum tanto
intervallo, quanta est alterius mo/es incomparatione. Si luna
et terra non retinerentur vi animali (!) aut alia aliqua
eequipollente, queelibet in suo circuitu, Terra adscenderet ad
Lunam quinquagesima quarta parte intervalli, Luna descen-
deret ad Terram quinquaginta tribus circiter partibus inter-
valli; ibi jungerentur, posito tamen quod substantia utriusque
sit unius et ejusdem densitatis.” Kepler, Astronomia nova,
seu Physica celestis de Motibus Stelle Martts, 1609. Introd.
fol. v. On the older views regarding gravitation, see Cosmuvs,
vol. ii. p. 691.

® «Si Terra cessaret attrahere ad se aquas suas, aque
marine omnes elevarentur et in corpus Lune influerent.
Orbis virtutis tractorie, quee est in Luna, porrigitur usque ad
terras, et prolectat aquas quacunque in verticem loci incidit
sub Zonam torridam, quippe in occursum suum quacunque in
verticem loci incidit, insensibiliter in maribus inclusis, sensi-
biliter ibi ubi sunt latissimi alvei Oceani propinqui, aquisque
spaviosa reciprocationis libertas.” (Kepler, 1.c.) ‘ Undasa
Luna trahi ut ferrum a Magnete.” .. . . Keplert Harmonice

c 2

90 COSMOS

dractoria) extends to the earth; and that this force, similar to
that exerted by the magnet on iron, would deprive the earth
of its water if the former should cease to attract it. Unfor-
tunately this great man was induced ten years afterwards, in
1619, probably from deference to Galileo, who ascribed the
ebb and flow of the ocean to the rotation of the earth, to re-
nounce his correct explanation, and depict the earth in the
Harmonice Mundi as a living monster, whose whale-like mode
of breathing occasioned the rise and fall of the ocean in re-
curring periods of sleeping and waking, dependant on solar
time. When we remember the mathematical acumen that
pervades one of the works of Kepler, and of which Laplace has
already made honourable mention,® it is to be lamented that
the discoverer of the three great laws of all planetary motion
should not have advanced on the path whither he had been led
by his views on the attraction of the masses of cosmical bodies.

Mundi, libri quinque, 1619, lib. iv. cap. 7, p. 162. The same
work which presents us with so many admirable views, amon
others, with the data of the establishment of the third law (that
the squares of the periodic times of two planets are as the
cubes of their mean distances), is distorted by the wildest
flights of fancy on the respiration, nutrition, and heat of the
earth-animal, on the soul, memory (memoria anime Terre),
and creative imagination (anime Telluris imaginatio) of this —
monster. This great man was so wedded to these chimeras,
that he warmly contested his right of priority in the views
regarding the earth-animal, with the mystic author of the
Macrocosmos, Robert Fludd, of Oxford, who is reported to have
participated in the invention of the thermometer. (Harm.
Mundi, p. 252.) In Kepler’s writings, the attraction of masses
is often confounded with magnetic attraction. ‘‘ Corpus solis
esse magneticum. Virtutem, que Planetas movet, residere
in corpore solis.” Stella Marts, pars i. cap. 32,34. Teo
each planet was ascribed a magnetic axis, which constantly
vointed to one and the same quarter of the heavens. (Apelt,
von. tepler's astron. Weltansicht, 1849, s. 738.
*® Compare Cosmos, p. 710 (and note).

x

INTRODUCTION. 91

Descartes, whc was encowed with greater versatility of
physical knowledge than Kepler, and who laid the foundation
ef many departments of mathematical physics, smdertook to
eomprise the whole world of phenomena, the heavenly sphere
and all that he knew concerning the animate and inanimate
parts of terrestrial nature, in a work entitled Trazté du Monde,
and also Summa Philosophie. The organisation of animals, and
especially that of man—a subject to which he devoted the
anatomical studies “of eleven years*—was to conclude the
work. In his correspondence with Father Mersenne, we
frequently find him complaining of his slow progress, and of the
difficulty of arranging so large a mass of materials. The Cosmos
which Descartes always called “his world,” (son monde) was
at length to have been sent to press at the close of the year
1633, when the report of the sentence passed by the Inquisition
at Rome on Galileo, which was first made generally known four
months afterwards, in October, 1633, by Gassendi and
Bouillaud, at once put a stop to his plans, and deprived pos-
terity of a great work, completed with much pains and infinite
eare. The motives that restrained him from publishing the
Cosmos were, love of peaceful retirement in his secluded
abode at Deventer, and a pious desire not to treat irreveren-
tially the decrees pronounced by the Holy Chair, against the
planetary movement of the earth.* In 1664, fourteen years
after the death of the philosopher, some fragments were first
printed under the singular title of Le Monde, ou Traité de la
Lumiére.* ‘The three chapters which treat of light, scarcely,

% See La Vie de M. Descartes, (par Baillet) 1691, P. 1,
p- 197, and Giuvres de Descartes, putliées par Victor Cousin,
tom. i. 1824, p. 101.

3% Lettres de Descartes au P. Mersenne, du 19 Nov. 1633,
ei du 5 Janvier 1634. (Baillet, P. 1. pp. 244-247.)

% The Latin translation bears the title, Mundus sive Dis-
sertatio de Lumine ut et de aliis Sensuum Oljectis primariis.
See Descartes, Opuscula gosthuma physica et mathematica,
Amst. 1704,

22 COSMOS.

howsver, constitute a fourth part cf the work; whilst those
sections which originally belonged to the Cosmos of Descartes,
and treated of the movement of the planets, and their distance
from the sun, of terrestrial magnetism, the ebb and flow of the
ocean, earthquakes, and volcanoes, have been transposed to
the third and fourth portions of the celebrated work, Principes
de la Pulosophie.

Notwithstanding its ambitious title, the Cosmotheoros of
Huygens, which did not appear till after his death, scarcely
deserves to be noticed in this enumeration of cosmological
efforts. It consists of the dreams and fancies of a great
man on the animal and vegetable worlds, of the most
remote cosmical bodies, and especially of the modifications
of form which the human race may there present. The reader
might suppose he were perusing Kepler’s Somnium <Astrono-
micum, or Kircher’s Iter Eataticus. As Huygens, like the
astronomers of our own day, denied the presence of air and
water in the moon,” he is much more embarrassed regarding

* «<Tunam aquis carere et aére: Marium similitudinew
in Luna nullam reperio. Nam regiones planas que montosis
multo obscuriores sunt, quasque vulgo pro maribus haberi
video et oceanorum mnominibus insigniri, in his ipsis,
longiore telescopio inspectis, cavitates exiguas Imesse com-
perio rotundas, umbris intus cadentibus; quod maris
superficiei convenire nequit; tum ipsi campi illi latiores
non prorsus equabilem superficiem preeferunt, cum diligen-
tius eas intuemur. Quod circa maria esse non possunt, sed
materia constare debent minus candicante, quam que est
partibus asperioribus in quibus rursus quedam viridiori
lumine ceeteras precellunt.” Hugenit Cosmotheoros, ed. alt.
1699, lib. 11, p. 114. Huygens conjectures however ‘that
Jupiter is agitated by much wind and rain, for “-ventorum
flatus ex illa nubium Jovialium mutabili facie cognoscitur,”’
(lib. i. p. 69). These dreams of Huygens, regarding the
inhabitants of remote planets, so unworthy of a man versed
in exact mathematics, have, unfortunately, been revived by
Emanuel Kant, in his admirable work Allgemeine Naturge
schichte ur” Theorie des Hienmels, 1755 (s. 173-192).

>

INTRODUCTION, 23

the existence of inhabitants in the moon, than of those in
the remoter planets, which he assumes to be “ surrounded with
vapours and clouds.”’

The immortal author of the Philosophie Naturalis Principia
Mathematica (Newton) succeeded in embracing the whole
uranological portion of the Cosmos in the causal connexion of
its phenomena, by the assumption of one all-controlling fun-
damental moving force. He first applied physical astronomy
to solve a great problem in mechanics, and elevated it to the
raak of a mathematical science. The quantity of matter in
every celestial body gives the amount of its attracting force; a
force which acts in an inverse ratio to the square of the distance,
and determines the amount of the disturbances, which not only
the planets but all the bodies in celestial space exercise on
each other. But the Newtonian theory of gravitation, so
worthy of our admiration from its simplicity and generality,
is not limited in its cosmical application to the uranologica.
sphere, but comprises also telluric phenomena, in directions
not yet fully investigated ; it affords the clue to the periodic
movements in the ocean and the atmosphere ; ® and solves the
problems of capillarity, of endosmosis, and of many chemi-
eal, electro-magnetic, and organic processes. Newton,®
even distinguished the attraction of masses, as manifested in
the motion of cosmical bodies and in the phenomena of

*% See Laplace (des oscillations de latmosphére, du flux
solaire et lunaire) in the Mécanique Céleste, livre iv. and in the
_ Exposition du Syst. du Monde, 1824, pp. 291-296.

*® Adjicere jam licet de spiritu quodam subtilissimo corpora
crassa pervadente et in lisdem latente, cujus vi et actionibus
particule corporum ad minimas distantias se mutuo aitrahunt
et contigue facte coherent. Newton, Princypra Phil. Nat.
(ed. Le Sueur et Jacquier, 1760) Schol. gen., t. ili. p. 676,
compare also Newton’s Opiicks, (ed. 1718). Query 81, pp.
305, 353, 367, 372. (Laplace, Syst. du Monde, p. 384, and
Cosmos, p. 44.)

24 COSMOK.

the tides, from molecular attraction, which acts at infinitely
small distances and in the closest contact.

Thus we see that among the various attempts which have been
made to refer: whatever is unstable in the sensuous world to
a single fundamental principle, the theory of gravitation is the
most comprehensive and the richest in cosmical results. It
is 1adeed true, that notwithstanding the brilliant progress that
has been made in recent times in steechiometry (the art of
calculating with chemical elements and in the relations of
volume of mixed gases) all the physical theories of matter have
not yet been referred to mathematically-determinable prin-
ciples of explanation. Empirical laws have been recognized,
and by means of the extensively diffused views of the atomic
or corpuscular philosophy, many points have been rendered
more accessible to mathematical investigation ; but owing tothe
unbounded heterogeneousness of matter and the manifold con-
ditions of aggregation of particles, the proofs of these empirical
laws cannot as yet by any means be developed from the theory
of contact-attraction, with that certainty which characterizes
the establishment of Kepler’s three great empirical laws derived
from the theory of the attraction of masses or gravitation.

At the time, however, that Newton recognized all move-
ments of the cosmical bodies to be the results of one and
the same force, he did not, like Kant, regard gravitation as an
essential property of bodies;® but considered it either as the

# Hactenus phenomena celorum et maris nostri pet vim
eravitatis exposui, sed causam gravitatis nondum assignavi.
Oritur utique hee vis a causa aliqua, que penetrat ad usque
centra solis et planetarum, sine virtutis diminutione; queque
agit non pro quantitate superficierum particularum, in quas
agit (ut solent causee mechanice), sed pro quantitate materie
solide.—Rationem harum gravitatis proprietatum ex phe-
nomenis nondum potui deducere et hypotheses non fingo.
Satis est quod gravitas revera existat et agat secundum leges
a nobis expositas. Newton, Principia Phil. Nat., p. 676.

.

INTRODUCTiON. 26

result of some higher and still unknown power, vr of ‘ the
centrifugal force of the ether, which fills the realms of space,
and is rarer within bodies, but increases in density outwards.
The latter view is set forth in detail in a letter to Robert
Boyle“ (dated February 28, 1678), which ends with the

“To tell us that every species of things is endowed with an
occult specific quality, by which it acts and produces manifest
effects, is to tell us nothing; but to derive two or three general
principles of motion from phenomena, and afterwards to tell
us how the properties and actions of all corporeal things follow
from those manifest principles, would be a very great step in
philosophy, though the causes of those principles were not yet
discovered: and therefore I scruple not to propose the prin-
ciples of motion, and leave their causes to be found out.”
Newton’s Opticks, p. 377. Ina previous portion of the same
work, at query 31, p. 351, he writes as follows: ‘ Bodies act
one upon another by the attraction of gravity, magnetism, and
electricity; and it is not improbable that there may be more
attractive powers than these. How these attractions may be
performed I do not here consider. What I call attraction
- may be performed by zmpulse, or by some other means unknown
tome. I use that word here to signify only in general any
force by which bodies tend towards one another, whatsoever
be the cause.”

4 «< ] suppose the rarer ether within bodies, and the denser
without them.”” Operum Newton, tomus iv. (ed. 1782, Sam.
Horsley,) p. 386. The above observation was made in refer-
ence to the explanation of the discovery made by Grimaldi of
_ the diffraction or inflection of light. At the close of Newton’s
letter to Robert Boyle, February 1678, p. 394, he says: “I
shall set down one conjecture more which came into my mind:
it is about the cause of gravity.” . . . . His correspondence
with Oldenburg (December 1675) shows that the great philo-
sopher was not at that time averse to the “ ether hypotheses.”’
According to these views, the impulse of material light causes
the ether to vibrate; but the vibrations of the ether alone,
which has some affinity to a nervous fluid, does not generate
light. In reference to the contest with Hooke, consult
Horsley, t iv. pp. 378-380.

26 COSMOS.

words, “I seek the cause of gravity in the ether.” Light
years afterwards, as we learn from a letter he wrote to Halley,
Newton entirely relinquished this hypothesis of the rarer and
denser ether.” Itis especially worthy of notice that in 1717,
nine years before his death, he should have deemed it necessary
expressly to sta‘e in the short preface to the second edition of
his Optics, that he did not by any means consider gravity as
an ‘essential property of bodies” ;“* whilst Gilbert, as early

® See Brewster's Life of Sir Isaac Newton, pp. 308-805.

“ Newton’s words “not to take gravity for an essential
property of bodies” in the ‘‘ Second Advertisement” contrast
with his remarks on the forces of attraction and repulsion,
which he ascribes to a// molecular particles, in order, according
to the theory of emission, to explain the phenomena of the
refraction and repulsion of the rays of light from reflecting
surfaces ‘* without their actual contact.” (Newton, Opiticks,
book ii., prop. 8, p. 241, and Brewster, Op. czt., p. 301.)
According to Kant, (see Die Metaphysischen Anfangsgrtinde
der Naturwissenschaft, 1800, s. 28,) we cannot conceive the
existence of matter without these forces of attraction and re-
pulsion. All physical phenomena are therefore reduced by
him, as previously by Goodwin Knight (Philos. Transact.
1748, p. 264), to the conflict of two elementary forces. In
the atomic theories which were diametrically opposed to
Kant's dynamic views, the force of attraction was referred, in
accordance with a view specially promulgated by Lavoisier,
to the discrete solid elementary molecules of which all bodies
are supposed to consist; while the force of repulsion was
attributed to the atmospheres of heat surrounding all element-
ary corpuscles. This hypothesis, which regards the so-called
caloric as a constantly expanded matter, assumes the existence
of two elementary substances, as in the mythical idea of two
kinds of ether. (Newton, Opticks, query 28, p. 339.) Here
the question arises, what causes this caloric matter to expand ?
Considerations on the density of molecules in comparison
with that of their aggregates (the entire body) lead, according
to atomic hypotheses, to the result, that the distance between
elementary corpuscles is far greater than their diameters.

s

INTRODUCTION. 27

as 1600, regarded magnetism as a force inherent in all matter.
So undetermined was even Newton, the profound and expe-
rienced thinker, regarding the ‘‘ ultimate mechanical cause”
uf all motion.

It is indeed a brilliant effort, worthy of the human mind, to
eomprise, in one organic whole, the entire science of nature from
the laws of gravity to the formative impulse (nisus formativus)
in animated bodies; but the present imperfect state of many
branches of physical science offers innumerable difficulties to
the solution of such a problem. The imperfectibility of all
empirical science, and the boundlessness of the sphere of obser:
vation, render the task of explaining the forces of matter
by that which is variable in matter, an impracticable one.
What has been already perceived by no means exhausts that
which is perceptible. If, simply referring to the progress of
science in modern times, we compare the imperfect physical
knowledge of Gilbert, Robert Boyle, and Hales, with that of
the present day, and remember that every few years are
characterized by an increasing rapidity of advance, we shall
be better able to imagine the periodical and endless changes
which all physical sciences are destined to undergo. New
substances and new forces will be discovered.

Although many physical processes, as those of light, heat
and electro-magnetism, have been rendered accessible to a
mathematical investigation, by being reduced to motion or
vibrations, we are still without a solution to those often mooted
and perhaps insolvable problems: the cause of chemical
differences of matter; the apparently irregular distribution of
the planets in reference to their size, density, the inclination
of their axes, the eccentricity of their orbits, and the num-
ber and distance of their satellites; the configuration of con-
tinents, and the position of their highest mountain chains.
Those relations in space, which we have referred to merely
by way of illustration, can at present be regarded only as

28 CO8MOS.

something existing in nature, as a fact, but which I cannot
designate as merely causal, because their causes and mutual
connection have not yet been discovered. They are the result
of occurrences in the realms of space coeval with the for-
mation of our planetary system, and of geognostie processes
in the upheaval of the outer strata of the earth into continents
and mountain chains. Our knowledge of the primeval ages
of the world’s physical history does not extend sufficiently far
to allow of our depicting the present condition of things as
one of development.“

Wherever the causal connection between phenomena has
not yet been fully recognized, the doctrine of the Cosmos, or the
physical description of the universe, does not constitute a
distinct branch of physical science. It rather embraces the
whole domain of nature, the phenomena of both the celestial
and terrestial spheres ——but embraces it only under the
single point of view of efforts made towards the knowledge
of the universe as a whole.“ As in the ‘“ exposition of past
events in the moral and political world, the histerian® can only
divine the plan of the government of the world, according
to human views, through the signs which are presented to him,
and not by direct insight ;” so also the enquirer into nature,
in his investigation of cosmical relations, feels himself pene-
trated by a profound consciousness that the fruits hitherto
yielded by direct observation and by the careful analysis ot
phenomena, are far from having exhausted the number of

impelling, producing, and formative forces.

“ Cosmos, pp. 79-82.
© Op. cit. pp. 36, 38-44.
* Wilhelm yon Humboldt, Gesammelie Werke, bd. i. s. 23.

A.

RESULTS OF OBSERVATIONS IN THE URANC LOGICAL PORTION
OF THE PHYSICAL DESCRIPTION OF THE WORLD.

WE again commence with the depths of cosmical space, and
the remote sporadic starry systems, which appear to te-
lescopic vision as faintly shining nebule. From these we
gradually descend to the double stars, revolving round one
common centre of gravity, and which are frequently bi-
coloured, to the nearer starry strata, one of which appears
to enclose our own planetary system; passing thence
to the air-and-ocean-girt terrestrial spheroid which we
inhabit. We have already indicated in the introduction to the
General Delineation of Nature,’ that this arrangement of ideas is
alone suited to the character of a work on the Cosmos, since
we cannot here, in accordance with the requirements of direct
sensuous contemplation, begin with our own terrestrial abode,
whose surface is animated by organic forces, and pass from
the apparent to the true movements of cosmical bodies.

The wranological, when opposed to the ¢elluric domain of
the Cosmos, may be conveniently separated into two divisions,
one of which comprises astrognosy, or the region of the fixed
stars, and the other our solar and planetary system. It is
unnecessary here to describe the imperfect and unsatisfac-
tory nature of such a nomenclature and such classifications.
Names were introduced into the physical sciences before the
differences of objects and their strict limitations were suffi-
ciently known.? The most important point, however, is the
connection of ideas, and the order in which the objects are to

1 Cosmos, pp. 62-66. ? Op. cit. pp. 38, 39.

20 COSMOS.

be considered. Tnnovations in the nomenclature of groups,
and a deviation from the meanings hitherto attached to well-
known names, only tend to distract and confuse the mind.

a. ASTROGNOSY. (Tue Domain oF THE Fixep SraRs,)

Nothing is stationary in space. Even the fixed stars
move, as Halley* endeavoured to show in reference to Sirius,
Arcturus, and Aldebaran, and as in modern times has been
incontrovertibly proved with respect to many others. The
bright star Arcturus has, during the 2100 years (since the
times of Aristillus and Hipparchus) that it has been observed,
changed its position in relation to the neighbouring fainter
stars 24 times the moon’s diameter. Encke remarks “ that
the star » Cassiopeie appears to have moved 34 lunar
liameters, and 61 Cygni about 6 lunar diameters, if the
ancient observations correctly indicated its position.” Con-
clusions based on analogy justify us in believing that there
is everywhere progressive, and perhaps also rotatory motion.
The term ‘“ fixed stars ” leads to erroneous preconceptions ; it
may have referred, in its earliest meaning among the Greeks,
to the idea of the stars being rivetted into the crystal vault of
heaven; or, subsequently, in accordance with the Roman
interpretation, it may indicate fixity or immobility. The
one idea involuntarily led to the other. In Grecian anti-
quity, in an age at least as remote as that of Anaximenes of
the Ionic school, or of Alemeon the Pythagorean, all stars
were divided into wandering (dorpa mAav@peva or mavynrd) and
non-wandering fixed stars (amAaveis dorépes or amhavi dotpa).4
Besides this generally adopted designation of the fixed stars,

’ Halley, in the Philos. Transact. for 1717, vol. xxx.
p- 736.

* Pseudo-Plut., de plac. Phiivs., ii. 15, 16; Stob. Eelog
phys., p. 582; Plato in the Timeus, p. 40.

.

ASTROGNOSY. 31

which Macrobius in his Somniuwm Scipionis, latinized by
Sphera aplanes,® we frequently meet in Aristotle (as if he
wished to introduce a new technical term) with the phrase
rivetted stars, evdedeuéva Gorpa, instead of dmdavq.® as a desig-
nation for fixed stars. From this form of speech arose the
expressions of sidera mfiza celo of Cicero, stellas quas
putamus afficas of Pliny, and astra fiza of Manilius, which
corresponds with our term fixed stars.’ This idea of fixity
leads to the secondary idea of immobility, of persistence in
one spot, and thus the original signification of the expressions
infixum or afficum sidus, was gradually lost sight of in the
Latin translations of the middle ages, and the idea of im-
mobility alone retained. This is already apparent in a highly
rhetorical passage of Seneca, regarding the possibility of dis-
covering new planets, in which he says (Nat. Quest., vii. 24):
*Credis autem in hoc maximo et pulcherrimo ¢orpore inter
innumerabiles stellas, que noctem decore vario distinguunt,

® Macrob., Somn. Scip., i. 9-10; stelle inerrantes, in Cicero
de nat. Deorum, iii. 20. , ’

* The principal passage in which we meet with the tech-
nical expression évdedeuéva dorpa, is in Aristot. de Calo, ii. 8,
p. 289.1. 34. p. 290, 1. 19, Bekker. This altered nomenclature
forcibly attracted my attention in my investigations into the
optics of Ptolemy, and his experiments on refraction. Pro-
fessor Franz, to whose philotogical acquirements I am indebted
for frequent aid, reminds me that Ptolemy (Syntaz, vii. 1,)
speaks of the fixed stars as affixed or rivetted; déomep
mpoomepuxdres. Ptolemy thus objects to the expression
ofaipa dmhavns (orbis inerrans); “in as far as the stars con
stantly preserve their relative distances they might rightly be
termed dmAaveis; but in as far as the sphere in which they
complete their course, and in which they seem to have grown,
as it were, has an independent motion, the designation dmAavys
is inappropriate if applied to the sphere.”

* Cicero, de nat Deorum, i. 13; Plin. ii. 6 and 2-4; Mani-
lius, ii. 35.

$2 COSMOS,

juee aéra minime vacuum et inertem esse patiuntur, quinque
solas esse, quibus exercere se liceat; ceteras stare fixum et
tmmobilem populum?’ ‘* And dost thou believe that in this
so great and splendid body, amongst innumerable stars, which
by their various beauty adorn the night, not suffering the air
to remain void and unprofitable, that there should be only five
stars to whom it is permitted to be in motion, whilst all the
rest remain a fixed and immoveable multitude.” This fixed
and immoveable multitude is nowhere to be found.

In order the better to classify the main results of actual
observations, and the conclusions or conjectures to which they
give rise, in the description of the universe, I will separate
the astrognostic sphere into the following sections:—

I. The considerations on the realms of space and the
bodies by which they appear to be filled.

II. Natural and telescopic vision, the scintillation of the
stars, the velocity of light, and the photometric experiments on
the intensity of stellar light.

III. The number, distribution, and colour of the stars;
the stellar swarms, and the milky way which is interspersed
with a few nebule.

IV. The newly appeared and periodically changing stars,
and those that have disappeared.

VY. The proper motion of the fixed stars, the problematical
existence of dark cosmical bodies; the parallax and measured
distance of some of the fixed stars.

VI. The double stars, and the period of their revolution
round a common centre of gravity.

VII. The nebule which are interspersed in the Magel-
lanic clouds with numerous stellar masses, the black spots

(coal-bags) in the vault of heaven,

i,

THE REALMS OF SPACE, AND CONJECTURES REGARDING THAT
WHICH APPEARS TO OCCUPY THE SPACE INTERVENING
BETWEEN THE HEAVENLY BODIES.

THatT portion of the physical description of the universe
which treats of what occupies the distant regions of the
heavens, filling the space between the globular cosmical bodies,
and is imperceptible to our organs, may not unaptly be
compared to the mythical commencement of ancient history.
In infinity of space, as well as in eternity of time, all things
are shrouded in an uncertain and frequently deceptive twi-
light. The imagination is here doubly impelled to draw
from its own fulness, and to give outline and permanence to

these indefinite changing forms.* This observation will, I

trust, suffice to exonerate me from the reproach of confound-
ing that which has been reduced to mathematical certainty,
by direct observation or measurement, with that which is
founded on very imperfect induction. Wild reveries belong
to the romance of physical astronomy; yet the mind fa-
miliar with scientific labours, delights in dwelling on sub-
jects such as these, which, intimately connected with the
present condition of science, and with the hopes which it
inspires, have not been deemed unworthy of the earnest atten-

tion of the most distinguished astronomers of our day.

By the influence of gravitation, or general gravity, as well
as by light and radiating heat.® we are brought in contact, as

® Cosmos, vol. i. p. 71. (Compare the admirable observa-
tions of Encke, Ueber die Anordnung des Sterns ystems, 1844,8. 7.)
? Cosmos, vol. i. pp. 145, 146

VOL. Ill. 1p)

34 COSMOS.

we may with great probability assume, not only with our own
Sun, but also with all the other luminous suns of the firma-
ment. The important discovery of the appreciable resistance
which a fluid filling the realms of space is capable of oppos-
ing to a comet having a period of revolution of five years,
has been perfectly confirmed by the exact accordance of
numerical relations. Conclusions based upon analogies may
fill up a portion of the vast chasm which separates the certain
results of a mathematical natural pbilosophy from conjec-
tures verging on the extreme, and therefore obscure and
barren confines of all scientific development of mind.

From the infinity of space,—an infinity, however, doubted
by Aristotle,*—follows the idea of its immeasurability. Se-
parate portions only have been rendered accessible to measure-
ment, and the numerical results, which far exceed the grasp
of our comprehension, become a source of mere puerile grati-
fication to those who delight in high numbers, and imagine
that the sublimity of astronomical studies may be heightened
by astounding and terrific images of physical magnitude. The
distance of 61 Cygni from the Sun is 657000 semi-diameters
of the Earth’s orbit; a distance which light takes rather more
than ten years to traverse, whilst it passes from the Sun to
the Earth in 8’ 1778. Sir John Herschel conjectures, from
his ingenious combination of photometric calculations," that
if the stars in the great circle of the Milky Way which he
saw in the field of his twenty-feet telescope were newly-arisen
luminous cosmical bodies, they would have required 2000
years to transmit to us the first ray of light. All attempts to
present such numerical relations fail, either from the immen-
sity of the unit by which they must be measured, or from

© Aristot. de Celo, 1, 7, p. 276; Bekker.
® Sir John Herschel, Outlines of Astronomy, 1849, § 803,
p 541.

‘

THE PROPAGATION OF LIGHT. 34

the high number yielded by the repetition of this unit
Bessel yery truly observes that ‘the distance which light
traverses in a year is not more appreciable to us than the
distance which it traverses in ten years. Therefore every
endeavour must fail to convey to the mind any idea of a
magnitude exceeding those that are accessible on the earth.”
This overpowering force of numbers is as clearly manifested
in the smallest organisms of animal life as in the milky way
of those self-luminous suns which we call fixed stars. What
masses of Polythalamie are inclosed, according to Ehren-
berg, in one thin stratum of chalk! This eminent investi-
gator of nature asserts that one cubic inch of the Bilin
polishing slate, which constitutes a sort of mountain cap
forty feet in height, contains 41000 millions of the micro-
scopic Galionella distans; while the same volume contains
more than 1 billion 750000 millions of distinct individuals
of Galionella ferruginea.* Such estimates remind us of the
treatise named Arenarius (Wappirns) of Archimedes—of the
sand-grains which might fill the universe of space! If the
starry heavens, by incalculable numbers, magnitude, space,
duration, and length of periods, impress man with the con-
viction of his own insignificance, his physical weakness,
and the ephemeral nature of his existence; he is, on the
other hand, cheered and invigorated by the consciousness of
having been enabled, by the application and development of
intellect, to investigate very many important points in refer-
ence to the laws of Nature and the sidereal arrangement
of the universe.

Although not only the propagation of light, but also a special
form of its diminished intensity, the resisting medium acting

4% Bessel, in Schumacher’s Jahrbuch ftir 1839, s. 50.
% Ehrenberg, Abhandl. der Berl. Akad., 1238, s. 59; also
in his Infusionsthiere, s. 170.

ng

36 COSMOS.

on the periods of revolution of Encke’s comet, and the evapo

ration of many of the large tails of comets, seem to prove that the
regions of space which separate cosmical bodies are not void,"
but filled with some kind of matter; we must not omit to
draw attention to the fact, that among the now current
but indefinite expressions of “the air of heaven,” “ cosmical
(non-luminous) matter,” and “ ether,” the latter, which has
been transmitted to us from the earliest antiquity of Southern
and Western Asia, has not always expressed the same idea.
Among the natural philosophers of India, ether (dkd’sa) was
regarded as belonging to the pantschatd, or five elements, and
was supposed to be a fluid of infinite subtlety, pervading the
whole universe, and constituting the medium of exciting life,
as well as of propagating sound.” Etymologically considered,
dkd’sa signifies, according to Bopp, ‘luminous or shining,
and bears, therefore, in its fundamental signification, the
same relation to the ‘ether’ of the Greeks as shining does to
burning.”

4 Aristotle (Phys. Auscult., iv. 6-10, pp. 218-217, Bekker.)
proves, in opposition to Leucippus and Democritus, that there
is no unfilled space—no vacuum in the universe.

16 Akd’sa signifies, according to Wilson’s Sanscrit Dic-
tionary, “the subtle and ethereal fluid supposed to fill and
pervade the universe, and to be the peculiar vehicle of life
and sound.” “The word dékd’sa (luminous, shining) is derived
from the root kd’s (to shine), to which is added the preposi-
tion d. The quintuple of all the elements is called pantschatd,
or pantschatra, and the dead are, singularly enough, desig-
nated as those who have been resolved into the five elements
(prapta pantschatra). Such is the interpretation given in the
text of Amarakoscha, Amarasinha’s Dictionary.”—(Bopp.)
Colebrooke’s admirable treatise on the Sankhya Philosophy,
treats of these five clements; see Zransact. of the Asiat. Soc.,
vol. i. Lond. 1827, p. 31. Strabo refers, according to
Megasthenes, (xv. § 59, p. 718, Cas.) to the all-forming fifth
element of the Indians, without, however, naming it.

»

COSMICAL ETHER. 37

In the dogmas of the Ionic philosophy of Anaxagoras and
Empedocles, this ether (aiénp) differed wholly from the actual
(denser) vapour-charged air (4jp) which surrounds the earth,
and “ probably extends as far as the moon.” It was of “a fiery
nature, a brightly-beaming, pure fire-air,"* of great subtlety
and eternal serenity.” This definition perfectly coincides
with its etymological derivation from ai@ew to burn, for which
Plato and Aristotle, from a predilection for mechanical views,
singularly enough substituted another (deieiv), on account of
the constancy of the revolving and rotatory movement.” The

46 Empedocles, v. 216, calls the ether raydavdwr, brightly-
beaming, and therefore self-luminous.

7 Plato, Cratyl. 410 B., where we meet with the expression
devBenp. Aristot. de Ceelo, 1, 3, p. 270, Bekk. says in oppo-
sition to Anaxagoras : aiéépa ™poo @vopacay Tov dvarara TOmov,
amd tov Gey dei TOV aidioy xpdvov Oepevor TY emovupiay avT@.
‘Avagaydpas dé KaTakeXpnrat T® ovdpatt TOUT@ ov Kadas* évoudcer
yap aiéépa dyti mupds. We find this more circumstantially re-
ferred toin Aristot. Meteor., 1, 3, p. 339, lines 21-34, Bekk.:
“The so-called ether has an ancient designation, which
Anaxagoras seems to identify with fire; for, according to
him, the upper region is full of fire, and to be considered
as ether; in which, indeed, he is correct. For the ancients
appear to have regarded the body which is in @ constant state
of movement, as possessing a divine nature, and therefore
called it ether, a substance with which we have nothing
analogous. Those, however, who hold the space surrounding
bodies to be fire no less than the bodies themselves, and who
look upon that which lies between the earth and the stars as
air, would probably relinquish such childish fancies if they
properly investigated the results of the latest researches of
mathematicians.” (The same etymology of this word, im-
plying rapid revolution, is referred to by the Aristotelian,
or Stoic, author of the work De Mundo, cap. 2, p. 892, Bekk.)
Professor Franz has correctly remarked, ‘“ that the ‘play of
words in the designation of bodies in eternal motion (capa dei
Geov) and of the divine (8eiov) alluded to in the Meteorologica,
is strikingly characteristic of the Sreek type of imagination,

38 CCEHOR.

idea of the subtlety and tenuity of the upper ether does not
appear to have resulted from a knowledge that the air on
mountains is purer and less charged with the heavy vapours
of the earth, or that the density of the strata of air decreases
with their increased height. In as far as the elements of
the ancients refer less to material differences of bodies, or
even to their simple nature (their incapacity of being decom-
posed), than to mere conditions of matter, the idea of the upper
ether (the fiery air of heaven) has originated in the primary
and normal contraries of heavy and light, lower and upper,
earth and fire. ‘These extremes are separated by two mler-
mediate elementary conditions, of which the one, water, ap-
proximates most nearly to the heavy earth, and the other, air,
to the lighter element of fire.

Considered as a medium filling the regions of space, the
ether of Empedocles presents no other analogies excepting

and affords additional evidence of the inaptitude of the an-
cients for etymological inquiry.’’ Professor Buschmann calls
attention to a Sanscrit term, dschtra, ether or the atmosphere,
which looks very like the Greek ai@jp, with which it has been
compared by Vans Kennedy, in his Researches into the Origin
and A finity of the principal Languages of Asia and Europe, 1828,
p. 279. This word may also be referred to the root (as, asch)
to which the Indians attach the signification of shining or
beaming.

#%® Aristot. de Calo, iv. 1, and 3-4, pp. 308, and 311-312,
Bekk. If the Stagirite withholds from ether the character of
a fifth element, which indeed is denied by Ritter ( Geschichte
der Philosophie, th. iii. s. 259), and by Martin (Etudes sur
le Timée de Platon, t. ii. p. 150); it is only because, ac-
cording to him, ether, as a condition of matter, has no con-
trary. (Compare Biese, Philosophie des Aristotiles, bd. x1.
s.66.) Amongst the Pythagoreans, ether, as a fifth element,
was represented by the fifth of the regular bodies, the dode-
cahedron, composed of twelve pentagons. (Martin, t. i
pp. 245-250. )

s

COSMICAL ETHER 39

those of subtlety and tenuity witb the ether, by whose trans-
verse vibrations modern physicists have succeeded so happily
in explaining, on purely mathematical principles, the pro-
pagation of light, with all its properties of double refrac-
tion, polarisation, and interference. The natural philosophy
of Aristotle further teaches that the ethereal substance
penetrates all the living organisms of the earth—both plants
and animals; that it becomes in these the principle of vital
heat, the very germ of a psychical principle, which, uninflu-
enced by the body, stimulates men to independent activity."
These visionary opinions draw down ether from the higher
regions of space to the terrestrial sphere, and represent it
as a highly rarefied substance constantly penetrating through
the atmosphere and through solid bodies; precisely similar
to the vibrating light-ether of Huygens, Hooke, and modern
physicists. But what especially distinguishes the older Ionic
from the modern hypothesis of ether, is the original assump-
tion of luminosity, a view, however, not entirely advocated
by Aristotle. The upper fire-air of Empedocles is expressly
termed brightly radiating (maypavéwr), and is said to be
seen by the inhabitants of the earth in certain phenomena,
gleaming brightly through fissures and chasms (xaopara) which
occur in the firmament.”

The numerous investigations that have been made m recent
times regarding the intimate relation between light, heat,
electricity, and magnetism, render it far from improbable that,
as the transverse vibrations of the ether which fills the regions
of space give rise to the phenomena of light, the thermal and
electro-magnetic phenomena may likewise have their origin
in analogous kinds of motion (currents). It is reserved for
future ages to make great discoveries in reference to these

See the proofs collected by Biese, op. cit., bd. xi s. 93.
* Cosmos, vol. i. p 143.

49 COSMOS.

subjects. Light, and radiating heat, which is inseparable
from it, constitute a main cause of motion and organic
life, both in the non-luminous celestial bodies, and on the
surface of our planet." Even far from its surface, in the
interior of the earth’s crust, penetrating heat calls forth electro-
magnetic currents, which exert their exciting influence on
the combinations and decompositions of matter,—on all for-
mative agencies in the mineral kingdom—on the disturbance
of the equilibrium of the atmosphere,—and on the functions
of vegetable and animal organisms. If electricity moving in
currents develops magnetic forces, and if, in accordance with
an early hypothesis of Sir William Herschel,” the sun itself
is in the condition of ‘a perpetual nerthern light,” (I should
rather say of an electro-magnetic storm), we should seem
warranted in concluding that solar light, transmitted in the
regions of space by vibrations of ether, may be accompanied
by electro-magnetic currents.

Direct observations on the periodic changes in the declina-
tion, inclination, and intensity of terrestrial magnetism, have,
it is true, not yet shown with certainty that these conditions

*! Compare the fine passage on the influence of the sun’s
rays, in Sir John Herschel’s Outlines of Astronomy, p. 237:
“‘ By the vivifying action of the sun’s rays, vegetables are
enabled to draw support from inorganic matter, and become,
in their turn, the support of animals and of man, and the
sources of those great deposits of dynamical efficiency which
are laid up for human use in our coal strata. By them the
waters of the sea are made to circulate in vapour through the
air, and irrigate the land, producing springs and rivers. By
them are produced all disturbances of the chemical equilibrium
of ‘the elements of nature, which, by a series of compositions
and decompositions, give rise to new products, and originate
a transfer of materials.”’ j

% Philos. Transact, for 1795, vol. lxxxv. p. 318; John
Herschel, Outlines of Astr., p. 238; see also Cosmos, vol. i
p. 183.

>

RADIATING HEAT. 4;

are affected by the different positions of the sun or moon,
notwithstanding the latter’s contiguity to the earth. ‘The
magnetic polarity of the earth exhibits no variations that can
be referred to the sun, or which perceptibly affect the pre-
cession of the equinoxes.* The remarkable rotatory or oscil-
latory motion of the radiating cone of light of Halley’s
comet, which Bessel observed from the 12th to the 22nd of
October, 1835, and endeavoured to explain, led this great
astronomer to the conviction that there existed a polar force,
*“whose action differed considerably from gravitation or the
ordinary attracting force of the sun; since those portions of
the comet which constitute the tail are acted upon by a repulsive
force proceeding from the body of the sun.”™ The splendid
comet of 1744, which was described by Heinsius, led my
deceased friend to similar conjectures.

The actions of radiating heat in the regions of space are
regarded as less problematical than electro-magnetic pheno-
mena. According to Fourier and Poisson, the temperature
of the regions of space is the result of radiation of heat from
the sun and ai/ astral bodies, minus the quantity lost by
absorption in traversing the regions of space filled with ether.™
Frequent mention is made in antiquity by the Greek and
Roman™ writers of this stellar heat; not only because, from

*8 See Bessel, in Schumacher’s Astr. Nachr., bd. xiii. 1836,
no. 300, s. 201.

* Bessel, op. ctt., s. 186-192, 229.

* Fourier, Théorie analytique de la Chaleur, 1822, p. ix.
(Annales de Chimie et de Physique, tom. iii. 1816, p. 350;
tom. iv. 1817, p. 128; tom. vi. 1817, p. 259; tom. xiii. 1820,

. 418). Poisson, in his Théorie mathématique de la Chaleur
(§ 196, p. 436, § 200, p. 447, and § 228, p. 521), attempts
to give the numerical estimates of the stellar heat (chaleur
stellaire) lost by absorption in the ether of the regions of
space.

* On the heating power of the stars, see Aristot. de Meteor.

42 Cosmas.

a universal.y prevalent assumption, the stars appertained tc
the region of the fiery ether, but because they were supposed
to be themselves of a fiery nature”’—the fixed stars and the
sun being, according to the doctrine of Aristarchus of Samos,
of one and the same nature. In recent times, the observa-
tions of the above-mentioned eminent French mathematicians,
Fourier and Poisson, have been the means of directing attention
to the average determination of the temperature of the regions
of space; and the more strongly since the importance of
such determinations on account of the radiation of heat from.
the earth’s surface towards the vault of heaven, has at length
been appreciated in their relation to all thermal conditions,
and to the very habitability of our planet. According to
Fourier’s Analytic Theory of Heat, the temperature of celestial
space (des espaces planétaires ou célestes) is rather below the
mean temperature of the poles, or even perhaps below the
lowest degree of cold hitherto observed in the polar regions.
Fourier estimates it at from — 58° to — 76° (from — 40°
to — 48° Reaum.). The icy pole (péle glacial), or the point
of the greatest cold, no more corresponds with the terrestrial
pole than does the thermal equator, which connects together
the hottest points of all meridians with the geographical
equator. <Arago concludes, from the gradual decrease of mean
temperatures, that the degree of cold at the northern ter-
restrial pole is — 13°, if the maximum cold observed by Captain
Back at Fort Reliance (62° 46’ lat.) in January, 1834, were
actually — 70° (— 56°°6 Cent., or — 45°-3 Reaum.).% The

1, 3, p. 340, lin. 28; and on the elevation of the atmospheric
strata at which heat is at the minimum, consult Seneca in Vat.
Quest.,ii. 10: “Superiora enim aéris calorem vicinorumsiderum
sentiunt.”

7 Plut. de plac. Philos., ui. 13.

% Arago, Sur la température du Pdle et des espaces célestes
in the Annuaire du Bureau des Long. pour 1828, p. 189, et

>

POLES OF GREATEST COLD. 43

lowest temperature that, as far as we know, has as yet been
observed on the earth, is probably that noted by Neveroff, at
Jakutsk, (62° 2’ lat.) on the 21st of January, 1838. “he in-
struments used in this observation were compared with his own
by Middendorff, whose operations were always conducted with
extreme exactitude. Neveroff found the temperature on the
day above named to be — 76° (or — 48° Reaum..).

Among the many grounds of uncertainty in obtaining a nume-
rical result for the thermal condition of the regions of space,
must be reckoned that of our inability at present to ascertain
the mean of the temperatures of the poles of greatest cold of the
two hemispheres, owing to our insufficient acquaintance with
the meteorology of the antarctic pole, from which the mean
annual temperature must be determined. I attach but little

pour 1834, p. 192; also Saigey, Physique du Globe, 1832,
pp. 60-76. Swanberg found, from considerations on re-
fraction, that the temperature of the regions of space was
— 58°°5. Berzelius, Jahresbericht fiir 1830, s. 54. Arago,
from polar observations, fixed it at — 70°; and Pectet at — 76°.
Saigey, by calculating the decrease of heat in the atmosphere,
from 367 observations made by myself in the chain of the
Andes and in Mexico, found it — 85°; and from thermome-
trical measurements made at Mont Blanc, and during the
xeronautic ascent of Gay-Lussac — 107°-2. Sir John Herschel
(Edinburgh Review, vol. 87, 1848, p. 223) gives it at — 132°
We feel considerable surprise, and have our faith in the cor-
rectness of the methods hitherto adopted somewhat shaken,
when we find that Poisson, notwithstanding that the mean
temperature of Melville Island (74° 47’ N. Lat.) is — 1° 66’,
gives the mean temperature of the regions of space at only
8°6, huving obtained his data from purely theoretical pre-
mises, according to which the regions of space are warmer
than the outer limits of the atmosphere (see the work already
referred to, § 227, p. 520); while Pouillet states it, from
actinometric experiments, to be as low as — 223°°6. See
Comptes rendus de l Académie des Sciences, tom. vii. 1838,
pp. 25-65

44 COSMOS.

physical probability to the hypothesis of Poisson, that the
different regions of space must have a very various tempera-
ture, owing to the unequal distribution of heat-radiating stars,
and that the earth, during its motion with the whole solar
system, receives its internal heat from without, while passing
through hot and cold regions.” .

The question whether the thermal conditions of the celestial
regions, and the climates of individual portions of space,
have suffered important variations in the course of ages, de-
pends mainly on the solution of a problem warmly discussed
by Sir William Herschel: whether the nebulous masses are
subjected to progressive processes of formation, while the cos-
mical vapour is being cundensed around one or more nuclei
in accordance with the laws of attraction? By such a
condensation of cosmival vapour, heat must be liberated, as
in every transition of gases and fluids into a state of solidifica-
tion.” If, in accordance with the most recent views, and
the important observations of Lord Rosse and Mr. Bond, we
may assume that all nebulee, including those which the highest
power of optical instruments has hitherto failed in resolving,
are closely crowded stellar swarms, our faith in this perpe-
tually augmenting liberation of heat must necessarily be in
some degree weakened. But even small consolidated cosmical
bodies which appear on the field of the telescope as distinguish-
able, luminous points, may change their density by combining
in larger masses ; and many phenomena presented by our own
planetary system lead to the conclusion, that planets have been
solidified from a state of vapour, and that their internal heat
owes its origin to the formative process of conglomerated matter.

9 See Poisson, Théorie Mathém. de la Chaleur, p. 438.
According to him, the consolidation of the earth's strata
began from the centre, and advanced gradually towards the
surface; § 193, p. 429. Compare also Cosmos, vol. i. p. 169.

© Cosmos, vol. i. pp. 67, 134. .

TEMPERATURE OF SPACE. 4é

It may at first sight seem hazardous to term the ‘zarfully
low temperature of the regions of space (which varies
between the freezing point of mercury and that of spirits
of wine) even indirectly beneficial to the habitable climates
of the earth and to animal and vegetable life. But in proof
of the accuracy of the expression, we need only refer to
the action of the radiation of heat. The sun-warmed surface
of our planet, as well as the atmosphere to its outermost
strata, freely radiate heat into space. The loss of heat
which they experience arises from the difference of tem-
perature between the vault of heaven and the atmaespheric
strata, and from the feebleness of the counter-radiation. How
enormous would be this loss of heat,*' if the regions of space,
instead of the temperature they now possess, and which we
designate as — 76° of a mercury thermometer, had a tempe-
rature of about — 1400° or even many thousand times lower!

It still remains for us to consider two hypotheses in relation
to the existence of a fluid filling the regions of space, of which

st «* Were there no atmosphere, a thermometer freely ex-
posed (at sunset) to the heating influence of the earth’s radia-
tion, and the cooling power of its own into space, would indicate
a medium temperature between that of the celestial spaces,
(— 132° Fahr.) and that of the earth’s surface below it, 82°
Fahr., at the equator, 32° Fahr., in the Polar Sea. Under
the equator then it would stand, on the average, at — 25°
Fahr., and in the Polar Sea at — 68° Fahr. The presence
of the atmosphere tends to prevent the thermometer so ex-
posed from attaining these extreme low temperatures : first,
by imparting heat by conduction; secondly, by impeding
radiation outwards.” Sir John Herschel, in the Edinburgh
Review, vol. 87, 1848, p. 222. ‘Si la chaleur des espaces
planétaires n’existait point, notre atmosphére éprouverait un
refroidissement, dont on ne peut fixer la limite. Probable-
ment la vie des plantes et des animaux serait impossible 4 la
surface du globe, ou reléguée dans ‘ne étroite zone de cette
surface.” (Saigey, Phystgue du Globe, p. 77.)

46 COSMOS.

one,—the less firmly based hypothesis,—refers tc the limited
transparency of the celestial regions ; and the other, founded
on direct observation and yielding numerical results, is de-
duced from the regularly shortened periods of revolution of
Encke’s comet. Olbers in Bremen, and, as Struve has ob-
served, Loys de Cheseaux at Geneva, eighty years earlier™
drew attention to the dilemma, that since we could not con-
ceive any point in the infinite regions of space unoccupied
by a fixed star, 2. e. a sun, the entire vault of heaven must
“appear as luminous as our sun if light were transmitted to us
‘n perfect intensity; or, if such be not the case, we must
assume that light experiences a diminution of intensity in its
passage through space, this diminution being more exces-
sive than in the inverse ratio of the square of the dis-
tance. As we do not observe the whole heavens to be almost
uniformly illumined by such a radiance of light (a subject
considered by Halley® in an hypothesis which he subse-
quently rejected) the regions of space cannot, according to
Cheseaux, Olbers, and Struve, possess perfect and absolute
transparency. The results obtained by Sir William Herschel
from gauging the stars,“ and from his ingenious experi-
ments on the space-penetrating power of his great telescopes,
seem to show, that if the light of Sirius in its passage to us

8 Traité de la Cométe de 1748, avec une Addition sur la
force de la Lumiere et sa Propagation dans léther, et sur la
distance des étoiles fixes; par Loys de Cheseaux (1744). On
the transparency of the regions of space, see Olbers, in Bode’s
Jahrbuch fir 1826, s. 110-121; and Struve, Etudes d’ Astr
Stellmre, 1847, pp. 83-93, and note 95. Compare also
Sir John Herschel, Outlines of Astronomy, § 798, and Cosmos,
vol. i. p. 142.

% Halley, On the Infinity of the Sphere of Fixed Stars,
in the Philos. Transact., vol. xxxi. for the vear 1720.
pp. 22-26. !

' Cosmos, vol. i. p. 70.

RESISTING MEDIUM. 47

through a gas2ous or ethereal fluid loses only sith of its in- |
tensity, this assumption, which gives the amount of tne
density of a fluid capable of diminishing light, would suttice te
explain the phenomena as they manifest themselves. Among
the doubts advanced by the celebrated author of ‘*The New
Outlines of Astronomy,’ against the views of Olbers and
Struve, one of the most important is that his twenty-feet
telescope shows, throughout the greater portion of the Milky
Way in both hemispheres, the smallest stars projected on a
black ground.®

A better proof, and one based, as we have already stated,
upon direct observation of the existence of a resisting fiuid,*
is afforded by Encke’s comet, and by the ingenious and im-
portant conclusion to which my friend was led in his observa-
tions on this body. This resisting medium, must, however, be
regarded as different from the all-penetrating light-ether, be-
cause the former is only capable of offering resistance inasmuch
as it cannot penetrate through solid matter. These observa-
tions require the assumption of atangentiai force to explain the
diminished period of revolution (the diminished major-axis of
the ellipse), and this is most directly afforded by the hypothesis
of a resisting fluid.” The greatest action is manifested during

* «Throughout by far the larger portion of the extent of the
Milky Way in both hemispheres, the general blackness of the
ground of the heavens, on which its stars are projected... .
In those regions where the zone is clearly resolved into stars,
well separated, and seen projected on a black ground, and
where we look out beyond them into space. ..... ae
John Herschel, Outlines of Astr., pp. 537, 539.

* Cosmos, vol. i. pp. 69, 70, 92; compare also Lap ‘ace,
Essai Philosophique sur les Probabilités, 1825, p. 138 ; Arago
in the dnnuaire du Bureau des Lon,. pour 1832, p. 188,
‘pri p- 216; and Sir John Herschel, Outlines of Astr.,

77.

* The oscillatory movement of the emanations from the

head of some comets, as in that of 1744, and in Hailey’s as

48 CUSMOS.

the twenty-five days immediately preeeding and succeeding
the comet’s perihelion passage. The value of the constant
is therefore somewhat different, because in the neighbour-
hood of the sun the highly attenuated, but still gravitating
strata of the resisting fluid, are denser. Olbers maintained®
that this fluid could not be at rest, but must rotate directly
round the sun; and therefore the resistance offered to retro-
grade comets, like Halley’s, must differ wholly from that
opposed to those comets having a direct course, like Encke’s.
The perturbations of comets having long periods of revolu-
tion, and the difference of their magnitudes and sizes, com-
plicate the results, and render it difficult to determine what
is ascribable to individual forces.

The gaseous matter constituting the belt of the Zodiacal
light may, as Sir John Herschel® expresses it, be merely the
denser portion of this comet-resisting medium. Although it
may be shown that all nebule are crowded stellar masses,
indistinctly visible, it is certain that innumerable comets fill
the regions of space with matter through the evaporation of
their tails, some of which have a length of 56000000 of miles.

observed by Bessel, between the 12th and 22nd of October,
1835, (Schumacher Astron. Nachr.,nos. 300, 302, §185, 282),
“may, indeed, in the case of some individuals of this class of
cosmical bodies, exert an influence on the translatory and
rotatory motion, and lead us to infer the action of polar forces
(§ 201, 229,) which differ from the ordinary attracting force
of the sun;’’ but the regular acceleration observable for
sixty-three years in Encke’s comet, (whose period of revolu-
tion is 34 years), cannot be regarded as the result of in-
eidental emanations. Compare on this cosmically important
subject, Bessel in Schum. Astron. Nachr., no. 289, s. 6, and
no. 810, s. 845-850, with Encke’s Treatise on the hypothesis
of the resisting medium, in Schum., no. 305, s. 265-274.

8% Olbers in Senum. Astr. Nachs.. no. 268, s. 58.

® Outlines of Astronomy, § 556, 537. |

LIMIT OF THE ATMOSPHERE. 49

Arayo has ingeniously shown, on optica: grounds,” that the
variable stars which always exhibit white light without any
change of colour in their periodical phases, might afford a
means of determining the superior limit of the density to be
assumed for cosmical ether, if we suppose it to be equal to
gaseous terrestrial fluids in its power of refraction.

The question of the existence of an ethereal fluid filling
the regions of space is closely connected with one warmly
agitated by Wollaston,“ in reference to the definite limit
of the atmosphere,—a limit which must necessarily exist at
the elevation where the specific elasticity of the air is equi-
poised by the force of gravity. Faraday’s ingenious experi-
ments on the limits of an atmosphere of mercury (that is,
the elevation at which mercurial vapours precipitated or
gold-leaf cease perceptibly to rise in an air-filled space;
have given considerable weight to the assumption of a
definite surface of the atmosphere “ similar to the surface
of the sea.’ Can any gaseous particles belonging to the
region of space blend with our atmosphere and produce
meteorological changes? Newton® inclined to the idea that

© « En assimalant la matiere trés rare qui remplit les espaces
célestes quant 4 ses propr vétés réfringentes aux gas terrestres, la
densité de cette matiére ne saurait dépasser une certaine limite
dont les observations des étoiles changeantes, p. e. celles d’ Algot
ou de B de Persée, peuvent assigner la valeur.” — Avago in the
Annuaire pour 1842, pp. 336-345. ‘On comparing the
extremely rare matter occupying the regions of space witi:
terrestrial gases, in respect to its refractive properties, we
shall find that the density of this matter cannot exceed a
definite limit, whose value may be obtained from observations
of variable stars, as, for instance, Algol or 8 Persei.”’

* See Wollaston, Philos. Transact. for 1822, p. 89; Sir
John Herschel, op. cit. § 34, 36.

# Newton, Prine. Mathem., t. iii. (1760) p. 671. * Vapores

YOL. I11, BK

50 COSMOS,

such might be the case. If we regard falling stars and
meteoric stones as planetary asteroids, we may be allowed
to conjecture that in the streams of the so-called November
yhenomena,” when, as in 1799, 1833 and 1834, myriads of
falling stars traversed the vault of heaven, and northern lights
were simultaneously observed, our atmosphere may have re-
ceived from the regions of space some elements foreign to it,
which were capable of exciting electro-magnetic processes.

qui ex sole et stellis fixis et caudis cometary oriuntur, in-
dere possunt in atmospheras planetarum... . 7 .
® Cosmos, yol. i. pp. 112, 124

51

II.

NATURAL AND TELESCOPIC VISION.—=SCINTILLATION OF
THE STARS.—VELOCITY OF LIGHT.—RESULTS OF PHO-
TOMETRY.

THE increased power of vision yielded nearly two hundred
and fifty years ago by the invention of the telescope, hasafforded
to the eye, as the organ of sensuous cosmical contemplation,
the noblest of all aids tewards a knowledge of the contents of
space, and the investigation of the configuration, physical.
character, and masses of the planets and their satellites. The
first telescope was constructed in 1608, seven years after the
death of the great observer, Tycho Brahe. Its earliest
fruits were the successive discovery of the satellites of Jupiter,
the Sun’s spots, the crescent-shape of Venus, the ring of
Saturn as a triple planetary formation, (planeta tergeminus,)
telescopic stellar swarms, and the nebule in Andromeda.' In
1634, the French astronomer, Morin, eminent for his observa-
tions on longitude, first conceived the idea of mounting a
telescope on the index bar of an instrument of measurement,
and seeking to discover Arcturus Ly day.* The perfection in

1 See Cosmos, vol. ii. pp. 699-718, with notes.

* Delambre, Histoire de 1 Astronomie moderne, tom. ii.
pp. 255, 269, 272. Morin, in his work, Scientia Longitu-
dinum, which appeared in 1634, writes as follows :—Applicatio
tubi optici ad alhidadam pro stells fixis prompte et accurate
mensurandis a me excogitata est. Picard had not, up to the
year 1667, employed any telescope on the mural circle; and
Hevelius, when Halley visited him at Dantzic in 1679, and
admired the precision of his measurement of altitudes, was
observing through improved slits or openings. (Baily’s Catal,
of Stars, p. 38.)

E2

52 COSMOS.

the graduation of the are would have failed entirely, or to a
considerable extent, in affording that greater precision of
observation at which it aimed. if optical and astronomicai
instruments had not been brought into accord, and the cor-
reetness of vision made to correspond with that of measure-
ment. The micrometer-application of fine threads stretched
in the focus of the telescope, to which that instrument owes
its real and invaluable importance, was first devised, six years
afterwards (1640), by the young and talented Gascoigne.*
While, as I have already observed, telescopic vision, obser-
vation, and measurement, extend only over a period of about
240 years in the history of astronomical science, we find,
without including the epoch of the Chaldeans, Egyptians, and
Chinese, that more than nineteen centuries have intervened
between the age of Timochares and Aristillus* and the dis-
coveries of Galileo, during which period the position and course
of the stars were observed by the eye alone, unaided by instru-
ments. When we consider the numerous disturbances which
during this prolonged period checked the advance of civiliza-
tion, and the extension of the sphere of ideas among the nations
inhabiting the basin of the Mediterranean, we are astonished
that Hipparchus and Ptolemy should have been so well
acquainted with the precession of the equinoxes, the com-
plicated movements of the planets, the two principal inequa-
lities of the moon, and the position of the stars; that Coper-

* The unfortunate Gascoigne, whose merits remained su
long unacknowledged, lost his life, when scarcely twenty-
three years of age, at the battle of Marston-Moor, fought by
Cromwell against the royalists. See Derham in the Phzlos.
Transact., vol. xxx. for 1717-1719, pp. 603-610. To him
belongs the merit of a discovery which was long ascribed to
Picard and Auzout, and which has given an impulse pre-
viously unknown to practical astronomy, the principal objest
of which is to determine positions in the vault of heaven,

* Cosmos, vol. ii. p. 544.

DIOPTRIC TUBES. 53

nieuws shoula have had so great a knowledge of the true
system of the universe; and that Tycho Brahe should have
been so familiar with the methods of practical. astronomy
before the discovery of the telescope. Long tubes, which
were certainly employed by Arabian astronomers, and very
probably also by the Greeks and Romans, may indeed, in
some degree, have increased the exactness of the observations
by causing the object to be seen through diopters or slits.
Abul-Hassan speaks very distinctly of tubes, to the extre-
mities of which ocular and object diopters were attached; and
instruments so constructed were used in the observatory
founded by Hulagu at Meragha. If stars be more easily dis-
covered during twilight by means of tubes, and if a star be
sooner revealed to the naked eye through a tube than without
it, the reason lies, as Arago has already observed, in the
circumstance that the tube conceals a great portion of the
disturbing light (rayons perturbateurs) diffused in the atmo-
spheric strata between the star and the eye applied to the
tube. In like manner, the tube prevents the lateral impression
of the faint light which the particles of air receive at night
from all the other stars in the firmament. The intensity of
the image and the size of the star are apparently augmented
In a frequently emendated and much contested passage of
Strabo, in which mention is made of looking through tubes,
this “‘ enlarged form of the stars’ is expressly mentioned, and
is erroneously ascribed to refraction.®

® The passage in which Strabo (lib. iii. p. 138, Casaub.)
_ attempts to refute the views of Posidonius is given as follows,
according to the manuscripts :—‘The image of the sun is
enlarged on the seas at its rising as well as at its setting,
because at these times a larger mass of exhalations rises from
the humid element; and the eye, looking through these exha-
lations, sees images refracted into larger forms, as observed
through tubes. ‘The same thing happens when the setting

54 COSMOS.

Light, from whatever source it comes,—whether from the
sun, as solar light, or reflected from the planets; from the
fixed stars; from putrescent wood; or as the product of the
vital activity of glew-worms,—always exhibits the same con-

sun or moon is seen through a dry and thin cloud, when
those bodies likewise appear reddish.’ This passage has re-
cently been pronounced corrupt (see Kramer, in Strabonis Geogr.
1844, vol. i. p. 211), and 8 éddwy (through glass spheres) sub-
stituted for 8? aiAdv (Schneider, Eclog. phys., vol. ii. p. 278).
The magnifying power of hollow glass spheres, filled with
water (Seneca, i. 6), was, indeed, as familiar to the ancients
as the action of burning glasses or crystals (Aristoph. Vwd.,
v. 765), and that of Nero's emerald (Plin., xxxvii. 5); but
these spheres most assuredly could not have been employed
as astronomical measuring instruments. (Compare Cosmos,
vol. i. p. 619, and note {.) Solar altitudes, taken through thin
light clouds, or through volcanic vapours, exhibit no trace
of the influence of refraction. (Humboldt, Recueil d Ob-
serv, astr., vol. i. p. 128.) Colonel Baeyer observed no
anguler deviation in the heliotrope light on the passage of
streaks of mist, or even from artificially developed vapours,
and therefore fully confirms Arago’s experiments. Peters,
at Pulkowa, in- no case found a difference of 0’:017 on com-
paring groups of stellar altitudes, measured in a clear sky, and
through light clouds. See his Recherches sur la Parallaxe des
Etoiles, 1848, pp. 80, 140-143; also Struve’s Htudes Stel-
laires, p. 98. On the application of tubes for astronomical
observation in Arabian instruments, see Jourdain, Sur U Ob-
servatotre de Meragha, p. 27; and A. Sedillot, Mém. sur les
Instruments astronomiques des Arabes, 1841, p. 198. Arabian
astronomers have also the merit of having first employed
large gnomons with small circular apertures. _ In the colossal
sextant of Abu Mohammed al-Chokandi,.the limb, which was
divided into intervals of five minutes, received the image of the
sun. ‘A midi les rayons du soleil passaient par une ouver-
ture pratique dans la voite de l’observatoire qui couvrait l’in-
sttument, suivant le tuyau, et formaient sur la concavite du
sextant une image cir2ulaire, dont le centre donnait, sur l’are
pradué, le complemext de la hauteur du soleil. Cet instru.

PRISMATIC SPECTRA. 55

ditions of refraction.* But the prismatic spectra yielded ly
different sources of light (as the sun and the fixed stars)
exhibit a difference in the position of the dark lines (rates du
spectre) which Wollaston first discovered in 1808, and the posi-
tion of which was twelve years afterwards so accurately deter-
mined by Fraunhofer. While the latter observer counted 600
dark lines (breaks or interruptions in the coloured spectrum),
Sir David Brewster, by his admirable experiments with nitric
oxide, succeeded, in 1833, in counting more than 2000 lines.
It had been remarked that certain lines failed in the spec-
trum at some seasons of the year; but Sir David Brewster

ment differe de notre mural, qu’en ce qu'il etait garni d'un
simple tuyau au lieu d’une lunette.” ‘At noon, the rays of
the sun passed through an opening in thz dome of the observa-
tory, above the instrument, and following the tube formed in
the concavity of the sextant a cirsular image, the centre of
which marked the sun’s altitrde on the graduated limb.
This instrument in no way «itfered from our mural circle,
excepting that it was furnished with a mere tube instead of a
telescope.” Sedillot, pp. 37, 202, 205. Dioptric rulers (pin-
nule) were used by the Greeks and Arahs in determining the
moon’s diameter, and were constructed in such a manner, that
the circular aperture in the moving object diopter was larger
than that of the fixed ocular diopter, and was drawn out until
the lunar disc, seen through the ocular aperture, completely
filled the object aperture. Delambre, Hist. de I’ Astron. du
moyen age, p. 201; and Sédillot, p. 198. The adjustment of
the dioptric rulers of Archimedes, with round apertures or slits,
in which the direction of the shadows of two small cylinders
attached to the same index bar was noted, seems to have been
originally introduced by Hipparchus. (Baily, Hist. del Astron.
mod., 2nd ed. 1785, tom. i. p. 480.) Compare also, Theon
Alexandrin., Bas., 1538, pp. 257, 262 ; Les Hypotyp. de Proclus
Diadochus ed. Halma, 1820, pp. 107, 110; and Ptolem.
Almag., ed. Halma, tom. i. Par. 1813, p. vii.

* According to Arago; see M:igno, l?épert. d’ Cptique mo«
derne, 1847, p. 153.

53 COSMOS,

has shown that this phenomenon is owing to different altitudes
of the sun, and to the different absorption of the rays of light
in their passage through the atmosphere. In the spectra ot
the light reflected from the moon, from Venus, Mars, and the
clouds, we recognize, as might be anticipated, all the pecu-
uarities of the solar spectrum; but on the other hand, the
dark lines in the spectrum of Sirius differ from those ot
Castor, and the other fixed stars. Castor likewise exhibits
different lines from Pollux and Procyon. Amici has con-
firmed this difference, which was first indicated by Fraunhofer,
and has ingeniously called attention to the fact that in fixed
stars which now have an equal and perfectly white light the
dark lines are not the same. A wide and important field is
thus still open to future investigations,’ for we have yet to
distinguish between that which has been determined with
certainty, and that which is merely accidental and depending
on the absorbing action of the atmospheric strata.

We must here refer to another phenomenon, which is
powerfully influenced by the specific character of the source
of light. The light of incandescent solid bodies, and the
light of the electric spark, exhibit great diversity in the
number and position of Wollaston’s dark lines. From Wheat-
stone’s remarkable experiments with revolving mirrors it
would appear that the light of frictional electricity has a
greater velocity than solar light, in the ratio of 3 to 2; that
is to say, a velocity of 95908 miles in one second.

