COSMOS:

A SKETCH

A PHYSICAL DESCRIPTION OF THE UNIVERSE.

ALEXANDER VON HUMBOLDT.

TKANSLATED FBOM THE GEHMAN,

BY E. C. OTTE.

Nataraa vero rerum vis atquo majestas in omnibus momentis fide caret, si quis modo
partes ejus ac non totam complectatur animo.— Plin., Hist. Nat., lib. vil, c. L

VOL. III.

NEW YORK:

HARPER & BROTHERS, PUBLISHERS,
329 & 331 PEARL STREET,

FRANKLIN SQUARE.

1858.

CONTENTS OF VOL. III.

INTRODUCTION.

nv

Historical Review of the attempts made with the object of
considering the Phenomena of the Universe as a Unity
of Nature 6-25

SPECIAL RESULTS OF OBSERVATIONS IN THE
DOMAIN OF COSMICAL PHENOMENA

A. URANOLOGICAL PORTION of the physical description of the

world.— a. ASTROGNOSY 26-28

I. The realms of space, and conjectures regarding that which

appears to occupy the space intervening between the
heavenly bodies 29-41

II. Natural and telescopic vision, 41-73 ; Scintillation of the

stars, 73-83 ; Velocity of light, 83-89 ; Results of pho-
tometry, 89-102 41-102

III. Number, distribution, and color of the fixed stars, 103-

139; Stellar masses (stellar swarms), 139-143; The
Milky Way interspersed with a few nebulous spots,
143-151 103-151

IV. New stars, and stars that have vanished, 151-160 ; Va-

riable stars, whose recurring periods have been determ-
ined, 160-177; Variations in the intensity of the light
of stars whose periodicity is as yet uninvestigated, 177-
182 151-182

V. Proper motion of the fixed stars, 182-185 ; Problemat-

ical existence of dark cosmical bodies, 185-188 ; Par-
allax— measured distances of some of the fixed stars,
188-194; Doubts as to the assumption of a central
body for the whole sidereal heavens, 194-199 182-199

VI. Multiple, or double stars — Their number and reciprocal

distances. — Period of revolution of two stars round a
common center of gravity 199-21.*

IV CONTENTS.

TABLES.

Fag.

Photometric Tables of Stars 100-102

Clusters of Stars 141-143

New Stars 155-160

Variable Stars 172-177

Parallaxes 193

Elements of Orbits of double Stars ... 213

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 stata
of science permit, I have regarded as not unattainable, I
have, in the preceding volumes of Cosmos, considered Nature
in a two-fold point of view. In the first place, I have en-
deavored to present her in the pure objectiveness of external
phenomena ; and, secondly, as the reflection of the image im-
pressed by the senses upon the inner man, that is, upon his
ideas and feelings.

The external world of phenomena has been delineated un-
der the scientific form of a general picture of nature in her
two great spheres, the uranological and the telluric or ter-
restrial. This delineation begins with the stars, which glim-
mer amid nebulae in the remotest realms of space, and, pass-
ing from our planetary system to the vegetable covering of
the earth, descends to the minutest organisms which float in
the atmosphere, and are invisible to the naked eye. In order
to give due prominence to the consideration of the existence
of one common bond encircling the whole organic world, of
the control of eternal laws, and of the causal connection, as
far as yet known to us, of whole groups of phenomena, it was
necessary to avoid the accumulation of isolated facts. This
precaution seemed especially requisite where, in addition to
the dynamic action of moving forces, the powerful influence
of a specific difference of matter manifests itself in the ter-
restrial portion of the universe. Tho problems presented to
us in the sidereal, or uranological sphere of the Cosmos, are,
considering 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 re-
garding the revolving meteor-asteroids (aerolites) as portions
of our planetary system, their fall upon the earth constitutes
the sole means by which we are brought in contact with
cosmical substances of a recognizable heterogeneity.* I here
refer to the cause which has hitherto rendered terrestrial
phenomena less amenable to th rules of mathematical de-
duction than those mutually disturbing and readjusting move-
ments of the cosmical bodies, in which the fundamental force
of homogeneous matter is alone manifested.

I have endeavored, in my delineation of the earth, to ar-
range natural phenomena in such a manner as to indicate
their causal connection. In describing our terrestrial sphere,
I have considered its form, mean density, electro-magnetic
currents, the processes of polar light, and the gradations ac-
cording to which heat increases with the increase of depth.
The reaction of the planet's interior on its outer crust im-
plies the existence of volcanic activity ; of more or less con-
tracted 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 mountains 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 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 sedimentary rocks are
in the course of precipitation from fluids, which hold their
minutest particles in solution or suspension. Such a com-
parison of matter still in the act of development and solidi-
fication 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 chronolog-
ical succession of those formations in which lie entombed ex-
tinct 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, ransformation, and upheaval of ter-
restrial strata, exert, at certain epochs, an alternating actior
on all the special characteristics of the physical configura
tion of the earth's surface ; influencing the distribution of
fluids and solids, and the extension and articulation of con

• Cotmos, vol. i. (Harper's edit.), p 33-65, 136.

INTRODUCTION. 7

tinental masses in a horizontal and vertical direction. On
these relations depend the thermal conditions of oceanic cur-
rents, the meteorological processes in the aerial investment
of our planet, and the typical and geographical distribution
of organic forms. Such a 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 na-
ture will, however, be essentially weakened, if the picture
fail in warmth of color 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 ex-
ternal nature on the inner man. Here it was necessary to
observe even stricter limits. The boundless domain of the
world of thought, enriched for thousands of years by the vig-
orous 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 apa-
thetic 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 myste-
rious 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 labo-
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, can not 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 ani-
mal forms, whose several parts are derived from the organ-

* Cosmos, vol. i., p. 23-25 ; vol. ii., p. 25 and 97.

t Ibid., vol. ii., p. 38-43, and 56-60.

\ Ibid, vol. i., p. 357-359; vol. ii., p. 112-117.

8 COSMOS.

isms of the present world, and sometimes even from the relics
of extinct species.* Marvelous flowers and trees spring from
this mythic soil, as the giant ash of the Edda-Songs, the
world-tree Yggdrasil, whose branches tower above the heav-
ens, while one of its triple roots penetrates to the " foaming
caldron springs" of the lower world. t Thus the cloud-re-
gion 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 generations.

If the present work does not fully bear out its title, the
adoption of which I have myself designated as bold and in-
considerate, 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 col-
oring of which has been so essentially influenced by individ-
uality 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
physical universe, that is, the history of the recognition of
the universe as a whole, and of the unity of phenomena — a
recognition gradually developed during the course of two
thousand years.

In a work of so comprehensive a character, the object of
which is to give a scientific, and, at the same time, an ani-
mated description of nature, a first imperfect attempt must
rather lay claim to the merit of inciting than to that of sat-
isfying inquiry. A Book of Nature, worthy of its exalted
title, can nerer be accomplished until the physical sciences,
notwithstanding their inherent imperfectibility, shall, by theii

* M. von Olfer's Ueberreste vorweltlicher Riesenthiere in Beziehung auj
Ostasiatische Sagen in the Abh. der Berl. ATead., 1832, s. 51. On the
opinion advanced by Empedocles regarding the cause of the extinction
of the earliest animal forms, see Hegel's Geschichte der Philosophic,
bd. ii., 8. 344.

t See, for the world-tree Yggdrasil, and the rushing (foaming) cal-
dron-spring Hvergelmir, the Deutsche Mylhologie of Jacob Grimm, 1844,
B. 530, 756; also Mallet's Northern Antiquities (Bohn's edition), 1847
p. 410, 489, aud 492, and frontispiece to ditto.

INTRODUCTION. 9

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.

I think I have here sufficiently indicated the reasons which
determined me not to give greater extension to the general
picture of nature. It remains for this third and fourth volume
of my Cosmos to supply much that is wanting in the previ-
ous portions of the work, and to present those results of ob-
servation on which the present condition of scientific 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 in-
dulgence with which my undertaking has been received by
a large portion of the public, both at home and abroad, ren-
ders 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, be-
cause, according to my view of empirical — i. e., experiment-
al— science, they did not admit of being satisfied. These
explanatory observations involuntarily associate themselves
with historical recollections of the earlier attempts made to
discover the one universal idea to which all phenomena, in
their causal connection, might be reduced, as to a sole prin-
ciple.

The fundamental principle* of my work on the COSMOS,
as enunciated by me more than twenty years ago, in the
French and German lectures I gave at Paris and Berlin,
comprehended the endeavor to combine all cosmical phenom-
ena 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 ascending from these laws to the discovery of their causal
connection. Such an attempt to comprehend the plan of
the universe — the order of nature — must begin with a gen«
eralization of particular facts, and a knowledge of the con-

* Cotmot. vol. i., p. 48-50, and 68-77.

10 COSMOS.

ditions under which physical changes regularly and period-
ically manifest themselves ; and must conduct to the thought-
ful consideration of the results yielded by empirical observa-
tion, but not to " a contemplation of the universe based on
speculative deductions and development of thought alone, or
to a theory of absolute unity independent of experience."
We are, 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 upward of a century before Lord Bacon's time, by
Leonardo da Vinci, in these lew 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 still
content ourselves with the recognition of empirical laws ; but
the highest and more rarely attained aim of all natural in-
quiry must ever be the discovery of their causal connection. t
The most satisfactory and distinct evidence will always ap-
pear where the laws of phenomena admit of being referred
to mathematical principles of explanation. Physical cosmog-
raphy constitutes merely in some of its parts a cosmology.
The two expressions can not yet be regarded as identical.
The great and solemn spirit that pervades the intellectual

* Op. tit., vol. ii. p. 283.

t In the Introductory Observations, in Cosmos, vol. i., p. 50, it should
not have been generally stated that " the ultimate object of the experi-
mental sciences is to discover laws, and to trace- their progressive gen-
eralization." The clause " in many kinds of phenomena" should have
been added. The caution with which I have expressed myself in the
second volume of this work (p. 313), on the relation borne by Newton
to Kepler, can not, I think, leave a doubt that I clearly distinguish be-
tween the discovery and interpretation of natural laws, i.e., the explana-
tion 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 domaiu of thought, as the intellectual rec-
ognition of nature." Of Newton I said (p. 351): "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. New-
ton was enabled to give an explanation of the system of the universe,
because he succeeded 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 Herschel's address at
the fifteenth meeting of the British Association at Cambridge, 1845, p.
rlii. ; and Edinb. Rev., vol. 87, 1848, p. 180-183.

INTRODUCTION. 11

labor, of which the limits are here defined, arises from the
sublime consciousness of striving toward the infinite, and of
grasping all that is revealed to us amid the boundless and
inexhaustible fullness 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
principle which could explain all that is variable in the or-
ganic world, and all the phenomena revealed to us by sen-
suous perception. After men had for a long time, in accord-
ance with the earliest ideas of the Hellenic people, vener-
ated 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 prin-
ciples, the so-called elements of Nature, or to processes of
rarefaction and condensation, sometimes in accordance with
mechanical, sometimes with dynamic views. The hypothe-
sis 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 opinions on natural philosophy — a primeval evi-
dence and monument of the tendency of the human mind
to seek a generalization and simplification of ideas, not only
with reference to the forces, but also to the qualitative na-
ture of matter.

In the latter period of the development of the Ionic phys-
iology, Anaxagoras of Clazomense advanced from the postu-
late of simply dynamic forces of matter to the idea of a spirit
independent of all matter, uniting and distributing the homo-
geneous particles of which matter is composed. The world-
arranging Intelligence (vovg) controls the continuously pro-
gressing formation of the world, and is the primary source

* In the memorable passage (Metaph., xii., 8, p. 1074, Bekker") in
which Aristotle speaks of " the relics of an earlier acquired and subse-
quently lost wisdom," he refers with extraordinary freedom and sig-
nificance to the veneration of physical forces, and of gods in human
forms : " much," says he, " has been mythically added for the persua*
tion of the multitude, as also on account of the laws and for other useful
ends."

t The important difference in these philosophical directions rpdiroi,
is clearly indicated in Arist., Phys. Auscult., 1, 4, p. 187, Bekk. (Com-
pare Brandis, in the Rhein. Museum fur Philologie, Jahrg. iii., 8. 105.)

12 COSMOS.

of all motion, and therefore of all physical phenomena. An-
axagoras 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 ob-
served, the fall of meteoric stones ensues. This hypothesis
indicates the origin of those theories of rotatory motion which
more than two thousand years afterward attained considera-
ble cosmical importance from the labors of Descartes, Huy-
gens, and Hooke. It would be foreign to the present work
to discuss whether thg world- arranging Intelligence of the
philosopher of Clazomenae 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 con-
figuration (the five elementary forms), to the ideas of num-
bers, measure, harmony, and contrarieties. Things are re-
flected in numbers "which are, as it were, an imitative repre-
sentation (fj,ifj,7)aig) of them. The boundless capacity for rep-
etition, and the illimitability of numbers, is typical of the
character of eternity and of the infinitude of nature. The
essence of things may be recognized in the form of numerical
relations ; 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. J But in reference

* Cosmos, vol. i., p. 133-135 (note), and vol. ii., p. 309, 310 (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 down-
ward tendency." Hence Plutarch, in his work, De Fade in Orbe
Ltmte, p. 923, compares the moon, in consequence of its not falling to
the earth, to " a stone in a sling." For the actual signification of the
•nepiXupT)ai.s of Anaxagoras, compare Schaubach, in Anaxag. Clazom.
Fragm., 1827, p. 107-109.

t Schaubach, Op. cit., p. 151-156, and 185-189. Plants are likewise
said to be animated by the intelligence i>ot5f ; Aristot., De Plant., i., p.
815, Bekk.

t Compare, on this portion of Plato's mathematical physics, B6ckh,
De Platonico Syst. Caelestium Globorum, 1810 et 1811; Martin, Eludei
tur le Timie, torn, ii., p. 234-242; and Brandis, in the Geschichte der
GricchiKh-Rdmuchsn Philosophic, th. ii., abth. i., 1844, $ 375.

INTRODUCTION. 13

to ultimate principles (the elements, as it were, of the ele
ments), Plato exclaims, with modest diffidence1, " 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 in-
quirers into devious tracks, as is shown in the history of the
physical contemplation of the universe. " There dwells a
captivating charm, celebrated by all antiquity, in the simple
relations of time and space, as manifested in tones, numbers,
and lines."*

The idea of the harmonious government of the universe re-
veals itself in a distinct and exalted tone throughout the writ-
ings of Aristotle. All the phenomena of nature are depicted
in the Physical Lectures (Auscultationes Physicce) as mov-
ing, vital agents of one general cosmical force. Heaven and
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

* Cosmos, vol. ii., p. 351, note. Compare also Gruppe, Ueber die
Fragmente des Archytas, 1840, s. 33.

t Aristot.,Poto., vii., 4, p. 1326, and Metapk., xii., 7, p. 1072, 10, Bekk.,
and xii., 10, p. 1074-5. The pseudo-Aristotelian work, De Mundo,
which Osann ascribed to Chrysippus (see Cotmot, vol. ii., p. 28, 29),
also contains (cap. 6, p. 397) a very eloquent passage on the world-or-
derer and tcorld-sustainer.

t The proofs are collected in Ritter, History of Philotophy (Bohn,
1838-46), vol. iii., p. 180, et seq.

§ Compare Aristot., De Anima, ii., 7, p. 419. In this passage the
analogy with sound is most distinctly expressed, although in other por-
tions of his writings Aristotle has greatly modified his theory of vision.
Thus, in De Insomniis, 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 medium), but itself also acts upon the medium." He adduces in
evidence of the truth of this proposition, that a new and very pure me-
tallic mirror will, under certain conditions, when looked at by a woman,
retain on its surface cloudy specks that can not be removed without
difficulty. Compare also Martin, Etudes sur le Timfe de Platun., torn
ii. p. 159-163.

14 COSMOS.

— a movement of the medium between the eye and the object
Been — and not by emissions from the object or the eye. Hear-
ing is compared with sight, as sound is likewise 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 reflect-
ive reason, always includes the whole of nature, and the in-
ternal connection not only of forces, but also of organic forms.
In his book on the parts (organs) of animals, he clearly in-
timates his belief that throughout all animate beings there is
a scale of gradation, in which they ascend from lower to high-
er forms. Nature advances in an uninterrupted progressive
course of development, from the inanimate or " elementary"
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 imper-
ceptible."! 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 unconnect-
ed or out of place, as in a bad tragedy."}:

The endeavor 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, i. e., of
calling forth phenomena under definite conditions, prevented
the comprehension of the causal connection of even small
groups of physical processes. All things were reduced to the
ever-recurring contrasts of heat and cold, moisture and dry-
ness, primary density and rarefaction — even to an evolution
of alterations in the organic world by a species of inner divis-
ion (antiperistasis), which reminds us of the modern hypothesis
of opposite polarities and the contrasts presented by + and — .§

* Aristot., De partibus Amm., lib. iv., cap. 5, p. 681, lin. 12, Bekker.

t Aristot., Hist. Anim., lib. ix., cap. 1, p. 588, lin. 10-24, Bekker.
When any of the representatives of the four elements in the animal
kingdom on oar 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 organized beings which we find
in the extinct animal and vegetable forms of an earlier world.

t Aristot., Metaph., lib. xiii., cap. 3, p. 1090, lin. 20, Bekker.

§ The uvrnrepiiraait of Aristotle plays an important part in all hit

INTRODUCTION. 15

The so-calle"d 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 explana-
tions of meteorological or optical processes into a self-com-
placent diffuseness and a somewhat Hellenic verbosity. As
Aristotle's inquiries were directed almost exclusively to mo-
tion, and seldom to differences in matter, we find the funda-
mental 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 ab-
solute distinctness and certainty.

The impulse to which I refer indicates only the communi-
cation of motion as the cause of all terrestrial phenomena.
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 forma-
tions, and holding together all things as an absolute power.f
The main idea and these teleological views are not applied
to the subordinate processes of inorganic or elementary nature,
but refer specially to the higher organizations! of the animal
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 dis-

explanatious of meteorological processes ; so also in the works De Gen-
eralione et Interitu, lib. ii., cap. 3, p. 330 ; in the Meteorologicis, lib. i.,
cap. 12, and lib. iii., cap. 3, p. 372, and in the Problems (lib. xiv., cap.
3, lib. viii., No. 9, p. 888, and lib. xiv., No. 3, p. 909), which are at all
events based on Aristotelian principles. In the ancient polarity hypoth-
esis, /car* avrnrepiaTaaiv, similar conditions attract each other, and dis-
similar ones (-J- and — ) repel each other in opposite directions. (Com
pare Ideler, Meteorol. veterum Grcsc. et Rom., 1832, p. 10.) The op-
posite conditions, instead of being destroyed by combining together,
rather increase the tension. The ipvxpov increases the -Qeppov ; as in-
versely "in the formation 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, evap-
oration, and changes in the capacity of heat. See the able observations
of Paul Erman in the Abhandl. tier Berliner Akademie aufdasJahr 1825,
s. 128.

* " By the movement of the heavenly sphere, all that is unstable in
natural bodies, and all terrestrial phenomena are produced." — Aristot.,
Mtteor., i., 2, p. 339, and De Gener. et Corrupt., ii., 10, p. 336.

t Aristot., De Casio, lib. i., c. 9, p. 279 ; lib. ii., c. 3, p. 286 ; lib. ii., c
13, p. 292, Bekker. (Compare Biese, bd. i., s. 352-1, 357.)

t Aristot., Phys. Auscult., lib. ii., c. 8, p. 199; De Anima, lib. iii., o
12, p. 434 ; De Animal. General., lib. v., c. 1, p. 778, Bekker.

16 COSMOS.

tribution of masses) maintain the planets in their eternal oib-
its.* The stars here reveal the image of the divinity in the
visible world. We do not here refer, as its title might lead
to suppose, to the little pseudo- Aristotelian work entitled the
" Cosmos," undoubtedly a Stoic production. Although it de-
scribes the heavens and the earth, and oceanic and aerial
currents, with much truthfulness, and frequently with rhetor-
ical animation and picturesque coloring, it shows no tenden-
cy to refer cosmical phenomena to general physical princi-
ples based on the properties of matter.

I have purposely dwelt at length on the most brilliant pe-
riod of the Cosmical views of antiquity, in order to contrast
the earliest efforts made toward the generalization of ideas
with the efforts of modern times. In the intellectual move-
ment of centuries, whose influence on the extension of cos-
mical contemplation has been defined in another portion of
the present work.f the close of the thirteenth and the begin-
ning 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 Cos-
mographictis) of Albertus Magnus, the Picture of the World
(Imago Mundi) of Cardinal Petrus d'Alliaco (Pierre d'Ailly),
are works which, however powerfully they may have influ-
enced the age in which they were written, do not fulfill by
their contents the promise of their titles. Among the Italian
opponents of Aristotle's physics, Bernardino Telesio of Cosen-
za is designated the founder of a rational science of nature.
All the phenomena of inert matter are considered by him as
the effects of two incorporeal principles (agencies or forces)
— heat and cold. All forms of organic life — "animated"

* See the passage in Aristot., Meteor., xii., 8, p. 1074, of which there
is a remarkable elucidation in the Commentary of Alexander Aphro-
iisiensis. The stars are not inanimate bodies, but must be regarded as
active and living beings. (Aristot., De Casio, lib. ii., cap. 12, p. 292.)
They are the most divine of created things ; TO. -Qeiorepa TUV <j>avepuv.
(Aristot., De Casio, lib. i., cap. 9, p. 278, and lib. ii., cap. 1, p. 284.)

ip. 6, p. 400), me nigh anner is also called divine (cap.
That which the imaginative Kepler calls moving spirits (anima motruai)
in his work, Mysterium Cotmographicum (cap. 20, p. 71), is the distort-
ed idea of a force (virtus') whose main seat is in the sun (anima mun-
di), and which is decreased by distance in accordance with the laws of
light, and impels the planets in elliptic orbita. (Compare Apelt, Epoch
en der Gesch. der Mcnechheit, bd. i., e. 274.)
* Cotmot, vol. ii., p. 241-250.

INTRODUCTION. 17

plants and animals — are the effect of these two ever-divided
forces, of which the one, heat, specially appertains to the ce-
lestial, and the other, cold, to the terrestrial sphere.

"With yet more unbridled fancy, but with a profound spirit
of inquiry, Giordano Bruno of Nola attempted to comprehend
the whole universe, in three works,* entitled De la causa
Principio e Uno; Contcmplationi circa lo Infinite, Uni-
verso e Atondi innumerabili ; and De Minima et Maximo.
In the natural philosophy of Telesio, a cotemporary of Co-
pernicus, we recognize 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 dy-
namic theory of nature of Boscovich and Kant. The cos-
mical views of the Philosopher of Nola are purely meta-
physical, and do not seek the causes of sensuous phenomena
in matter itself, but treat of "the infinity of space, filled
with self - illumined worlds, of the animated condition of
those worlds, and of the relations of the highest intelligence
— God — to the universe."

Scantily endowed with mathematical knowledge, Giorda-
no Bruno continued nevertheless to the period of his fearful
martyrdomf an enthusiastic admirer of Copernicus, Tycho
Brahe, and Kepler. He was cotemporary with Galileo, but
did not live to see the invention of the telescope by Hans
Lippershey and Zacharias Jansen, and did not therefore wit-
ness the discovery of the " lesser Jupiter world," the phases
of Venus, and the nebulse. "With bold confidence in what
he terms the lume interno, ragione naturale, altezza dell'
intclletto (force of intellect), he indulged in happy conjec-
tures regarding the movement of the fixed stars, the planet

* Compare the acute and learned commentary on the works of the
Philosopher of Nola, in the treatise Jordano Bruno par Christian Bar-
tholmess, torn, ii., 1847, p. 129, 149, and 201.

t He was burned at Rome on the 17th of February, 1600, pursuant
to the sentence " ut qnam clementissime et citra sanguinis effusionem
puniretur." Bruno was imprisoned six years in the Piombi at Venice,
and two years in the Inquisition at Rome. When the sentence of death
was announced to him, Bruno, calm and unmoved, gave utterance to
the following noble expression: "Majori forsitan cum timore sententi-
am in me fertis quam ego accipiam." When a fugitive from Italy in
1580, he taught at Geneva, Lyons, Toulouse, Paris, Oxford, Marburg,
Wittenberg (which he calls the Athens of Germany), Prague, and Helm-
stedt, where, in 1589, he completed the scientific instruction of Duko
Henry Julius of Brunswick- Wolfenbuttel. — Bartholmess, torn . i , p. 167-
178. He also taught at Padua subsequently to 1592.

18 COSMOS.

ary 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 na-
ture, which were realized in later times.