The stimulus infused into all departments of optical science
by the important discovery of polarisation,® to which the in-
~enious Malus was led in 1808, by a casual observation of the

7 Ou the relation of the dark lines of the solar speetrum
in the Daguerreotype, see Compies rendus des séances de V Ava-
démie des Sciences, tom. xiv. 1842, pp. 902-904, and tom. xvi.
1843, pp. 402-407,

* Cosmos, vol. ii. p. 715.

POLARISATION OF LIGHT. 57

light of the setting sun, reflected from the windows of the Palais
du Luxembourg, has afforded unexpected results to science by
the more thorough investigation of the phenomena of double re-
fraction, of ordinary (Huygens’s) and of chromatic polarisation,
of interference, and of diffraction of light. Among these results,
may be reckoned the means of distinguishing between direct
and reflected light,® the power of penetrating, as it were, into
the constitution of the body of the sun and of its luminous
envelopes,” of measuring the pressure of atmospheric strata,

* Arago’s investigation of cometary light may here be
adduced as an instance of the important difference between
proper and reflected light. The formation of the comple-
mentary colours, red and green, showed by the application of
his discovery (in 1811) of chromatic polarisation, that the
light of Halley’s Comet (1835) contained reflected solar light.
I was myself present at the earlier experiments for comparing,
by means of the equal and unequal intensity of the images in
the polariscope, the proper light of Capella with the splendid
Comet, as it suddenly emerged from the rays of the sun at
the beginning of July. 1819. (See Annuaire du Bureau des
Long. pour 1836. p. 232; Cosmos, vol. i. p. 90; and Bessel in
Schumacher’s Jahrbuch fiir 1837, 169.)

10 Lettre de M. Arago d M. Alexandre de Humboldt, 1840,

. 37:—* A Taide dun polariscope de mon inyention, je
reconnus (avant 1820) que la lumiére de tous les corps ter-
restres incandescents, soldes ou liquides, est de la lumiére
naturelle, tant qu’elle emane du corps sous des incidences per-
pendiculaires. La lumiére, au contraire, qui sort de la surface
incandescente sous un angle aigu, offre des marques manifestes
de polarisation. Je ne m/arréte pas a te rappeler ici, comment
je déduisis de ce fait la conséquence curieuse que la lumiére
ne s “engendre pas seulement a la surface des corps; qu’une
portion nait dans leur substance méme, cette substance fit-
elle du platine. J’ai seulement besoin de dire qu’en répétant
la méme serie d’épreuves, et avec les mémes instruments sur la
lumiére que lance une substance gazeuse enflammée, on ne lui
trouve, sous quelque inclinaison que ce soit, aucun des caractéres
de la dumiére polarisée; que la lumiére des gaz, prise 4 la

58 COEMOS.

and even the smallest amount of water they contan, of
scrutinizing the depths of the ocean and its rocks by means of

sortie de la surface enflammée, est de la lumiére naturelle, ce
qui n’empéche pas qu'elle ne se polarise ensuite complétement
si on la soumet a des réfiexions ou a des réfractions conven-
ables. De la une méthode trés simple pour découvrir a 40
millions de lieues de distance la nature du soleil. La lumiére
provenant du bord de cet astre. la lumiére émanée de la matiére
solaire sous un angle argu, et nous arrivant sans avoir éprouve
en route des réflexions ou des refractions sensibles, offre-t-elle
des traces de polarisation, le’ soleil est un corps solide ou
liguide. S’il n’y a, au contraire, aucun indice de polarisation
dans la lumiére du bord, la partie incandescente du soleil est
gazeuse. C'est par cet enchainement méthodique d’ observations
qu’on peut arriver a des notions exactes sur la constitution
physique du soleil.” }
“By the aid of my polariscope I discovered (before
1820) that the light of all terrestrial objects in a state of
incandescence, whether they be solid or liquid, is natural
as long as it emanates from the object in perpendicular rays.
The light emanating from an incandescent surface at an acute
angle presents on the other hand manifest proofs of polarisation.
I will not pause to remind you that this circumstance has led
me to the remarkable conclusion that light is not generated on
the surface of bodies only, but that some portion is actually
engendered within the substance itself, even in the case of
platinum. I need only here observe, that in repeating the
same series of experiments (and with the same instruments) on
the light emanating from a burning gaseous substance, I could
not discover any characteristics of polarised light, whatever
might be the angle at which it emanated; and I found that the
light of gaseous bodies is natural light when it issues from the
burning surface, although this circumstance does not prevent its
subsequent complete polarisation, if subjected to suitable re-
flections or refractions. llence we obtain a most simple method
of discovering the nature of the sun at a distance of 40 millions
of leagues. For if the light emanating from the margin of the
sun, and radiating from the solar substance at an acute angle,
reach us without having experienced any sensible reflections
or refractions in its passage to the earth, and if it offer traces

POLARISATION OF LIGHT. 59

a tourmaline plate," and, in accordance with Newton's pre
diction, of comparing the chemical composition® of seve-
ral substances*® with their optical effects. It will be suffi-

of polarisation the sun must be a solid or a liquid body. But
if on the contrary the light emanating from the sun’s margin
give u. indications of polarisation, the incandescent portion
of the sun must be gaseous. Itis by means of such a method-
ical sequence of observations that we may acquire exact
ideas regarding the physical constitution of the sun.’’ (On the
Envelopes of the Sun, see Arago, in the Annuaire pour 1846,
p. 464.) I give all the circumstantial optical disquisitions which
I have borrowed from the manuscript or printed works of my
friend, in his own words, in order to avoid the misconceptions
to which the variations of scientific terminology might give
rise in re-translating the passages into French, or any other
of the various languages in which the Cosmos has appeared.

‘1 « Sur leffet d'une lame de tourmaline taillée parallélement
aux arétes du prisme servant, lorsqu'elle est convenablement
située, a éliminer en totalité les rayons refiéchis par la surface
de la mer et mélés a la lumiére provenant de l’écueil.””. “* On
the effect of a tourmaline plate cut parallel to the edges of the
prism, in concentrating (when placed in a suitable position)
all the rays of light reflected by the surface of the sea, and
blended with the light emanating from the sunken rocks.”
See Arago, Instructions de la Bonitte, in the Annuaire pour
1836, pp. 339-343.

'2@ Te Ja possibilité de déterminer les pouvoirs réfringents des
corps d’aprés leur composition chimique.” On the possibility
of determining the refracting powers of bodies aceording to their
chemical composition (applied to the ratio of the oxygen to the
nitrogen in atmospheric air, to the quantity of hydrogen con-
tained in ammonia and in water, to carbonic acid, aleohol and
the diamond). See Brot et Arago, Mémovre sur les affinités
des corps pour la lumiéere, Mars, 1806; also Meémozres mathem.
et phys. de U Institut, t. vii. pp. 327-346; and my Mémoire
sur les réfractions astronomiques dans la zone torride, in the
Recueil d’ Observ. astron., vol. i. pp. 115 and 122.

18 Expériences de M. Arago sur la puissance réfractive des
corps diaphanes (de lair sec et de lair humide) par le déplace-
ment des frunges, in Moigno, Lépertotre d Optique mod., 1847,
pp. 159-162.

60 COSMOS.

cient to mention the names of Airy, Arago, Biot, Brewster,
Cauchy, Faraday, Fresnel, John Herschel, Lloyd, Malus,
Neumann, Plateau, Seebeck,. . . . . to remind the scientific
reader of a succession of splendid discoveries, and of their
happy applications. The great and intellectual labours of
Thomas Young more than prepared the way for these im-
portant efforts. Arago’s polariscope and the observation of
the position of coloured fringes of diffraction (in consequence
of interference) have been extensively employed in the prose-
cution of scientific inquiry. Meteorology has made equal
advances with physical astronomy in this new path.

However diversified the power of vision may be in different
persons, there is nevertheless a certain average of organic
capacity, which was the same among former generations, as,
for instance, the Greeks and Romans, as at the present day.
The Pleiades prove that several thousand years ago, even as
now, stars which astronomers regard as of the 7th magnitude,
were invisible to the naked eye of average visual power.
The group of the Pleiades consists of one star of the 3rd
magnitude, Aleyone; of two of the 4th, Electra and Atlas ;
of three of the 5th, Merope, Maia, and Taygeta; of two
between the 6th and the 7th magnitudes, Pleione and Celeeno ;
of one between the 7th and the 8th, Asterope; and of many
very minute telescopic stars. I make use of the nomencla-
ture and order of succession at present adopted, as the same
names were amongst the ancients in fart applied to other
stars. The six first-named stars of the 3rd, 4th and 5th magni-
tudes were the only ones which could be readily distinguished.™

‘4 Hipparchus says (ad Arati Phen. 1, pag. 190, in Urano-
logio Petavii), in refutation of the assertion of Aratus, that
there were only six stars visible in the Pleiades :—“ One star
escaped the attention of Aratus. For when the eye is atten-
tively fixed on this constellation on a serene and mocnless
night, seven stars are visible, and it therefore seems strange

Vis] BILITY OF STARS. . Bl

OF these Ovid says (Fast. iv. 170),
** Quee septem dici, sex tamen esse solent.’’

One of the daughters of Atlas, Merope, the only one who
was wedded to a mortal, was said to have veiled herself
for very shame, or even to have wholly disappeared. This
is probably the star of about the 7th magnitude, which
we call Celeno; for Hipparchus, in his commentary on
Aratus, observes that on clear moonless nights seven stars
may actually be seen, Celeeno therefore must have been
seen, for Pleione, which is of equal brightness, is too near
to Atlas, a star of the 4th magnitude.

The little star, Aleor, which, according to Triesnecker, is
situated in the tail of the Great Bear, at a distance of
11’ 48” from Mizar, is, according to Argelander, of the 5th mag-
nitude, but overpowered by the rays of Mizar. It was called
by the Arabs, Saidak, “the Test,” because, us the Persian
astronomer Kazwini remarks, ‘“ It was employed as a test of

that Attalus, in his description of the Pleiades, should have
neglected to notice this oversight on the part of Aratus, as
though he regarded the statement as correct.”’ Merope is called
the invisible (wavahavns) in the Catasterisms (X XIII.) ascribed to
Eratosthenes. On a supposed connexion between the name
of the vevled (the daughter of Atlas) with the geographical
myths in the Meropis of Theopompus, as well as with the great
Saturnian Continent of Plutarch and the Atlantis, see my
Examen crit. de Uhist. de la Géographie, t. i. p. 170. Compare
also Ideler, Untersuchungen uber den Ursprung und die Bedeu-
tung der Sternnamen, 1809, p. 145; and in reference to astrono-
mical determination of place, consult Madler, Untersuch. tiber
die Fixstern-Systeme, th. ii. 1848, s. 836 and 166; also Baily
in the Mem. of the Astr Soc., vol. xiii. p. 33.

_ ™% See Ideler, Sternnamen, s.19and 25. Arago in manuscript
notices of the year 1847, writes as follows .—‘*On observe
qu'une lumiére forte fait disparaitre une lumiére faible placée
dans le yoisinage. Quelle peut en étre Ja cause’ II est pos-
sible physiologiquement que l’ébranlement communique a la
rétiue par la lumiére forte s’étend au dela des points que lg

62 CISMOS.

the power of vision.” Notwithstanding the low position
of the Great Bear under the tropics, I have very dis-
tinctly seen Alcor, evening after evening, with the naked

lumiére forte a frappes, et que cet ébranlement secondwire
absorbe et neutralise en quelque sorte l’ebranlement prove-
nant de la seconde et faible lumiére. Mais sans entrer dans
ces causes physiologiques, il y a une cause directe qu’on peut
indiquer pour la disparition de la faible lumiére: c’est que les
rayons provenant de la grande n'ont pas seulement formé une
image nette sur la rétine, mais se sont dispersés aussi sur toutes
les parties de cet organe a cause des imperfections de transparence.
de la cornée. Les rayons du corps plus brillant a en traversant
la cornée se comportent comme en traversant un corps legére-
ment depoli. Une partie des ces rayons refractés réguliére-
ment forme image méme de a, l’autre partie dispersée éclaire
la totalite de la rétine. C'est done sur ce fond lumineux que
se projette l'image de l'objet voisin 6. Cette derniére image
doit donc ou disparaitre ou étre affaiblie. De jour deux
causes contribuent a l’affaiblissement des étoiles. L’une de
ces causes c’est l'image distincte de cette portion de l’atmo-
sphére comprise dans la direction de l'étoile (de la portion
aérienne placée entre l’cil et l’étoile) et sur laquelle limage
de l’étoile vient de se peindre; l'autre cause c'est la lumiére
diffuse provenant de la dispersion que les défauts de la cornée
impriment aux rayons émanants de tous les points de l’atmo-
sphére visible. De nwt les couches atmospheériques inter-
posées entre l’cil et etoile vers laquelle on vise, n’agis-
sent pas; chaque etoile du firmament forme une image
plus nette, mais une partie de leur lumiére se trouve
dispersée a cause du manque de diaphanité de la cornee.
Le méme raisonnement s applique a une deuxiéme, troi-
siéme . .. . milliéme étoile. La retine se trouve done
éclairée en totalite par une lumiére diffuse, proportionnelle au
nombre de ces étoiles et a leur éclat. On congoit par la que
cette somme de lumiére diffuse affaiblisse ou fasse entiére-
ment disparaitre l'image de l’étoile vers laquelle on dirige la
vue.”

“We find that a strong light causes a fainter one placed
near it to disappear. What can be the cause of this phe-
nomenon? It is physiologically pussible that the vibratiou

VISIBILITY OF STARS. 63

eye, on the rainless shores of Cumana, and on the pla-
teaux of the Cordilleras, which are elevated nearly 13000
feet above the level of the sea, while I have seen it less
frequently and less distinctly in Europe and in the dry

communicated to the retina by strong light may extend
beyond the points excited by it; and that this secondary
vibration may in some degree absorb and neutralise that
arising from the second feeble light. Without, however,
entering upon these physiological considerations, there is a
direct cause to which we may refer the disappearance of
the feeble light: viz., that the rays emanating from the
strong light, after forming a perfect image on the retina,
are dispersed over all parts of this organ in consequence
of the imperfect transparency of the cornea. The rays of
the more brilliant body a, in passing the cornea, are affected
in the same manner as if they were transmitted through a
body whose surface was not perfectly smooth. Some of
these regularly refracted rays form the image a, whilst the
remainder of the dispersed rays illumine the whole of the
retina. On this luminous ground the image of the neigh-
bouring object 4 is projected. This last image must there-
fore either wholly disappear or be dimmed. By day two
causes contribute to weaken the light of the stars; one is the
distinct image of that portion of the atmosphere included in
the direction of the star (the aerial field interposed between
the eye and the star), and on which the image of the star is
formed, while the other is the light diffused by the dispersion
which the defects of the cornea impress on the rays emanat-
ing from all points of the visible atmosphere. A? night, the
strata of air interposed between the eye and the star to which
we direct the instrument, exert no disturbing action ; each star
in the firmament forms a more perfect image, but a portion of
the light of the stars is dispersed in consequence of the im-
perfect transparency of the cornea. The same reasoning
applies to a second, a third, or a thousandth star. The retina
then is entirely illumined by a diffused light. proportionate to
the number of the stars and to their brilliancy. Hence we
may imagine that the aggregate of this diffused light must
either weaken, or entirely obliterate the image of the star
towards which the eye is directed.”

64 COSMOS.

acmosphere of the Steppes of Northern Asia. The “imits
within which the naked eye is unable to separate two very
contiguous objects in the heavens depend, as Madler has
*ustly observed, on the relative brilliancy of the stars. The
two stars of the 3rd and 4th magnitudes, marked as a Capri-
corni, which are distant from each other six-and-a-half minutes,
can with ease be recognized as separate. Galle thinks that
e and 5 Lyre, being both stars of the 4th magnitude, may be
distinguished in a very clear atmosphere by:the naked eye,
although situated at a distance of only three-and-a-half minutes
from each other.

The preponderating effect of the rays of the neighbouring
planet is also the principal cause of Jupiter's satellites remain-
ing invisible to the naked eye; they are not all, however, as
has frequently been maintained, equal in brightness to stars of
the 5th magnitude. My friend, Dr. Galle, has found from
recent estimates, and by a comparison with neighbouring
stars, that the third and brightest satellite is probably of the
5th or 6th magnitude, whilst the others, which are of various
degrees of brightness, are all of the 6th or 7th magnitude
There are only few cases on record in which persons of ex-
traordinarily acute vision—that is to say, capable of clearly
distinguishing with the naked eye stars fainter than those of
the 6th magnitude,—have been able to distinguish the satellites
of Jupiter without a telescope. The angular distance of the
third and brightest satellite from the centre of the planet is
4’ 42”; that of the fourth, which is only 4th smaller than the
largest is 8’ 16”: and all yupiter’s satellites sometimes exhibit,
as Arago maintains, a more intense light for equal surfaces

3 Arago, in the Annuaire pour 1842, p. 284, and in the
Comptes rendus, tom. xv 1842, p. 750. (Schum. Aséron.
Nachr., no. 702.) I have instituted some calculations of mag-
nitudes, in reference to your conjectures on the visibility
of Jupiter's satellites,” writes Dr. Gaile, in letters addressed

RADIATIONS OF THE STARS. 65

than Jupiter himself; occasionally, however, as shown by
recent observations, they appear like gray spots on the planet.
The rays or tails, which to our eyes appear to radiate frow

the planets and fixed stars, and which were used, since the.
earliest ages of mankind, and especially amongst the Egyptians,

to me, ‘but I have found, contrary to my expectation
that they are not of the 5th magnitude, but, at most, only
of the 6th or even of the 7th magnitude. The 3rd and brightest
satellite alone appeared nearly equal in brightness to a neigh-
bouring star of the 6th magnitude. which I could scarcely
recognize with the naked eye, even at some distance from
Jupiter; so that, considered in reference to the bright-
ness of Jupiter, this satellite would probably be of the
5th or 6th magnitude if it were isolated from the planet.
The 4th satellite was at its greatest elongation, but yet I
could not estimate it at more than the 7th magnitude. The
rays of Jupiter would not prevent this satellite from being
seen if it were itself brighter. From a comparison of Alde-
baran with the neighbouring star @ Tauri, which is easily
recognized as a double star (at a distance of 54 minutes),
I should estimate the radiation of Jupiter at five or six minutes,
at the least, for ordinary vision.” These estimates cor-
respond with those of Arago, who is even of opinion that this
false radiation may amount in the case of some persons to double
this quantity. The mean distances of the four satellites from
th centre of the main planet are undoubtedly 1’51”, 2’57”, 442”,
aud 816”. ‘Si nous supposons que l'image de Jupiter, dans
certains yeux exceptionnels, s’épanouisse seulement par des
rayons d’une ou deux minutes d’amplitude, il ne semblera pas
impossible que les satellites soient de tems en tems apercus, sans
avoir besoin de recourir a l’artifice de l’amplification. Pour
verifier cette conjecture, j'ai fait construire une petite lunette
dans laquelle I objectif et l’oculaire ont a peu prés le méme foyer,
et qui dés lors ne grossit point. Cette lunette ne détruit pas
entiérement les rayons divergents, mais elle en réduit considér-
ablement la longueur. Cela a suffi pour qu'un satellite con-
venablement écarté de la planéte, soit devenu visible. Le fait a
ete constaté par tous les jeunes astronomes de |’ Observatoire.”
“ If we suppose that the image of Jupiter appears to the eves

TOL. Iii. F

66 COsMOS.

as pictorial representations to indicate the shining orbs of
heaven, are at least from five to six minutes in length. (These
lines are regarded by Hassenfratz as caustics on the crystalline
lens : intersections des deux caustiques.)

“The image of the star which we see with the naked eye
is magnified by diverging rays, in consequence of which it
occupies a larger space on the retina than if it were concen-

of some persons to be dilated by rays of only one or two
minutes, it is not impossible that the satellites may from time
to time be seen without the aid of magnifying glasses. In
order to verify this conjecture I caused a small instrument to
be constructed in which the object-glass and the eye-piece
had nearly the same focus, and which therefore did not mag-
nify. This instrument does not entirely destroy the diverging
rays, although it considerably reduces their length. This
method has sufficed to render a satellite visible when at a
sufficient distance from the planet. This observation has been
confirmed by all the young astronomers at the Observatory.”
(Arago in the Comptes rendus, tom. xv. 1842, p. 751.)

As a remarkable instance of acute vision and of the great
sensibility of the retina in some individuals who are able to
see Jupiter's satellites with the naked eye, I may instance
the case of a master tailor, named Schén, who died at
Breslau in 1887, and with reference to whom I have re-
ceived some interesting communications from the learred
and active director of the Breslau Observatory, Von Bogu:-
lawski. ‘‘ After having (since 1820) convinced ourselves, by
several rigid tests, that in serene moonless nights Schén was
able correctly to indicate the position of several of Jupiter's
satellites at the same time, we spoke to him of the emana-
tions and tails which appeared to prevent others from seeing
so clearly as he did, when he expressed his astonishment at
these obstructing radiations. From the animated discussions
between himself and the bystanders regarding the difficulty
of seeing the satellites with the naked eye, the conclusion
was obvious, that the planet and fixed stars must always
appear to Schén like luminous points having no rays. He
saw the third satellite the best, and the first very plainly when

NATURAL VISION. 67

trated in a single point. The impression on the nerves is
weaker. A very dense starry swarm, in which scarcely any
of the separate stars belong even to the 7th magnitude, may,
on the contrary, be visible to the unaided eye in consequence
of the images of the many different stars crossing each other
upon the retina, by which every sensible point of its surface is
more powerfully excited, as if by one concentrated image.” ”

it was at the greatest digression, but he never saw the second
and the fourth alone. When the air was not in a very favour-
able condition the satellites appeared to him like faint streaks
of light. He never mistook small fixed stars for satellites,
probably on account of the scintillating and less constant
light of the former. Some years before his death Schén com-
plained to me that his failing eye could no longer distinguish
Jupiter’s satellites, whose position was only indicated, even
in clear weather, by light faint streaks.” These circumstances
entirely coincide with what has been long known regarding
the relative lustre of Jupiter’s satellites, for the brightness and
quality of the light probably exert a greater influence than
mere distance from the main planet on persons of such great
perfection and sensibility of vision. Schén never saw the
second nor the fourth satellite. The former is the smallest of
all; the latter, although the largest after the third and the most
remote, is periodically obscured by a dark colour, and is gene-
rally the faintest of all the satellites. Of the third and the
first which were best and most frequently seen by the naked
eye, the former, which is the largest of all, is usually the
brightest, and of a very decided yellow colour; the latter
occasionally exceeds in the intensity of its clear yellow light
the lustre of the third, which is also much larger. (Midler,
Astr. 1846, s. 231-234, and 439.) Sturm and Airy, in the
Comptes rendus, t. xx. pp. 764-6, show how, under proper
conditions of refraction in the organ of vision, remote luminous
points may appear as light streaks.

Liimage épanowe dune étoile de 7éme grandeur
n’ébranle pas suffisamment la rétine: elle n’y fait pas naitre
une sensation appreciable de lumiére. Si l'image n’ééast
point épanowe (par des rayons divergents), la sensatiw

F2

68 COSMOS.

Telescopes, although in a much less degree, unfortunately also
give the stars an incorrect and spurious diameter ; but accord-,

aurait plus de force, et l’étoile se verrait. La premiére classe
d'étoiles invisibles 4 l’ceil nu ne serait plus alors la septiéme:

pour la trouver, il faudrait peut-étre descendre alors jusqu’a,
la 12€me. Considérons un groupe d’étoiles de 7éme grandeur.
tellement rapprochees les unes des autres que les intervalles

échappent necessairement a Toil. Sv la vision avait de la

netteté, si limage de chaque étoile était trés petite et bien

trxminée, l‘observateur aperceverait un champ de lumiére dont
chaque point aurait /’éclat concentré d'une étoile de 7éme gran-

deur. L’éclat concentré d'une etoile de 7éme grandeur suffit a

la vision a l’ceil nu. Le groupe serait donc visible a l’ceil nu.

Dilatons maintenant sur la rétine l’image de chaque étoile du

groupe; remplagons chaque point de l’ancienne image geéné-
rale par un petit cercle: ces cercles empiéteront les uns sur

les autres, et les divers points de la rétine se trouveront

éclairés par de la lumiére venant simultanément de plusieurs

étoiles. Pour peu qu’on y réefléchisse, il restera évident qu’

excepté sur les bords de l'image générale, l’aire lumineuse

ainsi éclairée a precisement, a cause de la superposition des

cercles, la méme intensité que dans le cas ot chaque étoile

n’éclaire qu’un seul point au fond de l’eil; mais si chacun

de ces points recoit une lumiére eégale en intensité a la

lumiére concentrée d’une étoile de 7éme grandeur, il est clair
que l'épanouissement des images indivrduelles des étoiles
contigues ne doit pas empécher la visibilite de l’ensemble.

Les instruments telescopiques ont, quoiqu’d un beaucoup

moindre degré, le défaut de donner aussi aux étoiles un
idiaméire sensible et factice. Avec ces instruments, comme a

Yoil nu, on doit done apercevoir des groupes, composes

détoiles inférieures en intensité a celles que les mémes

lunettes ou telescopes feraient apercevoir isolement.”

“The expanded image of a star of the 7th magnitude does
not cause sufficient vibration of the retina, and does not give
rise to an appreciable sensation of light. If the image were
not expanded (by divergent rays), the sensation would be
stronger and the star discernible. The lowest magnitude at
which stars are visible would not therefore be the 7th, but
some magnitude as low perhaps as the 12th degree. Let us

VISION. 69

ing to the splendid investigations of Sir William Herschel,'*
these diameters decrease with the increasing power of the in-
strument. This distinguished observer estimated that, at the
excessive magnifying power of 6500, the apparent diameter
of Vega Lyre still amounted to 0’36. In terrestrial objects
the form, no less than the mode, of illumination, determines
the magnitude of the smallest angle of vision for the naked

consider a group of stars of the 7th magnitude so close to
one another that the intervals between them necessarily escape
the eye. Jf the sight were very clear, and the image of each
star small and well defined, the observer would perceive a field
of light, each point of which would be equal to the concen-
trated brightness of a star of the 7th magnitude. ‘The concen-
trated light of a star of the 7th magnitude is sufficient to be
seen by the naked eye. The group, therefore, would be visible
to the naked eye. Let us now dilate the image of each star of
the group on the retina, and substitute a small circle for each
point of the former general image; thesc circles will impinge
upon one another, and the different points of the retina will
be illumined by light emanating simultaneously from many
stars. A slight consideration will show, that, excepting at
the margins of the general image, the luminous air has, in
consequence of the superposition of the circles, the same
degree of intensity as in those cases where each star illu-
mines only one single point of the retina; but if each of
these points be illumined by a light equal in intensity to the
concentrated light of a star of the 7th magnitude, it is evi-
dent that the dilatation of the individual images of contiguous
stars cannot prevent the visibility of the whole. Telescopic
instruments have the defect, although in a much less degree,
of giving the stars a sensible and spurious diameter. We
therefore perceive with instruments, no less than with the
naked eye, groups of stars, inferior in intensity to those which
the same telescopic or natural sight would recognize, if they
were isolated.” Arago, in the Annuaire du Bureau des Longi:
tudes pour lan 1842, p. 284.

%® Sir William Herschel, in the Philos. Transact. for 1808,
vol, 93, p. 225, and for 1805, vol. 94, p. 184. Compare alsa
Arago, in the Annuaire pour 1842, pp. 360-374.

70 COSMOS

eye. Adams very correctly observed that a long and slen-
der staff can be seen at a much greater distance than a
square whose sides are equal to the diameter of the staff.
A stripe may be distinguished at a greater distance than a
spot, even when both are of the same diameter. Arago has
made numerous calculations on the influence of form (outline
of the object) by means of angular measurement of distant
lightning conductors visible from the Paris Cbservatory. The
minimum optical visual angle at which terrestrial objects can
be recognized by the naked eye has been gradually estimated
lower and lower from the time when Robert Hooke fixed it
exactly at a full minute, and Tobias Mayer required 34” to
perceive a black speck on white paper, to the period of Leeu-
wenhoek’s experiments with spider's threads, which are visible
to ordinary sight at an angle of 4”°7. In the recent and
most accurate experiments of Hueck, on the problem of the
movement of the crystalline lens, white lines on a black
ground were seen at an angle of 1”:2; a spider's thread at
0”°6; and a fine glistening wire at scarcely 02. This pro-
blem does not admit generally of a numerical solution, since it
entirely depends on the form of the objects, their illumination,
their contrast with the back-ground, and on the motion or
rest, and the nature of the atmospheric strata in which the
observer is placed.

During my visit ata charming country-seat belonging to
the Marques de Selvalegre, at Chillo, not far from Quito,
where the long extended crests of the voleano of Pichincha
lay stretched before me ata horizontal distance, trigonometri-
cally determined at more than 90000 feet, I was much
struck by the circumstance that the Indians who were
standing near me distinguished the figure of my travelling
2ompanion Bonpland (who was engaged in an expedition to
he volcano) as a white point moving on the black basaltic sides
of the rock, soon7r than we could discover him with our teles-

VISIBILITY OF ORJECTS. 72

copes. The white moving image was soon detected with
the naked eye both by myself and by my friend the unfortu-
nate son of the Marques, Carlos Montufar, who subsequently
perished in the civil war. Bonpland was enveloped in a white
cotton mantle, the Poncho of the country; assuming the
breadth across the shoulders to vary from three to five feet,
according as the mantle clung to the figure or fluttered in the
breeze, and judging from the known distance, we found that
the angle at which the moving object could be distinctly seen,
varied from 7” to 12”. White objects on a black ground are,
_ according to Hueck’s repeated experiments, distinguished at a
greater distance than black objects on a white ground. The
light was transmitted in serene weather through rarefied strata
of air at an elevation 15360 feet abcve the level of the sea to
our station at Chillo, which was itself situated at an elevation
of 8575 feet. The ascending distance was 91225 feet, o1
about 17} miles. The barometer and thermometer stood at
very different heights at both stations, being probably at the
upper one about 17-2 inches and 46°4, while at the lower
station they were found, by accurate observation, to be 22:2
inches and 65°°7._Gauss’s heliotrope light, which has become
so important an element in German trigonometrical measure-
ments, has been seen with the naked eye reflected from the
Brocken on Hohenhagen, at a distance of about 227000 fect,
or more than 42 miles; being frequently visible at points
in which the apparent breadth of a three-inch mirror was
only 0°43.

The visibility of distant objects is modified by the absorp.
tion of the rays passing from the terrestrial object to. the
naked eye at unequal distances, and through strata of air
more or less rarefied and more or less saturated with moisture ;
by the degree of intensity of the light diffused by the radiation
of the particles of air; and by numerous meteorological pro-
cesses not yet fully explained. It appears from the old ex.

72 COSMOS.

periments of the accurate observer, Bouguer, that a difference
of 5th in the intensity of the light is necessary to render
objects visible. To use his own expression, we only negatively
see mountain-tops from which but little light is radiated, and
which stand out from the vault of heaven in the form of dark
masses ; their vis-bility is solely owing to the difference in the
thickness of the atmospheric strata extending respectively to
the object and to the horizon. Strongly illumined objects, such
as suow-clad mountains, white chalk cliffs, and conical rocks
of pumice-stone, are seen positively.

The distance at which high mountain summits may be
recognized from the sea is not devoid of interest in relation to
practical navigation, where exact astronomical determinations
are wanting to indicate the ship’s place. I have treated
this subject more at length in another work,” where I con-
sidered the distance at which the Peak of Teneriffe might be
seen.

The question whether stars can be seen by daylight with the
naked eye through the shafts of mines, and on very high
mountains, has been with me a subject of inquiry since my
early youth. I was aware that Aristotle had maintained™

% Humboldt, Rélation list. du Voyage aux Régions équinox.
tom. i. pp. 92-97; and Bouguer, 7raité d’ Optique, pp. 360
and 365. (Compare also Captain Beechey in the Manual
of Scientific Enquiry for the use of the Royal Navy, 1849,

Met .
90 The passage in Aristotle referred to by Buffon occurs in
a work where we should have least expected to find it—De
Generat. Anmal., v. 1. p. 780, Bekker. Literally trans-
lated, it runs as follows :—‘‘ Keenness of sight is as much
tke power of seeing far, as of accurately distinguishing
the differences presented by the objects viewed. These two
properties are not met with in the same individuals. For
he who holds his hand over his eyes, or looks through a
twhe, is not on that account more or less able to distinguish

VISIBILITY OF STARS. ‘3

that stars might occasionally be seen from caverns and cisterns,
as through tubes. Pliny alludes to the same circumstance, and
mentions the stars that have been most distinctly recognized
during solar eclipses. While practically engaged in mining
operations I was in the habit, during many years, of passing a
great portion of the day in mines where I could see the sky
through deep shafts, yet I never was able to observe a star ;
nor did I ever meet with any individual in the Mexican,
Peruyian, or Siberian mines, who had heard of stars having
been seen by day-light; although in the many latitudes, in
both hemispheres, in which I have visited deep mines, a suffi-.
ciently large number of stars must have passed the zenith to
have afforded a favourable opportunity for their being seen.
Considering this negative evidence, I am the more struck by the
highly credible testimony of a celebrated optician, who in his
youth saw stars by day-light, through the shaft of a chimney. *

differences of colour, although he will see objects at a greater
distance. Hence it arises that persons m caverns or cisterns
are occasionally enabled to see stars.”’ ‘The Grecian ’Opiypara,
aud more especially g¢péara, are, as an eye-witness, Pro-
fessor Franz, observes, subterranean cisterns or reservoirs
which communicate with the light and air by means of a
vertical shaft, and widen towards the bottom, like the neck
of a bottle. Pliny (lib. 1. cap. 14) says, “ Altitudo cogit
minores videri stellas; atfixas ccelo solis fulgor interdiu non
cerni, quum eque ac noctu luceant; idque manifestum fiat
defectu solis et prealtis putes.” Cleomedes (Cycl. Theor.,
p- 83, Bake) does not speak of stars seen by day, but
asserts ‘‘ that the sun, when observed from deep cisterns,
appears larger, on account of the darkness and the damp
air.”

#1 «We have ourselves heard it stated by a celebrated cpti-
cian that the earliest circumstance which drew his attentiot
to astronomy, was the regular appearance, at a certain hour,
for several successive days, of a considerable star, through
the shaft of a chimney.”’ John Herschel, Outlines of Asir.,
§ 61. The chimney-sweepers whom I have questioned agree

74 COSMOS.

Phenomena, whose manifestation depends on the accidental]
concurrence of favouring circumstances, ought not to be dis-
believed on account of their rarity.

The same principle must, I think, be applied to the asser-
tion of the profound investigator, Saussure, that stars have
been seen with the naked eye in bright day-light, on the
declivity of Mont Blanc, and at an elevation of 12757 feet.
‘‘Quelques-uns des guides m’ont assuré avoir vu des étoiles
en plein jour; pour mot je n’y songeais pas, en sorte que je
n’ai point été le temoin de ce phenoméne; mais lassertion
uniforme des guides ne me laisse aucun doute sur la réalité. U
faut d’ailleurs étre entiérement a l’ombre d'une épaisseur con-
sidérable, sans quoi l’air trop fortement éclairé fait evanouir la
faible clarté des étoiles.” ‘‘ Several of the guides assured me,”
says this distinguished Alpine inquirer, ‘‘ that they had seen
stars at broad day-light; not having myself been a witness of
this phenomenon, I did not pay much attention to it, but the
unanimous assertions of the guides left me no doubt of its
reality.™ It is essential, however, that the observer should
be placed entirely in the shade, and that he should even have
a thick and massive shade above his head, since the stronger
light of the air would otherwise disperse the faint image of
the stars.” These conditions are therefore nearly the same as
those presented by the cisterns of the ancients, and the chimneys
above referred to. I do not find this remarkable statement
(made on the morning of the 2nd of August, 1787,) in any
other description of the Swiss mountains. Two well-informed,

tolerably well in the statement that “they have never seen
stars by day, but that, when observed at night, through deer
shafts, the sky appeared quite near, and the stars larger.”
I will not enter upon any discussion regarding the connec-
tion between these two illusions.

% Consult Saussure, Voyage dans les Alpes, (Neuchatel,
1779, 4to.) tom. iv. § 2007, p. 199.

VISIBILITY OF STARS. 45

admirable observers, the brothers Hermann and Adolph Schla-
gentweit, who have recently explored the eastern Alps, as far
as the summit of the Gross Glockner, (13016 feet,) were never
able to see stars by daylight, nor could they hear any report of
such a phenomenon haying been observed amongst the goat-
herds and chamois hunters. Although I passed many years
in the Cordilleras of Mexico, Quito, and Peru, and frequently
in clear weather ascended, in company with Bonpland, to eleva-
tions of more than fifteen or sixteen thousand feet above the
level of the sea, I never could distinguish stars by day-light,
nor was my friend Boussingault more successful in his subse-
quent expeditions; yet the heavens were of an azure so
intensely deep, that a cyanometer (made by Paul of Geneva,)
which had stood at 39° when observed by Saussure on
Mont Blanc, indicated 46° in the zenith under the tropics at
elevations varying between 17000 and 19000 feet.% Under
the serene etherially-pure sky of Cumana, in the plains near
the sea-shore, I have frequently been able, after observing an
eclipse of Jupiter’s satellites, to find the planet again with the
naked eye, and have most distinctly seen it when the sun’s
dise was from 18° to 20° above the horizon.

The present would seem a fitting place to notice, although
eursorily, another optical phenomenon, which I only observed
once during my numerous mountain ascents. Before sunrise,
on the 22nd of June, 1799, when at Malpays, on the declivity
of the Peak of Teneriffe, at an elevation of about 11400 feet

above the sea’s level, I observed, with the naked eye, stars
near the horizon flickering with a singular oscillating motion.
Luminous points ascended, moved Jaterally, and fell back to
their former position. This phenomenon lasted only from

*% Humboldt, Essai sur la Géographie des Plantes, p. 103.
Compare also my Voy. aux Régions équinoz., tom. i. pp. 143
248

7S COSMOS.

seven to eight minutes, and ceased long before the sun's dise
appeared above the horizon of the sea. The same motion was
discernible through a telescope, and there was no doubt that
it was the stars themselves which moved. Did this change
of position depend on the much contested phenomenon of
lateral radiation? Does the undulation of the rising sun’s
disc, however inconsiderable it may appear when measured,
present any analogy to this phenomenon in the lateral alteration
. of the sun’s margin? Independently of such a consideration,
this motion seems greater near the horizon. This phenomenon
of the undulation of the stars was observed almost half a cen-
tury later at the same spot by a well-informed and observing
traveller, Prince Adalbert, of Prussia, who saw it both with
the naked eye and through a telescope. I found the obser-
vation recorded in the Prince’s manuscript journal, where he
had noted it down, before he learned, on his return from the
Amazon, that I had witnessed a precisely similar phenomenon.”

* Humboldt, in Fr. Von Zach’s Monatliche Correspondenz
zur Erd-und Himmels-Kunde, bd. i. 1800, s. 3896; also Voy. aux
Rég. équin., tom. i. p. 125.—** On croyait voir de petites fusees
lancées dans lair. Des points lumineux éleves de 7 4 8 degres,
paraissent d’abord se mouvoir dans le sens vertical, mais puis
se convertir en une veritable oscillation horizontale. Ces
images lumineux étaient des images de plusieurs etoiles agran-
dies (en apparence) par des vapeurs et revenant au meme
point d'ou elles étaient partis.”’ ‘‘ It seemed as if a number of
small rockets were being projected in the air; luminous points,
at an elevation of 7° or 8°, appeared moving, first in a vertical,
and then oscillating ina horizontal direction. These were the
i images of many stars, apparently magnified by vapours, and
returning to the same point from which they had emanated.”

*% Prince Adalbert of Prussia, Aws meinem Tagebuche,
1847, s. 213. Is the phenomenon IJ have described connected
with the oscillations of 10’-12”, observed by Carlini, in the
passage of the Polar star over the field of the great Milan
meridiat telescope? (See Zach's Correspondance astrono.

ASTRONOMICAL DISCOVERIES. 77

I was never able to detect any trace of lateral refraction on
the declivities of the Andes, or during the frequent mirages
in the torrid plains or Llanos of South America, notwith-
standing the heterogeneous mixture of unequally heated
atmospheric strata. As the Peak of Teneriffe is so near us,
and is so frequently as:ended before sun-rise by scientific
travellers provided with instruments, I would hope that this
reiterated invitation on my part to the observation of the
undulation of the stars may not be wholly disregarded.

I have already called attention to the fact that the basis
of a very important part of the astronomy of our planetary
system was already laid before the memorable years 1608 and
1610, and therefore before the great epoch of the invention of
telescopic vision, and its application to astronomical purposes.
The treasure transmitted by the learning of the Greeks and
Arabs, was augmented by the careful and persevering labours
of George Purbach, Regiomontanus (7. e. Johann Miiller) and
Bernhard Walther of Niirnberg. To their efforts succeeded a
bold and glorious development of thought—the Copernican
system ; this again was followed by the rich treasures derived
from the exact observations of Tycho Brahe, and the combined
acumen and persevering spirit of calculation of Kepler. Two
great men, Kepler and Galileo, occupy the most important
turning-point in the history of measuring astronomy ; both
indicating the epoch that separates observation by the
naked eye, though aided by greatly improved instruments of
measurement, from ¢elescopic vision. Galileo was at that
period forty-four, and Kepler thirty-seven years of age; Tycho

mique et géog., vol. li. 1819, p. 84.) Brandes (Gehler’s
Umgearb. phys. WGrtersb, bd. iv s. 549) refers the pheno-
menon to mirage. The star-like heliotrope light has also
frequently been seen, by the admirable and skilful observer,
Colonel Baeyer, to oscillate to and fro, in a horizontal
direction.

78 COSMOR,

Brahe, the most exact of the measuring astronomers of that
great age, had been dead seven years. I have already men-
tioned, in a preceding volume of this work (see p. 711), that
none of Kepler’s contemporaries, Galileo not excepted, be-
stowed any adequate praise on the discovery of the three laws
which have immortalised his name. Discovered by purely
empirical methods, although more rich in results to the whole
domain of science, than the isolated discovery of unseen cosmical
bodies, these laws belong entirely to the period of natural
vision, to the epoch of Tycho Brahe and his observations;
although the printing of the work entitled Astronomia nova —
seu Physica ceelestis de motibus Stelle Martis, was not com-
pleted until 1609, and the third law, that the squares of the
periodic times of revolution of two planets are as the cubes of
their mean distances, was first fully developed in 1619, in the
Harmonice Mundi.

The transition from natural to telescopic vision which cha-
racterizes the first ten years of the seventeenth century, was
more important co astronomy (the knowledge of the regions of
space), than the year 1492, (that of the discoveries of Columbus)
in respect to our knowledge of terrestrial space. It not only in-
finitely extended our insight into creation, but also, besides en
riching the sphere of human ideas, raised mathematical science
to a previously unattained splendour, by the exposition of new
and complicated problems. Thus the increased power of the
organs of perception re-acts on the world of thought, to the
strengthening of intellectual force, and the ennoblement of
humanity. To the telescope alone we owe the discovery, in.
less than two-and-a-half centuries, of thirteen new planets,
of four satellite-systems, (the four moons of Jupiter, eight
satellites of Saturn, four, or perhaps six of Uranus, and one of
Neptune), of the sun’s spots and facule, the phases of Venus,
the form and height of the lunar mountains, the wintry polar
cones of Mars, the belts of Jupiter and Saturn, the rings of

ASTRONOMICAL DISCOVERIES. 72

the latter, the interior planetary comets of short periods of
revolution, together with many other phenomena which like-
wise escape the naked eye. While our own solar system,
which so long seemed limited to six planets and one moon,
has been enriched in the space of 240 years with the dis-
coveries to which we have alluded; our knowledge regarding
successive strata of the region of the fixed stars has unexpect-
edly beex still more increased. Thousands of nebule, stellar
swarms, and double stars, have been observed. The changing
position of the double stars which revolve round one common
centre of gravity has proved, like the proper motion of all
fixed stars, that forces of gravitation are operating in those
distant regions of space, as in our own limited mutually-
disturbing planetary spheres. Since Morin and Gascoigne
(not indeed till twenty-five or thirty years after the invention
of the telescope,) combined optical arrangements with mea-
suring instruments, we have been enabled to obtain more
accurate observations of the change of position of the stars.
By this means we are enabled to calculate, with the greatest
precision, every change in the position of the planetary bodies,
the ellipses of aberration of the fixed stars and their parallaxes,
and to measure the relative distances of the double stars even
when amounting to only a few tenths of a seconds-are. The
astronomical knowledge of the solar system has gradually ex-
tended to that of a system of the universe.

We know that Galileo made his discoveries of Jupiter's
satellites with an instrument that magnified only seven
diameters, and that he never could have used one of a higher
power than thirty-two. One hundred and seventy years later,
we find Sir William Herschel, in his investigations on the
magnitude of the apparent diameters of Arcturus (0:2 within
the nebula) and of Vega Lyre, using a power of 6500. Since
the middle of the seventeenth century, constant attempts have
been made to inerease the focal length of the telescope.

as noistly however cies the bease with instruments ot ~
a greater focal length, even of 122 feet; but the three object-
glasses in the possession of the Royal Society of London
whose focal lengths are respectively 128, 170, and 210 feet,
and which were constructed by Constantine Huygens, brother
of the great astronomer, were only tested by the latter, as
he expressly states,% upon terrestrial objects. Auzout, who
in 1663 constructed colossal telescopes without tubes, and
therefore without a solid connexion between the object-
glass and the eye-piece, completed an object glass, which,
with a focal length of 320 feet, magnified 600 times.”
The most useful application of these object-glasses, mounted
on poles, was that which led Dominic Cassini, between the
years 1671 and 1684, to the successive discoveries of the
eighth, fifth, fourth, and third satellites of Saturn. He made
use of object-glasses that had been ground by Borelli, Cam-
pani, and Hartsoeker. Those of the latter had a focal length
of 266 feet.

During the many years I passed at the Paris Observatory,
I frequently had in my hands the instruments made by
Campani, which were in such great repute during the reign
of Louis XIV; and when we consider the faint light of
Saturn's satellites, and the difficulty of managing instruments,

%* The remarkable artistical skill of Constantin Huygens,
who was private secretary to King William the Third, has
only recently been presented in its proper light by Uyten-
brock in the “ Oratio de fratribus Christiano atque Constantine
Hugenio, artis dioptrice cultoribus,” 1838; and by Prof.
Kaiser, the learned director of the Observatory at Leyden
(in Schumacher’s Astron. Nachr., no. 592, s. 246).

- ™ See Arago, in the Annuaire pour 1844, p. 381.

TELESCOPES. S81

worked by sizings only,¥ we cannot sufficiently admire the
skill and the untiring perseverance of the observer.

The advantages which were at that period supposed to be
obtainable only by gigantic length, led great minds, as is
frequently the case, to extravagant expectations. Auzout
considered it necessary to refute Hooke, who is said to have
proposed the use of telescopes having a length of upwards of
10000 feet, (or nearly two miles,) * in order to see animals in
the moon. A sense of the practical inconvenience of optical
instruments having a focal length of more than a hundred

% « Nous avons placé ces grands verres, tantot sur un grand
mat, tantét sur la tour de bois venue de Marly; enfin nous
les avons mis dans un tuyau monte sur un support en forme
déchelle a trois faces, ce quia eu (dans la découverte des
satellites de Saturne) le succés que nous en avions espéce.”
“We sometimes mounted these great instruments on a
high pole,” says Dominique Cassini, “and sometimes on the
wooden tower that had been brought from Marly; and we
also placed them in a tube mounted on a three-sided ladder,
a methed which, in the discovery of the satellites of Saturn,
gave us all the success we had hoped.” Delambre, Hist. de
V Astr. moderne, tom. ii. p. 785. Optical instruments having
such enormous focal lengths remind us of the Arabian instru-
ments of measurement—quadrants with a radius of about 190
feet, upon whose graduated limb the image of the sun was re-
ceived as in the gnomon, through a small round aperture. Such
a quadrant was erected at Samarcand, probably constructed
after the model of the older sextants of Al-Chokandi (which
were about 60 feet in height). Compare Sedillot, Prolégo-
ménes des Tables d’ Oloug. Beigh, 1847, p. lvii. and exxix.

® See Delambre, Hist. de 1 Astr. mod., t. ii. p. 594. The
mystic Capuchin Monk, Schyrle von Rheita, who how-
ever was well versed in optics, had already spoken in his
work, Oculus Enoch et Elie, (Anty. 1645) of the speedy prac-
ticability of constructing telescopes that should magnify 4000
times, by means of which the lunar mountains might be accu-
rately laid down. Compare also Cosmos, vol. ii. p. 705 (note).

VOL. III. G

82 COSMOS.

feet, led, through the influence of Newton, (in following out
the earlier attempts of Mersenne and James Gregory of
Aberdeen,) to the adoption, especially in England, of shorter
reflecting telescopes. The careful comparison made by Brad-
ley and Pond, of Hadley’s five-feet reflecting telescopes, with
the refractor constructed by Constantin Huygens, (which
had, as already observed, a focal length of 123 feet,) fully
demonstrated the superiority of the former. Short’s expen-
sive reflectors were now generally employed until 1759, when
John Dollond’s successful practical solution of the problem of
achromatism, to which he had been incited by Leonhard
Euler, and Klingenstierna, again gave preponderance to
refracting instruments. The right of priority which appears
to have incontestably belonged to the mysterious Chester
More, Esq., of More Hall in Essex, (1729,) was first made
known to the public, when John Dollond obtained a patent
for his achromatic telescopes.”

The triumph obtained by refracting instruments was not,
however, of long duration. In eighteen or twenty years
after the construction of achromatic instruments by John
Dollond, by the combination of crown with flint glass, new
fluctuations of opinion were excited by the just admiration
awarded, both at home and abroad, to the immortal labours
of a German, William Herschel. The construction of numerous
seven-feet and twenty-feet telescopes, to which powers of from
2200 to 6000 could be applied, was followed by that of his
forty-feet reflector. By this instrument he discovered, in
August and September, 1789, the two innermost satellites of
Saturn—Enceladus, the secend in order, and soon afterwards,
Mimas, the first or the one nearest to the ring. The dis- |
covery of the planet Uranus in 1781, was made with Herschel’s
seven-feet telescope, while the faint satellites of this planet

— --

%° Edinb. Encyclopedia, vol. xx. p. 479

TELESCOY!: ES. 83

were first observed by him in 1787, with a twenty-feet “ fron.
view” reflector." The perfection, unattained till then, which
this great man gave to his reflecting telescopes, in which light
was only once reflected, led, by the uninterrupted labour of
more than forty years, to the most important extension of all
departments of physical astronomy in the planetary spheres,
no less than in the world of nebule and double stars.

The long predominance of reflectors was followed, in the
earlier part of the nineteenth century, by a successful emula-
tion in the construction of achromatic refractors, and helio-
meters, paralactically moved by clockwork. A homogeneous,
perfectly smooth flint-glass, for the construction of object-
glasses of extraordinary magnitude, was manufactured in the
institutions of Utzschneider and Fraunhofer at Munich, and
subsequently in those of Merz and Mahler; and in the esta-
blishments of Guinand and Bontems, (conducted for MM. Lere-
bours and Cauchoix,) in Switzerland and France. It will be
sufficient in this historical sketch to mention, by way of
example, the large refractors made under Fraunhofer’s direc-
tions for the Observatories of Dorpat and Berlin, in which
the clear aperture was 9°6 inches in diameter, with a focal
length of 14-2 feet, and those executed by Merz and Mahler,
for the Observatories of Pulkowa and Cambridge, in the
United States of America;* they are both adjusted with

* Consult Struve, Etudes d’ Astr. stellaire, 1847, note 59.
p. 24. I have retained the designations of forty, twenty, and
seven-feet Herschel reflecting telescopes, although in other
parts of the work (the original German) I have used French
measurements. _ I have a :opted these designations not merely
on account of their gréater convenience, but also because they
have acquired historical celebrity from the important labours
both of the elder and younger Herschel in England, and of
the latter at Feldhausex, at the Cape of Good Hope.

® See Schumacher s Aséir. Nachr., no. 371 and 611. Cauchoix

a2

&4 COSMOS.

object-glasses of 15 inches in diameter, ar1 a focal length
of 22°5 feet. The heliometer at the Konigsberg Observatory,
which continued for a long time to be the largest in exist-
ence, has an aperture of 6°4 inches in diameter. This in-
strument has been rendered celebrated by the memorable
labours of Bessel. The well-illuminated and short dyalitic
refractors which were first executed by Plésl in Vienna, and
the advantages of which were almost simultaneously recognized
by Rogers in England, are of sufficient merit to warrant their
construction on a large scale.

During this period, to the efforts of which I have referred,
because they exercised so essential an influence on the ex-
tension of cosmical views, the improvements made in instru-
ments of measurement (zenith sectors, meridian circles, and
micrometers) were as marked in respect to mechanics as they
were to optics and to the measurement of time. Among the
many names distinguished in modern times in relation to in-
struments of measurement, we will here only mention those
of Ramsden, Troughton, Fortin, Reichenbach, Gambey, Ertel,
Steinheil, Repsold, Pistor, and Oertling ; in relation to chrono-
meters and astronomical pendulum clocks, we may instance
Mvige, Arnold, Emery, Earnshaw, Breguet, Jiirgensen,
Kessels, Winnerl, and Tiede; while the noble labours of
William and John Herschel, South, Struve, Bessel, and
Dawes, in relation to the distances and periodic motions of
the double stars, specially manifest the simultaneous perfec-
tion acquired in exact vision and measurement. Struye’s
classification of the double stars gives about 100 for the
number whose distance from one another is below 1”, and 336

and Lerebours have also constructed object-glasses of more
than 13°38 inches in diameter, and nearly 25 feet focal
length. <

TELESCOPES. 85

for those between 1” and 2”; the measurement in every
case being several times repeated.

During the last few years, two men, unconnected with any
industrial profession—the Earl of Rosse, at Parson’s Town,
(about fifty miles west of Dublin,) and Mr. Lassell, at Star-
field, near Liverpool, have, with the most unbounded liberality,
inspired with a noble enthusiasm for the cause of science,
constructed under their own immediate superintendence
two reflectors, which have raised the hopes of astronomers
to the highest degree.“ Lassell’s telescope, which has an
aperture only two feet in diameter, with a focal length
of twenty feet, has already been the means of discovering
one satellite of Nentune, and an eighth of Saturn, besides

8 Struve, Stellarum duplicium et multiplicium Mensure
micrometrice, pp. 2, 41.

* Mr. Airy has recently given a comparative description
of the methods of constructing these two telescopes, including
an account of the mixing of the metal, the contrivances
adopted for casting and polishing the specula and mounting
the instruments; Abstr. of the Astr. Soc., vol. ix. no. 5, March,
1849. The effect of Lord Rosse’s six-feet metallic reflector.
is thus referred to. (p. 120.) ‘The Astronomer Royal, Mr.
Airy, alluded to the impression made by the enormous light
of the telescope: partly by the modifications produced in
the appearances of nebule already figured, partly by the great
number of stars seen even at a distance from the Milky Way,
and partly from the prodigious brilliancy of Saturn. The
account given by another astronomer of the appearance of
Jupiter was, that it resembled a coach-lamp in the telescope;
and this well expresses the blaze of light which is seen in
the instrument.” Compare also Sir John Herschel, Outl. of
Astr., § 870. ‘The sublimity of the spectacle afforded by
the magnificent reflecting telescope constructed by Lord
Rosse of some of the larger globular clusters of nebule is
declared by all who have witnessed it, to be such as no
words can express. This telescope has resolved or rendered
resolvable multitudes of nebule which had resisted all inferior
powers.”

86 _ COSMOS.

which two satellites of Uranus have been again distinguished
The new colossal telescope of Lord Rosse has an aperture of
six feet, and is fifty-three feet inlength. It is mounted in the
meridian between two walls, distant twelve feet on either
side from the tube, and from forty-eight to fifty-six feet in
height. Many nebulz, which had been irresolvable by any
previous instruments, have been resolved into stellar swarms
by this noble telescope; while the forms of other nebulze
have now, for the first time, been recognized in their true
outlines. A marvellous eftulgence is poured forth from es
speculum. :
The idea of observing the stars by daylight with a tele-
scope first occurred to Morin, who with Gascoigne (about 1638,
before Picard and Auzout) combined instruments of measure-
ment with the telescope. Morin himself says,* “It was not
Tycho’s great observations in reference to the position of the
i;xed stars, when, in 1582, twenty-eight years before the in-
vention of the telescope, he was led to compare Venus by day
with the sun, and by night with the stars,” but ‘the simple
idea that Arcturusand other fixed starsmight, like Venus, when
once they had been fixed in the field of the telescope before
sunrise, be followed through the heavens, after the sun had
risen, that led him to a discovery which might prove of impor-
tance for the determination of longitude at sea.”’” No one was
able before him to distinguish the fixed stars in the presence of
the sun. Since the employment, by Romer, of great meridian
telescopes in 1691, observations of the stars by day have
been frequent and fruitful in results, having been, in some
cases, advantageously applied to the measurement of the
double stars. Struve states® that he has determined the
smallest distances of extremely faint stars in the Dorpat

* Delambre, Hist. de l’ Astron. moderne, t. ii. p. 255.
% Struve, Mens microm. p. xliv

TELESCOPES. 87

refractor, with a power of only 320, in so bright a crepus-
cular light, that he could read with ease at midnight. The
polar star has a companion of the 9th magnitude, which is
situated at only 18” distance: it was seen by day in the Dor-
pat refracting telescope, by Struve and Wrangel,™ and was in
like manner observed on one occasion by Encke and Arge-
lander.

Many conjectures have been hazarded regarding the cause
of the great power of the telescope at a time when the dif-
fused light of the atmosphere, by multiplied reflection, exerts
an obstructing action.™ This question, considered as an

* Schumacher’s Jahrbuch fiir 1839, s. 100.

* La lumiéere atmosphérique diffuse ne peut s’expliquer
par le reflet des rayons solaires sur la surface de séparation
des couches de différentes densités dont on suppose l’atmos-
phére composée. En effet, supposons le soleil place a
Thorizon, les surfaces de separation dans la direction du
zenith seraient horizontales, par conséquent la réflexion serait
horizontale aussi, et nous ne verrions aucune lumiére au
zenith. Dans la supposition des couches, aucun rayon ne
nous alriverait par voie d’une premiére réflexion. Ce ne
seraient que les réflexions multiples qui pourraient agir.
Done pour expliquer ly lumiére diffuse, il faut se figurer
l'atmosphére composée de molécules (sphériques, par exemple)
dont chacune donne une image du soleil 4 peu prés comme
les boules de verres que nous placons dans nus jardins, Lair
= est bleu, parceque daprés Newton, les molécules de
‘air ont [épatsseur qui convient a la réflexion des rayons
bleus. Il est done naturel que les petites images du soleil que
de tous cotés réfléchissent les molécules sphériques de l’air et
qui sont la lumiére diffuse aient une teinte bleue: mais ce
bleu n’est pas du bleu pur, c’est un blanc dans lequel le bleu
predomine. Lorsque le ciel n’est pas dans toute sa pureté et
que lair cst mélé de vapeurs visibles, la lumiére diffuse
regoit beaucoup de blanc. Comme la lune est jaune. le bleu
de lair pendant la nuit est un peu verdatre, c’est-a-dire, mé-
langé de bleu et de jaune.”’

“ We cannot cxplain the diffusion of atmospheric light by

88 COSMO#.

optica! problem, excited the strongest interest in the mind of
Bessel, whose too early death was so unfortunate for the
cause of science. In his long correspondence with myself, he
frequently reverted to this subject, admitting that he could not
arrive at any satisfactory solution. I feel confident it will not
be unwelcome to my readers, if I subjoin, in the form of a note,
some of the opinions of Arago,*” as expressed in one of the

the reflection of solar rays on the surface of separation of the —
strata of different density, of which we suppose the atmo- —
sphere to be composed. In fact, if we suppose the sun to be
situated on the horizon, the surfaces of separation in the
direction of the zenith will be horizontal, and consequently
the reflection would likewise be horizontal, and we should
not be able to see any light at the zenith. On the supposi- —
tion that such strata exist, no ray would reach us by means.
of direct reflection. Repeated reflections would be necessary
to produce any effect. In order, therefore, to explain the
phenomenon of diffused light, we must suppose the atmo-
sphere to be composed of molecules (of a spherical form,
for instance), each of which presents an image of the
sun somewhat in the same manner as an ordinary glass
ball. Pure air is blue, because, according to Newton,
the molecules of the air have the thickness necessary to
reflect blue rays. It is therefore natural that the small
images of the sun, reflected by the spherical molecules of the
atmosphere, should present a bluish tinge; this colour is not,
however, pure blue, but white, in which the blue predomi-
nates. When the sky is not perfectly pure and the atmo-
sphere is blended with perceptible vapours, the diffused light
is mixed with a large proportion of white. As the moon is
yellow, the blue of the air assumes somewhat of a greenish —
tinge by night, or, in other words, becomes blended with
yellow.” —MSS of 1847.

® Dun des Effets des Lunettes sur la Visibilité des étorlee,
(Lettre de M. Arago a M. de Humboldt en Déc. 1847.)

** L’cil n’est doué que d’une sensibilité circonscrite, borneée.
Quand la lumiére qui frappe la rétine, n’a pas assez d'inten-
sité, l'oeil ne sent rien. C'est par un manque d'intensité que
beaucoup d’ééozles, méme daus les nuits les plus profondes
échappent a nos observations. Les lunettes ont pour effet.

TELESCOPES. 89

numerous manuscripts to which I was permitted free access
_ during my frequent sojourn in Paris. According to the inge-

-nious explanation of my friend, high magnifying powers facili-
tate the discovery and recognition of the fixed stars, since

quant aux étoiles, d'augmenter l’intensité de l'image. Le
faisceau cylindrique de rayons paralléles venant d'une étoile,
qui s’appuie sur la surface de la lentille objective, et qui a
cette surface circulaire pour base, se trouve considérable-
ment resserré a la sortie de la lentille oculaire. Le diamétre
du premier cylindre est au diamétre du second, comme la
distance focale de l’objectif est a la distance focale de l’ocu-
laire, ou bien comme le diamétre de l’objectif est au dia-
métre de la portion doculaire qu’occupe le faisceau émergent.
Les intensités de lumiére dans les deux cylindres en question
(dans les deux cylindres, incident et emergent) doivent étre
entr’elles comme les étendues superficielles des bases. Ainsila
lumiére émergente sera plus condensée, plus intense que la
_lumiére naturelle tombant sur l’objectif, dans le rapport de la
surface de cet objectif a la surface circulaire de la base du fais-
ceau emergent. Le faisceau émergent, quand la lunette grossit,
étant plus étroit que le faisceau cylindrique qui tombe sur
Vobjectif, il est évident que la pupille, quelle que soit son
ouverture, recueillera plus de rayons par l’intermédiaire de la
lunette que sans elle. La lunette augmentera donc toujours
Vintensite de la lumiére des étozles.

* Le cas le plus favorable, quant a l’effet des lunettes, est
évidemment celui ot l'eil recoit la totalité du faisceau émer-
gent, le cas ot ce faisceau a moins de diamétre que la pupille.
Alors toute la lumiére que lobjectif embrasse, concourt, par
Yentremise du télescope, a la formation de l'image. A lil
nu, au contraire, wne portion seule de cette méme lumiére est

3 mise a profit; c’est la petite portion que la surface de la

pupille découpe dans le faisceau incident naturel. L’inten-
site de image télescopique d’une étoile est donc a l’intensité
de l'image a l’ceil nu, comme la surface de I’ oljectif est a celle
de la pupille.

“Ce qui précéde est relatif a la visibilité d un seul point, d’une
seule etoile. Venons a l’observation d’un objét ayant des
dimensions angulaires sensibles, 4 l’observation d'une planéte.

90 COSMOS.

they convey a greater quantity of intense light to the eye
without perceptibly enlarging the image; while, in accordance
with another law, they influence the aerial space on which
the fixed star is projected. The telescope, by separating,

Dans les cas les plus favorables, c’est-a-dire lorsque la pupille
recoit la totalite du pinceau émergent, l’intensité de l’image
de chaque point de la planéte se calculera par la proportion
que nous venons de donner. La quantité totale de lumiére
concourant a former J ensemble de Vimage a l ceil nu, sera done
aussi a la guantité totale de lumiére qui forme image de la
planéte a l’aide d’une lunette, comme la surface de la pupille
est a la surface de l’objectif. Les intensités comparatives,
non plus de points isolés, mais des deux images d'une planéte,
qui se forment sur la rétine 4 l’ceil nu, et par l'intermédiaire
d’une lunette, doivent evidemment dimenuer proportionnelle-
ment aux étendues superficielles de ces deux images. Les
dimensions Jinéatres des deux images sont entr’elles comme le
diamétre de l’objectif est au diamétre du faisceau émergent.
Le nombre de fois que la surface de l'image amplifiee surpasse
la surface de l'image a l’ceeil nu, s’obtiendra done en divisant
le carré du diameétre de lobjectif par le carré du diamétre du
Faasceau émergent, ou bien la surface del objectif par la surface
de la base circulaire du fatsceau émergent.

‘“‘ Nous avons deja obtenu le rapport des guantités totales dé
lumére qui engendrent les deux images d’une planéte, en divi-
sant la surface de l’objectif par la surface de la pupille. Ce
nombre est plus petit que le quotient auquel on arrive en
divisant la surface de l’objectif par la surface du faisceau émer-
gent. Il en resulte, quant aux planétes, qu’une lunette fait
moins gagner en intensité de lumiére, qu’elle ne fait perdre en
agrandissant da surface des images sur la rétine; l’intensite
de ces images doit donc aller continuellement en s‘affaiblissant
a mesure que le pouvoir amplificatif de la lunette ou du
telescope s’accroit.

‘‘L’atmosphére peut étre considérée comme une planéte a
dimensions indefinies. La portion qu’on en verra dans une
lunette, subira donc aussi la Jot d'affuiblissement que nous
venons d'indiquer. Le rapport entre l’intensité de la lumiére
d’une z’anéte et le champ de lumiére atmosphérique 4 travers

TELESCOPES. bs |

as it were, the illuminated particles of air sur unding
the object-glass, darkens the field of view, and diminishes
the intensity of its illumination. We are enabled to
see, however, only by means of the difference between the

lequel on la verra, sera le méme 4 I|’eeil nu et dans les lunettes
de tous les grossissements, de toutes les dimensions. Les
lunettes, sous le rapport de lintensité, ne favorisent done pas
la visibilité des planétes.

“Tl n’en est point ainsi des éfozles. L’intensité de l'image
d’une étoile est plus forte avec une lunette qu’a l’wil nu; au
contraire, le champ de la vision, uniformément éclairé dans
les deux cas par la lumiére atmosphérique, est plus clair a
Veil nu que dans la lunette. Il y a done deux raisons, sans
sortir des considérations d’intensité, pour que dans une lunette
Vimage de l’étoile prédomine sur celle de l’atmosphére, notable-
ment plus qua l'ceeil nu.

“Cette prédominance doit aller graduellement en aug-
mentant avec le grossissement. En effet, abstraction faite de
certaine augmentation du diamétre de l'étoile, conséquence
de divers effets de diffraction ou d’interférences, abstraction
faite aussi d’une plus forte réflexion que la lumiére subit sur
les surfaces plus obliques des oculaires de trés courts foyers,
Vintensité de la lumieére de l étoile est constante tant que |’ ouver-
ture de l’objectif ne varie pas. Comme on l’a vu, la clarté du
champ de la lunette, au contraire, diminue sans cesse 4 mesure
que le pouvoir amplificatif s’accroit. Done toutes autres
circonstances restant égales, une étoile sera d’autant plus
visible, sa predominence sur la lumiére du champ du télescope
sera d’autant plus tranchée qu’on fera usage d’un grossisse-
ment plus fort.”’