In the development of thought on cosmical relations, of
which the main forms and epochs have been already enu-
merated, Kepler 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 Philosophies Naturalis. For while the
eclectic Simplicius only expressed in general terms " that
the heavenly bodies were sustained from falling in conse-
quence of the centrifugal force being superior to the inher-
ent falling force of bodies and to the downward traction ;"
while Joannes Philoponus, a disciple of Ammonius Hermeas,
ascribed the movement of the celestial bodies to " a primi-
tive 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 center
of the planetary world, in the earth and in the moon, using
these memorable words, " Gravitatem non aliud esse quam
appetentiam quandam naturalem partibus inditam a divina
providentia opificis universorum, ut in unitatem integrita-
temque suam sese conferant, in formam globi coeuntes ;"
Kepler, in his introduction to the book De Stella MartisJ
was the first who gave numerical calculations of the forces
of attraction reciprocally exercised upon each other, accord-
ing to their relative masses, by the earth and moon. He

* Bartholmess, torn, ii., p. 219, 232, 370. 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 dis-
cussion has been directed in modern times to the relation existing be-
tween Bruno, his two Calabrian fellow-countrymen, Bernardino Tele-
sio and Thomas Campanella, and the platonic cardinal, Nicolaus Krebs
of Cusa. See Cosmos, vol. ii., p. 310, 311, note.

t " Si duo lapides in aliquo loco Mundi collocarentur propinqui in-
vicem, extra orbem virtutis tertii cognati corporis ; illi lapides ad simil-
itudinem duorum Magneticorum corporum coirent loco intermedio, qui-
libet accedens ad alterum tanto intervallo, quanta est alterius moles in
comparatione. Si luna et terra non retinerentur vi animali (!) aut alia
aliqua aequipollente, quselibet in suo circuitu, Terra adscenderet ad Lu-
nam quinquagesima quarta parte intervalli, Luna descenderet ad Ter-
rarn quinquaginta tribus circiter partibus intervalli; ibi jungerentur,
posito tamen quod substantia utriusque sit unius et ejusdem densitatis."
—Kepler, A&tronomia nova, seu Physica ccclestis de Motibus Stella Mar-
tis, 1609. Introd., fol. v. On the older views regarding gravitation,
see Cosmos, vrl. ii., p. 310.

INTRODUCTION. 19

distinctly adduces the tides as evidence* that the attractiv&
force of the moon (virtus tractoria) 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 forme]
should cease to attract it. Unfortunately, this great man
was induced, ten years afterward, in 1619, probably from
deference to Galileo, who ascribed the ebb and flow of the
ocean to the rotation of the earth, to renounce his correct
explanation, and depict the earth in the Harmonice Mundt
as a li ving monster, whose whale-like mode of breathing oc-
casioned the rise and fall of the ocean in recurring periods
of sleeping and waking, dependent on solar time. When we
remember the mathematical acumen that pervades one of the
works of Kepler, and of which Laplace has already made
honorable mention,t 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.

Descartes, who was endowed with greater versatility of
physical knowledge than Kepler, and who laid the founda-
tion of many departments of mathematical physics, under-
took to comprise the whole world of phenomena, the heav-

* " Si Terra cessaret attrahere ad se aquas suas, aquae marinse omnes
elevarentur et in corpus Luna? iufluerent. Orbis virtutis tractoriae, qua?
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,
sensibiliter ibi ubi sunt latissimi alvei Oceani propinqui, aquisque spa-
ciosa reciprocationis libertas." (Kepler, 1. c.) " Undas a Luna trahi
ut ferrum a Magnete." .... Kepleri Harmonice Mundi, libri quinque,
1619, lib. iv., cap. 7, p. 162. The same work which presents us with
so many admirable views, among others, with the data of the establish-
ment of the third law (that the squares of the periodic times of two
planets are as the cubes of their mean distance), is distorted by the
wildest flights of fancy on the respiration, nutrition, and heat of the
earth-animal, on the soul, memory (memoria animce Terra), and crea-
tive imagination (anima Tdluris 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 mys-
tic author of the Macrocosmcs, Robert Fludd, of Oxford, who is report-
ed to have participated in the invention of the thermometer. (Harm.
Mitndi, p. 252.) In Kepler's writings, the attraction of masses is often
confounded with magnetic attraction. " Corpus solis esse magneticum.
Virtutem, quae Planetas movet, residere in corpore solis." — Stella Mar
tit, pars iii., cap. 32, 34. To each planet was ascribed a magnetic axis,
which constantly pointed to one and the same quarter of the heavens.
CApelt, Joh. Kepler's Astron. Weltansicht, 1849, 8. 73.

t Compare Cosmos, vol. ii., p. 327 (and iiole

20 COSMOS.

enly sphere and all that he knew concerning the animate
and inanimate parts of terrestrial nature, in a work entitled
Traite du Monde, and also Summa Philosophies. The or-
ganization 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 hia
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 Gali-
leo, which was first made generally known four months aft-
erward, in October, 1633, by Gassendi and Bouillaud, at
once put a stop to his plans, and deprived posterity of a great
work, completed with much pains and infinite care. 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 irreverentially the
decrees pronounced by the Holy Chair against the planetary
movement of the earth. t In 1664, fourteen years after the
death of the philosopher, some fragments were first printed
under the singular title of Le Monde, ou Traite de la Lu-
miere."i. The three chapters which treat of light scarcely,
however, constitute a fourth part of the work ; while those
sections which originally belonged to the Cosmos of Des-
cartes, 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 Philosophic.

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 cos-
mical bodies, and especially of the modifications of form which

» See La Vie de M. Descartes (par Baillet), 1691, Part i., p. 197,
End CEuvret de Descartes, publiees par Victor Cousin, torn, i., 1824,
p. 101.

t Lsttres de Descartes au P. Mersenne, du, 19 Nov., 1633, et du 5 Jan-
vier, 1634. (Baillet, Part i., p. 244-247.)

\ The Latin translation bears the title Mundus give Dissertalio de
Lwmine itt et de aliis Sensuum Objectis primariis. See Descartes, Optu~
cula posthuma Physka et Mathematica, Amst., 1704.

INTRODUCTION. 21

the human race may there present. The reader might sup-
pose he were perusing Kepler's Somnium Astronomicum, or
Kircher's Iter Extaticus. 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 the exist-
ence of inhabitants in the moon than of those in the remoter
planets, which he assumes to be " surrounded with vapors
and clouds."

The immortal author of the Philosophic Naturalis Prin-
cipia Mathematica (Newton) succeeded in embracing the
whole uranological portion of the Cosmos in the causal con-
nection of its phenomena, by the assumption of one all-con-
trolling fundamental moving force. He first applied phys-
ical astronomy to solve a great problem in mechanics, and
elevated it to the rank 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 ra-
tio 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 admira-
tion from its simplicity and generality, is not limited in its
cosmical application to the uranological sphere, but com-
prises also telluric phenomena, in directions not yet fully
investigated ; it affords the clew to the periodic movements
in the ocean and the atmosphere,! and solves the problems
of capillarity, of endosmosis, and of many chemical, elec-

* " Lunam aqnis carere et afire : Marium similitudinem in Luna nul-
lam reperio. Nam regiones planas quae montosis multo obscuriores
eunt, quasque vulgo pro maribus haberi video et oceanorum nominibus
insigniri, in his ipsis, longiore telescopic inspectis, cavitates exiguas in-
esse comperio rotundas, umbris intus cadentibus; quod maris superfi-
ciei convenire nequit; turn ipsi campi illi latiores non prorsus eequabi-
lem superficiem praDferunt, cum diligentius eas intuemur. Quod circa
maria esse non possunt, sed materia constare debent minus candicante,
quam qute est partibus asperioribus in quibus rursus quanlam viridiori
lumine caeteras prsecellunt." — Hugenii Cosmotheorog, ed. alt. 1699, lib.
xi., p. 114. Huygens conjectures, however, that Jupiter is agitated by
much wind and rain, for " ventorum flatus ex ilia 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
iu exact mathematics, have, unfortunately, been revived by Emauuel
Kant, in his cdmirable work Allgemeine Naturgeschichte und Theorie
dtt Himmelt, 1755 (s. 173-192).

t See Laplace (des Oscillations de t 'Atmotphlre, du flux Solaire et
Lunaire} iu the Micanique Celeste, livre iv., and in the Exposition d*
Syst. du Monde, 1824, p. 291-296.

22 COSMOS.

tro-magnetic, and organic processes. Newton* even distin-
guished the attraction of masses , as manifested in the mo-
tion of cosmical bodies and in the phenomena of 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 grav-
itation is the most comprehensive and the richest in cosmic-
al results. It is indeed true, that notwithstanding the brill-
iant progress that has been made in recent times in strechi-
ometry (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 mathematic-
ally-determinable principles of explanation. Empirical laws
have been recognized, and by means of the extensively- dif-
fused views of the atomic or corpuscular philosophy, many
points have been rendered more accessible to mathematical
investigation ; but, owing to the unbounded heterogeneous-
ness of matter and the manifold conditions of aggregation of
particles, the proofs of these empirical laws can not as yet
by any means be developed from the theory of contact-at-
traction with that certainty which characterizes the estab-
lishment 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

* Adjicere jam licet de spiritu quodam subtilissimo corpora crassa
pervadente et in iisdem latente, cujus vi et actiouibus particulaj corpo-
rum ad minimas distantias se mutuo attrahunt et contiguae facta cohac-
rent. — Newton, Principia Phil. Nat. (ed. Le Sueur et Jacquier, 1760),
Schol. gen., t. iii., p. 676; compare also Newton's Optics (ed. 1718),
Query 31, p. 305, 353, 367, 372. (Laplace, Syst. du Monde, p. 384, and
Cosmos, vol. i., p. 63 (note).)

t Hactenus phaenomena coelorum et maris nostri per vim gravitatis
exposui, sed causam gravitatis nondum assignavi. Oritur utique haec
vis a causa aliqua, qua: penetrat ad usque centra solis et planetarum,
sine virtutis dimiuutione ; quaeque agit non pro quantitate superficierum
particularum, in quas agit (ut solent causae mechanics), sed pro quanti-
tate materiae solidao. — Rationem harum gravitatis proprietatum ex phae-
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. " To tell us that every spe-
cies of things is endowed witlr. an occult specific quality, by which it
acts and produces manifest effects, is to tell us nothing ; but to derive

INTRODUCTION. 23

result of some higher and still unknown power, or of " the
centrifugal force of the aether, which fills the realms of space,
and is rarer within bodies, but increases in density outward.
The latter view is set forth in detail in a letter to Robert
Boyle* (dated February 28, 1678), which ends with the
words, " I seek the cause of gravity in the sether." Eight
years afterward, as we learn from a letter he wrote to Hal
ley, Newton entirely relinquished this hypothesis of the rarer
and denser sether.f It is especially worthy of notice, that
in 1717, nine years before his death, he should have deemed
it necessary expressly to state, in the short preface to the sec-
ond edition of his Optics, that he did not by any means con-
sider gravity as an " essential property of bodies ;"J while

two or three general principles of motion from phenomena, and after-
ward to tell us how the properties and actions of all corporeal things
follow from those manifest principles, would be a very great step in phi-
losophy, though the causes of those principles were not yet discovered ;
and therefore I scruple not to propose the principles of motion, and leave
their causes to be found out." — Newton's Optics, p. 377. In a previ-
ous 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 at-
tractive powers than these. How these attractions may be performed
I do not here consider. What I call attraction may be performed by
impulse, or by some other means unknown to me. I use that word
lio <; to signify only in general any force by which bodies tend toward
on^ another, whatsoever be the cause."

* " I suppose the rarer sether within bodies, and the denser without
them." — Operum Newtoni, tomus iv. (ed. 1782, Sam. Horsley), p. 386.
The above observation was made in reference 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. 94, he
says : " I shall set down one conjecture more which came into my mind:
it is about the cause of gravity. . . ." His correspondence with Olden-
burg (December, 1675) shows that the great philosopher was not at
that time averse to the " aether hypotheses." According to these views,
the impulse of material light causes the aether to vibrate ; but the vibra-
tions of the sether alone, which fias some affinity to a nervous fluid, does
not generate light. In reference to the contest with Hooke, consult
Horsley, t. iv., p. 378-380.

t See Brewster's Life of Sir Isaac Newton, p. 303-305.

t 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 all molecu-
lar 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, Optict,
book ii., prop. 8, p. 241, and Brewster, Op. cit., p. 301.) According
to Kant (see Die Metaphysischen Anfangsgrunde der Naturwissenschaft,
1800, s. 28), we can not conceive the existence of matter without these
forces of attraction and repulsion. All physical phenomena are there-

24 COSMOS.

Gilbert, as early as 1600, regarded magnetism as a force in-
herent in all matter. So undetermined was even Newton,
the profound and experienced thinker, regarding the " ulti-
mate mechanical cause" of all motion.

It is indeed a brilliant effort, worthy of the human mind,
to comprise, in one organic whole, the entire science of na-
ture from the laws of gravity to the formative impulse (ni-
sus formativus) in animated bodies ; but the present imper-
fect state of many branches of physical science offers innu-
merable difficulties to the solution of such a problem. The
imperfectibility of all empirical science, and the boundless-
ness of the sphere of observation, render the task of explain-
ing 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 re-
ferring to the progress of science in modern times, we com-
pare the imperfect physical knowledge of Gilbert, Robert
Boyle, and Hales, with that of the present day, and remem-
ber 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 vi-
brations, we are still without a solution to those often mooted
and perhaps insolvable problems : the cause of chemical dif-
ferences 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-

fore reduced by him, as previously by Goodwin Knight (Pkilos. Trant-
act. 1748, p. 264), to the conflict of two elementary forces. In the at-
omic 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
elementary corpuscles. This hypothesis, which regards the so-called
taloric as a constantly expanded matter, assumes the existence of two
elementary substances, as in the mythical idea of two kinds of tether.
(Newton, Optics, 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 dis-
tance between elementary corpuscles is i'ar greater than, their diameterg.

INTRODUCTION. 25

her 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
something existing in nature, as a fact, but which I can net
designate as merely causal, because their causes and mutual
connection have not yet been discovered. They are the re-
sult of occurrences in the realms of space coeval with the
formation of our planetary system, and of geognostic process-
es in the upheaval of the outer strata of the earth into con-
tinents and mountain chains. Our knowledge of the prime-
val ages of the world's physical history does not extend suf-
ficiently 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 terrestrial spheres, but embraces it only under the single
point of view of efforts made toward the knowledge of the
universe as a whole. "f As, in the " exposition of past events
in the moral and political world, the historian:): can only di-
vine 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 inquirer 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 of
phenomena are far from having exhausted the number of
impelling, producing, and formative forces.

* Cosmos, vol. i., p. 94-97. t Op. cit., p. 55-62.

t Wilhelra von Humboldt, Gesammdte Werke, bd. i., s. 23.

VOL. III.— B

RESULTS OF OBSERVATIONS IN THE URANOLOGICAL POR-
TION 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 tel-
escopic vision as faintly shining nebulce. From these we
gradually descend to the double stars, revolving round one
common center of gravity, and which are frequently bicol-
ored, to the nearer starry strata, one of which appears to in-
close 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 can not here, in accordance with the requirements of di-
rect 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 uranological, when opposed to the telluric domain
of the Cosmos, may be conveniently separated into two di-
visions, one of which comprises astro^nosy, or the region of
the fixed stars, and the other our solar and planetary sys-
tem. It is unnecessary here to describe the imperfect and
unsatisfactory nature of such a nomenclature and such class-
ifications. Names were introduced into the physical sci-
ences before the differences of objects and their strict limita-
tions were sufficiently known.f The most important point,
however, is the connection of ideas, and the order in which
the objects are to be considered. Innovations in the no-
menclature of groups, and a deviation from the meanings
hitherto attached to well-known names, only tend to dis-
tract and confuse the mind.

a. ASTROGNOSY. (THE DOMAIN OF THE FIXED STARS.)
Nothing is stationary in space. Even the fixed stars
move, as Halleyl: endeavored to show in reference to Sirius,

* Cosmos, vol. i., p. 79-83. f Op. cit., p. 56, 57

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

A8TROGNOSY. 27

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 Aristi.'lus and Hipparchus) that it has been ob-
served, changed its position in relation to the neighboring
fainter stars 2£ times the moon's diameter. Encke remarks
" that the star \i Cassiopeise appears to have moved 31 lunar
diameters, and 61 Cygni about 6 lunar diameters, if the an-
cient observations correctly indicated its position." Conclu-
sions based on analogy justify us in believing that there is
every where 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 riveted into the crys-
tal vault of heaven ; or, subsequently, in accordance with
the Roman interpretation, it may indicate fixity or immo-
bility. The one idea involuntarily led to the other. In Gre-
cian antiquity, in an age at least as remote as that of Anax-
imenes of the Ionic school, or of Alcmseon the Pythagorean,
all stars were divided into wandering (darpa TrAavcjjueva or
TrAavT/rd) and non-wandering fixed stars (drr^avelg aarepeg
or dTrXavfj darpa).* Besides this generally adopted desig-
nation of the fixed stars, which Macrobius, in his Somnium
Scipionis, Latinized by Sphcera aplanesj we frequently
meet in Aristotle (as if he wished to introduce a new tech-
nical term) with the phrase riveted stars, Ivdedeneva darpa,
instead of a^Xavr],% as a designation for fixed stars. From
this form of speech arose the expressions of sidera infixa
cado of Cicero, Stellas quas ^nctamus affixas of Pliny, and as-

9 Pseudo-Plut., De plac. Philos., ii., 15, 16 ; Stob., Eclog. Phys., p.
582 ; Plato, in the Timeeus, p. 40.

t Macrob., Sown. Scip., i., 9-10 ; slellce inerrantes, in Cicero, De Nat.
Deorum, iii., 20.

t The principal passage in which we meet with the technical expres-
sion hdedspeva uarpa, is in Aristot., De Caelo, ii., 8, p. 289, 1. 34, p. 290,
1. 19, Bekker. This altered nomenclature forcibly attracted my atten-
tion in my investigations into the optics of Ptolemy, and his experi-
ments on refraction. Professor Franz, to whose philological acquire-
ments I am indebted for frequent aid, reminds me that Ptolemy (Syn-
tax, vii., 1) speaks of the fixed stars as affixed or riveted; uanep Trpo-
OTreQvKOTee. Ptolemy thus objects to the expression a<j>aipa air'Xavfjc
(orltig inerrans) ; " in as far as the stars constantly preserve their rela
live distances, they might rightly be termed airhavtiq ; but in as far an
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
O7r/laf!?f is inappropriate if applied to the sphere."

tra fixa 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 affixum sidus was
gradually lost sight of in the Latin translations of the Mid-
dle Ages, and the idea of immobility alone retained. This
is already apparent in a highly rhetorical passage of Seneca,
regarding the possibility of discovering new planets, in which
he says (Nat. Queest., vii., 24), " Credis autem in hoc max-
imo et pulcherrimo corpore inter innumerabiles Stellas, quae
noctem decore vario distinguunt, quse ae'ra minime vacuum
et inertem esse patiuntur, quinque solas esse, quibus exer-
cere se liceat ; ceteras stare fixum et immobilempopulum?"
"And dost thou believe that in this so great and splendid
body, among innumerable stars, which by their various beau-
ty 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, while all the rest remain a fixed
and immovable multitude ?" This fixed and immovable mul-
titude 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 sep-
arate 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 color of the stars ; the
stellar swarms, and the Milky Way, which is interspersed
with a few nebulae.

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

V. The proper motion of the fixed stars ; the problematical
existence of dark cosmical bodies ; the parallax and meas-
ured distance of some of the fixed stars.

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

VII. The nebulas which are interspersed in the Magellanic
clouds with numerous stellar masses, the black spots (coal
bags) in the vault of heaven.

* Cicero, De Nat Deorutn, i., 13 ; Plin., ii., 6 and 24 ; Manillas, ii., 35

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

THAT 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 cosmic al
bodies, and is imperceptible to our organs, may not unaptly
be compared to the mythical commencement of ancient his-
tory. In infinity of space as well as in eternity of time, all
things are shrouded in an uncertain and frequently deceptive
twilight. The imagination is here doubly impelled to draw
from its own fullness, 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 famil-
iar with scientific labors delights in dwelling on subjects
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 attention of
the most distinguished astronomers of our day.

By the influence of gravitation, or general gravity, as well
as by light and radiating heat,t we are brought in contact, as
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 resist-
ance which a fluid filling the realms of space is capable of
opposing 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 philosophy from
conjectures 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

* Cosmos, vol. i., p. 87. (Compare the admirable observations of
Encke, Ueber die Anordnung des Sternsystems, 1844, s. 7.)
t Cotmot, vol. i., p. 154, 155.

30 COSMOS.

by Aristotle* — follows the idea of its immeasurability. Sep •
arate portions only have been rendered accessible to meas-
urement, and the numerical results, which far exceed the
grasp of our comprehension, become a source of mere puerile
gratification to those who delight in high numbers, and im-
agine that the sublimity of astronomical studies may be
heightened by astounding and terrific images of physical mag-
nitude. The distance of 61 Cygni from the Sun is 657,000
semi-diameters of the Earth's orbit ; a distance which light
takes rather more than ten years to traverse, while it passes
from the Sun to the Earth in 8' 17"-78. 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 immensity of the unit by which they must be meas-
ured, or from the high number yielded by the repetition of
this unit. Bessel$ very 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. There-
fore every endeavor 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 clear-
ly 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 Polythalami® are inclosed, ac-
cording to Ehrenberg, in one thin stratum of chalk ! This
eminent investigator of nature asserts that one cubic inch of
the Bilin polishing slate, which constitutes a sort of mount-
ain cap forty feet in height, contains 41,000 millions of the
microscopic Galionella distans ; while the same volume con-
tains more than 1 billion 750,000 millions of distinct indi-
viduals of Galionella ferruginea.k Such estimates remind
us of the treatise named Arenarius (tpafifiirrj^) of Archime-
des— 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

* Aristot., De Casio, 1, 7, p. 276, Bekker.

t Sir John Herschel, Outlines of Astronomy, 1849, § 803, p. 541.
j Bessel, in Schumacher's Jahrluchfur 1839, s. 50.
$ Ehrenberg, Abhandl. der Berl. Akad., 1838, s. 59 ; also in his Info
rionsthiere, B. 170.

THE PROPAGATION OP LIGHT. 31

man with the conviction of his own insignificance, his phys-
ical 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 reference 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 on the periods of revolution of Encke's comet, and the
evaporation of many of the large tails of comets, seem to
prove that the regions of space which separate cosmical bod-
ies 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 Jieav-
en" " cosmical (non-luminous) matter" and " ether" the
latter, which has been transmitted to us from the earliest an-
tiquity of Southern and Western Asia, has not always ex-
pressed the same idea. Among the natural philosophers of
India, ether (aka'sa) was regarded as belonging to the pant-
scJiata, or five elements, and was supposed to be a fluid of
infinite subtlety, pervading the whole universe, and constitu-
ting the medium of exciting life as well as of propagating
sound.f Etymologically considered, aka'sa signifies, accord-
ing 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."

In the dogmas of the Ionic philosophy of Anaxagoras and
Empedocles, this ether (alOr^p) differed wholly from the act-
ual (denser) vapor-charged air (drjp) which surrounds the

* Aristotle (Phys. Auseu.lt., iv., 6-10, p. 213-217, Bekker) proves, in
opposition to Leucippus and Democritus, that there is no unfilled space
— no vacuum in the universe.

t Akd'sa signifies, according to Wilson's Sanscrit Dictionary, " the
subtle and ethereal fluid supposed to fill and pervade the universe, and
to be the peculiar vehicle of life and sound." " The word dlcd'sa (lu-
minous, shining) is derived from the root ka's (to shine), to which is
added the preposition d. The quintuple of all the elements is called
•pantsckatd, or pantschatra, and the dead are, singularly enough, desig-
nated as those who have been resolved into the five elements (prdpta
pantschatra'). Such is the interpretation given in the text of Amara-
koscha, Amarasinha's Dictionary." — (Bopp.) Colebrooke's admirable
treatise on the Sankhya Philosophy treats of these five elements ; see
Transact, of the Asiat. Soc., vol. i., Loud., 1827, p. 31. Strabo refers,
according to Megasthenes (xv., $ 59, p. 713, Gas.), to the all-forming
fifth element of the Indians, without, however, naming it.