“The eye is endowed with only a limited sensibility; for
when the light which strikes the retina is not sufficiently
strong, the eye is not sensible of any impression. In con-
sequence of deficient intensity, many stars escape our ob-
servation, even in the darkest nights. Telescopic glasses
have the effect of augmenting the intensity of the images of
the stars. ‘The cylindrical pencil of parallel rays emanating
from a star, and striking the surface of the object-glass, on
whose circular surface it rests as on a base, is considerably

92 COSMOS.

light of the fixed star and of the aerial field or the mass of air
which surrounds the star in the telescope. Planetary dises
present very different relations from the simple ray of the
image of a fixed star; since. like the aerial field (J'air aérienne),

contracted on emerging from the eye-piece. The diameter of
the first cylinder is to that of the second as the focal distance
of the object-glass is to the focal distance of the eye-piece.
or as the diameter of the object-glass is to the diameter of
the part of the eye-piece covered by the emerging rays. Tke
intensities of the light in these two cylinders (the incident nd
emerging cylinders) must be to one another as the superficies
of their bases. Thus, the emerging light will be more con-
densed, more intense, than the natural light falling on the
object-glass, in the ratio of the surface of this object-glass to -
the circular surface of the base of this emerging pencil. As
the emerging pencil is narrower in a magnifying instrument
than the cylindrical pencil falling on the object-glass, it is
evident that the pupil, whatever may be its aperture, will
receive more rays, by the intervention of the telescope, than
it could without. The intensity of the light of the stars will,
therefore, always be augmented, when seen through a telescope. ©

“The most favourable condition for the use of a telescope
is undoubtedly that in which the eye receives the whole of
the emerging rays, and, consequently, when the diameter of
the pencil is less than that of the pupil. The whole of the light
received by the object-glass then co-operates, through the
agency of the telescope, in the formation of the image. In
natural vision. on the contrary, a portion only of this light is
rendered available, namely, the small portion which enters
the pupil naturally from the incident pencil. The intensity of
the telescopic image of a star is, therefore, to the intensity
of the image seen with the naked eye, as the surface of the
object-glass 1s to that of the pupil.

“The preceding observations relate to the visibility of
one point, or one star. We will now pass on to the conside-
ration of an object having sensible angular dimensions, as,
for instance, a planet. Under the most favourable conditions
of vision, that is to say, when the pupil receives the whole
of the emerging pencil, the intensity of each point of the

TELESCOPES. 93

thoy lose in intensity of light by dilatation in the magnifying
telescope. It must be further observed, that the apparent
motion of the fixed star, as well as of the planetary disc, is
increased by high magnifying powers. This circumstance may

planet’s image may be calculated by the proportions we have
already given. ‘The ¢otal quantity of light contributing to
form the whole of the image, as seen by the naked eye, will,
therefore, be to the total quantity of the light forming the
image of the planet by the aid of a telescope, as the surface
of the pupil is to the surface of the object-glass. The com-
parative intensities, not of mere isolated points, but of the
images of a planet formed respectively on the retina of the
naked eye, and by the intervention of atelescope, must evidently
diminish proportionally to the superficial extent of these two
images. ‘The linear dimensions of the two images are to one
another as the diameter of the object-glass is to that of the
emerging pencil. We therefore obtain the number of times
that the surface of the magnified image exceeds the surface
of the image when seen by the naked eye by dividing the
square of the diameter of the olyect-glass by the square of the
diameter of the emerging pencil, or rather the surface of the
object-glass by the surface of the circular base of the emerging
encil,

en By dividing the surface of the object-glass by the surface
of the pupil, we have already obtained the ratio of the total
quantities of light produced by the two images of a planet.
This number is lower than the quotient which we obtain by
dividing the surface of the object-glass by the surface of the
emerging pencil. It follows, therefore, with respect to
planets, that a telescope causes us to gain less in intensity of
light than is lost by magnifying the surface of the images on
the retina; the intensity of these images must therefore
become continually fainter, in proportion as the magnifying
power of the telescope increases.

‘The atmosphere may be considered as a planet of indefinite
dimensions. ‘The portion of it that we see in a telescope
will therefore also be subject to the same law of diminution
that we have indicated The relation between the intensity of
the light of a planet and the field of atmospneric light through

94 : COSMOS.

facilitate the recognition of objects by day, in instruments
whose movements are not regulated paralacticaily by clock.
work, so as to follow the diurnal motion of the heavens.
Different points of the retina are successively excited. ‘* Very
faint shadows are not observed,” Arago elsewhere remarks,
‘‘until we can give them motion.”

In the cloudless sky of the tropics, during the driest season

which it is seen, will be the same to the naked eye and in
telescopes, whatever may be their dimensions and magnifying
powers. ‘Telescopes. therefore, do not favour the visibility of
planets in respect to the intensity of their light.

~ The same is not the case with respect to the stars. The
intensity of the image of a star is greater when seen with
the telescope than with the naked eye; the field of vision,
on the contrary, uniformly illumined in both cases by the
atmospheric light, is clearer in natural than in telescopic
vision. There are two reasons then, which, in connexion
with the consideration of the intensity of light, explain why
the image of a star preponderates in a telescope rather than
in the naked eye over that of the atmosphere.

“This predominance must gradually increase with the
increased magnifying power. In fact, deducting the constant
augmentation of the star’s diameter, consequent upon the
different effects of diffraction or interference, and deducting
also the stronger reflection experienced by the light on the
more oblique surfaces of ocular glasses of short focal lengths,
the intensity of the light of the star ts constant, as long as the
aperture of the object-glass does not vary. As we have
already seen, the brightness of the field of view, on the con-
trary, diminishes incessantly in the same ratio in which the
magnifying power increases. All other circumstances, there-
fore, being equal, a star will be more or less visible, and its
prominence on the field of the telescope will be more or less
marked, in proportion to the magnifying powers we employ.”
Arago, Manuscript of 1847.

I will further add the following passage from the Annuuire
du Bureau des Ing. pour 1846 (Notices Scient. par M. .trago),
p. 381.

TELESCOPES. 95

of ike year, I have frequently been able to find the pale dise
of Jupiter with one of Dolland’s telescopes, of a magnifying

power of only 95, when the sun was already from 15° to 18°

above the horizon. The diminished intensity of the light
of Jupiter and Saturn, when seen by day in the great Berlin
refractor, especially when contrasted with the equally reflected
light of the inferior planets, Venus and Mercury, frequently
excited the astonishment of Dr. Galle. Jupiter’s occul-

* L’expérience a montré que pour le commun des hommes,
deux espaces éclairés et contigus ne se distinguent pas l’un
de l’autre, 4 moins que leurs intensités comparatives ne pré- -
sentent, au minimum, une difference de 335. Quand une lu-
nette est tournée vers le firmament, son champ semble uni-
formement éclairé: c'est qu’ alors il existe, dans un plan
passant par le foyer et perpendiculaire a l’axe de l’objectif, une
mage indéfine de la région atmosphérique vers laquelle la
lunette est dirigée. Supposons qu’un astre, c’est-a-dire un objet
situé bien au-dela de l'atmosphére, se trouve dans la direction de
la lunette: son image ne sera visible qu'autant qu’elle augmen-
tera de ;};. au moins, lintensite de la portion de l image
focale indéfinie de latmosphére, sur laquelle sa propre image
limitée iva se placer. Sans cela, le champ visuel continuera a
paraitre partout de la méme intensité.”’

‘Experience has shown that, in ordinary vision, two illu-
minated and contiguous spaces cannot be distinguished from
each other, unless their comparative intensities present a mini-
mum difference of ;4,th. When a telescope is directed towards
the heavens, its field of view appears uniformly illumined:
there then exists in a plane passing through the focus, and
perpendicular to the axis of the object-glass, an indefinite
image of the atmospheric region towards which the instru-
ment is pointed. If we suppose a star, that is to say, an object
very far beyond the atmosphere, situated in the direction
of the telescope, its image will not be visible, except it exceed,
by at least z,th, the intensity of that portion of the indefinite
focal image of the atmosphere on which its kmited proper
image is thrown. Otherwise, the visual field will continue ta
appar everywhere of the same intensity.”

96 COSMOS.

tations have occasionally been observed by daylight, with
the aid of powerful telescopes, as in 1792, by Flaugergues, and
in 1820, by Struve. Argelander (on the 7th of December,
1849, at Bonn) distinctly saw three of the satellites of
Jupiter, a quarter of an hour after sunrise, with one of Fraun-
hofer’s five-feet telescopes. He was unable to distinguish
the fourth; but, subsequently, this and the other satellites
were observed emerging from the dark margin of the moon,
by the assistant-astronomer, Schmidt, with the eight-feet helio-
meter. The determination of the limits of the telescopic
visibility of small stars by daylight, in different climates,
and at different elevations: above the sea’s level, is alike
interesting in an optical and a meteorological point of
view.

Among the remarkable phenomena whose causes have been
much contested, in natural as well as in telescopic vision, we
must reckon the nocturnal scintillation of the stars. Ac-
cording to Arago’s investigations, two points must be spe-
cially distinguished in reference to this phenomenon ®—

* The earliest explanations given by Arago of scintillation
_ occur in the appendix to the 4th book of my Voyage aux
Régions équinoxiales, tom. i, p. 623. I rejoice that I am able
to enrich this section on natural and telescopic vision, with
the following explanations, which, for the reasons alr eady as-
signed, I subjoin in the original text.

Des causes de la scintillation des étorles.

‘Ce qu'il y a de plus remarquable dans le phénoméne de
la scintillation, ¢’est le changement de couleur. Ce change-
ment est beaucoup plus frequent que l’observation ordinaire
Vindique. En effet, en agitant la lunette, on transforme
Vimage dans une ligne ou un cercle, et tous les points de cette
ligne ou de ce cercle paraissent de couleurs différentes. C’est
la résultante de la superposition de toutes ces images que l'on
voit, lorsqu’on laisse la lunette immobile. Les rayons qui se
réunissent au foyer d’une lentille, vibrent d'accurd ou en
désaccord, s'ajoutent ou se détruisent, suivant aue les couches

SCINTILLATION OF THE STARS. 97

Firstly, Change in the intensity of the light. from a sudden de-
crease to perfect extinction and rekindling; Seccndly, Change
of colour. Both these alterations are more intense in reality
than they appear to the naked eye; for when the several
points of the retina are once excited, they retain the impression
of light which they have received, so that the disappearance,

qu ils ont traversées, ont telle ou telle refringence. L’ensemble
des rayons rouges peut se détruire seu/, si ceux de droite et de
gauche, et ceux de haut et de bas, ont traversé des milieux
inégalement réfringents. Nous avons dit sew/. parceque la
difference de réfringence qui correspond a la destruction du
rayon rouge, n’est pas la méme que celle qui améne la de-
struction du rayon vert, et réciproquement. Maintenant, si
des rayons rouges sont détruits, ce qui reste sera le blanc
moins le rouge, c’est-a-dire du vert. Si le vert au contraire
est détruit par interférence, l'image sera du blanc moins le vert,
e’est-a-dire du rouge. Pour expliquer pourquoi les planétes

' a grand diamétre ne’scintillent pas ou trés peu, il faut se rap-

peler que le disque peut étre considéré comme une aggrégation
d’étoiles ou de petits points qui scintillent isolément ; mais
les images de differentes couleurs que chacun de ces points
pris isolement donnerait, empietant les unes sur les autres,
formeraient du blane. Lorsqu’on place un diaphragme ou un
bouchon percé d’un trou sur l’objectif d’zne lunette, les étoiles
acquiérent un disque entouré d’une série d’anneaux lumineux.
Si l’on enfonce l’oculaire, le disque de i’étoile augmente de
diamétre, et il se produit dans son centre un trou obscur ; si on
Venfonce davantage, un point lumineux se substitue au point
noir. Un nouvel enfoncement donne naissance a un centre
noir, ete. Prenons la lunette lorsque le centre de l'image est
noir, et visons a une étoile qui ne scintille pas: le centre
restera noir, comme il ]’était auparavant. Si au contraire on
dirige la lunette a une étoile qui scintille, on verra le centre
de l'image lumineux et obscur par intermittence. Dans Ja
position ot le centre de l'image est occupé par un point lumi-
neux, on verra ce point disparaitre et renaitre successivement.
Cette disparition ou réapparition du point central est la preuve
directe de l’interférence variable des rayons. Pour bien con-
cevoir l'absence de lumiére au centre de ces images dilatees,

VoL. Itt. EH

98 COSMOS.

obscuration, and change of colour, in a star, are not perceived
by us to their full extent. The phenomenon of scintillation
is more strikingly manifested in the telescope, when the
instrument is shaken, for then different points of the retina
are successively excited, and coloured and frequently inter-
rupted rings are seen. The principle of interference explains

~

il faut se rappeler que les rayons réguliérement reéfractés par
Vobjectif ne se réunissent et ne peuvent par conséquent
interferer qu'au foyer: par conséquent les images dilatées que
ces rayons peuvent produire, resteraient toujours pleines (sans
trou). Si dans une certaine position de l’oculaire un trou se
présente au centre de l'image, c'est que les rayons réguliére-
ment réfractés interferent avec des rayons diffractés sur les
bords du diaphragme circulaire. Le phénoméne n’est pas
constant, parceque les rayons qui interférent dans un certain
moment, n'interférent pas un instant aprés, lorsqu‘ils ont
traversé des couches atmosphériques dont le pouvoir refringent
avarié On trouve dans cette expérience la preuye manifeste
du réle que joue dans le phénoméne de la scintillation l’inegale
réfrangibilité des couches atmosphériques traversées par les
rayons dont le faisceau est trés étroit. I] résulte de ces
considérations que l’explication des scintillations ne peut étre
rattachée qu’aux phénoméres des tnterférences lumineuses.
Les rayons des étoiles, apres avoir travers¢é une atmosphére
ou il existe des couches inégalement chaudes, inegalement
denses, inégalement humides, vont se réunir au foyer d'une
lentille, pour y former des images d’intensité et de couleurs
perpétuellement changeantes, c’est-a-dire des images telles
que la scintillation les présente. II y a aussi scintillation hors
du foyer des lunettes. Les explications proposées par Galileo,
Sealiger, Kepler, Descartes, Hooke, Huygens, Newton et John
Michell, que j’ai examiné dans un mémoire présente a
l'Institut en 1840 (Comptes rendus, t. x. p. 83), sont inad-
missibles. ‘Thomas Young, auquel nous devons les premiéres
lois des interférences, a cru inexplicable le phénoméne de le
scintillation. La fausseté de l’ancienne explication par des
vapeurs qui voltigent et déplacent, est deja prouvée par la
circonstance que nous voyons la scintillation des yeux, ce
qui supposerait un déplacement d'une minute. Les ondula-

-

RCINTILLATION OF THE STARS. 99

how the momentary coloured effulgence of a star may be fol-
lowed by its equally instantaneous disappearance or sudden
obscuration, in an atmosphere composed of ever-changing
strata of different temperatures, moisture, and density. The
undulatory theory teaches us generally that two rays of light
(two systems of waves) emanating from one source (one centre

a

tions du bord du soleil sont de 4” a 5”, et peut-étre des
piéces qui manguent, done encore effet de l’interférence des
rayons.”’

On the causes of the scintillation of the stars.

“The most remarkable feature in the phenomenon of the
stars’ scintillation is their change of colour. This change is
of much more frequent occurrence than would appear from
ordinary observation. Indeed, on shaking the telescope the
image is transformed into a line or circle, and all the points of
this line or circle appear of different colours. We have here
the results of the superposition of all the images seen when
the telescope is at rest. The rays united in the focus of a
lens, vibrate in harmony or at variance with one another,
and increase or destroy one another according to the various
degrees of refraction of the strata through which they have
passed. The whole of the red rays alone can destroy one
another, if the rays to the right and left, above and below
them have passed through unequally refracting media. We
have used the term alone, because the difference of refraction
necessary to destroy the red ray is not the same as that which
is able to destroy the green ray, and wee versa. Now, if the
red rays be destroyed, that which remains will be white minus
red, that is to say green. If the green on the other hand be
destroyed by inierference, the image will be white minus green,
that is to say red. To understand why planets having large
diameters should be subject to little or no scintillation, it must
be remembered that the disc may be regarded as an aggrega-
tion of stars, or of small points, scintillating independently of
each other, while the images of different colours presented. by
each of these points taken alone would impinge upon one
another and form white. If we place a diaphragm or a cork
pierced with a hole on the object-glass of a telescope, the
stars present a disc surrounded by a series of luminous rings,

H2

100 COSMOS.

of commotion), destroy each other by inequality of path;
that the light of one ray added to the light of the other
produces darkness. When the retardation of one system o
waves in reference to the other amounts to an odd number
of semi-undulations, both systems endeavour to impart simui.
taneously to the same molecule of ether equal but opposite
velocities ; so that the effect of their combination is to produce
rest in the molecule, and therefore darkness. In some cases,

——

On pushing in the eye-piece, the dise of the star inereases
in diameter and a dark point appears in its centre; when the
eve-piece is made to recede still further into the instrument,
a luminous point will take the place of the dark point. On
causing the eye-piece to recede still further, a black centre
will be observed. If while the centre of the image is black
we point the instrument to a star which does not scintiliate.
it will remain black as before. If, on the other hand, we
point it to a scintillating star, we shall see the centre ef the
image alternately luminous and dark. In the position in
which the centre of the image is occupied by a luminous point,
we shall see this point alternately vanish and reappear. Thig
disappearance and reappearance of the central point is a
direct proof of the variable interference of the rays. In order
to comprehend the absence of light from the centre of these
dilated images, we must remember that rays regularly refracted
by the object-glass do not reunite and cannot consequently
interfere except in the focus; thus the images produced by
these rays will always be uniform and without a central point.
If in a certain position of the eye-piece, a point is observed
in the centre of the image, it is owing to the interference of
the regularly refracted rays with the rays diffracted on the
margins of the circular diaphragm. The phenomenon is not
constant, for the rays which interfere at one moment no
longer do so in the next, after they have passed through atmos-
pheric strata possessing a varying power of refraction. We
here meet with a manifest proof of the important part
played in the phenomenon of scintillation by the unequal
refrangibility of the atmospheric strata traversed by rays
united in a verv narrow pencil.”

SCINTILLATION OF THE STARS, 101

the refrangibility of the different strata of air intersecting the
rays of light exerts a greater influence on the phenomenon
than the difference in length of their path.“

The intensity of scintillations varies considerably in the
different fixed stars, and does not seem to depend solely on
their altitude and apparent magnitude, but also on the nature
of their own light. Some, as for instance Vega, flicker less
than Arcturus and Procyon. The absence of scintillation in
planets with larger discs, is to be ascribed to compensation
and to the neutralizing mixture of colours proceeding frcm
different points of the disc. The disc is to be regarded as
an aggregate of stars which naturally compensate for the
light destroyed by interference, and again combine the

“It follows from these considerations that scintillation must
necessarily be referred to the phenomena of luminous inter-
ferences alone. The rays emanating from the stars, after
traversing an atmosphere composed of strata having different
degrees of heat, density, and humidity, combine in the focus of
a lens, where they form images perpetually changing in
intensity and colour, that is to say, the images presented by
scintillation. There is another form of scintillation, inde-
pendent of the focus of the telescope. The explanations of
this phenomenon advanced by Galileo, Scaliger, Kepler, Des-
cartes, Hooke, Huygens, Newton, and John Michell, which I
examined in a memoir presented to the institute in 1840
(Comptes Rendus, t. x. p. 83), are inadmissible. Thomas
Young, to whom we owe the discovery of the first laws of
interference, regarded scintillation as an inexplicable phe-
nomenon. ‘The erroneousness of the ancient explanation
which supposes that vapours ascend and displace one another,
is sufficiently proved by the circumstance that we see scintil-
lations with the naked eye, which presupposes a displacement
of a minute. The undulations of the margin of the sun arc
from 4” to 5”, and are perhaps owing to chasms or interruptions
and therefore also to the effect of interference of the rays of
light.” (Eatracts from Arago’s MSS. of 1847.)

“ See Arago, in the Annuaire pour 1831, p. 168.

102 COSMOS.

coloured rays into white light. For this reason we nost
rarely meet with traces of scintillation in Jupiter and Saturn,
but more frequently in Mercury and Venus, for the apparent
diameters of the discs of these last named planets diminish to
4-4 and 9”5. The diameter of Mars may also decrease to
3-3 at its conjunction. In the serene cold winter nights of
the temperate zone, the scintillation increases the magnificent
mpression produced by the starry heavens, and the more so
from the circumstance that, seeing stars of the 6th and 7th
magnitude flickering in various directions, we are led ta
imagine that we perceive more luminous points than the
unaided eye is actually capable of distinguishing. Hence
the popular surprise at the few thousand stars which accurate
catalogues indicate as visible to the naked eye! It was known
in ancient times by the Greek astronomers, that the flickering
of their light distinguished the fixed stars from the planets ;
but Aristotle, in accordance with the emanation and tan-
gential theory of vision, to which he adhered, singularly
enough ascribes the scintillation of the fixed stars merely
to a straining of the eye. ‘The rivetted stars (the fixed
stars), says he,“ “sparkle, but not the planets: for the
latter are so near, that the eye is able to reach them; but
in looking at the fixed stars (mpds dé rous pevovras) the eye
acquires a tremulous motion owing to the distance and. the
effort.”

In the time of Galileo, between 1572 and 1604,—an epoch
remarkable for great celestial events, when three stars® of
greater brightness than stars of the first magnitude suddenly
appeared, one of which, in Cygnus, remained luminous for
twenty-one years,—Kepler’s attention was specially directed
‘o scintillation as the probable criterion of the non-planetary

@ Aristot. de Calo, ii. 8, p. 290, Bekker.
*® Cosmos, vol. il. p. 709.

SCINTILLATION OF THE STARS. 10%

sature of a celestial body. Although well versed in the
seience of optics, in its then imperfect state, he was unable
to rise above the received notion of moving vapours.“ In
_ the Chinese Records of the newly appeared stars, according
to the great collection of Ma-tuan-lin, their strong scintillation
is occasionally mentioned. _

The more equal mixture of the atmospheric strata, in
and near the tropics, and the faintness or total absence of
scintillation of the fixed stars when they have risen 12° or
15° above the horizon, give the vault of heaven a peculiar
character of mild effulgence and repose. I have already
referred in many of my delineations of tropical scenery to this
characteristic, which was also noticed by the accurate ob-
servers, La Condamine and Bouguer, in the Peruvian plains,
and by Garcin,® in Arabia, India, and on the shores of the
Persian Gulf (near Bender Abassi).

As the aspect of the starry heavens, in the season of
the serene and cloudless nights of the tropics, specially
excited my admiration, I have been careful to note in my
journals the height above the horizon at which the scin-
tillation of the stars ceased in different hygrometric con-
ditions. Cumana and the rainless portion of the Peruvian
coast of the Pacific, before the season of the garua (mist)
had set in, were peculiarly suited to such observations. On
an average the fixed stars appear only to scintillate when less
than 10° or 12° above the horizon. At greater elevations,
they shed a mild, planetary light; but this difference is
most strikingly perceived, when the same fixed stars are
watched in their gradual rising or setting, and the angles of
their altitudes measured, or calculated by the known time and

© Cause scintillationis, in Kepler, De Stella nova in pede
Serpeniarn, 1606, cap. xviii. pp. 92-97.

© tLettrede M. Garcin, Dr. en Med. a M. de Réaumur in
Hist. de 0 Académie Royale des Sciences, Année 1743, pp.
28-32.

104 CcOSsMO8.

latitude of tae place. In some serene and calm nights, the
region of scintillation extended to an elevation of 20° or even
25°; but a connection could scarcely ever be traced between
the differences of altitude or intensity of the scintillation
and the hygrometric and thermometric conditions, obsery-
able in the lower and only accessible region of the atmosphere.
I have observed, during successive nights, after considerable
scintillation of stars, having an altitude of 60° or 70°, when
Saussure’s hair-hygrometer stood at 85°, that the scintillation
entirely ceased when the stars were 15° above the horizon,
although the moisture of the atmosphere was so considerably
increased that the hygrometer had risen to 93°. The intricate
compensatory phenomena of interference of the rays of light
are modified, not by the quantity of aqueous vapour con-
tained in solution in the atmosohere, but by the unequal
distribution of vapours in the superimposed strata, and by
the upper currents of cold and warm air, which are not
perceptible in the lower regions of the atmosphere. The
scintillation of stars at a great altitude was also strikingly
increased during the thin yellowish red mist, which tinges
the heavens shortly before an earthquake. These obser-
vations only refer to the serenely bright and rainless seasons
of the year, within the tropics, from 10° to 12° north and
south of the equator. The phenomena of light exhibited
at the commencement of the rainy season, during the sun’s
zenith-passage, depend on very general, yet powerful, und
almost tempestuous causes. ‘The sudden decrease of the north-
east trade-wind, and the interruption of the passage of regular
upper currents from the equator to the poles, and of lower
currents from the poles to the equator, generate clouds, and
‘hus daily give rise, at definite recurring periods, to storms of
wind and torrents of rain. 1 have observed during several
successive years that in regions where the scintillation of the
fixed stars is of rare occurrence, the approach of the rainy

SCINTILLATION OF THE STARS. 105

season is announced many days beforehand, by a flickering
light of the stars at great altitudes above the horizon. This
phenomenon is accompanied by sheet lightning, and single
flashes on the distant horizon, sometimes without any visible
cloud, and at others darting through narrow, vertically ascend-
ing columns of clouds. In several of my writings I have
endeavoured to delineate these precursory characteristics and
physiognomical changes in the atmosphere.

The second book of Lord Bacon’s Novum Organum giv2.
us the earliest views on the velocity of light and the pro-
bability of its requiring a certain time for its transmission,
He speaks of the time required by a ray of light to traverse
the enormous distances of the universe, and proposes the
question whether those stars yet exist which we now see
shining.” We are astonished to meet with this happy con-

* See Voyage aux Régions équin., t. i. pp. 511 and 512,
and t. ii. pp. 202-208; also my Views of Nature, pp. 16, 138,

‘En Arabie, de méme qu’a Bender-Abassi, port fameux du
Golfe Persique, l’air est parfaitement serein presque toute
Pannée. Le printemps, l’eté, et l'automne se passent, sans
qu’on y voie la moindre rosée. Dans ces mémes temps tout
le monde couche dehors sur le haut des maisons. Quand on
est ainsi couché, il n’est pas possible d’exprimer le plaisir qu’on
prend a contempler la beaute du ciel, l’éclat des étoiles. C’est
une lumiére pure, ferme et éclatante, sans étincellement. Ce
n’est qu’au milieu de l’hiver que la scintillation, quoique trés
foible, s’y fait apercevoir.”’

“In Arabia,” says Garcin, “as also at Bender-Abassi, a
celebrated port on the Persian Gulf, the air is perfectly serene
throughout nearly the whole of the year. Spring, summer,
and autumn, pass without exhibiting a trace of dew. During
these seasons all the inhabitants sleep on the roofs of their
houses. It is impossible to describe the pleasure experienced
in contemplating the beauty of the sky, and the brightness
of the stars, while thus lying in the open air. The light of
the stars is pure, steady, and brilliant; and it is only in the
middle of the winter, that a slight degree of scintillation is
observed.” Garcin, in Hist. de [ Acad. des Sc., 17438, p. 30.

1 In speaking of the decewtions occasioned by the velocity of

10€ Cosmos,

jecture in a work whose intellectual author was far behind
his contemporaries in mathematical, astronomical, and phy-
sical knowledge. The velocity of reflected solar light was
first measured by Rémer, (November, 1675,) by comparing the
periods of occultation of Jupiter's satellites ; while the velocity
of the direct light of the fixed stars was ascertained (in the
autumn of 1727) by means of Bradley’s great discovery of
aberration, which afforded objective evidence of the translatory
movement of the earth, and of the truth of the Copernican
system. In recent times a third method of measurement has
been suggested by Arago, which is based on the phenomena
of light observed in a variable star, as, for instance, Algol in
Perseus. To these astronomical methods may be added one

sound and light, Bacon says :—‘‘ This last instance, and others
of a like nature, have sometimes excited in us a most marvel-
lous doubt, no less than whether the image of the sky and stars
is perceived as at the actual moment of its existence, or rather
a little after, and whether there is not (with regard to the
visible appearance of the heavenly bodies) a true and apparent
place which is observed by astronomers in parallaxes. It ap-
peared so incredible to us that the images or radiations of
heavenly bodies could suddenly be conveyed through such
immense spaces to the sight, and it seemed that they ought
rather to be transmitted in a definite time. That doubt, how-
ever, as far as regards any great difference between the true and
apparent time, was subsequently completely set at rest, when
we considered. .... ” The works of Francis Bacon, vol. xiv.
Lond. 1831 (Novwm Organum), p. 177. He then recals the
correct view he had previously announced precisely in the
manner of the ancients. Compare Mrs. Somerville’s Connexion
of the Physical Sciences, p. 36; and Cosmos, vol. i. p. 145.

* See Arago’s explanation of his method in the Annuaire
du, Bureau des Longitudes pour 1842, pp. 337-3438. ‘* L’ob-
servation attentive des phases d’Algol a six mois d intervalle
servira 4 déterminer directement la vitesse de la lumiére de
eette étoile. Prés du maximum et du minimum le change-
ment d’intensité s’opére lentement ; il est au contraire rapide
& certaines €poques intermédiares entre celles qui corresp)-

SCINTILLATION OF THE STARS. 107

of terrestrial measurement, lately conducted with much in-
genuity and success by M. Fizeau in the neighbourhood of
Paris. It reminds us of Galileo’s early and fruitless experi-
ments with two alternately obscured lanterns.

Horrebow and Du Hamel estimated the time occupied in
the passage of light from the sun to the earth at its mean
distance, according to Rémer’s first observations of Jupi-
ter’s satellites, at‘14’ 7”, Cassini, at 14’ 10”; while Newton®*

dent aux deux états extrémes, quand Algol, soit en diminuant,
soit en augmentant d’eclat, passe pour la troisiéme grandeur.”

“The attentive observation of the phases of Algol at a six-
month interval will serve to determine directly the velocity of
that star’s light. Near the maximum and the minimum the
change of intensity is very slow; it is, on the contrary, rapid
at certain intermediate epochs between those corresponding
to the two extremes, when Algol, either diminishing or in-
creasing in brightness, appears of the third magnitude.

® Newton, Opticks, 2nd ed. (London, 1718), p. 325.
** Light moves from the sun to us in seven or eight minutes
of time.” Newton compares the velocity of sound (1140
feet in 1”) with that of light. As, from observations on
the occultations of Jupiter’s satellites (Newton’s death oc-
curred about half a year before Bradley’s discovery of aberra-
tion) he calculates that light passes from the sun to the earth, a
distance, as he assumed, of 70 millions of miles, in 7’ 30”; this
result yields a velocity of light equal to 1555555 miles in a
second. The reduction of these [ordinary] to geographical
miles (60 to 1°) is subject to variations according as we assume
the figure of the earth. According to Encke’s accurate calcula-
tions in the Jahrbuch fur 1852, an equatorial degree is equal
to 6$°1637 English miles. According to Newton’s data we
should therefore have a velocity of 134944 geographical miles.
Newton however assumed the sun’s parallax to be 12”. If
this, according to Encke’s calculation of the transit of Venus,
be 8”-57116, the distance is greater, and we obtain for the
velocity of light (at seven and a half minutes) 188928 geo-
graphical, or 217783 ordinary miles, in a second of time;
therefore too much, as before we had toolittle, It is certainly
very remarkable, although the circumstance has been over.

108 COSMOS. |

approximated very remarkably to the truth when he gave
it at 7° 30”. Delambre,™ who did not take into account
any of the observations made in his own time, with the

looked by Delambre (Hist. de _Astronomie Moderne, tom. ii.
p. 658,) that Newton (probably basing his calculations upon
more recent English observations of the first satellite) should
have approximated within 47” to the true result, (namely, that
of Struve, which is now generally adopted,) while the time
assigned for the passage of light over the semi-diameter of
the earth’s orbit continued to vacillate between the very high
amounts of 11’ and 14’ 10”, from the period of Rémer’s dis-
covery, in 1675, to the beginning of the 18th century. The
first treatise in which Rémer, the pupil of Picard, com-
municated his discovery to the Academy, bears the date
of November, 22, 1675. He found, from observations of
forty emersions and immersions of Jupiter’s satellites, “a
retardation of light amounting to 22 minutes for an inter-
val of space, double that of the sun’s distance from the
earth.” (Mémoires de 1 Acad. de 1666-1699, tom. x. 1730,
p. 400.) Cassini does not deny the retardation, but he does
not concur in the amount of time given, because, as he
erroneously argues, different satellites presented different
results. Du Hamel, secretary to the Paris Academy, (Regie
Scientiarum Academie Historia, 1698, p. 148,) gave from 10
to 11 minutes, seventeen years after Romer had left Paris,
although he refers to him; yet we know, through Peter
Horrebow (Basis <Astronomie sive Triduum Roemerianum,
1735, pp. 122-129), that Romer adhered to the result of 11’,
when in 1704, six years before his death, he purposed bringing
out a work on the velocity of light; the same was the case
with Huygens (Tract. de Lumine, cap. i. p. 7). Cassini's
method was very different ; he found 7’ 5” for the first satellite,
and 14’ 12” for the second, having taken 14’ 10” for the basis
of his tables for Jupiter pro peragrando diametri semissi. The
error was therefore on the increase. (Compare Horrebow,
Triduum, p. 129; Cassivi, Hypothéses et Satellites de Jupiter
in the Mém. de ? Acad., 1666-1699, tom. vill. pp. 435, 475;
Delambre, Hist. de ?Astr. mod., tom. i. pp. 751, 782; Du
Hamel, Physica, p. 435.)
Delambre, Hist. de 7’ Astr. mod., tom. ii. p. 653.

SCINTILLATION OF THE STARS. 109

exception of those of the first satellite, found 8 13” 2
Encke has very justly noticed the great importance of under-
taking a special course of observations on the occultations
of Jupiter’s satellites, in order to arrive at a correct idea
regarding the velocity of light, now that the perfection at-
tained in the construction of telescopes warrants us in hoping
that we may obtain trustworthy results.

Dr. Busch,” of Kénigsberg, who based his calculations on
Bradley’s observations of aberration, as re-discovered by Rigaud
of Oxford, estimated the passage of light from the sun to
the earth at 8’ 12”:14, the velocity of stellar light at 167976
miles in a second, and the constant of aberration at 20”°2116;
but it would appear, from the more recent observations on
aberration carried on during eighteen months by Struve with
the great transit instrument at Pulkowa,™ that the former

St Reduction of Bradley's observations at Kew and Wansted,
1836, p. 22; Schumacher’s Astr. Nachr., bd. xiii. 1836,
no. 309; (compare Miscellaneous Works and Correspon-
dence of the Rev. James Bradley, by Prof. Rigaud, Oxford,
1832). On the mode adopted for explaining aberration
in accordance with the theory of undulatory light, see
Doppler in the Adhl. der Kén. bihmischen Gesellschaft der
Wiss. 5te Folge. bd. iii. s. 754-765. It is a point of extreme
importance in the history of great astronomical discoveries, that
Picard, more than half a century before the actual discovery
and explanation by Bradley of the cause of aberration, probably
from 1667, had observed a periodical movement of the Polar:
star to the extent of about 20”, which could “neither be the
effect of parallax or of refraction. and was very regular at
opposite seasons of the year.” (Delambre, Hist. de I Astr.
moderne, tom. ii. p. 616.) Picard had nearly ascertained the
velocity of direct light before his pupil, Romer, made known
that of reflected light.

® Schum. Astr. Nachr., bd. xxi. 1844, no. 484; Struve,
Etudes d Astr. stellaire, pp. 103, 107 (compare Cosmos, vol. is
p. i144.) The result given in the Annuaire pour 1842, p.
287, for the velocity of light in a second, is 808000 kilomenes,
or 77000 leagues (each of 4000 metres), which corresponds

110 cosmos,

of these numbers should be considerably increased, The
result of these important observations gave 8’ 17’-78; from
which, with a constant of aberration of 20”:4451, and Encke’s
correction of the sun’s parallax in the year 1835, together
with his determination of the earth’s radius, as given in his
Astronomusches Jahrbuch ftir 1852, we obtain 166196 geo-
graphical miles for the velocity of light in a second. The
probable error in the velocity seems scarcely to amount to
eight geographical miles. Struve’s result for the time which
light requires to pass from the sun to the earth differs about
yisth from Delambre’s (8’ 13:2), which has been adopted
by Bessel in the Zab. Regiom., and has hitherto been followed
in the Berlin Astronomical Almanack. The discussion on this
subject cannot, however, be regarded as wholly at rest. Great
doubts still exist as to the earlier adopted conjecture that the
velocity of the light of the polar star was smaller than that of
its companion in the ratio of 133 to 134.

M. Fizeau, a physicist, distinguished alike for his great
acquirements and for the delfcacy of his experiments, has sub-
mitted the velocity of light to a terrestrial measurement, by
means of an ingeniously constructed apparatus, in which arti-
ficial light (resembling stellar light) generated from oxygen and
hydrogen, is made to pass back by means of a mirror between
Suresne and La Butte Montmartre, over a distance of 28321 feet
to the same point from which it emanated. <A disc having 720
teeth, which made 12-6 rotations in a second, alternately ob-

to 215834 miles, and approximates most nearly to Struve’s
recent result, while that obtained at the Pulkowa Obser-
vatory is 189746 miles. On the difference in the aberra-
tion of the light of the Polar star and that of its companion,
and on the doubts recently expressed by Struve, see Midler,
Astronomie, 1849, s. 8393. William Richardson gives as the
result of the passage of light from the sun to the earth 8’ 19”°28,
from which we obtain a velocity of 215392 miles in a seeend.
(Mem. of the Astron, Soc., vol. iv. P. i. p. 68.)

SCINTILLATION OF THE STARS. 111

secured the ray of light and allowed it to be seen between the
teeth on the margin. It was supposed from the marking of a
zounter (compteur) that the artificial light traversed 56642
feet, or the distance to and from the stations in ¢z4,,th part
of a second, whence we obtain a velocity of 191460 miles in
a second. ‘This result therefore approximates most closely
to Delambre’s (which was 189173 miles) as obtained from.
Jupiter's satellites.

Direct observations and ingenious reflections on the ab- —
sence of all coloration during the alternation of light in the
variable stars—a subject to which I shall revert in the sequel
—led Arago to the result, that, according to the undulatory
theory, rays of light of different colour, which consequently
have transverse vibrations of very different length and velocity,
move through space with the same rapidity. The velocity of
transmission and the refraction differ therefore in the interior of
the different. bodies through which the coloured rays pass.™

% Fizeau gives his result in leagues, reckoning 25 (and
consequently 4452 metres) to the equatorial degree. He
estimates the velocity of light at 70000 such leagues, or
about 210000 miles in the second. On the earlier experi-
ments of Fizeau, see Comptes rendus, tom. xxix. p. 92. In
Moigno, Répert. d’ Optique moderne, P. ili. p. 1162, we find
this velocity given at 70843 leagues (of 25=1°) or about
212529 miles, which approximates most nearly to the result
of Bradley, as given by Busch.

% « T)’aprés la théorie mathématique dans le systéme des
ondes, les rayons de differentes couleurs, les rayons dont les
pndulations sont inégales, doivent néanmoins se propager dans
}Ether avec la méme vitesse. Il n’y a pas de difference a cet
egard entre la propagation des ondes sonores, lesquelles se
propagent dans l’air avec la méme rapidité. Cette egalité de
propagation des ondes sonores est bien établie expérimentale.
ment par la similitude d’effet que produit une musique donnée
a toutes distances du lieu ot l’on l’exécute. La principale
difficulté, je dirai l’unique difficulté, qu’on eit élevée cantre le

112 COSMOS.

For Arago’s observations have shown that refraction in the prism
is not altered by the relation of the velocity of light to that
of the earth’s motion. All the measurements coincide in the
result, that the light of those stars towards which the earth is

systéme des ondes, consistait done a expliquer, comment la
vitesse de propagation des rayons de differentes couleurs dans
les corps differents pouvait étre dissemblable et servir 4 rendre
compte de l’inégalite de refraction de ces rayons ou de la dis-
persion. On a montré recemment que cette difficulté n’est
pas insurmontable; qu’on peut constituer l’Ether dans les
corps inégalement denses de maniére que des rayons 4 ondu-
lations dissemblables sy propagent avec des vitesses inégales :
reste 4 déterminer, si les conceptions des geométres a cet égard
sont conformes a la nature des choses. Voici les amplitudes
des ondulations déduites experimentalement d'une série de
faits relatif aux interférences :

Vio aces. 3

Jaune LL en es

Rouge se a er eeiere

La vitesse de transmission des rayons de différentes couleurs
dans les espaces célestes est la méme dans le systéme des
ondes et tout-a-fait indépendante de |’étendue ou de la vitesse
des ondulations.”

‘“‘ According to the mathematical theory of a system of
waves, rays of different colours, having unequal undulations,
must nevertheless be transmitted through ether with the
same velocity. There is no difference in this respect from:
the mode of propagation of waves of sound which are
transmitted through the atmosphere with equal velocity.
This equality of transmission in waves of sound may be well
demonstrated experimentally by the uniformity of effect pro-
duced by music at all distances from the source whence it
emanates. The principal, I may say the only objection, ad-
vanced against the undulatory theory, consisted in the diffi-
culty of explaining how the velocity of the propagation of rays
of different colours through different bodies could be dissimi-
iar, while it accounted for the inequality of the refraction of the
rays or of their dispersion. It has been recently shown that

VELUCITY OF LIGHT. 113

moving presents the same index of refraction as the light of those
from which it isreeeding. Using the language of the emission
hypothesis, this celebrated observer remarks, that bodies send
forth rays of all velocities, but that among these different velo-
cities one only is capable of exciting the sensation of light.

this difficulty is not insurmountable, and that the ether
may be supposed to be transmitted through bodies of unequal
density in such a manner that rays of dissimilar systems of
wayes may be propagated through it with unequal velocities ;
but it remains to be determined whether the views advanced
by geometricians on this question are in unison with the actual
nature of things. ‘The following are the lengths of the undu-
lations, as experimentally deduced from a series of facts in

relation to interference : £3;
AGG ea. oa oe oes: 02000428
OW eg nas gs Or OOOSS1

tg ie ees a ve OOOO RO

The velocity of the transmission of rays of different colours
through celestial space, is equal in the system of waves,
and is quite independent of the length or the velocity of
the undulations.” Arago, MS. of 1849. Compare also the
Annuaire pour 1842, pp. 333-336. The length of the lumi-
nous wave of the ether, and the velocity of the vibrations,
determine the character of the coloured rays. To the violet,
which is the most refrangible ray, belong 662, while to the
red, (or least refrangible ray with the greatest length of wave,)
there belong 451 billions of vibrations in the second.

% « J’ai prouve, il y a bien des années, par des observations
directes que les rayous des étoiles vers lesquelles la Terre
marche, et les rayons des étoiles dont la Terre s’éloigne, se
réfractent exactement de la méme quantité. Un tel résultat
ne peut se concilier avec la théorie de l’émission qu’a laide
d'une addition importante a faire a cette théorie: il faut ad-
mettre que les corps lumineux émettent des rayons de toutes
les vitesses, et que Jes seuls rayons d’une vitesse déterminée
sent visibles, qu’eux seuls produisent dans l’@il la sensation
de lumiére. Dans la théorie de l’emission, le rouge, le jaune,
le vert, Le bleu, le violet solaires sout respectivement accompag-

VOL, IIT. I

it4 COSMOS,

On comparing the velocities of solar, stellar, and terres-
trial light, which are all equally refracted in the prism,
with the velocity of the light of frictional electricity, we
are disposed, in aceordance with Wheatstone’s ingeniously
conducted experiments, to regard the lowest ratio in which
the latter exceeds the former as 3:2. According to the lowest
results of Wheatstone’s optical rotatory apparatus, electric

nés de rayons pareils, mais obscurs par défaut ou par excés
de vitesse. A plus de vitesse correspond une moindre refrae-
tion, comme moins de vitesse entraine une réfraction plus
grande. Ainsi chaque rayon rouge visible est accompagne de
rayons obscurs de la méme nature, qui se réfractent les uns
plus, les autres moins que lui: ainsi 7 existe des rayons dans
les stries noires de la portion rouge du spectre ; la méme chose
doit étre admise des stries situees dans les portions jaunes,
vertes, bleues et violettes.”’

‘‘T showed many years ago, by direct observations, that the
rays of those stars towards which the earth moves, and the rays
of those stars from which it recedes, are repeated in exactly
the same degree. Such a result cannot be reconciled with the
theory of emission, unless we make the important admission
that lz:minous bodies emit rays of all velocities, and that only
rays of a determined velocity are visible, these alone being
capable of impressing the eye with the sensation of light. In
the theory of emission, the red, yellow, green, blue, and violet
solar rays, are respectively accompanied by like rays, which
are, however, dark from deficiency or excess of velocity.
Excessive velocity is associated with a slight degree of re-
fraction, while a smaller amount of velocity involves a slighter
degree of refraction. ‘Thus, every visible red ray is accom-
panied by dark rays of the same nature, of which some are
more, and others less, refracted than the former; there are
consequently rays m the black lines of the red portion of the
spectrum ; and the same must be admitted in reference to the
lines situated in the yellow, green, blue, and violet portions.”
Arago, in the Comptes rendus de I’ Acad. des Sciences, t. Xvi.
1843, p. 404. Compare also t. viii. 1839, p. 326, and Pois-
son, 7raité de Mécanique, ed. ii: 1833, t. 1. § 168. Accord-
.ng to the undulatory theory, the stars emit waves of extremely
various trausverse velocities of oscillations.

7ELOCITY OF LIGHT. 115

light traverses 288000 miles in a second.* If we reckon
189938 miles for stellar light, according to Struve’s observa-
tions on aberration, we obtain the difference of 95776 miles
as the greater velocity of electricity in one second.

These results are appurently opposed to the views advanced
by Sir William Herschel, according to which solar and stellar
light are regarded as the effects of an electro-magnetic pro-
cess—a perpetual northern light. I say apparently, for nd one
will contest the possibility that there may be several very
different magneto-electrical processes in the luminous cosmical
bodies, in which light—the product of the process—may
possess a different velocity of propagation. To this conjec-
ture may be added the uncertainty of the numerical result
yielded by the experiments of Wheatstone, who has himself
admitted that they are not sufficiently established, but need
further confirmation before they can be satisfactorily compared
with the results deduced from observations on aberration and
on the satellites.

The attention of physicists has been powerfully attracted to
the experiments on the velocity of the transmission of elec-

® Wheatstone in the Philos. Transact. of the Royal Soc. for
1834, pp. 589, 591. From the experiments described in this
paper it would appear that the human eye is capable of per-
ceiving phenomena of light, whose duration is limited to the
millionth part of a second (p. 591). On the hypothesis re-
ferred to in the text, of the supposed analogy between the light
of the sun and polar light. see Sir John Herschel’s Results of
Astron. Observ. at the Cape of Good Hope, 1847, p. 351.
Arago, in the Comptes rendus pour 1838, t. vii. p. 956, has
referred to the ingenious application of Breguet’s improved.
Wheatstone’s rotatory apparatus for determining between the
theories of emission and undulation, since, according to the
former. light moves more rapidly through water than through
air, while, according to the latter, it moves more rapidly
through air than through water. (Compare also Comptes rendus
pour 1850, t. xxx. pp. 489-495, 556.),

12

n6 COsMOF,

wicity, recenty conducted in the United States by Walker
during the course of his electro-telegraphic determinations of
the terrestrial longitudes of Washington, Philadelphia, New
York, and Cambridge. According to Steinheil’s description of
these experiments, the astronomical clock of the Observatory
at Philadelphia was brought to correspond so perfectly with
Morse’s writing apparatus on the telegraphic line, that this
clock marked its own course by points on the endless paper
fillets of the apparatus. The electric telegraph instantaneously
eonveys each of these clock times to the other stations, indi-
cating to these the Philadelphia time by a succession of similar
points on the advancing paper fillets. In this manner arbitrary
signs, or the instant of a star's transit, may be similarly noted
down at the station by a mere movement of the observer's finger
on the stop. ‘‘ The special advantage of the American method
zonsists,” as Steinheil observes, ‘in its rendering the determi-
nation of time independent of the combination of the two senses,
sight and hearing, as the clock notes its own course, and indicates
the instant of a star’s transit (with a mean error, according to
Walker’s assertion, of only the 70th part of a second.) A
eonstant difference between the compared clock times at Phila-
delphia and at Cambridge is dependent upon the time occupied
by the electric current in twice traversing the closed circle
between the two stations.”

Eighteen equations of condition, from measurements made
on conducting wires of 1050 miles, gave for the velocity of
transmission of the hydro-galvanic current 18700 miles,”

® Steinheil in Schumacher’s Ast. Nachr., no. 679 (1849),
s. 97-100; Walker in the Proceedings of the American Philo-
sophical Society, vol. v. p. 128. (Compare earlier propositions
uf Pouillet in the Comptes rendus, t. xix. p. 1886.) The more
recent ingenious experiments of Mitchel, Director of the Obser-
vatory at Cincinnati (Gould's Astron. Journal, Dec. 1849. p. 3,
On the velocity of the s‘ectrie wave), and the investigations of

VELOCITY OF ELECTRICIT: 117

which is fifteen times less than that of the electrie current in
Wheatstone’s rotatory discs. As in Walker’s remarkable expe-
riments ¢wo wires were not used, but half of the conduction,
to use a conventional mode of expression, passed through
the moist earth, we should seem to be justified in concluding
that the velocity of the transmission of electricity depends upon
the nature as well as the dimensions® of the medium. Bad
conductors in the voltaic circuit become more powerfully heated
than good conductors; and the experiments lately made by
Riess® show that electric discharges are phenomena of a very
“various and complicated nature. The views prevailing at the
present day regarding what is usually termed “ connection
through the earth’ are opposed to the hypothesis of linear,
molecular conduction between the extremities of the wires,
and to the conjectures of the impediments te conduction, of
accumulation, and disruption in a current; since what was
formerly regarded as intermediate conduction in the earth is
now conjectured to belong exclusively to an equalisation or
restoration of the electric tension.

Although it appears probable, from the extent of accuracy

Fizeau and Gounelle at Paris, in April, 1850, differ both from
Wheatstone’s and Walker’s results. The experiments recorded
in the Comptes rendus, t. xxx. p. 489, exhibit striking differ-
ences between iron and copper as conducting media.

® See Poggendorff's Annalen, bd. Ixxiii. 1848, s. 337, and
Pouillet, Comptes rendus, t. xxx. p. 501.

%® Riess, in Poggend. Ann., bd. 78, s. 433. On the non-eon-
_ duction of the intermediate earth see the important experiments
of Guillemin Sur le courant dans une pile isolée et sans commu-
nication entre les péles in the Comptes rendus, t. xxix. p. 521.
‘Quand on remplace un fil par la terre, dans les télégraphes
electriques, la terre sert plutot de reservoir commun, que de
moyen d’union entre les deux extremités du fil.” ‘‘ When the
earth is substituted for half the circuit in the electric tele-
graph, it serves rather as a common reseryoir than as a means
of connexion between the two extremities of the wire.”

118 COSMOS.

at present attainable in this kind of observation, that the
constant of aberration, and consequently the velocity of light,
is the same for all fixed stars, the question has frequently been
mooted, whether it be not possible that there are luminous
cosmical bodies, whose light does not reach us, in conse-
quence of the particles of air being turned back by the force
of gravitation exercised by the enormous masses of these bodies.
The theory of emission gives a scientific form to these imagi-
native speculations.” I here only refer to such views because
it will be necessary in the sequel that we should consider certain

@ Madler, Asér., s. 380; also Laplace according to Moigno,
Répertoire d’ Optique moderne, 1847, t. i. p. 72. ‘Selon la
théorie de l’émission on croit pouvoir démontrer que si le
diamétre d'une étoile fixe serait 250 fois plus grand que celui
du soleil, sa densité restant la méme, l'attraction exercée a sa_
surface detruirait la quantite de mouvement, de la molécule
lumineuse émise, de sorte qu’elle serait invisible a de grandes
distances.’ ‘* It seems demonstrable by the theory of emission
that if the diameter of a fixed star be 250 times greater than
that of the sun—its density remaining the same—the attraction
exercised on the surface would destroy the amount of motion
emitted from the luminous molecule; so that it would be in-
visible at great distances.” If, with Sir William Herschel,
we ascribe to Arcturus an apparent diameter of 0”°1, it
follows that the true diameter of this star is only eleven times
greater than that of our sun. (Cosmos, vol. i. p. 138.) From the
above considerations on one of the causes of non-luminosity
the velocity of light must be very different in cosmical bodies
of different dimensions. This has, however, by no means been
confirmed by the observations hitherto made. Arago says in
the Comptes rendus, t. viii. p. 326, * Les expériences sur Legale
deviation prismatique des étoiles, vers lesquelles la terre
marche ou dont elle s’éloigne, rend compte de l’egalité de
vitesse apparente de toutes les étoiles.”” ‘‘ Experiments made
on the equal prismatic deviation of the stars towards which
the earth is moving, and from which it is receding, explain
the apparent equality of velocity in the rays of all the
stars.”’

STELLAR LIGHT. 119

peculiarities of motion ascribed to Procyon, which appeared
to indicate a disturbance from dark cosmical bodies. It is the
object of the present portion of this work to notice the
different directions to which scientific inquiry had inclined,
at the period of its composition and publication, and thus to
indicate the individual character of an epoch in the sidereal
as well as the telluric sphere.

The photometric relations (relations of brightness) of the
self-luminous bodies with which the regions of space are filled,
have for more than two thousand years been an object of
scientific observation and inquiry. The description of the
starry firmanent did not only embrace determinations of places,
the relative distances of luminous cosmical bodies from one
another and from the circles depending on the apparent course
of the sun and on the diurnal movement of the vault of heaven;
but it also considered the relative intensity of the light of the
stars. The earliest attention of mankind was undoubtedly
directed to this latter point; individual stars having received
names before they were arranged with others into groups and
constellations. Among the wild tribes inhabiting the densely
wooded regions of the Upper Orinoco and the Atabapo, where
from the impenetrable nature of the vegetation I could only
observe high culminating stars for determinations of latitude,
I frequently found that certain individuals, more especially
old men, had designations for Canopus, Achernar, the feet of
the Centaur and @ in the Southern Cross. If the catalogue of
the constellations known as the Catasterisms of Eratosthenes,
can lay claim to the great antiquity so long ascribed to it,
(between Autolycus of Pitane and Timocharis, and therefore
nearly a century and a half before the time of Hipparchus,)
_ we possess in the astronomy of the Greeks a limit for the period
when the fixed stars had not yet been arranged according to
their relative magnitudes. In the emuneration of the stars
belonging to each constellation, as given in the Catasterisms,

- 120 COSMCS.

frequent reference is made to the number of the largest and
most luminous or of the dark and less easily recognized stars;
but we find no relative comparison of the stars contained in
the different constellations. The Catasterisms are, according to
Bernhardy, Baehr, and Letronne, more than two hundred years
less ancient than the catalogue of Hipparchus, and are besides
a careless compilation and a mere extract from the Poeticum
Astronomicum (ascribed to Julius Hyginus),ifnot from the poem
‘Epuijs of the older Eratosthenes. The catalogue of Hipparchus,
which we possess in the form given to it in the Almagest,
contains the earliest and most important determination of
classes of magnitude (gradations of brightness) of 1022 stars,
and therefore of about th of all the stars in the firmament
visible to the naked eye, and ranging from the 1st to the 6th
magnitude inclusive. It remains undetermined whether these
estimates are all due to Hipparchus, or whether they do not
rather appertain in part to the observations of Timocharis or
Aristyllus, which Hipparchus frequently used.

This work constituted the important basis on which was
established the science of the Arabs and of the astronomers
of the middle ages: the practice, transmitted to the nine-
teenth century, of limiting the number of stars of the first
magnitude to 15 (although Madler counts 18, and Riimker
after a more careful observation of the southern celestial]
hemisphere upwards of 20) takes its origin from the classifi-
cation of the Almagest, as given at the close of the table of
stars in the eighth book. Ptolemy, referring to natural vision,
called all stars dark which were fainter than those of his 6th
class; and of this class, he singularly enough only instances

*! Eratosthenes, Catasterismi, ed. Schaubach, 1795, and
E~atosthenica, ed. G. Bernhardy, 1822, p. 110-116. A
distinction is made between stars Aapmpovs (peyddovs) and
auavpods (cap. 2, 11, 41). Ptolemy also limits of duépporan
*n those stars which do not regularly belong to a constellation,

-MAGNIYUDES OF STARS. 121

49 stars distributed almost equally over both hemispheres.
Considering that the catalogue enumerates about one-fifth
of all the fixed stars visible to the naked eye, it should,
according to Argelander’s investigations, have given 640 stars
of the 6th magnitude.’ The nebulous stars (vededoeideis) of
Ptolemy and of the Pseudo-Eratosthenian Catasterisms, are
mostly small stellar swarms,® appearing like nebule in the
clearer atmosphere of the southern hemisphere. I more
particularly base this conjecture on the mention of a nebula in
the right hand of Perseus. Galileo, who, like the Greek and
Arabian astronomers, was unacquainted with the nebula in
Andromeda which is visible to the naked eye, says in his
Nuncius sidereus, that stelle nebulose are nothing more than
stellar masses scattered in shining groups through the ether
(areole sparsim per ethera fulgent).@ The expression (Ta»
peydror rakis), the order of magnitudes, although referring only
to lustre, led, as early as the ninth century, to hypotheses on the
diameters of stars of different brightness :“ as if the intensity
of light did not depend on the distance, volume, and mass,
as also on the peculiar character of the surface of a cosmical
body in more or less fayouring the process of light.

At the period of the Mongolian supremacy, when, in the
fifteenth century, astronomy flourished at Samarcand, under
Timur Ulugh Beig, photometric determinations were facilitated
by the subdivision of each of the six classes of Hipparchus
and Ptolemy into three subordinate groups; distinctions, for
example, being drawn between the small, intermediate, and

@ Ptol. Almag. ed. Halma, tom. ii. p. 40, and in Eratosth.
Catust., cap. 22, p. 18. # d¢ xepadd al 4 dpmy dvanros éparas,
bia de vehehadovs cvorpodis Soxet ticw dpacba. ‘Thus, tod,
Geminus, Phen. (ed. Hilder, 1590), p. 46.

® Cosmos, vol. ii. pp. 713-14.

* Muhamedis Alfragani Chronologica et Ast. Elementa,
1590, zap. xxiv. p. 118. '

122 COSMOS.

large stars of the se2ond magnitude—an attempt which reminds
us of the decimal gradations cf Struve and Argelander.®
This advance in photometry, by a more exact determination
of degrees of intensity, is ascribed in Ulugh Beig’s tables to
Abdurrahman Sufi, who wrote a work “on the knowledge of
the fixed stars,” and was the first who mentions one of the
Magellanic clouds under the name of the White Ox. Since
the discovery and gradual improvement of telescopic vision,
these estimates of the gradations of light have been extended
far below the sixth class. The desire of comparing the in-
crease and decrease of light in the newly appeared stars in
Cygnus and Ophiuchus (the former of which continued
luminous for twenty-one years), with the brightness of other
stars, called attention to photometric determinations. The
so-called dark stars of Ptolemy, which were below the 6th
magnitude, received numerical designations according to the
relative intensity of their light. ‘* Magnitudes, from the 8th
down to the 16th,” says Sir John Herschel, “are familiar to
those who are in the practice of using powerful instruments.”
But at this faint degree of brightness, the denominations for
the different gradations in the scale of magnitudes are very
undetermined, for Struve occasionally classes, among the 12th
or 138th, stars which Sir John Herschel designates as belonging
to the 18th or 20th magnitudes.

The present is not a fitting place to discuss the merits
of the very different methods which have been adopted for the
measurement of light within the last hundred-and-fifty years,
from Auzout and Huygens to Bouguer and Lambert; and
from Sir William Herschel, Rumford, and Wollaston, to

® Some MSS. of the Almagest refer to such subdivisions
or intermediate classes, as they add the words peiar or «Adoows
to the determination of magnitudes. (Cod. Paris, no. 2389.)
Tycho expressed this increase or diminution by points.

*® Sir John Herschel, Outlines of Ast~., pp. 520-27.

PHULUMETRIC METHODS. 123

Steinheil and Sir John Herschel. It will be sufficient for the
cbject of this work briefly to indicate the different methods.
These were a comparison of the shadows of artificial lights,
differing in numbers and distance; diaphragms; plane glasses
of different thickness and colour; artificial stars formed by
reflection on glass spheres ; the juxta-position of two seven-feet
telescopes, separated by a distance which the observer could
pass in about a second; reflecting instruments in which two
stars can be simultaneously seen and compared, when the tele-
scope has been so adjusted that the star directly observed gives
two images of like intensity ;* an apparatus having, (in front

% This is the application of reflecting sextants to the
iletermination of the intensity of stellar light; of this instru-
ment I made greater use when in the tropics than of the
diaphragms recommended to me by Borda. I began my in-
vestigation under the clear skies of Cumana, and continued
them subsequently till 1808, but under less favourable con-
ditions, on the elevated plateaux of the Andes, and on the
coasts of the Pacific, near Guayaquil. I had formed an arbi-
trary scale in which I marked Sirius, as the brightest of all
the fixed stars, equal to 100; the stars of the first magnitude
between 100 and 80, those of the second magnitude between
80 and 60, of the third between 60 and 45, of the fourth
between 45 and 30, and those of the fifth between 30 and 20:
I especially measured the constellations of Argo and Grus, in
which I thought I had observed alterations since the time of
Lacaille. It seemed to me after a careful combination of
magnitudes, using other stars as intermediate gradations, that
Sirius was as much brighter than Canopus, as a Centauri
than Achernar. My numbers cannot, on account of the above
_ mentioned mode of classification, be compared directly with-
those which Sir John Herschel made public as early as 1838.
(See my Recueil d’Observ. astr., vol. i. p. lxxi., and Relat,
hist. du Voyage aux Régions équin., t. i. pp. 518 and 624;
also Lettre de M. de Humboldt a M. Schumacher en Fevr. 1839,
in the Aszr. Nachr., no. 374.) In this letter I wrote as follows:
“M. Arago, qui posséde des moyens photometriques entiére-
ment differents de ceux qui ont ete publiés jusqu’ici, m’avait
tassuré sur la partie des erreurs qui pouvaient provenir du

124 COSMOR.

of the object-glass,) a mirror and diaphragms, whose rota.
tion is measured on a ring; telescopes with divided object-
glasses, on either half of which the stellar light is received.
through a prism; astrometers® in which a prism reflects the

changement d’inclinaison d’un miroir entamé sur la face in-
térieure. Il blame d’ailleurs le principe de ma méthode et le
regarde comme peu susceptible de perfectionnement, non seule-
ment a cause de la difference des angles entre l’étoile vue
directement et celle qui est amenée par réflexion, mais surtout
parceque le résultat de la mesure d’intensité dépend de la
partie de l’ceil qui se trouve en face de l’oculuire. I] ya erreur
lorsque la pupille n’est pas trés exactement a la hauteur de la
limite inférieure de la portion non entamée du petit miroir.”
** M. Arago, who possesses photometric data, differing entirely
from those hitherto published, had instructed me in reference to
those errors which might arise from a change of inclination of a
mirror silvered on its inner surface. He moreover blames
the principle of my method, and regards it as little susceptible
of correctness, not only on account of the difference of angles
between the star seen directly and by reflection; but espe-
cially because the result of the amount of intensity depends
on the part of the eye opposite to the ocular glass. There
will be an error in the observations when the pupil is not
exactly adjusted to the elevation of the lower limit of the un-
plated part of the small mirror.”

®Compare Steinheil, Hlemente der Helligkeits-Messungen am
Sternenhimmel, Miinchen 1836, (Schum. Astr. Nachr. no. 609,)
and Sir J. Herschel, Results of Astronomical Observations made
during the years 1834-1838 at the Cape of Good Hope (Lond.
1847), pp. 353-357. Seidel attempted in 1846 to determine
by means of Steinheil’s photometer the quantities of light of
several stars of the first magnitude, which attain the requisite
legree of latitude in our northern latitudes. Assuming Veg?
to be=1, he finds for Sirius 5:13; for Rigel, whose lustr
appears to be on the increase, 1:30 ; for Arcturus 0°84 ; for Ca-
pella 0°83; for Procyon 0°71; for Spica 0°49; for Atair 0°40;
for Aldebaran 0°36; for Deneb 0°35; for Regulus 0°34; for
Pollux 0°30; he does not give the intensity of the light of
Betelgeuze, on account of its being a variable star, as was parti.
cularly manifested between 1836 and 1889. (Outlines, p 523.)

PHOTOMETRY. 125

image of the moon or of Jupiter, and concentrates it through
a lens at different distances into a star more or less bright.
Sir John Herschel, who has been more zealously engaged than
any other astronomer of modern times in making numerical
determinations in both hemispheres of the intensity of light,
confesses that the practical application of exact photometric
methods muststill beregarded asa “ desideratum in astronomy,’
and that ‘photometry is yet in its infancy.” The increasing
interest taken in variable stars, and the recent celestial phe-
nomenon of the extraordinary increase of light exhibited ir
the year 1837 in a star of the constellation Argo, has made
astronomers more sensible of the importance of obtaining
certain determinations of light.

It is essential to distinguish between the mere arrangement
of stars according to their lustre, without numerical estimates
of the intensity of light (an arrangement adopted by Sir John
Herschel in his Manual of Scientific Enquiry prepared for the
use of the Navy), and classifications in which intensity of
light is expressed by numbers, under the form of so-called
relations of magnitude, or by more hazardous estimates of
the quantities of radiated light. The first numerical scale,
based on estimates calculated with the naked eye, but im-

® Compare for the numerical data of the photometric results
4 tables of Sir John Herschel’s Astr. Obs. at the Cape, a) p. 841;
b) pp. 367-371; c) p. 440; and d) in his Outlines of Astr., pp. 522
-525, 645-646. For a mere arrangement without numbers
see the Manual of Scientific Enquiry prepared for the use of the
Navy, 1849, p.12. In order to improve the old conventional
mode of classing the stars according to magnitudes, a scale of
photometric magnitudes consisting in the addition of 0°41, as
explained more in detail in Astr. Obs. at the Cape, p. 370,
has been added to the vulgar scale of magnitudes in the
Outlines of Astronomy, p. 645, and these scales are subjoined
to this portion of the present work, together with a list of
aorthern and southern stars.

136 - COSMOS.

proved Ly an ingenious elaboration of the materia.s” probably
deserves the preference over any other approximative method
practicable in the present imperfect condition of photometrical
instruments, however much the exactness of the estimates
must be endangered by the varying powers of individual ob-
servers—the serenity of the atmosphere—the different altitudes
of widely distant stars, which can only be compared by means
of numerous intermediate stellar bodies—and above all by the
unequal colour of the light. Very brilliant stars of the
Ist magnitude, such as Sirius and Canopus, a Centauri and
Achernar, Deneb and Vega, on account of their white light,
admit far less readily of comparison by the naked eye
than fainter stars below the 6th and 7th magnitudes. Such
a comparison is even more difficult when we attempt to
contrast yellow stars of intense light, like Procyon, Capella,
or Atair, with red ones, like Aldebaran, Arcturus, and Betel-
geux.”