32 COSMOS.

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 co-
incides with its etymological derivation from aWeiv, to burn,
for which Plato and Aristotle, from a predilection for me-
chanical views, singularly enough substituted another (del-
6elv), on account of the constancy of the revolving and rota-
tory movement.! The 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 vapors of the earth, or that the dens-
ity of the strata of air decreases with their increased height.
In as far as the elements of the ancients refer less to mate-
rial differences of bodies, or even to their simple nature (their
incapacity of being decomposed), 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 vxAfire. These extremes

* Empedocles, v. 216, calls the ether irapfavouv, brightly-beaming,
and therefore self-luminous.

t Plato, Cratyl., 410 B., where we meet with the expression aetdsrip.
Aristot., De Casio, 1, 3, p. 270, Bekk., says, in opposition to Anaxagoras:
aidtpa rrpoffuvofiaaav TOV UVUTUTU TOTTOV, U.TTO TOT delv act rbv aldiov
Xpovov -QfUfvoi. TTJV snuwpiav avru. 'Avagayopaf t)e KaraKixpilfai ru
ov6/j.aTi TovTCf) ov KO^uf • bvoftd&t yap aWepa avrl irvpoc.. We find this
more circumstantially referred to in 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 up-
per region is full of fire, and to be considered as ether ; in which, in-
deed, he is correct. For the ancients appear to have regarded the body
which is in a 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 re-
linquish such childish fancies if they properly investigated the results of
the latest researches of mathematicians." (The same etymology of this
word, implying rapid revolution, is referred to by the Aristotelian, or
Stoic, author of the work De Mundo, cap. 2, p. 392, Bekk.) Professor
Franz has correctly remarked, "That the play of words in the designa-
tion of bodies in eternal motion (aufta uei dtov') and of the divine (tfftov)
alluded to in the Meteoroloeica, is strikingly characteristic of the Greek
type of imagination, and affords additional evidence of the inaptitude of
the ancients for etymological inquiry." Professor Buschmann calls at-
tention to a Sanscrit term, dschtra, ether or the atmosphere, which looks
very like the Greek aidr/p, with which it has been compared by Vans
Kennedy, in his Researches into the Origin and Affinity of the principal
Languages of Asia and Europe, 1828, p. 279. This word may also be
ich

referred to the root (as, asch), to which the Indians attach the signifi
cation of shining or beaming.

COSMICAL ETHER. 33

are separated by two intermediate elementary conditions, of
which the one, water, approximates 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
those of subtlety and tenuity with the ether, by whose trans-
verse vibrations modern physicists have succeeded so hap-
pily in explaining, on purely mathematical principles, the
propagation of light, with all its properties of double refrac-
tion, polarization, and interference. The natural philosophy
of Aristotle further teaches that the ethereal substance pen-
etrates 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 (-rrafi^avouv), and is said to be
seen by the inhabitants of the earth in certain phenomena,
gleaming brightly through fissures and chasms (^da/zara)
which occur in the firmament.^

The numerous investigations that have been made in re-
cent times regarding the intimate relation between light,
heat, electricity, and magnetism, render it far from improba-
ble 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

• Aristot., De Ccelo, iv., 1, and 3-4, p. 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 Philosophic, th. iii., s.
259), and by Martin (Etudes sur le Timte de Platan., t. ii., p. 150), it ia
only because, according to him, ether, as a condition of matter, has no
contrary. (Compare Biese, Philosophic des Aristoteles, bd. xi., s. 66.)
Among the Pythagoreans, ether, as a fifth element, was represented by
the fifth of the regular bodies, the dodecahedron, composed of twelve
pentagons. (Martin, t. ii., p. 245-250.)

t See the proofs collected by Biese, op. cit., bd. xi., s. 93.

t Cosmos, vol. i., p. 153.

B2

34 COSMOS.

have their origin in analogous kinds of motion (currents). It
is reserved for future ages to make great discoveries in ref-
erence to these 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 influ-
ence on the combinations and decompositions of matter — on
all formative agencies in the mineral kingdom — on the dis-
turbance 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 ac-
cordance with an early hypothesis of Sir "William Herschel,t
the sun itself is in the condition of " a perpetual northern
light" (I should rather say of an electro-magnetic storm), we
should seem warranted in concluding that solar light, trans-
mitted in the regions of space by vibrations of ether, may be
accompanied by electro-magnetic currents.

Direct observations on the periodic changes in the decli-
nation, inclination, and intensity of terrestrial magnetism,
have, it is true, not yet shown with certainty that these con-
ditions 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 precession of the equinoxes. t The remarkable rotatory
or oscillatory motion of the radiating cone of light of Halley's
comet, which Bessel observed from the 12th to the 22d of
October, 1835, and endeavored to explain, led this great as-
tronomer to the conviction that there existed a polar force,

Compare the fine passage on me influence of the sun's rays in Sir
n Herschel's Outlines of Astronomy, p. 237 : " By the vivifying ac-
tion of the sun's rays, vegetables are enabled to draw support from in-

organic 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 coo1, strata. By them the wa-
ters of the sea are made to circulate in v*»pT through the air, and irri-
gate 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."

t Philos. Transact, for 1795, vol. Ixxxv., p. 318 ; John Herschel, Out-
lines of Astr., p. 238; see also Cosmos, vol. i., p. 189.

t See Bessel, in Schumacher's Astr. Nachr., bd. xiii., 1836, No. 300,
B. 201.

RADIATING HEAT. ' 35

" 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 re-
pulsive 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.

T/te actions of radiating heat in the regions of space are
regarded as less problematical than electro-magnetic phenom-
ena. According to Fourier and Poisson, the temperature of
the regions of space is the result of radiation of heat from the
sun and all astral bodies, minus the quantity lost by absorp-
tion in traversing the regions of space filled with ether, t
Frequent mention is made in antiquity by the Greek and
RomanJ writers of this stellar heat ; not only because, from
a universally prevalent assumption, the stars appertained to
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 mathemati-
cians, Fourier and Poisson, have been the means of direct-
ing attention to the average determination of the tempera-
ture of the regions of space ; and the more strongly since the
importance of such determinations on account of the radia
tion of heat from the earth's surface toward 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 planetaires
ou celestes) is rather below the mean temperature of the
poles, or even, perhaps, below the lowest degree of cold hith-
erto observed in the polar regions. Fourier estimates it at
from — 58° to — 76° (from — 40° to — 48° Reaum.). The icy
pole (pole glacial), or the point of the greatest cold, no more

* Bessel, op. cif., 8. 186-192, 229.

t Fourier, Thforie Analytique de la Chaleur, 1822, p. ix. (Annalet
de Chimie et de Physique, torn, iii., 1816, p. 350; torn, iv., 1817, p. 128;
torn, vi., 1817, p. 259 ; torn, xiii., 1820, p. 418.) Poisson, in his Thlorie
Mathematiqve de la Chaleur (§ 196, p. 436, $ 200, p. 447, and $ 228, p.
521), attempts to give the numerical estimates of the stellar heat (cha-
leur stellaire) lost by absorption in the ether of the regions of space.

t On the heating power of the stars, see Aristot., De Meteor., 1, 3,
p. 340, lin. 28 ; and on the elevation of the atmospheric strata at which
heat is at the minimum, consult Seneca, in Nat. Qu&st., ii., 10: ''So-
periora enim afiris calorem vicinoruin siderum sentiurt."

$ Plut., Deplac. Philos., ii., 13.

corresponds with the terrestrial pole than does the thermal
equator, which connects together the hottest points of al]
meridians with the geographical equator. Arago concludes,
from the gradual decrease of mean temperatures, that the
degree of cold at the northern terrestrial pole is — 13°, if the
maximum cold ohserved by Captain Back at Fort Reliance
(62° 46' lat.) in January, 1834, were actually — 70° ( — 56°-6
Cent., or — 450>3 Reaum.).* The lowest temperjtlure 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. The instruments used in
this observation were compared with his own by Middendorff,
whose operations were always conducted with extreme ex-
actitude. Neveroff found the temperature on the day above
named to be — 76° (or — 48° Reaum.).

Among the many grounds of uncertainty in obtaining a
numerical 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 great-
est cold of the two hemispheres, owing to our insufficient ac-
quaintance with the meteorology of the antarctic pole, from
which the mean annual temperature must be determined. I
attach but little physical probability to the hypothesis of Pois-
son, that the different regions of space must have a very va-
rious temperature, owing to the unequal distribution of heat-
radiating stars, and that the earth, during its motion with the

* Arago, Sur la Temperature du P6le et des espaces Celestes, in the
Annuaire du Bureau des Long, pour 1825, p. 189, et pour 1834, p. 192;
also Saigey, Physique du Globe, 1832, p. 60-76. Swanberg found, from
considerations on refraction, that the temperature of the regions of space
was — 58°.5. — Berzelius, Jahresbericht fur 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 observa-
tions made by myself in the chain of the Andes and in Mexico, found it
— 85° ; and from thermometrical measurements made at Mont Blanc,
and during the aeronautic 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 correctness 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, having obtained his data from purely theoretical
premises, 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 Comptet Rendus de I' Academic det Science!,
torn, vii., 1838, p. 25-65.

TEMPERATURE OF SPACE. 37

whole solar system, receives its internal heat from without
while passing through hot and cold regions.*

The question whether the thermal conditions of the celes-
tial 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-
mic al vapor is being condensed around one or more nuclei in
accordance with the laws of attraction ? By such a con-
densation of cosmical vapor, heat must be liberated, as in
every transition of gases and fluids into a state of solidifica-
tion.t If, in accordance with the most recent views, and
the important observations of Lord Rosse and Mr. Bond, we
may assume that all nebulae, including those which the high-
est power of optical instruments has hitherto failed in resolv-
ing, are closely crowded stellar swarms, our faith in this per-
petually augmenting liberation of heat must necessarily be
in some degree weakened. But even small consolidated cos-
mical bodies which appear on the field of the telescope as
distinguishable luminous points, may change their density
by combining in larger masses ; and many phenomena pre-
sented by our own planetary system lead to the conclusion
that planets have been solidified from a state of vapor^ and
that their internal heat owes its origin to the formative pro-
cess of conglomerated matter.

It may at first sight seem hazardous to term the fearfully
low temperature of the regions of space (which varies be-
tween 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 ac-
tion 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 temperature between
the vault of heaven and the atmospheric strata, and from the
feebleness of the counter-radiation. How enormous would
be this loss of heat.J if the regions of space, instead of the

* See Poisson, Tklorie Maih6m. de la Chaleur, p. 438. According
to him, the consolidation of the earth's strata began from the center, ana
advanced gradually toward the surface ; $ 193, p. 429. Compare also
Cosmos, vol. i., p. 176, 177. t Cosmos, vol. i., p. 83, 84, 144.

t " Were there no atmosphere, a thermometer freely exposed (at sun-

38 COSMOS.

temperature they now possess, and which we designate as
— 76° of a mercury thermometer, had a temperature of about
— 1400° or even many thousand times lower !

It still remains for us to consider two hypotheses in rela-
tion to the existence of a fluid filling the regions of space,
of which one — the less firmly-based hypothesis— -refers to the
limited transparency of the celestial regions ; and the other,
founded on direct observation and yielding numerical results,
is deduced 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, i. e., a sun, the entire vault of heaven must ap-
pear as luminous as our sun if light were transmitted to us
in perfect intensity ; or, if such be not the case, we must as-
sume that light experiences a diminution of intensity in its
passage through space, this diminution being more excessive
than in the inverse ratio of the square of the distance. As
we do not observe the whole heavens to be almost uniformly
illumined by such a radiance of light (a subject considered
by Halleyf in an hypothesis which he subsequently rejected),
the regions of space can not, according to Cheseaux, Olbers,
and Struve, possess perfect and absolute transparency. The
results obtained by Sir William Herschel from gauging the

«p

set) to the heating influence of the earth's radiation, and the cooling
power of its own into space, would indicate a medium temperature be-
tween that of the celestial spaces (—132° Fahr.) and that of the earth's
surface below it, 82° Fahr., at the equator, 3*° 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 exposed from attaining these ex-
treme low temperatures : first, by imparting heat by conduction ; sec-
ondly, by impeding radiation outward." — Sir John Herschel, in the
Edinburgh Review, vol. 87, 1848, p. 222. " Si la chaleur des espaces
planetaires n'existait point, notre atmosphere 6prouverait un refroidis-
sement, dont on ne peut fixer la limite. Probablement la vie des plantes
et des animaux serait impossible a la surface du globe, ou releguee dans
une etroite zone de cette surface." (Saigey, Physique du Globe, p. 77.)

* Traiti de la Comete de 1743, avec une Addition sur la force de la
Lumiere et sa Propagation dans l'6ther, ct sur la distance des etoiles fixes;
par Loys de Cheseaux (1744). On the transparency of the regions of
space, see Olbers, in Bode's Jahrbuckfur 1826, s. 110-121 ; and Struve,
Etudes d'Astr. Slellaire, 1847, p. 83-93, and note 95. Compare also
Sir John Herschel, Outlines of Astronomy, $ 798, and Cosmos, vol. i., p.
151, 152.

t Halley, On the Infinity of the Sphere of Fixed Stars, in the Philos.
Transact., vol. xxxi., for tfie year 1720, p. 22-26.

RESISTING MEDIUM. 39

stars,* and from his ingenious experiments on the space-pen-
etrating power of his great telescopes, seem to show, that if
the light of Sirius in its passage to us through a gaseous or
ethereal fluid loses only T£7tb of its intensity, this assump-
tion, which gives the amount of the density of a fluid capa-
ble of diminishing light, would suffice to explain the phe-
nomena 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 hem-
ispheres, the smallest stars projected on a black ground. t

A better proof, and one based, as we have already stated,
upon direct observation of the existence of a resisting fluid,}
is afforded by Encke's comet, and by the ingenious and im-
portant conclusion to which my friend was led in his observ-
ations on this body. This resisting medium must, however,
be regarded as different from the all-penetrating light-ether,
because the former is only capable of offering resistance in-
asmuch as it can not penetrate through solid matter. These
observations require the assumption of a tangential 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

* Cosmos, vol. i., p. 86, 87.

t "Throughout by far the larger portiou 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. . . ."
—Sir John Herschel, Outlines of Astr., p. 537, 539.

t Cosmos, vol. i., p. 85, 86, 107 ; compare also Laplace, Essai Philos-
ophique sur les Probability's, 1825, p. 133 ; Arago, in the Annuaire du
Bureau des Long, pour 1832, p. 188, pour 1836, p. 216; and Sir John
Herschel, Outlines of Astr., $ 577.

§ The oscillatory movement of the emanations from the head of some
comets, as in that of 1744, and in Halley's, as observed by Bessel, be-
tween the 12th and 22d of October, 1835 (Schumacher, Astron. Nachr.,
Nos. 300, 302, § 185, 232), "may indeed, in the case of some individ-
uals of this class of cosmical bodies, exert an influence on the transla-
tory 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 revolution is 3§ years), can not be regarded as
the result of incidental emanations. Compare, on this cosmically im-
portant subject, Bessel, in Schum., Astron. Nachr., No. 289, s. 6, and
No. 310, s. 345-350, with Encke's Treatise on the hypothesis of the re-
sisting medium, in Schum., No. 305, s. 265-274

40 COSMOS.

is manifested during the twenty-five days immediately pre-
ceding and succeeding the comet's perihelion passage. The
value of the constant is therefore somewhat different, because
in the neighborhood of the sun the highly attenuated but
still gravitating strata of the resisting fluid are denser. 01-
bers maintained* that this fluid could not be at rest, but
must rotate directly round the sun, and therefore the resist-
ance offered to retrograde 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 revolution, and the difference of their magni
tudes and sizes, -complicate the results, and render it diffi-
cult to determine what is ascribable to individual forces.

The gaseous matter constituting the belt of the zodiacal
light may, as Sir John Herschelf expresses it, be merely the
denser portion of this comet-resisting medium. Although it
may be shown that all nebulae 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 56, 000, 000 of
miles. Arago has ingeniously shown, on optical grounds,^
that the variable stars which always exhibit white light
without any change of color in their periodical phases, might
afford a means of determining the superior limit of the dens-
ity 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 WolJaston,§ 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 equipoised
by the force of gravity. Faraday's ingenious experiments on

* Gibers, in Schum., Astr. NacJir., No. 268, a. 58.

t Outlines of Astronomy, $ 556, 597.

t "En assimilant la mature ires rare qui remplit les espaces celestes
quant a ses proprietes refringentes aux gas terrestres, la densite de cette
matiere nt saurait depasser itne certaine limite dont les observations des
eloilcs chcngeantes, p. e. celles d1 Algol oudc/3 de Persic, peuvent assigner
la valeur." — Arago, in the Annuaire pour 1842, p. 336-345. " On com
paring the extremely rare matter occupying the regions of space with
terrestrial gases, in respect to its refractive properties, we shall find that
the density of this matter can not exceed a definite limit, whose value
may be obtained from observations of variable stars, as, for instance,
Algol or (3 Persei."

§ See Wollaston, Philos. Transact, for 1822, p. 89,' Sir John Herschel,
op. eit., $ 34, 36.

FIRST TELESCOPE, 41

the limits of an atmosphere of mercury (that is, the elevation
at which mercurial vapors precipitated on gold leaf cease
perceptibly to rise in an air-filled space) have given consid-
erable 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 ? New-
ton* inclined to the idea that such might be the case. If
we regard falling stars and meteoric stones as planetary as-
teroids, we may be allowed to conjecture that in the streams
of the so-called November phenomena,! 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 received from the regions of space
some elements foreign to it, which were capable of exciting
electro-magnetic processes.

II.

NATURAL AND TELESCOPIC VISION.— SCINTILLATION OF THE STARS
—VELOCITY OF LIGHT.— RESULTS OF PHOTOMETRY.

THE increased power of vision yielded nearly two hundred
and fifty years ago by the invention of the telescope, has af-
forded to the eye, as the organ of sensuous cosmical contem-
plation, the noblest of all aids toward a knowledge of the
contents of space, and the investigation of the configuration,
physical character, and masses of the planets and their sat-
ellites. 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 satel-
lites 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 nebulae in
Andromeda. J In 1634, the French astronomer Morin, emi-
nent for his observations on longitude, first conceived the idea
of mounting a telescope on the index bar of an instrument
of measurement, and seeking to discover Arcfurus by day.$

* Newton, Princ. Mathem., t. iii. (1760), p. 671: "Vapores qui ex
sole et stellis fixis et caudis cometarum oriuiitur, incidere posswit in at-
mosphaeras planetarum " t Cosmos, vol. i., p. 124-135.

t See Cosmos, vol. ii., p. 317-335, with notes.

$ Delambre, Histoire de C Astronomic Moderne, torn, ii., p. 255, 269

42 COSMOS.

The perfection in the graduation of the arc would have failed
entirely, or to a considerable extent, in affording that great-
er precision of observation at which it aimed, if optical and
astronomical instruments had not been brought into accord,
and the correctness of vision made to correspond with that
of measurement. The micrometer-application of fine threads
stretched in the focus of the telescope, to which that instru-
ment owes its real and invaluable importance, was first de-
vised, six years afterward (1640), by the young and talented
Gascoigne.*

While, as I have already observed, telescopic vision, ob-
servation, 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, Egyp-
tians, and Chinese, that more than nineteen centuries have
intervened between the age of Timochares and Aristillusf
and the discoveries of Galileo, during which period the posi-
tion and course of the stars were observed by the eye alone,
unaided by instruments. When we consider the numerous
disturbances which, during this prolonged period, checked the
advance of civilization, and the extension of the sphere of
ideas among the nations inhabiting the basin of the Medi-
terranean, we are astonished that Hipparchus and Ptolemy
should have been so well acquainted with the precession of
the equinoxes, the complicated movements of the planets, the
two principal inequalities of the moon, and the position of the
stars ; that Copernicus should 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,

272. Morin, in his work, Seientia Longitudinum, which appeared in
1634, writes as follows: Applicatio tubi optici ad alkidadam pro slellit
fans 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. (Daily's Catal. of Stars, p. 38.)

* The unfortunate Gascoigne, whose merits, remained so long unac-
knowledged, 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 Philos. Transact., vol. xxx., for 1717-1719, p. 603
-610. To him belongs the merit of a discovery which was long ascribed
to Picard and Auzout, and which has given an impulse previously un-
known to practical astronomy, the principal object of which is to de-
termine positions in the vault of heaven.

t Cosmos, vol. iL, p. 177, 1F8.

DIOPTRIC TUBES. 43

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 observa-
tions by causing the object to be seen through diopters or slits.
Abul-Hassan speaks very distinctly of tubes, to the extremi-
ties 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
discovered 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 atmos
pheric 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 fre-
quently emendated and much contested passage of Strabo, in
which mention is made of looking through tubes, this " en-
larged form of the stars" is expressly mentioned, and is erro-
neously 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 ris-
ing as well as at its setting, because at these times a larger mass of ex-
halations rises from the humid element ; and the eye, looking through
these exhalations, sees images refracted into larger forms, as observed
through lubes. The same thing happens when the setting sun or moon
is seen through a dry and thin cloud, when those bodies likewise appear
reddish." This passage has recently been pronounced corrupt (see
Kramer, in Strabonis Geogr., 1844, vol. i., p. 211), and 81 vdAwv (through
glass spheres) substituted for 61 avhuv (Schneider, Eclog. Phyt., vol. ii.,
p. 273). The magnifying power of hollow glass spheres, filled with
water (Seneca, i., 6), was, indeed, as familiar to the ancients as the ac-
tion of burning-glasses or crystals (Aristoph., Nub., 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. ii., p. 245, and note J.) Solar altitudes, taken
through thin, light clouds, or through volcanic vapors, exhibit no trace
of the influence of refraction. (Humboldt, Recveil d'Obterv. Astr., vol.
i., p. 123.) Colonel Baeyer observed no angular deviation in the heli-
otrope light on the passage of streaks of mist, or even from artificially
developed vapors, and therefore fully confirms Arago's experiments.
Peters, at Pulkowa, in no case found a diiference of 0"'017 on compar-
ing groups of stellar altitudes, measured in a clear sky, and through
light clouds. See his Recherche* sur la Parallaxe des Etoiles, 1848, p.
80, 140-143 ; also Struve's Etudes Stellaires, p. 98. On the application
of tubes for astronomical observation in Arabian instruments, see Jour-

44 COSMOS.

Light, from whatever source it comes — whether from th«
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 glow-worms — always exhibits the same con-
ditions of refraction.* But the prismatic spectra yielded by
different sources of light (as the sun and the fixed stars) ex-
hibit a difference in the position of the dark lines (raies du
spectre) which Wollaston first discovered in 1808, and the po-
sition of which was twelve years afterward so accurately de-
termined by Fraunhofer. While the latter observer counted
600 dark lines (breaks or interruptions in the colored spec-
trum), Sir David Brewster, by his admirable experiments with
nitric oxyd, succeeded, in 1833, in counting more than 2000
lines. It had been remarked that certain lines failed in the
spectrum at some seasons of the year ; but Sir David Brew-
ster has shown that this phenomenon is owing to different al-
titudes of the sun, and to the different absorption of the rays
of light in their passage through the atmosphere. In the spec-
dam, Sur V Obseroatoire de Meragha, p. 27 ; and A. Sedillot, Mem. sur
les Instruments Astronomiques des Arabes, 1841, p. 198. Arabian astron-
omers 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 ouverture pratique dans la voflte de 1'observatoire qui couvrait
{'instrument, suivaut le tuyau, et formaient sur la concavite du sextant
une image circulaire, dont le centre donnait, sur 1'arc gradue, le com
plement de la hauteur du soleil. Cet instrument 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 the dome of the
observatory, above the instrument, and, following the tube, formed in
the concavity of the sextant a circular image, the center of which marked
the sun's altitude on the graduated limb. This instrument in no way
differed from our mural circle, excepting that it was furnished with a
mere tube instead of a telescope."— Sedillot, p. 37, 202, 205. Dioptric
rulers (pinnulce) were used by the Greeks and Arabs 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 disk, seen
through the ocular aperture, completely filled the object aperture. —
Delambre, Hist, de VAstron. du Moyen Age, p. 201 ; and S6dillot, p. 198.
The adjustment of the dioptric rulers of Archimedes, with round aper-
tures or slits, in which the direction of the shadows of two small cylin-
ders attached to the same index bar was noted, seems to have been orig-
inally introduced by Hipparchus. (Baily, Hist, de VAstron. Mod., 2d
ed., 1785, torn, i., p. 480.) Compare also Theon Alexandria, Bas., 1538,
p. 257, 262; Les Hypotyp. de Prochis Diadockus, ed. Halma, 1820, p
107, 110 ; and Ptolem. Almag., ed. Halma, torn, i., Par., 1813, p. Ivii.
* According to Arago. See Moigno, Rtpert. d'Optique Moderne, 1847
p. 153.