Sir John Herschel has endeavoured to determine the rela-
tion between the intensity of solar light, and that of a star of
the lst magnitude by a photometric comparison of the moon
with the double-star « Centauri of the southern hemisphere,
which is the third in brightness of all the stars. He thus
fulfilled (as had been already done by Wollaston) a wish
expressed by John Michell” as early as 1767. Sir John
Herschel found from the mean of eleven measurements con-
ducted with a prismatic apparatus; that the full moon was
27408 times brighter than « Centauri. According to Wol-
laston the light of the sun is 801072 times brighter than

7 Argelander, Durchmusterung des nérdl. Himmels zwi-
schen 45° und 80° Decl. 1846, s. xxiv.—-xxvi.; Sir John
Herschel, Ast. Observ. at the Cape of Good Hope, pp. 327
340, 365,

2 Op. cit., p. 304, and Outl., p. 522.

% Philos. Transact., vol. lvii. for the year 1767, p. 234.

PHOTOMETRY. 127

the full moon ;* whence it follows that the light transmitted
to us from the sun is to the light which we receive from «
Centauri as 22000 millions to1. It seems therefore very pro-
bable, when, in accordance with its parallax, we take into
account the distance of the star, that its (absolute) proper
.uminosity exceeds that of our sun by 2-3, times. Wollaston
found the brightness of Sirius 20000 million times fainter
than thatof the sun. From what we at present believe to be
the parallax of Sirius (0230) its actual (absolute) intensity of
light exceeds that of the sun 63 times.“ Our sun there-
fore belongs, in reference to the intensity of its process of
light, to the fainter fixed stars. Sir John Herschel esti-

7% Wollaston, in the Philos. Transact. for 1829, p. 27.
Herschel’s Outlines, p. 553. Wollaston’s comparison of the
light of the sun with that of the moon was made in 1799, and
was based on observations of the shadows thrown by lighted
wax tapers, while in the experiments made on Sirius in 1826
and 1827, images reflected from thermometer bulbs were em-
ployed. ‘The earlier data of the intensity of the sun’s light,
compared with that of the moon, differ widely from the results
here given. They were deduced by Michelo and Euler, from
theoretical grounds at 450000 and 374000, and by Bouguer,
from measurements of the shadows of the light of wax tapers,
at only 300000. Lambert assumes Venus, in her greatest inten-
sity of light, to be 3000 times fainter than the full moon. Ac-
cording to Steinheil, the sun must be 3286500 times further
removed from the earth than it is, in order to appear, like Arc-
turus, to the inhabitants of our planet (Struve, Stellarum Com-
positarum Mensure Micrometrice, p. clxiii.) ; and according to
Sir John Herschel the light of Arcturus exhibits only half the
intensity of Canopus; (Herschel, Observ. at the Cape, p. 34.)
All these conditions of intensity, more especially the impor-
tant comparison of the brightness of the sun, the full moon, and
of the ash-coloured light of our satellite which varies so greatly
according to the different positions of the earth considered as
a reflecting body, deserve further and serious investigation.

% Qutl. of Astr., p. 553; Astr. Observ. at the Cape, p. 363

128 COSMOR, ~

mates the intensity of the light of Sirius to be equal to the
light of nearly two hundred stars of the 6th magnitude. Since
it is very probable, from analogy with the experiments already
made, that all cosmical bodies are subject to variations both
in their movements through space and in the intensity of
their light, although such variations may occur at very long
and undetermined periods, it is obvious, considering the de-
pendence of all organic life on the sun’s temperature and
on the intensity of its light, that the perfection of photo-
metry constitutes a great and important subject for scientific
inquiry. Such an improved condition of our knowledge can
render it alone possible to transmit to future generations
numerical determinations of the photometric condition of the
firmament. By these means we shall be enabled to explain
numerous geognostic phenomena relating to the thermal history
of our atmosphere, and to the earlier distribution of plants
and animals. Such considerations did not escape the in-
quiring mind of William Herschel, who, more than half a
century ago, before the close connection between electricity
and magnetism had been discovered, compared the ever
luminous cloud-envelopes of the sun's body with the polar
light of our own terrestrial planet.”

Arago has ascertained that the most certain method for the
direct measurement of the intensit of light consists in observing
the comple.aentary condition of the coloured rings seen by trans-
mission and reflection. I subjoin in a note,” in his own words,

% William Herschel On the nature of the sun and fixed stars
in the Philos. Transact. for 1795, p. 62; and On the changes
that happen to the fixed stars in the Philos. Transact. for 1796,
p- 186. Compare also Sir John Herschel, Odserv. at. the
Cape, pp. 350-352.

% Extract of a Letter from M. Arago to M. de Humboldt,
May, 1850.

Mesures photométriques.
*« {} n’existe pas de Photométre proprement. dit, c’est-a-dire

PHOTOMETEY. 129

the results of my friend’s photometric “method, to which he
has added an account of the optical principle on which his
cyanometer is based.

The so called relations of the magnitude of the fixed stars, as

d’instrament donnant ]’intensité d’une lumiére isolée; le Pho-
tométre de Leslie, 4 l'aide duquel il avait eu laudace de
vouloir comparer la lumiére de la lune a la lumiére du soleil,
par des actions calorifiques, est complétement défectueux. J‘ai
prouvé, en effet, que ce pretendu Photométre monte quand
on l’expose a la lumiére du soleil, qu'il descend sous l’action
‘de la lumiére du feu ordinaire, et qu'il reste complétement
stationnaire lorsqu il regoit la lumiére d'une lampe d’Argand.
Tout ce qu’on a pu faire jusqu'ici, c'est de comparer entr’elles
deux lumiéres en présence, et cette comparaison n'est méme a
labri de toute objection que lorsqu’on raméne ces deux
lumiéres a l’égalité par un affaiblissement graduel de la lumiére
la plus forte. C’est comme criterium de cette égalité que j’ai
employé les anneaux colorés. Si on place l'une sur l'autre deux
lentilles d’un long foyer, il se forme autour de leur point de
contact des anneaux colorés tant par voie de réflexion que
par voie de transmission. Les anneaux réfléchis sont com-
plementaires en couleur des anneaux transmis; ces deux
series d’anneaux se neutralisent mutuellement quand les deux
lumiéres qui les forment et qui arrivent simultanément sur
les deux lentilles, sont égales entr’elles.

* Dans le cas contraire on voit des traces ou d’anneaux
reflechis ou d’anneaux transmis, suivant que la lumiére qui
forme les premiers, est plus forte ou plus foible gue la lumiire
a laquelle on doit les seconds. C'est dans ce sens seulement
que les anneaux colorés jouent un rdle dans les mesures de
a lumiére auxquelles je me suis livré.”’

(b.) Cyanometre.

** Mon cyanométre est une extension de mon polariscope.
Je dernier instrument, comme tu sais, se compose d’un tube
ferme a l'une de ses extrémités par une plaque de cristal de
roche perpendiculaire a l’axe, de 5 millimétres d’épaisseur ;
et d’un prisme doué de la double réfraction, placé du cété de
l'oeil. Parmi les couleurs variées que donne cet appareil,
lorsque Ce la | umiére polarisée Je traverse, et qu’on fait tourner

VoL. III. K

130 COSMOS.

given in our cataiogues and maps of the stars. sometimes indi
cate as of simultaneous occurrence that which belongs to very
different periods of cosmical alterations of light. The order
of the letters which, since the beginning of the seventeenth

_—

le prisme sur lui-méme, se trouve par un heureux hasard la
nuance du bleu de ciel. Cette couleur bleue fort affaiblie,
c’est-a-dire trés mélangée de blanc lorsque la lumiére est pres-
que neutre, augmente d'intensite—progressivement, 4 mesure
que les rayons qui penétrent dans l’instrument, renferment
une plus grande proportion de rayons polarisés.

‘‘Supposons done que le polariscope soit dirigé sur ene
feuille de papier blanc; qu’entre cette feuille et la lame de
cristal de roche il existe une pile de plaques de verre suscep-
tible de changer d'inclinaison, ce qui rendra la lumiére eéclair-
ante du papier plus ou moins polarisee; la couleur bleue
fournie par l'instrument va en augmentant avec l’inclinaison de
la pile. et l'on s’arréte lorsque cette couleur parait la méme
que celle de la région de l’'atmosphére dont on veut deéter-
miner la teinte cyanométrique, et qu'on regarde a lceil nu
immédiatement 4 cété de l’instrument. La mesure de cette
teinte est donnée par l’inclinaison de la pile. Si cette derniére
partie de l'instrument se compose du méme nombre de plaques
et d'une méme espéce de verre, les observations faites dans
divers lieux seront parfaitement comparables entr’elles.”

(a.) Photometric Measurements.

“There does not exist a photometer properly so called, that
is to say, no instrument giving the intensity of an isolated light;
for Leslie’s photometer, by means of which he boldly supposed
that he could compare the light of the moon with that of the
sun, by their caloric actions, is utterly defective. I found, in
fact, that this pretended photometer rose on being exposed to
the light of the sun, that it fell when exposed to a moderate
fire, and that it remained altogether stationary when brought
near the light of an Argand lamp. All that has hitherto
been done has been to compare two lights when contiguous
to one another, but even this comparison cannot be relied on
unless the two lights be equalized, the stronger being gradually
reduced to the intensity of the feebler. For the purpose of
judging of this ineguality I employed coloured rings.

PHOTOMETRY. 1éi

century. have been added to the stars in the generally con-
suited Uranometria Bayert, are uot, as was long supposed,
certam indications of these alterations of light. Argeiander
has ably shown, that the relative brightness of the stars cannot

placing on one another two lenses of a great focal length, co-
loured rings will be formed round their point of contact as much
by means of reflection as of transmission. The colours of the
reflected rings are complementary to those of the transmitted
rings; these two series of rings neutralise one anether when
the two lights by which they are formed and which fall
simultaneously on the two lenses are equal.

‘In the contrary case, we meet with traces of reflected or
transmitted rings, according as the light by which the former
are produced, is stronger or fainter than that from which
the latter are formed. It is only in this manner that co-
loured rings can be said to come into play in those photo-
metric measurements to which I have directed my attention.”

é (b.) Cyanometer.

“My cyanometer is an extension of my polariscope. This
latter instrument, as you know, consists of a tube closed at one
end by a plate of rock crystal, cut perpendicular to its axis,
and 5 millimétres in thickness; and of a double refracting
prism placed near the part to which the eye is applied. Among
the varied colours yielded by this apparatus, when it is
traversed by polarised light and the prism turns on itself, we
fortunately find a shade of azure. This blue, which is very
faint, that is to say mixed with a large quantity of white when
the light is almost neutral, gradually increases in intensity in
proportion to the quantity of polarised rays which enter the
instrument.

“Let us suppose the polariscope directed towards a sheet
of white paper; and that between this paper and the plate
of rock crystal there is a pile of glass plates capable of being
variously inclined, by which means the illuminating light of
the paper would be more or less polarised; the blue colour
yielded by the instrument will go on increasing with the in-
clination of the pile ; and the process must be continued unti:
the colour appears of the same intensity with the region
of the atmosphere whose cyanometrical tinge is to be detez’-

K J

132 COSMOS.

be inferred from the alphabetical order of the letters, and that
Bayer was influenced in his choice of these letters, by the
- form and direction of the constellations.”

PHOTOMETRIC ARRANGEMENT OF THE FIXED STARS,

I close this section with a table taken from Sir John
Herschel’s Outlnes of Astronomy, pp. 645 and 646. Iam
indebted for the mode of its arrangement, and for the follow-
ing lucid exposition, to my learned friend Dr. Galle, from
whose communication, addressed to me, in March, 1850, I
extract the subjoined observations :—

‘The numbers of the photometric scale in the Outlines of
Astronomy have been obtained by adding throughout 0°41
to the results calculated from the vulgar scale. Sir John
Herschel arrived at these more exact determinations by ob-
serving their ‘‘ sequences” of brightness, and by combining
these observations with the average ordinary data of magni-
tudes, especially on those given in the catalogue of the Astro-
nomical Society for the year 1827. (See Odserv. at the Cape,
pp. 804-352.) The actual photometric measurements of seve-
ral stars as obtained by the Astrometer (op. ett. p. 353), have
not been directly employed in this catalogue, but have only
served generally to show the relation existing between the
ordinary scale (of 1st, 2nd, 3rd. &c., magnitudes) to the actual
photometric quantities of individual stars. This comparison
has given the singular result that our ordinary stellar magni-
tudes (1, 2,3...) decrease in about the same ratio as a star of
the 1st magnitude when removed to the distances of 1, 2,3...

mined, and which is seen by the naked eye in the immediate
vicinity of the instrument, The amount of this colour is given
by the inclination of the pile; and if this portion of the appa-
ratus consist of the same number of plates formed of the same
kind of glass, observations made at different places may readily
be compared together.” :

™ Argelander de fide Uranometrie Bayert, 1842, pp. 14-23.
* In eadem classe littera prior majorem splendorem nullo modo
indicat” (§ 9). Bayer did not therefore show that the light
of Castor was more intense in 1603 tha: that of Pollux.

PHOTOMETRIC SCALE. 18%

by which its brightness, according to photometric law, would
attain the values 1,4, 23, .,th...(Observ. at the Cape, pp. 371,
372; Outlines, pp.521, 522); in order, however, to make this
accordance still greater, it is only necessary to naise our pre-
viously adopted stellar magnitudes about half a magnitude (or
more accurately considered 0°41)so that a star of the 2°00 mag-
nitude would in future be called 2°41, and star of 2°50 would be-
come 2°91, andsoforth. Sir John Herschel therefore proposes
that this “‘ photometric” (raised) scale shall in future be adopted
( Observ. at the Cape, p.372,and Outlines, p. 522)—a proposition
in which we cannot fail toconcur. For while on the one hand
the difference from the vulgar scale would hardly be felt (O00-
serv. at the Cape, p. 372); the table in the Outlines (p. 645)
may, on the other hand, serve as a basis for stars down to the
fourth magnitude. The determinations of the magnitudes of
the stars according to the rule, that the brightness of the stars
of the lst, 2nd, 3rd, 4th magnitude is exactly as 1, 4, 3,,4,...as
is now shown approximatively, is therefore already practicable.
Sir John Herschel employs aCentauri as the standard star of the
first magnitude, for his photometric scale, and as the unit for the
quantity of light ( Outlines, p. 523; Observ. at the Cape, p. 372).
If therefore we take the square of a star’s photometric mag-
nitude, we obtain the inverse ratio of the quantity of its light
to that of aCentauri. Thus for instance if « Orionis have a pho-
tometric magnitude of 3, it consequently has 1 of the light of
a Centauri. The number 3 would at the same time indicate
that «x Orionis is 3 times more distant from us than a Centauri,
provided both stars be bodies of equal magnitude and bright-
ness. If another star, as for instance Sirius, which is four
times as bright, were chosen as the unit of the photometric
magnitudes indicating distances, the above conformity to law
would not be so simple and easy of recognition. It is also
worthy of notice that the distance of a Gentauri has been
ascertained with some probability, and that this distance is
the smallest of any yet determined. Sir John Herschel
demonstrates (Outlines, p. 521,) the inferiority of other scales
to the photometric, which progresses in order of the squares,
1, 4. 4, zy. . . He likewise treats of geometric progressions, as
for instance, 1. 4, 3, 4,... or 1, 4, 4, s4.... The gradations
employed by yourself in your observations under the equator,
during your travels in America, are arranged in a kind of

134 COSMOS,

‘arithmetical progression (Recueil d’Observ. Astron., vol. i.
p. lxxi., and Schumacher’s Astron. Nachr. no. 374). These
scales however correspond less closely than the photometric
scale of progression (by squares) with the vulgar scale. In
the following table the 190 stars have been given from the
Outlines, without reference to their declination, whether
southern or northern, being arranged solely in accordance
with their magnitudes.”’

List of 190 stars from the Ist to the 8rd magnitude, arranged
according to the determinations of Sir John Herschel, giving
the ordinary magnitudes with greater accuracy, and likewise
the magnitudes in accordance with his proposed photometric
classification :—

STaRs OF THE Frrst MAGNITUDE.

Magnitude. Magnitude,
Star. Star.
Vulg. | Phot. Vulg. | Phot.
INI cred yenil 0°08 | 0°49 fa Orionis ......... 10: | 1°48
» Argus (Var.) ...| — — fa Eridani ......... 1:09 | 1:50
Canopus ......... 0°29 | 0°70 Aldebaran ...... 1°13.) fee
a Centauri ......... 0°59 | 1°00 | 6 Centauri......... 117 | 1°58
Arcturus .........] 0°77 | 1118 Ja Crucis............ 1°2 16
Rigel: | adios tad 0°82 | 1:23 Antares ......... 1°2 1G!
Capella ....<..0+s 1°0,3' | Usd 308 ee Balas cuss coass 1:28 | 1°69
Be SIVEOS. cciarcnne des 1:0 14: Spica 1°38 | 1°79
Procyon ......... LM: 12: .

Magnitude. Magnitude.
Star. Star.

Vulg. | Phot. Vulg. | Phot.

Fomalhaut ......| 1°54 | 1°95 ]|A Scorpii ......... 1:87 | 2°28
RRO as cc eiecn nis 1°57 | 1°98 Ja Cygni............] 1°90 | 2°31
Pollux 16: | 2°0: Castor ............ | 1°94 | 2°35
Regulus ......... 16 2:0: Je Ursee(Var.) ... | 1°95 -| 2°36

wn MOTT seg ssp Bos 166 | 2°07 |} a Urse Var.) ... | 1:96 | 2°37
y Crucis ............| 1°78 | 2°14 | Orionis ......... 2°01 | 2°42
FROME Cans'conc cmt 184° 1 B26 03 Argus... .. vseseses 2°08 | 2-44
+ Canis ......... vee | 2°86 || 2°37 Fa Perse ............ | 207 | Zed

PHOTOMETRIC SCALE.

135

Srars oF THE Seconp MacnirupE—continued.

Magnitude. Magnitude.
Star. Star.

Vulg. | Phot. Vulg. Phot.
Prargus <.2......... 2°08 | 2°49 |-y Leonis............ 2:34 275
oe ae 2°18 | 2°59 3 Gruis .| 2°36 . 2°77
n Ursze (Var.) 2°18 | 2°59 fa Arietis 2°40 | 2°81
y Orionis ........ 218 | 2°59 [o Sagittarii ...... 2°41 | 2°82
a Triang austr 2°23 | 2°64 Argus .. 2°42 | 2°83
¢ Sagittarii ...... 2°26 | 267 |Z Urse .. 2°43 | 2°84
B Tauri . 228 | 2°69 | 6 Andromede 245 | 2°86
Polaris; .5.3..< 2-28 |) 269 | 6 Ceti <.:........... 2°46 | 2°87
@ :Scorpii:........ 2°29 | 2°70 JA Argos............ 2°46 | 2°87
eT VOree.5.,... 2°30 | 271 | 6 Aurige ......... 2°48 | 2°89
& Canis 2°32 | 2°73 | y Andromede ...| 2°50 | 2°91

a Pavonis ......... 2°33 | 2°74

Srars oF THE THIRD MAGNITUDE.

Magnitude. Magnituds.
Star. Star.

Vulg. | Phot. Vulg. | Phot.

y Cassiopeie ...... 2°52 | 2°93 Je Argus .. 2°80 | 3°21
a Andromede ....| 2°54 | 2°95 Je Bootis.....,...... 2°80 | 3°21
@ Centauri ......... 254 | 2°95 [a Lupi . 2°82 | 3°23
a Cassiopeie ...... 2°57 | 2°98 Je Centauri ......... 2°82 | 3°23
SPINOR) 4.4,.35<--0 2°58 | 299 |» Canis .. 285 | 3°26
= Orionis, ....,...... 2°59 | 3:00 [8 Aquarii ......... 2°85 | 3°26
y Geminorum 2°59 | 300 [6 Scorpii............ 2°86 | 3:27
§ Orionis............ 2-61 | 3:02 |e Cygni............| 2°88 | 3°29
Algol (Var.) 2°62 | 3°03 | n Ophiuchi.. cy apa 2°89 | 3°50

é Pegasi aie: tees 2°62 | 3°03 | y Corvi ............] 290 | 3°31
y Draconis ......... 2°62 | 303 [a Cephei............| 2°90 | 3°31
Pe ROOMS, . onc5.25:-- 2°63 | 3°04 [6d Centauri ......... 2°91 | 3°32
a Ophiuchi......... 2°63 | 3°04 [a Serpentis ...... 292 | 3°33
8 Cassiopeie ...... 2°63 | 3°04 [0 Leonis...... ..... | 2°94 | 3°35
ob Dia 263 ! 3°04 [« Argus. 2°94 | 3°35
a Pegasi .. 2-65 | 3:06 |B Corvi 2:95 | 3°36
coe g ee Eig. 2°65 | 3°06 | 6 Scorpii ......... 2°96 | 3°37
y Centauri ......... 2:68 | 3°09 |Z Centauri......... 2°96 | 3°37
a Coron 2°69 | 3°10 |Z Ophiuchi.. 2°97 | 3°38
y Ursee 271 | 3:12 | a Aquarii 2°97 | 3°38
& COMP .......2°..: 271 | 3°12 | w Argus...........: 2°98 | 339
SS ee 2°72 | 3°13 | y Aquile ......... 2°98 | 3°39
B Ura 2°77 | 3°18 | 0 Cassiopeia ......| 2°99 | 3°40
a Pheenieis ......... | 2°78 | 3°19 | é Centauri.........| 2°99 | 3°40

STaRS OF THE THIRD MacnirupE—conitinued.

COSMOS.

Magnitude. Magnitude
Star, | Star.

Vulg. | Phot. Vulg. | Phot
a Leporis ......... 3°00 | 3:41 | y Persei ............ 3°34 | 3°75
6 Ophiuchi......... | 3°00 | 8:41 Jw Urse ............ 3:35 | 376
f Sagittarii ...... 3°01 | 3:42 | 6 Triang. bor. 3°35 | 3°76
n Bootis............ 3°01 | 3°42 | wScorpii ......... 3°35 | 3°76
n Draconis........| 3°02 | 348 | 8 Leporis ......... 3°35 | 3°76
mw Ophiuchi 3°05 | 3°46 | y Lupi cicee | OOO fer
8 Draconis......... 306 | 3°47 | 0 Persei............| 836 | 3°77
BS Tabree stig acc 3°07 | 3°48 |) Urse ...........| 8:36 | 877
y Vinwinis iiss 3°08 | 3:49 |e Aurige (Var.).. | 3°37 | 3°78
fe PRON: is is00 3°08 | 3:49 |v Scorpii............ | 8°37 | 3°78
Gi Bros. ois: 3:09 | 8°50 Je Orionis ......... 3°37 | 3:78
Y PORRS ses eedcc-see 3-11 | 3°52 | y Lyncis............| 839 | 8°80
0 Sagittarii ...... 3°11 | 8°52 [2 Draconis......... 8°40 | 3°81
a Libre 3°12: | 8:58 fia Aree.........ccccee 3°40 | 3°81
dX Sagittarii ...... 3°13 | 3°54 | Sagittarii......... 3°40 | 3°81
PE I eae a 3:14 | 3°55 | w Herculis......... 341 | 382
é Virginis? -...... 3°14 | 3°55 | 8 Can. min.? ...... 3°41 | 3°82
a Columbe ...... 8:15 | S-SO 0 e Tauts joi scccce 3°42 | 3°83
S Aurige .........| 3°17 | 3:58 | ¢ Draconis 3°42 | 3°83
6 Herculis......... 3°18 | 3-59 | « Geminorum 342 | 3°83
« Centauri......... 3°20 | 3-61 | y Bootis............ | 3°48 | 3°84
6 Capricorni ...... 3°20 | 3:61 | « Geminorum 3°43 | 3°84
€ Corvi ............ | 8°22 | 3-63 | a Musce 3°43 | 3°84
a Can. ven. ...... 3°22 | 3°63 [a Hydri? ......... 3°44 | 3°85
8 Ophiuchi ...... 3:23 | 2-64 Ir Scorpii ......... 3°44 | 3°85
& Cygni............ | 8:24 | 8-65 46 Herculis......... 3°44 | 385
i, RES cas ecate 3:26 | 3-67 | 06 Geminorum 3°44 | 3°85
yn Tauri?............ | 8°26 | 3-67 [po Orionis ......... 3°45 | 386
B Eridani ......... 326 | 3-67 16 Cephei ......... 3°45 | 3°86
S Argus 3:26 | 3:67 13 Urse ......5.:... 3°45 | 3°86
DORAVILLE vvncsb scenes 3°27 | 3:68 |¢ Hydre ......... 3:45 | 3°86
& Persei 3°27 | 3-68 | y Hydre ......... 3°46 | 3°87
Z Herculis......... 3°28 | 3-69 | 6 Triang. austr. 8:46 | 387
6 OPV cosy .cecee: | OOO T aOR & OYMD - ceed cca 3°46 | 3°87
TINE a cecservs 3°29 | 3:70 |» Aurige ......... 3°46 | 3°87
y. Ura. mis, :..:... 3:30 | 3-71 | y Lyre .... 3°47 | 388
y Pegasi . 8:31 | 3-72 |» Geminorum 3°48 | 3°89
RIM chacveik owas 3°31 | 3-72 | y Cephei ......... 848 | 3°89
a Toucani ......... 3°32 | 3°73 [« Urse ............ 3°49 | 3:90
8 Capricorni ...... 3 32 | 3:73 | « Cassiopeie ...... 3°49 | 3:90
hE cae cate sox 332 | 3:73 [3% Aquile ........ 8 50 | 3:91
AOU oo 25.04. 3°32 | 3:73 |o Scorpii 350 | 3:91
BM paces sand 333 | 874 |r Argus 3°50 | 3 91

PHOTOMETRIC SCALE. 137

“ The following short table of the photometric quantities of
17 stars of the 1st magnitude (as obtained from the photome-
tric scale of magnitudes) may not be devoid of interest:

Sirius ; <j ‘ : ‘ . 4165
» Argus ; : ; , : _—
Canopus . ; F mete ste . 2°041
@ Centauri . ? : ; : . 1:000
Arcturus . “ 7 : ; Pape | or 9.
Rigel . F 3 ; : ‘ . 0°661
Capella. . ‘ ° ‘ . 07510
a Lyrae ‘ . ° ° ; . 0°510

Procyon . ° ‘ . . . 0°510
aOrionis. . j ‘* A 2 . 0°489
aEridani . ; ; > . . 0°444

Aldebaran . : ’ j . 0°444

8 Centauri . ; , : = . 0°401
a Crucis : j 4 ; - . 0-391
Antares. 3 ‘ A , . 0°391

aAquile . i ‘ y ban . 0°350
Spica : ‘ ‘ ‘ : . 0312

‘*: The following is the photometric quantity of stars strictly
belonging to the 1, 2.0... 6 magnitudes in which the
quantity of the light of a Centauri is regarded as the unit :”

htagnitude on the vulgar scale. Quantity of Light.
1-00 0 500
2°00 0-172
3°00 0°086
4°00 0-051
5°00 0°034

£00 0-94

138

MTL.

NUMBER, DISTRIBUTION, AND COLOUR OF THE FIXED
STARS,— STELLAR MASSES (STELLAR SWARMS), — THK
MILKY WAY INTERSPERSED WITH A FEW NEBULOUS
SPOTS.

WE have already, in the first section of this fragmentary As-
trognosy, drawn attention to a question first mooted by Olbers.'
If the entire vault of heaven were covered with innumerable
strata of stars, one behind the other, as with a wide-spread
starry canopy, and light were undiminished in its passage
through space, the sun would. be distinguishable only by
its spots, the moon would appear as a dark disc, and amid
the general blaze not a single constellation would be
visible. During my sojourn in the Peruvian plains, between
the shores of the Pacific and the chain of the Andes, I was
vividly reminded of a state of the heavens, which, though
diametrically opposite in its.cause to the one above referred
to, constitutes an equally formidable obstacle to human
knowledge. A thick mist obscures the firmament in this region
for a period of many months, during the season, called el
tiempo de la garua. Nota planet, not the most brilliant stars
of the southern hemisphere, neither Canopus, the southern
Cross, nor the feet of the Centaur, are visible. It is frequently
almost impossible to distinguish the position of the moon.
If by chance the outline of the sun’s disc .be visible during
the day it appears devoid of rays, as if seen through
coloured glasses, being generally of a yellowish red, some-

1 Vide supra, p. 46 and note.

NUMBER OF THE FIXED STARS. 139

times of a white, and occasionally even of a bluish green
colour. The mariner, driven onwards by the cold south cur-
rents of the sea, is unable to recognize the shores, and in the
absence of all observations of latitude sails past the harbours
which he desired to enter. A dipping needle alone could, as
I have elsewhere shown, save him from this error, by the
local direction of the magnetic curves.?

Bouguer and his coadjutor, Don Jorge Juan, complained,
long before me, of the ‘‘unastronomical sky of Peru.” A
graver consideration associates itself with this stratum of
vapours in which there is neither thunder nor lightning, in
consequence of its incapacity for the transmission of light or
electric charges, and above which the Cordilleras, free and
cloudless, raise their elevated plateaux and snow-coveret
summits. According to what modern geology has taught us
to conjecture regarding the ancient history of our atmosphere,
its primitive condition, in respect to its mixture and density,
must have been unfavourable to the transmission of light.
When we consider the numerous processes which in the pri-
mary world may have led to the separation of the solids,
fluids, and gases around the earth’s surface, the thought invo-
luntarily arises how narrowly the human race escaped being
surrounded with an untransparent atmosphere, which though
perhaps not greatly prejudicial to some classes of vegetation,
would yet have completely veiled the whole of the starry
canopy. All knowledge of the structure of the universe wou.d
thus have been withhe!d from the inquiring spirit of man.
Excepting our own globe,and perhaps the sun and the moon,
nothing would have appeared to us to have been created. An
isolated triad of stars—the sun, the moon, and the earth—would
have appeared the sole occupants of space. Deprived of a
great, and indeed of the sublimest portion of his ideas of

—

* Cosmos, vol. i. p. 171 and note.

140 COSMOS.

the Cosmos, man would have been left without all those in-
citements which, for thousands of years, have incessantly ime
pelled him to the solution of important problems, and have
exercised so beneficial an influence on the most brilliant
progress made in the higher spheres of mathematical develop-
ment of thought. Before we enter upon an enumeration of
what has already been achieved, let us dwell for a moment on
the danger from which the spiritual development of our race
has escaped, and the physical impediments which would have
formed an impassable barrier to our progress.

In considering the number of cosmical bodies which fill
the celestial regions, three questions present themselves to
our notice. How many fixed stars are visible to the naked
eye? How many of these have been gradually catalogued,
and their places determined according to longitude and lati-
tude, or according to their right ascension and declination ?
What is the number of stars from the 1st to the 9th and 10th
magnitudes, which have been seen in the heavens by means
of the telescope? These three questions may, from the ma-
terials of observation at present in our possession, be deter-
mined at least approximatively. Mere conjectures based on
the gauging of the stars in certain portions of the Milky Way,
differ from the preceding questions, and refer to the theo-
retical solution of the question: How many stars might be
distinguished throughout the whole heavens with Herschel’s
twenty-feet telescope, including the stellar light ‘* which is
supposed to require 2000 years to reach our earth ?’’®

The numerical data which I here publish in reference to
this subject, are chiefly obtained from the final results of my
esteemed friend Argelander, director of the Observatory at
Bonn. I have requested the author of the Durchmusterung

On the space-penetrating power of telescopes, see Sit
John Herschel, Outlines of Astr., § 803.

NUMBER OF THE FIXED STARS. 141

@2s nordlichen Himmels (Survey of the Northern Heavens) to
sibmit the previous results of Star-catalogues to a new
and careful examination. In the lowest class of stars visible
to the naked eye, much uncertainty arises from organic differ-
ence in individual observations; stars between the 6th and
7th magnitude being frequently confounded with those strictly
belonging to the former class. We obtain, by numerous
combinations, from 5000 to 5800, as the mean number of the
stars throughout the whole heavens visible to the unaided eye.
Argelander* determines the distribution of the fixed stars ac-

* T cannot attempt to include in a note ad/ the grounds on
which Argelander’s views are based. It will suffice if I
extract the following remarks frcm his own letters to me:
«Some years since (1843,) you recommended Captain Schwink
to estimate from his Mappa Coelestis, the total number of stars
from the Ist to the 7th magnitude inclusive, which the heavens
appeared to contain; his calculations give 12148 stars for the
space between 30° south and 90° north declination; and conse-
quently, if we conjecture that the proportion of stars is the same
from 30° S. D. to the South Pole, we should have 16200 stars of
the above-named magnitudes throughout the whole firmanent.
This estimate seems to me to approximate very nearly to the
truth. It is well known, that on considering the whole mass,
we find each class contains about three times as many stars
as the one preceding. (Struve, Catalogus Sieilarum duplicium,
p. xxxiv; Argelander, Bonner Zonen, s. xxvi.) I have given
in my Uranometria, 1441 stars of the 6th magnitude, north of
the equator, whence we should obtain about 3000 for the
whole heavens; this estimate does not, however include the
stars of the 6:7 mag., which would be reckoned among those
of the 6th, if only entire classes were admitted into the cal-
culation. I think the number of the last-named stars might
be assumed at 1000, according to the above rule, which would
give 4000 stars for the 6th, and 12000 for the 7th, or 18000
for the 1st to the 7th inclusive. From other considerations
on the number of the stars of the 7th magnitude, as given.in
my zones,—namely 2257, (p. xxvi.) and allowing for those
“hich have been twice or oftener observed, and for those

142 COSMOS.

cording to difference of magnitude, down to the 9th, in about
the following proportion,—
Ist Mag. 2nd Mag. 38rd Mag. 4th Mag. 5th Mag.
20 65 190° 425 1100
6th Mag. 7th Mag. 8th Mag. 9th Mag.
3200 138000 40000 142000

which have probably been overlooked, I approximated some-
what more nearly to the truth. By this method, I found 2340
stars of the 7th magnitude, between 45° and 80° N. D.; and
therefore, nearly 17000 for the whole heavens. Struve, in
his Description de [ Observatoire de Poulkova, p. 268, gives
13400 for the number of stars down to the 7th magnitude, in
the region of the heavens explored by him (from — 15° to +
90°), whence we should obtain 21300 for the whole firma-
ment. According to the Introduction to Weisse’s Catal. e
Zonis Regiomontanis, ded. p. xxxii. Struve found in the zone
extending from — 15° to + 15° by the calculus of probabili-
ties, 3903 stars from the lst to the 7th, and therefore 15050
for the entire heavens. This number is lower than mine,
because Bessel estimated the brighter stars nearly half a mag-
nitude lower than I did. We can here only arrive at a mean
result, which would be about 18000 from the Ist to the 7th
magnitudes inclusive. Sir John Herschel, in the passage of the
Outlines of Astronomy. p. 521, to which you allude, speaks
only of ‘‘ the whole number of stars already registered, down to
the seventh magnitude inclusive, amounting to from 12000 to
15000.” As regards the fainter stars, Struve finds within the
above-named zone, (from — 15° to + 15°) for the faint stars.
of the 8th magnitude, 10557, for those of the 9th. 37739.
and consequently, 40800 stars of the 8th, and 145800 of the
9th magnitude for the whole heavens. Hence, according to
Struve, we have from the Ist to the 9th magnitude inclusive,
15100 + 40800 + 145800 = 201700 stars. He obtained
these numbers by a careful comparison of those zones or parts
of zones, which comprise the same regions of the heavens,
deducing by the calculus of probabilities the number of stars
actually present from the numbers of those common to, o-
different, in each zone. As the calculation was made from
a very large number of stars, it is Ceserving of great

NUMBER OF THE FIXED STARS. 145

The number of stars distinctly visible to the naked eye
(amounting in the horizon of Berlin to 4022, and in that. of

confidence. Bessel has enumerated about 61000 different
stars from the Ist to the 9th inclusive, in his collective
zones between — 15° and + 45°, after deducting such stars
as have been repeatedly observed, together with those
of the 9°10 magnitude; whence we may conclude, after
taking into account such as have probably been overlooked,
that this portion of the heavens conjains about 101500
stars of the above-named magnitudes. My zones between
+ 45° and + 80°, contain about 22000 stars, (Durchmus-
terung des nordl. Himmels, s. xxv.) which would leave
about 19000, after deducting 3000 for those belonging to
the 9°10 magnitude. My zones are somewhat richer than
Bessel's, and I do not think we can fairly assume a larger
number than 2850, for the stars actually existing between
their limits (+ 45° and + 80°); whence we should obtain
130000 stars to the 9th magnitude inclusive, between — 15°
and + 80°. This space is, however, only 0°62181 of the
whole heavens, and we therefore obtain 209000 stars for the
entire number, supposing an equal distribution to obtain
throughout the whole firmament; these numbers again closely.
approximate to Struve’s estimate, and indeed, not impro-
bably exceed it to a considerable extent. since Struve
reckoned stars of the 9°10 magnitude among those of
the 9th. The numbers which, according to my view, may
be assumed for the whole firmament, are therefore as follows :
Ist mag., 20; 2nd,65; 3rd, 190; 4th, 425; 5th, 1100; 6th,
3200; 7th, 13000; 8th, 40000; 9th, 142000; and 200000
for the entire number of stars from the Ist to the 9th magni-
tude inclusive.

If you would contend that Lalande (Hist. céleste, p. iv.) has
given the number of stars observed by himself with the naked
eye at 6000, I would simply remark that this estimate con-
tains very many that have been repeatedly observed, and
that after deducting these, we obtain only about 3800 stars
for the portion of the heavens betweer.—26° 30’ and + 90°
observed by Lalande. As this space is 0°72310 of the whole
heavens, we should again have for this zone 5255 stars visibly

144 COSMOS.

Alexandria to 4638,) appears at first sight strikingly small.‘
If we assume the moon’s mean semi-diameter at 15’ 33”°5, it
would require 195,291 surfaces of the full moon to cover the
whole heavens. If we further assume that the stars are uni-
formly distributed, and reckon in round numbers 200000
stars from the Ist to the 9th magnitude, we shall have nearly
a single star for each full-moon surface. This result ex-
plains why, also, at any given latitude, the moon does not

to the naked eye. An examination of Bode’s Uranography
(containing 17240 stars), which is composed of the most hete-
‘ rogeneous elements, does not give more than 5600 stars from
the 1st to the 6th magnitude inclusive, after deducting the
nebulous spots and smaller stars as well as those of the 6°7th
magnitude, which have been raised to the 6th. A similar
estimate of the stars registered by La Caille between the
south pole and the tropic of Capricorn, and varying from the
Ist to the 6th magnitude, presents for the whole heavens two
limits of 3960 and 5900, and thus confirms the mean result
already given by yourself. You will perceive that I have en-
deavoured to fulfil your wish for a more thorough investigation
of these numbers, and I may further observe that M. Heis of
Aix-la-Chapelle has for many years been engaged in a very
careful revision of my Uranometrie. From the portions of this
work already complete, and from the great additions made to
it by an observer gifted with keener sight than myself, I find
2836 stars from the lst to the 6th magnitude inclusive for
the northern hemisphere, and therefore, on the pre-supposi-
tion of equal distribution, 5672 as the number of stars visible
throughout the whole firmament to the keenest unaided
vision.” (From the MSS. of Prof. Argelander, March, 1850.)
® Schubert reckons the number of stars, from the 1st to the
6th magnitude, at 7000 for the whole heavens (which closely
approximates to the calculation made by myself in Cosmos,
vol. i. p. 140,) and upwards of 5000 for the horizon of Paris.
He gives 70000 for the whole sphere, including stars of the
9th magnitude. (Astronomie, th. iii. s. 54.) These numbers
are all much too high. Argelander finds only 58000 from the
lst to the 8th magnitude. ,

NUMBER OF THE FIXED STARS. 145

more frequently conceal stars visible to the naked eye. If the
calculation of occultations of the stars were extended to those.
of the 9th magnitude, a stellar eclipse would, according to
Galle, occur on an average every 44’ 30”, for in this period
the moon traverses a portion of the heavens equal in extent to
its own surface. It is singular that Pliny, who was undoubtedly
acquainted with Hipparchus’s catalogue of stars, and who
comments on his boldness in attempting as it were ‘to leave.
heaven as a heritage to posterity,” should have enumerated
only 1600 stars visible in the fine sky of Italy!* In this
enumeration he had, however, descended to stars of the Sth,
whilst half a century later Ptolemy indicated only 1025 stars
down to the 6th magnitude.

Since it has ceased to be the custom to class the fixed stars
merely according to the constellations to which they belong, and
they have been catalogued according to determinations of place,
that is,in their relationsto the great circles of the equator or the
ecliptic, the extension as well as the accuracy of star catalogues
has advanced with the progress of science and the improved

¢ « Patrocinatur vastitas cceli, immensa disereta altitudine, in
duo atque septuaginta signa. Hee sunt rerum et animantium
effigies, in quas digessere ceelum periti. In his quidem mille
sexcentas adnotavere stellas, insignes videlicet effectu visuve”’
...». Plin., un. 41.—** Hipparchus nunquam satis laudatus, ut
quo nemo magis approbayverit cognationem cum homine siderum
animasque nostras partem esse cceli, novam stellam et aliam
in vo suo genitam deprehendit, eyusque motu, qua die fulsit,
ad dubitationem est adductus, anne hoe szepius fieret move-
renturque et esx quas putamus affixas; itemque ausus rem
etiam Deo improbam, adnumerare posteris stellas ac sidera ad
nomen expungere, organis excogitatis, per que singularum
loca atque magnitudines signaret, ut facile discerni posset ex
ec, non modo an obirent nascerenturve, sed an omnino aliqua
transirent moverenturve, item an crescerent minuerenturque,
ceelo in hereditate cunctis relicto, si quisquam qui cretionem
eam caperet inventus esset.” Plin., ii. 26,

VOL. ITT. PA

146 COSMOS.

construction of instruments. No catalogues of the stars com-
piled by Timocharis and Aristyllus (283, B.c.) have reached us;
but although, as Hipparchus remarks in the fragment “on the
length of the year,” cited in the seventh book of the Almagest
(cap. 8, p. xv. Halma,) their observations were conducted in
a very rough manner (mdvv ddocxepés) there can be no doubt
that they both determined the declination of many stars, and
that these determinations preceded, by nearly a century and
a half, the table of fixed stars compiled by Hipparchus. This
astronomer is said to have been incited by the phenomenon of
a new star to attempt a survey of the whole firmament, and
endeavour to determine the position of the stars; but the truth.
of this statement rests solely on Pliny’s testimony, and has
often been regarded as the mere echo of a subsequently in-
vented tradition.’ It does indeed seem remarkable that
Ptolemy should not refer to the circumstance, but yet it must
be admitted that the sudden appearance of a brightly luminous
star in Cassiopeia (November, 1572,) led Tycho Brahe to
eompose his catalogue of the stars. According to an in-
genious conjecture of Sir John Herschel,® the star referred to
by Pliny may have been the new star which appeared in
Scorpio in the month of July of the year 134 before our era,
(as we learn from the Chinese Annals of the reign of Wou-ti,
of the Han dynasty.) Its appearance occurred exactly six
years before the epoch at which, according to Ideler’s .uvesti-
gations, Hipparchus compiled his catalogue of the stars.
Edward Biot, whose early death proved so great a loss to
science, found a record of this celestial phenomenon in
the celebrated collection of Ma-tuan-lin, which contains an

7 Delambre, Hist. de [ Astr. anc., tom. i. p. 290, and Hisz.
del’ Astr. mod., tom. il. p. 186.

® Outlines, § 831; Edward Biot sur les Etoiles Extraordi-
naires observées en Chine, in the Connaissance des temps pour
1846.

EARLY ASTRONOMY. 147

account of all the comets and remarkable stars observed be
tween the years B.c. 613, and a.p. 1222.

The tripartite didactic poem of Aratus,® to whom we are
indebted for the only remnant of the works of Hipparchus that
has come down to us, was composed about the period of Era-
tosthenes, Timocharis, and Aristyllus. The astronomical non-
meteorological portion of the poem is based on the uranography
of Eudoxusof Cnidos. The catalogue compiled by Hipparchus is
unfortunately not extant; but, according to Ideler,” it probably
constituted the principal part of his work, cited by Suidas,
**On the arrangement of the region of the fixed stars and the
celestial bodies,” and contained 1080 determinations of posi-
tion for the year B.c. 128. In Hipparchus’s other Commentary
on Aratus the positions of the stars, which are determined
more by equatorial armille than by the astrolabe, are referred
to the equator by right ascension and declination; while in
Ptolemy’s catalogue of stars, which is supposed to have been en-
tirely copied from that of Hipparchus, and which gives 1025
stays, together with five so-called nebule, they are referred by
longitudes and latitudes to the ecliptic." On comparing the

® It is worthy of remark that Aratus was mentioned with
approbation almost simultaneously by Ovid (dmor., i. 15,)
and by the Apostle Paul, at Athens, in an earnest discourse
directed against the Epicureans andStoics. Paul(dets, ch. xvii.
vy. 28), although he does not mention Aratus by name, un-
doubtedly refers to a verse composed by him (Phen., y. 5) on
the close communion of mortals with the Deity.

% Ideler, Untersuchungen tiber den Ursprung der Sternnamen,
8. xxx.-xxxy. Baily in the Mem. of the Astron. Soc., vol. xiii.
1843, pp. 12 and 15, also treats of the years according to our
era, to which we must refer the observations of Aristyllus, as
well as the catalogues of the stars compiled by Hipparchus
(128, and not 140, B.c.) and by Ptolemy (138 a.p.).

% Compare Delambre, Hist. de 1 Astr. anc., tom. i. p. 184;
tom. ii. p. 260. The assertion, that Hipparchus, in additiou
to the right ascension and declination of the stars, also indi.

L2

143 . CUSMOS.

number of fixed stars in the Hipparcho-Ptolemaic Catalogue,
Almagest, ed. Halma, t. ii. p. 83, (namely, for the 1st mag., 15
stars; 2nd, 45; 3rd, 208; 4th, 474; 5th, 217; 6th, 49,) with
the numbers of Argelander as already given, we find, as might
be expected, a great paucity of stars of the 5th and 6th magni-
tudes, and also an extraordinarily large number of those belong-
ing to the 8rd and 4th. The vagueness in the determinations
of the intensity of light in ancient and modern times renders
direct comparisons of magnitude extremely uncertain.

cated their positions in his catalogue, according to longitude
and latitude, as was done by Ptolemy, is wholly devoid of
probability and in direct variance with the .4/magest, book vii.
cap. 4, where this reference to the ecliptic is noticed as some-
thing new, by which the knowledge of the motions of the
fixed stars round the pole of the ecliptic may be facilitated.
The table of stars with the longitudes attached, which Petrus
Victorius found in a Medicean Codex and published with the
life of Aratus at Florence in 1567, is indeed ascribed by him
to Hipparchus, but without any proof. It appears to be a
mere rescript of Ptolemy’s catalogue from an old manuscript
of the Almagest, and does not give the latitudes. As Ptolemy
was imperfectly acquainted with the amount of the retrogres-
sion of the equinoctial and solstitial points (4/mazq., vii. c. 2,
. 13, Halma), and assumed it about =2.5, too slow, the catalogue
which he determined for the beginning of the reign of Anto-
ninus (Ideler, op. cit. s. xxxiv.) indicates the positions of the
stars at a much earlier epoch (for the year 63 a.p.) (Regarding
the improvements for reducing stars to the time of Hippar-
chus, see the observations and tables as given by Encke in
Schumacher’s Astron. Nachr.,no. 608.s. 118-126.) The earlier
epoch to which Ptolemy unconsciously reduced the stars in his
catalogue, corresponds tolerably well with the period to which
we may refer the Pseudo-Eratosthenian Catasterisms, which, as
I have already elsewhere observed, are more recent than the
time of Hyginus, who lived in the Augustine age, but appear
to be taken from him and have no connection with the poem
of Hermes by the true Eratosthenes. (Hratosthemica, ed.
Bernhardy, 1822, pp. 114, 116, 129.) These Pseudo-Eratos-
thenian Catasterisms contain, moreover, scarcely 700 indi-~
vidual stars distributed among the mythizal constellations.

EFARLY CATALOGUES. } 4%

Although the so-called Ptolemaic catalogue of the fixed
stars enumerated only one-fourth of those visible to the
naked eye at Rhodes and Alexandria, and, owing to erroneous
reductions of the precession of the equinoxes, determined their
‘positions as if they had been observed in the year 63 of our
era; yet, throughout the sixteen hundred years immediately
following this period, we have only three original catalogues
of stars, perfect for their time; that of Ulugh Beg (1437), that
of Tycho Brahe (1600), and that of Hevelius (1660). During
the short intervals of repose which, amid tumultuous revolu-
tions and deyastations of war, occurred between the ninth and
fifteenth centuries, practical astronomy, under Arabs, Persians,
and Moguls (from Al-Mamun, the son of the great Harun Al-
Raschid, to the Timurite, Mohammed Taraghi Ulugh Beg, the
son of Shah Rokh) attained an eminence till then unknown.
The astronomical tables of Ebn-Junis (1007), called the Hake-
mitic tables, in honour of the Fatimite Calif, Aziz Ben-Hakem
Biamrilla, afford evidence, as do also the Llkhanie tables™ of
Nassir-Eddin Tusi (who founded the great observatory at
Meragha, near Tauris, 1259), of the advanced knowledge of
the planetary motions,—the improved condition of measuring
instruments, and the multiplication of more accurate methods
differing from those employed by Ptolemy. In addition to
clepsydras,* pendulum-oscillations® were already at this period
employed in the measurement of time.

*® Cosmos, vol. ii. pp. 594-5. The Paris Library contains
a manuscript of the Ilkhanic Tables by the hand of the son of
Nassir-Eddin. They derive their name from the title “ IIkhan,”
assumed by the Tartar princes who held rule in Persia.
Reinaud, Introd. de la Géogr. d’ Aboulféda, 1848, p. cxxxix.

* For an account of clepsydras, see Beckmann’s Inventions,
vol. i. 8341, e¢ seg. (Bohn’s edition. )—Zd.

® Sedillot fils, Prolégoménes des Tables Astr. d’ Oloug-Bey,
1847, p. cxxxiv. note 2. Delambre, Hist. del’ Astr. du moyen
dge, p. 8.

150 COSMOS.

The Arabs had the great merit of showing how tables might
be gradually amended by a comparison with observations.
Ulugh Beg’s catalogue of the stars, originally written in
Persian, was entirely completed from original observations
made in the Gymnasium at Samarcand, with the exception
of a portion of the southern stars enumerated by Ptolemy,“
and not visible in 39° 52’ lat. (?) It contains only 1019
positions of stars, which are reduced to the year 1487. A
subsequent commentary gives 300 other stars, observed by
Abu-Bekri Altizini in 1533. Thus we pass from Arabs,
Persians, and Moguls, to the great epoch of Copernicus, and
nearly to that of Tycho Brahe.

The extension of navigation in the tropical seas, and in
high southern latitudes, has, since the beginning of the six-
teenth century, exerted a powerful influence on the gradual
extension of our knowledge of the firmament, though in
a less degree than that effected a century later by the ap-

% In my investigations on the relative value of astronomical
determinations of position in Central Asia (Asze centrale,
t. 111. pp. 581-596), I have given the latitudes of Samarcand
and Bokhara according to the different Arabic and Persian
MSS. contained in the Paris.Library. I have shown that the
former is probably more than 39° 52’, whilst most of the best
manuscripts of Ulugh Beg give 39° 37’, and the Kitab al-athual
of Alfares, and the Kanum of Albyruni give 40°. I would
again draw attention to the importance, in a geographical no
less than an astronomical point of view, of determining the
longitude and latitude of Samarcand by new and trustworthy
observations. Burnes’s Travels have made us acquainted with
the latitude of Bokhara, as obtained from observations of
culmination of stars; which gave 39° 43’ 41”. There is there-
fore only an error of from 7 to 8 minutes in the two fine Persian
and Arabic MSS. (Nos. 164 and 2460) of the Paris Library.
Major Rennell, whose combinations are generally so suc-
cessful, made an error of about 19’ in determining the latitude
of Bokhara. (Humboldt, Asie centrale, t. ili. p. 592, and
Sedillot in the Prolégoménes d’ Oloug-Beg, pp. cxxili.—¢xxv.)

PROGRESS OF ASTRONOMY. 153

plication of the telescope. Both were the means of revealing
new and unknown regions of space. I have already in other
works considered the reports circulated first by Americus
Vespucius, then by Magellan, and Pigafetta (the companion of
Magellan and Elcano), concerning the splendour of the southern
sky; and the descriptions given by Vicente Yafiez, Pinzon,
and Acosta, of the black patches (Coal Sacks), and by
Anghiera and Andrea Corsali of the Magellanic clouds. A
merely sensuous contemplation of the aspect of the heavens
here also preceded measuring astronomy. The richness of the
firmament near the southern pole, which, as is well known, is
on the contrary peculiarly deficient in stars, was so muck
exaggerated that the intelligent Polyhistor Cardanus indi-
cated in this region 10000 bright stars which were said t
have been seen by Vespucius with the naked eye.*

Friedrich Houtman and Petrus Theodori of Embden (who,
according to Olbers, is the same person as Dircksz Keyser)
now first appeared as zealous observers. They measured dis-
tances of stars at Java and Sumatra; and at this period the
most southern stars were first marked upon the celestial maps
of Bartsch, Hondius, and Bayer, and by Kepler’s industry
were inserted in Tycho Brahe’s Rudolphine tables.

Scarcely half a century had elapsed from the time of Ma-
gellan’s circumnayigation of the globe before Tycho com-
menced his admirable observations on the positions of the
fixed stars, which far exceeded in exactness all that had hitherto
been done in practical astronomy, not excepting even the la-
borious observations of the Landgrave William IV. at Cassel.
Tycho Brahe’s catalogue, as revised and published by Kepler,
contains no more than 1000 stars, of which one-fourth at

*. Cosmos, pp. 664-8; Humboldt, Examen crit. de 1 His-
toire de la Géogr.,t. iv. pp. 8321-336; t. v. pp. 226-238.

© Cardant Paralipomenon, lib. viii. cap. 10. (Opp., t. ix.
ed. Lugd. 1663, p. 508.)

152 COSMOS.

most belong to the sixth magnitude: This catalogue, and that
of Hevelius, which was less frequently employed, and con-
tained 1564 determinations of position for the year 1660, were
the last which were made by the unaided eye, owing their
compilation in this manner to the capricious disinclination of
the Dantzig astronomer to apply the telescope to purposes of
measurement. ;

This combination of the telescope with measuring instru-
ments—the union of telescopic vision and measurements—at
length enabled.astronomers to determine the position of stars
below the sixth magnitude, and more especially between the
seventh and the twelfth. The region of the fixed stars might
now for the first time be said to be brought within the
reach of observers. Enumerations of the fainter telescopic
stars, and determinations of their position, have not only
yielded the advantage of making a larger portion of the regions
of space known to us by the extension of the sphere of observa-
tion, but they have also (what is still more important) indirectly
exercised an essential influence on our knowledge of the struc-
ture and configuration of the universe, on the discovery of new
planets, and on the more rapid determination of their orbits.
When William Herschel conceived the happy idea of as it were
casting a sounding line in the depths of space, and of counting
during his gaugings the stars which passed through the field of
his great telescope,” at different distances from the Milky Way,
the law was discovered that the number of stars increased
in proportion to their vicinity to the Milky Way—a law which
gave rise to the idea of the existence of large concentric rings
filled with millions of stars which constitute the many-cleft
Galaxy. The knowledge of the number and the relative posi-
tion of the faintest stars facilitates (as was proved by Galle’s
rapid and felicitous discovery of Neptune, and by that of
several of the smaller planets) the recognition of planetary

" Cosmos, vol. i. pp. 71-73.

IMPORTANCE OF CATALOGUES, 153

eosmical bodies which change their positions, moving as it were
between fixed boundaries. Another circumstance proves even
more distinctly the importance of very complete catalogues of
the stars. Ifa new planet be once discovered in the vault of
heaven, its notification in an older catalogue of positions will
materially facilitate the difficult calculation of its orbit. The
indication of a new star which has subsequently been lost sight
of, frequently affords us more assistance than, considering the
slowness of its motion, we can hope to gain by the most careful
measurements of its course through many successive years.
Thus the star numbered 964 in the catalogue of Tobias Mayer
has proved of great importance for the determination of Uranus,
and the star numbered 26266 in Lalande’s catalogue” for that
of Neptune. Uranus, before it was recognized as a planet, had,
as is now well known, been observed twenty-one times; once,
as already stated, by Tobias Mayer, seven times by Flamstead,
once by Bradley, and twelve times by Le Monnier. It may be
said that our increasing hope of future discoveries of planetary
bodies rests partly on the perfection of our telescopes (Hebe,
at the time of its discovery in July, 1847, was a star of the 8°9
magnitude, while in May, 1849, it was only of the 11th mag-
nitude), and partly, and perhaps more, on the completeness of
our star-catalogues, and on the exactness of our observers.
The first catalogue of the stars which appeared after the
epoch when Morin and Gascoigne taught us to combine tele-
scopes with measuring instruments, was vhat of the southern

~

% Baily, Cat. of those stars in the ** Histoire Céleste’”’ of
Jerome de Lalande, for which tables of reduction to the epoch
1800 have been published by Prof. Schumacher, 1847, p. 1195.
On what we owe to the perfection of star catalogues see the
remarks of Sir John Herschel in Cat. of the British Assoc.,
1845, p. 4, § 10. Compare also, on stars that have disap-
peared, Schumacher, Astr. Nachr., no. 624, and Bode, Jahrb.
fur 1817, s. 249

154 COSMOS.

stars compiled by Halley. It was the result of a short resi«
dence at St. Helena in the years 1677 and 1678, but, singu-
larly enough, does not contain any determinations below
the 6th magnitude. Flamstead had, indeed, begun his
great Star Atlas at an earlier period; but the work of this
celebrated observer did not appear till 1712. It was suc-
ceeded by Bradley’s observations (from 1750 to 1762), which
led to the discovery of aberration and nutation, and have been
rendered celebrated by the undamenta Astronomie of our
countryman Bessel (1818),” and by the stellar catalogues of La
Caille, Tobias Mayer, Cagnoli, Piazzi, Zach, Pond, Taylor,
Groombridge, Argelander, Airy, Brisbane, and Riimker.

_ We here only allude to those works which enumerate a great
and important part™ of the stars of the 7th to the 10th magni-

1% Memoirs of the Royal Astron. Soc., vol. xiii. 1843,
pp. 33 and 168.

* Bessel, Fundamenta Astronomie pro anno 1755, deducta
ex observationibus viri incomparabilis James Bradley in Specula
astronomica G'renovicensi, 1818. Compare also Bessel, Tabule
Regiomontane reductionum observationum astronomicarum ab
anno 1750 usque ad annum 1850 computate (1830).

1 T here compress into a note the numerical data taken
from star catalogues, containing lesser masses and a smaller
number of positions, with the names of the observers, and
the number of positions attached :—La Caille, in scarcely
ten months, during the years 1751 and 1752, with instru-
ments magnifying only eight times, observed 9766 southern
stars, to the 7th magnitude inclusive, which were reduced to
the year 1750 by Henderson; Tobias Mayer, 998 stars to
1756; Flamstead, originally only 2866, to which 564 were
added by Baily’s care; (Mem. of the <Astr. Soc., vol. iv.
pp. 1291-64); Bradley, 3222, reduced by Bessel to the year
1755; Pond, 1112; Piazzi, 7646 to 1800; Groombridge,
4243, mostly circumpolar stars, to 1810; Sir Thomas Brisbane,
and Rimker, 7385 stars, observed in New Holland, in the
years 1822-1828; Airy, 2156 stars, reduced to the year
1845; Rimker, 12000 on the Hamburg horizon ; Argelander

STAR CATALOGUES. 155

tude which occupy the realms of space. The catalogue known
under the name of Jerome de Lalande’s, but which is, however,
solely based on observations made by his nephew, Francois
de Lalande, and by Burckhardt between the years 1789 and
1800, has only recently been duly appreciated. After having
been carefully revised by Francis Baily, under the direction of
the “ British Association for the Advancement of Science,” (in
1847,) it now contains 47390 stars, many of which are of the
9th and some even below that magnitude. Harding, the disco-
verer of Juno, catalogued above 50000 stars in twenty-seven
maps. JBessel’s great work on the exploration of the celestial
zones, which comprises 75000 observations (made in the years
1825-1833 between — 15° and + 45° declination) has been
continued from 1841 to 1844 with the most praiseworthy care,
as faras + 80° decl., by Argelander at Bonn. Weisse of Cracow,
under the auspices of the Academy of St. Petersburgh, has re-
duced 31895 stars for the year 1825, (of which 19788 belonged
to the 9th magnitude) from Bessel’s zones, between — 15°
and + 15° decl. ;* and Argelander’s exploration of the
northern heavens from + 45° to + 80° decl. contains about
22000 well determined positions of stars.

I cannot, I think, make more honourable mention of the
great work of the star maps of the Berlin Academy, than by
quoting the words used by Encke, in reference to this under-
taking, in his oration to the memory of Bessel :—‘ With
the completeness of catalogues is connected the hope that

(Cat. of Abo,) 560; Taylor, (Madras,) 11015. The British
Association Catalogue of Stars, (1845,) drawn up under Baily’s
superintendence, contains 8377 stars from the Ist to 74 magni-
tudes. For the southern stars we have the rich catalogues
of Henderson, Fallows, Maclear, and Johnson at St. Helena.

™ Weisse, Posttiones medie stellarum fixarum in Zonis
Regiomontanis a Besselio inter —15° et + 15° decl. observa-
tarum ad anrum 1825 reducte, (1846); with an important
Preface by Struve.

156 COSMOS.

by a careful comparison of the different aspects of the heavens
with those stars which have been noted as fixed points, we
may be enabled to discover all moving celestial bodies, whose
change of position can scarcely, owing to the faintness of their
light, be noted. by the unaided eye, and that we may in this
manner complete our knowledge of the solar system. While
Harding’s admirable atlas gives a perfect representation. of
the starry heavens—as far as Lalande’s Histoire Céleste, on
which it is founded, was capable of affording such a picture—
Bessel, in 1824, after the completion of the first main section
of his zones, sketched a plan for grounding on this basis a
more special representation of the starry firmament, his
object being not simply to exhibit what had been already
observed, but likewise to enable astronomers by the complete-
ness of his tables at once to recognize every new celestial
phenomenon. Although the star maps of the Berlin Aca-
demy of Sciences, sketched in accordance with Bessel’s plan,
may not have wholly completed the first proposed cycle,
they have nevertheless contributed in a remarkable degree
to the discovery of new planets, since they have been the prin-
cipal if not the sole means to which, at the present time (1850),
we owe the recognition of seven new planetary bodies.”* Of
the twenty-four maps designed to represent that portion of
the heavens which extends 15° on either side of the equator,
our Academy has already contributed sixteen. These contain,
as far as possible, all stars down to the 9th magnitude and
many of the 10th.

The present would seem a fitting place to refer to the
average estimates which have been hazarded on the number
of stars throughout the whole heavens, visible to us by the
aid of our colossal space-pcnetrating telescopes. Struve
assumes for Herschel’s twenty-feet reflector, which was em-

—_

* Encke, Geddchinissrede auf Bessel, 8. 13.

DISTRIBUTION OF THE FIXED STARS. 157

ployed in making the celebrated star-gauges or sweeps, that a
magnifying power of 180 would give 5800000 for the number
of stars lying within the zones extending 30° on either side of
the equator, and 20374000 for the whole heavens. Sir

Villiam Herschel conjectured that 18 millions of stars in the
Milky Way, might be seen by his still more powerful forty-
feet reflecting telescope.™

After a careful consideration of all the fixed stars, whether
visible to the naked eye or merely telescopic, whose positione
are determined, and which are recorded in catalogues, we turt
to their distribution and grouping in the vault of heaven.

As we have already observed, these stellar bodies, from the
inconsiderable and exceedingly slow (real and apparent) change
of position exhibited by some of them—partly owing to pre-
cession and to the different influences of the progression of our
solar system, and partly to their own proper motion—may be
regarded as landmarks in the boundless regions of space,
enabling the attentive observer to distinguish all bodies that
move among them with a greater velocity or in an opposite
direction—consequently all which are allied to telescopic
comets and planets. The first and predominating interest ex-
cited by the contemplation of the heavens is directed to the
fixed stars, owing to the multiplicity and overwhelming mass
of these cosmical bodies; and it is by them that our highest
feelings of admiration are called forth. The orbits of the
planetary bodies appeal rather to inquiring reason, and, by
presenting to it complicated problems, tend to promote the
development of thought in relation to astronomy.

Amid the innumerable multitude of great and small stars
which seem scattered, as it were by chance, throughout: the
vault of heaven, even the rudest nations separate single

* Compare Struve, Etudes d’ Astr. stellaire, 1847, pp. 66 and
72; Cosmos, vol. i. p. 140; and Midler, Astr., 4te Aufl. § 417,

158 COSMOS.

(and almost invariably the same) groups, among which certain
bright stars catch the observer’s eye, either by their proxi-
mity to each other, their juxtaposition, or, in some cases, by
a kind of isolation. This fact has been confirmed by recent
and careful examinations of several of the languages of so-
called savage tribes. Such groups excite a vague sense of
the mutual relation of parts, and have thus led to their
receiving names, which, although varying among different
races, were generally derived from organic terrestrial objects.
Amid the forms with which fancy animated the waste and
silent vault of heaven, the earliest groups thus distinguished
were the seven-starred Pleiades, the seven stars of the Great
Bear, subsequently (on account of the repetition of the same
form) the constellation of the Lesser Bear, the belt of Orion
(Jacob’s staff), Cassiopeia, the Swan, the Scorpion, the
Southern Cross (owing to the striking difference in its direc-
tion before and after its culmination), the Southern Crown,
the Feet of the Centaur (the Twins, as it were, of the
Southern hemisphere), &c.

Wherever steppes, grassy plains or sandy wastes present a
far-extended horizon, those constellations whose rising or
setting corresponds with the busy seasons and requirements of
pastoral and agricultural life, have become the subject of atten-
tive consideration, and have gradually led to a symbolising
connection of ideas. Men thus became familiarised with the
aspect of the heavens before the development of measuring
astronomy. They soon perceived that. besides the daily move-
ment from east to west, which is common to all celestial bodies,
the sun has a far slower proper motion in an opposite direc-
tion. The stars which shine in the evening sky sink lower
every day, until at length they are wholly lost amid the
rays of the setting sun; while, on the other hand, those stars
wich were shining in the morning sky, before the rising of
‘he sun, recede further and further from it. In the ever-

}

DISTRIBUTION OF THE FIXED STARS. 1593

changing aspect of the starry heavens, successive constellations
are always coming to view. A slight degree of attention suf-
fices to show that these are the same which had before vanished
in the west; and that the stars which are opposite to the sun,
setting at its rise, and rising at its setting, had about half-a-
year earlier been seen in its vicinity. From the time of
Hesiod to Eudoxus, and from the latter to Aratus and Hip-
parchus, Hellenic literature abounds in metaphoric allusions to
the disappearance of the stars amid thesun’s rays, and their ap-
pearance in the morning twilight,—their heliacal setting and
rising. An attentive observation of these phenomena yielded
the earliest elements of chronology, which were simply ex-
pressed in numbers, while mythology, in accordance with the
more cheerful or gloomy tone of national character, continued
simultaneously to rule the heavens with arbitrary despotism.
The primitive Greek sphere, (I here again, as in the history
of the physical contemplation of the universe,* follow the in-
vestigations of my intellectual friend Letronne,) had become
gradually filled with constellations, without being in any de-
gree considered with relation to the ecliptic. ‘Thus Homer and
Hesiod designate by name individual stars and groups; the
former mentions the constellation of the Bear (‘ otherwise
known as the Celestial Wain, and which alone never sinks into
the bath of Oceanos,”’) Bootes, and the Dog of Orion ; the latter
speaks of Sirius and Arcturus, and both refer to the Pleiades,
the Hyades, and Orion.*% Homer’s twice repeated assertion
that the constellation of the Bear alone never sinks into the
ocean, merely allows us to infer that in his age, the Greek
sphere did not yet comprise the constellations of Draco, Cepheus
and Ursa Minor, which likewise do not set. The statement
does not prove a want of acquaintance with the existence of

*% Cosmos, p. 533.
% Ideler, Unters. iiber die Sternnamen, s. xi. 47, 189, 144,
243; Letronne, Sur 1’ Origine du Zodiaque Girec, 1840, p. 25.

160 COSMOR.

the separate stars forming these three catasterisms, but simpls
an ignorance of their arrangement into constellations. <A
long and frequently misunderstood passage of Strabo (lib. i.
p- 3, Casaub.) on Homer, J/. xviii. 485-489, specially proves
a fact—important to the question,—that in the Greek sphere
the stars were only gradually arranged in constellations. Homer
has been unjustly accused of ignorance, says Strabo, as if he had
known of only one instead of two Bears. It is probable that
the lesser one had net yet been arranged in a separate group ;
and that the name did not reach the Hellenes, until after the
Pheenicians had specially designated this constellation and made
use of it for the purposes of navigation. All the scholia on
Homer. Hyginus and Diogenes Laertius, ascribe its introduc-
tion to Thales. In the Pseudo-Eratosthenian work to which
we have already referred, the lesser Bear is called douwixn (or
as it were the Pheenician guiding star). A century later
(Ol. 71,) Cleostratus of Tenedos, enriched the sphere with the
constellations of Sagittarius, Toéérns, and Aries, Kpids.

The introduction of the Zodiac into the ancient Greek
sphere coincides according to Letronne with this period of the
domination of the Pisistratide. Kudemus of Rhodes, one of
the most distinguished pupils of Aristotle, and author of a
« History of Astronomy,” ascribes the introduction of this
Zodiacal belt rod Cwdvaxod Siafwors, also Cwidvios Kukhos) to
(Enopides of Chios, a contemporary of Anaxagoras.” The
idea of the relation of the planets and fixed stars to the sun’s

* Letronne, op. cit., p. 25; and Carteron, Analyse des Re-
cherches de M. Letronne sur les représentations zodiacales, 1848,
p- 119. “It is very doubtful whether Eudoxus (Ol. 103) ever:
made use of the word ¢wdvaxcs. We first meet with it in
Euclid, and in the. Commentary of Hipparchus on Aratus
(Ol. 160). The name ecliptic, exAeumrixds, is also very recent.”
Compare Martin in the Commentary to Theonis Smyriat
Platonici [aber de Astronomia, 1849, pp. 50, 60.

ZODIACAL SIGNS. 161

eurse, the division of the ecliptic into twelve equal parts
(Dodecatomeria) originated with the ancient Chaldeans, and
very probably came to the Greeks, at the beginning of the
fifth, or even in the sixth century before our era, direct from
Chaldea, and not from the Valley of the Nile. The Greeks
merely separated-from the constellations, named in their
primitive sphere, those which were nearest to the ecliptic,
and could be used as signs of the zodiac. If the Greeks
had borrowed from another nation anything more than the idea
and number of the divisions (Dodecatomeria) of a zodiac,—if
they had borrowed the zodiac itself with its signs,—they
would not at first have contented themselves with only
eleven constellations. The Scorpion would not have been
divided into two groups; nor would zodiacal constellations
have been introduced, (some of which, like Taurus, Leo, Pisces,
and Virgo, extend over a space of 385° to 48°, while
others, as Cancer, Aries, and Capricornus, occupy only from

* Letronne, Orig. du Zod., p. 25; and Analyse crit. des
Représ. zod., 1846, p. 15. Ideler and Lepsius also consider it
probable ‘“‘ that the knowledge of the Chaldean zodiac, as
well in reference to its divisions as to the names of the latter,
had reached the Greeks in the 7th century before our era,
although the adoption of the separate signs of the zodiac in
Greek astronomical literature was gradual and of a subse-
quent date.” (Lepsius, Chronologie der Atgypter, 1849, s. 65
and 124.) Ideler is inclined to believe that the Orientals had
names but not constellations for the Dodecatomeria, and
Lepsius regards it as a natural assumption ‘ that the Greeks
at the period when their sphere was for the most part unfilled
should have added to their own the Chaldean constellations,
from which the twelve divisions were named.” But are we
not led on this supposition to inquire why the Greeks had at
first only eleven signs instead of introducing all the twelve
belonging to the Chaldean dodecatomeria? If they intro-
duced the twelve signs they are hardly likely to have removed
one in order to replace it at a subsequent period.

VoL. III. es

162 COSMOS,

19° to 23°), which are inconveniently grouped to the north
and south of the ecliptic, either at great distances from
each other, or, like Taurus and Aries, Aquarius and Capri-
cornus, so closely crowded together as almost to encroach on
each other. These circumstances prove that catasterisms
previously formed were converted into signs of the zodiac.
The sign of Libra, according to Letronne’s conjecture,
was introduced at the time of, and perhaps by Hip-
parchus. It is never mentioned by Eudoxus, Archimedes,
Autolycus, or even by Hipparchus in the few fragments of
his writings which have been transmitted to us (excepting
indeed in one passage, probably falsified by a: copyist.)”
The earliest notice of this new constellation occurs in

* On the passage referred to in the text, and interpolated
_by a copyist of Hipparchus, see Letronne, Orzg. du Zod., 1840,
p- 20. As early as 1812, when I was much disposed to
believe that the Greeks had been long acquainted with the
sign of Libra, I directed attention in an elaborate memoir
(on all the passages in Greek and Roman writers of an-
tiquity, in which the Balance occurs as a sign of the
zodiac) to that passage in Hipparchus (Comment. in Aratum,
lib. iii, cap. 2) which refers to the @npsov held by the Centaur
(in his fore-foot) as well as to the remarkable passage of
Ptolemy, lib. ix. cap. 7 (Halma, t. ii.p. 170). In the latter
the Southern Balance is named with the affix xara Xadéaious,
and is opposed to the pincers of the Scorpion in an observation,
which was undoubtedly not made at Babylon, but by some of
the astrological Chaldeans, dispersed throughout Syria and
Alexandria. (Vues des Cordilléres et Monumens des peuples indi-
genes del’ Amérique, t. ii. p. 880.) Buttman maintained, what
is very improbable, that the xnAat originally signified the two
scales of the Balance, and were subsequently by some miscon-
ception converted into the pincers of a Scorpion. (Compare
Ideler, Untersuchungen uber die astronomischen Beobachtungen
der Alten., s. 374, and Ueber die Sternnamen, s. 174-177, with
Carteron, Recherches de M. Letronne,p.113.) Itis a remark-
able circumstance connected with the analogy between

ZODIACAL SIGNS, 162

Geminus and Varro, scarcely half a century before ow
era; and as the Romans, from the time of Augustus
to Antoninus, became more strongly imbued with a pre-
dilection for astrological inquiry, those constellations which
“lay in the celestial path of the sun” acquired an ex-
aggerated and fanciful importance. The Egyptian zodi-
acal constellations found at Dendera, Esneh, the Propylon of
Panopolis, and on some mummy-cases, belong to the first
half of this period of the Roman dominion, as was maintained
by Visconti and Testa, at a time when the necessary materials
for the decision of the question had not been collected, and the
wildest hypothesis still prevailed regarding the signification
of these symbolical zodiacal signs, and their dependence on
the precession of the equinoxes. The great antiquity which,
from passages in Manu’s Book of Laws, Valmiki’s Ramayana
and Amarasinha’s Dictionary, Augustus William von Schlegel
attributed to the zodiacal circles found in India, has been
rendered very doubtful by Adolph Holtzmann’s ingenious
investigations.”

many of the names of the twenty-seven “‘ houses of the moon,”
and the Dodecatomeria of the zodiac, that we also meet with
the sign of the Balance among the Indian Nakschatras (Moon-
houses), which are undoubtedly of very great antiquity. (Vues
des Cordilléres, t. ii. pp. 6-12.)

*® Compare A. W. von Schlegel Ueber Sternbilder des
Thierkreises im alten Indien, in the Zeitschrift fiir die Kunde
des Morgenlandes, bd. i. Heft 3. 1837, and his Commentatio de
Zodiact antiquitate et origine, 1839, with Adolph Holtzman,
Ueber den griechischen Ursprung des indischen Thierkreises, 1841,
s. 9, 16, 23. ‘* The passages quoted from Amorakoscha, and
Ramayana,” says the latter writer, “‘ admit of undoubted inter-
pretation, and speak of the zodiac in the clearest terms; but
if these works were composed before the knowledge of the Greek
signs of the zodiac could have reached India, these passages
ought to be carefully examined for the purpose of ascertaining
whether they may not be comparatively modern interpolations.”

M2

164 COSMOS.

The artificial grouping of the stars into constellations which
arose incidentally during the lapse of ages—the frequently in-
convenient extent and indefinite outline—the complicated
designations of individual stars in the different constellations—
the various alphabets which have been required to distinguish
them, as in Argo—together with the tasteless blending of mythi-
cal personages with the sober prose of philosophical instruments,
shemical furnaces, and pendulum clocks, in the southern
hemisphere—have led to many propositions for mapping the
heavens in new divisions, without the aid of imaginary
figures. This undertaking appears least hazardous in respect
to the southern hemisphere, where Scorpio, Sagittarius, Cen-
taurus, Argo, and Eridanus alone possess any poetic interest.”

The heavens of the fixed stars (orbis inerrans of Apuleius)
and the inappropriate expression of fixed stars, (astra fixa of
Manilius) remind us, as we have already observed in the in-
troduction to the Astrognosy,” of the connexion, or rather
confusion of the ideas of insertion, and of absolute immo-
bility or fixity. When Aristotle calls the non-wandering
celestial bodies (amAavi dorpa) rivetted (€vdedepeva), when Pto-
lemy designates them as engrafted (mpoomeduxdres), these
terms refer specially to the idea entertained by Anaximenes

5! Compare Buttman, in Berlin astron. Jahrbuch fur 1822,
s. 98, Olbers on the more recent constellations in Schumacher’s
Jahrbuch fiir 1840, s. 2838-241, and Sir John Herschel,
Revision and Rearrangement of the Constellations, with special
reference to those of the Southern Hemisphere, in the Memoirs
of the Astr. Soc., vol. xii. pp. 201-224, (with a very exact
distribution of the southern stars from the Ist to the 4th
magnitude). On the occasion of Lalande’s formal discussion
with Bode on the introduction of his domestic cat and of a
reaper (Messier /) Olbers complains that in order “ to find space
in the firmament for King Frederick's glory, Andromeda
must lay her right arm in a different place from that which it
had occupied for 3000 years !” |

*® Vide supra, pp. 30-31, and note.

THE FIXED STARS. 165

of ihe crystalline sphere of heaven. The apparent motion
of all the fixed stars from east to west, while their relative dis-
tances remained unchanged, had given rise to this hypothesis.
‘The fixed stars (drhavq dorpa) belong to the higher and more
distant regions, in which they are rivetted, like nails, to the
erystalline heavens; the planets (dorpa mAavapeva or mAavyra),
which move in an opposite direction, belong to a lower and
nearer region.” ** As we find in Manilius, in the earliest ages
of the Caesars, that the term s¢el/a fixa was substituted for
infixa, or affixa, it may be assumed that the schools of Rome
attached thereto at first only the original signification of
rivetied, but as the word fixus also embraced the idea of immo-
bility, and might even be regarded as synonymous with emmotus
and immobilis, we may readily conceive that the national opinion,
or rather usage of speech, should gradually have associated with
stella fixa the idea of immobility, without reference to the fixed
sphere to which it was attached. In this sense Seneca might
term the world of the fixed stars fixwm et immobilem populum.

Although, according to Stobeus, and the collector
of the “Views of the Philosophers,’ the designation
*‘erystal vault of heaven” dates as far back as the early
period of Anaximenes, the first clearly defined signifi-
cation of the idea on which the term is based, occurs
in Empedocles. ‘This philosopher regarded the heaven of
the fixed stars as a solid mass, formed from the ether which
had been rendered crystalline and rigid by the action of fire.*

*% According to Democritus and his disciple Metrodorus,
Stob. Eelog. phys., p. 582.

* Plut. de plac. phil. ii. 11; Diog. Laert., viii. 77; Achil-
es Tat. ad Arat. cap. 5, Eym-, xpvoraddon rovrov (roy odpavir)
civai now, ex Tov mayer@dovs ocvAdeyévra; in like manner we
only meet with the expression crystal-léke in Diog. Laert., viii.
77, and Galenus, Hist. phil., 12, (Sturz, Hmpedocles Agrigent
t. i. p. 321). Lactantius de opificio Dei, ec. 17. “An, s
mihi quispiam dixerit eneum esse ceelum, aut vitreum, aut,

156 COSMOS.

According to his theory the moon is a body conglomerated
‘like hail) by the action of fire, and receives. its light

ut Empedocles ait, aerem glaciatum, statimne assentiat quia
celum ex qua materia sit, ignorem:” “If any one were
to tell me that the heavens are made of brass, or of glass,
or, as Empedocles asserts, of frozen air, I should incon-
tinently assent thereto, for I am ignorant of what substance
the heavens are composed.” We have no early Hellenic
testimony of the use of this expression of a glass-like or
vitreous heaven (calum vitrewm), for only one celestial body,
the sun, is called by Philolaus, a glass-like body, which throws
upon us the rays it has received from the central fire.
(The view of Empedocles, referred to in the text, of the reflec-
tion of the sun’s light from the body of the moon, (supposed
to be consolidated in the same manner as _hail-stones,) is fre-
quently noticed by Plutarch, apud Euseb. Prep. Evangel. 1,
pag. 24. D, and de facie in orbe Lune, cap. 5). Where Uranos
is described as xaAxeos and o«dnpeos by Homer and Pindar, the
expression refers only to the idea of steadfast, permanent, and
imperishable, as in speaking of brazen hearts and brazen
voices. Volcker wher Homerische Geographie, 1830, s. 5.
The earliest mention before Pliny, of the word xpvoradXos
when applied to ice-.ike, transparent rock-crystal occurs in
Dionysius Periegetes, 781, Aelian, xv. 8, and Strabo, xvi
p. 717, Casaub. The opinion, that the idea of the erystalline
heavens being a glacial vault (aer glaciatus of Lactantius)
arose amongst the ancients, from their knowledge of the
decrease of temperature, with the increase of height in the
strata of the atmosphere, as ascertained from ascending great
heights and from the aspect of snow-covered mountains, is
refuted by the circumstance that they regarded the fiery ether
as lying beyond the confines of the actual atmosphere, and
the stars as warm bodies. (Aristot., Meteor. 1, 3, de Calo, 11,
7, p. 289). In speaking of the music of the spheres (Aristot.
de Calo, 11, p. 290), which according to the views of the
Pythagoreans is not perceived by men, because it is con-
tinuous, whereas tones can only be heard when they
are interrupted by silence, Aristotle singularly enough main-
tains that the movement of the spheres generates heat in
the air below them while they are themselves not heated.

THE FIXED STARS. 167

from the sun. ‘The original idea of transparency, congela-
tion, and solidity, would not, according to the physics of the

Their vibrations produce heat, but nosound. “The motion
of the sphere of the fixed stars is the most rapid, (Aristot. de
Calo, ii. 10, p. 291); as this sphere and the bodies attached
to it are impelled in a circle, the subjacent space is heated
by this movement, and hence heat is diffused to the surface
of the earth.” (Meteorol. 1,3, p. 340.) It has always struck
me as a circumstance worthy of remark, that the Stagirite
should constantly avoid the word crystal heaven; for the ex-

ression, ‘‘ rivetted stars’’ (€vdedeueva dorpa), which he uses,
indicates a general idea of solid spheres, without, however,
specifying the nature of the substance. We do not meet
with any allusion to the subject in Cicero, but we find in his
Commentator Macrobius, (Cic. Somnium Scipionis, 1, e. 20,
p. 99, ed. Bip.) traces of freer ideas on the diminution of
temperature, with the increase of height. According to him,
eternal cold prevails in the outermost zones of heaven. “Ita
enim non solum terram sed ipsum quoque ceelum, quod vere
mundus vocatur, temperari a sole certissimum est, ut extre-
mitates ejus, que via solis longissime recesserunt, omni ¢a-
reant beneficio caloris, et una frigoris perpetuitate torpescant.”’
** For as it is most certain that, not only the earth, but the
heavens themselves, which are truly called the universe, are
rendered more temperate by the sun, so also their con-
fines, which are most distant from the sun, are deprived
of the benefits of heat, and languish in a state of perpetual
cold.”” These confines of heaven (extremitates cel), in which
the Bishop of Hippo (Augustinus, ed. Anty. 1700, 1, p. 102,
and iii. p. 99) placed a region of icy-cold water near Saturn
the highest, and therefore the coldest. of all the planets, are
within the actual atmosphere, for beyond the outer limits of
this space lies, according to « somewhat earlier expression of
Macrobius, (1, c. 19, p. 93.) the fiery ether which enigmatically
enough, does not prevent this eternal cold: ‘ Stelle supra
ceelum locate, in ipso purissimo «there sunt, in quo omne
quidgquid est, lux naturalis et sua est, quee tota cum igne suo
ita sphere solis incumbit, ut cceli zone, que procul a sole
sunt, perpetuo fiigore oppresse sint.” ‘The stars above
the heavens arc situated in the pure ether, in which all

168 COSMOS.

ancients,™ and their ideas of the solidification of fluids, have
referred directly to cold and ice; but the affinity between
KptoraAdos, Kpvos, and kpvoraive, as well as this comparison
with the most transparent of all bodies gave rise to the
more definite assertion that the vault of heaven consisted of
ice or of glass. Thus we read in Lactantius: ‘ Colum aerem
glaciatum esse,” and ‘‘ vitreum cclum.” Empedocles un-
doubtedly did not refer to the glass of the Pheenicians, but
to air, which was supposed to be condensed into a transparent
solid body by the action of the fiery ether. In this comparison
with ice, (kpvoraddos) the idea of transparency predominated ;
no reference being here made to the origin of ice through cold,
but simply to its conditions of transparent condensation.
While poets used the term crystal], prose writers (as found in
the note on the passage cited from Achilles Tatius, the com-
mentator of Aratus) limited themselves to the expression
crystalline or erystal-like, xpvoraddoédyjs. In like manner
mayos (from miyyvveOa, to become solid), signifies a piece of ice
—its condensation being the sole point referred to.

The idea of a crystalline vault of heaven was handed down
to the middle ages by the Fathers of the Church, who believed
the firmament to consist of from 7 to 10 glassy strata, incasing
one another like the different coatings of an onion. This sup-
position still keeps its ground in some of the monasteries of

things, whatever they may be, have a natural and proper light
of their own,” (the region of self-luminous stars) ‘‘ which so
impends over the sphere of the sun with all its fire, that those
zones of heaven which are far from the sun are oppressed by
perpetual cold.” My reason for entering so circumstantially
into the physical and meteorological ideas of the Greeks and
Romans, is simply because these subjects, except in the works
of Ukert, Henri Martin, and the admirable fragment of the
Meteorologia Veterum of Julius Ideler, have hitherto been very
imperfectly, and for the most part superficially, considered.

* The ideas that fire has the power of making rigid, ‘Aristot.

VAULT OF HEAVEN. 169

Southern Europe, where! was greatly surprised to hear a vene-
rable prelate express an opinion in reference to the fall of aero-
lites at Aigle, which at that time formed a subject of considerable
interest, that the bodies we called meteoric stones with vitri-
fied crusts were not portions of the fallen stone itself, but
simply fragments of the crystal vault shattered by it in its
fall. Kepler, from his considerations of comets which
intersect the orbits of all the planets,” boasted, nearly two
hundred and fifty years ago, that he had destroyed the 77
concentric spheres of the celebrated Girolamo Fracastoro, as
well as all the more ancient retrograde epicycles. The ideas
entertained by such great thinkers as Eudoxus, Meneechmus,
Aristotle, and Apollonius Pergzeus, respecting the possible me-
chanism and motion of these solid, mutually intersecting spheres
by which the planets were moved; and the question whether they
regarded these systems of rings as mere ideal modes of repre-
sentation, or intellectual fancies, by means of which difficult
problems of the planetary orbits might be solved or determined
approximately; are subjects of which I have already treated

Probl., xiv. 11,) and that the formation of ice itself may be
promoted by heat, are deeply-rooted in the physics of the
ancients, and based on a fanciful theory of contraries (An-
tiperistasis)—on obscure conceptions of polarity (of exciting
opposite qualities or conditions). (Cosmos, p. 14, and note.)
The quantity of hail produced was considered to be propor-
tional to the degree of heat of the atmospheric strata. (Aristot.
Meteor.,i. 12.) In the winter fishery on the shores of the
Euxine, warm water was used to increase the ice formed in the
neighbourhood of an upright tube. (Alex. Aphrodis., fol. 86,
and Plut. de primo frigido, c. 12.)

* Kepler expressly says in his Stella Marts, fol. 9: “ Soe
lidos orbes rejeci.”” “I have rejected the idea of solid orbs;”
and in the Stella Nova, 1606, cap. 2. p. 8: ** Planete in puro
sethere, perinde atque aves in aére cursus suos conficiunt.”
‘*The planets perform their course in the pure ether as
birds pass through the air.” Compare, also, p. 122. He in.

{70 COSMOS,

in another place,” and which are not devoid of interest in our
endeavours to distinguish the different periods of development
which have characterised the history of astronomy.

Before we pass from the very ancient, but artificial zodiacal
grouping of the fixed stars, as regards their supposed inser-
tion into solid spheres, to their natural and actual arrangement,
and to the known laws of their relative distribution, it will be
necessary more fully to consider some of the sensuous pheno-
mena of the individual cosmical bodies—their extending
rays, their apparent, spurious disc, and their differences of
colour. In the note referring to the invisibility of Jupiter’s
satellites, I have already spoken of the influence of the
so-called tails of the stars, which vary in number, position,
and length in different individuals. Indistinctness of vision
(la vue indistincte) arises from numerous organic causes,
depending on aberration of the sphericity of the eye, diffraction
at the margins of the pupil, or at the eye-lashes, and on the
more or less widely diffused irritability of the retina from the
excited point.* I see very regularly eight rays at angles of 45°

clined, however, at an earlier period, to the idea of a solid icy
vault of heaven congealed from the absence of solar heat:
‘- Orbis ex aqua factus gelu concreta propter solis absentiam.”’
(Kepler, Epit. Astr. Copern., i. 2, p. 51.) Two thousand years
before Kepler, Empedocles maintained that the fixed stars
were rivetted to the crystal heavens, but that the planets were
free and unrestrained”’ (rods Se mAavynras aveioOa). (Plut. plac.
phil., ii. 18; Emped. 1, p. 335 Sturz; Euseb. Prep. evang., xv.
30, col. 1688, p. 839.) It is difficult to conceive how, ac-
cording to Plato in the Timeeus (72m., p. 40, B., see Bohn’s
edition of Plato, vol. ii. p. 844, but not according to Aris-
totle,) the fixed stars, rivetted as they are to solid spheres,
could rotate independently. *” Cosmos, vol. ii. pp. 696-7.

* Vide supra, p. 64, and note.

» «+ Les principales causes de la vue indistincte sont: aber-
ration de sphéricité de I’ceil, diffraction sur les bords de la pu-
pille, communication d’i:ritabilité 4 des points yoisins sur la

INDISTINCT VISION. 171

in stars from the Ist to the 3rd magnitude. As, aceording to
Hassenfratz, these radiations are caustics intersecting one

rétine. La vue confuse est celle ot le foyer ne tombe pas ex-
actement sur la rétine, mais tombe au-devant ou derriére la
rétine. Les queues des étoiles sont l’effet de la vision indis-
tincte, autant qu’elle dépend de la constitution du cristallin.
D’aprés un trés ancien mémoire de Hassenfratz (1809) ‘ les
queues au nombre de 4 ou 8 qu offrent les étoiles ou une bougie
vue a 25 métres de distance, sont les caustiques du cristallin
formées par l’intersection des rayons réfracteés.’ Ces caustiques
se meuvent a mesure que nous inclinons la téte.—La propriété
de la lunette de terminer l'image fait qu’elle concentre dans
un petit espace la lumiére qui sans cela en aurait occupé un
plus grand. Cela est vrai pour les étoiles fixes et pour les
disques des planétes. La lumiére des étoiles qui n’ont pas
de disque réels, conserve la méme intensité, quel que soit le
grossissement. Le fond de l’air duquel se détache l’étoile
dans la lunette, devient plus noir par le grossissement qui di-
late les molécules de l’air qu’embrasse le champ de la lunette.
Les planétes 4 vrais disques deviennent elles-mémes plus
_ pales par cet effet de dilatation.—Quand la peinture focale est
nette, quand les rayons partis d'un point de l'objet se sont
concentrés en un seul point dans l'image, l’oculaire donne des
résultats satisfaisants. Si au contraire les rayons émanés d’un
point ne se réunissent pas au foyer en un seul point, s’ils y
forment wn petit cercle, les images de deux points contigus de
l'objet empiétent nécessairement l’une sur l’autre ; leurs rayons
se confondent. Cette confusion la lentille oculaire ne saurait
la faire disparaitre. L/office qu’elle remplit exclusivement,
c'est de grossir; elle grossit tout ce qui est dans l'image, les
défauts con.me le reste. Les étoiles n'ayant pas de diamétres
angulaires sensibles, ceux qu’elles conservent toujours, tiennent
pour la plus grande partie au manque de perfection des instru-
mens (a la courbure moins réguliére donnée aux deux faces de
la lentille objective) et 4 quelques défauts et aberrations de
notre cil. Plus une étoile semble petite, tout étant égal quant
au diamétre de l’objectif, au grossissement employé et a 1 eclat
de | étoile observée, et plus la lunette a de perfection. Or le
meilleur moyen de juger si les étoiles sont trés petites, si des
points sont representés au foyer par des simples points, c’est

172 COSMOS,

another on the crystalline lens, they necessarily move
according to the direction in which the head is in-

évidemment de viser a des étoiles excessivement rapprochées
entr’elles et de voir si dans les étoiles doubles connues leg
images se confondent, si elles empiétent l'une sur l'autre, ou
bien si on les apercgoit bien nettement séparées.”

*- The principal causes of indistinct vision are: aberration of
the sphericity of the eye, diffraction at the margins of the
pupil,and irritation transmitted to contiguous points of the retina.
Indistinct vision exists where the focus does not fall exactly on
the retina, but either somewhat before or behind it. The tails
of the stars are the result of indistinctness of vision, as far as it
depends on the constitution of the crystalline lens. According
to a very old paper of Hassenfratz (1809) ‘ the 4 or 8 tails
which surround the stars or a candle seen at a distance
of 25 metres [82 feet], are the caustics formed on the erystal-
line lens by the intersection of refracted rays.’——These caustics
follow the movements of the head.—The property of the tele-
scope in giving a definite outline to images, causes it to con-
centrate in a small space, the light which would otherwise be
more widely diffused. ‘This obtains for the fixed stars and for
the discs of planets. The light of stars having no actual
discs, maintains the same intensity, whatever may be the mag-
nifying power of the instrument. The aerial field from which
the star is projected in the telescope is rendered more black
by the magnifying property of the instrument, by which the
molecules of air inc'uded in the field of view are expanded.
Planets having actual discs become fainter from this effect of
expansion. When the focal image is clearly defined, and
when the rays emanating from one point of the object are con-
centrated into one point in the image, the ocular focus affords
satisfactory results. But if, on the contrary, the rays ema-
nating from one point do not reunite in the focus into one
point, but form a small circle, the images of two contiguous
points of the object will necessarily impinge upon each other ;
and their rays will be confused. This confusion cannot be
removed by the ocular ; since the only part it performs is that
of magnifying. It magnifies everything comprised in the
image, including its defects. As the stars have no sensible
angular diameters, those which they present are principally

RAYS OF THE STARS. 173

elined. Some of my astronomical friends see three, or at
most four rays above, and none below the star. It has always
appeared extraordinary to me, that the ancient Egyptians
should invariably have given only five rays to the stars (at
distances, therefore, of 72°); so that a star in hieroglyphies
signifies, according to Horapollo, the number five.“

The rays of the stars disappear when the image of the radiat-
ing star is seen through a very small aperture made with a
needle in a card, and I have myself frequently observed both
Canopus and Sirius in thismanner. The same thing occurs in
telescopic vision through powerful instruments, when the stars
appear either as intensely luminous points, or as exceed-
ingly small discs. Although the fainter scintillation of the
fixed stars in the tropics conveys a certain impression of
repose, a total absence of stellar radiation would, in my
opinion, impart a desolate aspect to the firmament, as seen by
the naked eye. [Illusion of the senses, optical illusion, and
indistinct vision, probably tend to augment the splendour of
the luminous canopy of heaven. Arago long since proposed

owing to the imperfect construction of the instrument (to the
different curvatures of the two sides of the object-glass), and
to certain defects and aberrations pertaining to the eye itself,
The smaller the star appears, the more perfect is the instru-
ment, providing all relations are equal as to the diameter of
the object-glass, the magnifying power employed, and the
brightness of the star. Now the best means of judging
whether the stars are very small, and whether the points are
represented in the focus by simple points, is undoubtedly that
of directing the instrument to stars situated very near each
other, and of observing whether the images of known double
stars are confused, and impinging on each other, or whether
they can be seen separate and distinet.” (Arago, M.S. of
1834 and 1847.)

* Hassenfratz, Sur les rayons divergens des Etoiles in

’ Delamétherie, Journal de Physique, tom. lxix. 1809, p. 324.
“® Horapollinis Niloi Hieroglyphica, ed. Con. Leemans,

174 COSMOS.

the question, why fixed stars of the first magnitude, notwith-
standing their great intensity of light, cannot be seen when
rising ahove the horizon in the same manner as under similar
circumstances we see the outer margin of the moon’s disc.@
Even the most perfect optical instruments, and tLose hav-
ing the highest magnifying powers, give tothe fixed stars
spurious discs (diamétres factices); ‘the greater aperture,”
according to Sir John Herschel, “even with the same mag-
nifying power giving the smaller disc.” Occultations of the
stars by the moon’s dise show that the period occupied in
the immersion and emersion is so transient that it cannot be
estimated at a fraction of a second of time. The frequent oc-
currence of the so-called adhesion of the immersed star to the
moon’s disc, is a phenomenon depending on inflection of light
in no way connected with the question of the spurious dia-
meter of the star. We have already seen that Sir William
Herschel, with a magnifying power of 6500, found the diame-
ter of Vega 0"°36. The image of Arcturus was so dimin-
ished in a dense mist, that the dise was below 0"-2. It is
worthy of notice that, in consequence of the illusion occasioned
by stellar radiation, Kepler and Tycho, before the invention

1835, cap. 18, p. 20. The learned editor notices, how-
ever, in refutation of Jomard’s assertion (Descr. de l Egypte,
tom. vii. p. 423), that a star, as the numerical hieroglyphic
for 5, has not yet been discovered on any monument or
papyrus-roll. (Horap., p. 194.)

I found an opinion prevalent among the sailors of the
Spanish ships of the Pacific, that the age of the moon might
be determined before the first quarter, by looking at it
through a piece of silk and counting the multiplied images.
Here we have a phenomenon of diffraction observed through
fine slits.

“© Outlines, § 816. Arago has caused the spurious dia-
meter of Aldebaran to increase from 4” to |5” in the instru
ment by diminishing the object-glass.

THE COLOUR OF THE STARS. 175

of the telescope, respectively ascribed to Sirius a diameter
of 4’ and of 2’ 20”.

The alternating light and dark rings which surround the
small spurious discs of the stars when magnified two or
three hundred times, and which appear iridescent when
seen through diaphragms of different form, are likewise the
result of interference and diffraction, as we learn from the
observations of Arago and Airy. The smallest obiects which
can be distinctly seen in the telescope as luminous points,
may be employed as a test of the perfection in construc-
tion and illuminating power of optical instruments, whether
refractors or reflectors. Amongst these we may reckon mul-
tiple stars, such as « Lyre, and the 5th and 6th star discovered
by Struve, in 1826, and by Sir John Herschel in 1832, in the
trapezium of the great nebula of Orion,® forming the qua-
druple star @ of that constellation.

A difference of colour in the proper light of the fixed stars,

“ Delambre, Hist. de Tl Astr. moderne, tom. i. p. 1938;
Arago, Annuaire, 1842, p. 366.

* «'Two excessively minute, and very close companions, to
perceive both of which, is one of the severest tests which can be
applied 10 a telescope.” (Outlines, § 837. Compare also Sir
John Herschel, Observations at the Cape, p. 29; and Arago,
in the Annuaire pour 1834, pp. 302-305.) Among the dif-
ferent planetary cosmical bodies by which the illuminating
power of a strongly magnifying optical instrument may be
tested. we may mention the Ist and 4th satellites of Uranus, re-
discovered by Lassell and Otto Struve in 1847, the two inner-
most and the 7th satellite of Saturn (Mimas, Enceladus, and
Bond’s Hyperion), and Neptune's satellite discovered by Lassell.
The power of penetrating into celestial space occasioned
Bacon, in an eloquent passage in praise of Galileo, to whom
he erroneously ascribes the invention of telescopes, to com-
pare these instruments to ships which carry men upon an
unknown ocean :—*“ Ut propriora exercere possint cum ceeles-
tibus commercia.” (Works of Francis Bacon, 1740, vol. i.
Novum Organum, p. 361.)

176 : COSMUR,

as well as in the reflected light of the planets, was recognized
at a very early period; but our knowledge of this remarkable
phenomenon has been greatly extended by the aid of telescopic
vision, more especially since attention has been so especially
directed to the double stars. We do not here allude to the
change of colour which, as already observed, accompanies
scintillation even in the whitest stars, and still less to the
transient and generally red colour exhibited by stellar light
uear the horizon, (a phenomenon owing to the character of
the atmospheric medium through which we see it,) but to the
white or coloured stellar light radiated from each cosmical
body, in consequence of its peculiar luminous process, and the
different constitution of its surface. The Greek astronomers
were acquainted with red stars only, while modern science has
discovered, by the aid of the telescope, in the radiant fields of
the starry heaven, as in the blossoms of the phanero-
gamia, and in the metallic oxides, almost all the gradations of
the prismatic spectrum between the extremes of refrangibility of
the red and the violet ray. Ptolemy enumerates in his catalogue
of the fixed stars six (dmdxippor) fiery red stars, viz: Arcturus
Aldebaran, Pollux, Antares, a Orionis (in the right shoulder),

“ The expression iméxippos, which Ptolemy employs indis-
criminately to designate the six stars named in his catalogue,
implies a slightly marked transition from fiery-yellow to fiery-
red; it therefore refers, strictly speaking, to a fiery-reddish
colour. He seems to attach the general predicate €av@ds,
fiery-yellow, to all the other fixed stars. (dlmag., viii. 3 ed.
Halma, tom. ii. p. 94.) Kueppds is, according to Galen, (Meth.
med. 12,) a pale fiery-red inclining to yellow. Gellius com-
pares the word with melinus. which, according to Servius, has
the same meaning as “ gilvus” and * fulvus.”’ As Sirius
is said by Seneca (Nat. Quest., i. 1) to be redder than Mars,
and belongs to the stars called in the Almagest tmdéxippo.,
there can be no doubt that the word implies the predominance,
or, at all events, a certain proportion of red rays. The asser-
tion tkat the affix mosidos, which Aratus, v. 327, attaches te

COLOUR OF THE STARS, 177
and Sirius. Cleomedes even compares Antares in Scorpio
with the fiery red Mars,” which is called both wvpéds and
mupoetdrs.

Of the six above named stars, five still retain a red or
reddish light. Pollux is still indicated as a reddish, but
Castor as a greenish star.“ Sirius therefore affords the
only example of an historically proved change of colour,
for it has at present a perfectly white light. A great
physical revolution® must therefore have occurred at the
surface or in the photosphere of this fixed star, (or remote
sun, as Aristarchus of Samos called the fixed stars) before
the process could have been disturbed by means of which
the less refrangible red rays had obtained the preponderance,
through the abstraction or absorption of other complementary

Sirius, has been ¢ranslated by Cicero as “ rutilus,”’ is erro-
neous. Cicero says, indeed, v. 348:—
‘** Namque pedes subter rutilo cum lumine claret,
Fervidus ille Canis stellarum luce refulgens ;”

but * rutilo cum lumine”’ is not a ¢ranslation of mosidos, but
the mere addition of a free translation. (From letters ad-
dressed to me by Professor Franz.) ‘ If,” as Arago observes
(Annuaire. 1842. p. 351), ‘the Roman orator, in using the
term rutilus, purposely departs from the strict rendering of
the Greek of Aratus, we must suppose that he recognized the
reddish character of the light of Sirius.”

# Cleom., Cycl. Theor., i. ii. p. 59.

Madler. Astr. 1849, s. 391.

® Sir John Herschel, in the Edinb. Review, vol. 87,
1848, p. 189, and in Schum. Astr. Nachr., 1839, no. 372:—
** It seems much more likely that in Sirius a red colour should
be the effect of a medium interfered, than that in the short
space of 2000 years so vast a body should have actually under-
gone such a material change in its physical constitution. It
may be supposed owing to the existence of some sort of cos-
mical cloudiness, subject to internal movements, depending on
causes of which we are ignorant.” (Compare Arago in the
Annuaire pour 1842, pp. 350-358.)

YWOL. Iti. N

178 COSMOS.

rays, either in the photosphere of the star itself, or in the
moving cosmical clouds by which it is surrounded. It is to
be wished that the epoch of the disappearance of the red
colour of Sirius had been recorded by a definite reference to the
time, as this subject has excited a vivid interest in the minds
of astronomers since the great advance made in modern
optics. At the time of Tycho Brahe the light of Sirius was un-
doubtedly already white, for when the new star which appeared
in Cassiopeia, in 1572, was observed in the month of March,
1573, to change from its previous dazzling white colour to a
reddish hue, and again became white in January, 1574, the red
appearance of the star was compared to the colour of Mars and
Aldebaran, but not to that of Sirius. M. Sédillot, or other phi-
lologists conversant with Arabic and Persian astronomy, may
perhaps some day succeed in discovering evidenee of the
earlier colour of Sirius, in the periods intervening from El-
Batani (Albategnius) and El-Fergani (Alfraganus) to Abdur-
rahman Sufi and Ebn-Junis (that is, from 880 to 1007), and
from Ebn-Junis to Nassir-Eddin and Ulugh-Beg (from 1007
to 1437).

El-Fergani (properly Mohammed Ebn-Kethir El-Fergani),
who conducted astronomical observations in the middle of the
tenth century at Rakka (Aracte) on the Euphrates, indicates
as red stars (stelle ruffe of the old Latin translation of 1590)
Aldebaran, and, singularly enough,” Capella, which is now
yellow and has scarcely a tinge of red, but he does not men-
tion Sirius. If at this period Sirius had been no longer red,
it would certainly be a striking fact that El-Fergani, who
invariably follows Ptolemy, should not here indicate the

© In Muhamedis Alfragani chronologicu et astronomica
Elementa, ed. Jacobus Christmannus, 1590, cap. 22, p. 97,
we read:—*‘‘ Stella ruffa in Tauro Aldebaran; stella ruffa in
Geminis que appellatur Hajok, hoc est Capra.” Alhgoe,
Ayuk are, however, the ordinary names for Capella Aurige,

— a ——'?

SIRIUS 179

change of colour in so celebrated a star. Negative proofs are
however not often conclusive, and indeed El-Fergani makes no
reference in the same passage to the colour of Betelgeux (a
Orionis), which is now red, as it was in the age of Ptolemy.
It has long been acknowledged that of all the brightest
luminous fixed stars of heaven, Sirius takes the first and most
important place, no less in a chronological point of view, than
through its historical association with the earliest develop-
ment of human civilization in the valley of the Nile. The era
of Sothis—the heliacal rising of Sothis (Sirius)—on which
Biot has written an admirable treatise, indicates, according to
the most recent investigations of Lepsius,” the complete ar-
rangements of the Egyptian calendar into those ancient epochs,
including nearly 3300 years before our era, ‘ when not only
the summer solstice, and consequently the beginning of the
rise of the Nile, but also the heliacal rising of Sothis, fell on the
day of the first water-month (or the first Pachon).” I will
collect in a note the most recent, and hitherto unpublished,
etymological researches on Sothis or Sirius from the Coptic,
Zend, Sanscrit, and Greek, which may perhaps be acceptable
to those who, from love for the history of astronomy, seek

in the Arabic and Latin Almagest. Argelander justly observes,
in reference to this subject, that Ptolemy in the astrological work
(TerpdsBros oivragis), the genuine character of which is testi-
fied by the style as well as by ancient evidence, has associated
planets with stars according to similarity of colour, and has
thus connected Martis stella, Que urit sicut congrutt wgneo
wpsius colori, with Aurige stella, or Capella, (Compare
Ptol., Quadripart. Construct., libri iv. Basil, 1551, p. 383.)
Riccioli (Almagestum novum, ed. 1650, tom. i. pars i. lib. 6,
cap. 2, p. 394) also reckons Capella together with Antares,
Aldebaran, and Arcturus among red stars.

" See Chronologie der Aigypter, by Richard Lepsius, bd. i.
1849, s. 190-195, 213. The complete arrangement of the
Egyptian calendar is referred to the earlier part of the year
$285 before our era, 7. e. about a century and a half after the

n%

180 COSMOR.

in languages and their affinities, monuments of the earlier
conditions of knowledge.®

building of the great pyramid of Cheops-Chufu, and 940 years
before the period generally assigned to the Deluge. (Compare
Cosmos, vol. ii. p. 475 and note.) In the calculations based
on the circumstance of Colonel Vyse having found that the
inclination of the narrow subterranean passage leading into the
interior of the pyramid, very nearly corresponded to the angle
26° 15’, which, in the time of Cheops (Chufu), was attained
by the star « Draconis, which indicated the pole, at its inferior
culmination at Gizeh, the date of the building of the pyramid
is not assumed at 3430 B.c, as given in Cosmos according
to Letronne, but at 3970 B.c. (Outlines of Astr., § 319.)
This difference of 540 years tends to strengthen the assump-
tion, that a Drac. was regarded as the pole-star, as in 3970 it
was still at a distance of 3° 44’ from the pole.

® J have extracted the following observations from letters
addressed to me by Professor Lepsius (February, 1850). ** The
Egyptianname of Sirius is Sothzs, designated as a female star;
hence, 7 2@6s is identified in Greek with the goddess Sote
(more frequently S7¢ in hieroglyphics,) and in the temple of
the great Ramses at Thebes with Isis-Sothis (Lepsius, Chron.
der Aigypter, bd. i. s. 119, 186). The signification of the
root is found in Coptic, and is allied with a numerous family
of words, the members of which, although they apparently
differ very widely from each other, admit of being arranged
somewhat in the following order. By the threefold transfer-
enceof the verbal signification, we obtain from the original mean-
ing, to throw out—projicere (sagittam, telum)—first, seminare,
to sow; next, extendere, to extend or spread (as spun threads;)
and lastly, what is here most important, to radiate light and
lo shine (as stars and fire). From this series of ideas we may
deduce the names of the divinities, Sats (the female archer) ;
Sothis, the radiating, and Seth, the fiery. We may also hiero-
glyphically explain sz or se¢i, the arrows as well as the ray; seta,
to spin; se¢w, scattered seeds. Sothis is especially the brightly
radiating, the star regulating the seasons of the year and
periods of time. The small triangle, always represented yellow.
which is a symbolical sign for Sothis, is used to designate the

radiating sun when ar1vnged in numerous triple rows issuing

THE COLOUR OF THE STARS. 181

Besides Sirius, Vega, Deneb, Regulus, and Spica, are at the
present time decidedly white ; and among the small double

ina downward direction from the sun’s disk. Seth is the fiery
scorching god, in contradistinction to the warming, fructifying
water of the Nile, the goddess Satis who inundates the soil.
She is also the goddess of the cataracts, because the overflowing
of the Nile began with the appearance of Sothis in the heavens
at the summer solstice. In Vettius Valens the star itself is
called 394 instead of Sothis; but neither the name nor the
subject admits of our identifying Zhoth with Seth or Sothis, as
Ideler has done. (Handbuch der Chronologe, bd. 1. 8. 126.)”
(Lepsius, bd. i. s. 136.)

I will close these observations taken from the early Egyp-
tian periods with some Hellenic, Zend, and Sanscritetymologies:
“Seip, the sun,” says Professor Franz, ‘‘is an old root, differing
only in pronunciation from ep, Gépos, heat, summer, in which
we meet with the same change in the vowel sound as in teipos
and répos or répas. The correctness of these assigned relations
of the radicals celp and 6ep, 6€pos, is proved not only by the em-
ployment of Oepeiraros in Aratus, v. 149 (Ideler, Sternnamen,
s. 241), but also by the later use of the forms celpos, vetpids, and
aeipivds hot, burning, derived from geip. It is worthy of notice
that cvespa or Oetpwa ivdria is used the same as Oepiva ivaria,
light summer clothing. The form céipios seems, however, to
have had a wider application; for it constitutes the ordinary
term appended to all stars influencing the summer heat : hence,
according to the version of the poet. Archilochus, the sun was
geiptos dorip, while Ibycus calls the stars generally ceipsa,
luminous. It cannot be doubted that it is the sun to which
Archilochus refers in the words, wodAovs pev adrod ceipios
karavavet o€ds €\Adurav. According to Hesychius and Suidas,
Sciptos does indeed signify both the sun and the Dog-star; but
I fully coincide with M. Martin, the new editor of Theon of
Smyrna, in believing that the passage of Hesiod (Opera et
Dies, v. 417,) refers to the sun, as maintained by Tzetzes and
Proclus, and not to the Dog-star. From the adjective oeiptos,
which has established itself as the ‘ epitheton perpetuum’ of the
Dog-star, we derive the verb cetpidy, which may be translated
‘to sparkle.’ Aratus, v. 331, says of Sirius, df€a cecpider, * it
sparkles strongly.’ When standing alone, the word 2epqy, the

182 COSMOS.

stars Struve enumerates about 300, in which both stars are
white.* Procyon, Atair, the Pole Star, and more especially
B Ursee Min. have a more or less decided yellow light. We
have already enumerated among the larger red or reddish

Siren, has a totally different etymology; and your conjecture,
that it has merely an accidental similarity of sound with the
brightly shining star Sirius, is perfectly well-founded. The
opinion of those who, according to Theon Smyrneeus (Liber de
Astronomia, 1850, p. 202), derive Ze:pyv from ceiprdgew (a more-
over unaccredited form of cetptay) is likewise entirely erroneous.
While the motion of heat and light is implied by the expres-
sion geipios, the radical of the word 2e:pyy represents the flow-
ing tones of this phenomenon of nature. It appears to me
probable, that Zepyv is connected with «pew (Plato, Cratyl.
398 D, 1d yap ctpew A€yew éori,) in which the original sharp
aspiration passed into a hissing sound.” (From letters of
Prof. Franz to me, January, 1850.)

The Greek Seip, the sun, easily admits, according to Bopp, “ of
being associated with the Sanscrit word svar, which does not
indeed signify the sun itself, but the heavens, (as something
shining.) The ordinary Sanscrit denomination for the sun is
stirya, a contraction of svdrya, which is not used. The root
svar signifies in general ¢o shine. The Zend designation for the
sun is Avare, with the A instead of the s. The Greek ep, Oépos
and @epyds comes from the Sanscrit word gharma (Nom.
gharmas,) warmth, heat.”

The acute editor of the Rigveda, Max Miiller, observes,
that ‘the special Indian astronomical name of the Dog-star,
Lubdhaka, which signifies a hunter, when considered in re-
ference to the neighbouring constellation Orion, seems to indi-
cate an ancient Arian community of ideas regarding these groups
of stars.” He is moreover principally inclined “to derive Seipsos
from the Veda word stra (whence the adjective sadrya,) and
the root sz, to go, to wander; so that the sun and the brightest
of the stars, Sirius, were originally called wandering stars.”
(Compare also Pott, Etymologische Forschungen, 1833,
s. 130.

* iesivi Stellarum compositarum Mensure micrometriva,
1837, p. Ixxiv. et Ixxxiui.

THE COLOUR OF THE STARS. 183

stars Betelgeux, Arcturus, Aldebaran, Antares, and Pollux.
Riimker finds y Crucis of a fine red colour, and my old friend,
Captain Bérard, who is an admirable observer, wrote from
Madagascar in 1847, that he had for some years seen a
Crucis growing red. The star 7 Argis, which has been
rendered celebrated by Sir John Herschel’s observations, and
to which I shall scon refer more circumstantially, is under-
going a change in colour, as well as in intensity of light. In
the year 1843, Mr. Mackay noticed at Calcutta that this star
was similar in colour to Arcturus, and was therefore reddish
yellow;® but in letters from Santiago de Chili, in Feb.
1850, Lieutenant Gilliss speaks of it as being of a darker
colour than Mars. Sir John Herschel, at the conclusion of
his Observations at the Cape, gives a list of seventy-six ruby-
coloured small stars, of the 7th to the 9th magnitude, some of
which appear in the telescope like drops of blood. The majo-
rity of the variable stars are also described as red and reddish.”
the exceptions being Algol in Caput Medusee, 8 Lyre and <
Auriga, which have a pure white light. Mira Ceti, in which
a periodical change of light was first recognized, has a strong
reddish light; but the variability observed in Algol and
8 Lyre, proves that this red colour is not a necessary condi-
tion of a change of light, since many red stars are not
variable. The faintest stars in which colours can be dis-
tinguished belong, according to Struve, to the 9th and 10th
magnitudes. Blue stars were tirst mentioned by Mariotte,”
1686, in his Traité des Couleurs. The light of a Lyre is
bluish ; and a smaller stellar mass of 34 minutes in diameter
in the southern hemisphere consists, according to Dunlop, of
blue stars alone. Among the double stars there are many in

% Sir John Herschel, Observations at the Cape, p. 34
% Madler’s Astronomie, s. 436.

% Cosmos, vol. ii. p. 713.

" Arago, Annuaire pour 1842, p. 348.

184 COSMUS.

which the principal sta: is white, and the companion blue;
and some in which both stars have a blue light,* (as 8 Serp.
and 59 Androm.) Occasionally, as in the stellar swarm neat
« of the Southern Cross, which was mistaken by Lacaille for
a nebulous spot, more than a hundred variously-coloured red,
green, blue, and bluish-green stars are so closely thronged to-
gether that they appear in a powerful telescope “like a superb
piece of fancy jewellery.” *

The ancients believed they could recognize a ) remarkable
symmetry in the arrangement of certain stars of the Ist
magnitude. Thus their attention was especially directed
to the four so-called regal stars which are situated at op-
posite points of the sphere, Aldebaran and Antares, Re-
gulus and Fomalhaut. We find this regular arrangement,
of which I have already elsewhere treated,™ specially referred
to in a late Roman writer, Julius Firmicus Maternus,™ who
belonged to the age of Constantine. The differences of right
ascension in these regal stars, stelle regales, are 11h. 57m. and
12h.49m. Theimportance formerly attached to this subject is
probably owing to opinions transmitted from the East, which
gained a footing in the Roman empire under the Cesars,
together with a strong national predilection for astrology.
The leg, or north star of the Great Bear, (the celebrated star
_of the Bull’s leg in the astronomical representations of Den-
dera, and in the Egyptian Book of the Dead) is perhaps the
star indicated in an obscure passage of Job (ch. ix. ver. 9),
in which Arcturus, Orion, and the Pleiades are contrasted with
‘the chambers of the south,” and in which the four quarters

® Struve, Stelle comp., p. |xxxil.

© Sir John Herschel, Observations at the Cape, pp. 17, 102.
(‘* Nebule and Clusters, No. 3435.’’)

© Humboldt, Vues des Cordilléres et Monumens des peuples
tndigénes de l' Amérique, tom. ii. p. 55.

@ Julii Firmict Materni Astron., Sikri viii. Basil, 1551,
lib. vi. cap. 1. p. 150.

SOUTHERN STARS. 185

of the heavens in like manner are indicated by these four
groups.*

While a large and splendid portion of the southern heavens
beyond stars having 53° S. Decl. were unknown in ancient
times, and even in the earlier part of the middle ages, the know-
ledge of the southern hemisphere was gradually completed
about a century before the invention and application of the
telescope. At the time of Ptolemy there were visible on the
horizon of Alexandria, the Altar, the feet of the Centaur,
the Southern Cross, then included in the Centaur, and
according to Pliny also called Cesaris Thronus, in honour
of Augustus, and Canopus (Canobus) in Argo, which is
called Ptolem@on by the scholiast to Germanicus.* In the

@ Lepsius, Chronol. der digypter, bd. i. s. 143. In the
Hebrew text mention is made of Asch, the giant (Orion?), the
many stars (the Pleiades, Gemut?) and ‘* the Chambers of the
South.” The Septuagint gives: 6 mov ‘Ededda cat ‘Eorepov
nas Apkrovpoy kal rayeia vorov.

The early English translators, like the Germans and Dutch,
understood the first group referred to in the verse to signify
the stars in the Great Bear. Thus we find in Coverdale’s
version, “* He maketh the waynes of heaven, the Orions, the
vii. stars and the secret places of the south.”-—Adam Clarke’s
Commentary on the Old Testament.—(TR.)

% Tdeler, Sternnamen, s. 295. ;

* Martianus Capella changes Ptoleme@on into Ptolemeus ;
both names were devised by the flatterers at the court of the
Egyptian sovereigns. Amerigo Vespucci thought he had
seen three Canopi, one of which was quite dark (fosco), Cuno-
pus ingens et niger of the Latin translation : most probably one
of the black coal-sacks. (Humboldt, Hzamen crit. de la Géogr.
tom. v. pp. 227, 229.) In the above-named Elem. chronol. et
Astron. by El Fergani (p. 100), it is stated that the Christian
pilgrims used to call the Sohel of the Arabs (Canopus) the
star of St. Catherine, because they had the gratification of
observing it, and admiring it as a guiding star when they
journeyed from Gaza to Mount Sinai. In a fine episode to
the Ramayana, the oldest heroic poem of Indian antiquity, the

186 COSMOS.

catalogue of the A.magest, Achernar, a star of the 1st mag-
nitude, the last in Eridanus, (Achir el-nahr, in Arabic,) is also
given, although it was 9° below the horizon. A report of the

stars in the vicinity of the South Pole are declared for a
singular reason to have been more recently created than the
northern. When Brahminical Indians were emigrating
from the north-west to the countries around the Ganges,
from the 30th degree of north latitude to the lands of the
tropics, where they subjected the original inhabitants to
their dominion, they saw unknown stars rising above the
horizon as they advanced towards Ceylon. In accordance
with ancient practice, they combined these stars into new
constellations. A bold fiction represented the later-seen
stars as having been subsequently created by the mira-
culous power of Visvamitra, who threatened “the ancient
gods that he would overcome the northern hemisphere,
with his more richly starred southern hemisphere.” (A. W.von
Schlegel, in the Zeitschrift fur die Kunde des Morgenlandes,
bd. i. s. 240.) While this Indian myth figuratively depicts
the astonishment excited in wandering nations by the aspect
of a new heaven (as the celebrated Spanish poet, Garcilaso
de la Vega, says of travellers, ‘‘they change at once their
country and stars,” mudan de pays y de estrellas,) we are
powerfully reminded of the impression that must have been
excited, even in the rudest nations, when, at a certain part of
the earth’s surface, they observed large, hitherto unseen stars
appear in the horizon, as those in the feet of the Centaur, in
the Southern Cross, in Eridanus or in Argo, whilst those
with which they had been long familiar at home wholly dis-
appeared. The fixed stars advance towards us, and again
recede, owing to the precession of the equinoxes. We
have already mentioned that the Southern Cross was 7°
above the horizon, in the countries around the Baltic, 2900
years before our era; at a time, therefore, when the great
pyramids had already existed five hundred years. (Compare
Cosmos, pp. 139 and 660.) ‘‘ Canopus, on the other hand, can
never have been visible at Berlin, as its distance from the
South Pole of the ecliptic amounts to only 14°. It would have
required a2 distance of 1° more to bring it within the limits of
visibility for our horizon.”

DISTRIBUTION OF STARS. 187

existence of this star must therefore have reached Ptolemy
through the medium of those who had made voyages to the
southern parts of the Red Sea, or between Ocelis and the Mala-
bar emporium, Muziris.* Though improvements in the art of
navigation led Diego Cam, together with Martin Behaim, along
the western coasts of Africa, as early as 1484, and carried Bar-
tholomew Diaz in 1487, and Gama in 1497 (on his way to
the East Indies), far beyond the equator, into the Antarctic
Seas, as far as 35° south lat., the first special notice of the
.arge stars and nebulous spots, the first description of the
** Magellanic clouds” and the “ coal-sacks,’” and even the
fame of ‘‘ the wonders of the heavens not seen in the Medi-
terranean,” belong to the epoch of Vincenze Yaiiez Pinzon,
Amerigo Vespucci, and Andrea Corsali, between 1500 and
1515. The distances of the stars of the southern hemis-
phere were measured at the close of the 16th and the be-
ginning of the 17th century.*

Laws of relative density in the distribution of the fixed
stars in the vault of heaven, first began to be recognized
when Sir William Herschel, in the year 1785, conceived the
happy idea of counting the number of stars which passed at
different heights and in various directions over the field of view,
of 15’ in diameter, of his twenty-feet reflecting telescope. Fre-
quent reference has already been made in the present work to
his laborious process of “‘ gauging the heavens.”’ The field of
view each time embraced only z54455th of the whole hea-
vens; and it would therefore require, according to Struve,
eighty-threee years to gauge the whole sphere by a similar pro-
cess.” In investigations of the partial distribution of stars,
we must specially consider the class of magnitude to which

* Cosmos, vol. ii. pp. 538, 539.

® Olbers in Schumacher’s Jahrb. fiir 1840, s. 249, and
Cosmos, vol. i. p. 51.

* Etudes d Astr. stellaire, note 74, p. 31.

188 COSMOS

they photometrically belong. If we limit our attention to the
bright stars of the first three or four classes of magni-
tudes, we shall find them distributed on the whole with
tolerable uniformity,® although in the southern hemisphere,
from ¢ Orionis to a Crucis. they are locally crowded together
in a splendid zone in the direction of a great circle. The
various opinions expressed by different travellers on the
relative beauty of the northern and southern hemispheres,
frequently, I believe, depends wholly on the circumstance,
that some of these observers have visited the southern regions
at a period of the year when the finest portion of the con-
stellations culminate in the day-time. It follows, from the
gaugings of the two Herschels in the northern and southern
hemispheres, that the fixed stars from the 5th and 6th to the
10th and 15th magnitudes (particularly, therefore, telescopic
stars) increase regularly in density as we approach the
galactic circle (6 yaAagias xikdos); and that there are therefore
poles rich in stars, and others poor in stars, the latter being
at right angles to the principal axis of the Milky Way. The
density of the stellar light is at its minimum at the poles of
the galactic circle; and it inereases in all directions, at first
slowly, and then rapidly, in proportion to the increased
galactic polar distance.

By an ingenious and careful consideration of the results of
the gauges already made, Struve found that on the average
there are 29°4 times (nearly 30 times) as many stars in the
centre of the Milky Wavy as in regions surrounding the
galactic poles. In northern galactic polar distances of
0°, 30°, 60°, 75°, and 90°, the relative numbers of the stars
in a telescopic field of vision of 15’ diameter, are 4:15, 6°52,
17°68, 30°30, and 122:00. Notwithstanding the great simi-
larity in the law of increase in the abundance of the stars, we

8° Outhnes of Astr., § 785.

CLUSTERS OF STARS. 189

again find in the comparison of these zones, an absolute pre-
ponderance® on the side of the more beautiful southern
heavens.

When in 1843 I requested Captain Schwinck (of the
Engineers) to communicate to me the distribution according
to right ascension of the 12148 stars (from the Ist to the 7th
inclusive), which, at Bessel’s suggestion, he had noted in his
Mappa celestis, he found in four groups—

Right Ascension 50° to 140° 3147 stars.

: 140° 230° S's«2627—,,
5 230° 320° «3523_—o#«,
e 320 50° 2851s,

These groups correspond with the more exact results of the
Etudes stellaires, according to which the maxima of stars
of the 1st to the 9th magnitude occur in the right ascension
6h. 40m. and 18h. 40m., and the minima in the right ascen-
sion of lh. 30m. and 13h. 30m.”

It is essential that, in reference to the conjectural structure
of the universe and to the position or depth of these strata
of conglomerate matter, we should distinguish among the
countless number of stars with which the heavens are
studded, those which are scattered sporadically, and those
which occur in separate, independent, and crowded groups.
The latter are the so-called stellar clusters or swarms, which
frequently contain thousands of telescopic stars in recogniz-
able relations to each other, and which appear to the unaided
eye as round nebule, shining like comets. These are, the

® Op. cit.,§ 795, 796; Struve, Etudes d’ Astr. stell. pp. 66,
73, (and note 75).

7 Struve, p. 59. Schwinck finds in his maps, R. A. 0°—90°,
2858 stars; R. A. 90 — 180°, 3011 stars; R. A. 180 — 270°,
2688 stars; R. A. 270° — 360, 3591 stars; sum total, 12148,
stars to the 7th magnitude.

190 COSMOS,

nebulous stars of Eratosthenes™ and Ptolemy, the nebulose
of the Alphonsine Tables in 1483, and the same of which
Galileo said in the Nuncitus sidereus, ** Sicut areole sparsim
per ethera subfulgent.”

These clusters of stars are either scattered separately
throughout the heavens, or closely and irregularly crowded
together, in strata, as it were, in the Milky Way, and in the
Magellanic clouds. The greatest accumulation of globular clus-
ters, and the most important in reference to the configuration of
the galactic circle, occurs in a region of the southern heavens”
between Corona Australis, Sagittarius, the tail of Scorpio, and
the Altar. (R. A. 16h. 45m.-19h.) All clusters in and near
the Milky Way are not, however, round and globular; there
are many of irregular outline, with but few stars and not a
very dense centre. In many globular clusters the stars are
uniform in magnitude, in others they vary. In some
few cases they exhibit a fine reddish central star.% (R. A.
2h. 10m.; N. Decl. 56° 21’.) It is a difficult problem in
dynamics to understand how such island-worlds, with their
multitude of suns, can rotate free and undisturbed. Nebulous
spots and clusters of stars appear subject to different laws
in their local distribution, although the former are now
very generally assumed to consist of very small, and still
more remote stars. The recognition of these laws must
specially modify the conjectures entertained of what has
been boldly termed the “structure of the heavens.” It is
moreover worthy of notice that, with an instrument of equal
aperture and magnifying power, round nebulous spots are
-more easily resolved into clusters of stars than oval ones.

™ On the nebula in the right hand of Perseus, (near the hilt

of his sword,) see Eratosth. Catast., c. 22, p. 51, Schaubach.
™ John Herschel’s Observations at the Cape, § 105, p. 136.
7 Outlines, § 864-869, pp. 591-596 ; Madler’s Astr., s. 764.
™ Observations at the Cape, § 29, p. 19.

CLUSTERS OF STARS 191

I will content myself with naming the following among the
isolated systems of clusters and swarms of stars.

The Pleiades: doubtless known to the rudest nations
from the earliest times; the mariner’s stars—Pleias, am rot
mheiv, (from mAeiy, to sail,) according to the etymology of the
old scholiast of Aratus, who is probably more correct than
those modern writers, who would derive the name from
mdéos, plenty. The navigation of the Mediterranean lasted
from May to the beginning of November, from the early
rising to the early setting of the Pleiades.

Presepe in Cancer: according to Pliny, nubecula quam
Presepia vocant inter Asellos, a vepédvov of the Pseudo-Eratos-
thenes.

The cluster of stars on the sword-hilt of Perseus, frequently
mentioned by Greek astronomers.

Coma Berenices, like the three former, visible to the naked eye.

A cluster of stars near Arcturus (No. 1663), telescopic:
R. A. 18h. 34m. 12s., N. Decl. 29° 14’; more than a thousand
stars from the 10th to the 12th magnitude.

Cluster of stars between n and ¢ Herculis, visible to the
naked eye in clear nights. A magnificent object in the
telescope (No. 1968), with a singular radiating margin;
R. A. 16h. 35m. 37s., N. Decl. 36° 47’; first described by
Halley in 1714.

A cluster of stars near » Centauri; described by Halley
as early as 1677; appearing to the naked eye as a round
cometic object, almost as bright as a star of the 4th or
5th magnitude; in powerful instruments it appears com-
posed of countless stars of the 13th to the 15th magnitude,
crowded together and most dense towards the centre;
R. A. 13h. 16m. 38s., S. Decl. 46° 35’; No. 3504 in Sir John
Herschel’s catalogue of the clusters of the southeru hemisphere,
15’ in diameter. (Observations at the Cape, pp. 21, 105;
Outlines of Astr., p. 595.)

192 | COSMOS.

Cluster of stars near « of the Southern Cross (No. 3435),
composed of many-coloured small stars from the 12th to
the 16th magnitude, distributed over an area of ~.th of a
square degree; a nebulous star, according to Lacaille, but so
completely resolved by Sir John Herschel that no nebulous
mass remained; the central star deep red. (Observations at
the Cape, pp. 17, 102, pl. 1, fig. 2.)

Cluster of stars, 47 Toucani, Bode; No. 2322 of Sir John
Herschel's catalogue, one of the most remarkable objects in the
southern heavens. I was myself deceived by it for several even-
ings, imagining it to be a comet, when, on my arrival at Peru, I
saw it in 12° south lat. rise high above the horizon. The visi-
bility of this cluster to the naked eye is increased by the
circumstance, that, although in the vicinity of the lesser
Magellanic cloud, it is situated in a part of the heavens con-
taining no stars, and is from 15 to 20’indiameter. It is ofa
pale rose colour in the interior, concentrically enclosed by a
white margin composed of small stars (14th to 16th mag.)
of about the same magnitude, and presenting all the charac-
teristics of the globular form.”

A cluster of stars in Andromeda’s girdle near y of this
constellation. The resolution of this celebrated nebula
into small stars, upwards of 1500 of which have been re-
cognized, appertains to the most remarkable discoveries
in the observing astronomy of the present day. The merit of
this discovery is due to Mr. Geo. Bond, assistant astronomer™
at the Observatory of Cambridge, United States, (March,

% «¢ A stupendous object—-a most magnificent globular
cluster,” says Sir John Herschel, ‘‘ completely insulated, upon
a ground of the sky perfectly b/ack throughout the whele
breadth of the sweep.” Observations at the Cape, pp. 18 and
51, Pl. iii. fig. 1; Outhnes, § 895, p. 615.

% Bond, in the Memoirs of the American Academy of Arta
and Sciences, new series, vol. iii. p. 75.

CLUSTERS OF STARS. 193

1848,) and testifies to the admirable illuminating power ot
the refractor of that Observatory which has an object-glass
fifteen inches in diameter; since even a reflector with a
specuium of eighteen inches in diameter did not reveal “a
trace of the presence of a star." Although it is probable
that the cluster in Andromeda was, at the close of the tenth
century, already recorded as a nebula of oval form, it is more
certain that Simon Marius (Mayer of Guntzenhausen), the
same who first observed the change of colour in scintillation,”
perceived it on the 15th of December, 1612; and that he was
the first who described it circumstantially, as a new starless
and wonderful cosmical body, unknown to Tycho Brahe. Half
a century later, Boulliaud, the author of Astronomia philolaica,
occupied himself with the same subject. This cluster of stars
which is 23° in length and more than 1° in breadth, is spe-
cially distinguished by two remarkable very narrow black
streaks, parallel to each other, and to the longer axis of the
cluster, which, according to Bond’s investigations, traverse the
whole length like fissures. This configuration vividly reminds
us of the singular longitudinal fissure, in an unresolved ne-
bula of the southern hemisphere, No. 3501, which has been
described and figured by Sir John Herschel. (Observations at
the Cape, pp. 20, 105, pl. iv. fig. 2.)