POLARIZATION OF LIGHT. 45

tra of the light reflected from the moon, from Venus, Mars,
and the clouds, we recognize, as might be anticipated, all the
peculiarities of the solar spectrum ; but, on the other hand,
the dark lines in the spectrum of Sirius differ from those of
Castor and the other fixed stars. Castor likewise exhibits dif-
ferent lines from Pollux and Procyon. Amici has confirmed
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 distin-
guish between that which has been determined with certain-
ty 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 pow-
erfully 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 Wheatstone's
remarkable experiments with revolving minors, it would ap-
pear that the tight of frictional electricity has a greater veloc-
ity than solar light in the ratio of 3 to 2 ; that is to say, a ve-
locity of 95,908 miles in one second.

The stimulus infused into all departments of optical science
by the important discovery of polarization,! to which the in-
genious Malus was led in 1808 by a casual observation of the
light of the setting sun reflected from the windows of the Pa-
lais du Luxembourg, has aflbrded unexpected results to sci-
ence by the more thorough investigation of the phenomena of
double refraction, of ordinary (Huygens's) and of chromatic po-
larization, 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,

* On the relation of the dark lines on the solar spectrum in the Da-
guerreotype, see Comptes Rendus des S6ance» de I'Acadtmie des Science*,
torn, xiv., 1842, p. 902-904, and torn, xvi., 1843, p. 402-407.

t Cosmos, vol. ii., p. 332.

t Arago's investigation of cometary light may hero be adduced as an
instance of the important difference between proper and reflected light.
The formation of the complementary colors, red and green, showed by
the application of his discovery (in 1811) of chromatic polarization, 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 of 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

46 COSMOS.

as it were, into the constitution of the body of the eun and
of its luminous envelopes,* of measuring the pressure of at-

du Bureau des Long, pour 1836, p. 232 ; Cosmos, vol. i., p. 105 ; aud Bes-
eel, in Schumacher's Jahrbuchfur 1837, 1G9.)

* Lettre de M. Arago a M. Alexandre de Humboldt, 1840, p. 37 : "A
1'aide d'un polariscope de mon invention, je reconnus (avant 1820) quo
la lumiere de tous les corps terrestres incandescents, solides ou liquides,
est de la lumiere naturelle, tant qu'elle emane du corps sous des inci-
dences perpendiculaires. La lumiere, au contraire, qui sort de la surface
incandescente sous un angle aigu, offre des marques manifestos de po-
larisation. Je ne m'arrete pas a te rappeler ici, comment je d6duisis
de ce fait la consequence curieuse que la lumiere ne s'eugendre pas
seulement a la surface des corps ; qu'une portion nalt dans leur sub-
ttance ineme, cette substance fut-elle du platine. J'ai seulement besoin
de dire qu'en repetant la meme serie d'epreuves, et avec les m£mes
instruments sur la lumiere que lance une substance gazeuse enflammee,
on ne lui trouve, sous quelque incllnaison que ce soit, aucun des carac-
teres de la lumiere polarisee; que la lumiere des gaz, prise a la sortie
de la surface enflammee, est de la lumiere naturelle, ce qui n'empeche
pas qu'elle ne se polarise ensuite completement si on la soumet a des
reflexions ou a des refractions conveuables. De la une methode trea
simple pour decouvrir a 40 millions de lieues de distance la nature du
soleil. La lumiere proveuant du hard de cet astre, la lumiere emanee
de la matiere solaire sous un angle aigu, et nous arrivant sans avoir
eprouve en route des reflexions ou des refractions sensibles, offre-t-elle
des traces de polarisation, le soleil est un corps solide ou liquide. S'il
n'y a, au contraire, aucun indice de polarisation dans la lumiere du bord,
la parte incandescente du soleil est gazeuse. C'est par cet euchainement
methodique 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 polar-
ization. I will not pause to remind you that this circumstance has led
me to the remarkable conclusion that light is not generated on the sur-
face of bodies only, but that some portion is actually engendered within
the substance itself, even in the case of platinum. I need only here ob-
serve, that in repeating the same series of experiments (aud with the
same instruments) on the light emanating from a burning gaseous sub-
stance, I could not discover any characteristics of polarized light, what-
ever 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 sur-
face, although this circumstance does not prevent its subsequent com-
plete polarization, if subjected to suitable reflections or refractions.
Hewoe 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 reflec-
tions or refractions in its passage to the earth, and if it offer traces of
polarization, the sun must be a solid or a liquid body. Put if, on the
contrary, the light emanating from tke sun's margin giv- no indications
of polarization, the incandescent portion of the sun inuetbe %a»euu». it

POLARIZATION OF LIGHT. 47

mospheric strata, and even the smallest amount of water they
contain, of scrutinizing the depths of the ocean and its rocks
by means of a tourmaline plate,* and, in accordance with
Newton's prediction, of comparing the chemical compositionf
of several substances^ with their optical effects. It will be
sufficient to mention the names of Airy, Arago, Biot, Brew-
ster, Cauchy, Faraday, Fresnel, John Herschel, Lloyd, Ma-
lus, Neumann, Plateau, Seebeck, to remind the sci-
entific reader of a succession of splendid discoveries and of
their happy applications. The great and intellectual labors
of Thomas Young more than prepared the way for these im-
portant efforts. Arago's polariscope and the observation of
the position of colored fringes of diffraction (in consequence
of interference) have been extensively employed in the pros-
ecution of scientific inquiry. Meteorology has made equal
advances with physical astronomy in this new path.

However diversified the power of vision may be in differ-
ent persons, there is nevertheless a certain average of organ-
is by means of such a methodical 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 retranslating the passages
into French, or any other of the various languages in which the Cosmos
has appeared.

* " Sur 1'effet d'une lame de tourmaline taillee parallelement aux
aretes du prisme servant, lorsqu'elle est convenablement situee, a 61i-
miner en totalite les rayons reflechis par la surface de la mer et meles £
la lumiere provenant de 1'ecueil." " 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 Bonite, in the Annuaire pour 1836, p. 339

343.

t " De la possibilit6 de d6terminer les pouvoirs refringents des corps
d'apres leur composition chimique." On the possibility of determining
the refracting powers of bodies according to their chemical composition

applied to the ratio of the oxygen to the nitrogen in atmospheric air,
to the quantity of hydrogen contained in ammonia and in water, to car-
bonic acid, alcohol, and the diamond). See Biot ct Arago, Mtmoire
sur les Ajfinites des Corps pour la Lumiere, Mars, 1806; also Mlmoirts
Mathem. et Phys. de V Inslilut, t. vii., p. 327-346 ; and my M6moire gur
les Refractions Astronomiques dans la Zone Torride, in the Recueit
d'Obsew. Astron., vol. i., p. 115 and 122.

t Experiences de M. Arago sur la puissance Refractive des Corps D\-
aphanes (de I' air sec ct de I' air humide) par le Replacement des Franges,
iu Moigno, Repertoire d'Oplique Mod., 1847, p. 159-K52.

48 COSMOS.

fc capacity, which was the same among former generation!,
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 sev-
enth magnitude, wera invisible to the naked eye of average
visual power. The group of the Pleiades consists of one
star of the third magnitude, Alcyone ; of two of the fourth,
Electra and Atlas ; of three of the fifth, Merope, Maia, and
Taygeta ; of two hetween the sixth and the seventh magni-
tudes, Pleione and Celseno ; of one between the seventh and
the eighth, Asterope ; and of many very minute telescopic
stars. I make use of the nomenclature and order of succes
sion at present adopted, as the same names were among the
ancients in part applied to other stars. The six first-named
stars of the third, fourth, and fifth magnitudes were the only
ones which could be readily distinguished.* Of these Ovid
says (Fast., iv., 170),

" Qua; 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 seventh magnitude, which we
call Celajno ; for Hipparchus, in his commentary on Aratus,
observes that on clear moonless nights seven stars may ac-
tually be seen. Celseno, therefore, must have been seen, for
Pleione, which is of equal brightness, is too near to Atlas, a
star of the fourth magnitude.

The little star Alcor, which, according to Triesnecker, is
situated in the tail of the Great Bear, at a distance of 11'

* Hipparchus says (ad Arati Phcen., 1, p. 190, in Uranologio Pctavii),
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 attentively fixed on this constellation on a serene and
moonless night, seven stars are visible, and it therefore seems strange
that Attains, 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 (•nava<j>avjjf') in
the Catasterisms (XXIII.) ascribed to Eratosthenes. On a supposed
connection between the name of the veiled (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 Ex
amen Grit, de VHist. de la Geographic, t. i., p. 170. Compare also Ideler
Untersuchungen fiber den Ursprung imd die Bedeutung der Sternnamen,
1809, p. 145; and in reference to astronomical determination of place,
consult Madler, Unttrsucli. ubet die Fixstern-Systeme, th. ii., 1848, s. 38
and 166 ; also Baily in the Mem. of the Astr. Soc., vol. xiii., p. 33.

VISIBILITY OF STARS. 49

48 from Mizar, is, according to Argelander, of the fifth
magnitude, but overpowered by the rays of Mizar. It was
called by the Arabs Saidak, " the Test," because, as the Per-
sian astronomer Kazwini* remarks, " It was employed as a

* See Ideler, Sternnamen, s. 19 and 25. Arago, in manuscript notices
of the year 1847, writes as follows: " On observe qu'une lumiere forte
fait disparaltre une lumiere faible placee dans le voisinage. Quelle
peut en etre la cause ? II est possible physiologiquement que 1'ebran-
lement communique k la retine par la lumiere forte s'etend au del& des
points que la lumiere forte a frappes, et que cet ebranlement secon-
daire absorbe et neutralise en quelque sorte 1'ebranlement provenant de
la seconde et faible lumiere. Mais sans entrer dans ces causes physio-
logiques, il y a une cause directe qu'on peut indiquer pour la dispari-
tion de la faible lumiere : c'est que les rayons provenant de la grande
n'ont pas seulement forme une image nette sur la retine, mais se sont
disperses aussi sur toutes les parties de cet organe £ cause des imper-
fections de transparence de la cornee. Les rayons du corps plus bril-
lant a en traversant la cornee se comportent comme en traversant un
corps legerement depoli. Une partie des ces rayons refractes reguliere-
ment forme 1'image neme de a, 1'autre partie disperses eclaire la totalite
de la retine. C'est done sur ce fond lumineux que se projette 1'image
de 1'objet voisin b. Cette derniere image doit done ou disparaltre ou
etre affaiblie. De jour deux causes contribuent £ 1'affaiblissement des
etoiles. L'une de ces causes c'est 1'image distincte de cette portion de
ratmosphere comprise dans la direction de 1'etoile (de la portion aeri-
enne placee entre 1'oeil et 1'etoile) et sur laquelle 1'image de 1'etoile vient
de se peindre ; 1'autre cause c'est la lumiere diffuse provenant de la dis-
persion que les defauts de la cornee imprlment aux rayons emanants de
tous les points de 1'atmosphere visible. De nuit les couches atmosphe-
riques interposees entre 1'oeil et 1'etoile vers laquelle on vise, n'agissent
pas ; chaque etoile du firmament forme une image plus nette, mais une
partie de leur lumiere se trouve dispersee a, cause du manque de dia-
phanite de la cornee. Le me me raisonnement s'applique 4 une deux-
icme, troisieme .... millidme etoile. La retine se trouve done eclai-
ree en totalite par une lumiere diffuse, proportionnelle au nombre de
ces etoiles et a leur eclat. On con^oit par 1& que cette somme de lu-
miere diffuse affaiblisse ou fasse entierement disparaitre 1'image do
1'etoile vers laquelle on dirige la vue."

" We find that a strong light causes a fainter one placed near it to dis-
appear. What can be the cause of this phenomenon ? It is physiolog-
ically possible that the vibration communicated to the retina by strong
light may extend beyond the points excited by it; and that this secondary
vioration may in some degree absorb and neutralize that arising from the
second feeble light. Without, however, entering upon these physiologic-
al considerations, there is a direct cause to which we may refer the disap-
pearance 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 th.2 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, while the remainder of the dispersed
rays illumine the whole jf the retina. On this luminous ground the
VOL. III.— C

60 COSMOS.

test of the power of vision." Notwithstanding the low po-
sition of the Great Bear under the tropics, I have very dis-
tinctly seen Alcor, evening after evening, with the naked
eye, on the rainless shores of Cumana, and on the plateaux
of the Cordilleras, which are elevated nearly 13,000 feet
above the level of the sea, while I have seen it less frequent-
ly and less distinctly in Europe and in the dry atmosphere
of the Steppes of Northern Asia. The limits within which
the naked eye is unable to separate two very contiguous ob-
jects in the heavens depend, as Madler has justly observed,
on the relative brilliancy of the stars. The two stars of the
third and fourth magnitudes, marked as a Capricorni, which
are distant from each other six and a half minutes, can with
ease be recognized as separate. Galle thinks that £ and 6
Lyrse, being both stars of the fourth magnitude, may be dis-
tinguished in a very clear atmosphere by the naked eye, al-
though situated at a distance of only three and a half min-
utes from each other.

The preponderating effect of the rays of the neighboring
planet is also the principal cause of Jupiter's satellites re-
maining invisible to the naked eye ; they are not all, how-
ever, as has frequently been maintained, equal in brightness
to stars of the fifth magnitude. My friend, Dr. Galle, has
found from recent estimates, and by a comparison with
neighboring stars, that the third and brightest satellite is
probably of the fifth or sixth magnitude, while the others,
which are of various degrees of brightness, are all of the sixth
or seventh magnitude. There are only few cases on record
in which persons of extraordinarily acute vision — that is to
say, capable of clearly distinguishing with the naked eye

image of the neighboring object b is projected. This last imago must
therefore 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 em-
anating from all points of the visible atmosphere. At 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 dispered
in consequence of the imperfect 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 num-
ber of the stars and to their brilliancy. Hence we may imagine that
the aggregate of this diffused light must either weaken, or entirely ob-
literate the imago of tlie star toward which the eye is directed."

VISIBILITY OF STARS. 51

gtars fainter than those of the sixth magnitude — have been
able to distinguish the satellites of Jupiter without a tele-
scope. The angular distance of the third and brightest sat-
ellite from the center of the planet is 4' 42" ; that of the
fourth, which is only one sixth smaller than the largest, is
8' 16" ; and all Jupiter's satellites sometimes exhibit, as Ar-
ago maintains,* a more intense light for equal surfaces than

* Arago, in the Annuaire pour 1842, p. 284, and in the Compte*
Rendus, torn, xv., 1842, p. 750. (Schutn., Astron. Nachr., No. 702.)
" I have instituted some calculations of magnitudes, in reference to your
conjectures on the visibility of Jupiter's satellites," writes Dr. Galle, in
letters addressed to me, " but I have found, contrary to my expecta-
tions, that they are not of the fifth magnitude, but, at most, only of the
sixth, or even of the seventh magnitude. The third and brightest sat-
ellite alone appeared nearly equal in brightness to a neighboring star
of the sixth magnitude, which I could scarcely recognize with the naked
eye, even at some distance from Jupiter ; so that, considered in refer-
ence to the brightness of Jupiter, this satellite would probably be of the
fifth or sixth magnitude if it were isolated from the planet. The fourth
satellite was at its greatest elongation, but yet I could not estimate it at
more than the seventh magnitude. The rays of Jupiter would not pre-
vent this satellite from being seen if it were itself brighter. From a
comparison of Aldebaran \vith the neighboring star 6 Tauri, which is
easily recognized as a double star (at a distance of 5J minutes), I should
estimate the radiation of Jupit«r at five or six minutes, at least, for or-
dinary vision." These estimates correspond 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 the center of the main planet are undoubtedly 1' 51",
2' 57", 4' 42", and 8' 16". " Si nous supposons que 1'image de Jupiter,
dans certains yeux exceptionnels, s'epanouisse seulement par des ray-
ons d'une ou deux minutes d'amplitude, il ne semblera pas impossible
que les satellites soient de terns en terns aper9us, sans avoir besoin de
recourir a 1'artifice de 1'amplification. Pour verifier cette conjecture,
j'ai fait construire une petite lunette dans laquelle 1'objectif et 1'ocu-
laire ont a peu pres le menie foyer, et qni des lors lie grossit point.
Cette lunette ne detruit pas eutierement les rayons divergents, mais
elle en reduit considerablement la longueur. Cela a suffi your qu'un
satellite convenablement 6cart6 de la plandte, soil devenu visible. Le
fait a ete constate par tous les jeunes astronomes de 1'Observatoire."
" If we suppose that the image of Jupiter appears to the eyes of some
persons to be dilated by rays of only one or two minutes, it is nit im-
possible that the satellites may from time to time be seen without the
aid of magnifying glasses. In order to verify this conjecture, I caased
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
itify. This instrument does not entirely destroy the diverging rays, al
though 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, torn, xv., 1842, p.

52 COSMOS.

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 from the
planets and fixed stars, and which were used, since the ear-
liest ages of mankind, and especially among the Egyptians,
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-

As a remakable 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
Schbn, who died at Breslau in 1837, and with reference to whom I have
received some interesting communications from the learned and active
director of the Breslau Observatory, Von Boguslawski. " After having
(since 1820) convinced ourselves, by several rigid tests, that in serene
moonless nights Schbn was able correctly to indicate the position of sev-
eral of Jupiter's satellites at the same time, we spoke to him of the em-
anations and tails which appeared to prevent others from seeing so
clearly as he did, when he expressed his astonishment at these ob-
structing radiations. From the animated discussions between himself
and the by-standers 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 Schbii like luminous points having no rays.
He saw the third satellite the best, and the first very plainly when it
was at the greatest digression, but he never saw the second and the
fourth alone. When the air was not in a very favorable 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
Schbn complained 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 coin-
cide with what has been long known regarding the relative luster 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. Schbii 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 color, and is generally 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 color ; the
latter occasionally exceeds in the intensity of its clear yellow light the
luster of the third, which is also much larger. (Madler, Astr., 1846,
s. 231-234, and 439.) Sturm and Airy, in the Complex Rendut, t. xx.,
p. 764-6, show how, under proper conditions of refraction in the organ
of vision, remote luminous poin'a may appear as light streaks.

NATURAL VISION. 53

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 seventh magnitude,
may, on the contrary, be visible to the unaided eye in con-
sequence 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 concen-
trated image."*

* " L'image fpanouie d'ane etoile de 7eme grandeur n'ebranle pas
suffisamment la retine : elle n'y fait pas naitre une sensation apprecia-
ole de lumiere. Si 1'image n'etait point epanouie (par des rayons di-
vergents), la sensation aurait plus de force, et 1'etoile se verrait. La
premiere classe d'etoiles invisibles a 1'ceil nu ne serait plus alors la sep-
tieme: pour la trouver, il faudrait peut-etre descendre alors jusqu'a la
12etne. Considerons un groupe d'etoiles de 7eme grandeur tellement
rapproch6es les unes des autres que les intervalles echappent necessaire-
ment a 1'oeil. Si la vision avait de la nettete, si 1'image de chaque etoile
etait tres petite et bien termin&e, 1'observateur aperceverait un champ
de lumiere dont chaque point aurait Veclat concentre d'une etoile de
7eme grandeur. I? eclat concentre d'une etoile de 7eme grandeur suffit
a la vision a 1'oeil nu. Le groupe serait done visible a I'ojil nu. Di-
latons maintenant sur la retine 1'image de chaque etoile du groupe ;
remplasons chaque point de 1'ancienne image generale par un petit cer-
cle : ces cercles empieteront les uns sur les autres, et les divers points
de la retine se trouveront eclaires par de la lumiere venaut simultan -
ment de plusieurs etoiles. Pour peu qu'on y reflechisse, il restera evi-
dent qu' excepte sur les bords de 1'image g6nerale, 1'aire lumineuse
ainsi eclairee a precisement, a cause de la superposition des cercles, la
m£me inteusite que dans le cas ou chaque etoile n'eclaire qu'un seul
point au fond de 1'ceil ; mais si chacun de ces points re<joit une lumiere
6gale en intensity a la lumiere concentree d'une etoile de 7eme gran-
deur, il est clair que 1'epanouissement des images individuelles des
fetoiles contigues ne doit pas empecher la visibilite de 1'ensemble. Les
instruments telescopiques ont, quoiqu'a un beaucoup momdre degre, le
defaut de donner aussi aux etoiles un diamitre sensible et factice. Avec
ces instruments, comme & 1'ceil nu, on doit done apercevoir des groupes,
composes d'etoiles inferieures en intensite a celles que les memea lu-
nettes ou telescopes feraient apercevoir isolement."

" The expanded image of a star of the seventh magnitude doen not
cause sufficient vibration of the retina, and does not give rise to an ap-
preciable sensation of light. If the image were not expanded (by di-
vergent rays), the sensation would be stronger and the star discernible.
The lowest magnitude at which stars are visible would not therefore
be the seventh, but some magnitude as low perhaps as the twelfth de-
gree. Let us consider a group of stars of the seventh magnitude so
close to one another that the intervals between them necessarily escape
the eye. If 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 concentrated brightness of a star
of the seventh magnitude. The concentrated light of a star of the sev-
enth 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

54 COSMOS.

Telescopes, although in a much less degree, unfortunately
also give the stars an incorrect and spurious diameter ; but,
according to the splendid investigations of Sir William Her-
echel,* these diameters decrease with the increasing power
of the instrument. This distinguished observer estimated
that, at the excessive magnifying power of 6500, the appar-
ent diameter of Vega Lyrae still amounted to 0"36. In ter-
restrial objects, the form, no less than the mode of illumina-
tion, determines the magnitude of the smallest angle of vision
for the naked eye. Adams very correctly observed that a
long and slender 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. Ara-
go 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 Observa-
tory. The minimum optical visual angle at which terres-
trial 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 pa-
per, to the period of Leeuwenhoek's experiments with spi-
der'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

image of each star of the group on the retina, and substitute a small
circle for each point of the former general image ; these 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 superposi-
tion of the circles, the same degree of intensity as in those cases where
each star illumines only one single point of the retina ; but if each of
these points be illumined by a light equal in intensity to the concen-
trated light of a star of the seventh magnitude, it is evident that the
dilatation of the individual images of contiguous stars can not prevent
the visibility of the whole. Telescopic instruments have the defect,
although in a much less degree, of giving the stars a sensible and spu.
rious 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 iso-
lated."— Arago, in the Annuaire du Bureau des Longitudes pour Van
1842, p. 284.

* Sir William Herschel, in the Philos. Transact, for 1803, vol. 93,
p. "225, and for 1805, vol. 94, p. 184. Compare also Arago, in the An
nuairepour 1842, p. 360-374.

VISIBILITY OP OBJECTS. 55

lens, white lines on a black ground were seen at an angle
of l"-2; a spider's thread at 0"-6 ; and a fine glistening
wire at scarcely 0"'2. This problem does not admit gen-
erally 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 at a charming country-seat belonging to
the Marquess de Selvalegre at Chillo, not far from Q,uito,
where the long-extended crests of the volcano of Pichincha
lay stretched before me at a horizontal distance, trigonomet-
rically determined at more than 90,000 feet, I was much
struck by the circumstance that the Indians who were stand-
ing near me distinguished the figure of my traveling com-
panion Bonpland (who was engaged in an expedition to the
volcano) as a white point moving on the black basaltic sides
of the rock, sooner than we could discover him with our tel-
escopes. The white moving image was soon detected with
the naked eye both by myself and by my friend the unfor-
tunate son of the marquess, Carlos Montufar, who subsequent-
ly 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, distinguish-
ed at a greater distance than black objects on a white ground.
The light was transmitted in serene weather through rar-
efied strata of air at an elevation 15,360 feet above the
level of the sea to our station at Chillo, which was itself sit-
uated at an elevation of 8575 feet. The ascending distance
was 91,225 feet, or 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 ob-
servation, to be 22-2 inches and 65°-7. Gauss's heliotrope
light, which has become so important an element in German
trigonometrical measurements, has been seen with the naked
eye reflected from the Brocken on Hohenhagen, at a distance
of about 227,000 feet, or more than 42 miles, being fre-
quently visible at points in which the apparent breadth of a
three-inch mirror was only 0"'43.

56 COSMOS.

The visibility of distant objects irf 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 moist-
ure ; by the degree of intensity of the light diffused by the
radiation of the particles of air ; and by numerous meteoro-
logical processes not yet fully explained. It appears from
the old experiments of the accurate observer Bouguer that
a difference of ^th 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 visibility is solely owing to
the difference in the thickness of the atmospheric strata ex-
tending respectively to the object and to the horizon. Strong
ly-illumined objects, such as snow-clad mountains, white
chalk cliffs, and conical rocks of pumice-stone, are seen pos-
itively.

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 determina-
tions are wanting to indicate the ship's place. I have treat-
ed this subject more at length in another work,* where I
considered 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, Relation Hist, du Voyage aux Regions Equinox., torn.
i., p. 92-97; and Bouguer, Traiti d'Optique, p. 360 and 365. (Com-
pare, also, Captain Beechey, in the Manual of Scientific Inquiry for the
Use of the Royal Navy, 1849, p. 71.)

t The passage in Aristotle referred to by Buffon occurs in a work
•where we should have least expected to find it — De Generat. Animal.,
\. i., p. 780, Bekker. Literally translated, it runs as follows : " Keen-
ness of sight is as much the power of seeing far as of accurately distin-
guishing 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 tube, is not, on that account,
more or less able to distinguish differences of color, although he will see
objects at a greater distance. Hence it arises that persons in cavern*
or cisterns are occasionally enabled, to see stars." The Grecian 'Ooiiy/za-
ra, and more especially (ppeara, are, as an eye-witness, Professor Franz,
observes, subterranean cisterns or reservoirs which communicate with
the light and air by means of a vertical shaft, and widen toward the bot-
tom, like the neck of a bottle. Pliny (lib. ii., cap. 14) §ays, " Altituda

FISIBILITT OP STARS. 57

that stars might occasionally be seen from ctverns and cis-
terns, as through tubes. Pliny alludes to the same circum-
stance, 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 ob-
serve a star ; nor did I ever meet with any individual in
the Mexican, Peruvian, or Siberian mines who had heard of
stars having been seen by daylight ; although in the many
latitudes, in both hemispheres, in which I have visited deep
mines, a sufficiently large number of stars must have passed
the zenith to have afforded a favorable 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 daylight through the
shaft of a chimney.* Phenomena, whose manifestation de-
pends on the accidental concurrence of favoring circum-
stances, ought not to be disbelieved 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 daylight, on the de-
clivity of Mont Blanc, and at an elevation of 12,757 feet
" Ctuelques-uns des guides m'ont assure avoir vu des etoiles
en plein jour ; pour moi je n'y songeais pas, en sorte que je
n'ai point ete le temoin de ce phenomene ; mais I' assertion
uniforme des guides ne me laisse aucun doute sur la rea-
lite. II faut d'ailleurs etre entitlement a 1'ombre d'une epais-
seur considerable, sans quoi 1'air trop fortement eclaire fait
evanouir la faible clarte des etoiles." " Several of the guides
assured me," says this distinguished Alpine inquirer, "that

cogit minores videri Stellas ; affixas ccelo-solis fulgor interdiu non cerni,
quum aeque ac noctu luceant ; idque manifesto m fiat defectu soils et prce-
altis puteis." 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."
* " We have ourselves heard it stated by a celebrated optician that
the earliest circumstance which drew his attention to astronomy waa
the regular appearance, at a certain hour, for several successive days,
of a considerable star, through the shaft of a chimney." — John Herschel,
tlines of Astr., § 61. The chimney-sweepers whom I have ques-

Ontlines of Astr., $ 61. The chimney-sweepers whom I have ques-
tioned agree tolerably well in the statement that " they have never seen
stars by day, but that, when observed at night, through deep shafts, the
sky appeared quite near, and the stars larger." I will not enter upon
any discussion regarding the connection between these two illusions.

C 2

58 COSMOS

they had seen stars at broad daylight : not having myself
been a witness of this phenomenon, I did not pay much at-
tention 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 dis-
perse 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 moniing of
the 2d of August, 1787) in any other description of the Swiss
mountains. Two well-informed, admirable observers, the
brothers Hermann and Adolph Schlagentweit, who have re-
cently explored the eastern Alps as far as the summit of the
Gross Glockner (13,016 feet), were never able to see stars
by daylight, nor could they hear any report of such a phe-
nomenon having been observed among the goatherds 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 ele-
vations 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
subsequent 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 ele-
vations varying between 17,000 and 19,000 feet.f 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
gun's disk was from 18° to 20° above the horizon.

The present would seem a fitting place to notice, although
cursorily, another optical phenomenon, which I only observed
once during my numerous mountain ascents. Before sunrise,
on the 22d of June, 1799, when at Malpays, on the decliv-
ity of the Peak of Teneriffe, at an elevation of about 11,400
feet above the sea's level, I observed with the naked eye

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

t Humboldt, Essai sur la G6ographie des Plantes, p. 103. Compare
also my Voy. aux Regions Equinox, torn, i., p. 143, 248.

UNDULATION OP THE STARS. 5»

cars near the horizon flickering with a singular oscillating
motion. Luminous points ascended, moved laterally, and
feii back to their former position. This phenomenon lasted
only from seven to eight minutes, and ceased long before the
sun's disk 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 disk, 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 century later at the same spot
by a well-informed and observing traveler, Prince Adalbert
of Prussia, who saw it both with the naked eye and through
a telescope. I found the observation 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 wit-
nessed a precisely similar phenomenon.! 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, notwithstanding the het-
erogeneous mixture of unequally-heated atmospheric strata.
As the Peak of Tenerifie is so near us, and is so frequently

* Humboldt, in Fr. von Zach's Monatliche Correspondenz zur Erd-
und Himmels-Kunde, bd. i., 1800, s. 396 ; also Voy. aux R6g. Equin.,
torn, i., p. 125 : " On croyait voir de petites fusses lancees dans 1'air.
Des points lumineux eleves de 7 a 8 degres, paraissent d'abord se mou-
voir dans le sens vertical, mais puis se convertir en une veritable oscil-
lation horizontale. Ces images lumineux etaient des images de plu-
sieurs etoiles agrandies (en apparence) par des vapeurs et revenant au
meme point d'ou elles etaient partis." " It seemed as if a number of
sinall rockets were being projected in the air ; luminous points, at an
elevation of 7° or 8°, appeared moving, first in a vertical, and then os-
cillating iu a horizontal direction. These were the images of many
stars, apparently magnified by vapors, and returning to the same point
from which they had emanated."

t Prince Adalbert of Prussia, Aus meinem Tagebuche, 1847, s. 213.
Is the phenomenon I 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 meridian telescope ? (See Zach's Corres-

endance Astronomique et Giog., vol. ii., 1819, p. 81.) Brandes (Geh-
's Umgearb. Phys. Wortersb., bd. iv., s. 549) refers the phenomenon
to mirage. The star-like heliotrope light has also frequently been seen,
by the admirable and skillful observer, Colonel Baeyer, to oscillate to
and fro in a horizontal direction.

60 COSMOS.

ascended before sunrise by scientific travelers 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 in-
vention of telescopic vision, and its application to astronom-
ical purposes. The treasure transmitted by the learning of
the Greeks and Arabs was augmented by the careful and
persevering labors of George Purbach, Regiomontanus (i. 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 his-
tory of measuring astronomy ; both indicating the epoch that
separates observation by the naked eye, though aided by
greatly improved instruments of measurement, from tele-
scopic vision. Galileo was at that period forty-four, and
Kepler thirty-seven years of age ; Tycho Brahe, the most
exact of the measuring astronomers of that great age, had
been dead seven years. I have already mentioned, in a pre-
ceding volume of this work (see vol. ii., p. 328), that none of
Kepler's cotemporaries, Galileo not excepted, bestowed any
adequate praise on the discovery of the three laws which
have immortalized his name. Discovered by purely empir-
ical methods, although more rich in results to the whole do-
main of science than the isolated discovery of unseen cos-
mical bodies, these laws belong entirely to the period of nat-
ural vision, to the epoch of Tycho Brahe and his observa-
tions, although the printing of the work entitled Astronomia
nova seu Physica codestis de motibus Stella Martis was
not completed 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
characterizes the first ten years of the seventeenth century
was more important to astronomy (the knowledge of the re-
gions of space) than the year 1492 (that of the discoveries

ASTRONOMICAL DISCOX ERIB3. t51

of Columbus) in respect to our knowledge of terrestrial space.
It not only infinitely extended our insight into creation, but
also, besides enriching the sphere of human ideas, raised
mathematical science to a previously unattained splendor,
by the exposition of new and complicated problems. Thus
the increased power of the organs of perception reacts 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 faculse, the phases of Venus, the form and height
of the lunar mountains, the wintery polar zones of Mars, the
belts of Jupiter and Saturn, the rings of the latter, the inte-
rior planetary comets of short periods of revolution, together
with many other phenomena which likewise escape the na-
ked 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 discoveries to which we
have alluded, our knowledge regarding successive strata of
the region of the fixed stars has unexpectedly been still more
increased. Thousands of nebulae, stellar swarms, and double
stars, have been observed. The changing position of the
double stars which revolve round one common center of
gravity has proved, like the proper motion of all fixed starb,
that forces of gravitation are operating in those distant re-
gions 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 tel-
escope) combined optical arrangements with measuring in-
struments, 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 pre-
cision, every change in the position of the planetary bodies,
the ellipses of aberration of the fixed stars and their paral-
laxes, and to measure the relative distances of the double
stars even when amounting to only a few tenths of a sec-
onds-arc. The astronomical knowledge of the solar system
has gradually extended 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 diam-
eters, and that he never could have used one of a higher
power than thirty-two. One hundred and seventy years later,

62 COSMOS.

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 Lyrte, using a power of 6500. Since
the middle of the seventeenth century, constant attempts
have been made to increase the focal length of the telescope.
Christian Huygena, indeed, in 1655, discovered the first sat-
ellite of Saturn, Titan (the sixth in distance from the center
of the planet), with a twelve-feet telescope ; he subsequent-
ly, however, examined the heavens with instruments of a
greater focal length, even of 122 feet ; but the three object-
glasses in the possession of the Royal Society of Londonj
whose focal lengths are respectively 123, 170, and 210 feet,
and which were constructed by Constantin 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 connection between the object-glass
and the eye-piece, completed an object-glass, which, with a
focal length of 320 feet, magnified 600 times.f 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 ob-
ject-glasses that had been ground by Borelli, Campani, 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 Cam-
pani, 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, worked
by strings only,| we can not sufficiently admire the skill and
the untiring perseverance of the observer.

* 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 Uytenbrock in the " Oratio de fratribiis
Christiano atque Constantino Hugenio, artis dioptricae cultoribus," 1838;
and by Prof. Kaiser, the learned director of the Observatory at Leyden
(in Schumacher's Astron. Nachr., No. 592, s. 246).

t See Arago, in the Annuaire pour 1844, p. 381.

t " Nous avons place ces grands verres, tantot sur un grand m&t, tan-
tot sur la tour de bois venue de Marly ; enfiu nous les avons mis dans
un tuyau monte sur un support en forme d'6chelle & trois faces, ce qui
a eu (dans la decouverte des satellites de Saturne) le succSs que nous
en avions esp6r&." " We sometimes mounted these great instruments
on a high pole," says Dominique Caasini, " and sometimes on the wood-

TELESCOPES. 63

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 upward of
10,000 feet (or nearly two miles),* in order to see animals
in the moon. A sense of the practical inconvenience of op-
tical instruments having a focal length of more than a hund-
red 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 expens-
ive 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 re-
fracting 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. f

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 fluctua-

en tower that had been brought from Marly ; and we also placed them
in a tube mounted on a three-sided ladder, a method which, in the dis-
covery of the satellites of Saturn, gave us all the success we had hoped."
— Delambre, Hist, de VAstr. Moderne, torn, ii., p. 785. Optical instru-
ments having such enormous focal lengths remind us of the Arabian in-
struments olmeasurement— -quadrants with a radius of about 190 feet,
upon whose graduated limb the image of the sun was received as in the
gnomon, through a small round aperture. Such a quadrant was erect-
ed at Samarcand, probably constructed after the model of the older sex-
tants of Al-Chokandi (which were about 60 feet in height). Compare
Sedillot, P 'rottgomenes det Tables d'Oloug-Beg, 1847, p. Ivii. and cxxix.

* See Delambre, Hist, de VAstr. Mod., t. ii., p. 594. The mystic
Capuchin monk, Schyrle von Rheita, who, however, was well versed
in optics, had already spoken in his work, Oculus Enoch et Elite (Autv.,
1645), of the speedy practicability of constructing telescopes that should
magnify 4000 times, by means of which the lunar mountains might b«
accurately laid down. Compare also Cosmos, vol. ii., p. 323 (note).

t Edinb. Encyclopedia, vol. xx., p. 479.

tions of opinion were excited by the just admiration award-
ed, both at home and abroad, to the immortal labors 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 second in order, and^soon after-
ward, Mimas, the first, or the one nearest to the ring. The
discovery of the planet Uranus in 1781 was made with
Herschel's seven-feet telescope, while the faint satellites of
this planet were first observed by him in 1787, with a twen-
ty-feet "front view" reflector.* The perfection, unattained
till then, which this great man gave to his reflecting tele-
scopes, in which light was only once reflected, led, by the
uninterrupted labor of more than forty years, to the most
important extension of all departments of physical astron-
omy in the planetary spheres, no less than in the world of
nebulae and double stars.

The long predominance of reflectors wus followed, in the
earlier part of the nineteenth century, by a successful emu-
lation in the construction of achromatic refractors, and heli-
ometers, paralactically moved by clock-work. A homoge-
neous, perfectly smooth flint glass, for the construction of
object-glasses of extraordinary magnitude, was manufactured
in the institutions of Utzschneider and Fraunhofer at Mu-
nich, and subsequently in those of Merz and Mahler ; and in
the establishments of Guinand and Bontems (conducted for
MM. Lerebours 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 Fraunho-
fer's directions 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 ;t they are both adjusted with

* Consult htruve, 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 adopted these
designations not merely on account of their greater convenience, but
also because they have acquired historical celebrity from the important
labors both of the elder and younger Herschel in England, and of the
latter at Feldhausen, at the Cape of Good Hope.

t See Schumacher's Astr. Nachr., No. 371 and 611. Cauchoix and

TELESCOPES. 65

object-glasses of 15 inches in diameter, and a focal length
of 22-5 feet. The heliometer at the Konigsberg Observa-
tory, which continued for a long time to be the largest in
existence, has an aperture of 6'4 inches in diameter. This
instrument has been rendered celebrated by the memorable
labors of Bessel. The well-illuminated and short dyalitic
refractors, which were first executed by Plosl 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 refer-
red, because they exercised so essential an influence on the
extension of cosmical views, the improvements made in in-
struments 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 instruments of measurement, we will here only mention
those of Ramsden, Troughton, Fortin, Reichenbach, Gam-
bey, Ertel, Steinheil, Repsold, Pistor, and Oertling ; in rela-
tion to clironometers and astronomical pendulum clocks, we
may instance Mudge, Arnold, Emery, Earnshaw, Breguet,
.Rirgens^n, Kessels, "Winnerl, and Tiede ; while the noble la-
Ws of \Yilliam and John Herschel, South, Struve, Bessel,
and Dawes, in relation to the distances and periodic motions
of the double stars, specially manifest the simultaneous per-
fection acquired in exact vision and measurement. Struve's
classification of the double stars gives about 100 for the num-
ber whose distance from one another is below 1", and 336
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
Starfield, near Liverpool, have, with the most unbounded
liberality, inspired with a noble enthusiasm for the cause of
science, constructed under their own immediate superintend-
ence two reflectors, which have raised the hopes of astron-
omers to the highest degree. t Lassell's telescope, which has

Lerebours have also constructed object-glasses of more than 13 -3 inches
in diameter, and nearly 25 feet focal length.

* Struve, Stellarum duplicium el multiplicium Mensurce Micrometricee,
p. 2, 41.

t Mr. Airy has recently given a comparative description of the meth-
ods of constructing these two telescopes, including an account of the

66 COSMOS.

an aperture only two feet in diameter, with a focal length
of twenty feet, has already been the means of discovering
one satellite of Neptune, and an eighth of Saturn, besides
which two satellites of Uranus have been again distinguish-
ed. The new colossal telescope of Lord Rosse has an aper-
ture of six feet, and is fifty-three feet in length. It is mount-
ed in the meridian between two walls, distant twelve feet
011 either side from the tube, and from forty-eight to fifty-six
feet in height. Many nebulae, which had been irresolvable
by any previous instruments, have been resolved into stellar
swarms by this noble telescope ; while the forms of other
nebulae have now, for the first time, been recognized in their
true outlines. A marvelous effulgence is poured forth from
the 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
measurement with the telescope. Morin himself says,* "It
was not Tycho's great observations in reference to the posi-
tion of the fixed stars, when, in 1582, twenty-eight years
before the invention 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 Arcturus and other fixed stars
might, 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 importance for the determination of
longitude at sea." No one was able before him to distin-
guish the fixed stars in the presence of the sun. Since the

mixing of the metal, the contrivances adopted for casting and polishing
the specula and mounting the instruments. — Abatr. of the Astr. Soc.,
vol. ix., No. 5, March, 1849. The effect of Lord Rosse's six feet metal-
lic reflector is thus referred to (p. 120): "The astronomer royal, Mr.
Airy, alluded to the impression made by the enormous light of the tel-
escope ; partly by the modifications produced in the appearances of
nebulas already figured, partly by the great number of stars seen even
at a distance from the Milky Way, and partly from the prodigious brill-
iancy of Saturn. The account given by another astronomer of the ap-
pearance of Jupiter was, that it resembled a coach-lamp in the tele-
scope; and this well expresses the blaze of light which is seen in the
instrument." Compare also Sir John Herschel, Oull. of Astr., § 870.
" The sublimity of the spectacle afforded by the magnificent reflecting
telescope constructed by Lord Rosse of some of the larger globular clus-
ters of nebulae, is declared by all who have witnessed it to be such as
no words can express. This telescope has resolved or rendered resolv-
able multitudes of nebula? which had resisted all inferior powers."
* Delambre, Hist, de V Astr on. Moderne, t. ii., p. 255.

TELESCOPES. 67

employment, by Homer, of great meridian telescopes in 1691,
observations of the stars by day have been frequent and fruit-
ful in results, having been, in some cases, advantageously
applied to the measurement of the double star's. Struve
states* that he has determined the smallest distances of ex-
tremely faint stars in the Dorpat refractor, with a power of
only 320, in so bright a crepuscular light that he could read
with ease at midnight. The polar star has a companion of
the ninth magnitude, which is situated at only 18" distance :
it was seen by day in the Dorpat refracting telescope by
Struve and Wrangel,f and was in like manner observed on
one occasion by Encke and Argelander.

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, ex-
erts an obstructing action.^ This question, considered as an

* Strove, Metis. Microm., p. xliv.

t Schumacher's Jahrbuchfur 1839, s. 100.

j La lumiere atmospherique diffuse ne peut s'expliquer par le reflet
des rayons solaires sur la surface de separation des couches de difleren-
tes densites dont on suppose 1'atmosphere composee. En eflet, suppo-
sons le soleil place a 1'horizon, les surfaces de separation dans la direc-
tion du zenith seraient horizontales, par consequent la reflexion serait
horizontale aussi, et nous ne verrions aucune lumiere au zenith. Dana
la supposition des couches, aucun rayon ne nous arriverait par voie
d'une premiere reflexion. Ce ne seraient que les reflexions multiples
qui pourraient agir. Done pour expliquer la lumiere diffuse, il faut se
figurer 1'atmosphere composee de molecules (spheriques, par exemple)
dont chacune uonne une image du soleil a peu pres comme les boulea
de verres que nous plasons dans nos jardius. L'air pur est bleu, par-
ceque d'apres Newton, les molecules de 1'air ont Vepaisseur qui convi-
ent a la reflexion des rayons bleus. II est done naturel que les petites
images du soleil que de tous cotes reflechissent les molecules sphe-
riques de 1'air et qui sont la lumiere diffuse aient une teinte bleue :
mais ce bleu n'est pas du bleu pur, c'est uu blanc dans lequel le bleu
predomine. Lorsque le ciel n'est pas dans toute sa purete et que 1'air
est me!6 de vapeurs visibles, la lumiere diffuse resoit beaucoup de
blanc. Comme la lune est jaune, le bleu de 1'air pendant la nuit est un
peu verdatre, c'est-a-dire, melange de bleu et de jaune."

" We can not explain the diffusion of atmospheric light by the reflec-
tion of solar rays on the surface of separation of the strata of different
density, of which we suppose the atmosphere to be composed. In fact,
if we suppose the sun to be situated on the horizon, the surfaces of sep-
aration in the direction of the zenith will be horizontal, and consequent-
ly the reflection would likewise be horizontal, and we should not be
able to see any light at the zenith. On the supposition 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, there-
fore, to explain the phenomenon of diffused light, we must suppose the
atmosphere to be composed of molecules (of a spherical form, for in

68 COSMOS.

optical 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. 1 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

stance), each of which presents an image of the sun somewhat in the
game manner as an ordinary glass ball. Pure air is blue, because, ac-
cording to Newton, the molecules of the air have the thickness neces
sary 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 color is not, however, pure blue, but white,
in which the blue predominates When the sky is not perfectly pure
and the atmosphere is blended with perceptible vapors, 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.

* D'vn des Effcts dcs Lunettes sur la Visibility des etoiles. (Lctlre de
M. Arago a M. de Humboldt en Die., 1847.)

" L'ceil n'est done que d'une sensibilite circonscrite, bornee. Quand
la lumiere qui frappe la retine, n'a pas assez d'intensite, 1'oeil ne sent
rien. C'est par un manque d'intensite que beaucoup d.' etoiles, mdme
dans les nuits les plus profondes echappent a nos observations. Les lu-
nettes ont pour effet, quant aux etoiles, d'augmenter 1'intensite de 1'image.
Le faisceau cylindrique de rayons paralleles venant d'une etoile, qui
s'appuie sur la surface de la lentille objective, et qui a cette surface cir-
culaire pour base, se trouve considerablement resserre a la sortie de la
lentille oculaire. Le diametre du premier cylindre est au diametre
du second, comme la distance focale de 1'objectif est a la distance fo-
cale de Poculaire, ou bieu comme le diametre de 1'objectif est au dia-
metre de la portion d'oculaire qu'occupe le faisceau emergent. Les iii-
tensites de lumiere dans les deux cylindres en question (dans les deux
cylindres, incident et emergent) doiveut etre entr'elles comme les eten-
dues superficielles des bases. Ainsi la lumiere emergente sera plus con-
densee, plug intense que la lumiere naturelle tombant sur 1'objectif, dans
le rapport de la surface de cet objectif a la surface circulaire de la base
du faisceau emergent. Le faisceau Emergent, quand la lunette grosrit,
etant plus etroit que le faisceau cylindrique qui tombe sur 1'objectif, il
est evident que la pupille, quelle que soit son cMverture, recueillera plus
de rayons par 1'intermediaire de la lunette que sans elle. La lunette
augmentera done toujours 1'intensite de la lumiere des ttoilei.

" Le cas le plus favorable, quant a 1'effet des lunettes, est evidemment
celui ou 1'ceil re9oit la totalite du faisceau emergent, le cas ou ce fais-
ceau a moins de diametre que la pupille. Alors toute la lumiire que
1'objectif embrasse, concourt, par 1'entremise du telescope, a la forma-
tion de 1'image. A 1'ceil nu, au contraire, une portion seule de cetto
meme lumiere est mise a profit ; c'est la petite portion que la surface
de la pupille decoupe dans le faisceau incident naturel. L'intensit^ do
1'image telescopique d'une etoile est done & 1'intensite de 1'image &
1'ceil nu, comme la surface de 1'objectif est a celle de la pupille.

" Ce qui precede est relatif a la visibilite d'uu seul point, d'uno seulo

TELESCOPES. 69

in one of the numerous manuscripts to which I was permit-
ted free access during my frequent sojourn in Paris. Ac-

etoile. Venons a 1'observation d'un objet ayant des dimensions an
gulair«w seusibles, a 1'observation d'une planete. Dans les cas les plus
lavorables, c'est-a-dire lorsque la pupille re^oit la totalite du pinceaa
emergeut, 1'intensite de 1'image de ckaque point de la planete se calcu-
lera par la proportion que nous venons de donner. La quantite totalt
de lumiere concourant a former V ensemble de 1'image a Tceil nu, sera
done aussi a la quantite totale de lumiere qui forme 1'image de la pla-
nete A 1'aide d'uue lunette, comme la surface de la pupille est 4 la sur-
face de 1'obiectif. Les intensites comparatives, non plus de pointe
isoles, mais des deux images d'une planete, qui se forment sur la retina
a 1'oeil nu, et par I'iutermediaire d'une lunette, doivent evidemment
diminuer proportionuellement aux etendues superficielles de ces deux im-
ages. Les dimensions lineaires des deux images sont entr'elles comme
le diametre de 1'objectif est au diametre du faisceau emergent. Le
nouibre de fois que la surface de 1'image amplifiee surpasse la surface
de 1'image a 1'oeil nu, s'obtiendra done en divisant le carre du diametre
de 1'objeclifpa.r le carre du diametre du faisceau Emergent, ou bien la sur-
face de I'objeclif par la surface de la base circulaire du faisceau emergent.
" Nous avons deja obtenu le rapport des quantites totales de lumiere
qui engendrent les deux images d'une planete, en divisant la surface de
1'objectif par la surface de la pupille. Ce nombre est plus petit que le
quotient auquel on arrive en divisant la surface de 1'objectif par la sur-
face du faisceau Emergent. II en resulte, quant aux planetes, qu'une
lunette lait moins gagtier en intensite de lumiere, qu'elle ne fait perdre
en agrandissaut la surface des images sur la retine; 1'intensite de ces
images doit done aller continuellement en s'afiaiblissant a mesure que
le pouvoir amplificatif de la lunette ou du telescope s'accroit.