Notwithstanding the important discoveries for which we
are indebted to Lord Rosse and his colossal telescope, I
have not included the great nebula in Crion’s belt in this
selection of remarkable clusters of stars, as it appeared to me
more appropriate to consider those portions of it which have
been resolved, in the section on Nebula.

The greatest accumulation of clusters of stars, although by
no means of nebule, cecurs in the Milky Way,” (Galazias,

™ Outlines, § 874, p. 601.

% Delambre, Hist. del Astr. moderne, t. i. p- 697,

” We are indebted for the first and only complete description
VOL. III. 9

194 COSMOS,

the celestial river of the Arabs,”) which forms almost a great
circle of the sphere, and is inclined to the equator at an angle
of 68° The poles of the Milky Way are situated in Right
Ascension 12h. 47m. N. Decl. 27°; and R. A. Oh. 47m. S.
Decl. 27°; the south galactic pole therefore lies near Coma
Berenices, and the northern between Phcenix and Cetus.
While all planetary local relations are referred to the ecliptic,—
the great circle in which the plane of the sun’s path intersects
the sphere—we may as conveniently refer many of the
local relations of the fixed stars, as, for instance, that of their
accumulation or grouping, to the nearly complete circle of
the Milky Way. Considered in this light, the latter is to
the sidereal world what the ecliptic is to the planetary

of the Milky Way, in both hemispheres, to Sir John Herschel,
in his Results of Astronomical Observations, made during the
years 1834-1838, at the Cape of Good Hope, § 316-335,
and still more recently in the Outlines of Astronomy, § 787-
799. Throughout the whole of that section of the Cos-
mos which treats of the directions, ramifications, and various
contents of the Milky Way, I have exclusively followed the
above named Astronomer and Physicist. (Compare also
. Struve, Etudes dA str. stellaire, pp. 35-79 ; Madler, Ast., 1849,
§ 213; Cosmos, vol. i. pp. 88, 140, and 305.) I need scarcely
here remark that in my description of the Milky Way, in
order not to confuse certainties with uncertainties, I have
not referred to what I had myself observed with instruments
of a very inferior illuminating power, in reference to the very
great inequality of the light of the whole zone, during my
long residence in the southern hemisphere, and which I have
recorded in my journals.

* The comparison of the ramified Milky Way with a
celestial river, led the Arabs to designate parts of the con-
stellation of Sagittarius, whose bow falls in a region rich in
stars, as the cattle going to drink, and to associate with them the
ostrich, which has so little need of water. (Ideler, Untersuch-
ungen tiber den Ursprung und die Bedeutung der Sternnamen,
§ 78, 183, and 187; Niebuhr, Beschreibung von Arabien, s. 112.)

MILKY WAY. 195

world of our solar system. The Milky Way cuts tne equator
in Monoceros, between Procyon and Sirius, R. A. 6h. 54m.,
(for 1800), and in the left hand of Antinous, R. A. 19h. 15m.
The Milky Way, therefore, divides the celestial sphere into
two somewhat unequal halves, whose areas are nearly as 8 to
9. In the smaller portion lies the vernal solstice. The Milky
Way varies considerably in breadth in different parts of
its course. At its narrowest, and at the same time most
brilliant, portion, between the prow of Argo and the Cross,
and nearest to the Antarctic pole, its width is scarcely 3°
or 4°; at other parts it is 16°, and in its divided portion,
between Ophiuchus and Antinous, as much as 22.° William
Herschel has observed, that judging from his star-gaugings, the
Milky Way would appear in many regions to have 6° or 7°
greater width than we should be disposed to ascribe to it from
the extent of stellar brightness visible to the naked eye.*
Huygens, who examined the Milky Way with his twenty-
three feet refractor, declared, as early as the year 1656, that
the milky whiteness of the whole Galactic zone was not to be
ascribed to irresolvable nebulosity. A more careful application
of reflecting telescopes of great dimensions and power of light
has since proved, with more certainty, the correctness of the
conjectures advanced by Democritus and Manilius, in re-
ference to the ancient path of Phaéton, that this milky
glimmering light was solely owing to the accumulated strata
of small stars, and not to the scantily interspersed nebule.
This effusion of light is the same at points, where the whole
can be perfectly resolved into stars, and even in stars which
are projected on a black ground, wholly free from ne-
bulous vapour.“ It is a remarkable feature of the Milky

8 Qutiines, p. 529; Schubert, Asé., th. iii. s. 71.

* Struve, Etudes d@Astr. stellaire, p. 41.

® Cosmos, vol. i. p. 140.

* « Stars standing on a clear black ground.” (Qdservatwns
02

196 . COSMOS.

Way, that .t should so rarely exhibit any globular clusters
and nebulous spots of a regular or oval form ;® while both are
met with in great numbers at a remote distance from it; as,
for instance, in the Magellanic clouds, where isolated stars,
globular clusters in all conditions of condensation, and ne-
bulous spots of a definite oval or a wholly irregular form,
are intermingled. A remarkable exception to the rarity of
globular clusters in the Milky Way, occurs in a region be-
tween R. A. 16h. 45m. and 18h. 44m. between the Altar, the
Southern Crown, the head and body of Sagittarius, and the
tail of the Scorpion.*® ‘We even find betweens and 6 of the
latter one of those annular nebule, which are of such extremely
rare occurrence in the southern hemisphere.

In the field of view of powerful telescopes (and we must
remember that, avcording to the calculations of Sir William

at the Cape, p. 891). ‘* This remarkable belt (the Milky Way,
when examined through powerful telescopes) is found (won-
derful to relate!) ¢o consist entirely of stars scattered by millions,
like glittering dust on the black ground of the general heavens.”’
Outlines, pp. 182, 537, and 539.

% « Globular clusters, excepting in one region of small ex-
tent (between 16h. 45m. and 19h. in R. A.) and nebule of
regular elliptic forms, are comparatively rare in the Milky
Way, and are found congregated in the greatest abundance
in a part of the heavens the most remote possible from that
circle.” (Outlines, p. 614.) Hugyens himself, as early as 1656,
had remarked the absence of nebulosity and of all nebulous
spots in the Milky Way. In the same place where he mentions
the first discovery and delineation of the great nebulous spots
in the belt of Orion, by a twenty-eight-feet refractor (1656),
he says (as I have already remarked at p. 713 and note), viam
lacteam perspicillis inspectam nullas habere nebulas, and that
the Milky Way, like all that has been regarded as nebulous
stars, is a great cluster of stars. The passage is to be found
in Hugeniw Opera varia, 1724, p. 593.

© Observations at the Cape, § 105, 107, and 328. On the
aunular nebulw, No. 3686, see p. 114.

MILKY WAY. 197

Herschel, a twenty-feet instrument penetrates 900, and a
forty-feet one 2800 distances of Sirius) the Milky Way
appears as diversified in its sidereal contents as it is irregular
and indefinite in its outlines and limits when seen by the un-
aided eye. While in some parts the Milky Way exhibits,
throughout a large space, the greatest uniformity in the light
and apparent magnitudes of the stars, in others the most
brilliant patches of closely-crowded luminous points are inter-
rupted by granular or reticular darker™ intervals containing
but few stars; and in some of these intervals in the interior
of the Galaxy not the smallest star (of the 18m. or 20m.) is
to be discovered. It almost seems as though, in these regions,
we actually saw through the whole starry stratum of the
Milky Way. In gauging with a field of view of 15’ diameter,
fields presenting on an average forty or fifty stars are almost
immediately succeeded by others exhibiting from 400 to 500.
Stars of the higher magnitudes often occur in the midst of the
most minute telescopic stars, whilst all the intermediate classes
are absent. Perhaps those stars which we regard as be-
longing to the lowest order of magnitudes do not always ap-
pear as such, solely on account of their enormous distance, but
also because they actually have a smaller volume and less con-
siderable development of light.

In order rightly to comprehend the contrast presented by the
greater brilliancy, abundance, or paucity of stars, it will be ne-
cessary to compare regions most widely separated from each other.
The maximum of the accumulation and the greatest lustre of
stars are to be found between the prow of Argo and Sagittarius,
or, to speak more exactly, between the Altar, the tail of the
Scorpion, the hand and bow of Sagittarius, and the right foot
of Ophiuchus. “No region of the heavens is fuller of objects,

* “Intervals absolutely dark and completely void of any star
of the smallest telescopic magnitude.” Outlines, p. 586.

198 _ COSMOS.

beautiful and remarkable in themselves, and rendered stiil
more so by their mode of association” and grouping.® Next in
brightness to this portion of the southern heavens is the pleasing
and richly-starred region of our northern hemisphere in Aquila
and Cygnus, where the Milky Way branches off in different
directions. While the Milky Way is the narrowest under the
foot of the Cross, the region of minimum brightness (where
there is the greatest paucity of stars in the Galactic zone) is
in the neighbourhood of Monoceros and Perseus.

The magnificent effulgence of the Milky Way in the
southern hemisphere is still further increased by the circum-
stance, that between the star » Argis, which has become so
celebrated in consequence of its variability, and @ Crucis, under
the parallels of 59° and 60° south lat., it is intersected at an angle
of 20° by the remarkable zone of very large and probably very
proximate stars, to which belong the constellations Orion,
Canis Major, Scorpio, Centaurus, and the Southern Cross. The
direction of this remarkable zone is indicated by a great circle
passing through « Orionis and the foot of the Cross. The pic- ©

%® «No region of the heavens is fuller of objects, beautiful
and remarkable in themselves, and rendered still more so by
their mode of association, and by the peculiar features as-
sumed by the Milky Way, which are without a parallel in any
other part of its course.” Observations at the Cape, p. 386.
This vivid description of Sir John Herschel entirely coincides
with the impressions I have myself experienced. Capt. Jacob,
of the Bombay Engineers, in speaking of the intensity of light
in the Milky Way, in the vicinity of the Southern Cross, re-
marks with striking truth, ‘‘ Such is the general blaze of star-
light near the Cross from that part of the sky, that a person
is immediately made aware of its having risen above the
horizon, though he should not be at the time looking at the
heavens, by the increase of general illumination of the atmo-
sphere, resembling the effect of the young moon.” (See Piazzi
Smyth, On the orbit of a Centaurz, in the Transact. of the Royat
Soc. of Edinburgh, vol. xvi. p. 445.)

MILKY WAY. 199

turesque effect of the Milky Way, if I may use the expression,
is increased in both hemispheres by its various ramifications.
It remains undivided for about two-fifths of its length. Ac-
cording to Sir John Herschel’s observations the branches
separate in the great bifurcation, at a Centauri,” and not at
8 Cent., as given in our maps of the stars, or, as was asserted by
Ptolemy,” in the constellation of the Altar; they reunite again
in Cygnus.

In order to obtain a general insight into the whole course
and direction of the Milky Way with its subdivisions, we
will briefly consider its parts, following the order of their
Right Ascension. Passing through y and ¢« Cassiopeic, the
Milky Way sends forth towards s Persei a southern branch
which loses itself in the direction of the Pleiades and Hyades.
The main stream, which is here very faint, passes on through
Auriga, over the three remarkable stars «, ¢, 7, the Heedi of
thatconstellation, preceding Capella between the feet of Gemini
and the horns of the Bull, (where it intersects the ecliptic
nearly in the solstitial colure,) and thence over Orion’s club to
the neck of Monoceros, intersecting the equinoctial (in 1800
at R.A.6h.54m. From this point the brightness considerably
increases. At the stern of Argo one branch runs southward to
y Argis, where it terminates abruptly. The main stream is
continued to 33° S. Decl., where, after separating in a fan-
like shape (20° in breadth) it again breaks off, so that there is
a wide gap in the Milky Way in the line from y to A Argis.
It begins again in a similar fan-like expansion, but contracts
at the hind feet of the Centaur and before its entrance into

® Outlines, § 789, 791; Observations at the Cape, § 325.

* Almagest, lib. viii. cap. 2, (t. ii. pp. 84, 90, Halma),
Ptolemy’s description is admirable in some parts, especially
when compared with Aristotle’s treatment of the subject of
the Milky Way, in Meteor. (lib. i. pp. 29, 34, according to
Ideler’s edition)

20/) COSMOS.

the Southern Cross, where it is at its narrowest part, aud 16
only °° or 4° in width. Soon after this che Milky Way again
expands into a bright and broad mass, which encloses 8 Cen-
tauri as-well as a and 8 Crucis, and in the midst of which lies
the black pear-shaped coal-sack, to which I shall more specially
refer in the 7th section. In this remarkable region, somewhat
below the coal-sack, the Milky Way approaches nearest to
the South Pole.

The above-mentioned bifurcation, which begins at a Cen-
tauri, extended, according to older views, to the constellation
Cygnus. Passing from a Centauri, a narrow branch runs
northwards in the direction of the constellation Lupus, where
it seems gradually lost; a division next shows itself at y
Norme. ‘The northern branch forms irregular outlines till it
reaches the region of the foot of Ophiuchus, where it wholly
disappears ; the most southern branch then becomes the main-
stream, and passes through the Altar and the tail of the Seor-
pion, in the direction of the bow of Sagittarius, where it
intersects the ecliptic in 276° long. It next runs in an irre-
gular patchy and winding stream through Aquila, Sagitta, and
Vulpecula up to Cygnus; between e, a, and y, of which con-
stellation a broad dark vacuity appears, which, as Sir John
Herschel says, is not unlike the southern coal-sack, and
serves as a kind of centre for the divergence of three great
streams." One of these, which is very vivid and conspi-
cuous, may be traced running backward, as it were, through
8 Cygni and s Aquila, without, however, blending with the
stream already noticed, which extends to the foot of Ophiuchus,
A considerable offset or protuberant appendage is also
thrown off by the northern stream from the head of Cepheus,

Outlines, p. 531. The strikingly dark spot between
a and y Cassiopeie is also ascribed to the contrast with the
brightness by which ‘it is surrounded. See Struve, Etudes

stell., note 58.

MILKY WAY. 201

and therefore near Cassiopeia, (from which constellation we
began our description of the Milky Way) towards Ursa Minor
and the pole.

From the extraordinary advancement which the applica-
tion of large telescopes/has gradually effected in our know-
ledge of the sidereal contents and of the differences in the con-
centration of light observable in individual portions of the
Milky Way, views of merely optical projection have been re-
placed by others referring rather to physical conformation.
Thomas Wright of Durham,” Kant, Lambert, and at first
also Sir William Herschel, were disposed to consider the form
of the Milky Way, and the apparent accumulation of the stars
within this zone, as a consequence of the flattened form and
unequal dimensions of the world-island (starry stratum,) in
which our solar system is included. The hypothesis of the
uniform magnitude and distribution of the fixed stars has
recently been attacked on many sides. The bold and gifted
investigator of the heavens, Wm. Herschel, in his last works,
expressed himself strongly in favour of the assumption of an
annulus of stars; a view which he had contested in the talented
treatise he composed in 1784. The most recent observations
have favoured the hypothesis of a system of separate concentric
rings. The thickness of these rings seems very unequal; and
the different strata whose combined stronger or fainter light
we receive, are undoubtedly situated at very different altitudes,

® De Morgan has given an extract of the extremely rare
work of Thomas Wright of Durham, (Theory of the Universe,
London, 1750,) p. 241 in the Philos. Magazine, ser. iii.
no. 32. Thomas Wright, to whose researches the attention
of astronomers has been so permanently directed since the
beginning of the present century, through the ingenious
speculations of Kant and Wiliiam Herschel, observed only
with a reflector of one foot focal length.

* Efaff, in Will. Herschel's stimmil. Schriften, bd. i. (1826)
s. 78-81; Struve, Etudes stell., pp. 35-44.

202 - COSMOS.

t.e. at very unequal distances from us; but the relative bright.
ness of the separate stars which we estimate as of the 10th te
the 16th magnitude, cannot be regarded as affording sufficient
data to enable us in a satisfactory manner to deduce numeri.
cally from them the radius of their spheres of distances.™

In many parts of the Milky Way the space-penetrating
power of instruments is sufficient to resolve whole star-clouds,
and to show the separate luminous pvuints projected on the dark
starless ground of the heavens. We here actually look through
as into free space. ‘It leads us,’’ says Sir John Herschel,‘ irre-
sistibly to the conclusion that in these regions we see fairly
through the starry stratum.’”® In other region. we see as it
were through openings and. fissures, remote world-islands, or
outbranching portions of the annular system; in other parts,
again, the Milky Way has hitherto been fathomless, even with
the forty-feet telescope.* Investigations on the different in-
tensity of light in the Milky Way, as well as on the magni-
tudes of the stars, which regularly increase in number from the
galactic poles to the circle itself (an increase especially ob-
servable for 30° on either side of the Milky Way in stars
below the 11th magnitude,” and therefore in 44 of all the

1

* Encke, in Schumacher’s Astr. Nachr., no. 622, 1847,
s. 341-346.

% Outlines, pp. 586, 537, where we find the following
words on the same subject :—‘ In such cases it is equally
impossible not to perceive that we are looking through a sheet
of stars nearly of a size, and of no great thickness compared
with the distance which separates them from us,”

*% Struve, Etudes stell., p. 63. Sometimes the largest
instruments reach a portion of the heavens, in which the
existence of a starry stratum, shining at a remote distance, is
only announced by “ an uniform dotting or stippling of the
field of view.” See, in Observations at the Cape, p. 390, the
section ‘On some indications of very remote telescopic
branches of the Milky Way, or of an independent siderea]
system or systems bearing a resemblance to such branches.”’

% Observations at the Cape, § 314.

MILKY WAY. 293

stars), have led the most recent investigator of the southern
hemisphere to remarkable views and probable results in re-
ference to the form of the galactic annular system, and
what has beea boldly called the suwn’s place in the world-
island to which this annular system belongs. The place
assigned to the sun is eccentric, and probably near a point
where the stratum bifurcates or spreads itself out into twa
sheets,” in one of those desert regions lying nearer to the
Southern Cross than to the opposite node of the Milky Way.”
“The depth at which our system is plunged in the sidereal
stratum, constituting the galaxy, reckoning from the southern
surface or limit of that stratum, is about equal to that distance
which on a general average corresponds to the light of a star
of the 9th or 10th magnitude, and certainly does not exceed
that corresponding to the 11th.” Where, from the peculiar
nature of individual problems, measurements and the direct
evidence of the senses fail,we see but dimly those results which
intellectual contemplation, urged forward by an intuitive im-
pulse, is ever striving to attain.

*® Sir William Herschel, in the Philos. Transact. for 1785,
p. 21; Sir John Herschel, Observations at the Cape, § 293.
Compare also Struve, Descr. de I’Observatoire de Poulkova,
1845, pp. 267-271. |

* «T think,” says Sir John Herschel, “ it is impossible to
view this splendid zone from a Centauri to the Cross without
an impression amounting almost to conviction, that the
Milky Way is not a mere stratum, but annular; or, at least,
that our system is placed within one of the poorer or almost
vacant parts of its general mass, and that eccentrically, so as
to be much nearer to the region about the Cross than to that
diametrically opposite to it.” (Mary Somerville, On the
Connexion of the Physical Sciences, 1846, p. 419.)

1® Observations at the Cape, § 315.

294 COSMOS.

IV.

NEW STARS AND STARS THAT HAVE VANISHED.—VARIABLR
| STARS, WHOSE. RECURRING PERIODS HAVE BEEN DETER-
. MINED.—VARIATIONS IN THE INTENSITY OF THE LIGHT
OF STARS WHOSE PERIODICITY IS AS YET UNINVESTI-

' GATED.

New Srars.—The appearance of hitherto unseen stars in
the vault of heaven, especially the sudden appearance of
strongly scintillating stars of the first magnitude, is an
occurrence in the realms of space which has ever excited
astonishment. This astonishment is the greater, in propor-
tion as such an event as the sudden manifestation of what
was before invisible, but which nevertheless is supposed
to have previously existed, is one of the very rarest phe-
nomena in nature. While in the three centuries from
1500 to 1800, as many as forty-two comets, visible to
the naked eye, have appeared to the inhabitants of the
northern hemisphere—on an average, fourteen in every
hundred years—only eight new stars have been observed
throughout the same period. The rarity of the latter be-
comes still more striking, when we extend our consideration
to yet longer periods. From the completion of the Alphonsine
tables, an important epoch in the history of astronomy, down
to the time of William Herschel—that is, from 1252 to
1800—the number of visible comets is estimated at about
sixty-three, while that of new stars does not amount to more
than nine. Consequently, for the period during which, in the
civilized countries of Europe, we may depend on possessing
a tolerably correct enumeration of both, the proportion of
new stars to comets visible to the naked eye is as one ty

NEW STARS. 203

seven. We shall presently show that if from the tail-less
comets we separate the new stars which, according to the
records of Ma-tuan-lin, have been observed in China, and
go back to the middle of the second century before the
Christian era, that for about 2000 years scarcely more than
twenty or twenty-two of such phenomena can be adduced
with certainty.

Before I proceed to general considerations, it seems not
inappropriate to quote the narrative of an eye-witness, and
by dwelling on a particular instance to depict the vividness
of the impression produced by the sight of a new star. ‘On
my return to the Danish islands, from my travels in Germany,”
says Tycho Brahe, ‘‘I resided for some time with my uncle,
Steno Bille (ut aulice vite fastidium lenirem), in the old and
pleasantly situated monastery of Herritzwadt; and here I
made it a practice not to leave my chemical laboratory until
the evening. Raising my eyes, as usual, during one of my
walks, to the well-known vault of heaven, I observed, with
indescribable astonishment, near the zenith, in Cassiopeia, a
radiant fixed star, of a magnitude never before seen. In my
amazement, I doubted the evidence of my senses. However,
to convince myself that it was no illusion, and to have the testi-
mony of others, I summoned my assistants from the labora-
tory, and inquired of them, and of all the country people
that passed by, if they also observed the star that had thus
suddenly burst forth. Isubsequently heard that, in Germany,
waggoners and other common people first called the attention
of astronomers to this great phenomenon in the heavens—a
circumstance which, as in the case of non-predicted comets,
furnished fresh occasion for the usual raillery at the expense of
the learned.

‘This new star,’ Tycho Brahe continues, ‘I found to be with-
out a tail, not surrounded by any nebula, and perfectly like all
other fixed stars, with the exception that it scintillated more

206 - COSMOS.

strongly than stars of the first magnitude. Its brightnesa
was greater than that of Sirius, a Lyre, or Jupiter. For
splendour, it was only comparable to Venus when nearest
to the earth (that is, when only a quarter of her dise is illu-
minated). Those gifted with keen sight could, when the air
was clear, discern. the new star in the day-time, and even at
noon. At night, when the sky was overcast, so that all
other stars were hidden, it was often visible through the clouds,
if they were not very dense (nubes non admodum densas).
Its distances from the nearest stars of Cassiopeia, which
throughout the whole of the following year I measured with
great care, convinced me of its perfect immobility. Al-
ready, in December, 1572, its brilliancy began to diminish,
and the star gradually resembled Jupiter; but by January,
1573, it had become less bright than that planet. Successive
photometric estimates gave the following results: for Febru-
ary and March, equality with stars of the first magnitude
(stellarum affixarum primi honoris—for Tycho Brahe seems to
have disliked using Manilius’s expression of stellee fixe); for
April and May, with stars of the second magnitude; for July
and August, with those of the third; for October and November,
those of the fourth magnitude. Towards the month of No-
vember, the new star was not brighter than the eleventh
in the lower part of Cassiopeia’s chair. The transition to
the fifth and sixth magnitude took place between December,
1573, and February, 1574. In the following month, the new
star disappeared, and, after having ‘shone seventeen months,
was no longer discernible to the naked eye.” (The telescope
was not invented until thirty-seven years afterwards.)

The gradual diminution of the star’s luminosity was more-
over invariably regular; it was pot (as is the case in the
present day with 7 Argis, though indeed that is not to be
called a new star) interrupted by several periods of re-kindling
or by increased intensity of light. Its colour also changed with

‘ NEW STARS. 207

its brightness (a fact which subsequently gave rise to many
-erroneous conclusions as to the velocity of coloured rays in
their passage through space). At its first appearance, as long
as it had the brilliancy of Venus and Jupiter, it was for two
months white, and then it/passed through yellow into red. In
the spring of 1573, Tycho Brahe compared it to Mars; after-
wards he thought that it nearly resembled Betelgeuze, the star in
the right shoulder of Orion. Its colour for the most part was like
the red tint of Aldebaran. In the spring of 1578, and especially
in May, its white colour returned (albedinem quandam sublivi-
dam induebat, qualis Saturni stelle subesse videtur). So it re-
mained in January, 1574; being, up to the time of its entire
disappearance in the month of March, 1574, of the fifth
magnitude,and white, but of a duller whiteness, and exhibiting
a remarkably strong scintillation in proportion to its faint-
ness.

The circumstantial minuteness of these statements! is of
itself a proof of the interest which this natural phenomenon
could not fail to awaken, by calling forth many important -
questions, in an epoch so brilliant in the history of astro-
nomy. For (notwithstanding the general rarity of the
appearance of new stars) similar phenomena, accidentally
crowded together within the short space of thirty-two
years, were thrice repeated within the observation of Euro-
pean astronomers, and consequently served to heighten the
excitement. The importance of star-catalogues, for ascer-

1 De admiranda Nova Stella, anno 1572, exorta in T; ycho
nis Brahe, <Astronomie instaurate Progymnasmata, 16038,
pp- 298-304, and 578 In the text I have closely followed
the account which Tycho Brahe himself gives. The very
doubtful statement (which is, however, repeated in several
astronomical treatises) that his attention was first called
to the phenomenon of the new star by a concourse of country
people, need not therefore be here noticed.

208 COSMOR.

taining .he date of the sudden appearance of any star, was
more and more recognized; the periodicity* (their re-appear- —
ance after many centuries) was discussed ; and Tycho Brahe
himself boldly advanced a theory of the process by which
stars might be formed and moulded out of cosmical vapour,
which presents many points of resemblance to that of
the great William Herschel. He was of opinion that the
vapoury cclestial matter which becomes luminous as it
condenses, conglomerates into fixed stars: ‘‘ Coli mate-
riam tenuissimam, ubique nostro visui et planetarum circuitibus
perviam, in unum globum condensatam, stellam effingere.”
This celestial matter, which is universally dispersed through
space, has already attained to a certain degree of condensation
in the Milky Way, which glimmers with a soft silvery bright-
ness. Accordingly, the place of the new star, as well as of
those which became suddenly visible in 945 and 1264, was on
the very edge of the Milky Way (quo factum est quod nova
stella in ipso galaxie margine constiterit). Indeed, some
went so far as to believe that they could discern the very spot
(the opening or hiatus) whence the nebulous celestial matter
had been drawn from the Milky Way.* All this reminds one

_ ? Cardanus, in his controversy with Tycho Brahe, went
back to the star of the Magi, which, as he pretended, was
identical with the star of 1572. Ideler, arguing from his
own calculations of the conjunctions of Saturn with Jupiter,
and from similar conjectures advanced by Kepler on the
appearance of the new star in Ophiuchus in 1604, supposes
that the star of the Magi, through a confusion of aorjp with
dorpov, which is so frequent, was not a single great star, but
a remarkable conjunction of stars,—the close approximation
of two brightly shining planets at a distance of less than a
diameter of the moon. TZychonis Progymnasmata, pp. 324-
330; contrast with Ideler, Handbuch der mathematischen und
technischen Chronologie, bd. ii. s. 399-407.

* Progymn., pp. 324-330. Tycho Brahe, in his theory of
the formation of new stars from the Cosmical vapour of the

VEMPORARY STARS. 209

of the theories of transition of the cosmical vapour :rto clus-
ters of stars, of an agglomerative force, of a concentration
to a central nucleus, and of hypotheses of a gradual formation
of solid bodies out of a vaporous fluid;—views which were
generally received in the beginning of the nineteenth cen-
tury, but which at present, owing to the ever-changing
fluctuations in the world of thought, are in many respects
exposed to new doubts.

Among newly-appeared temporary stars the following
(though with variable degrees of certainty) may be reckoned.
I have arranged them according to the order in which they
respectively appeared.

(a) 134 B.c. in Scorpio.

(6) 123 a.p. in Ophiuchus,

es Ra . in Centaurus.

mrad ye)

(e) 386 ,, in Sagittarius.

(f) 389 _ ,; in Aquila.

(g) 393 ,, in Scorpio.

(A) 827 ,, in Scorpio.
(#) 945. ,, between Cepheus and Cassiopeis.
(4) 1012 ,, in Aries. .

(2) 1203, in Scorpio.

(m) 1230, in Ophiuchus.

(n) 1264 ,, between Cepheus and Cassiopeia.
(0) 1572 __,, in Cassiopeia.

(p) 1578 ,,

(gq) 1584 ,, in Scorpio.

(r) 1600 ,, in Cygnus.

(s) 1604 _,, in Ophiuchus.

Milky Way, builds much on the remarkable passages of Aris-
totle on the connexion of the tails of comets (the vapoury
radiation from their nuclei with the galaxy to which I haye
already alluded. ‘Cosmos, vol. i. p. 88.)

VOL. III. P

210 CusSMOS,

CO A600 sas ES
(et) 0G205 os . in Vulpes.
(v) 1845 ,, - in Ophiuchus,

EXPLANATORY REMARKS,

(a) This star first appeared in July, 1384 years before our
era. We have taken it from the Chinese Records of Ma-
tuan-lin, for the translation of which we are indebted to the
learned linguist Edward Biot (Connaissance des Temps pour
lan 1846, p.61). Its place was between 8 and p of Scorpio.
Among the extraordinary foreign-looking stars of these records,
called also guest-stars, (é¢oiles hétes, “* Ke-sing,” strangers of a
singular aspect,) which are distinguished by the observers.
from comets with tails, fixed new stars and advancing tail-less
comets are certainly sometimes mixed up. But in the record
of their motion (Ke-sing of 1092, 1181, and 1458), and in
the absence of any such record, as also in the occasional
addition, *‘the Ke-sing dissolved” (disappeared), there is
contained, if not an infallible, yet a very important criterion.
Besides, we must bear in mind that the light of the nu-
cleus of all comets, whether with or without tails, is dull,
never scintillates, and exhibits only a mild radiance, whiie
the luminous intensity of what the Chinese call extraor-
dinary (stranger) stars, has been compared to that of
Venus,—a circumstance totally at variance with the na-
ture of comets in general, and especially of those with-
out tails. The star which appeared in 134 B.c., under the
old Han dynasty, may, as Sir John Herschel remarks, have
been the new star of Hipparchus, which, according to the
statement of Pliny, induced him to commence his catalogue
of the stars. Delambre twice calls this statement a fiction,
“une historiette.”” (Hist. de ’ Astr. anc., t. i. p. 290; and
Hist. de V Astr. mod., t. i. p. 186.) Since, according to
the express statement of Ptolemy (Almag. vii. p. 2, 13
Haima), the catalogue of Hipparchus belongs to the year
128 3.c., and Hipparchus (as I have already remarked else-
where) carried on his observations in Rhodes (and perhaps
also in Alexandria), from 162 to 127 B.c., there is nothing
ureconcilable with this conjecture. It is very probable that
the great Nicean astronomer had pursued his observations for

—_—

TEMPORARY STARS. 211

a considerable period before he conceived the idea of forming
a regular catalogue. The words of Pliny, ‘suo evo genita,”’
apply to the whole term of his life. After the appearance
of Tycho Brahe’s star in 1572, it was much disputed whether
the star of Hipparchus ought to be classed among new stars, or
comets without tails. Tycho Brahe himself was of the former
opinion (Progymn., pp. 319-325). The words “ejusque motu
addubitationem adductus,’ may undoubtedly lead to the
supposition of a faint, or altogether tail-less comet; but
Pliny’s rhetorical style admitted of such vagueness of ex-
pression.

(6) A Chinese observation. It appeared in December, a.p.
123, between a Herculis and z Ophiuchi. Ed. Biot, from
Ma-tuan-lin. (It is also asserted that a new star appeared in
the reign of Hadrian, about a.p. 130.)

(c) A singular and very large star. This also is taken
from Ma-tuan-lin, as well as the three following ones.

It appeared on the 10th of December, 173, between «
and 8 Centauri, and at the end of eight months disappeared,
after exhibiting the five colours one after another. ‘* Succes-
sivement”’ is the term employed by Ed. Biot in his trans-
lation. Such an expression would almost tend to suggest a
series of colours similar to those in the above described
star of Tycho Brahe; but Sir John Herschel more correctly
takes it to mean a coloured scintillation (Outlines, p. 563), and
Arago interprets in the same way a nearly similar expression
employed by Kepler when speaking of the new star (1604) in
Ophiuchus. (Annuaire pour 1842, p. 347.)

(d) This star was seen from March to August, 369.

(e) Between a and ¢ Sagittarii. In the Chinese Record
it is expressly observed, ‘‘ where the star remained (¢. e.
without movement) from April to July, 386.”

(f) A new star, close to a Aquile. In the year 389,
in the reign of the Emperor Honorius, it shone forth with
the brilliancy of Venus, according to the statement of Cus-
~inianus, who had himself seen it. It totally disappeared in
about three weeks.‘

* Other accounts place the appearance in the year 38?
or 398. Jacques Cassini, Elémens d’ Astronomie, 1740 (Etoile
nouvelles), p. 59.

P2

212 : CosMOs.

(g) March, 393. This star was also in Scorpio, in the tail of
that constellation. From the Records of Ma-tuan-lin.

(kh) The precise year (827) is doubtful. It may with
more certainty be assigned to the first half of the ninth century,
when in the reign of Caliph Al Mamoun the two famous Arabian
astronomers, Haly and Giafar Ben Mohammed Albumazar
observed at Babylon a new star, whose light, according to
their report, ‘equalled that of the moon in her quarters.”
This natural phenomenon likewise occurred in Scorpio. The
star disappeared after a period of four months.

(«) The appearance of this star (which is said to have
shone forth in the year 945, under Otho the Great), like
that of 1264, is vouched for solely by the testimony of the
Bohemian astronomer Cyprianus Leovitius, who asserts that
he derived his statements concerning it from a manuscript.
chronicle. He also calls attention to the fact, that these two
phenomena (that in 945 and that in 1264) took place between
the constellations of Cepheus and Cassiopeia, close to the
Milky Way, and near the spot where Tycho Brahe’s star
appeared in 1572. Tycho Brahe (Progym., pp. 331 and 709)
defends: the credibility of Cyprianus Leovitius, against the
attacks of Pontanus and Camerarius, who conjectured that the
statements arose from a confusion of new stars with long-
tailed comets.

(k) According to the statement of Hepidannus, the monk
of St. Gall (who died a.p. 1088, whose annals extend from
the year a.D. 709 to 1044), a new star of unusual magnitude
and of a brilliancy that dazzled the eye (oculos verberans),
was, for three months, from the end of May in the year 1012,
to be seen in the south, in the constellation of Aries. In
a most singular manner it appeared to vary in size, and
occasionally it could not be seen at all. ‘ Nova: stella
apparuit insolite magnitudinis, aspectu fulgurans: et. oculos
verberans non sine terrore. Que mirum in modum ali-
quando contractior, aliquando diffusior, etiam extinguebatur
interdum. Visa est autem per tres menses in intimis finibus
Austri, ultra omnia signa que videntur in celo.” (See Hepi-
danni Annales breves, in Duchesne, Historie Francorum
Scriptores, t. iii. 1641, p. 477. Compare also Schnurrer,
Chrontk der Seuchen, th. i. s. 201). To the manuscript made
use of by Duchesne and Goldast, which assigns, the pheno-

TEMPORARY STARS. 213

menon to the year 1012, modern historical criticism has,
however, preferred another manuscript which, as compared
with the former, exhibits many deviations in the dates
throwing them six years back. Thus, it places the appearance
of this star in 1006. (See Annalse Sangallenses majores, ir
Pertz, Monumenta Germania historica Scriptcrum, t. i. 1826
p. 81.) Even the authenticity of the writings of Hepidannus
has been called into question by modern critics. The singular
phenomenon of variability has been termed by Chladni the
conflagration and extinction of a fixed star. Hind (Notices of
the Astron. Soc., vol. viii. 1848, p. 156) conjectures that
this star of Hepidannus is identical with a new star, which
is recorded in Ma-tuan-lin, as having been seen in China,
in February, 1011, between ¢ and 9 of Sagittarius. But in
that case there must be an error in Ma-tuan-lin, not only in
the statement of the year, but also of the constellation in
which the star appeared.

(Z) Towards the end of July, 1203, in the tail of Scorpio.
According to the Chinese Record, this new star was “of a
bluish-white colour, without luminous vapour, and resembled
Saturn.” (Edouard Biot, in the Connaissance des Temps pour
1846, p. 68.)

(m) Another Chinese observation, from Ma-tuan-lin, whose
astronomical records, containing an accurate account of the
positions of comets and fixed stars, go back to the year 613
B.c., to the times of Thales and the expedition of Coleus of
Samos. This new star appeared in the middle of December,
1230, between Ophiuchus and the Serpent. It dissolved
towards the end of March, 1231.

(n) This is the star mentioned by the Bohemian astro-
nomer, Cyprianus Leovitius (and referred to under the 9th
star, in the year 945). About the same time (July, 1264), a
great comet appeared, whose tail swept over one half of the
heayens, and which, therefore, could not be mistaken for a
new star suddenly appearing between Cepheus and Cas-
siopeia.

{o) This is Tycho Brahe’s star of the 11th of November,
1572, in the Chair of Cassiopeia, R. A. 3° 26’; Decl. 63° 3’
(for 1800).

(p) February. 1578. Taken from Ma-tuan-lin. The con-
stellation is not given, but the intensity and radiation of the

14 COSMOS.

light must have been extraordinary, since the Chinese Record
uppends the remark, ‘‘a star as large as the sun!”’

(q) On the Ist of July, 1584, not far from of Scorpio;
also a Chinese observation.

(r) According to Bayer, the star 34 of Cygnus. Wilhelm
Jansen, the celebrated geographer, who for a time had been
the associate of Tycho Brahe in his observations, was the first,
as an inscription on his celestial globe testifies, to draw atten-
tion to the new star in the breast of the Swan, near the
beginning of the neck. Kepler, who, after the death of
Tycho Brahe, was for some time prevented from carrying on
any observations, both by his travels and want of instruments,
did not observe it till two years later, and indeed (what is
the more surprising, since the star was of the 3rd magni-
tude) then first heard of its existence. He thus writes :—
‘‘Cum mense Maio, anni 1602, primum litteris monerer de
novo Cygni phenomeno.” (Kepler, De Stella nova tertit
honoris in Cygno, 1606, which is appended to the work De
Stella nova wm Serpent., pp. 152, 154,164, and 167.) In
Kepler’s treatise it is nowhere said (as we often find asserted
in modern works) that this star of Cygnus upon its first
appearance was of the Ist magnitude. Kepler even calls it
** parva Cygni stella,” and speaks of it throughout as one of
the 3rd magnitude. He determines its position in R. A.
300° 46’; Decl. 36° 52’ (therefore for 1800: R. A, 302° 36’;
Decl. + 37° 27’). The star decreased in brilliancy, especially
after the year 1619, and vanished in 1621. Dominique
Cassini (see Jacques Cassini, Hlémens d’ Astr., p. 69) saw it,
in 1655, again attain to the 3rd magnitude, and then dis-
appear. Hevelius observed it again in November, 1665, at
first extremely small, then larger, but never attaining to the
3rd magnitude. Between 1677 and 1682 it decreased to
the 6th magnitude, and as such it has remained in the
heavens. Sir John Herschel classes it among the variable
stars, in which he differs from Argelander.

(s) After the star of 1572 in Cassiopeia, the most famous
of the new stars is that of 1604 in Ophiuchus (R. A. 259° 42’;
and S. Decl. 21° 15’, for 1800). With each of these stars a
great name is associated. The star in the right foot of
Ophiuchus was originally discovered, on the 10th of October,
1604, not by Kepler himself, but by his pupil, the Bohemian

TEMPORARY STARS. 215

astroncmer, Juhn Bronowski. It was larger than all stars of
the first order, greater than Jupiter and Saturn, but smaller
than Venus. Herlicius asserts that he had previously seen
it on the 27th of September. Its brilliancy was less than
that of the new star, discovered by Tycho Brahe in 1572.
Moreover, unlike the latter, it was not discernible in the day-
time. But its scintillation was considerably greater, and
especially excited the astonishment of all who sawit. As
scintillation is always a¢companied with dispersion of colour,
much has been said of its coloured, and continually changing
light. Arago (Annuaire pour 1834, pp. 299-301, and Ann.
pour 1842, pp. 345-347) has already called attention to the
fact that the star of Kepler did not by any means, like that
of Tycho Brahe, assume, at certain long intervals, different
colours, such as yellow, red, and then again white. Kepler
says expressly that his star, as soon as it rose above the
exhalations of the earth, was white. When he speaks of
the colours of the rainbow, it is to convey a clear idea of its
coloured scintillation. His words are: ‘*‘ Exemplo adamantis
multanguli, qui solis radios inter convertendum ad spectan-
tium oculos variabili fulgore revibraret, colores Iridis (stella
nova in Ophiucho) successive vibratu continuo reciprocabat.”
(De nova Stella Serpent., pp. 5 and 125.) In the beginning
of January, 1605, this. star was even brighter than Antares,
but less luminous than Arcturus. By the end of March in
the same year, it was described as betng of the 3rd magni-
tude. Its proximity to the sun prevented all observation for
four months. Between February and March, 1606, it totally
disappeared. The inaccurate statements as to the great
variations in the position of the new star, advanced by
Scipio Claramontius and the geographer Blaew, are scarcely
(as Jacques Cassini, Eiémens d’Astr., p. 65, long since
observed) deserving of notice, since they have been refuted
by Kepler’s more. trustworthy treatise. The Chinese Record
of Ma-tuan-lin mentions a phenomenon which exhibits some
points of resemblance, as to time and position, with this
sudden appearance of a new star in Ophiuchus. On the 30th
cf September, 1604, there was seen in China a reddish-
yellow (‘‘ ball-like?’’) star, not far from « of Scorpio. It
shone in the south-west till November of the same year,
when it became invisible. It re-appeared on the 14th of
January, 1605, in the south-east; but its light becaine

216 cosmos.

slightly duller by March, 1606. (Connaissance des Temps pour
1846, p. 59.) ‘The locality, * of the Scorpion, might easily
be confounded with the foot of Ophiuchus; but the expres-
sions south-west and south-east. its re-appearance, and the
circumstance that its ultimate total disappearance is not
mentioned, leave some doubts as to its identity.

(¢) This also is a new star of considerable magnitude and
seen in the south-west. It is mentioned in Ma-tuan-lin. No
further particulars are recorded.

(w) This is the new star discovered by the Carthusian monk
Anthelmus on the 20th of June, 1670, in the head of Vulpes,
(R. A. 294° 27’; Decl. 26° 47',) and not far from 8 Cygni.
At its first appearance, it was not of the first, but merely
of the 38rd magnitude, and on the 10th of August it
diminished. to the 5th. It disappeared after three months,
but showed itself again on the 17th of March, 1671, when it
was of the 4th magnitude. Dominique Cassini observed it
very closely in April, 1671, and found its brightness very
variable. The new star is reported to have regained its
original splendour after ten months, but in February, 1672, it
was looked for in vain. It did not re-appear until the 29th
of March in the same year, and then only as a star of the 6th
magnitude; since that time it has never been observed.
(Jacques Cassini, Elémens d Astr., pp. 69-71.) These
phenomena induced Dominique Cassini to search for stars
never before seen (by him!). He maintained, that he had
discovered fourteen such stars of the 4th, 5th, and 6th
magnitudes, (eight in Cassiopeia, two in Eridanus, and four
near the North Pole). From the absence of any precise data
as to their respective positions, and especially since, like
those said to have been. discovered by Maraldi between 1694
and 1709, their existence is more than questionable, they
cannot be introduced in our present list. (Jacques Cassini,
Klémens d’ Astron., pp. 73-77; Delambre, Hist. de 1’ Astr.
mod., t. li. p. 780).

(v) A hundred and seventy-eight years elapsed after the
appearance of the new star in Vulpes without a similar
phenomenon having occurred, although in this long interva.
the heavens were most carefully explored and its stars
counted, by the aid of a more diligent use of telescopes
and by comparison with more correct catalogues of the star&

NEW &fai8 217

On the 28th of April, 1848, at Mr. Bishop’s private observa-
tory, (South Villa, Regent's Park,) Hind made the important
discovery of a new reddish-yellow star of the 5th magnitude
in Ophiuchus (R. A. 16° 50’ 59”; S. Decl. 12° 39’ 16”, for
1848). In the case of no other new star have the novelty of
the phenomenon, and the invariability of its position, been
demonstrated with greater precision. At the present time
(1850) it is scarcely of the 11th magnitude, and according to
Lichtenberger’s accurate observations it will most likely soon
disappear. (Notices of the Astr. Soc., vol. viii. pp. 146 and
155-158.)

The above list of new stars, which within the last two
thousand years have suddenly appeared and again disappeared.
is probably more complete than any before given, and may
justify a few general remarks. We may distinguish three
classes: new stars which suddenly shine forth and then after
a longer or shorter time disappear; stars whose brightness is
subject to a periodical variability which has been already
determined ; and stars, like » Argis, which suddenly exhibit
an unusual increase of brilliancy, the variations of whicn
are still undetermined. All these phenomena are, most
probably, intrinsically related to each othe:. The new star
in Cygnus (1600) which, after its total disappearance (at
least to the naked eye) again appeared and continued as a
star of the 6th magnitude, leads us to infer the affinity of
the two first kinds of celestial phenomena. The celebrated
star discovered by Tycho Brahe in Cassiopeia in 1572 was
considered, even while it was still shining, to be identical
with the new star of 945 and 1264. The period of 300
years which Goodricke conjectured, has been reduced by
Keill and Pigott to 150 years. The partial intervals of the
actual phenomena, which perhaps are not very numerically
accurate, amount to 319 and 308 years. Arago® has pointed
out the great improbability that Tycho Brahe’s star of 1572
belongs to those which are periodically variable. Nothing as

' § Arago, Annuaire peur 1842, p. 382.

218 COSMOS.

yet seems to justify us in regarding all new stars as variable
in long periods, which from their very length have remained
unknown to us. If, for instance, the self-luminosity of all
the suns of the firmament is the result of an electro-magnetic
process in their photospheres, we may consider this process
of light as variable in many ways, without assuming any
local or temporary condensations of the celestial ether, or any
intervention of the so-called cosmical clouds. It may either
occur only once or recur periodically, and either regularly oz
irregularly. The electrical processes of light on our earth,
which manifest themselves either as thunder-storms in the
regions of the air, or as polar effluxes, together with much
apparently irregular variation, exhibit. nevertheless a certain
periodicity dependent both on the seasons of the year and the
hours of the day; and this fact is, indeed, frequently observed
in the formation for several consecutive days, during per-
fectly clear weather, of a small mass of clouds in particular
regions of the sky, as is proved by the frequent failures in
attempts to observe the culmination of stars.

The circumstance, that almost all these new stars burst
forth at once with extreme brilliancy, as stars of the Ist
magnitude, and even with still stronger scintillation, and that
they do not appear, at least to the naked eye, to increase
gradually in brightness, is, in my opinion, a singular
peculiarity, and one well deserving of consideration. Kepler*
attached such weight to this. criterion, that he refuted the
idle pretension of Antonius Laurentinus Politianus, to having
seen the star in Ophiuchus (1604) before Bronowski, simply
by the circumstance that Laurentinus had said—‘* Apparuit
nova stella parva et postea de die in diem crescendo apparuit
lumine non multo inferior Venere, superior Jove.” There
are only three stars which may be looked upon in the light
of exceptions, that did not shine forth at once as of the Ist

——

$ Kepler, De Stella nova in pede Serp., p. 3.

NEW STARS. 219

magnitude; viz. the star which appeared in Cygnus in 1600,
and that in Vulpes in 1670, which were both of the 3rd,
and Hind’s new star in Ophiuchus in 1848. which is of the
évh magnitude.

It is much to be regretted, as we Lave already observed,
tha‘ after the invention of the telescope in the long period
ef 178 years, only two new stars have been seen, whereas
these phenomena have sometimes occurred in such rapid
succession, that at the end of the fourth century four
were observed in twenty-four years; in the thirteenth
century, three in sixty-one years; and during the era of
Tycho Brahe and Kepler at the end of the sixteenth and
beginning of the seventeenth centuries, no less than six were
observed within a period of thirty-seven years. Throughout
this examination I have kept in view the Chinese obser-
vations of extraordinary stars, most of which, according to
the opinion of the most eminent astronomers, are deserving
of our confidence. Why it is that of the new stars seen in
Europe, that of Kepler in Ophiuchus (1604) is in all pro-
bability recorded in the records of Ma-tuan-lin, while that
of Tycho in Cassiopeia (1572) is not noticed, I for my part
am as little able to explain as I am to account for the
fact, that no mention was made in the sixteenth century,
among European astronomers, of the great luminous pheno-
menon which was observed in China in February, 1578. The
difference of longitude (114°) could only in a few instances
account for their not being visible. Whoever has been
engaged in such investigations, must be well aware that the
want of record either of political events or natural pheno-
mena, either upon the earth or in the heavens, is not inva-
riably a proof of them never having taken place; and on com-
paring together the three different catalogues which are given
ul Ma-tuan-lin, we actually find comets (those for instance of
1385 and 1495), mentioned in one but omitted in the others,

220 . COSMUS. *

Kven the earlier astronomers (Tycho Brahe and Kepler), as
well as the more modern (Sir John Herschel and Hind) have
called attention to the fact that the great majority (four-
fifths, I make it) of all the new stars described both in
Europe and China, have appeared in the neighbourhood of
or within the Milky Way. If that which gives so mild and
nebulous a light to the annular starry strata of the Milky
Way is, as is more than probable, a mere aggregation of small
telescopic stars, 'T'ycho Brahe’s hypothesis, which we have
already mentioned, of the formation of new, suddenly-shining
fixed stars, by the globular condensation of celestial vapour,
falls at once to the ground. What the influence of gravi-
tation may be among the crowded strata and clusters of
stars, supposing them to revolve round certain central
nuclei, is a question not to be here determined, and belongs
to the mythical part of Astrognosy. Of the twenty-one
new stars enumerated in the above list, five (those of 134,
3938, 827, 1203, and 1584) appeared in Scorpio, three in
Cassiopeia and Cepheus (945, 1264, 1572), and four in
Ophiuchus (123, 1230, 1604, 1848). Once, however (1012),
one was seen in Aries at a great distance from the Milky
Way (the star seen by the monk of St. Gall). Kepler
himself, who however considers as a new star that de-
scribed by Fabricius, as suddenly shining in the neck of
Cetus in the year 1596, and as disappearing in October of
the same year, likewise advances this position as a proof to
the contrary. (Kepler, De Stella Nova Serp., p. 112.) Is it
allowable to infer, from the frequent lighting up of such stars
in the same constellations, that in certain regions of space—
those, namely, where Cassiopeia and Scorpio are to be seen
the conditions of their illuminations are favoured by certain
local relations? Do such stars as are peculiarly fitted for
the explosive temporary processes of light, especially lie in
those directions?

VANISHED STARS. 221

The stars whose luminosity was of the shortest duration,
were those of 389, 827, and 1012. In the first of the above-
- named years, the luminosity continued only for three weeks ;
in the second, four months; in the third, three. On the other
hand, Tycho Brahe’s star in Cassiopeia continued to shine for
seventeen months; while Kepler's star in Cygnus (1600) was
visible fully twenty-one years before it totally disappeared.
It was again seen in 1655, and still of the 3rd magnitude,
as at its first appearance, and afterwards dwindled down tc
the 6th magnitude, without, however (according to Arge-
lander’s observations), being entitled to rank among pe-
riodically variable stars.

STARS THAT HAVE DISAPPEARED.—The observation and
enumeration of stars that have disappeared is of importance for
discovering the great number of small planets which probably
belong to our solar system. Notwithstanding, however, the
great accuracy of the catalogued positions of telescopic fixed
stars and of modern star-maps, the certainty of conviction that
a star in the heavens has actually disappeared since a certain
epoch can only be arrived at with great caution. Errors of
actual observation, of reduction, and of the press,” often dis-
figure the very best catalogues. The disappearance of a

7 On instances of stars which have not disappeared, see
Argelander in Schumacher’s <Astronom. Nachr., no. 624,
s. 371. To adduce an example from antiquity, I may point
to the fact that the carelessness with which Aratus com-
piled his poetical catalogue of the stars has led to the
often-renewed question, whether Vega Lyre is a new star
vr one which varies. in long periods. For instance, Aratus
asserts that the constellation of Lyra consists wholly of small
stars. It is singular that Hipparchus, in his Commentary,
does not notice this mistake, especially as he censures Aratus
for his statements as to the relative intensity of light in
the stars of Cassiopeia, and Ophiuchus. All this. however,
is only accidental and not demonstrative; for when Ara-

222 COSMO&.

heavenly body from the place in which it had before been
distinctly seen, may be the result of its own motion as much
as of any such diminution of its photometric process (whether
on its surface or in its photosphere), as would render thc
waves of light too weak to excite our organs of sight.
What we no longer see, is not necessarily annihilated. The
idea of destruction or combustion, as applied to disappearing
stars, belongs to the age of Tycho Brahe. Even Pliny,
in the fine passage where he is speaking of Hippar-
chus, makes it a question: Stelle an obirent nasceren-
turve? The apparent eternal cosmical alternation of existence
and destruction is not annihilation; it is merely the transition
of matter into new forms, into combinations which are sub-
ject to new processes. Dark cosmical bodies may by a
renewed process of light again become luminous.

PERIODICALLY VARIABLE Stars. — Since all is in
motion in the vault of heaven, and everything is variable
both in space and time, we are led by analogy to infer
that as the fixed stars universally have not merely an appa-
rent, but also a proper motion of their own, so their surfaces
or luminous atmospheres are generally subject to those
changes which recur, in the great majority, in extremely long

tus also ascribes to Cygnus none but stars “of moderate
brilliancy,” Hipparchus expressly refutes this error, and
adds the remark, that the bright star in the Swan (Deneb)
is little inferior in brilliancy to Lyra (Vega Lyre). Pto-
lemy classes Vega among stars of the lst magnitude, and
in the Catasterisms of Eratosthenes (cap. 25), Vega is
called Aevxdy kai Aaumpov. Considering the many inaccuracies
of a poet, who never himself observed the stars, one is
not much disposed to give credit to the assertion that it was
only between the years 272 and 127 B.c., «.¢., between
the times of Aratus and Hipparchus, that the star Vega
Lyre (Fidicula of Pliny, xviii. 25,) became a star of the Ist

Inegnitude

PERIODICAL STARS. 223

and therefore unmeasured and probably undeterminable periods,
or which, in a few, occur without being periodical, as it were,
by a sudden revolution, either for a shorter or for a longer
time. The latter class of phenomena (of which a remarkable
instance is furnished in our own days by a large star in Argo)
will not be here discussed, as our proper subject is those
fixed stars whose periods have already been investigated and
ascertained. It is of importance here to make a distinc-
tion between three great sidereal phenomena, whose con-
nexion has not as yet been demonstrated; namely, variable
stars of known periodicity; the instantaneous lighting up
in the heavens of so-called new stars; and sudden changes
in the luminosity of long-known fixed stars, which pre-
viously shone with uniform intensity. We shall first of all
dwell exclusively on the first kind of variability; of this the
earliest instance accurately observed is furnished (1638) by
Mira, a star in the reck of Cetus. The East-Friesland
pastor, David Fabricius (the father of the discoverer of the
spots on the sun), had certainly already observed this star
on the 13th of August, 1596, as of the 3rd magnitude, and
in October of the same year he saw it disappear. But it
was not until forty-two years afterwards that the alternating,
recurring variability of its light, and its periodic changes,
were discovered by the Professor Johann Phocylides Holwarda,
Professor of Francker, This discovery was further followed
in the same century by that of two other variable stars 8 Persei
(1669), described by Montanari, and x Cygni (1687) by Kirch.

The irregularities which have been noticed in the periods,
together with the additional number of stars of this class which
have been discovered haye, since the beginning of the nine.
teenth century, awakened the most lively interest in this
complicated group of phenomena. From the difficulty of
the subject, and from my own wish to be able to set down
in the present work the numerical elements of this variability

224 COSMOS.

(as being the most important result of all observations), so
far as in the present state of the science they have been
ascertained, I have availed myself of the friendly aid of that
astronomer who of all our contemporaries has devoted him-
self with the greatest diligence, and with the most brilliant
success, to the study of the periodically varying stars. The
doubts and questions called forth by my own labours I con-
fidently laid before my worthy friend Argelander, the director
of the Observatory at Bonn; and it is to his manuscript com-
munications that I am solely indebted for all that follows,
which for the most part has never before been published.
The greater number of the variable stars, although not
all, are of a red or reddish colour.. Thus, for instance,
besides B Persei (Algol in the head of Medusa), 8 Lyre
and e Aurige have also a white light. The star » Aquile
is rather yellowish; so also in a still less degree is ¢ Gemi-
norum. The old assertion that some variable stars (and
especially Mira Ceti) are redder when their brilliancy is_
on the wane than on the increase, seems to be groundless.
Whether in the double star a Herculis (in which, according to
Sir John Herschel, the greater star is red, but according to
Struve yellow, while its companion is said to be dark blue)
the small companion, estimated at between the 5th to the
7th magnitude, is itself also variable, appears very pro-
blematical. Struve® himself merely says. Suspicor minorem
esse variabilem. Variability is by no means a necessary

® Compare Madler, Asér., s. 488, note 12, with Struve
Stellarum compos. mensure microm. pp. 97 and 98, star 2140.
‘I believe,” says Argelander, ‘‘ it is extremely difficult with
« telescope having a great power of illumination to estimate
rightly the brightness of two such different stars as the
two components of a Herculis. My experience is strongly
against the variability of the companion; for during my many
observations iu the day-time with the telescopes of the

VAKIABLE STARS. 925

concomitant of redness. There are many red stars some of
them very red—as Arcturus and Aldebaran—in which, how-
- ever, no variability has as yet been discovered. And it is
also more than doubtful in the case of a star of Cepheus
(No. 7582 of the catalogue of the British Association),
which, on account of its extreme redness, has been called
by William Herschel the Garnet Star (1782).

It would be difficult to indicate the number of periodically
variable stars for the reason that the periods already deter-
mined are all irregular and uncertain, even if there were no
other reasons. ‘The two variable stars of Pegasus, as well as
a Hydre, e« Aurige, and a Cassiopeie, have not the certainty
that belongs to Mira Ceti, Algol, and § Cephei. In inserting
them, therefore, in a table, much will depend on the degree
of certainty we are disposed to be content with. Argelander,
as will be seen from the table at the close of this investiga-
tion, reckons the number of satisfactorily determined periods
at only twenty-four.®

The phenomenon of variability is found not only both in
red, and in some white stars, but also in stars of the most
diversified magnitude; as, for example, in a star of the Ist
magnitude, a Orionis; by Mira Ceti, a Hydra, a Cassiopei,
and 8 Pegasi, of the 2nd magnitude; 8 Persei, of the 2°3rd
magnitude; and in 7 Aquile, and Lyre, of the 3-4th mag-
nitude. There.are also variable stars, and indeed in far
greater numbers, of the 6th to the 9th magnitude; such as

meridian circles of Abo, Helsingfors, and Bonn, I have never
seen a Herculis single, which would assuredly have been the
case if the companion at its minimum were of the seventh
magnitude. I believe the latter to be constant, and of the
Sth or 56th magnitude.

* Madler'’s Table (Astron., s. 485) contains eighteen stars,
with widely differing numerical elements. Sir John Herschel
enumerates more than forty-five, including those mentioned
in the notes. Gudlines, § 819-826.

WX. 111. a

222. CcOSsNOS,

the variabiles Corone, Virginis, Cancri, et Aquarii. The star
x Cygni likewise presents very great fluctuations at its maximum.

That the periods of the variable stars are very irregular
has been long known; but that this variability, with all its
apparent irregularity, is subject to certain definite laws,
was first established by Argelander. This he hopes to be
able to demonstrate in a longer and independent treatise of
his own. Inthe case of y Cygni he considers that two pertur-
bations in the period—the one of 100, the other of 84—are
more probable than a single period of 108. Whether such
disturbances arise from changes in the process of light which
is going on in the atmosphere of the star itself, or from the
periodic times of some planet which revolves round the
fixed star or sun x Cygni, and by attraction influences the
form of its photosphere, is still a doubtful question. The
greatest irregularity in change of intensity has unquestionably
been exhibited by the variabilis Scuti (Sobieski’s shield).
For this star diminishes, from the 5°4th, down to the 9th
magnitude ; and moreover, according to Pigott, it once totally
disappeared at the end of the last century. At other times
the fluctuations in its brightness have been only from the
65th to the 6th magnitude. The maximum of the variations
of xy Cygni have been between the 67th and 4th magnitude ;
of Mira, from the 4th to the 2°1st magnitude. On the other
hand, in the duration of its periods 8 Cephei shows an ez-
traordinary, and indeed of all variable stars the greatest
regularity, as is proved by the 87 minima observed between
the 10th of October, 1840, and 8th of January, 1848, and
even later. In the case of e Aurige, the variation of its
brilliancy discovered by that indefatigable observer, Heis,
of Aix-la-Chapelle,” extends only from the 3°4th to the 4°d5th
magnitude.

% Argelander, in Schumacher's Astron. Nachr., bd. XAViL
(1848), wo. 624, s. 369.

VAKIABLE STARS, 22;

A great difference in the maximum of brightness is exhibited
by Mira Ceti. In the year 1779, for instance (on the 6th of
November), Mira was only a little dimmer than Aldebaran, and
indeed not unfrequently brighter than stars of the 2nd mag-
nitude; whereas at other times this variable star scarcely
attained to the intensity of the light of 6 Ceti, which is of the
4th magnitude. Its mean brightness is equal to that of y Ceti
(3rd magnitude). If we designate by 0 the brightness of the
faintest star visible to the naked eye, and that of Aldeba-
ran by 50, then Mira has varied in its maximum from 20 to
47. Its probable brightness may be expressed by 380: it is
oftener below than above this limit. The measure of its
excess, however, when it does occur, is in proportion more
considerable. No certain period of these oscillations has as
yet been discovered. There are however indications of a
period of 40 years, and another of 160.

The periods of variation in different stars vary as 1:250.
The shortest period is unquestionably that exhibited by 8
Persei, being 68 hours and 49 minutes; so long at least as
that of the polar star is not established at less than two
days. Next to 8 Persei come 8 Cephei (5d. 8h. 49m.),
» Aquile (7d. 4h. 14m.), and ¢ Geminorum (10d. 3h. 35m.).
The longest periods are those of 30 Hydree Heyelii, 495 days;
x Cygni, 406 days; Variabilis Aquarii, 388 days; Serpentis
S, 867 days; and Mira Ceti, 332 days. In several of the vari-
able stars it is well established that they increase in brilliancy
more rapidly than they diminish. This phenomenon is the
most remarkable in 6 Cephei. Others, as for instance 8
Lyre, have an equal period of augmentation and diminution
of light. Occasionally, indeed, a difference is observed in this
respect in the same stars, though at different epochs in their
process of light. Generally Mira Ccti (as also 8 Cephei) is
more rapid in its augmentation than in its diminution; “ut

in the former the contrary has also been obsery xd.
Q2

228 COSMOS. —

Periods within periods have been distinetly observed in
the case of Algol, of Mira Ceti, of 8 Lyre, and with great
probability also in x Cygni. The decrease of the period of
Algol is now unquestioned. Goodricke was unable to per-
ceive it, but Argelander has since done so; in the year 1842
he was enabled to compare more than 100 trustworthy’
observations ‘comprising 7600 periods), of which the ex-
tremes differed from each other more than 58 years. (Schu.
macher’s Astron. Nachr., nos. 472 and 624.) The decrease
in the period is becoming more and more observable." For
the periods of the maximum of Mira (including the maximum
of brightness observed by Fabricius in 1596), a formula ™

u< Tf,’ says Argelander, “I take for the 0 epoch the
minimum brightness of Algol, in 1800, on the 1st of January,
‘at 18" 1™ mean Paris time, I obtain the duration of the
periods for :—
—1987 .. 2° 20" 48™, or 59416 + 0*:316

4408 ‘. 58*737 + 05-094
iar ake 58°°393 + 0175
aes Mule a5 58°-154 + 0*-039
+2328 .. 3 58-193 + 0°-096

48885 .. * 57°-971 + 08-045
+5441 ., af 55°182 + 03,348

“ In this table the numbers have the following signification :—
if we designate the minimum epoch of the Ist of Jan. 1800,
by 0, that immediately preceding by — 1, and that immediately
following by +1, and so on, then the duration between — 1987
and — 1986 would be exactly 2° 20° 48™ 59*416, but the
duration between + 5441 and + 5442 would be 2* 20° 48™
55182; the former applies to the year 1784, the latter to
the year 1842.

«The numbers which follow the signs + are the probable
errors. ‘That the diminution becomes more and more rapid,
is shown as well by the last number as by all my observations
since 1847.”

1% Argelander’s formula for representing all observations
of the maxima of Mira Ceti is, as communicated by himself,
as follows :—

VARIABLE STARS. 229

Las been established by Argelander, from which all the
maxima can be so deduced that the probadle error in a long
period of variability, extending to 331d. 8h. does not in the
mean exceed 7 days, while, on the hypothesis of an uniform
period, it would be 15 days.

The double maximum and minimum of 8 Lyre, in each
of its periods of nearly 13 days, was from the first correctly
ascertained by its discoverer, Goodricke (1784); but it has
been placed still more beyond doubt** by very recent obser-
vations. It is remarkable that this star attains to the same
brightness in both its maxima; but in its principal minimum
it is about half a magnitude fainter than in the other. Since
- the discovery of the variability of 8 Lyre, the period in a
period has probably been on the increase. At first the vari-
ability was more rapid, then it became gradually slower; and
this decrease in the length of time reached its limit between

1751 Sep. 9°76 + 3319-3363 E.
+105, sin. (289° E+ 86° 23’) +1842, sin. (42°F +231° 42’)
+3349, sin. (8° E + 170° 19’) + 65%3, sin. (15° E + 6° 377)
where E represents the number of maxima which have oc-
curred since Sept. 9, 1751, and the co-efficients are given
in days. Therefore, for the current year (E being = 109),
the following is the maximum :—
1751 Sep. 9:76 + 86115°65 + 87-44 — 12%24,
+ 18°59 + 27434 = 1850 Sep. 84:54.

* The strongest evidence in favour of this formula is, that it
represents even the maximum of 1596, ( Cesmos, vol. il. p.713,)
which, on the supposition of a uniform period, would deviate
more than 100 days. However, the laws of the variation of
the light of this star appear so complicated, that in par-
ticular cases—e. g. for the accurately observed maximum
of 1840—the formula was wrong by many days (nearly
twenty-five).”

* Compare Argelander’s essay written on the occasion of
the centenary jubilee of the K6nigsberg University, and en-
titled, De Stella 8 Lyre Variabin, 1844.