" L'atmosphere peut etre consideree comme une planete a dimen-
sions indefiuies. La portion qu'on en verra dans une lunette, subira
done aussi la loi d'affaiblissement que nous venons d'indiquer. Le rap*
port entre 1'intensite de la lumiere d'une planete et le champ de lumiere
atinospherique a travers lequel on la verra, sera le memo a 1'ceil nu et
dans les lunettes de tous les grossissements, de toutes les dimensions.
Les lunettes, sous le rapport de Vintensite, ne favorisent done pas la visi-
bilite des planetes.

" II n'eu est point ainsi des etoiles. L'intensite de 1'image d'une etoile
est plus forte avec une lunette qu'a I'o3il nu ; au contraire, le champ de
la vision, uuiformement eclaire dans les deux cas par la lumiere atmos-
pherique, est plus clair a I'osil nu que dan« la lunette. II y a done deux
raisons, sans sortir des considerations d'intensite, pour que dans une lu-

ette de 1'image de 1'etoile predomine sur celle de 1'atmosphere, nota-

lement plus qu'a I'oail nu.

" Cette predominance doit aller graduellement en augmentant avec
le grossissement. En efiet, abstraction faite de certaine augmentation
du diametre de 1'etoile, consequence de divers effets de diffraction ou
d1 'interferences, abstraction faite aussi d'une plus forte reflexion que la
lumiere subit sur les surfaces plus obliques des oculaires de tres courts
foyers, V intensite dc la lumiere de Vetoile est constante tant que 1'ouver-
ture de 1'objectif ne varie pas. Comme ou 1'a vu, la clarte du champ
de la lunette, au contraire, diminue sans cesse a mesure que le pouvoir
amplificatif s'accroit. Done toutes autres circoustances restant egales,
uue etoile sera d'autant p.1'!* visible, sa predouiiuence sur la lumiere tin

70 COSMOS.

cording to the ingenious explanation of my friend, high rnag»
nify ing powers facilitate the discovery and recognition of the

champ du telescope sera d'autaut plus tranchee qu'on lera usage d'un
grossissemont 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 consequence of deficient intensity, many
stars escape our observation, 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 abase, is considerably 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 tho
part of the eye-piece covered by the emerging rays. The intensities
of the light in these two cylinders (the incident and emerging cylin-
ders) must be to one another as the superficies of their bases. Thus,
the emerging light will be more condensed, more intense, than the nat-
ural 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 interven-
tion 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 favorable condition for the use of a telescope is undoubt
edly 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 im
age of a star is, therefore, to the intensity of the image seen with the
naked eye, as the surface of the object-glass is 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 consideration of an o*bject having
sensible angular dimensions, as, for instance, a planet. Under the most
favorable conditions of vision, that is to say, when the pupil receives
the whole of the emerging pencil, the intensity of each point of the plan-
et's image may be calculated by the proportions we have already given.
The total 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 compar-
ative intensities, not of mere isolated points, but of the images of a plan-
et formed respectively on the retina of the naked eye, and by the in-
tervention of a telescope, 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 iui-

TELESCOPES. 71

fixed stars, since they convey a greater quantity of intense
light to the eye without perceptibly enlarging the image ;

age when seen by the naked eye by dividing the square of the diameter
of the object-glass by the square of the diameter of the emerging pencil, or
rather the surface of the abject-glass by the surface of the circular bate
of the emerging pencil.

" By dividing the surface of the object-glass by the surface of the pu
pil, \ve 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 dimen-
sions. 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 at-
mospheric light through which it is seen, will be the same to the naked
eye and in telescopes, whatever may be their dimensions and magnify-
ing powers. Telescopes, therefore, do not favor 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 tel-
escopic vision. There are two reasons, then, which, in connection 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 is 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 contrary, diminishes inces-
santly in the same ratio in which the magnifying power increases. All
other circumstances, therefore, 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 0/1847.

I will further add the following passage from the Annuaire du Bu-
reau des Long, pour 1846 (Notices Scient. par M. Arago), p. 381 :

" L'experience a montre que pour le commun des hommes, deux
espaces eclaires et contigus ne se distingueut pas 1'un de Pautre, a inoius
que leurs intensites comparatives ne presentent, au minimum, une dif
ference de •$$. Quand une lunette est tournee vers le firmament, son
champ semble nniformement eclaire : c'est qu' alors il existe, dans un
plan passant par le foyer et perpendiculaire a 1'axe de 1'objectiC un«
image indefinie de la region atmospherique vers laquelle la lunette est
dirigee. Supposous qu'un astre. c'est-a-dire uu objet situe bieii au-

72 COSMOS.

while, in accordance with another law, they influence the
aerial space on which the fixed star is projected. The tele-
scope, by separating, as it were, the illuminated particles of
air surrounding the object-glass, darkens the field of view,
and diminishes the intensity of its illumination. We are en-
abled to see, however, only by means of the difference be-
tween the light of the fixed star and of the aerial field or the
mass of air which surrounds the star in the telescope. Plan-
etary disks present very different relations from the simple
ray of the image of a fixed star ; since, like the aerial field
(fair aerienne), they 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 disk, is increased by high magnifying powers.
This circumstance may facilitate the recognition of objects
by day, in instruments whose movements are not regulated
paralactically by clock-work, so as to follow the diurnal mo-
tion of the heavens. Different points of the retina are suc-
cessively 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 sea-
son of the year, I have frequently been able to find the pale
disk of Jupiter with one of Dollond's telescopes, of a magni-
fying 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
delA de 1'atmosphere, se trouve dans la direction de la lunette : son
image ne sera visible qu'autant qu'elle augmentera de ^Vi au moins,
1'intensite de la portion de 1'image focale indifinie de 1'atmosphere, sur
laquelle sa propre image limitfe ira se placer. Sans cela le champ
visuel continuera a paraitre partout de la meme intensity."

" Experience has shown that, in ordinary vision, two illuminated and
contiguous spaces can not be distinguished from each other unless their
comparative intensities present a minimum difference of inj-th. When
a telescope is directed toward 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 im-
age of the atmospheric region toward which the instrument is pointed.
If we suppose a star, that is to say, an object very far beyond the atmos-
phere, situated in the direction of the telescope, its image will not be
visible except it exceed, by at least g^-th, the intensity of that portion
of the indefinite focal image of the atmosphere on which its limited
proper image is thrown. Otherwise the visual field will continue to
appear esery where of the same intensity. '

SCINTILLATION OF THE STARS. 73

occultations have occasionally been observed by daylight,
with the aid of powerful telescopes, as in 1792,tby Flau-
gergues, and in 1820, by Struve. Argelander (on the 7th
of December, 1849, at Bonn) distinctly saw three of the sat
ellites of Jupiter, a quarter of an hour after sunrise, with
one of Fraunhofer'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 heliometer. The determination of the limits of
the telescopic visibility of small stars by daylight, in differ-
ent 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. Accord-
ing to Arago's investigations, two points must be specially dis-
tinguished in reference to this phenomenon* — firstly, change

* The earliest explanations given by Arago of scintillation occur in
the appendix to the 4th book of my Voyage avx Regions Equinoxialet,
torn, i., p. 623. I rejoice that I am able to enrich this section on nat-
ural and telescopic vision with the following explanations, which, for
the reasons already assigned, I subjoin in the original text.

Des causes de la scintillation des ttoiles.

lation, c'est le changement de couleur. Ce changement est beaucoup
plus frequent que 1'observation ordinaire 1'indique. En effet, en agi-
tant la lunette, on transforme 1'image dans uue ligne ou un cercle, et
tous les points de cette ligne ou de ce cercle paraissent de couleure dif-
ferentes. C'est la resultante de la superposition de toutes ces images
que 1'on voit, lorsqu'on laisse la lunette immobile. Les rayons qui so
reunissent au foyer d'une lentille, vibrent d'accord ou en disaccord,
s'ajoutent ou se detruisent, suivant que les couches qu'ils ont traver-
sees, ont telle ou telle refringence. L'ensemble des rayons rouges petit
se detruire seul, si ceux de droite et de gauche, et ceux de haut et de
bas, ont traverse des milieux inegalement refringents. Nous avons dit
seul, parceque la difference de refringence qui correspond a la destruc
tion du rayon rouge, n'est pas la meme que cella qui amene la destruc-
tion du rayon vert, et reciproquement. Main tenant, si des rayons rou ges
sont detruits, ce qui reste sera le blanc moins le rouge, c'est-a-dire du
vert. Si le vert au contraire est detruit par interference, 1'image sera
du blanc moins le vert, c'est-a-dire du rouge. Pour expliquer pourquoi
les planetes a grand diametre ne scintillent pas ou tres peu, il faut se
rappeler que le disque peut £tre consider^ comme une aggregation
d'^toiles ou de petits points qui scintillent isol^ment; mais les images
de differentes couleurs que chacun de ces points pris isol^ment don-
nerait, empietant les unes sur les autres, formeraient du blanc. Lors-
qu'on place un diaphragme ju un bouchou perce d'uii trou sur 1'objec-
VOL III.— D

74 COSMOS.

in the intensity of the light, from a sudden decrease to perfect
extinction and rekindling ; secondly, change of color. Both

tif d'une lunette, les etoiles acquiere'nt un disque entoure d'une serie
d'anneaux lumineux. Si 1'on enfonce 1'oculaire, le disque de 1'eioilo
augmente de diamctre, et il se produit dans son centre un trou obscur ;
si on 1'enfonce davantage, un point lumineux se substitue au point noir.
Un nouvel enfoncemeut donne naissance a un centre noir, etc. Pro
nons la lunette lorsque le centre de 1'image est noir, et visons a uno
£toile qui ne sciatillo pas : le centre restera noir, comme il l'6tait au-
paravant. Si au contraire on dirige la lunette & une 4toile qui scintille,
on verra le centre de 1'image lumineux et obscur par intermittence.
Dans la position ou le centre de 1'image est occup6 par un point lumi-
neux, on verra ce point disparaltre et renaitre successivement. Cette
disparition ou reapparition du point central est la preuve directe de
I' interference variable des rayons. Pour bien concevoir 1'absence de
lumiere au centre de ces images dilatees, il faut se rappeler quo les
rayons regulierement refractes par 1'objectif ne se reunisseut et ne peu-
vent par consequent interferer qu'au foyer : par consequent les images
dilatees que ces rayons peuvent produire, resteraient toujours pleines
(sans trou). Si dans une certaine position de 1'oculaire un trou se pre-
sente au centre de 1'image, c'est que les rayons r6gulierement refrac-
ted inierferent avec des rayons diffractes sur les bords du diaphragme
circulaire. Le phenomene n'est pas constant, parceque les rayons qui
interferent dans un certain moment, n'interferent pas un instant apres,
lorsqu'ils ont traverse des couches atmospheriques dont le pouvoir r6-
fringent a varie. On trouve dans cette experience la preuve manifesto
du role que joue dans le ph^nomene de la scintillation 1'inegale refran-
gibilit^ des couches atmospheriques traversees par les rayons dont le
faisceau est tres etroit. II r^sulte de ces considerations que 1'explica-
tion des scintillations ne pent etre rattachee qu'aux phenomenes des
interference* lumineuses. Les rayons des etoiles, apres avoir traverse
nne atmosphere ou il existe des couches in^galement chaudes, inegale-
ment denses, inegalement humides, vont se reiinir au foyer d'une len-
tille, pour y former des images d'intensite et de couleurs perp6tuelle-
ment changeantes, c'est-£-dire des images telles que la scintillation les
presente. II y a aussi scintillation hors du foyer des lunettes. Les ex-
plications proposers par Galileo, Scaliger, Kepler, Descartes, Hooke,
Huygens, Newton et John Michell, que j'ai examin6 dans un tnemoife
presente a 1'Institut en 1840 (Comptes Rcndus, t. x., p. 83), sont inad-
missibles. Thomas Young, auquel nous devons les premieres lois des
interferences, a cru inexplicable le phenomene de la scintillation. La
faussete de 1'ancienne explication" par des vapeurs qui voltigent et d6-
placent, est deja prouvee par la circonstance que nous voyons la scin-
tillation des yeux, ce qui supposerait un deplacement d'une minute.
Les ondulations du bord du soleil sont de 4" a 5", et peut-etre des pie-
ces qui manquent, done encore effet de 1'interference des rayons."

On the causes of the scintillation of the stars.

" The most remarkable feature in the phenomenon of the stars' scin-
tillation is their change of color. 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
nil the points of this line or circle appear of different colors. We havo
here the results of the superposition of all the images seen when the
toleacope is at rest. The rays united in the focus of a leas vibrate in

SCINTILLATION OF THE STARS. 75

these alterations are more intense in reality than they appear
to the naked eye ; for when the several points of the retina

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 ono 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 vice versa. Now, if the red rays be destroyed, that which re-
mains will be white minus red, that is to say, green. If the green, on
the other hand, be destroyed by interference, 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 remem-
bered that the disk may be regarded as an aggregation of stars or of
small points, scintillating independently of each other, while the images
of different colors 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 disk surrounded by a series of luminous rings. On push-
ing in the eye-piece, the disk of the star increases in diameter, and a
dark point appears in its center ; when the eye-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 center will be observed. If, while the center of the image is
black, we point the instrument to a star which does not scintillate, it
will remain bkck as before. If, on the other hand, we point it to a scin-
tillating star, we shall see the center of the image alternately luminous
and dark. In the position in which the center of the image is occu-
pied by a luminous point, we shall see this point alternately vanish and
reappear. This 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 center of these dilated im-
ages, we must remember that rays regularly refracted by the object-
glass do not reunite, and can not, 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 center of the image, it is owing to the inter-
ference 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 atmospheric strata possessing a varying
power of refraction. We here meet with a manifest proof of the im-
portant part played in the phenomenon of scintillation by the unequal
refrangibility of the atmospheric strata traversed by rays united in a
very narrow pencil."

" It follows from these considerations that scintillation mast necessa-
rily be referred to the phenomena of luminous interferences alone The
rays emanating from the stars, after traversing an atmosphere composed
of strata having different degrees of heat, density, and humidity, com-
bine in the focus of a lens, where they form images perpetually chang-
ing in intensity and color, that is to say, the images presented by scin-
tillation. There is another form of scintillation, independent of the fo
cus of the telescope. The explanations of this phenomenon advanced

76 COSMOS.

are once excited, they retain the impression of light which
they have received, so that the disappearance, obscuration
and change of color in a star are not perceived by us to their
full extent. The phenomenon of scintillation is more striking-
ly manifested in the telescope when the instrument is shaken,
for then different points of the retina are successively excited,
and colored and frequently interrupted rings are seen. The
principle of interference explains how the momentary colored
effulgence of a star may be followed by its equally instanta-
neous 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) em-
anating from one source (one center 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 of waves in reference to the other
amounts to an odd number of semi-undulations, both systems
endeavor to impart simultaneously 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, the refrangibility of the different
strata of air intersecting the rays of light exerts a greater in-
fluence on the phenomenon than the difference in length of
their path.*

The intensity of scintillations varies considerably in the dif-
ferent 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 instancfe Vega, flicker less than
Arcturus and Procyon. The absence of scintillation in plan-
ets with larger disks is to be ascribed to compensation and to
the naturalizing mixture of colors proceeding from different
points of the disk. The disk is to be regarded as an aggregate

oy Galileo, Scaliger, Kepler, Descartes, 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 phenomenon. The erroneous-
ness of the ancient explanation, which supposes that vapors ascend and
displace one another, is sufficiently proved by the circumstance that we
see scintillations with the naked eye, which presupposes a displace
ment of a minute. The undulations of the margin of the sun are from
4" to 5", and are perhaps owing to chasms or interruptions, and there-
fore also to the effect of interference of the rays of light." (Extrac/i
from Arago's MSS. of 1847.)

* See Arago, in the Annuaire pour 1831 p. 1C8.

SCINTILLATION CP THE STARS. 77

of stars which naturally compensate for the light destroyed
by interference, and again combine the colored rays into white
light. For this reason, we most rarely meet with traces of
scintillation in Jupiter and Saturn, but more frequently in
Mercury and Venus, for the apparent diameters of the disks
of these last-named planets diminish to 4"*4 and 9"'5. The
diameter of Mars may also decrease to 3"-3 at its conjunc-
tion. In the serene cold winter nights of the temperate zone,
the scintillation increases the magnificent impression produced
by the starry heavens, and the more so from the circumstance
that, seeing stars of the sixth and seventh magnitude flicker-
ing in various directions, we are led to imagine that we per-
ceive 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 vis-
ible to the naked eye ! It was known in ancient times by
the Greek astronomers that the flickering of their light dis-
tinguished the fixed stars from the planets ; but Aristotle, in
accordance with the emanation and tangential theory of vi-
sion, to which he adhered, singularly enough ascribes the scin-
tillation of the fixed stars merely to a straining of the eye.
" The riveted 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 (rrpdf 6e rouf
fj,£VovTa$), 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 starsf 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
to scintillation as the probable criterion of the non-planetary
nature of a celestial body. Although well versed in the sci-
ence of optics, in its then imperfect state, he was unable to
rise above the received notion of moving vapors.J 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 scintil-

* Aristot., De Ccelo, ii., 8, p. 290, Bekker.
t Cosmos, vol. ii., p. 326.

t Causa scintillationis, in Kepler, De Stella nova in pede Serpcntara,
1606, cap. xviii., p. 92-97.

lation of the fixed stars when they have risen 12° or 15°
above the horizon, give the vault of heaven a peculiar char-
acter of mild effulgence and repose. I have already referred
in many of iny delineations of tropical scenery to this charac-
teristic, which was also noticed by the accurate observers 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 scintillation of the
stars ceased in different hygrometric conditions. Cumana
and the rainless portion of the Peruvian coast of the Pacific,
before the season of the garua (mist) had set in, were pecul-
iarly 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 per-
ceived when the same fixed stars are watched in their grad-
ual rising or setting, and the angles of their altitudes meas-
ured or calculated by the known time and latitude of the
place. In some serene and calm nights, the region of scin-
tillation extended to an elevation of 20° or even 25° ; but a
connection could scarcely ever be traced between the differ-
ences of altitude or intensity of the scintillation and the hy-
grometric and thermometric conditions, observable in the low-
er and only accessible region of the atmosphere. I have ob-
served, during successive nights, after considerable scintilla-
tion of stars, having an altitude of 60° or 70°, when Saus-
sure's hair-hygrometer stood at 85°, that the scintillation en-
tirely ceased when the stars were 15° above the horizon, al-
though the moisture of the atmosphere was so considerably
increased that the hygrometer had risen to 93°. The intri-
cate compensatory phenomena of interference of the rays of
light are modified, not by the quantity of aqueous vapor con-
tained in solution in the atmosphere, but by the unequal dis-
tribution of vapors in the superimposed strata, and by the
upper currents of cold and warm air, which are not percept-
ible in the lower regions of the atmosphere. The scintilla-
tion of stars at a great altitude was also strikingly increased
during the thin yellowish red mist which tinges the heavens

* Lettre de M. Garcin, Dr. en Med. a M. de RSavmur, in Hist, de
TAcadtmie Royale des Sciences,' Annie 1743, p. 28-32.

SCINTILLATION OF THE STARS. 79

Bhort\y before an earthquake. These observations only refer
to the serenely bright and rainless seasons of the year with-
in the tropics, from 10° to 12° north and south of the equa-
tor. The phenomena of light exhibited at the commence-
ment of the rainy season, during the sun's zenith-passage,
depend on very general, yet powerful, and almost tempestu-
ous causes. The sudden decrease of the northeast 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 thus daily give rise,
at definite recurring periods, to storms of wind and torrents
of rain. I 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 season is an-
nounced many days beforehand by a flickering light of the
stars at great altitudes above the horizon. This phenome-
non is accompanied by sheet lightning, and single flashes on
the distant horizon, sometimes without any visible cloud, and
at others darting through narrow, vertically ascending col-
umns of clouds. In several of my writings I have endeav-
ored to delineate these precursory characteristics and physi-
ognomical changes in the atmosphere.*

The second book of Lord Bacon's Novum Organum gives
us the earliest views on the velocity of light and the prob-
ability 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

* See Voyage aux Regions Equin., t. i., p. 511 and 512, and t. ii., p.
202-208; also my Views of Nature, p. 16, 138.

En Arabie, de meme qu'a Bender-Abassi, port fameux du Golfe

Persique, 1'air est parfaitement serein presque toute 1'annee. Le prin-
temps, l'et£, et 1'automne se passent, sans qu'on y voie la moindre rosee.
Dans ces raemes temps tout le monde couche dehors sur le haut dea
maisons. Quand on est ainsi couche, il n'est pas possible d'exprimer le
plaisir qu'on prend 4 contempler la beaute du ciel, 1'eclat des etoiles.
C'est une lumiere pure, ferme et eclatante, sans 4tincellement. Ce n'est
qu'au milieu de 1'hiver que la scintillation, quoique tres foible, s'y fait
apercevoir."

" In Arabia," says Garciu, "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 ex-
hibiting 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, dt
PAcad. de* Sc., 1743, p. 30.

80 COSMOS.

question whether those stars yet exist which we now see
shining.* We are astonished to meet with this happy con-
jecture in a work whose intellectual author was far behind
his cotemporaries in mathematical, astronomical, and phys-
ical knowledge. The velocity of reflected solar light was
first measured by Homer (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 discov-
ery 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. f To these astronomical meth-
ods may be added one of terrestrial measurement, lately con-
ducted with much ingenuity and success by M. Fizeau in
the neighborhood of Paris. It reminds us of Galileo's early

* In speaking of the deceptions occasioned by the velocity of sound
and light, Bacon says : " This last instance, and others of a like nature,
have sometimes excited in us a most marvelous doubt, no less than
•whether the image of the sky and stars is percei ved 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
appeared so incredible to us that the images or radiations of heavenly
bodies could suddenly be conveyed through such immense spaces to the
eight, and it seemed that they ought rather to be transmitted in a def-
inite time. That doubt, however, 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 (Novum Organutn), p. 177. He then recalls the cor-
rect view he had previously announced precisely in the manner of the
ancients. Compare Mrs. Somerville's Connection of the Physical Sci-
ences, p. 36, and Cosmos, vol. i., p. 154, 155.

t See Arago's explanation of his method in the Annuaire du Bureau
des Longitudes pour 1842, p. 337-343. " L'observation attentive des
phases d'Algol i six mois d'intervalle servira a determiner directement
la vitesse de la lumiere de cette etoile. Pres du maximum et du mini-
mum le changement d'intensite s'opere lentement ; il est au contraire
rapide a certames epoques interme'diares entre celles qui correspondent
aux deux etats extremes, quand Algol, soil en diminuant, soit en aug-
mentant d'dclat, passe pour la troisieme grandeur."

" The attentive observation of the phases of Algol at a six-months in-
terval 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 be-
tween those corresponding to the two extremes, when Algol, either di
minishing or increasing in Brightness, appears of the third magnitude.

SCINTILLATION OF THE STARS. 81

and fruitless experiments with two alternately obscured lan-
terns.

Horrebow and Du Hamel estimated the time occupied in
the passage of light from the sun to the earth at its mean dis-
tance, according to Romer's first observations of Jupiter's satel-
lites, at 14' 7", then 11' ; Cassini at 14' 10" ; while Newton*

* Newton, Optics, 2d ed. (London, 1718), p. 325. " Light moves
from the sun to us in seven or eight minutes of time." Newton com-
pares 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 occurred 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 ve-
locity of light equal to 155,555| 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 calculations in the Jahrbuch fur 1852, an equatorial degree is
equal to 69-1637 English miles. According to Newton's data, we should
therefore have a velocity of 134,944 geographical miles. Newton, how-
ever, 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)
188,928 geographical, or 217,783 ordinary miles, in a second of time ;
therefore too much, as before we had too h'ttle. It is certainly very re-
markable, although the circumstance has been overlooked by Delambre
(Hist, de V Astronomic Moderne, torn, ii., p. 653), that Newton (proba-
bly basing his calculations upon more recent English observations of
the first satellite) should have approximated within 47" to the true re-
sult (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 Earner's discovery in 1675 to the be-
ginning of the eighteenth century. The first treatise in which RSmer,
the pupil of Picard, communicated 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 interval of space double that of the sun's
distance from the earth." (Memoirs de VAcad. de 1666-1699, torn, 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 (Regies Scientiarum Academics Historia, 1698, p.
143), gave from 10 to 11 minutes, seventeen years after RSmer had left
Pans, although he refers to him ; yet we know, through Peter Horre-
bow (Basis Astronomic sive Trvluum Roemerianum, 1735, p. 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 satel-
lite, and 14' 12" for the second, having taken 14' 10" for the basis of
his tables for Jupiter pro pcragrando diametri semissi. The error waa
therefore on the increase. (Compare Horrebow, Triduum, p. 129 ; Gas-
sini, Hypotheses et Satellites de Jupiter iu the M6m de VAcad., 166G-

D 2

82 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 excep-
tion of those of the first satellite, found 8' 13"-2. Encke
has very justly noticed the great importance of undertaking
a special course of observations on the occultations of Jupi-
ter's satellites, in order to arrive at a correct idea regarding
the velocity of light, now that the perfection attained in the
construction of telescopes warrants us in hoping that we may
obtain trustworthy results.

Dr. Busch,t of Konigsberg, who based his calculations on
Bradley's observations of aberration, as rediscovered by Bi-
gaud of Oxford, estimated the passage of light from the sun
to the earth at 8' 12"- 14, the velocity of stellar light at
167,976 miles in a second, and the constant of aberration
at 20"-2116 ; but it would appear, from the more recent ob-
servations on aberration carried on during eighteen months
by Struve with the great transit instrument at Pulkowa,t
that the former of these numbers should be considerably in-

1699, torn, viii., p. 435, 475; Delambre, Hist, de VAstr. Mod., toin. ii.,
p. 751, 782 ; Du Hamel, Physica, p. 435.)

* Delambre, Hist, de VAstr. Mod., torn, ii., p. 653.

t Reduction of Bradley's Observations at Kew and Wangled, 1836, p.
22; Schumacher's Astr. Nachr., bd. xiii., 1836, No. 309 (compare Mis-
cellaneous Works and Correspondence of the Rev. James Bradley, by
Prof. Rigaud, Oxford, 1832). On the mode adopted for explaining ab-
erration in accordance with the theory of undulatory light, see Doppler,
in iheAbhl. derKon. bohmischen 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. Moderns, torn, ii., p.
616.) Picard had nearly ascertained the velocity of direct light before
his pupil, R6mer, made known that of reflected light.

\ Schum., Astr. Nachr , bd. xxi., 1844, No. 484 ; Struve, Eludes d'Astr.
Stellaire, p. 103, 107 (compare Cosmos, vol. i., p. 153, 154). The re-
suit given in the Annuaire pour 1842, p 87, for the velocity of light
in a second, is 308,000 kilomenes, or 77,000 leagues (each of 4000
metres), which corresponds to 215,834 miles, and approximates most
nearly to Struve's recent result, while that obtained at the Pulkowa
Observatory is 189,746 miles. On the difference in the aberration of
the light 01 the polar star and that of its companion, and on the doubts
recently expressed by Struve, see Madler, Astronomic, 1849, s. 393.
William Richardson gives as the result of the passage of light from the
Bun to the earth 8' 19"-28, from which we obtain a velocity of 215,392
milei in a second. (Mem. of the Astren. Soc., vol. iv., Part i.. p. 68.)

SCINTILLATION OF THE STARS. 83

creased. 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 Astronomisches Jahrbuch fur 1852,
we obtain 166,196 geographical 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 7TTrth from Delambre's (8' 13"'2),
which has been adopted by Bessel in the Tab. Regiom., and
has hitherto been followed in the Berlin Astronomical Al-
manac. The discussion on this subject can not, 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 compan-
ion in the ratio of 133 to 134.

M. Fizeau, a physicist, distinguished alike for his great
acquirements and for the delicacy of his experiments, has
submitted the velocity of light to a terrestrial measurement,
by means of an ingeniously constructed apparatus, in which
artificial light (resembling stellar light) generated from oxy-
gen and hydrogen is made to pass back, by means of a mir-
ror between Suresne and La Butte Montmartre, over a dis-
tance of 28,321 feet, to the same point from which it ema-
nated. A disk having 720 teeth, which made 12-6 rotations
in a second, alternately obscured the ray of light and allowed
it to be seen between the teeth on the margin. It was sup-
posed from the marking of a counter (compteur) that the
artificial light traversed 56,642 feet, or the distance to and
from the stations in T^7?th part of a second, whence we ob-
tain a velocity of 191,460 miles in a second.* This result,
therefore, approximates most closely to Delambre's (which
was 189,173 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 se-

* Fizean gives his result in leagues, reckoning 25 (and consequently
4452 metres) to the equatorial degree. He estimates the velocity of
light at 70,000 such leagues, or about 210,000 miles in the second. On
the earlier experiments of Fizeau, see Comptes Rendvt, torn, xxix., p. 92.
In Moigno, Rupert. tfOptique Moderne, Part iii., p. 1162, we find this
velocity given at 70,843 leagues (of 25=1°), or about 212,529 miles,
which approximates most nearly to the result of Bradley, as given by
Busch.

84 COSMOS.

quel — led Arago to the result that, according to the undu-
latory theory, rays of light of different color, which conse
quently have transverse vibrations of very different length
and velocity, move through space with the same rapidity.
The velocity of transmission and refraction differ, therefore,
in the interior of the different bodies through which the col-
ored rays pass ;* for Arago's observations have shown that

* " D'apres la theorie mathematique dans le systeme des ondes, les
rayons de differentes couleurs, les rayons dont les ondulations sont ine-
gales, doivent neanmoins se propager dans I'ether avec la meme vi-
tesse. H n'y a pas de difference a cet egard entre la propagation des
ondes sonores, lesquelles se propagent dans 1'air avec la memo rapidite.
Cette 6galit6 de propagation des ondes sonores est bien etablio experi-
mentalement par la similitude d'effet que produit une musique donnee
& toutes distances du lieu ou 1'on 1'execute. La principale difficulte,
je dirai 1'unique difficulte, qu'on cut elev6e contre le systeme des ondes,
consistait done a expliquer, comment la vitesse de propagation des ray-
ons de differentes couleurs dans les corps differents pouvait etre dissem-
blable et servir a rendre compte de 1'inegalite de refraction de ces ray-
ons ou de la dispersion. On a montre r6cemment que cette difBculte
n'est pas insurmontable ; qu'on peut constituer I'ether dans les corps
inegalement denses de maniere que des rayons a ondulations dissem-
blables s'y propagent avec des vitesses inegales : reste a determiner, si
les conceptions des geometres a cet egard sont conformes a la nature
des choses. Voici les amplitudes des ondulations deduites experimen-
talement d'une serie de fails relatif aux interferences :

mm.

Violet 0-000423

Jaune 0-000551

Rouge 0-000620

La vitesse de transmission des rayons de diffe>entes couleurs dans le»
espaces celestes est la meme dans le systeme des ondes et tout-a-fait
Ind^pendante de 1'etendue ou de la vitesse des ondulations."

" According to the mathematical theory of a system of waves, rayi
of different colors, having unequal undulations, must nevertheless be
transmitted through ether with the same velocity. There is no differ-
ence hi 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 demon
strated experimentally by the uniformity of effect produced by music
at all distances from the source whence it emanates. The principal, I
may say the only objection, advanced against the undulatory theory,
consisted in the difficulty of explaining how the velocity of the propa-
gation of rays of different colors through different bodies could be dis
similar, while it accounted for the inequality of thd "^fraction of the
rays or of their dispersion. It has been recently shown* that this diffi
culty is not insurmountable, and that the ether may be supposed to bo
transmitted through bodies of unequal density in such a manner that
rays of dissimilar systems of waves 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 act-
ual nature of things. The following are the lengths of the undulations

VELOCITY OF LIGHT. 85

refraction in the prism is not altered by the relation of the
velocity of light to that of the earth's motion. All the meas-
urements coincide in the result, that the light of those stars
toward which the earth is moving presents the same index
of refraction as the light of those from which it is receding.
Using the language of the emission hypothesis, this celebra-
ted observer remarks, that bodies send forth rays of all ve-
locities, but that among these different velocities one only
is capable of exciting the sensation of light.*

as experimentally deduced from a series of facts in relation to inter-
ference :

mm.

Violet 0-000423

Yellow 0-000551

Red 0-000620

The velocity of the transmission of rajs of different colors through ce-
lestial 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, p. 333-336. The length of the
luminous wave of the ether, and the velocity of the vibrations, determ-
ine the character of the colored 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 vibra-
tions in the second.

* " J'ai prouve, il y a bien des annees, par des observations directes
que les rayons des Stoiles vers lesquelles la Terre marche, et les ray-
ons des etoiles dont la terre s'eloigne, se refractent exactement de la
meme quantite. Un tel resultat ne pent se concilier avec la tkforie de
remission qu'a 1'aide d'une addition importante a faire a cette theorie :
il faut admettre que les corps lumineux emettent des rayons de toutes
les vitesses, et que les seuls rayons d'une vitesse determined sont visi-
bles, qu'eux seuls produisent dans Tcei! la sensation de lumiere. Dans
la theorie de 1'emission, le rouge, le jaune, le vert, le bleu, le violet so-
laires sont respectivement accompagnes de rayons pareils, mais obscurs
par defaut ou par exces de vitesse. A plus de vitesse correspond une
moindre refraction, comtne moins de vitesse entraine une refraction plus
grande. Ainsi chaque rayon rouge visible est accompagne de rayons
obscurs de la meme nature, qui se refractent les uns plus, les autres
moins que lui : ainsi il existe des rayons dans les stries noiret de la por-
tion rouge du spectre ; la meme chose doit etre admise des stries situ
ees dans les portions jaunes, vertes, bleues et violettes."

" I showed many years ago, by direct observations, that the rays of
those stars toward which the earth moves, and the rays of those stars
from which it recedes, are repeated in exactly the same degree. Such
a result can not be reconciled with the theory of emistion, unless we
make the important admission that luminous bodies emit rays of all ve-
locities, 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 so-
lar rays are respectively accompanied by like rays, which are, how-
ever, dark from deficiency or excess of velocity. Excessive velocity is

86 COSMOS.

On comparing the velocities of solar, stellar, and terres-
trial light, which are all equally refracted in the prism,
with the velocity of th& light of frictional electricity, we are
disposed, in accordance with Wheatstone's ingeniously con-
ducted 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
light traverses 288,000 miles in a second.* If we reckon
189,938 miles for stellar light, according to Struve's observ-
ations on aberration, we obtain the difference of 95,776 miles
as the greater velocity of electricity in one second.

These results are apparently opposed to the views ad-
vanced by Sir William Herschel, according to which solar
and stellar light are regarded as the effects of an electro-
magnetic process — a perpetual northern light. I say ap-
parently, for no 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 propaga
tion. To this conjecture may be added the uncertainty of
the numerical result yielded by the experiments of Wheat-
stone, who has himself admitted that they are not sufficient-
ly established, but need further confirmation before they can

associated with a slight degree of refraction, while a smaller amount of
velocity involves a slighter degree of refraction. Thus every visible
red ray is accompanied by dark rays of the same nature, of which some
are more, and others less, refracted than the former ; there are conse-
quently rays in the black lines of the red portion of the spectrum ; and
the same must be admitted in reference to the lines situated in the yel
low, green, blue, and violet portions." — Arago, in the Comptes Rendus
de VAcad. des Sciences, t. xvi., 1843, p. 404. Compare also t. viii., 1839,
p. 326, and Poisson, Traite de Mccanique, ed. ii., 1833, t. i., $ 168. Ac-
cording to the undulatory theory, the stars emit waves of extremely
various transverse velocities of oscillations.

* Wheatstone, in the Philos. Transact, of the Royal Soc.for 1834, p.
589, 591. From the experiments described in this paper, it would ap
pear that the human eve is capable of perceiving phenomena of light,
whose duration is limited to the millionth part of a second (p. 591).
On the hypothesis referred to in the text, of the supposed analogy be-
tween the light of the sun and polar light, see Sir John Herschel's Re-
mit* of Aitron. 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 in-
genious application of Breguet's improved Wheatstone's rotatory ap-
paratus for determining between the theories of emission and undula-
tion, 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 Ren-
dus pour 1850, t. xxx., p. 489-495, 556.)

VELOCITY OF ELECTRICITY. 87

be satisfactorily compared with the results deduced from ob-
servations on aberration and on the satellites.

The attention of physicists has been powerfully attracted
to the experiments on the velocity of the transmission of
electricity, recently conducted in the United States by Walk-
er during the course of his electro-telegraphic determina-
tions of the terrestrial longitudes of Washington, Philadel-
phia, 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 tele-
graphic line, that this clock marked its own course by points
on the endless paper fillets of the apparatus. The electric
telegraph instantaneously conveys each of these clock times
to the other stations, indicating to these the Philadelphia
time by a succession of similar points on the advancing pa-
per fillets. In this manner, arbitrary signs, or the instant
of a star's transit, may be similarly noted down at the sta-
tion by a mere movement of the observer's finger on the stop.
"The special advantage of the American method consists,"
as Steinheil observes, " in its rendering the determination 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
constant difference between the compared clock times at
Philadelphia 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 18,700 miles,*
which is fifteen times less than that of the electric current
in Wheatstone's rotatory disks. As in Walker's remarkable
experiments two zvires were not used, but half of the con-

* Steinheil, in Schumacher's Astr. Naekr., No. 679 (1849), s. 97-100;
Walker, in the Proceedings of the American Philosophical Society, vol.
v., p. 128. (Compare earlier propositions of Pouillet in the Comptes
Rendus, t. xix., p. 1386.) The more recent ingenious experiments of
Mitchel, Director of the Observatory at Cincinnati (Gould's Astron.
Journal, Dec., 1849, p. 3, On the Velocity of the Electric Wave'), and the
investigations of Fizeau and Gounelle at Paris, in April, 1850, differ
both from Wheatstone's and Walker's results. The experiments re-
corded in the Comptes Rendut, t. xxx., p. 439, exhibit striking differ
ences between iron and copper as conducting media.

88 COSMOS.

duction, 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 experi-
ments lately made by Eiessf 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 to conduction, of accumulation, and disruption
in a current, since what was formerly regarded as interme-
diate conduction in the earth is now conjectured to belong
exclusively to an equalization or restoration of the electric
tension.

Although it appears probable, from the extent of accura-
cy 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 fre-
quently been mooted whether it be not possible that there
are luminous cosmical bodies whose light does not reach us,
in consequence 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 imaginative speculations.^ I here only refer

* See PoggendorflPs Annalen, bd. Ixxiii., 1848, s. 337, and Pouillet,
Comptes Rendus, t. xxx., p. 501.

t Riess, in PoggendorfTs Ann., bd. 78, s. 433. On the non-conduc
tion of the intermediate earth, see the important experiments of Guille-
miu, Sur le courant dans une pile isolte ct sans communication entre let
pdles in the Comptes Rendus, t. xxix., p. 521. " Quand on remplace
un fil par la terre, dans les telegraphes electriques, la terre sort plut6t
de reservoir commun, quo de moyen d'union entre les deux extremi-
tes du fil." " When the earth is substituted for half the circuit in the
electric telegraph, it serves rather as a common reservoir than as a
means of connection between the two extremities of the wire."

t Madler, Astr., a. 380; also Laplace, according to Moigno, Repertoire
d'Optique Moderne, 1847, t. i., p. 72 : " Selon la theorie de l'6mission
on croit pouvoir demontrer que si le diametre d'une 6toile fixe serait 250
fois plus grand que celui du soleil, sa densite restant la meme, 1'attrac-
tion exercee a sa surface detruirait la quantite de mouvement, de la
moldcule lumineuse Praise, de sorte qu'elle serait invisible a de gramles
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

STELLAR LIGHT. 89

to such views because it will be necessary in the sequel that
we should consider certain peculiarities ef 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 scien-
tific 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 ob-
ject of scientific observation and inquiry. The description
of the starry firmament did not only embrace determinations
of places, the relative distances of luminous cosmical bodies
from one another and from the circles depending on the ap-
parent course of the sun and on the diurnal movement of
the vault of heaven, but it also considered the relative in-
tensity of the light of the stars. The earliest attention of
mankind was undoubtedly directed to this latter point, in-
dividual stars having received names before they were ar-
ranged Avith others into groups and constellations. Among
the wild tribes inhabiting the densely- wooded regions of the
Upper Orinoco and the Atabapo, where, from the impene-
trable 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 a in the Southern Cross. If the catalogue of the con-
stellations known as the Catasterisjns of Eratosthenes can
lay claim to the great antiquity so long ascribed to it (between
Autolycus of Pitane and Timocharis, and therefore nearly a

would destroy the amount of motion emitted from the luminous mole-
cule, so that it would be invisible 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. 148.) From the above con-
siderations 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 expe-
riences sur 1'egale deviation prismatique des etoiles, vers lesquelles la
terre marche ou dont elle s'eloigne, rend compte de I'6galit6 de vitesse
apparente de toutes les etoiles." "Experiments made on the equal
prismatic deviation of the stars toward which the earth is moving, and
from which it is receding, explain the apparent equality of velocity in
the ray« of all the stars."

90 COSMOS.

century and a half before the time of Hipparchus), we pos-
sess 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 enumeration of the
stars belonging to each constellation, as given in the Catas-
terisms, frequent reference is made to the number of the
largest and most luminous, or of the dark and less easily rec-
ognized stars ;* but we find no relative comparison of the
stars contained in the different constellations. The Catas-
terisms 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), if not from the poem 'Epju^f of the older
Eratosthenes. The catalogue of Hipparchus, which we pos-
sess in the form given to it in the Almagest, contains the ear-
liest and most important determination of classes of magni-
tude (gradations of brightness) of 1022 stars, and therefore
of about one fifth of all the stars in the firmament visible to
the naked eye, and ranging from the first to the sixth mag-
nitude 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 hem-
isphere, upward of 20), takes its origin from the classifica-
tion of the Almagest, as given at the close of the table of
stars in the eighth book. Ptolemy, referring to natural vi-
sion, called all stars dark which were fainter than those of
his sixth class ; and of this class he singularly enough only
instances 49 stars distributed almost equally over both hem-
ispheres. 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

* Eratosthenes, Catasterismi, ed. Schaubach, 1795, and Eratotthenica,
ed. G. Bernhardy, 1822, p. 110-116. A distinction is made between
stars hafinpovc (jieyuTiOvf) and afjtavpovf (cap. 2, 11, 41). Ptolemy also
limits ol {ipopfyuToi to those stars which do not regularly belong to a con-
stellation.

MAGNITUDES OF STARS. 91

640 stars of .the sixth magnitude. The nebulous stars (ve-
deXoeLdds') of Ptolemy and of the Pseudo-Eratosthenian Ca-
iasterisms are mostly small stellar swarms,* appearing like
nebulae 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 Nuntius sidereus that stellce nebulosts are nothing
more than stellar masses scattered in shining groups through
the ether (areolce, sparsim per cethera fulgent).^ The ex-
pression (r&v fj,eydA.d)v raft^), the order of magnitudes, al-
though referring only to luster, led, as early as the ninth cen-
tury, to hypotheses on the diameters of stars of different bright-
ness ;J as if the intensity of light did not depend on the dis-
tance, volume, and mass, as also on the peculiar character
of the surface of a cosmical body in more or less favoring the
process of light.

At the period of the Mongolian supremacy, when, in the
fifteenth century, astronomy nourished at Samarcand, under
Timur Ulugh Beg, photometric determinations were facili-
tated by the subdivision of each of the six classes of Hippar-
chus and Ptolemy into three subordinate groups ; distinctions,
for example, being drawn between the small, intermediate,
and large stars of the second magnitude — an attempt which
reminds us of the decimal gradations of Struve and Argelan-
der.§ This advance in photometry, by a more exact determ-
ination of degrees of intensity, is ascribed in Ulugh Beg's
tables to Abdurrahman Sufi, who wrote a work " on the
knowledge of the fixed stars," and was the first who men-
tions 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 increase and decrease of light in the newly-

* Plot. Almas., ed Halma, torn, ii., p. 40, and in Eratosth. Catast.,
cap. 22, p. 18: rj de KtQa/.Tj Kai ij apnr) uvaifTOf dparai, 6ia de ve0e?.u<5ot»f
avarpo<j>jjc do/ccl TLGIV opuadai. Thus, too, Geminus, Pheen. (ed. Hilder,
1590), p. 46. t Cosmos, vol. ii., p. 330, 331.

t Muhamedis Alfragani Chronologica et Ast. Elementa, 1590, cap.
xxiv., p. 118.

$ Some MSS. of the Almagest refer to such subdivisions or interme-
diate classes, as they add the words pei&v or ehdaauv to the determ-
ination of magnitudes. (Cod. Paris, No. 2389.) Tycho expressed thia
increase or diminution by points.

92 COSMOS.

appeared stars in Cygnus and Ophiuchus (tie former of which
continued luminous for twenty-one years), with the bright-
ness of other stars, called attention to photometric determina-
tions. The so-called dark stars of Ptolemy, which were he-
low the sixth magnitude, received numerical designations
according to the relative intensity of their light. " Magni-
tudes, from the eighth down to the sixteenth," 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 twelfth or thirteenth stars
which Sir John Herschel designates as belonging to the
eighteenth or twentieth 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, K-umford, and Wollaston, to Stein-
heil and Sir John Herschel. It will be sufficient for the ob-
ject 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-glass-
es of different thickness and color ; artificial stars formed by
reflection on glass spheres ; the juxtaposition 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 telescope has been so adjusted that the star directly ob-
served gives two images of like intensity ;t an apparatus hav»

* Sir John Herschel, Outlines of Astr., p. 520-27.

t This is the application of reflecting sextants to the determination
of the intensity of stellar light ; of this instrument I made greater use
when in the tropics than of the diaphragms recommended to me by
Borda. I began my investigation under the clear skies of Cumana, and
continued them subsequently till 1803, but under less favorable condi-
tions, on the elevated plateaux of the Andes, and on the coasts of the
Pacific, near Guayaquil. I had formed an arbitrary 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 can not, on accoupt of tho

PHOTOMETRIC METHODS. 93

ing (iii front of the object-glass) a mirror and diaphragms,
whose rotation is measured on a ring ; telescopes with di-
vided object-glasses, on either half of which the stellar light
is received through a prism ; astrometers* in which a prism
reflects the 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 zealous-
ly 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 must still be regarded as a " de-
above-mentioned mode of classification, be compared directly with
those which Sir John Herschel made public as early as 1838. (See my
Recneil d'Observ. Astr., vol. i., p. Ixxi., and Rclat. Hist, du Voyage aux
Regions Equin., t. i., p. 518 and 624; also Lettre de M. de Humboldt a
M. Schumacher en Fevr., 1839, in the Astr. Nachr., No. 374.) In this
letter I wrote as follows : " M. Arago, qui possede des moyens photo-
metriques entierement difierents de ceux qui ont ete publics jusqu'ici,
m'avait rassure sur la partie des erreurs qui pouvaient provenir du change-
ment d'inclinaison d'un miroir entame sur la face interieure. H blame
d'ailleurs le principe de ma methode et le regarde comme peu suscep-
tible de perfectionnement, non seulement a cause de la difference des
angles entre 1'etoile vue directement et celle qui est amenee par reflex-
ion, mais surtout parceque le resultat de la mesure d'intensite dfepend
de la partie de 1'ceil qui se trouve en face de 1'oculaire. II y a erreur
lorsque la pupille n'est pas tres exactement a la hauteur de la limite in-
ferieure de la portion non eutamee du petit miroir." " M. Arago, who
possesses photometric data differing entirely from those hitherto pub-
lished, 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 lit-
tle susceptible of correctness, not only on account of the difference of
angles between the star seen directly and by reflection, but especially
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 observ-
ations when the pupil is not exactly adjusted to the elevation of the
lower limit of the unplated part of the small mirror."