230 cosso8,

the years 1840 and 1844. During that time its period was
nearly invariable ; at present it is again decidedly on the des
crease. Something similar to the double maximum of 8 Lyra
occurs in 8Cephei. There isa tendency to a second maximum,
in so far as its diminution of light does not proceed uniformly ;
but after having been for some time tolerably rapid, it comes
to a stand, or at least exhibits a very inconsiderable diminu-
tion which suddenly becomes rapid again. In some stars it
would almost appear as though the light were prevented from
fully attaining a second maximum. in x Cygni it. is very
probable that two periods of variability prevail,—a longer one
of 100 years, and a shorter one of 84.

The question whether, on the whole, there is greater
regularity in variable stars of very short than in those of
very long periods, is difficult to answer. The variations from
an uniform period can only be taken relatively; 7. e. in parts of
the period itself. ‘To commence with long periods, x Cygni,
Mira Ceti, and 30 Hydree, must first of all be considered. In
x Cygni, on the supposition of a uniform variability, the
deviations from a period of 406:0634 days, (which is the
most probable period,) amount to 39°4 days. Even though a
portion of these deviations may be owing to errors of
observation, still at least 29 or 80 days remain beyond doubt;
?. e. one-fourteenth of the whole period. In the case of
Mira Ceti,” in a period of 331:340 days, the deviations
amount to 55°5 days, even if we do not reckon the
observations of David Fabricius. If, allowing for errors of
observation, we limit the estimate to 40 days, we still obtain
one-eighth; consequently, as compared with x Cygni, nearly

% The work of Jacques Cassini (Elémens d’Astronomie,
1740, pp. 66-69), belongs to tie earliest systematic attempts
to investigate the mean duration of the period of the variation
of Mira Ceti.

VARIABLE STARS, 231

twice as great a deviation. in the ease of 30 H:-dre, which
has a period of 495 days, it is stili greater, probably one-fifth.
It is only during the last few years (since 1840, and still
later) that the variable stars with very short periods have
been observed steadily, and with sufficient accuracy; so that
the problem in question, when applied to them, is still more
difficult of solution. From the observations, bcwever, which
have as yet been taken, less considerable deviations seet: to
occur. In the case of » Aquile (with a period of 7d. 4h.)
they only amount to one-sixteenth or one-seventeenth of the
whole period; in that of 8 Lyre (period 12d. 21h.) to one
twenty-seventh or one-thirtieth; but the inquiry is still
exposed to much uncertainty as regards the comparison of
long and short periods. Of 8 Lyre between 1700 and 1800
periods have been observed; of Mira Ceti, 279; of x
_ Cygni, only 145.

The question that has been mooted, whether stars which
have long appeared to be variable in regular periods, ever
cease to be so, must apparently be answered. in the negative.
As among the constantly variable stars there are some which
at one time exhibit a very great, and at another a very small
degree of variability, (as, for instance, variabilis Scuti,) so,
it seems, there are also others whose variability is at certain
times so very slight, that, with our limited means, we are
unable to detect it. To such belongs variabilis Coron bor.
(No. 5236 in the Catalogue of the British Association),
recognized as variable by Pigott, who observed it for a
considerable time. In the winter of 1795-6 this star became
totally invisible; subsequently it again appeared, and the
variations of its light were observed by Koch. In 1817,
Harding and Westphal found that its brightness was nearly
constant, while in 1824 Olbers was again enabled te perceive
a variation in its luminosity. Its constancy now again
returned, and from August, 1843, to September, 1845, was

232 cosmos.
established by Argelander. At the-end of September, a ‘resk
diminution of its light commenced. By October, the «tar

was no longer visible in the comet-seeker, but it appeared

again in February, 1846, and by the beginning of June had
Since then it has
maintained this magnitude, if we overlook some small

reached its usual magnitude (the 6th).

fluctuations whose very existence has not been established
with certainty. To this enigmatical class of stars belong
also variabilis Aquarii, and probably Janson and Kepler's
star in Cygnus of 1600, which we have already mentiones

among the new stars.

TABLE of the Variable Stars by F. Argelander,

"
7

Name of the Length of Brightness in the Name of Discoverer and
No. Star. Period. Maximum. {Minimum.| “ate of Discovery.
D. H. M. |Magnitude) Magnit.
1 | o Ceti , 331 20 —| 4 to 271 0 | Holwarda 1639
2| 8 Persei . 2 20 49 2°3 4 | Montanari 1669
8 |x Cygni . .| 406 1380|67to 4 0 | Gottfr. Kirch 1687.
4 | 30 Hydre Hev. | 495——J| 5to 4 0! Maraldi 1704
5 | Leonis R, 420 M.} 312 18 — 5 0 | Koch 1782
6 |» Aquilae . 7 414 3 4 5°4 | H. Pigott 1784
7 | 6 Lyree 12 21 45 3°4 4°5 | Goodricke 1784
8 | 6 Cephei 5 8 49 4°3 54 | Ditto 1784
9 | a Herculis 66 8— 3 3°4 | Wm. Herschel 1795
10.| Corone R . 323 — — 6 0 | E. Pigott 1795
11 | Scuti R 7117 — |6°5 to 5°4 |9to 6 | Ditto 1795
12 | Virginis R . | 145 21—] 7 to 67 0 | Harding — 1809
13 | Aquarii R . | 888 13 — |. 9 to 6°7 0 | Ditto 1810
14 | Serpentis R 359 — — 6°7 0 | Ditto 1826
15 | Serpentis S 367 5—| 8 to7'8 0 | Ditto 1828
16 | Cancri R 380 —- — 7 0 | Schwerd 1829
17 | a Cassiopeize 79 3— 2 3°2 | Birt 1831 |
18 | a Orionis . 196 — — 1 1:2 | John Herschel 1836
19 | a Hydree 55 — — 2 2°3 | Ditto 1837_
20 | « Aurigee t 3°4 4°5 | Heis 1846
21 |Z Geminorum 10 38 35 4°3 5°4 | Schmidt 1847—
22 |B Pegasi . ~ | 4023 — 2 2°3 | Ditto -848-
28 | Pegasi R | 350 — — 8 0 | Hind 1848
24 | Caneri S q 78 0 | Ditto 1849

I i

VARIABLE STARS. 233

EXPLANATORY REMARKS.

The 0 in the column of the minima indicates that the
star is then fainter than the 10th magnitude. For the
purpose of clearly and conveniently designating the smaller
variable stars, which for the most part have neither names
nor other designations, I have allowed myself to append to
them capitals, since the letters of the Greek and the smaller
Latin alphabet have, for the most part, been already employed
by Bayer.

Besides the stars adduced in the preceding table, there
are almost as many more which are supposed to be variable,
since their magnitudes are set down differently by different
observers. But as these estimates were merely occasional,
and have not been conducted with much precision, and as
different astronomers have different principles in estimating
magnitudes, it seems the safer course not to notice any such
cases, until the same observer shall have found a decided
variation in them at different times. With all those adduced
in the table this is the case; and the fact of their periodical
‘change of light is quite established, even where the period
‘itself has not been ascertained. ‘The periods given in the
table are founded, for the most part, on my own examination
of all the earlier observations that have been published, and
on my own observations within the last ten years, which have
not as yet been published. Exceptions will be mentioned in
the following notices of the several stars.

In these notices the positions are those for 1850, and are
expressed in right ascension and declination. The frequently
‘repeated term gradation indicates a difference of brightness,
which may be distinctly recognized even by the naked eye, or
in the ease of those stars which are invisible to the unaided
‘sight, by a Frauenhofer’s comet-seeker of twenty-five and
-a-half inches focal length. For the brighter stars above the
6th magnitude, a gradation indicates about the tenth part
of the difference by which the successive orders of mag-
‘nitude differ from one another; for the smaller stars the
-usual classifications of magnitude are considerably closer.

(1) o Ceti, R. A. 32° 57’, Decl. —3° 40’; aiso called Mira,
“on account of the wonderful change of light which was first
observed in this star. As early as the latter half of the
seventeenth century, the periodicity of this star was recog-
nized, and Bouillaud fixed the duration of its period at 333

234 COSMOS.

days; it was found, however, at the same time, that this durae
-tion was sometimes longer, and sometimes shorter, and that
the star at its greatest brilliancy appeared sometimes brighter,
and sometimes fainter. This has been subsequently fully
confirmed, Whether the star ever becomes perfectly invisible
is as yet undecided; at one time, at the epoch of its minimum
it has been observed of the 11th or 12th magnitude, at another,
it could not be seen even with the aid of a three or a four-
feet telescope. This much is certain, that for a long period
it is fainter than stars of the 10th magnitude. But few ob-
servations of the star at this stage have as yet been taken;
most having commenced when it had begun to be visible
to the naked eye as a star of the 6th magnitude. From this
period the star increases in brightness at first with great
rapidity, afterwards more slowly, and at last, with a searcely
perceptible augmentation; then again, it diminishes at first
slowly, afterwards rapidly. On a mean the period of aug-
mentation of light from the 6th magnitude extends to 50 days;
that of its decrease down to the same degree of brightness
takes 69 days; so that the star is visible to the naked eye for —
about four months. However, this is only the mean duration
of its visibility; occasionally it has lasted as long as five
months, whereas, at other times it has not been visible for
more than three. In the same way, also, the duration both
of the augmentation and of the dimmution of its light is
subject to great fluctuations, and the former is at all times
‘slower than the latter: as, for instance, in the year 1840,
when the star took sixty-two days to arrive at its greatest
brightness, and then in forty-nine days became invisible to
the naked eye. The shortest period of increase that has as
yet been observed took place in 1679, and lasted only thirty
days; the longest (of sixty-seven days) occurred in 1709.
‘The decrease of light lasted the longest in 1839, being then
ninety-one days; the shortest in the year 1660, when it was
completed in nearly fifty-two days. Occasionally, the star
at the period of its greatest brightness exhibits for a whole
month together scarcely any perceptible variation; at others,
a difference may be observed within a very few days. On
some occasions after the star had decreased in brightness for
several weeks there was a period of perfect cessation; or, at
‘Igast, a scarcely perceptible diminution of light during several
days: this was the case in 1678 and in 1847.

¥YARIABLE STARS. 235

The maximum brightness, as already remarked, is by no
means always the same. If we indicate the brightness of the
faintest star that is visible to the naked eye by 0, and that of
Aldebaran, (a Tauri,) a star of the Ist magnitude, by 50,
then the maximum of light of Mira fluctuates between 20
and 47, 7. e. between the brightness of a star of the 4th, and
of the lst or 2nd magnitude: the mean brightness is 28, or
that of the star y Ceti. But the duration of its periods is
still more irregular: its mean is 331d. 20h., while its fluc-
tuations have extended to a month; for the shortest time
that ever elapsed from one maximum to the next was only
806 days, the longest on the other hand 367 days. These
irregularities become the more remarkable, when we compare
the several occurrences of greatest brightness with those which
would take place if we were to calculate these maxima on
the hypothesis of an uniform period. ‘The difference between
calculation and observation then amounts to 50 days, and
it appears, that for several years in succession those differ-
ences are nearly the same, and in the same direction. This
evidently indicates that the disturbance in the phenomena
of light is one of a very long period. More accurate cal-
culations, however, have proved that the supposition of one
disturbance is not sufficient, and that several must be
assumed, which may, however, all arise from the same cause;
one of these recurs after 11 single periods; a second, after 88 ;
a third, after 176; and a fourth, after 264. From hence arises
the formula of sines (given at p. 228, note 12), with which,
indeed, the several maxima very nearly accord, although
deviations still exist which cannot be explained by errors of
observation.

(2) 8 Persei, Algol; R. A. 44° 36’, Decl. + 40° 22’.
Although Geminiano Montanari observed the variability of
this star in 1667, and Maraldi likewise noticed it, it was
Goodricke that first, in 1782, discovered the regularity of the
variability. The cause of this is probably that this star does
not, like most other variable ones, gradually increase and
diminish in brightness, but for 2d. 13h. shines uniformly as a
star of the 2°3rd magnitude, and only appears less bright for
7 or 8 hours, when it sinks to the 4th magnitude. The
augmentation and diminution of its brightness are not quite
regular; but when near to the minimum, they proceed with
greater rapidity; whence the time of least brightness may

236 cosmos

be accurately calculatec to within 10 to 15 minutes. It ig
moreover remarkable that this star,.after having inereased
in light for about an hour, remains, for nearly the same
period at the same br ightness, and then begins once more per-
ceptibly to increase. Till very recently the duration of the
period was held to be perfectly uniform, and Wurm was able
‘to present all observations pretty closely, by assuming it to
be 2d. 21h. 48m. 584s. However, a more accurate calculation,
in which was comprehended a space of time nearly twice
as long as that at Wurm’s command, has shown that the
period becomes gradually shorter. In the year 1784, it was
2d. 20h, 48m, 59°4s., and in the year 1842, only 2d. 20h.
48m. 55:2s.. Moreover, from the most recent observations
it becomes very probable that this diminution of the period
is at present proceeding more rapidly than before, so that
for this star also a formula of sines, for the disturbance of
its period, will in time be obtained. Besides, this diminu:
tion will be accounted for, if we assume that Algol comes —
nearer to us by about 2000 miles every year, or recedes from
us thus far less each succeeding year; for in that case his
light would reach us as much sooner every year, as the de-
crease of the period requires; 7. e. about the twelve thou-
sandth of a second. If this be the true cause, a formula of
sines must eventually be deduced.

(3) x Cygni, R.A. 296° 12’, Decl. +32° 32’. This star
also exhibits nearly the same irregularities as Mira. The
deviations of the observed maxima from those calcuiated for
a uniform period amount to 40 days, but are considerably
diminished by the introduction of a disturbance of 8} single
periods, and of another of 100 such periods. In its maximum
this star reaches the mean brightness of a faint 5th magni-
tude, or one gradation brighter than the star 17 Cygni.
The fluctuations, however, are in this case also very consi-
derable, and have been observed from 13 gradations below
the mean to 10 above it. ‘At this lowest maximum the star
weuld be perfectly invisible to the naked eye, whereas, on the
contrary, in the year 1847, it could be seen without the aid
of a telescope for fully 97 days; its mean visibility extends
to 52 days, of which, on the mean, it is 20 days on the
increase, and 82 on the decrease.

(4) 80 Hydra Hevelii, R. A. 200° 23’, Decl. — 22°30’. Of
this star which, from its position in the heavens, ie only

< VARIABLE STARS. 237

visible for a short time during every year, all that can be said
is, that both its period and its maximum brightness are sub-
ject to very great irregulari ities.

(5) Leonis R, = 420 Mayeri; R.A. 144° 52’, Decl.

‘+ 12° 7. This star is. often confounded with 18 and 19
Leonis, which are close to it; and in consequence has been
very little observed; sufficiently, however, to show that the
period is somewhat irregular. Its brightness at the maximum
seems also to fluctuate through some gradations.
. (6) » Aquilz, called also » Antinoi; R. A. 296° 12’, Decl.
+ 0° 37’. The’ period of this star is tolerably uniform,
7d. 4h. 13m. 53s.; observations, however, prove that at
long intervals of time trifling fluctuations occur in it, not
amounting to more than 20 seconds. The variation of light
proceeds so regularly, that up to the present time no devia-
tions have been discovered which could not be accounted
for by errors of observation. In its minimum, this star is
one gradation fainter than + Aquile; at first it increases
slowly, then more rapidly, and afterwards again more slowly;
and in 2d. 9h. from its minimum, attains to its greatest
brightness, in which it is nearly three gradations brighter
than 8, but two fainter than @ Aquile. From the maximum
its brightness does not diminish quite so regularly; for when
the star has reached the brightness of 8 (7. e. in 1d. 10h. after
the maximum), it changes more slowly than either before or
afterwards.

(7) 6 Lyre, R. A. 281° 8’, Decl. + 33° 11’; a star
remarkable from the fact of its having two maxima and two
minima. When it has been at its. faintest light, one-third
of a gradation fainter than ¢ Lyre. it rises in 3d. 5h. to its first
maximum, in which it remains three-fourths of a gradation
fainter than y Lyre. It then sinks in 3d. 3h. to its second
minimum, in which its light is about five gradations greater
than that of ¢ After 3d. 2h. more. it again reaches, i in its
second maximum, to the brightness of the first ; and afterwards,
in 8d. 12h., declines once more to its greatest faintness; so
that, in 12d. 21h. 46m. 40s. it runs through all its variations
of light. ‘This duration of the period, however, only applies
to the years 1840 to 1844; previously it had been shorter—-
in the year 1784, by about ‘adh. ; ; in 1817 and 1818, by more
than an hour; and, at present, a shortening of it is again
clearly perceptible. There is therefore uo doubt that in the

238 COSMOS.

case of this star the disturbance of its period may be expressed
by a formula of sines.

(8) ?Cephei, R. A. 335° 54’, Decl. + 57° 39’. Of all the
known variable stars, this exhibits in every respect the greatest
regularity. The period of 5d. 8h. 47m. 394s. is given by
all the observations from 1784 to the present day, allowing
for errors of observation, which will account for all the slight
differences exhibited in the course of the alternations of
light. This star is in its minimum three-quarters of a
gradation brighter than ¢; in its maximum, it resembles « of
the same constellation (Cepheus). It takes 1d. 15h. to pass
from the former to the latter; but, on the other hand, moré
than double that time, viz. 3d. 18h. to change again to its
minimum: during eight hours of the latter period, however,
it scarcely changes at all, and very inconsiderably for a whole
day.

19) a Herculis, R.A. 256° 57’, Decl. + 14° 34’; an ex-
tremely red double star, the variation of whose light is in every
respect very irregular. Frequently, its light scarcely changes
for months together; at other times, in the maximum, it is
nearly five gradations brighter than in the minimum;
consequently, the period also is still very uncertain. The dis-
coverer of the star’s variation had assumed it to be sixty-three
days. I at first set it down at ninety-five, until a careful
reduction of all my observations made during seven years at
length gave me the period assigned in the text. Heis believes
that he can represent all the observations by assuming a
period of 184-9 days, with two maxima and two minima. |

(10) Corone R, R.A. 235° 36’, Decl. + 28° 37’. This
star is variable only at times: the period set down has been
calculated by Koch from his own observations, which unfortu-
nately have been lost.

(11) Seuti R, R.A. 279° 52’, Decl. — 5° 51’. The varia-
tions of brightness of this star are at times confined within a
very few gradations, whereas at others it diminishes from the
5th to the 9th magnitude. It has been too little observed to
determine when any fixel rule prevails in these deviations.
The duration of the period is also subject to considerable
fuctuations.

(12) Virginis R, R. A. 187° 43’, Decl. + 7°49’. It main-
tains its period and its maximum brightness with tolerable
reguiarity ; some deviations, however, do oceur, whick appear

VARIABLE STARS. 239

to me too considerable to be ascribed merety to errors of
observation.

(13) Aquarii R, R. A. 354° 11’, Decl. — 16° 6’.

(14) Serpentis R, R. A. 235° 57’, Decl. + 15° 36’.

(15) Serpentis 8, R. A. 228° 40’, Decl. + 14° 52’.

(16) Cancri R, R. A. 122° 6’, Decl. + 12° 9.

Of these four stars, which have been but very slightly ob-
served, little more can be said than what is given in the table.

(17) a Cassiopeie, R.A. 8° 0’, Decl. + 55° 43’. This star
is very difficult to observe. The difference between its
maximum and minimum only amounts to a few gradations,
and is, moreover, as variable as the duration of the period.
This circumstance explains the varying statements on this
head. ‘That which I have given, which satisfactorily repre-
sents the observations from 1782 to 1849, appears to me the
most probable one.

(18) @ Orionis, R. A. 86” 46’, Decl. + 7° 22’. The varia-
tion in the light of this star likewise amounts to only four
gradations from the minimum to the maximum. For 914
days it increases in brightness, while its diminution extends
over 1044, and is imperceptible from the twentieth to the
seventieth day after the maximum. Occasionally its varia-
bility is scarcely noticeable. It is a very red star.

(19) a Hydre, R. A. 140° 3’, Decl. — 8° 1’. Of all the
variable stars, this is the most difficult to observe. and its
period is still altogether uncertain. Sir John Herschel sets it
down at from twenty-nine to thirty days.

(20) « Aurige, R. A. 72° 48’, Decl. + 43° 36’. The
alternation of light in this star is either extremely irregular, or
else, in a period of several years, there are several maxima and
minima——a question which cannot be decided for many years.

(21) ¢ Geminorum, R. A. 103° 48’, Decl. + 20° 47’.
This star has hitherto exhibited a perfectly regular course in
the variations of its light. Its brightness at its minimum keeps
the mean between » and v of the same constellation; in the
maximum it does not quite reach that of a. It takes 4d. 21h.
to attain its full brightness, and 5d. 6h. for its diminution.

(22) 3 Pegasi, R. A. 344° 7’, Decl. + 27° 16’. Its period
is pretty well ascertained, but as to the course of its variation
of light nothing can as yev be asserted.

(23) Pegasi R, R. A. 844° 47’, Decl. + 9° 48.

240. . COSMOS,

: (24) Caneri S, R. A. 128° 50’, Decl. + 19° 34’.
Of these two stars, nothing at present can be said.

Bonn, August, 1850. Fr. ARGELANDER.

VARIATION oF LIGHT IN STARS WHOSE PERIODICITY IS
Unascertainep.—In the scientific investigation of important
natural phenomena, either in the terrestrial or in the side-
real sphere of the Cosmos, it is imprudent to connect toge-
ther, without’ due consideration, subjects which, as regards
their proximate causes, are still involved in obscurity. On
this account we are careful to distinguish stars which have
appeared and again totally disappeared (as in the star in Cas-
siopeia, 1572);—stars which have newly appeared and not
again disappeared (as that in Cygnus, 1600);—variable stars
with ascertained periods (Mira Ceti, Algol); and stars whose ©
intensity of light varies, of whose variation, however, the
periodicity is as yet unascertained (as » Argus). It is by no
means improbable, but still does not necessarily follow that
these four kinds of phenomena® have perfectly similar causes
in the photospheres of those remote suns, or in the nature of
their surfaces. |

As we commenced our account of new stars with the most

% Newton (Philos. Nat. Principia mathem., ed. Le Seur
et Jacquier, 1760, tom. iii. p. 671) distinguishes only two
kinds of these sidereal phenomena. ‘Stelle fixe que per
vices apparent et evanescunt, queque paulatim crescunt, '
videntur revolyendo partem lucidam et partem obscuram per
vices ostendere.’’ The fixed stars which alternately appear
und vanish and which gradually increase, appear by turns to
show an illuminated and a dark side. This explanation of
the variation of light had been still earlier advanced by
Riecioli. With respect to the caution necessary in predi.
eating periodicity, see the valuable remarks of Sir John Her«
echel, in his Observations at the Cupe, § 261.

VARIABLE STARS 24)

remarkable of this class of celestial phenomena—the sudden
appearance of Tycho Brahe’s star—so, influenced by similar
considerations, we shall begin our statements concerting the
variable stars whose periods have not yet been ascertained,
with the unperiodical fluctuations in the light of » Argts, which
to the present day are still observabie. This star is situated
in the great and magnificent constellation of the Ship, ‘the
glory of the southern skies.” Halley, as long ago as 1677, on
his return from his voyage to St. Helena, expressed strong
doubts concerning the alternation of light in the stars of Argo,
especially on the shield of the prow and on the deck (domdioxn
and xardorpepa), whose relative orders of magnitude had been
given by Ptolemy.** However, in consequence of the little
reliance that can be placed on the positions of the stars as set
down by the ancients, of the various readings in the several
MSS. of the Almagest, and of the vague estimates of inten-
sity of light, these doubts failed to lead to any result. Accord-
ing to Halley's observation in 1677, 7 Argts was of the 4th
magnitude; and by 1751, it was already of the 2nd, as ob-
served by Lacaille. The star must have afterwards returned
to its fainter light, for Burchell, during his residence in
Southern Africa, from 1811 to 1815, found it of the 4th
magnitude; from 1822 to 1826, it was of the 2nd, as seen
by Fallows and Brisbane; in February, 1827, Burchell, who
happened at that time to be at San Paolo, in Brazil, found
it of the 1st magnitude. perfectly equal to @ Crucis. Aftei
a year, the star returned to the 2nd magnitude. It was of
this magnitude when Burchell saw it on the 29th of Febru-
ary, 1828, in the Brazilian town of Goyaz; and it is thus
set down by Johnson and Taylor, in their catalogues for the
period between 1829 and 1833. Sir John Herschel also, at

*® Delambre, Hist. de Astron. ancienne, tom. ii. p. 280,
and Hist. de l’ Astron. au 18iéme Siécle, p. 119.

VOL. (TI. BR

242 COSMOS.

the Cape of Good Hope, estimated it as being between the
2nd and Ist magnitude, from 1834 to 1837,

When, on the 16th of December, 1837, this famous astro-
nomer was preparing to take the photometric measurements
of the innumerable telescopic stars, between the 11th and
16th magnitudes, which compose the splendid nebula around
n Argis, he was astonished to find this star, which had so often
before been observed, increase to such intensity of light that
it almost equalled the brightness of # Centauri, and exceeded
that of all other stars of the 1st magnitude, except Canopus
and Sirius. By the 2nd of January, 1838, it had for that
time reached the maximum of its brightness. Itsoon became
fainter than Arcturus; but in the middle of April, 1838, it
still surpassed Aldebaran. Up to March, 1848, it continued
to diminish, but was even then a star of the 1st magnitude ;
ufter that time, and especially in April, 1848, it began to
increase so much in light, that, according to the obser-
vations of Mackay at Calcutta, and Maclear at the Cape,
» Argis became more brilliant than Canopus, and almost
equal to Sirius.’ This intensity of light was continued
almost up to the beginning of the present year (1850).
A distinguished observer, Lieutenant Gilliss, who com-
mands the Astronomical Expedition sent by the Govern-
ment of the United States to the Coast of Chili, writes
from Santiago, in February, 1850: ‘“» Argis, with its
yellowish-red light, which is darker than that ef Mars, is
at present next in brilliancy to Canopus, and is brighter
than the united light of # Centauri.” ?* Since the appearance

7 Compare Sir John Herschel’s Observations at the Cape,
§ 71-78 ; and Outlines of Astron., § 830 (Cosmas, vol. i. p. 144).
8 Letter of Lieutenant Gilliss, astronomer of the Observa-
tory at Washington, to Dr. Fliigel, Consul of the United
States of North America at Leipsic (in manuscript). ‘The

VARIABLE STARS, 24°

of the new stars in Ophiuchus in 1604, no fixed star ha
attained to such an intensity of light, and for so long a
period—now nearly seven years. In the 175 years (from
1677 to 1850) during which we have reports of the magnitude
of this beautiful star in Argo, it has undergone from eight to
nine oscillations in the augmentation and diminution of its
light. As an incitement to astronomers to continue their
observations on the phenomenon of a great but unperiodical
variability in » Argis, it was fortunate that its appearance
was coincident with the famous five years’ expedition of Sir
John Herschel to the Cape.

In the case of several other stars, both isolated and double,
observed by Struve (Stellarum compos. Mensure Microm.,
pp- Ixxi.-lxxiii.) similar variations of light have been no-
ticed, which have not as yet been ascertained to be periodical.
The instances which we shall content ourselves with adducing,
are founded on actual photometrical estimations and calcu-
lations made by the same astronomer at different times, and
not on the alphabetical series of Bayer’s Uranometry. In
his treatise De fide Uranometrie Bayeriane, 1842, (p. 15,)
Argelander has satisfactorily shown that Bayer did not by
any means follow the plan of designating the brightest stars
by the first letters of the alphabet; but that, on the contrary,
he arranged the letters by which he designated stars of equal
magnitude according to the positions of the stars in a con-
stellation, beginning usually at the head, and proceeding, iv
regular order, down to the feet. The order of letters in

cloudless purity and transparency of the atmosphere, which
last for eight months, at Santiago, in Chili, are so great, that
Lieutenant Gilliss, (with the jirst great telescope ever con-
structed in America, having a diameter of 7 inches, con-
atructed by Henry Fitz of New York, and William Young cf
Philadelphia), was able clearly to recognize <he sixth star in
the trapezium of Orion.

944 COSMOS.

Bayer’s Uranometria has long led to a belief that a change
of light has taken place in a Aquile, in Castor Geminorum,
and in Alphard of Hydra.

Struve, in 1838, and Sir John Herschel, observed Capella
increase in light. The latter new finds Capella much brighter
than Vega, though he had always before considered it fainter.”
Galle and Heis come to the same conclusion, from their pre-
sent comparison of Capella and Vega. The latter finds Vega
between 5 and 6 gradations, consequently more than half a
magnitude, the fainter of the two.

The variations in the light of some stars in the constellations
of the Greater and of the Lesser Bear are deserving of especia.
notice. ‘The star » Urse majoris,’’ says Sir John Herschel
‘is at present certainly the most brilliant of the seven brigh;
stars in the Great Bear, although, in 1837, s unquestionably
held the first place among them.” This remark induced me
to consult Heis, who so zealously and carefully occupies
himself with the variability of stellar light. The follow-
ing,” he writes, “is the order of magnitude which results
from my observations, carried on at Aix-la-Chapelle between
1842 and 1850: 1.¢ Urse majoris, or Alioth; 2. a, or
Dubhe; 8. #, or Benetnasch; 4. 8, or Mizar; 5. B; 6.y; 7. 2
The three stars, ¢, «, and », of this group are nearly equal
in brightness, so that the slightest want of clearness in the
atmosphere might render their order doubtful; ¢ is decidedly
fainter than the three before mentioned. The two stars 8
and y, (both of which are decidedly duller than {) are nearly
equal to each other; lastly 4, which in ancient maps is usually

%” Sir John Herschel (Odservaiions at the Cape, pp. 334,
350, note 1, and 440). For older observations of Capeila and _
Vega, see William Herschel, in the Philos. Transact., 1797,
p- 807, 1799, p. 121; and Beae’s Jahrbuch fiir 1810, s. 148.
Argelander, on the other Land, advances many doubts as :
to the variation of Capella avd of the stars of the Bear.

VARIABLE STARS. 245

set down as of the same magnitude with B and y, is by
more than a magnitude fainter than these; ¢ is decidedly
variable. Although in general this star is brighter, I have
nevertheless in three years observed it on five occasions
to be undoubtedly fainter than a. I also consider 8 Ursex
majoris to be variable, though I am unable to give any fixed
periods. In the years 1840 and 1841, Sir John Herschel
found 8 Urse minoris much. brighter than the Polar star:
whereas still earlier, in May, 1846, the contrary was ob-
served by him. He also conjectures 8 to be variable.¥
Since 1843, I have, as a rule, found Polaris fainter than 6
Ursee minoris; but from October, 18438, to July, 1849, Polaris
was, according to my registers, 14 times brighter than 8.
I have had frequent opportunities of convincing myself that
the colour of the last-named star is not always equally red;
it is at times more or less yellow, at others. most decidedly
red.” ** All tie pains and labour spent in determining the
relative brightness of the stars will never attain any certain
result until the arrangement of their magnitudes from mere
estimation shall have given place to methods of measurement
founded on the progress of modern optical science.* The
possibility of attaining such an object need not be despaired
of by astronomers and physicists.

The probably great physical similarity in the process of

*” Observations at the Cape, § 259, note 260.

* Heis, in his Manuscript Notices of May, 1850; also
Observations at the Cape, p. 325; and P. von Boguslawski.
Uranus for 1848, p. 186. The asserted variation of », a, and 3
Urse maj. is also confirmed in Outlines, p.559. See Madler,
Astr., p. 432. On the succession of the stars which, from
their proximity, will in time mark the north pole, until, after

the lapse of 12000 years, Vega, the brightest of all possible
polar stars, will take their place.

® Cosmos, vide supra, p. 128.

Meger

246 COSMOS.

light in-all self-luminous stars (1n the central body of our own
planetary system, and in the distané suns or fixed stars) has
long and justly directed attention to the importance® and
significance which attach to the periodical or non-periodical
variation in the light of the stars in reference to clima-
tology generally ;—to the history of the atmosphere, or
the varying temperature which our planet has derived in
the course of thousands of years from the radiation of the
sun;—with the condition of organic life, and its forms of
development in different degrees of latitude. The variable
star in the neck of the Whale (Mira Ceti) changes from
the 2nd magnitude to the 11th, and sometimes vanishes
altogether; we have seen that 9 Argis has increased from
the 4th to the 1st magnitude, and among the stars of this
class has attained to the brilliancy of Canopus, and almost to
that of Sirius. Supposing that our own sun has passed
through only a very few of these variations in intensity
of light and heat, either in an increasing or decreasing
ratio, (and why should it differ from other suns?) such a
change, such a weakening or augmentation of its light-pro-
cess, may account for far greater and more fearful results
for our own planet than any required for the explanation of
all geognostic relations, and ancient telluric revolutions.
William Herschel and Laplace were the first to agitate these
views. If I have dwelt upon them somewhat at length, it is
not because I would seek exclusively in these the solution of
the great problem of the changes of temperature in our earth,
The primitive high temperature of this planet at its forma-
tion, and the solidification of conglomerating matter—the

% William Herschei, On the Changes that happen to the
Fixed Stars, in the Philos. Transact. tor 1796, p. 186. Sir
John Herschel in the Observations at the Cape, pp. 350-352;
as also in Mrs. Somerville’s excellent work, Connexion of the
Paysical Sciences, 1£46, p. 407.

VARIAELE STARS. 247

radiation of heat from the deeper strata of the earth through
open fissures, and through unfilled veins—the greater power
of electric currents—a very different distribution of sea and
land;—may also, in the earliest epochs of the earth’s
existence, have rendered the diffusion of heat independent of
latitude; that is to say, of position relatively to a centrai
body. Cosmical considerations must not be limited merety
to astrognostic relations.

Vv.

FROPER MOTION OF THE FIXED STARS.~—-PROBLEMATICAL
EXISTENCE OF DARK COSMICAL BODIES.—PARALLAX.-—
MFASURED DISTANCES OF SOME OF THE FIXED STARS.
— DOUBTS AS TO THE ASSUMPTION OF A CENTRAL BODY
FOR THE WHOLE SIDEREAL HEAVENS.

Tue heaven of the fixed stars, in contradiction to its very
name, exhibits, not only changes in the intensity of light,
but also further variation from the perpetual motion of the
individual stars. Allusion has already been made to the
fact that, without disturbing the equilibrium of the star-
systems, no fixed point is to be found in the whole heavens,
and that of all the bright stars observed by the earliest of the
Greek astronomers, not one has kept its place unchanged. In
the case of Arcturus, of » Cassiopeie, and of a double star in
Cygnus, this change of position has, by the accumulation
of their annual proper motion during 2000 years, amounted
respectively to 24, 34, and 6 moon’s diameters. In the
course of 3000 years about twenty fixed stars will have
changed their places by 1° and upwards.' Since the proper
motions of the fixed stars rise from ;!,th of a second to
7°7 seconds (and consequently differ, at the least, in the
ratio of 1:154), the relative distances also of the fixed stars

1 Encke, Betrachtungen uber die Anordnung des Stern--
systems, 8. 12. Vide supra, p. 30. Madler, Asér., s. 445.

PROPER MOTION OF THE STARS. 249

from each other, and the configuration of the constellations
themselves, cannot in long periods remain the same. The
Southern Cross will not always shine in the heavens exactly
in its present form; for the four stars of which it consists
move with unequal velocity in different paths. How many
thousand years will elapse before its total dissolution, cannot
be calculated. In the relations of space and the duration of
time, no absolute idea can be attached to the terms great and
smali.

In order to comprehend under one general point of view the
changes that take place in the heavens, and all the modifications
which in the course of centuries occur in the physiognomic
character of the vault of heaven, or in the aspect of the firma-
ment from any particular spot, we must reckon as the active
causes of this change: (1), the precession of the equinoxes
and the nutation of the earth’s axis, by the combined opera-
tion of which new stars appear above the horizon, and others
become invisible; (2), the periodical and non-periodical varia-
tions in the brightness of many of the fixed stars; (3), the
sudden appearance of new stars, of which a few have
continued to shine in the heavens; (4), the revolution of
telescopic double stars round a common centre of gravity.
Among these so-called fixed stars which change slowly and
unequally both in the intensity of their light and in their
position, twenty principal planets move in a more rapid
course, five of them being accompanied by twenty satellites.
Besides the innumerable, but undoubtedly rotatory fixed
stars, forty moving planetary bodies have up to this time
(October, 1850) been discovered. In the time of Copernicus
and of Tycho Brahe, the great improver of the science of
observation, only seven were known. Nearly two hundred
comets, five of which have short periods of revolution and are
interior, or, in other words, are inclosed within those of the

250 COSMOS.

principal pianets, still remain to be mentioned in our list of
planetary bodies. Next to the actual planets and the new
cosmical bodies which shine forth suddenly as stars of the
Ist magnitude, the comets, when, during their usually brief
appearance they are visible to the naked eye, contribute the
most vivid animation to the rich pictwre—I had almost said
the impressive landscape—of the starry heavens.

The knowledge of the proper motion of the fixed stars
is closely connected historically with the progress of the
science of observation through the improvement of instru-
ments and methods. The discovery of this motion was first
rendered practicable when the telescope was combined with
graduated instruments; when from the accuracy of within a
minute of an are (which after much pains Tycho Brahe firs:
succeeded in giving to his observations on the Island of Hver)
astronomers gradually advanced to the accuracy of a second
and the parts of a second ;—and when it became possibie to
compare with one another results separated by a long series of
years. Such a comparison was made by Halley with respect to
the positions of Sirius, Arcturus, and Aldebaran, as determined
by Ptolemy in his Hipparchian catalogue, 1844 years before.
By this comparison he considered himself justified (1717) in
announcing the fact of a proper motion in the three above-
named fixed stars.2 The high and well-merited attention
which, long subsequent even to the observations of Flamstead
and Bradley, was paid to the table of right ascensisns con-
tained in the Zriduwm of Rémer, stimulated Tobias Mayer
(1756), Maskelyne (1770), and Piazzi (1800), to compare

* Halley, in the Philos. Transact. for 1717-1719, vol. xxx.
p. 736. The essay, however, referred solely to variations
in latitude. Jacques Cassini was the first to add varia-
tions in longitude. (Arago, in the Annuare pour 1842,

p. 387.)

PROPER MUTION OF ‘THE STARS. 251

Rémer’s observations with more recent ones.* The proper
motion of the stars was in some degree recognized as a general
fact, even in the middle of the last century; but for the more
precise and numerical determination of this class of pheno-
mena we are indebted to the great work of William Herschel
in 1783, founded on the observations of Flamstead,‘ and still
more to Bessel and Argelander’s successful comparison of
Bradley's ‘ Positions of the Stars for 1755” with recent
catalogues.

The discovery of the proper motion of the fixed stars has
proved of so much the greater importance to physical astro-
nomy, as it has led to a knowledge of the motion of our own
solar system through the star-filled realms of space, and,
indeed, to an accurate knowledge of the direction of this
motion. We should never have become acquainted with this
fact, if the proper progressive motion of the fixed stars were
so small as to elude all our measurements. The zealous
attempts to investigate this motion, both in its quantity and
its direction, to determine the parallax of the fixed stars,
and their distances, have, by leading to the improvement and
perfection of arc-graduation and optical instruments in
connexion with micrometric appliances, contributed more
than anything else to raise the science of observation to the
height which, by the ingenious employment of great meridian-
circles, refractors, and heliometers, it has attained, especially
since the year 1830.

Tke quantity of the measured proper motions of the stars
varies, as we intimated at the commencement of the pre-
sent section, from the twentieth part of a second almost to
eight seconds. The more luminous stars have in general
a slower motion than stars from the 5th to the 6th and

* Delambre, Hist. de [ Astron. moderne, t. ii. p. 658,
Also in Hist. de 0 Astron. au 18éme siécle, p. 448.
* Philos. Traxsact., vol. xxiii. p. 138.

252 COSMOS.

7th magnitudes.* Seven stars have revealed an unusually
great motion, namely :—Arcturus, lst magnitude (27:25) ;
e Centauri, lst magnitude (3°58) ;* « Cassiopeie, 6th mag-
nitude (3°”74); the double star, d Eridani, 5-4 magnitude
(4”°08); the double star 61 Cygni, 5-6 magnituce, (5”-123),
discovered by Bessel in 1812, by means of a comparison with
Bradley’s observations; a star in the confines of the Canes
Venatici,’ and the Great Bear, No. 1830 of the catalogue of
the circumpolar stars by Groombridge, 7th magnitude (ac-
cording to Argelander, 6974); « Indi (7:74. according to
D’Arrest);* 2151 Puppis, 6th magnitude (7’°871). The
arithmetical? mean of the several proper motions of the fixed
stars in all the zones into which the sidereal sphere has been
divided by Madler, would scarcely exceed 0”°102. |

An important inquiry into the “ Variability of the proper
motions of Procyon and Sirius,” in the year 1844, a short

5 Bessel, in the Jahrbuch von Schumacher fir 1839, s. 38.
Arago, Annuaire pour 1842, p. 889.

a Centauri, see Henderson and Maclear, in the Monoths
of the Astron. Soc., vol. xi. p. 61; and Piazzi Smyth, in the
Edinburgh T ransact., vol. xvi. p. 447. The proper motion
of Arcturus, 2”°25 (Baily, in the same Memozrs, vol. v. p. 165),
considered as that of a very bright star, may be called very
large in comparison with Aldebaran, 0”°185 (Madler, Central-
sonne, 8. 11), and @ Lyre, 0”-400. Among the stars of the
lst magnitude, a Centauri, with its great proper motion of
3”°58, forms a very remarkable exception. The proper motion
of the binary system of Cygnus amounts, according to Bessel
(Schum. Astr. Nachr., bd. xvi. s. 93), to 5”°123.

7 Schumacher’s Asétr. Nachr., no. 455.

8 Op. cit., no. 618, s. 276. D’Arest founds this result on
comparisons of Lacaille (1750) with Brisbane (1825), and of
Brisbane with Taylor (1835). The star 2151, Puppis, has a
proper motion of 7871, and is of the 6th magnitude,
(Maclear, in Madler’s Uniers. uber die Fiastern-Systeme, th.
ii. s. 5.

° Schum. Asétr. Nachr., no. 661, s. 201.

PROPER MOTION OF THE STARS. 253

“in.e, therefore, before the beginning of his last and painful
illness, led Bessel, the greatest astronomer of our time, to the
conviction ‘‘ that stars whose variable motion becomes appa-
rent by means of the most perfect instruments, are parts of
systems confined to very limited spaces in proportion to their
great distances from one another.” This belief in the exis-
tence of double stars, one of which is devoid of light, was so
firmly fixed in Bessel’s mind, as my long correspondence with
him testifies, that it excited the most universal attention,
partly on his account, and partly from the great interest
which independently attaches itself to every enlargement of
our knowledge of the physical constitution of the sidereal
heavens. ‘The attracting body,” this celebrated observer
remarked, ‘“‘ must be very near either to the fixed star which
reveals the observed change of position, or to the sun. As,
however, the presence of no attracting body of considerable
mass at a very small distance from the sun, has yet been
perceived in the motions of our own planetary system, we are
brought back to the supposition of its very small distance from
a star, as the only tenable explanation of that change in the
proper motion which, in the course of a century, becomes
appreciable.” ” Ina letter (dated July, 1844) in answer to
one in which I had jocularly expressed my anxiety regard-
ing the spectral world of dark stars, he writes: “At all
events, I continue in the belief that Procyon and Sirius are
true double stars, consisting of a visible and an invisible star.
No reason exists for considering luminosity an essential pro-
perty of these bodies. The fact that numberless stars are
visible, is evidently no proof against the existence of an
equally incaleulable number of invisible ones. The physical
difficulty of a change in the proper motion, is satisfactorily
set aside by the hypothesis of dark stars. No blame attaches

%” Schum. Asétr. Nachr., nos. 514-534.

254 COSMOS.

to the simple supposition that the change ot velocity only
takes place in consequence of the action of a force, and that
forces act in obedience to the Newtonian laws.”

A year after Bessel’s death, Fuss, at Struve’s suggestion,
renewed the investigation of the anomalies of Procyon and
Sirius, partly with new observations with Ertel’s meridian-
telescope at Pulkowa, and partly with reductions of, and
comparisons with, earlier observations. The result, in the
opinion of Struve and Fuss™ proved adverse to Bessel’s
assertion. A laborious investigation which Peters has now
completed at Kénigsberg, on the other hand, justifies it; as
does also a similar one advanced by Schubert, the calculator
for the North American Nautical Almanack.

The belief in the existence of non-luminou¢ stars was
diffused even among the ancient Greeks, and especially in
the earliest ages of Christianity. It was assumed that
among the fiery stars which are nourished by the celestial
vapours, there revolve certain other earthlike bodies, which,
however, remain invisible to us.’ The total extinction of
new stars, especially of those so carefully observed by Tycho
Brahe and Kepler in Cassiopeia and Ophiuchus, appears to
corroborate this opinion. Since it was at the time conjec-
tured that the first of these stars had already twice appeared,
and that too at intervals of nearly 300 years, the idea of
annihilation and total extinction naturally gained little or
no credit. The immortal author of the Mécanique Céleste bases
his conviction of the existence of non-luminous masses in the
Universe on these same phenomena of 1572 and 1604:
** These stars that have become invisible after having sur-
passed the brilliancy of Jupiter, have not changed their place

" Struve, Etudes d’ Astr. stellaire, Texte, p. 47, Notes, pp.
26, and 51-57; Sir John Herschel, Outl., § 859 and 860.
® Origen, in Gronov. Thesau»., ¢. x. p. 271.

PROPER MOTION OF YHE STARS. 256

during the time of their being visible.” (The luminous pro-
cess in them has simply ceased.) ‘* There exist therefore in
celestial space dark bodies of equal magnituder, and probably
in as great numbers as the stars.””"* So also Madler, in his
Untersuchungen tiber die Fixstern-Systeme, says: *—*‘* A dark
body might be a central body; it might, like our own sun,
be surrounded in its immediate neighbourhood only by dark
bodies like our planets. ‘ The motions of Sirius and Procyon,
pointed out by Bessel, force us to the assumption that there
are cases where luminous bodies form the satellites of dark
masses.” Jt has been already remarked that the advocates
ot the emanation theory consider these masses as both invisible,
and also as radiating light: invisible, since they are of such
huge dimensions that the rays of light emitted by them (the
molecules of light) being impeded by the force of attraction,
are unable to pass beyond a certain limit. If, as may
well be assumed, there exist, in the regions of space, dark
invisible bodies in which the process of light-producing
vibration does not take place, these dark bodies cannot fall
within the sphere of our own planetary and cometary system,
or at all events their mass can only be very small, since
their existence is not revealed to us by any appreciable
disturbances.

The inquiry into the quantity and direction of the motion of
the fixed stars, (both of the true motion proper to them, and
also of their apparent motion, produced by the change in tha
place of observation, as the earth moves in its orbit,) the

* Laplace, Expos. du Syst. du Monde, 1824, p. 3895.
Lambert, in his Kosmologische Briefe, shows remarkable ten-
dency to adopt the hypothesis of large dark bodies.

Madler, Untersuch. tiber die Fixstern-Systeme, th. ii. (1848),
s. 3; and his Astronomy, s. 416.

‘© Cosmos, vol. iii. p. 117 and note: Laplace, in Zach’s
silig. Geogr. Ephem., bd. iv. s. 1; Madler, Ast. s 3938.

256 COSMOS.

determination of the distances ot the fixed stars from the
suu, by ascertaining their paratlar; and the conjecture as tv
the part in universal space towards which our planetary system
is moving—are three problems in astronomy, which, through
the means of observation already successfully employed in
their partial solution, are closely connected with each other.
Every improvement in the instruments and methods which
have been used for the furtherance of any one of these difficult
and complicated problems, has been beneficial to the others.
I prefer commencing with the parallaxes and the determination
of the distances of certain fixed stars, to complete that which
especially relates to our present knowledge of isolated fixed
stars.

As early as the heginning of the seventeenth century,
Galileo had suggested the idea of measuring the ‘“ certainly
very unequal distances of the fixed stars from the solar
system,” and indeed with great ingenuity, was the first to
point out the means of discovering the parallax: not by
determining the stars’ distance from the zenith or the pole,
‘but by the careful comparison of one star with another
very near it.”” He gives, in very general terms, an account
of the micrometrical method, which William Herschel,
(1781,) Struve, and Bessel subsequently made use of.
*Perché io non credo,” says Galileo,* in his third dialogue
(Giornata terza), ‘che tutte le stelle siano sparse in una
sferica superficie egualmente distanti da un centro; ma stimo,
che le loro lontananze da noi siano talmente varie, che
aleune ve ne possano esser 2 e 3 volte pid remote di aleune
altre; talché quando si trovasse col telescopio qualche piccio-
lissima stella vicinissima ad alcuna delle maggiort, e che

% Onvere di Galileo Galilei, vol. xii. Milano, 1811, p. 206.
This remarkable passage, which expresses the possibility and
the project of a measurement, was pointed out by Araga ;
see his Annuaire pour 1842, p 382.

GISTANCES OF THE STARS. 257

pero quella fusse altissima, potreble accadere che qualche sen-
sibil mutazione succedesse tra di loro.” ‘* Wherefore I do
‘not believe,” says Galileo, in his third discourse (Giornata
terza), “that all the stars are scattered over a spherical
superficies, at equal distances from a common centre; but lam
of opinion that their distances from us are so various that
some of them may be two or three times as remote as
others, so that when some minute star is discovered by
the telescope close to one of the larger, and yet the
former is highest, it may be that some sensible change
might take place among them.” ‘The introduction of the
Copernican system imposed, as it were, the necessity of nume-
rically determining, by means of measurement, the change
of direction occasioned in the position of the fixed stars by
the earth’s semi-annual change of place in its course round
the sun. Tycho Brahe’s angular determinations, of which
Kepler so successfully availed himself, do not manifest any
»erceptible change arising from parallax in the apparent posi-
tions of the fixed stars, although, as I have already stated,
they are accurate to a minute of the are. For this the
Copernicans long consoled themselves with the reflection, that
the diameter of the earth’s orbit (1654 millions of geographical
miles) was insignificant, when compared to the immense
distance of the fixed stars.

The hope of being able to determine the existence of parallax
must accordingly have been regarded as dependent on the
perfection of optical and measuring instruments, and on the
possibility of accurately measuring very small angles. As long
as such accuracy was only secure within a minute, the non-
observance of parallax merely testified to the fact, that the dis-
tance of the fixed stars must be more than 3438 times the earth’s
mean distance from the sun, or semi-diameter of its orbit."

™ Bessel, in Schumacher’s Jahrb. fir 1839, 5. 511.
VOL. TI. 5

258 COSMOS.

This Jower limit of distances rose to 206265 semi-diameters
when certainty to a second was attained in the observations
of the great astronomer, James Bradley; and in the brilliant
period of Frauenhofer’s instruments, (by the direct measure-
ment of about the 10th part of a second of arc) it rose still
higher to 2062648 mean distances of the earth. The labours
and the ingeniously contrived zenith apparatus of Newton’s
great contemporary, Robert Hooke (1669), did not lead to the
desired end. Picard, Horrebow, (who worked out Rémer’s
rescued observations) and Flamstead, believed that they had
discovered parallaxes of several seconds, whereas they had con-
founded the proper motions of the stars with the true changes
from parallax, On the other hand, the ingenious John Michell
(Phil, Trans. 1767, vol. lvii. pp. 234-264), was of opinion
that the parallaxes of the nearest fixed stars must be less than
0”-02, and in that case could only ‘ become perceptible when
magnified 12000 times.’’ In consequence of the widely dif-
fused opinion, that the superior brilliancy of a star must inva-
riably indicate a greater proximity, stars of the 1st magnitude,
as, for instance, Vega, Aldebaran, Sirius, and Procyon, were,
with little success, selected for observation by Calandrelli and
the meritorious Piazzi (1805). These observations must be
classed with those which Brinkley published in Dublin
(1815), and which ten years afterwards were refuted by Pond,
and especially by Airy. An accurate and satisfactory know-
ledge of parallaxes, founded on micrometric measurements,
dates only from between the years 1832 and 1838.

Although Peters,® in his valuable work on the distances
of the fixed stars (1846), estimates the number of parallaxes
hitherto discovered at 33, we shall content ourselves with
referring to 9, which deserve greater, although very different,
degrees of confidenee, and which we shall, consider iw the
probable order of their determinations.

® Struve, dst. stell., p. 104.

DISTANCES OF THE STARS. 259

The first place is due to the star 61 Cygni, which
Bessel has rendered so celebrated. The astronomer of
KG6nigsberg determined, in 1812, the large proper motion

of this double star, (below the 6th magnitude,) but it was

not until 1838, that, by means of the heliometer, he dis-
covered its parallax. Between the months of August, 1812,
and November, 1813, my friends Arago and Mathieu institu-
tuted a series of numerous observations, for the purpose of
finding the parallax of the star 61 Cygni, by measuring its

' distance from the zenith. In the course of their labours they

arrived at the very correct conclusion that the parallax of
this star was less than half a second.” So late as 1815 and

#” Arago, in the Connaissance des Temps pour 1834, p. 281:
—‘* Nous observames avec beaucoup de soin, Mr. Mathieu
et moi, pendant le mois d’Aoit, 1812, et pendant le mois de
Novembre suivant, la hauteur angulaire de ]’étoile audessus
de lhorizon de Paris. Cette hauteur, a la seconde époque,
ne surpasse la hauteur angulaire a la premiére que de 0”°66.
Une parallaxe absolue d’une seule seconde aurait néces-
sairement amené entre ces deux hauteurs une difference de
1”-2. Nos observations n’indiquent done pas que le rayon
de l’orbite terreste, que 39 millions de lieues soient vus de
la 61° du Cygne sous un angle de plus d'une demi-seconde.
Mais une base vue perpendiculairement soutend un angle d’une
demi-seconde quand on est éloigne de 412 mille fois sa lon-
gueur. Donc la 61° du Cygne est au moins a une distance de
la terre égale 4 412 mille fois 39 millions de lieues.”
‘** During the month of August, 1812, and also during the fol-
lowing November, Mr. Mathieu and myself very carefully
observed the altitude of the star above the horizon, at Paris.
At the latter period its altitude only exceeded that of the
former by 0”°66. An absolute parallax of only a single second
would necessarily have occasioned a difference of 1:2 be-
tween these heights. Our observations do not therefore
show that a semi-diameter of the earth’s orbit, or 39 millions
of leagues, are seen from the star 61 of Cygnus, at an angle
of more thau 0”5. Buta base viewed perpendicularly sub-

& 2

260. COSMOS.

1816, Bessel, to use his own words, ‘had arrived at no ava |
able result.”*® The observations taken from August, 1837, to ©
October, 1838, by means of the great heliometer erected in
1829, first led him to the parallax of 0’:3483, which corresponds
with a distance of 592200 mean distances of the earth, and
a period of 94 years for the transmission of its light. Peters
confirmed this result in 1842, by finding 0”-3490, but sub-
sequently changed Bessel’s result into 0”-3744 by a correction
for temperature.”

tends an angle of 0”:5 only when it is observed at a distance
of 412000 times its length. Therefore the star 61 Cygni is
situated at a distance from our earth at least equal to 412
thousand times 39 miilions of leagues.”

'® Bessel, in Schum. Jahrb. 1839, s. 39-49, and in the
Astr. Nachr., no. 866, gave the result 0”-3136, as a first
approximation. His later and final result was 0’:3483. (As¢r.
Nachr., no. 402, in bd. xvii. s. 274.) Peters obtained by
his own observations the following, almost identical, result,
of 0”:3490. (Struve, Asér. stell., p. 99.) The alteration which,
after Bessel’s death, was made by Peters in Bessel’s cal-
culations of the angular measurements, obtained by the
K6nigsberg heliometer, arises from the circumstance that
Bessel expressed his intention (Astr. Nachr., bd. xvii. s. 267)
of investigating further the influence of temperature on
the results exhibited by the heliometer. This purpose he had
in fact partially fulfilled in the first volume of his Astronomische
Untersuchungen, but he had not applied the corrections of
temperature to the observations of parallax. This application
was made by the eminent astronomer Peters (Ergdnzungsheft
zu den Astr. Nachr., 1849, s.56), and the result obtained.
owing to the corrections of temperature, was, 0’°3744 instead
of 03483.

41 This result of 0’-3744 gives, according to Argelander, as
the distance of the double star 61 Cygni from the sun, 550900
mean distances of the earth from the sun, or 45576000
millions of miles, a distance light traverses in 3177 mean days,
To judge from the three consecutive statements of parallax

DISTANCES OF THE STARS. 261

The parallax of the finest double star of the
southern hemisphere (a Centauri) has been calculated at
0”-9128 by the observations of Henderson, at the Cape of
Good Hope, in 1832, and by those of Maclear, in 1839.*
According to this statement it is the nearest of all the fixed
stars that have yet been measured, being three times nearer
than 61 Cygni. !

The parallax of « Lyre has long been the object of
Struve’s observations. The earlier observations (1836) gave*
between 0”:07 and 0”°18; later ones gave 0”°2613, and a dis-
tance of 771400 mean distances of the earth, with a period
of twelve years for the transmission of its light.* But Peters
found the distance of this brilliant star to be much greater,
since he gives only 0”°103 as the parallax. This result con-
trasts with another star of the lst magnitude (« Centauri),
and one of the 6th (61 Cygni).

The parallax of the Polar Star has been fixed by Peters at
0”-106, after many comparisons of observations made be-
tween the years 1818 and 1838; and this is the more satisfae-
tory, as the same comparisons give the aberration at 20”-455.¥

given by Bessel, 03136, 0”-3483, and 0”:3744, this celebrated
double star has apparently come gradually nearer to us in
light passages amounting respectively to 10, 94, and 8,4 years.

* Sir John Herschel, Outlines, pp. 545 and 551. Madler
‘Astr., s. 425) gives in the case of a Centauri, the parallax
0”-9213 instead of 0”:9128.

*% Struve, Stell. compos. Mens. microm., pp. clxix.—clxxii.
Airy makes the parallax of « Lyre, which Peters had pre-
viously reduced to 01 still lower, indeed too small to be
measureable by our present instruments. (Mem. of the Royal
Astr. Soc., vol. x. p. 270.)

* Struve, on the Micrometrical admeasurements by the
Great Refractor at Dorpat, (Oct. 1839.) in Sehum., Asér.
Nachr., no. 396, s. 178.

* Peters, in Struve, Asér. sétell., p. 109.

202 COSMOS.

The parallax of Arcturus, according to Peters, is 0”:127
Riimker’s earlier observations with the Hamburgh meridian
circle had made it considerably larger. The parallax of another
star of the 1st magnitude, Capella, is still less, being, according
to Peters, 0”°046.

The star No. 1830 in Groombridge’s Catalogue, which,
according to Argelander, showed the largest proper motion
of all the stars that hitherto have been observed in the
firmament, has 4 parallax of 0”:226, according to 48 zenith
distances which were taken with much accuracy by Peters
during the years 1842 and 1843. Faye had believed it to
be five times greater, 1:08, and therefore greater than the
parallax of « Centauri.*

Probable

Fixed Star. Parallax. este, Name of Observer.

a Centauri. . . 0”: 913 0”-07¢ Henderson and Maclear

61 Cygni . . .| 078744 07-020 | Bessel
Sirius. . 0”: 230 ; . | Henderson
1830 Groombridge 0”: 226 | 0”141 | Peters
« Urse Maj. . .| 0” 183 | 0”°106 | Peters
Arcturus.) '. | 0% 127 |= O*O7S Peters
a lyre. ae Ee Oe 0”-038 Peters
Polatia = 4 in) > eh se OCT A08 0”°012 Peters

Capella... .} 0”: 046 | -0”°200 Peters

It does not in general follow from the results hitherto
obtained that the brightest stars are likewise the nearest
to us. Although the parallax of @ Centauri is the greatest
of all at present known, on the other hand, Vega Lyre,
Arcturus, and especially Capella, have parallaxes from three to
eight times less than a star of the 6th magnitude in Cygnus.
Moreover, the two stars which after 2151 Puppis and s Indi
show the most rapid proper motion, viz. the star just men-
tioned in the Swan (with an annual motion of 5”128), and

* Peters, in Struve, Astr. Sfell., p. 101.

DISTANCES OF THE STARS. 268

No. 1830 of Groombridge, which in France is called Arge-
lander’s star (with an annual motion of 6”-974), are three
and four times more distant from the sun than « Centauri,
which has a proper motion of 3”-58. Their volume, mass,
intensity of light,” proper motion, and distance from our
solar system, stand in various complicated relations to each
other. Although, therefore, generally speaking, it may be
probable that the brightest stars are nearest to us, still there
may be certain special very remote small stars, whose photo-
spheres and surfaces, from the nature of their physical con-
stitution, maintain a very intense luminous process. Stars
which from their brilliancy we reckon to be of the 1st magni-
tude, may be further distant from us than others of the 4th,
or even of the 6th magnitude. When we pass by degrees
from the consideration of the great starry stratum of which
our solar system is a part, to the particular subordinate sys-
tems of our planetary world, or to the still lower systems of
Jupiter's and Saturn’s moons, we perceive central bodies
surrounded by masses in which the successive order of
magnitude and of intensity of the reflected light does not
seem to depend on distance. The immediate connexion sub-
sisting between our still imperfect knowledge of parallaxes,
and our knowledge of the whole structural configuraticn of the
universe, lends a peculiar charm to those investigations which
relate to the distances of the fixed stars.

Human ingenuity has invented for this class of investiga-
tions methods totally different from the usual ones, and which,
being based on the velocity of light, deserve a brief mention
in this place. Savary, whose early death proved such a loss
to the physical sciences, had pointed out how the aberration of
light, in double stars, might be used for determining the paral-

7 On the proportion of the amount of proper motion ta
the proximity of the brighter stars. See Struve, Sfevl.
compos. Mensure microm., p. cixiv.

264 COSMOS.

laxes. If, for instance, the plane of the orbit which the secon-
dary star describes around the ce1.tral body is not at right angles
to the line of vision from the earth to the double star, but
coincides nearly with this line of vision itself, then the secon-
dary star in its orbit will likewise appear to describe nearly a
straight line, and the points in that portion of its orbit which
is turned towards the earth will all be nearer to the observer
than the corresponding points of the second half, which is
turned away from the earth. Such a division into two halves
produces not a real but an apparent unequal velocity, with
which the satellite in its orbit recedes from, or approaches, the
observer. If the semi-diameter of this orbit were so great
that light would require several days or weeks to traverse
it, then the time of the half revolution through its more
remote side will prove to be longer than the time in the
side turned towards the observer. The sum of the two un-
equal times will always be equal to the ¢rue periodic time;
for the inequalities caused by the velocity of light reciprocally
destroy each other. From these relations of duration, it is
possible, according to Savary’s ingenious method of changing
days and parts of days into a standard of length, (on the as-
sumption that light traverses 14356 millions of geographical
miles in twenty-four hours), to arrive at the absolute mag-
nitude of a semi-diameter of the earth’s orbit; and the distance
of the central body and its parallax may be then deduced
from a simple determination of the angle under which the
radius appears to the observer.™

In the same way that the determination of the parallaxes
instructs us as to the distances of a small number of the fixed
stars, and as to the place which is to be assigned to them in
the regions of space, so the knowledge of the measure and

* Savary, in the Connaissance des Temps pour 1830, pp. 56
~69, and pp. 163-171; and Struve, zbid. p. clxiv.

PROPER MOTION OF THE STARS. 265

Juration of proper motion, that is to say, of the changes which
take place in the positions of self-luminous stars, throws some
ight on two mutually dependent problems; namely, the motion
of the solar system,” and the position of the centre of gravity in
the heaven of the fixedstars. That which can only be reduced
in so very incomplete a manner to numerical relations, must for
that very reason be ill calculated to throw any clear light onsuch
causal connexion. Of the two problems just mentioned, the
first alone (especially since Argelander’s admirable investiga-
tion) admits of being solved with a certain degree of satis-
factory precision; the latter has been considered with much
acuteness by Madler, but according to the confession of this
astronomer himself.™ his attempted solution is, in consequence
of the many mutually compensating forces which enter into it,
devoid ‘‘ of anything like evidence amounting to a complete
and scientifically certain proof.”

After carefully allowing for all that is due to the precession
of the equinoxes, the nutation of the earth’s axis, the aber-
ration of light, and the change of paiallax caused by the earth’s
revolution round the sun, the remaining annual motion of
the fixed stars comprises at once that which is the con-
sequence of the translation in space of the whole solar sys-
tem, and that also which is the result of the actual proper
motion of the-fixed stars. In Bradley’s masterly labours on
nutation, contained in his great treatise of the year 1748, we
meet with the first hint of a translation of the solar system,
and in a certain sense also with suggestions for the most
desirable methods of observing it. ‘For if our own solar
system be conceived to change its place with respect to abso-

*® Cosmos, vol. i. p. 136.

*® Madler, Astronomie, s. 414.

Arago, in his Annuaire pour 1842, p- 383, was the
first to call attention to this remarkable passage of Brad-
ley’s. See, in the same Annuaire, the section on the trans-
lation of the entire solar system, pp. 389-399.

266 COSMOR.

1ute space, this might, in process of time, occasior an appar-
ent change in the angular distances of the fixed stars; and in
such a case, the places of the nearest stars beir g more affected
than of those that are very remote, their relative positions
might seem to alter, though the stars themselves were really
immoveable. And on the other hand, if our own system be at
rest, and any of the stars really in motion, this might likewise
vary their apparent positions, and the more so, the nearer they
are to us, or the swifter their motions are, or the more pro-
per the direction of the motion is, to be rendered perceptible
by us. Since, then, the relative places of the stars may be
changed from such a variety of causes, considering that
amazing distance at which it is certain some of them are
placed, it may require the observations of many ages to deter-
mine the laws of the apparent changes even of a single star;
much more difficult, therefore, it must be to settle the laws
relating to all the most remarkable stars.”’

After the time of Bradley, the mere possibility, and the
greater or less probability, of the movement of the solar system,
were in turn advanced in the writings of Tobias Mayer, Lam-
bert, and Lalande ; but William Herschel had the great merit
of being the first to verify the conjecture by actual observations
(1783, 1805, and 1806). He found (what has been confirmed,
and more precisely determined by many later and more accurate
inquiries,) that our solar system moves towards a point
near to the constellation of Hercules, in R.A. 260° 44’, and,
N. Decl. 26° 16’ (reduced to the year 1800). Argelander,
by a comparison of 319 stars, and with a reference to Lun-
dahl’s investigations, found it for 1800: R.A. 257° 541,
Decl. + 28° 49’'2; for 1850, R. A. 258° 23’°5, Decl. + 28° 456.
Otto Struve (from 392 stars) made it to be for 1800:
R, A. 261° 269, Decl. + 37° 355; for 1850, 261° 52°6,
Decl. 37° 330. According to Gauss,™ the point in question

* In a letter addressed to me; see Schum. Asér. Nachr.,
no. 622, s, 348.

a”

MOTION OF THE STARS. 267

falls within a quadrangle, whose extremes are, R. A. 258° 46,
and Decl. 30° 40’; R. A. 258° 42’, Decl. + 30° 57’: R. A. 259°
13’, Decl, + 81° 9’; R. A. 260° 4’, Decl. + 30° 32’.

It still remained to inquire what the result would be
if the observations were directed only to those stars of the
southern hemisphere which never appear above the horizon in
Europe. To this inquiry Galloway has devoted his especial
attention. He has compared the very recent calculations
(1880) of Johnson at St. Helena, and of Henderson at the
Cape of Good Hope, with the earlier ones of Lacaille and
Bradley (1750 and 1757). The result® for 1790 was, R. A.
260° 0’, Decl. 34° 23’; therefore for 1800 and 1850, 260° 5’
+ 34° 22’ and 260° 33’, + 34° 20’. This agreement with the
results obtained from the northern starsis extremely satisfactory.

If then the progressive motion of our solar system
may be considered as determined within moderate limits,
the question naturally arises: Is the world of the fixed
stars composed merely of a number of neighbouring partial
systems divided into groups, or must we assume the
existence of an universal relation, a rotation of all self-lumi-
nous celestial bodies (suns) around one common centre of
gravity which ts either filled with matter, or void?
We here, however, enter the domain of mere con-
jecture, to which, indeed, it is not impossible to give a
scientific form, but which, owing to the incompleteness of
the materials of observation and analogy which are at pre-
sent before us, can by no means lead to the degree of evidence
attained by the other parts of astronomy. The fact that we are
ignorant of the proper motion of an infinite number of very
small stars from the 10th to the 14th magnitude, which appear
to be scattered among the brighter ones, especially in the im-
portant part of the starry stratum to which we belong, the

* Galloway, on the Motion of the Solar System, in the
Philos. Transact. 1847, p. 98.

268 COSMO,

annuli of the Milky Way, is extremely prejudicial to tiie
profound mathematical treatment of problems so difficult of
solution. The contemplation of our own planetary sphere,
whence we ascend. from the small partial systems of the moons
of Jupiter, Saturn, and Uranus, to the higher and general solar
system, has naturally led to the belief, that the fixed stars
might in a similar manner be divided into several indivi-
dual groups, and separated by immense intervals of space,
which again (in a higher relation of these systems one to
another) may be subject to the overwhelming attractive
force of a great central body, (one sole sun of the whole
aniverse).* The inference here advanced and founded
on the analogy of ourown solar system, is, however, re-
futed by the facts hitherto observed, In the multiple stars
two or more self-luminous stars (suns) revolve, not round
one another, but round an external and distant centre of
gravity. No doubt something similar takes place in our own
planetary system, inasmuch as the planets do not properly
move round the centre of the solar body, but around the com-
mon centre of gravity of all the masses in the system. But
this common centre of gravity falls, according to the rela

tive positions of the great planets Jupiter and Saturn, some

times within the circumference of the sun’s body, but oftener
out of it. The centre of gravity, which in the case of the
double stars is a void, is accordingly in the solar system at
one time void, at another occupied by matter. All that has
been advanced with regard to the existence of a dark
central body in the centre of gravity of doubie stars, or at
least of one originally dark, but faintly illuminated by the

% The value or worthlessness of such views has been
discussed by Argelander in his essay, ‘* Ueber die eigene
Bewegung der Sonnensystems, hergeleitet aus der eagenen
Bewegung der Sterne, 1837, 8. 39.

-% See Cosmos, vol. i. p. 135. (Bohn’s ed.) (Madler, Asér.
p. 400.)

MOTION OF THE STARS. 269"

borrowed light of the planets which revolve round it, belongs
to the ever enlarging realm of mythical hypotheses.

It is a more important consideration, and one more de-
serving of thorough investigation, that, on the supposition of
a revolving movement, not only of the whole of our planetary
system which changes its place, but also for the proper
motion of the fixed stars at their various distances, the centre
of this revolving motion must be 90° distant™® from the point
towards which our solar system is moving. In this connexion of
ideas the position of stars possessing a great or very small
proper motion becomes of considerable moment. Argelan-
der has examined, with his usual caution and aeuteness, the
degree of probability with which we may seek for a general
centre of attraction for our starry stratum in the constel-
lation of Perseus.” Méadler, rejecting the hypothesis of the
existence of a central body, preponderating in mass, as the
universal centre of gravity, seeks the centre of gravity
in the Pleiades, in the very centre of this group, in or
near * to the bright star » Tauri (Alcyone). The present is

* Argelander, ibid. p. 42; Madler, Centralsonne, s. 9, and
Astr., s. 408.

* Argelander, ibid. p. 48; and in Schum. Asér. Nachr.,
no. 566. Guided by no numerical investigations, but fol-
lowing the suggestions of fancy, Kant long ago fixed upon
Sirius, and Lambert upon the nebula in the belt of Orion,
as the central body of our starry stratum. (Struve, As¢r.
Stell., p. 17, no. 19.)

%* Madler, Astr., s. 880, 400, 407, and 414; in his Cen-
tralsonne, 1846, pp. 44-47; in Untersuehungen iiber die
Fixstern-Systeme, th. ii. s. 183-185. Alcyone is in R. A,
54° 30’, Decl. 23° 36’, for the year 1840. If Aleyone’s
parallax were really 0”-0065, its distance would be equal
to 314 million semi-diameters of the earth's orbit, and thus
it would be 50 times further distant from us than the distance
of the double star 61 Cygni, according to Bessel’s earliest
calculation. The light which comes to the earth from the

270 COSMOS.

not the place to discuss the probability or improbability ® of
such an hypothesis. Praise is, however, due to the eminently
active director of the Observatory at Dorpat, for having by
his diligent labours determined the positions and proper
motions of more than 800 stars, and at the same time excited
investigations which, if they do not lead to the satisfactory
solution of the great problem itself, are nevertheless caleu-
lated to throw light on kindred questions of physical as-
tronomy.

sun in 8’ 18-2, would in that case take 500 years to pass
from Alcyone totheearth. The fancy of the Greeks delighted
itself in wild visions of the height of falls. In Hesiod’s
Theogonia, v. 722-725, it is said, speaking of the fall of the
Titans into Tartarus: ‘If a brazen anvil were to fall from.
heaven nine days and nine nights long, it would reach the earth
on the tenth.”” This descent of the anvil in 777600 seconds
of time gives an equivalent in distance of 309424 geographical
miles, (allowance being made, according to Galle’s caleula-
tion, for the considerable diminution in the force of attrac-
tion at planetary distances,) therefore 14 times the distance
of the-moon from the earth. But, according to the Jliad,i. .
v. 592, Hephaestus fell down to Lemnos in one day, “‘ when
but a little breath was still in him.” The length of the chain
hanging down from Olympus to the earth, by which all the
gods were challenged to try and pull down Jupiter (Zhad, viii.
v. 18), is not given. The image is not intended to convey
an idea of the height of heaven, but of Jupiter’s strength and
omnipotence.

* Compare the doubts of Peters, in Schum. Asétr. Nachr.,
1849, s. 661, and Sir John Herschel, in the Outl. of Astr.,
p. 589:—“In the present defective state of our know-
ledge respecting the proper motion of the smaller stars, we
cannot but regard all attempts of the kind as to a certain ex-
tent premature, though by no means to be discouraged as
forerunners of something more decisive.”

£71

¥ | F

YO£YIFLE OR DOUBLE STARS.— THEIR NUMBERS AND
RECIPROCAL DISTANCES.—PERIOD OF REVOLUTION OF
TWO SUNS ROUND A COMMON CENTRE OF GRAVITY.

WHEN, in contemplating the systems of the fixed stars, we
descend from hypothetical, higher, and more general con-
siderations to those of a special and restricted nature, we
enter a domain more clearly determined, and better calculated
for direct observation. Among the multiple stars, to which
belong the denary or double stars, several self-luminous cosmical
bodies (suns) are connected by mutual attraction, which
necessarily gives rise to motions in closed curved lines.
Before actual observation had established the fact of the revolu-
tion of the double stars, such movements in closed curves were
only known to exist in our own planctary solar system. On
this apparent analogy inferences were hastily drawn, which
for a long time gave rise to many errors. As the term
“double stars’ was indiscriminately applied to every pair of
stars, the close proximity of which precluded their separation
by the naked eye (as, in the case of Castor, a Lyre, 8 Orionis,
and @ Centauri) this designation naturally comprised two
classes of multiple stars: firstly, those which, from their in-
cidental position in reference to the observer, appear in close
proximity, though in reality widely distant and belonging to
totally different strata; and, secondly, those which, from their
actual proximity, are mutually dependent upon each other

* Compare Cosmos, vol. i. pp. 136-139. (Struve, tder
Doppelsterne nach Dorpater Micrometer-Messungen von \824
bis 1887, s. 11.)

272 COSMOS.

in mutual attraction and reciprocal action, and thus constitute
a particular, isolated, sidereal system. The former have long
been called optically, the latter physically, double stars. By
reason of their great distance, and the slowness of their ellip-
tical motion, many of the latver are frequently confounded
with the former. As an illustration of this fact, Alcor, (a star
which had engaged the attention of many of the Arabian
astronomers, because, when the air is very clear, and the organs
or vision peculiarly sharp, this small star is visible to the naked
eye together with @ in the tail of Ursa Major, forms, in the
fullest sense of the term, one of these opéecal combinations,
without any closer physical connexion. In sections II. and
III, I have already treated of the difficulty of separating
by the naked eye adjacent stars, with the very unequal in-
tensity of light, of the influence of the higher brilliancy and
the stars’ tails, as well as of the organic defects which pro-
duce indistinct vision.

Galileo, without making the double stars an especial object
of his telescopic observations (to which his low magni-
fying powers would have proved a_ serious obstacle),
mentious (in a famous passage of the Giornata terza of his
Discourses, which has already been pointed out by Arago) the
use which astronomers might make of optically double stars
(quando si trovasse nel telescopio qualche picciolissima stella
vicinissima ad alcuna delle maggiori) for determining the
parallax of the fixed stars As late as the middle of the

* Vide supra. As a remarkable instance of acuteness of
vision, we may further mention, that Méstlin, Kepler’s
teacher, discovered with the naked eye fourteen, and some
of the ancients nine, of the stars in the Pleiades. (Madler,
Untersuch. tiber die Fixtern-Systeme, th. ii. s. 36.)

* Vide supra. Doctor Gregory of Edinburgh also, in 1675,
(consequently thirty-three years after Galileo’s decease), ree

DOUBLE STARS.. 273

- iast century, scarcely twenty double stars were set down in
the stellar catatogues, if we exclude all those at a greater
distance from each other than 32"; at present—a hundred
years later (thanks chiefly to the great labours of Sir Wil-
liam Herschel, Sir John Herschel, and Struve), about 6000
have been discovered in the two hemispheres. -To the earliest ©
described double stars* belong ¢ Ursee maj. (7th September,
1700, by Gottfried Kirch), a Centauri (1709, by Feuillée),
y Virginis (1718), 2 Geminorum (1719), 61 Cygni (1753),
(which, with the two preceding, was observed by Bradley,
both in relation to distance and angle of direction), p Ophi-
uchi, and @ Cancri. The number of the double stars recorded
has gradually increased, from the time of Flamstead
who employed a micrometer, down to the star-catalogue
‘of Tobias Mayer, which appeared in 1756. Two acutely
speculative thinkers, endowed with great powers of com-
bination, Lambert (Photometria, 1760; Kosmologische Briefe
tiber die Einrichtung des Weltbaues, 1761) and John Michell.
1767, though they did not themselves observe double stars
were the first to diffuse correct views upon the relations of
their attraction in partial bimary systems. Lambert, like
Kepler, hazarded the conjecture that the remote suns (fixed
stars) are, like our own sun, surrounded with dark bodies,
planets, and comets; but of the fixed stars proximate to
each other,® he believed, however much on the other hand
he may appear inclined to admit the existence of dark
central bodies, ‘that within a not very long period they
completed a revolution round their common centre of gravity.”

commended the same parallactic meth od ; see Thomas Birch
Hist. of the Royal Soc., vol. iii. 1757, p. 225. Bradley
(1748) alludes to this method at the phichastin of his ceie-
brated treatise on Nutation.

* Madler, Asétr., s. 477.

* Arago, in the Annuaire pour 1842, p. 400.

VOL, III, Tt

274 COSMOK.

Michell® who was not acquainted with the ideas of Kant and
Lambert, was the first who applied the calculus of proba-
bilities to small groups of stars, which he did with great
ingenuity, especially to multiple stars, both binary and qua-
ternary. He showed that it was 500000 chances to 1 that
the collocation of the six principal stars in the Pleiades did
not result from accident, but that, on the contrary, they owed
their grouping to some internal and reciprocal relation, He
was so thoroughly convinced of the existence of luminous stars,
revolving round each other, that he ingeniously proposed to
employ these partial star-systems to the solution of certain
astronomical problems.”

* An Inquiry into the probable parallax and magnitude
of the fixed stars, from the quantity of light which they afford
us, and the particular circumstances of their situation, by
the Rev. John Mitchell; in the Philos. Transact., vol. lvii.
‘pp. 234-261.

7 John Michell, cdd., p. 238. “If it should hereafter be
found that any of the stars have others revolving about them
(for no satellites by a borrowed light could possibly be visible),
we should then have the means of discovering .... .
Throughout the whole discussion he denies that one of the
two revolving stars can be a dark planet shining with a
reflected light, because both of them, notwithstanding their
distance, are visible to us. Calling the larger of the two the
“Central Star,” he compares the density of both with the
density of our sun, and merely uses the word “ satellite ”
relatively to the idea of revolution, or of reciprocal motion ;
he speaks of the “greatest apparent elongation of those
stars, that revolve about others as satellites.” He fur-
ther says, at pp. 243 and 249: “We may conclude with the
highest probability (the odds against the contrary opinion
_ being many million millions to one) that stars form a kind of
system by mutual gravitatien. It is highly probable in par-
ticular, and next to a certainty in general. that such double
stars as appear to consist of two or more stars placed near
together are under the influence of some general law, such

perhaps as gravity. .... * (Consult also Arago, in «ume

DOUBLE STARS. eg

Christian Mayer, the Manheim astronomer, has the great
merit of having first (1778) made the fixed stars a special
object of research, by the sure method of actual observations.
The unfortunate choice of the term satellites of the fixed stars,
and the relations which he supposed to exist among the
stars between 2° 30’ and 2° 55’ distant from Arcturus, exposed
him to bitter attacks from his contemporaries, and among
these to the censure of the eminent mathematician, Nicolaus
Fuss. That dark planetary bodies should become visible by
reflected light, at such an immense distance, was certainly
improbable. No value was set upon the results of his care-
fully conducted observations, because his theory of the phe-
nomena was rejected; and yet Christian Mayer, in his re-
joinder to the attack of Father Maximilian Hell, Director
of the Imperial Observatory at Vienna, expressly asserts
“that the smaller stars, which are so near the larger, are
either illuminated, naturally dark planets, or that both of
these cosmical bodies—the principal star and its companion
—are self-luminous suns revolving round each other.” The

Annuaire pour 1834, p. 308, and Ann. 1842, p. 400.) No great
reliance can be placed on the individual numerical results of
the calculus of probabilities given by Michell: as the hypotheses
that there are 230 stars in the heavens which, in intensity of
light, are equal to 8 Capricorni, and 1500 equal to the six
greater stars of the Pleiades, are manifestly incorrect. The
ingenious cosmological treatise of John Michell ends with a
very bold attempt to explain the scintillation of the fixed stars
by a kind of “ pulsation in material effluxes of light ’—an
elucidation not more happy than that which Simon Marius, one
of the discoverers of Jupiter’s satellites (see Cosmos, vol. ii.
p. 404,) has given at the end of his Mundus Jovialis (1614)
But Michell has the merit of having called attention to the
fact (p. 263) that the scintillation of stars is always aceom-
panied by a change of colour. “ Besides their brightness
there is in the scintillation of the fixed stars a change of
golour.” (Vide supra.)
r2

276 COSMO.

importance of Christian Mayer’s labours has, long after his
death, been thankfully and publicly acknowledged by Struve
and Midler. In his two treatises, Vertheidigung neuer Beo-
bachtungen von Fixstern-trabanten (1778), and Dissertatio de
novis in Coelo sidereo Phenomenis (1779), eighty double stars
are described as observed by him, of which sixty-seven are
less than 32” distant from each other. Most of these were
first discovered by Christian Mayer himself, by means of the
excellent eight-feet telescope of the Manheim Mural Quad-
rant; ‘‘many even now constitute very difficult objects of
observation, which none but very powerful instruments are
capable of representing, such as g and 71 Herculis, s Lyre,
and w Piscium.”” Mayer, it is true, (as was the practice long
after his time,) only measured distances in right ascension
and declination by meridian instruments, and pointed out,
from his own observations, as well as from those of earlier
astronomers, changes of position; but from the numerical
value of these he omitted to deduct what (in particular cases)
was due to the proper motion of the stars.®

These feeble, but praiseworthy beginnings were followed
by Sir William Herschel’s colossal work on the multiple
stars, which comprises a period of more than twenty-five
years. For although Herschel’s first catalogue of double
stars was published four years after Christian Mayer’s treatise
on the same subject, yet the observations of the former go
back as far as 1779—#indeed, even to 1776, if we take into
consideration the investigations on the trapezium in the
great nebula of Orion. Almost all we at present know of
the manifold formation of the double stars has its origin
in Sir William Herschel’s work. In the catalogues of 1782,

® Struve, in the Recueil des Actes de ia Séance publique de
[ Acad. Imp. des Sciences de St. Pétersbourg, le 29 Dée
1832, pp. 48-50. Madler, Asér., s. 478.

DOUBLE STARS. 277

1788, and 1804, he has not only set down and determined
the pesition and distance of 846 double stars,’ for the most
part first discovered by himself, but, what is far more impor-
tant than any augmentation of number, he applied his
sagacity and power of observation to all those points which
have any bearing on their orbits, their conjectured periodic
times, their brightness, contrasts of colours, and classification
according to the amount’ of their mutual distances. Full
of imagination, yet always proceeding with great caution, it
was not till the year 1794, while distinguishing between
optically and physically double stars, that he threw out
his preliminary suggestions as to the nature of the relation of
the larger star to its smaller companion. Nine years after-
wards, he first explained his views of the whole system of
these phenomena, in the 98rd volume of the Philosophical
Transactions. ‘The idea of partial star-systems, in which
several suns revolve round a common centre of gravity, was
then firmly established. The stupendous influence of attrac-
tive forces, which in our solar system extends to Neptune, a
distance 30 times that of the earth (or 2488 millions of
geographical miles) and which compelled the great comet
of 1680 to return in its orbit, at the distance of 28 of
Neptune’s semi-diameters (853 mean distances of the earth,
or 70800 millions of geographical miles), is also manifested
in the motion of the double star 61 Cygni, which, with a
parallax of 0”-3744, is distant from the sun 18240 semi-
diameters of Neptune’s orbit (7. e. 550900 ecarth’s mean
distances, or 45576000 millions of geographical miles).

® Philos. Transact. for the year 1782, pp. 40-126; for 1783.
pp. 112-124; for 1804, p. 87. Regarding the observations
_ on which Sir William Herschel founded his views respecting
the 846 double stars, see Madler, in Schumacher’s Jahrbuch
fur 1839, s. 59, and his Untersuchungen tiber die Fixstern-
Systeme, th. i. 1847, s. 7.

978 COSMOS.

But although Sir William Herschel so clearly discerned the
causes and general connexion of the phenomena, still, in the
first few years of the nineteenth century, the angles of posi-
tion derived from his own observations, owing to a want of
due care in the use of the earlier catalogues, were confined —
to epochs too near together to admit of perfect certainty in
determining the several numerical relations of the periodic
times, or the elements of their orbits. Sir John Herschel him-
self alludes to the doubts regarding the accuracy of the assigned
periods of revolution of « Geminorum (334 years instead of
520, according to Madler),"° of y Virginis (708 instead of 169),
and of y Leonis (1424 of Struve’s great catalogue), a splendid
golden and reddish-green double star (1200 years).

After William Herschel, the elder Struve (from 1818 to
1842), and Sir John Herschel (from 1819 to 1838), availing
themselves of the great improvements in astronomical instru-
ments, and especially in micrometrical applications, have,
with praiseworthy diligence, laid the proper and special
foundation of this important branch of astronomy. In 1820,
Struve published his first Dorpat Table of double stars,
796 in number. This was followed in 1824 by a second,
containing 3112 double stars, down to the 9th magnitude,
in distances under 32”, of which only about one-sixth had
been before observed. To accomplish this work, nearly
120000 fixed stars were examined by means of the great
Fraunhofer refractor. Struve’s third Table of multiple stars
appeared in the year 1837, and forms the important work
Stellarum compositarum Mensure micrometrice.“ It contains —

10 Madler, zbid., th. i. s. 255. For Castor we have two
old observations of Bradley, 1719 and 1759 (the former taken —
in conjunction with Pond, the latter with Maskelyne), and
two of the elder Herschel, taken in the years 1779 and 1803.
For the period of revolution of y Virginis, see Miadler,
Fixstern-Syst., th. ii. s. 284-40, 1848.

" Struve, Mensure microm., pp. 40 and 234-248. On the

DOUBLE STARS. 279

2787 double stars, several imperfectly observed objects being
carefully excluded.

Sir John Herschel’s unwearied diligence, during his four
years’ residence in Feldhausen, at the Cape of Good Hope,
which, by contributing to an accurate topographical know-
ledge of the southern hemisphere, constitutes an epoch in
astronomy,'* has been the means of enriching this number by
the addition of more than 2100 double stars (which, with
few exceptions, had never before been observed). All these
African observations were taken by a twenty-feet reflecting
telescope; they were reduced for the year 1830, and are in-
cluded in the six catalogues which contain 3346 double stars,
and were transmitted by Sir John Herschel to the Astronomical
Society for the 6th and 9th parts of their valuable Memoirs.®
In these European catalogues are laid down the 380 double
stars which the above celebrated astronomer had observed in
1825, conjointly with Sir James South.

We trace in this historical sketch the gradual advance
made by the science of astronomy towards a thorough know-
ledge of partial, and especially of binary systems. The num-
ber of double stars (those both optically and physically double)
may at present be estimated with some certainty at about 6000,
if we include in our calculation those observed by Bessel
with the excellent Fraunhofer heliometer, by Argelander"™

whole 2641 + 146, 7. e. 2787 double stars have been ob-
served. (Madler, in Schum. Jahrd., 1839, s. 64.)

” Sir John Herschel, Astron. Observ. at the Cape of Good
Hope, pp. 165-303.

8 Tbid., pp. 167 and 242.

* Argelander, in order carefully to investigate their proper
motion, examined a great number of fixed stars. See his
essay, entitled “ DL. X Stellarum fixarum positiones media,
tneunte anno 1830, ex observ. Aboe habitis (Helsingforsia,
1825).” Madler (Ast¢r.,s. 625) estimates the number of mul-
tiple stars in the northern hemisphere, discovered at Pulkowz
since 1837, at not less than 600.

280 COSMOS

at Abo (1827-1835), by Encke and Galle, at Berlin (1836
and 1839), by Preuss and Otto Struve, in Pulkowa (since
the catalogue of 1837), by Madler, in Dorpat, and by Mitchell,
in Cincinnati (Ohio) with a seventeen-feet Munich refractor.
How many of these 6000 stars, which appear to the naked
eye as if close together, may stand in an zmmediak relation of
attraction to each other, forming systems of their own, and
revolving in closed orbits—or, in other words, how many are
so-called physical (revolving) double stars—is an important
problem, and difficult of solution. More revolving compa-
nions are gradually but constantly being discovered. Ex-
treme slowness of motion, or the direction of the plane of the
orbit as presented to the eye, being such as to render the posi-
tion of the revolving star unfavourable for observation, may
long cause us to class physically double stars among those
which are only optically so; that is, stars of which the proximity
is merely apparent. But a distinctly-ascertained appreciable
motion is not the only criterion. The perfectly uniform
motion in the realms of space, (?.e. a common progressive
movement, like that of our solar system, including the
earth and moon, Jupiter, Saturn, Uranus, and Neptune,
with their satellites,) which in the case of a considerable
number of multiple stars has been proved by Argelander and
Bessel, bears evidence that the principal stars and their
companions stand in undoubted relation to each other im
separate partial systems. Madler has made the interesting
remark, that whereas previous to 1836, among 2640 doubie
stars that had been catalogued, there were only 58 in which
a difference of position had been observed with certainty, and
105 in which it might be regarded as more or less proba-
dle; at present, the proportion of physically double stars to
optically double stars has changed so greatly in favour cf the
former, that among the 6000 double stars, according to a
table published in 1849, 650 are known in which a change of

DOUBLE STARS. 281

relative position can be incontestably proved.* The earliest
gomparison gave one-sixteenth, the most recent gives one-
ninth, as the proportion of the cosmical bodies which, by an
observed motion both of the primary star and the companion,
are manifestly proved to be physically double stars.

Very little has as yet been numerically determined re-
garding the relative distribution of the binary star-systems
throughout space, not only in the celestial regions, but even
on the apparent vault of heaven. In the northern hemi-
sphere, the double stars most frequeutly occur in the directior
of certain constellations (Andromeda, Bootes, the Great Bear,
the Lynx, and Orion). For the southean hemisphere Sir John
Herschel has obtained the unexpected result ‘that in the
extra-tropical regions of this hemisphere the number of
multiple stars is far smaller than that in the corresponding
portion of the northern.” And yet these beautiful southern
regions have been explored under the most favourable cir-
cumstances, by one of the most experienced of observers,
with a brilliant twenty-feet reflecting telescope which sepa-
rated stars of the 8th magnitude, at distances even of three-
quarters of a second."*

% The number of fixed stars in which proper motion has
been undoubtedly discovered (though it may be conjectured
in the case of all) is slightly greater than the number of
double stars in which change of position has been observed.
(Madler, Asér., s. 394, 490, and 520-540.) Results obtained
by the application of the Calculus of Probabilities, according
as the several reciprocal distances of the double stars are
between 0” and 1”, 2” and 8”, or 16” and 382”, are given by
Struve, in his Mens microm., p. xciv. Distances less than 0"°8
have been taken, and experiments with very complicated
systems have confirmed the astronomer in the hope that these
estimates are mostly correct within 0”"1. (Struve, uber Doppel-
sterne nach Dorpater Beob., s. 29.)

4 Sir John Herschel, Observations at the Cape, p. 166.

282 COSMOS.

The frequent occurrence of contrasted colours constitutes an
extremely remarkable peculiarity of multiple stars. Struve, in
his great work" published in 1837, gave the following results
with regard to the colours presented by six hundred of the
brighter double stars. In 3875 of these, the colour of both
principal star and companion was the same and equally in-
tense. In 101, a mere difference of intensity could be dis-
cerned. The stars with perfectly different colours were 120
in number, or one-fifth of the whole; and in the remaining
four-fifths the principal and companion stars were uniform
in colour. In nearly one-half of these six hundred, the
principal star and its companion were white. Among those
of different colours, combinations of yellow with blue (as in
« Cancri), and of orange with green, (as in the ternary star
y Andromedz, )'* are of frequent occurrence.

Arago was the first to call attention to the fact that the
diversity of colour in the binary systems principally, or at
least in very many cases, has reference to the complementary
colours—the subjective colours, which when united form
white.” It is a well known optical phenomenon that a faint

" Struve, Mensure microm., pp. xxvii to Ixxxiv.

% Sir John Herschel, Outlines of Astr., p. 579.

1° Two glasses, which exhibit complementary colours, when
placed one upon the other, are used to exhibit whe images
of the sun. During my long residence at the Observatory
at Paris, my friend very successfully availed himself of this
contrivance,—instead of using shade glasses to observe the
sun’s disc. The colours to be chosen are red and green,
yellow and blue, or green and violet. ‘ Lorsqu’une lumi-
ére forte se trouve auprés d’une lumiére faible, la derniére
prend la teinte complementaire de la prémiere. C’est la le con-
traste; mais comme le rouge n’est presque jamais pur, on peut
tout aussi bien dire que le rouge est complémentaire du bleu.
Les couleurs voisines du spectre solaire se substituent.”
* When a strong light is brought into contact with a feeble
one, the latter assumes the complementary colour of the for-

LOUBLE STARS. 283

white light appears green when a strong red light is brought
near it ; and that a white light becomes blue when the stronger
surrounding light is yellowish. Arago, however, with his
usual caution, has reminded us of the fact that even though
_ the green or blue tint of the companion star is sometimes the
result of contrast, still on the whole it is impossible to deny
the actual existence of’ green or blue stars.” There are

mer. This is the effect of contrast; but as red is scarcely
ever pure, it may as correctly be said that red is the ‘com-
plementary of blue: the colours nearest to the solar spectrum
reciprocally change.” (Arago, MS. of 1847.)

* Arago, in the Connaisance des Temps pour Van 1828,
pp. 299-300; and in the Annuaire pour 1834, pp. 246-250 ;
pour 1842, pp. 347-350: “ Les exceptions que je cite,
seater que javais bien raison en 1825 de wm introduire

notion physique du contraste dans la question des étoiles
doubles qu’avee la plus grande réserve. Le bleu est la
couleur réelle de certaines étoiles. Il résulte des observations
recueillies jusqu’ici que le firmament est non seulement par-
semé de soleils rouges et yaunes, comme le savaient les anciens,
mais encore de soleils bleus et verts. C'est au tems et a des
observations futures 4 nous apprendre si les étoiles vertes et
bleues ne sont pas des soleils déja en voie de décroissance; si
les différentes nuances de ces astres n’indiquent pas que la
combustion s’y opére a différens degrés; sila teinte, avec excés
de rayons les plus réfrangibles, que présente souvent la petite
étoile, ne tiendrait pas a la force absorbante d’une atmosphére
que développerait l'action de létoile, ordinairement beaucoup
plus brillante, qu’elle accompagne.”’ ‘‘The exceptions I have
named proved that in 1825 I was quite right in the cautious re-
servations with which I introduced the physical notion of con-
trast in counexion with double stars. Blue is the real colour
of certain stars. The result of the observations hitherto made
proves that the firmament is studded not only with red and
yellow suns, (as was known long ago to the ancients,) but also
with dlwe and green suns. Time and future observations must
determine whether red and blue stars are not suns, the bright-
ness of which is already on the wane; whether the varied
appearances of these orbs do not indicate the degree of com-

284 cosmos.

instances in which a brilliant white star (1527 Leonis, 1768
Can. ven.) is accompanied bya small blue star; others, where
ina double star (8 Serp.) both the principal and its companion
are blue. In order to determine whether the contrast of
colours is merely subjective, he proposes (when the distance
allows) to cover the principal star in the telescope by a thread
or diaphragm. Commonly it is.only the smaller star that is
blue: this, however, is not the case in the double star 23
Orionis (696 in Struve’s Catalogue, p. ]xxx.); where the prin-
cipal star is bluish, and the companion pure white. If im the
multiple stars the differently coloured suns are frequently
surrounded by planets invisible to us, the latter, being dif-
ferently illuminated, must have their white, blue, red, and
green days.*

As the periodical variability® of the stars is, as we have
already pointed out, by no means necessarily connected
with their red or reddish colour, so also colouring in gene-
ral, or a contrasting difference of the tones of colour be-

bustion at work within them; whether the colourand the excess
of the most refrangible rays often presented by the smaller
of two stars be not owing to the absorbing force of an atmo-
sphere developed by the action of the accompanying star,
which is generally much the more brilliant of the two.” (Arago
in the Annuaire pour 1834, pp. 295-3801.)

41 Struve, Ueber Doppelsterne nach Dorpater Beobachtungen,
1837, s. 33-36, and Menswre microm. p. \xxxiii., enumerates
sixty-three double stars, in which both the principal and’
companion are blue or bluish, and. in which therefore the
colours cannot be the effect of contrast. When we are forerd
to compare together the colours of double stars, as reported
by several astronomers, it is particularly striking to observe
how frequently the companion of a red or orange-coloured
star is reported by some observers as blue, and by others
as green.

3 Arago, Annuaire pour 1834, p. 802.

* Vide supra, pp. 175-183.

DOUBLE STARS. 285

tween the principal star and its companion is far from being
peculiar to the multiple stars Circumstances which we find
to be frequent, are not on that account necessary conditions
of the phenomena; whether relating to a pericdical change
of light, or to the revolution in partial systems round a
common centre of gravity. A careful examination of the
right double stars (and colour can be determined even in
those of the 9th magnitude) teaches that, besides white,
all the colours of the solar spectrum are to be found in the
double stars, but that the principal star, whenever it is not
white, approximates in general to the red extreme (that of
the least refrangible rays), but the companion to the violet
extreme (the limit of the most refrangible rays). The reddish
stars are twice as frequent as the blue and bluish; the white
are about 24 times as numerous as the red and reddish. It
is moreover remarkable that a great difference of colour is
usually associated with a corresponding difference in bright-
ness. In two cases—in ¢ Bootis, and y Leonis—which,
from their great brightness can easily be measured by
powerful telescopes, even in the day-time, the former con-
sists of two white stars of the 3rd and 4th magnitudes,
and the latter of a principal star of the 2nd, and of a
companion of the 3°5th, magnitude. This is usually called
the brightest double star of the northern hemisphere, whereas
a Centauri™ and @ Crucis, in the southern hemisphere, sur-

* «This superb double star (a Cent.) is beyond all com-
parison the most striking object of the kind in the heavens,
and consists of two individuals, both of a high ruddy or orange
colour, though that of the smaller is of a somewhat more
sombre and brownish cast.” (Sir John Herschel, Odbserva-
tions at the Cape of Good Hope, p. 300.) And, according
to the important observations taken by Captain Jacob, of the
Bombay Engineers, between the years 1846 and 1848, the
principal star is estimated of the lst magnitude, and the
satellite from the 2°5th to the 8rd magnitude. (Zransact. a!
the Royal Soc. of Edinb., vol. xvi. 1849, p. 451.)

28€E COSMUs.

pass al] the other double stars in brillianey. As in { Bootis,
so also in # Centauri and y Leonis, we observe the rare
combination of two great stars with only a slightly different
intensity of light.

No unanimity of opinion yet prevails respecting the vari-
able brightness in multiple stars, and especially in that of
companions. We have already ™ several times made men-
tion of the somewhat irregular variability of lustre in the
orange-coloured principal star in « Herculis. Moreover, the
fluctuation in the brightness of the nearly equal yellowish
stars (of the 8rd magnitude) constituting the double star
y Virginis and Anon. 2718, observed by Struve, (1831-1833,)
probably indicates a very slow rotation of both suns upon
their axes. Whether any actual change of colour has ever
taken place in double stars (as, for instance, in y Leonis and
y Delphini); whether their white light becomes coloured,
and on the other hand, whether the coloured light of the
isolated Sirius has become white, still remain undecided
questions.” Where the disputed differences refer only to
faint tones of colour, we should take into consideration the
power of vision of the observer, and if refractors have not
been employed, the frequently reddening influence of the
metallic speculum.

Among the multiple systems we may cite as ternaries,
€ Libre, ¢ Cancri, 12 Lyncis, 11 Monoc.); as quaternaries
102 and 2681 of Struve’s Catalogue, a Andromede, s Lyre:
in 6 Orionis, the famous trapezium of the greater nebula of
Orion, we have a combination of six,—probably a system
subject to peculiar physical attraction, since the five smaller
stars (6°3m.; 7m.; 8m.; 11°3m.; and 12m.) follow the proper
motion of the principal star 4°7m. No change in their reia-

— oe ee

*® Cosmos, vol. iii. p. 224 and note.
* Struve, tiber Doppelst. nach Dorp. Beob., s. 33,
Ihid., s. 35

DOUBLE STARS. 287

tive positions has yet been observed.” In the ternary com-
binations of € Libre and ¢ Cancri, the periodical movement
of the *wo companions has been recognized with great cer.
tainty. The latter system consists of three stars of the
8rd magnitude, differing very little in brightness, and the
nearer companion appears to have a motion ten times more
rapid than the remoter one.

The number of the double stars, the elements of whose
orbits it has been found possible to determine, is at present
stated at from fourteen to sixteen.* Of these ¢ Herculis
has twice completed its orbit since the epoch of its first
discovery, and during this period has twice (1802 and 1831)
presented the phenomenon of the apparent occultation of
one fixed star by another. For the earliest calculations of
the orbits of double stars, we are indebted to the industry of
Savary (¢ Ursa Maj.), Encke (70 Ophiuchi), and Sir John
Herschel. These have been subsequently followed by Fessel,
Struve, Madler, Hind, Smyth, and Captain Jacob. Savary’s
and Encke’s methods require four complete observations,
taken at sufficient intervals from each other. The shortest
periods of revolution are thirty, forty-two, fifty-eight, and
seventy-seven years; consequently, intermediate between the
periods of Saturn and Uranus; the longest that have been
determined with any degree of certainty exceed five hundred
years, that is to say, are nearly equal to three times the period
of Le Verrier’s Neptune. The eccentricity of the elliptical
orbits of the double stars, according to the investigations
hitherto made, is extremely considerable; resembling that of
comets, increasing from 0°62 (¢ Coron), up to 0°95 (a Cen-
tauri). The least eccentric interior comet—that of Faye—

*® Madler, Astr.,s. 517. Sir John Herschel, Outl., p. 568.
** Compare Madler, Untersuch. tiber die Firstern-Systene,
th. i s. 225-275; th. ii. s. 285-240; and bis Asér., s. 541.

Sir . .hn Herschel, Outl., p. 573.

283 CORMS,

Las an eccentricity of 0°55, or less than that of the orbits of
the two double stars just mentioned. According to Madler’s
and Hind’s caleulations, 7 Corone and Castor exhibit much
less eccentricity, which in the former is 0°29, and in the latter
0°22 or 0:24. In these double stars the two suns describe
ellipses which come very near to those of two of the smaller
principal planets.in our solar system, the eccentricity of
the orbit of Pallas being 0°24, and that of Juno, 0°25.

If, with Encke, we consider one of the two stars in a binary
system, the brighter, to be at rest, and on this supposition
refer to it the motion of the companion, then it follows from
the observations hitherto made that the companion describes
round the principal star a conic section, of which the latter
is the focus; namely, an ellipse in which the radius vector
of the revolving cosmical body passes over equal superficial
areas in equal times. Accurate measurements of the angles
of position and of distances, adapted to the determination of
orbits, have already shown, in a considerable number of
double stars, that the companion revolves round the princi-
pal star considered as stationary, impelled by the same gra-
vitating forces which prevail in our own solar system. This
firm conviction, which has only been thoroughly attained
within the last quarter of a century, marks a great epoch in
the history of the development of higher cosmical knowledge.
Cosmical bodies, to which long use has still preserved the
name of fixed stars, although they are neither rivetted to
the vault of heaven nor motionless, have been observed
to occult each other. The knowledge of the existence of
partial systems of independent motion tends the more to
enlarge our view, by showing that these movements are
themselves subordinate to more genera: movements animat-
ing the regions of space

283

Elements of the Orbits of Double Stars.

i

*, t Period of
Name. Semi-Major | Eecentricity. | Revolution Calculator.

Axis. in years.
(1) & Ursae Maj. | 3”°857 0°4164 58°262 |Savary 18380
3"°278 0°3777 60°720 | John Herschel
Tables of 1849
2"°295 0°4037 61:300 | Midler 1847
‘G) p Ophiuchi...| 4328 0°4300 73°862 | Encke 1832
(3) f Herculis ...| 1208 0°4320 80°22 | Midler 1847
(4) Castor .........| 8086 0°7582 252°66 | John Herschel
Tables of 1849
5"°692 0°2194 519°77 | Midler 1847
6"°300 0°2405 632°27 | Hind 1849
(5) y Virginis ...| 38”°580 0°8795 182712 | John Herschel
Tables of 1849
3"°863 0°8806 169°44 | Miidler 1847
(8) a Centauri ...| 15"°500 0°9500 77°00 | Captain Jacob

1848
VOL Ill. u

INDEX TO VOL. II.

AcHROMATIC telescopes, 82.

Adalbert, Prince, of Prussia, his
observations on the undulation
of the stars, 76.

Alcor, a star of the constellation
Ursa Major, employed by the
Persians as a test of vision, 61,
272.

Alcyone, one of the Pleiades, ima-
gined the centre of gravity of the
solar system by Madler, 269.

Alphonsine tables, date of their
construction, 204.

Anaxagoras of Clazomenz, his the-
ory of the world-arranging intel-
ligence, 9; origin of the modern
theories of rotatory motion, 10.

Andromeda’s girdle, nebula in, 192.

Arago, M., letters and communica-
tions of, to M. Humboldt, 57,
61, 87, 88, 96, 128, 282; on the
effect of telescopes on the visi-
bility of the stars, 88; on the
velocity of light, 106, 111; on
photometry, 123, 128; his cyanc-
meter, 129.

Aratus, a fragment of the work of
Hipparchus preserved in, 147.
Archimedes, his “* Arenarius,’’ 35.

Arcturus, true diameter of, 118.

Argelander, his view of the number
of the fixed stars, 141; his addi-
tions to Bessel’s catalogue, 155 ;
on periodically variable stars,
224.

» Argis, changes in colour and
brilliancy of, 183, 241.

_ Aristotle, his distinct apprehension

of the unity of nature, 11—14;

his defective solution of the pro-

blem, 14; doubts the infinity of
space, 34; his idea of the genera-
tion of heat by the movement of

the spheres, 166.

U

Astrognosy, th: domain of the fixed
stars, 30.

Astronomy, he observation of
groups of fixed stars, the first
step in, 158; very bright single
stars, the first named, 119.

Atmosphere, limits of the, 49;
effects of an untransparent, 139.

Augustine, St., cosmical views of,
167.

Autolycus of Pitane, era of, 119.

Auzout’s object-glasses, 80.

Bacon, Lord, the earliest views on
the velocity of light found in his
“ Novum Organum,” 105.

Baily, Francis, his revision of De
Lalande’s Catalogue, 155.

Bayer’s lettering of the stars of any
constellation not an evidence of
their relative brightness, 132.

Bérard, Captain, on the change of
colour of the star y Crucis, 183.

Berlin Academy, star-maps of the,
155.

Bessel, on repulsive force, 41; his
star-maps have been the principal
means of the recognition of seven
new planets, 156; calculation of
the orbits of double stars by, 287.

Binary stars, 271.

Blue stars, 183; less frequent than
red, 285.

Blue and green suns, the probable
cause of their colour, 283.

Bond, of the Cambridge Observa-
tory, United States, his resolu-
tion of the nebula in Andro-
meda’s girdle into small stars,
192.

Brewster, Sir David, on the dark
lines of the prismatic spectra, 55.

British Association, their edition of
Lalande’s Catalogue, 155.

2

{

Bruno, Giordano, his cosmical views,
17; his martyrdom, 17.

Busch, Dr., his estimate of the ve-
locity of light incorrect, 109.

Catalogues, astronomical, their great
importance, 153; future disco-
veries of planetary bodies mainly
dependent on their completeness,
153; list of, 154; Halley’s, Flam-
stead’s, and others, 154; La-
lande’s, Harding’s, Bessel’s, 155.

Catasterisms of Eratosthenes, 119.

a Centauri, Piazzi Smyth on, 198,
252; the nearest of the fixed
stars that have yet been mea-
sured, 261.

Central body for the whole sidereal
heavens, existence of, doubtful,
268.

Chinese Record of extraordinary
stars (of Ma-tuan-lin), 146, 210
—215; deserving of confidence,
219.

Clusters of stars, or stellar swarms,
189; list of the principal, 191.
Coal-sacks, a portion of the Milky
Way in the southern hemisphere

so called, 185.

Coloured rings afford a direct mea-
sure of the-intensity of light, 128.

Coloured stars, 175; evidence of
change of colour in some, 177;
Sir John Herschel’s hypothesis,
177; difference of colour usually
accompanied by difference of
brightness, 285.

Comets, information regarding celes-
tial space, derived from observa-
tion on, 36, 47; number of visi-
ble ones, 204.

Concentric rings of stars, a view
favoured by recent observation,
201,

Constellations, arrangement of stars
into, very gradual, 160

Contrasted colours of double stars,
282.

Cosmical contemplation, extension
of. in the middle ages, 16.

‘

2 |

Cosmical vapour, question as to
condensation of, 44; Tycho
Brahe’s and Sir William Her-
schel’s theories, 208. »

‘‘ Cosmos,’ a pseudo-Aristotelian
work, 16.

Crystal vault of heaven, date of the
designation, 165 ; its signification
according to Empedocles, 165;
the idea favoured by the Fathers
of the Church, 168.

Cyanometer, Arago’s, 129.

Dark cosmical bodies, question of,
222, 255.

Delambre, on the velccity of light,
108.

Descartes, his cosmical views, 21 ;
suppresses his work from defer-
ence to the Inquisition, 21.

Dioptric tubes, the precursors of
the telescope, 53.

Direct and reflected light, 57.
Distribution of the fixed stars, ac-
cording to right ascension, 189.
Dorpat table (Struve’s) of multiple

stars, 278.

Double stars, the name too indis-
criminately applied, 271; distri-
bution into optical and physical,
272; pointed out by Galileo as
useful in determining the parallax,
272; vast increase in their ob-
served number, 273, 279; those
earliest described, 273 ; number
in which a change of position has
been proved, 280; greater num-
ber of double stars in the north-
ern than in the southern hemi-
sphere, 281; occurrence of con-
trasted colours, 282; calculation
of their orbits, 287; table of the
elements, 289.

Earth-animal, Kepler and Fludd’s
fancies regarding the, 20.

Edda-Songs, allusion to, 4, 5.

Egypt, zodiacal constellaticns of,
their date, 163.

Ca

Egyptian calendar, period of the
complete arrangement of the, 179.

Ehrenberg, on the incalculable num-
ber of animal organisms, 35.

Electrical light, velocity of trans-
mission of, 114.

Electricity, transmission of, through
the earth, 117.

Elements, Indian origin of the ay-
pothesis of four or five, 9.

Emanations from the head of some
comets, 47.

Encke, his accurate calculation of
the equivalent of an equatorial
degree, 107 ; on the star-maps of
the Berlin Academy, 156; an
early calculator of the orbits of
double stars, 287; his theory of
their motion, 288.

Encke’s comet, considerations on
space, derived from periods of
revolution of, 36; a resisting
medium proved from observation
on, 47.

Ether, different meanings of, in the
East and the West, 36, 37.

Ether (A‘é@’sa, in Sanscrit), one of
the Indian five elements, 36.

Ether, the, fiery, 42.

Euler’s comparative estimate of the
light of the sun and moon, 177.

Fixed stars, the term erroneous, 30,
164; scintillation of the, 96 ; va-
riations in its intensity, 101 ; our
sun one of the fainter fixed stars,
127; photometric arrangement of,
132; their number, 141 ; number
visible at Berlin with the naked
eye, 143; at Alexandria, 144;
Struve and Herschel’s estimates,
157 ; grouping of the, 157 ; distri-
bution of the, 189; proper motion
of the, 248; parallax, 256; num-
ber of, in which proper motion
has been discovered, greater than
of those in which change of posi-
tion has been observed, 281.

Fizeau, M., his experiments on the
velocity of light, 107, 110.

Formula for computing variation of
light of astar, by Argelander, 228.

Galactic circle, average number of
stars in, and beyond the, 188.
Galileo indicates the means of dis-

covering the parallax, 256.

Galle, Dr., on Jupiter’s satellites,
64; on the photometric arrange-
ment of the fixed stars, 132.

Garnet star, the, a star in Cepheus,
so called by William Herschel,
225.

Gascoigne applies micrometer
threads to the telescope, 52

Gauging the heavens, by Sir William
Herschel, 187; length of time
necessary to complete the pro-
cess, 187.

Gauss, on the point of translation
in space of the whole solar sys-
tem, 266.

Gilliss, Lieutenant, on the change
of colour of the star 7 Argis,
183.

Gravitation, not an essential pro-
perty of bodies, but the result of
some higher and still unknown
power, 24.

Greek sphere, date of the, 160, 162.

Green and blue suns, 283.

Groups of fixed stars, recognised
even by the rudest nations, 157;
usually the same groups, as the
Pleiades, the Great Bear, the
Southern Cross, &c., 158.

Halley asserted the motion of Sirius
and other fixed stars, 30.

Hassenfratz, his description of the
rays of stars as caustics on the
crystalline lens, 66, 171.

Heat, radiating, 41.

Hepidannus, monk of Saint Gall,
a new star recorded by, 213, 220.

Herschel, Sir William, on the vivi-
fying action of the sun’s rays, 40;
his estimate of the number of the
fixed stars, 157; his ‘‘ gauging
the heavens,’’ and its result, 187.

{ 4

Jerschel, Sir John, on the trans- |
mission of light, 34; on the in-
fluence of the sun’s rays, 40;
compares the sun to a perpetual
northern light, 40; on the atmo-
sphere, 45; on the blackness of
the ground of the heavens, 47;
on stars seen in daylight, 73; on
photometry, 125; photometric
arrangement of the fixed stars,
132; on the number of stars
actually registered, 142; on the
cause of the red colour of Sirius,
177; on the Milky Way, 196;
on the sun’s place, 203; on the
determined periods of variable
stars, 225; number of double
stars the elements of whose orbits
have been determined, 287.

Hieroglyphical signification of a
star, according to Horapollo, 173.

Hind’s discovery of a new reddish-
yellow star of the 5th magnitude,
in Ophiuchus, 217; has since
sunk to the llth magnitude,
217; calculation of the orbits of
double stars by, 287.

Hipparchus, on the numbe. of the
Pleiades, 60; his catalogue con-
tains the earliest determination
of the classes of magnitude of the
stars, 120; a fragment of his
work preserved to us in Aratus,
147.

iloltzmann, on the Indian zodiacs,
163.

Ijomer, not an authority on the
state of Greek astronomy in his
day, 160, 166.

Humboldt, Alexander von, works
of, quoted in various notes:—
Ansichten der Natur, 105.

Asie Centrale, 150.
Rssai sur la Géographie des
Plantes, 75.

Examen critique de I’ Histoire
de la Géographie, 61, 151.
Lettre a M. Schumacher, 123,

185.

4

Recueil d’Observations Astro-
nomiques, 54, 59, 123.
Relation Historique du Voyage
aux Régionséquinoxiales, 72,
75, 105, 123.
Vue des Cordilléres et Monu-
mens des Peuples indigénes
de ’ Amérique, 162, 180.
Humboldt, Wilhelm von, quoted, 28.
Huygens, Christian, his ambitious
but unsatisfactory Cosmotheus,
22; examined the Milky Way,
195.
Huygens, Constantine, his improve-
ments in the telescope, 80.
Hvergelmir, the cauldron-spring of
the Edda-Songs, 5.

Indian fiction regarding the stars of
the Southern hemisphere, 187.
Indian theory of the five elements

(Pantschaté), 36.
Indian zodiacs, their high antiquity
doubtful, 163.

Jacob, Capt., on the intensity of
light in the Milky Way, 198;
calculation of the orbits of double
stars, by, 287.

Joannes Philoponus, on gravitation,
19.

Jupiter’s satellites, estimate of the
magu*tudes of, 64; case in which
they were visible by the naked
eye, 66; occultations of, observed
by daylight, 80.

Kepler, his approach to the mathe-
matical application of the theory
of gravitation, 18; rejects the
idea of solid orbs, 169.

Lalande, his Catalogue, revised by
Baily, 155.

Lassel’s telescope, discoveries made
by means of, 85.

Lepsius, on the Egyptian name
(Sothis) of Sirius, 180.

Leslie’s photometer, defects of, 129.

Libra, the constellation, date of ita

€
L

introduction into the Greek
sphere, 162.

Light, always refracted, 54; pris-
matic spectra differ in number of
dark lines according to their
source, 55, 56; polarisation of,
57; velocity of, 105; ratio of
solar, lunar, and stellar, 126;
variation of, in stars of ascer-
tained and unascertained period-
icity, 228, 240.

Light of the sun and moon, Euler’s
and Michelo’s estimates of the
comparative, 127,

Limited transparency of the celestial
regions, 46.

Macrobius, ‘‘ Sphzra aplanes’’ of,
31.

Madler, on Jupiter’s satellites, 67;
on the determined periods of
variable stars, 225; on future
polar stars, 245; on non-lumi-
nous stars, 255; on the centre of
gravity of the solar system, 269.

Magellanic clouds, known to the
Arabs, 122.

Magnitude of the stars, classes of,
120, 121.

Malus, his discoveries regarding
light, 57.

**Mappa cecelestis’’? of Schwinck,
189.

Ma-tuan-lin, a Chinese astrono-
mical record of, 146.

Mayer, Christian, the first special
observer of the fixed stars, 275.
Melville Island, temperature of, 43.
Michell, John, 126; applies the
calculus of probabilities to small
groups of stars, 274; little re-
liance to be placed in its indivi-

dual numerical results, 275.

Michelo’s comparative estimate of
the light of the sun and moon,
177.

Milky Way, average number of stars
in, and beyond the, according to
Struve, 188; intensity of its light
in the vicinity of the Southern

ee

Cross, 198; its course and direc-
tion, 199; most of the new stars
have appeared in its neighbour-
hood, 220.

Morin proposes the application o.
the telescope to the discovery of
the stars in daylight, 51, 86.

Motion, proper, of the fixed stars,
248; variability of, 252.

Multiple stars, 175, 271; variable
brightness of, difference of opinion
regarding, 286.

Nebule, probably closely crow?.d
stellar swarms, 44.

Neptune, the planet, its orbit used
as a measure of distance of 61
Cygni, 277.

New stars, 204; their small num-
ber, 204; Tycho Brahe’s descrip-
tion of one, 205; its disappear-
ance, 206; speculations as to
their origin, 218; most have ap-
peared near the Milky Way,
220.

Newton, embraces by his theory of
gravitation the whole uranological
portion of the Cosmas, 23.

Non-luminous stars, problematical
existence of, 254.

Numerical results, exceeding the
grasp of the comprehension, fur-
nished alike by the minutest
organisms and the so-called fixed
stars, 34; encouraging views on
the subject, 35.

Optical and physical double stars,
272; often confounded, 272.

Orbits of double stars, calculation
of the, 287; their great eccentri-
city, 287; hypothesis, that the
brighter of the two stars is at
rest, and its companion revolves
about it, probably correct, and a
great epoch in cosmical know-
ledge, 288.

Orion, the six stars of the trapezium
of the nebula of, probably subject
to peculiar physical attraction, 287,

Bed

Pantschata, or Pantschatra, the
Indian theory of the five elements,
36.

Parallax, means of discovering the,
pointed out by Galileo, 256;
number of parallaxes hitherto
discovered, 258; detail of nine
of the best ascertained, 259.

Penetrating power of the telescope,

Periodically changeable stars, 222.

Periods within periods of varia-
able stars, 228; Argelander on,
228.

Peru, climate of, unfavourable to
astronomical observations, 139.

Peters, on parallax, 261.

Photometric relations of self-lumi-
nous bodies, 119; scale, 132.

Photometry, yet in its infancy, 125;
first numerical scale of, 126;
Arago’s method, 128.

Plato, on ultimate principles, 11.

Pleiades, one of the, invisible to the
naked eye of ordinary visual
power, 60; described, 191.

Pliny estimates the number of stars
visible in Italy at only 1600,
145.

Poisson, his view of the consolida-
tion of the earth’s strata, 44.

Poiarisation of light, 57—60.

Poles of greatest cold, 43.

Pouillet’s estimate of the tempe-
rature of space, 43.

Prismatic spectra, 55; difference of
the dark lines of, 56.

Ptolemy, his classification of the
stars, 120; southern constella-
tions known to, 185.

Pulkowa, number of multiple stars
discovered at, 279.

Pythagoreans, mathematical sym-
bolism of the, 10.

Quaternary systems of stars, 286.
Radiating heat, 41.

Ratio of various colours among the
mustiple and double stars, 285.

Rays of stars, 66, 17i, number of,
indicate distances, 173; disappear
when the star is viewed through a
very small aperture, 173.

Red stars, 176; variable stars mostly
red, 224.

Reflecting sextants applied to the
determination of the intensity of
stellar light, 123.

Reflecting and refracting telescopes,
82.

Regal stars of the ancients, 184.

Resisting medium, proved by obser-
vations on Encke’s and other
comets, 47.

Right ascension, distribution of
stars according to, by Schwinck,
189,

Rings, coloured, measurement of
the intensity of light by, 128.
Rings, concentric, of stars, the hy-
pothesis of, favoured by the most

recent observations, 201.

Rosse’s, Lord, his great telescope,
85; its services to astronomy, 85.

Ruby-coloured stars, 183.

Saint Gall, the monk of, observed
a new star distant from the
Milky Way, 220.

Saussure asserts that stars may be
seen in daylight on the Alps, 74;
the assertion not supported by
other travellers’ experience, 75.

Savary, on the application of the
aberration of light to the deter-
mination of the parallaxes, 264;
an early calculator of the orbits
of double stars, 287.

Schlegel, A. W. von, probably mis-
taken as to the high antiquity of
the Indian zodiacs, 163.

Schwinck, distribution of the fixed
stars in his ‘* Mappa ceelestis,’’
189.

Scintillation of the stars, 96; varia-
tions in its intensity, 101; men-
tioned in the Chinese records,
103; little observed in tropical

ee |

regions, 103, always acco.npanied
by a change of colour, 275.

Seidel, his attempt to determine the
quantities of light of certain stars
of the 1st magnitude, 124.

Self-luminous cosmical bodies, or
suns, 271.

Seneca, on discovering new planets,
31.

Simplicius, the Eclectic, contrasts
the centripetal and centrifugal
forces, 10; his vague view of gra-
vitation, 18.

Sirius, its absolute intensity of
light, 127; historically proved to
have changed its colour, 177; its
association with the earliest de-
velopment of civilization in the
valley of the Nile, 179; etymolo-
gical researches concerning, 180.

Smyth, Capt. W. H., calculations
of the orbits of double stars by,
287.

Smyth, Piazzi, on the Milky Way,
199; on a Centauri, 252.

Sothis, the Egyptian name of Sirius,
179.

South, Sir James, observation of
380 double stars by, in conjunc-
tion with Sir John Herschel,
279.

Southern constellations known to
Ptolemy, 185.

Southern Cross, formerly visible on
the shores of the Baltic, 186.

Southern hemisphere, in parts re-
markably deficient in constella-
tions, 151; distances of its stars,
first measured about the end of
the 16th century, 187.

Space, conjectures regarding, 33;
compared to the mythic period of
history, 33; fallacy of attempts
at measurement of, 34; portions
between cosmical bodies not void,
36; its probable low tempera-
ture, 42.

Spectra, the prismatic, 55; dif-
ference of the dark lines of,
according to their sources, 56.

?

‘¢ Spheeraaplanes”’ of Macrobius, 31

Spurious diameter of stars, 174.

Star of the Magi, Ideler’s explana-
tion of the, 208.

Star of St. Catherine, 185.

Star systems, partial, in which seve-
ral suns revolve about a common
centre of gravity, 277.

Stars, division into wandering and
non-wandering, dates at least from
the early Greek period, 30; mag-
nitude and visibility of the, 60;
seen through shafts of chimneys,
73; undulation of the, 75; ob-
servation of, by daylight, 86;
scintillation of the, 96; variations
in its intensity, ]01; the brightest
the earliest named, 119; rays of,
66, 171—173; colour of, 175;
distribution of, 189; concentric
rings of, 201; variable, 218;
vanished, 2213; periodically
changeable, 222; non-luminous,
of doubtful existence, 254 ; ratio
of coloured stars, 285.

Steinheil’s experiments on the velo-
city of the transmission of elec-
tricity, 116; his photometer, 124.

Stellar clusters, or swarms, 189.

Struve, on the velocity of light, 109;
his estimate of the number of the
fixed stars, 157; on the Milky
Way, 188; his Dorpat tables,
278; on the contrasted colours
of multiple stars, 282; calcula-
tion of the orbits of double stars
by, 287.

Sun, the, described as ‘‘a perpetual
northern light,’’ by Sir William
Herschel, 40; in intensity of
light, merely one of the fainter
fixed stars. 127; its place pro-
bably in a comparatively desert
region of the starry stratum, and
eccentric, 203.

Suns, self-luminous cosmical bodies,
271.

Table of photometric arrangement
of 190 fixed stars, 134; of 17

c 8

siar: of Ist magnitude, 137; of
tne variable stars, by Argelander,
232, and explanatory remarks,
233—240 ; of ascertained paral-
laxes, 262; of the elements of
the orbits of double stars, 289.
Telescope, the principle of, known
to the Arabs, and probably to the
Greeks and Romans, 53; disco-

veries by its means, 78; succes--

sive improvements of the, 80;
enormous focal length of some,
81; Lord Rosse’s, 85; Bacon’s
comparison of, to discovery ships,
175; penetrating power of the,
196.

Telesio, Bernardino, of Cosenza, his
views of the phenomena of inert
matter, 16.

Temperature, low, of celestial space,
42; uncertainty of results yet
obtained, 43; its influence on the
climate of the earth, 45.

Temporary stars, list of, 209 ; notes
to, 210—217.

Ternary stars, 286.

Timur Ulugh Beig, improvements
in practical astronomy in the
time of, 121.

Translation in space of the whole
solar system, 265; first hinted
by Bradley, 265; verified by
actual observation by William
Herschel, 266; Argelander,
Struve, and Gauss’s views, 266.

Trapezium in the great nebula of
Orion, investigated by Sir William
Herschel, 276.

Tycho Brahe, his vivid description
of the appearance of a new star,
205; his theory of the formation
of such, 208.

‘« Ultimate mechanical cause” of all
motion, unknown, 27.

Undulation of the stars, 75.

Undulations of rays ot light, various
lengths of, 112.

Unity of nature distinctly taught by
Aristotle, 11—14.

|

Uranological and telluric domain of
the Cosmos, 29.

Uranus observed as a star by Flam-
stead and others, 153.

Vanished stars, 221; statements
about such to be received with
great caution, 221.

Variable brightness of multiple and
double stars, 285.

Variable stars, 218; mostly of a red
colour, 224; irregularity of their
periods, 226; table of, 232.

Velocity of light, 105; methods of
determining, 106; applied to the
determination of the parallax, 265.

Visibility of objects, 70 ; how modi-
fied, 71.

Vision, natural and telescopic, 51 ;
average natural, 60; remarkable
instances of acute natural, 66, 70.

Wheatstone’s experiments with re-
volving mirrors, 56; velocity of
electrical light determined by,
114.

White Ox, name given to the nebula
now known as one of the Magel-
lanic clouds, 122.

Wollaston’s photometric researches,
127.

Wright, of Durham, his view of the
origin of the form of the Milky
Way, 201.

Yggdrasil, the world-tree of the
Edda-Songs, 4, 5.

Zodiac, period of its introduction
into the Greek sphere, 160; its
origin among the Chaldeans, 161;
the Greeks borrowed from them
only the idea of the division, and
filled its signs with their own
catasterisms, 161; great antiquity
of the Indian very doubtful, 163.

Zodiaca] light, Sir John Herschel on
the, 4

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BAXTER WRAY. :
Parlour and Playground Games.
By Mrs. Laurence GoMME,

BELL’S CATHEDRAL SERIES.

$llustrated Msonograpbs in Dandy Size.

EDITED BY
GLEESON WHITE anp E. F. STRANGE.
In specially designed cloth cover, crown 8vo. 15s. 6d. each.

Now Ready.
CANTERBURY. By HARTLEY WITHERS. 3rd Edition, revised. 37 Illustrations,
CHESTER. By CHARLES HIATT. 2nd Edition, revised. 35 Illustrations,
DURHAM. By J. E. BYGATE, A.R.C.A. 44 Illustrations,
EXETER. By Percy ADDLESHAW, B.A. 2nd Edition, revised. 35 Illustrations.
GLOUCESTER. By H. J. L. J. MAss&, M.A. 4g Illustrations.
HEREFORD. By A. HuGH FISHER; A.R.E. 40 Illustrations.
LICHFIELD. By A. B. CLIFTON. 42 Illustrations.
LINCOLN. ByA. F. KENDRICK, B.A. 2nd Edition, revised. 46 Illustrations.
NORWICH. By C. H. B. QUENNELL. 38 Illustrations.

OXFORD. By Rev. Percy DEARMER, M.A. 2nd Edition, revised. 34 Illus-
trations.

PETERBOROUGH. By Rev. W. D. SWEETING.. 2nd Edition, revised,
51 Illustrations.

ROCHESTER. By G. H. PALMER, B.A. 2nd Edition, revised. 38 Illustrations.
SALISBURY. By GLEESON WHITE. 2nd Edition, revised. 50 Illustrations.
SOUTHWELL. By Rev. ARTHUR DiMocK, M.A. 37 Illustrations.

WELLS. By Rev. Percy DEARMER, M.A. 43 Illustrations.
WINCHESTER. By P. W. SERGEANT. 2nd Edition, revised. 50 Illustrations
YORK. By A. CLuUTTON-BrRock, M.A. 41 Illustrations.

In the Press.

CARLISLE. By C. K. Exey. BRISTOL. By H. J. L. J. Mass#, M.A.
ST. ay By Rev. ArTHuUR Dimock, | ST. ALBANS By Rev. W. D. SwzerIna.
RIPON. By Cecit Hatiett, B.A, eta ie oe By Hi. © COM BSIE

ST. DAVID’S. By Puitie Rosson,
= A.R.LB.A. IRONSIDE Bax.
ELY. By Rev. W. D. Swzetine, M A. GLASGOW. By P. Maccrecor CHAL-
WORCESTER. By E. F. StRaAnGE. MERS, I.A., F.S.A.(Scot.).
Uniform with above Series.e Now ready.
ST. MARTIN’S CHURCH, CANTERBURY. By the Rev. Canon RouTLEDGE.
BEVERLEY MINSTER. By Cuarves Hiatr.

WIMBORNE MINSTER and CHRISTCHURCH PRIORY. By the Rev. T.
PERKINS, M.A,

TEWKESBURY ABBEY. By H. J. L. J. Mass, M.A.
WESTMINSTER ABBEY. By Cuar.es Hiatt.

ST. ASAPH and BANGOR. By P. B.

‘The volumes are handy in size, moderate in price, well illustrated, and written in a
scholarly spirit, The history of cathedral and city is intelligently set forth and accompanied
by a descriptive survey of the building in all its detail, The illustrations are copious and well
selected, and the series bids fair to become an indispensable companion to the cathedral
tourist in England.’—7imes.

‘ We have so frequently in these columns urged the want of cheap, well-illustrated and
well-written handbooks to our cathedrals, to take the place of the out-of-date publications of
local booksellers, that we are glad to hear that they have been taken in hand by Messrs.
George Bell & Sons.’—S?. James's Gazette.

*

42°; 3)

WEBSTER’S
INTERNATIONAL
DICTIONARY

OF THE ENGLISH LANGUAGE.

2118 Pages. 3500 Illustrations.

PRICES:

Cloth, 1/. 11s. 6¢.; half calf, 2/. 2s.; half russia, 2/7. 55.; full calf,
2/. 8s.; full russia, 2/. 12s.; half morocco, with Patent Marginal Index,
2/. 8s.; full calf, with Marginal Index, 2/. 12s..Also bound in 2 vols.,
cloth, 17. 145. ; half calf, 27, 125.; half russia, 2/. 18s.; full calf, 3/. 3s. ;
full russia, 3/. 155.

The Appendices comprise a Pronouncing Gazetteer of the World,
Vocabularies of Scripture, Greek, Latin, and English Proper Names,
a Dictionary of the Noted Names of Fiction, a Brief History of the
English Language, a Dictionary of Foreign Quotations, Words, Phrases,
Proverbs, &c., a Biographical Dictionary with 10,000- names, &c., &c.

‘We believe that, all things considered, this will be found to be the best
existing English dictionary in one volume. We do not know of any work
similar in size and price which can approach it in completeness of a vocabu-
lary, variety of information, and general usefulness.’—Guardian,

‘The most comprehensive and»the most useful of its kind.’

National Observer,

‘We recommend the New Webster to every man of business, every
father of a family, every teacher, and almost every student—to everybody,
in fact, who is likely to be posed at an unfamiliar at half-understood word or
phrase.’ ~— St. James's Gazette.

Prospectuses, with Specimen Pages, on Application.
THE ONLY AUTHORISED AND COMPLETE EDITION.

LONDON: GEORGE BELL & SONS, YORK STREET,
, COVENT GARDEN.!
S. & S. 10.99." ;

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UNIVERSITY OF CALIFORNIA, BERKELE’
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