* Compare Steinheil, Elemente der Helligkeils-Messungen am Sternen-
himmel Munchen, 1836 (Schum., Astr. Nachr., No. 609), and John Her-
schel, Results of Astronomical Observations made during the Years 1834
-1838 at the Cape of Good Hope (Lond., 1847), p. 353-357. Seidel at-
tempted 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 degree of latitude in our northern latitudes. Assuming
Vega to be =1, he finds for Sirius 5-13 ; for Rigel, whose luster appears
to be on the increase, 1-30; for Arcturus, 0-84; for Capella, 0-83; for
Procyon, 071; for Spica, 0-49; for Atair, 0-40; for Aldebaran, 0-36;
for Deneb, 0-35; for Regulns, 0-34; for Pollux, 0-30; he does not give
the intensity of the light of Betelgeux, on account of its being a varia-
ble star, as was particularly manifested between 1836 and 1839. (Ont
tiite*, p. 523 )

94 COSMOS.

eideratum in astronomy," and that " photometry is yec /*. *«
infancy." The increasing interest taken in variable swrs,
and the recent celestial phenomenon of the extraordinary in-
crease of light exhibited in the year 1837 in a star of the con-
stellation 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 luster, without numerical estimates
of the intensity of light (an arrangement adopted by Sir John
Herschel in his Manual of Scientific Inquiry 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 improved by
an ingenious elaboration of the materials! probably deserves
the preference over any other approximative method practi-
cable in the present imperfect condition of photometrical in-
struments, however much the exactness of the estimates must
be endangered by the varying powers of individual observers
— 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 color of the light. Very brilliant stars of the first
magnitude, such as Sirius and Canopus, a Centauri and Acher-
nar, Deneb and Vega, on account of their white light, admit
far less readily of comparison by the naked eye than fainter
stars below the sixth and seventh magnitudes. Such a com-
parison 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 Betelgeux.J

* Compare, for the numerical data of the photometric results, four
tables of Sir John Herschel's Astr. Obs. at the Cape, a), p. 341 ; b), p.
367-371 ; c), p. 440 ; and d), in his Outlines of Astr., p. 522-525, 645-
646. For a mere arrangement without numbers, see the Manual of
Scientific Inquiry prepared for the Use of the Navy, 1819, p. 12. In
order to improve the old conventional mode of classing the stars accord-
ing 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 northern and southern stars.

t Argelander, Durchmusterung des nordl. Himmels zwischen 45° und
80° Decl. 1846, s. xxiv.-xxvi. ; Sir John Herschel, Astr. Obscrv. al the
Cape of Good Hope, p. 327, 340, 365.

t Op. cit., p. 304, aud Outl., p. 522.

PHOTOMETRY. 95

Sir John Herschcl has endeavored to determine the rela-
tion between the intensity of solar light and that of a star of
the first magnitude by a photometric comparison of the moor,
with the double star a 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 ex-
pressed by John Michell* as early as 1767. Sir John Her-
schel found from the mean of eleven measurements conduct-
ed with a prismatic apparatus, that the full moon was 27,408
times brighter than a Centauri. According to Wollaston, the
light of the sun is 801,072 times brighter than the full moon ;f
whence it follows that the light transmitted to us from the
sun is to the light which we receive from a Centauri as
22,000 millions to 1. It seems, therefore, very probable,
when, in accordance with its parallax, we take into account
the distance of the star, that its (absolute) proper luminosity
exceeds that of our sun by 2f- times. Wollaston found the
brightness of Sirius 20,000 million times fainter than that of
the sun. From what we at present believe to be the paral-
lax of Sirius (0-"230), its actual (absolute) intensity of light
exceeds that of the sun 63 times4 Our sun therefore be-
longs, in reference to the intensity of its process of light, to
the fainter fixed stars. Sir John Herschel estimates the in-
tensity of the light of Sirius to be equal to the light of nearly

* Philos. Transact., vol. Ivii., for the year 1767, p. 234.

t Wollaston, in the Philos. Transact, for 1829, p. 27. Herschel'a
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 employed. The earlier data of the intensity of the sun'a
light, compared with that of the moon, differ widely from the results
here given. They were deduced by Michelo and Euler, from theoret-
ical grounds, at 450,000 and 374,000, and by Bouguer, from measure-
ments of the shadows of the light of wax tapers, at only 300,000. Lam-
bert assumes Venus, in her greatest intensity of light, to be 3000 times
fainter than the full moon. According to Steinheil, the sun must be
3,286,500 times further removed from the earth than it is, in order to
appear like Arcturus to the inhabitants of our planet (Struve, Stellarum
Compositarnm Mcnsuree Micrometricee, p. clxiii.); and, according to
Sir John Herschel, the light of Arcturus exhibits only half the intensity
of 3anopus. — Herschel, Observ. at the Cape, p. 34. All these conditions
of intensity, more especially the important comparison of tho bright
ness of the sun, the full moon, and of the ash-colored light of our satel-
lite, which varies so greatly according to the different positions of the
earth considered as a reflecting body, deserve further and serious in-
vestigation.

\ Quit. <>f Astr., p. 553 ; Aslr. Observ. at the Cape, p. 363.

96 COSMOS.

two hundred stars of the sixth 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 unde-
termined periods, it is obvious, considering the dependence
of all organic life on the sun's temperature and on the intens-
ity of its light, that the perfection of photometry 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 determ-
inations of the photometric condition of the firmament. By
these means we shall be enabled to explain numerous geog-
nostic phenomena relating to the thermal history of our at-
mosphere, and to the earlier distribution of plants and ani-
mals. Such considerations did not escape the inquiring mind
of William Herschel, who, more than half a century ago, be-
fore the close connection between electricity and magnetism
had been discovered, compared the ever-luminous cloud-en-
velopes of the sun's body with the polar light of our own ter-
restrial planet.*

Arago has ascertained that the most certain method for
the direct measurement of the intensity of light consists in
observing the complementary condition of the colored rings
seen by transmission and reflection. I subjoin in a note,t in

* 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. Gomparo
also Sir John Herschel, Obsero. at the Cape, p. 350-352.

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

(a.) Mesurcs Photom6triqucs.

" II n'existe pas de photometre proprement dit, c'est-a-dire d'instru-
ment donuant 1'intensite d'une lumiere isol^e ; le photometre de Les-
lie, a 1'aide duquel il avail eu 1'audace de vouloir comparer la lumiere
de la lune a la lumiere du soleil, par des actions calonfiques, est com-
pletement defectueux. .T'ai prouve, en effet, que ce preteudu photo-
metre monte quand on 1'expose a la lumiere du soleil, qu'il descend
sous 1'action de la lumiere du feu ordinaire, et qu'il reste complete-
ment stationnaire lorsqu'il re9oit la lumiere d'une lampe d'Argand'.
Tout ce qu'on a pu faire jusqu'ici, c'est de comparer entr'elles deux lu-
mieres en presence, et cette comparaison n'est meme a 1'abri de toute
objection que lorsqu'on ramene ces deux lumieres a I'egalit^ par un
amublissement graduel de la lumiere la plus forte. C'est comme crite-
rium de cette egalit6 que j'ai employ^ les anneaux colores. Si on place
I'une sur 1'autre deux lentilles d'un long foyer, il se forme autour de
leur point de contact des anneaux colored tant par voie de reflexion que
par voi 5 de transmission. Les anueaux reflechia sout conipleineutaires

PHOTOMETRY. 97

his own words, the results of my friend's photometric method,
to which he has added an account of the optical principle
oa which his cyanometer is based.

en couleur des anneaux transmis; ces deux series d'anneaux se neu-
tralisent mutuellement qoand les deux lumieres qui les Ibrment et qui
arrivent simultanement sur les deux lentilles, sont egales entr'elles.

" Dans le cas contraire on voit des traces ou d'anneaux reflechis ou
d'anneaux transrais, suivant quo la lumiere qui forme les premiers, est
plus forte ou plus foible que la lumiere a laquelle on doit les seconds.
C'est dans ce sens settlement que les anneaux colores jouent un role
dans les mesures de la lumiere auxquelles je me suis livre."

(6.) Cyanometre.

" Mon cyanometre est une extension de mon polariscope. Ce der-
nier instrument, comma tu sais, se compose d'un tube ferme £ 1'une de
ses extremites par une plaque de cristal de roche perpendiculaire a
I'axe, de 5 millimetres d'epaisseur ; et d'un prisme doue de la double
refraction, place du cote de 1'oeil. Parmi les couleurs variees que
donne cet appareil, lorsque de la lumiere polarisee le traverse, et qu'on
fait tourner le prisme sur lui-meme, se trouve par un heureux basard la
nuance du bleu de ciel. Cette couleur bleue fort afiaiblie, c'est-4-dire
tres melangee de blanc lorsque la lumiere est presque neutre, aug-
mente d'intensite — progressivement, a mesure que les rayons qui pene-
trent dans 1'instrumeut, renferment une plus grande proportion de ray-
ons polarises.

" Supposons done que le polariscope soit dirige sur une feuille de pa-
pier blanc ; qu'entre cette feuille et la lame de cristal de roche il ex-
iste une pile de plaques de verre susceptible de changer d'inclinaison,
co qui rendra la lumiere eclairante du papier plus ou nioins polarisee ;
la couleur bleue fournie par 1'instrument va en augmentant avec 1'in-
clinaison de la pile, et 1'on s'arrete lorsque cette couleur parait la meme
que celle de la region de 1'atmosphere dont on veut determiner la teinte
cyanometrique, et qu'ou regarde & 1'ceil nu immecliatement a cote de
1'instrumeut. La mesure de cette teiute est don nee par 1'inclinaison de
la pile. Si cette derniere partie de 1'instrument se compose du meme
nombre de plaques et d'une meme espece de verre, lea 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 com
pare 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 can not 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 inequality I employed col-
ored rings. On placing on one another two lenses of a great focal
length, colored rings wdl be formed round their point of contact as
much by means of reflection as of transmission. The colors of the r&
VOL, III— E

98 COSMOS.

The so-called relations of the magnitude cf the fixed star*
as given in our catalogues and maps of the stars, sometimes
indicate 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 seven-
teenth century, have been added to the stars in the general-
ly consulted Uranometria Bayeri, are not, as was long sup-
posed, certain indications of these alterations of light. Arge-
lander has ably shown that the relative brightness of the
stars can not 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.*

fleeted rings are complementary to those of the transmitted rings ; these
two series of rings neutralize one another when the two lights by which
they aro formed, and which fall simultaneously on the two lenses, are
equal.

" In the contrary case, we meet with traces of reflected or transmit-
ted 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 colored rings can ba said to come into play in
those photometric measurements to which I bavi diracted my atten-
tion."

(b.) Cyanometer.

" My cyanometer is an extension of my polariscope. This latter in-
strument, as you know, consists of a tube closed at ono end by a plate
of rock crystal, cut perpendicular to its axis, and 5 millimetres in thick-
ness ; and of a double refracting prism placed near the part to which
the eye is applied. Among the varied colors yielded by this apoaratus,
when it is traversed by polarized light and the prism turns on itself, wo
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
polarized rays which enter the instrument.

" Let us suppose the polariscope directed toward 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 polar-
ized ; the blue color yielded by the instrument will go on increasing
•with the inclination of the pile ; and the process must be continued un-
til the color appears of the same intensity with the region of the atmos-
phere whose cyanometrical tinge is to be determined, and which is
seen by the naked eye in the immediate vicinity of the instrument.
The amount of this color is given by the inclination of the pile ; and if
this portion of the apparatus 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, Defde Uranomelria: Bayeri, 1842, p. 14-23. "In ea-
dem classe littera prior majorem splendorem nullo modo indicat" (§
9). Bayer did not, therefore, show that the light of Castor was more
intense in 1603 than that of Pollux.

PHOTOMETRIC SCALE. 99

PHOTOMETRIC ARRANGEMENT OF THE FIXED STARS.

I close this section with a table taken from Sir John Herschel's Out
ines of Astronomy, p. 645 and 64G. I am indebted for the mode of its
arrangement, and for the following 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 Astron-
omy have been obtained by adding throughout 0-41 to the results calcu-
lated from the vulgar scale. Sir John Herschel arrived at these more
exact determinations by observing their " sequences" of brightness, and
by combining these observations with the average ordinary data of mag-
nitudes, especially on those given in the catalogue of the Astronomical
Society for the year 1827. See Observ. at the Cape, p. 304-352. The
actual photometric measurements of several stars as obtained by the
Astrometer (op. cit., 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, 2d, 3d, &c., magnitudes) to the act-
ual photometric quantities of individual stars. This comparison has
given the singular result that our ordinary stellar magnitudes ( 1, 2, 3 . . .)
decrease in about the same ratio as a star of the first magnitude when
removed to the distances of 1, 2, 3 ... by which its brightness, accord-
ing to photometric law, would attain the values 1, Jth, ^th, -pg-th . . .
(Observ. at the Cape, p. 371, 372 ; Outlines, p. 521, 522) ; in order, how-
ever, to make this accordance still greater, it is only necessary to raise
our previously adopted stellar magnitudes about half a magnitude (or,
more accurately considered, 0-41), so that a star of the 2-00 magnitude
would in future be called 2-41, and star of 2-50 would become 2-91,
and so forth. Sir John Herschel therefore proposes that this " photo-
metric" (raised) scale shall in future be adopted (Observ. at the Cape,
p. 372, and Outlines, p. 522) — a proposition in which we can not fail to
concur ; for while, on the one hand, the difference from the vulgar scale
would hardly be felt (Observ. at the Cape, p. 372), the table in the Out-
lines (p. (>45) 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 first,
second, third, fourth magnitude is exactly as 1, jth, ith, -p^th ... as is
now shown approximatively, is therefore already practicable. Sir John
Herschel employs a Centauri as the standard star of the first magnitude
for his photometric scale, and as the unit for the quantity of light (Out-
lines, p. 523; Observ. at the Cape, p. 372). If, therefore, we take the
square of a star's photometric magnitude, we obtain the inverse ratio
of the quantity of its light to that of a Centauri. Thus, for instance, if
K Orionis have a photometric magnitude of 3, it consequently has ^th
of the light of a Centauri. The number 3 would at the same time in-
dicate that K Orionis is 3 times more distant from us than a Centauri,
provided both stars be bodies of equal magnitude and brightness. 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 recog-
nition. It is also worthy of notice, that the distance of a Centauri has
been ascertained with some probability, and that this distance is the
smallest of any yet determined. Sir John Henchel demonstrates ( Out-
lines, p. 521) the inferiority of other scales to the photometric, which

100 COSMOS.

progresses in order of the squares, 1, £th, £th, Jffth ... He likewise
treats of geometric progressions, as, for instance, 1, 1, Jth, |th, ... or 1,
^d, £th, ^th. .... The gradations employed by yourself in your ob-
servations under the equator, during your travels in America, are ar-
ranged in a kind of arithmetical progression (Recueil d'Observ. Atlron.,
vol. i., p. Ixxi., 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 first to the third magnitude, arranged accord-
ing to the determinations of Sir John Herschel, giving the ordinary
magnitudes with greater accuracy, and likewise the magnitudes in ac-
cordance with his proposed photometric classification :

STARS OF THE FIRST MAGNITUDE.

Star.

Magnitude.

Star.

Magnitude.

Sirius

Vulg.

008

0-29
059
077
082
1-0
10
1-0

Phot.

0-49

0-70
1-00
1-18
1-23
1-4
1-4
1-4

a Orionis

Vulg.

1-0
1-09
1-1
1-17
1-2
1-2
1-28
1-38

Phot.

1-43
150
15
1-58
1-6
1-6
1 69
1-79

tl Argus (Var.)

a Eridani

Canopus

Aldebaran

a Centauri.... . .

8 Centauri

Arcturus

a Crucis

Rigel

An tares

Capella

a Aquila? .........

a. Lyra?

Spica

Procyon

STARS OF THE SECOND MAGNITUDE.

Star.

Magnitude.

Star.

Magnitude.

Fomalhaut

Vulg.l Phot

1-541-95
1-57 1-98
1-6 2-0
1-6 20
1-66207
1-73214
l-84!225
1-862-27
1-872-28
1-90!231
1-94|235
1-95236
1-96:2-37
2-01242
2-03 2 44
2-072-48
2-082-49
2182-59
2-18259
2-18259

a Triang austr.

2^
2-26
2-28
228
229
230
232
233
234
2-36
2-40
241
2-42
243
2-45
2-46
2-46
2-48

M

Phot.

264
2-67
269
2-69
270
271
273
2-74
275
2-77
281
2-82
2-83
284
2-86
2-87
28""
289
291

ft Crucis

e Sagittarii

Pollux

3 Tauri

Regulus

Polaris

a Gruis . .. .......

6 Scorpii

a Hydra

e Orionis

6 Canis

e Can is

a Pavonis

y Leonis

a Cygni

8 Gruis

Castor

a Arietis ........

E Ursse (Var )

a Sagittarii

a Ursae (Var )

6 Argus

f Orionis

£ Ursae

8 Argus . ... . .

8 Andromeda?

/? Ceti

A Argus . ........

e Argus

i? Ursae (Var )

y Andromedse

y Orionis

PHOTOMETRIC SCALE.

STARS OF THE THIRD MAGNITUDE.

101

Masmtmle.

Magnitude.

y Cassiopeiae

Vulg.

•J 52
254
2-54
2-57
2-58
259
259
2-61
2-62
2-62
2 62
263
263
263
263
265
265
2-68
269
2-71
2-71
2-72
2-77
2-78
2-80
280
2-82
2-82
2-85
2-85
286
2-88

Phot.

2-93
2-95
2-95
2-98
2-99
300
300
3-02
3-03
3-03
3-03
3-04
3-04
3-04
3-04
306
3-06
3-09
3-10
3-12
3-12
3-13
3-18
3-19
3-21
3-21
3-23
323
326
326
3-27
'VQ

f Sagittarii

Vulg.

3-01
3-01
302
305
3-06
307
3-08
3-08
3-09
311
3-11
312
313
3-14
3-14
3-15
3-17
3-18
320
320
322
322
3-23
324
3-26
3-26
326
326
327
327
3-28
3 28
3-29
330
331
331
3-^2
332
332
332
333
334
335
335
3-35
335
33G
336
336
337

Phot.

342
3-42
343
346
347
348
349
349
350
352
352
353
354
355
355
356
358
359
361
3-61
3 63
3-63
3-64
365
3-67
367
3-67
367
368
368
369
369
370
3-71
372
372
373
373
373
373
374
375
3-76
3 76
376
376
377
377
377
a-78

a Andromedae .....

77 Bootis

6 Centauri

77 Draconis

a Cassiopeiae ........

TT Ophiuchi

/3 Canis

i3 Draconis

* Orionis

3 Librae

y Geminorum

y Virginis

i Orionis . .

u Argns . .

Algol (Var )

3 Arietis

y Pegasi

6 Sa^ittarii

(3 Leonis

a Libras

a Ophiuchi ... ...

* Sagittarii

3 Cassiopeiae

3 Lupi

y Cygni . ...

e Virginis 1 .

a Pegasi

a Columbae

3 Pegasi

i9- Aurigae .

y Centauri

3 Herculis

a Coronas

i Centauri

y Ursae

6 Capricorni

e Scorpii

6 Corvi

f Argus

a Can. ven.

B Ursa

3 Ophiuchi

Phcenicis

6 Cygni

Argus

e Persei

Bootis

TJ Tauri

Lupi

3 Eridani

Centauri

& Argus

Canis

3 Hydri

Aquarii

f Persei

Scorpii . .

f Herculis

Cygni

E Corvi

TI Ophiuchi

2893-30
290331
290.331
2913-32
2 92 3 33
294335
2943-35
2 95 3 36
296337
2-96337
2-973-38
*-973-38
298339
298,339
2 99 3 40
2-99340
3-003-41
3003-41

i Aurigae

y Corvi

y Urs. Min

a Cephei

T) Pegasi

6 Centauri

3 Arae

a Serpentis

a Toucani

6 Leonis

3 Caprieorni

K Argus

p Argus

3 Corvi

£ Aquilae

B Scorpii

3 Cygni

f Centauri

y Persei..

C Ophiuchi ..

u Ursae.. .

a Aquani

Tf Scorpii

3 Leporis

6 Cassiopeias

y Lupi

d Centauri
a Leporis .............

I Persei

^ Ursse

6 Ophiuchi ..

e Aurigae (Var.) ..

102

Star.

M^utudp.

Star.

MHgmtii.l..-.

v Scorpii

Vulg.

3-37
337
339
3-40
340
340
3-41
3-41
342
3-42
3-42
343
343
343
344
344
344

Phot

3-78
3-78
3-80
3-81
381
3-81
3-82
3-82
383
383
383
3-84
384
3-84
385
385
385

<5 Geminorum

Z&

3-45
3-45
345
3-45
3-46
346
3-46
3-46
3-47
348
348
349
349
350
350
3-50

Phot.

3-85
3-86
386
3-86
3-86
3-87
3-87
387
3-87
3-88
389
389
3-90
3-90
391
391
391

i Orionis

o Orionis ...

y Lyncis

(3 Cephei

tfUrsae

f Hydra

rr Sagittarii ......

y Hydrae

TT Herculis .

f3 Triang. austr

/3 Can. min. 1

t Ursae

f Tauri

tj Aurigae ...

(5 Draconis

y Lyrae .........

p Geminorum

T) Geminorum

y Bootis

y Cephei

e Geminorum

K Ursas

a Muscae

e Cassiopeiae ....

a Hydri?

1? Aquilae

T Scorpii

a Scorpii

6 Herculis

r Argus

" The following short table of the photometric quantities
of seventeen stars of the first magnitude (as obtained from
the photometric scale of magnitudes) may not be devoid of
interest :"

Sirius 4-165

7i Argus

Canopus 2-041

aCentauri 1-000

Arcturus 0-718

Rigel 0-661

Capella 0-510

aLyrae 0-510

Procyon 0-510

" The following is the photometric quantity of stars strict-
ly belonging to the 1st, 2d 6th magnitudes, in which

the quantity of the light of a Centauri is regarded as the
unit :"

a Orionis ....
a Eridani ....
Aldebaran. .
j3 Centauri . . .
a Crucis
Antares ....
a Aquilae ....
Spica . .

0-489
.0-444
0-444
0-401
.0-391
.0-391
.0-350
0-312

Magnitude on
the vulgar scale.

1-00
2-00
3-00

Quantity
of light

0-500
0-172
0-086

Magnitude on
the vulgar scale.

4-00
5-00
6-00

Quantity
of light.

0-051
0-034
0-024

III.

NUMBER, DISTRIBUTION, AND COLOR OF THE FIXED STARS. — STEL-
LAR MASSES (STELLAR SWARMS).— THE MILKY WAY INTERSPERSED
WITH A FEW NEBULOUS SPOTS.

We have already, in the first section of this fragmentary
Astrognosy, 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 disk,
and amid the general blaze not a single constellation would
be visible. During my sojourn in the Peruvian plains, be-
tween 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 hu-
man 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. Not a 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 disk be
visible during the day, it appears devoid of rays, as if seen
through colored glasses, being generally of a yellowish red,
sometimes of a white, and occasionally even of a bluish green
color. The mariner, driven onward 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 harbors
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. f

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
vapors, 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-covered

* Vide supra, p. 38, and note.

t Cotmos, vol. i., p. 178, and note.

104 COSMOS.

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 unfavorable 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 in-
voluntarily arises how narrowly the human race escaped be-
ing 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 would thus have been withheld 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 occu-
pants of space. Deprived of a great, and, indeed, of the sub-
limest portion of his ideas of the Cosmos, man would have
been left without all those incitements which, for thousands
of years, have incessantly impelled him to the solution of
important problems, and have exercised so beneficial an in-
fluence on the most brilliant progress made in the higher
spheres of mathematical development 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 im-
passable 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 lat-
itude, or according to their right ascension and declination ?
"What is the number of stars from the first to the ninth and
tenth magnitudes which have been seen in the heavens by
means of the telescope ? These three questions may, from
the materials of observation at present in our possession,
be determined 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 theoretical solution of the question : How many stars
might be distinguished throughout the whole heavens with

NUMBER OF THE FIXED STARS. 105

Herschel's twenty-feet telescope, including the stellar light,
" which is supposed to require 2000 years to reach oui
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
des nordlichen Himmeh (Suney of the Northern Heav-
ens) to submit 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 or-
ganic difference in individual observations ; stars between
the sixth and seventh magnitude being frequently confound-
ed 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 vis-
ible to the unaided eye. Argelanderf determines the distri-

* On the space-penetrating power of telescopes, see Sir John Her-
schel, Outlines of Astr., § 803.

t I can not attempt to include in a note all the grounds on which
Argelander's views are based. It will suffice if I extract the following
remarks from 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 first to the seventh magnitude in-
clusive, which the heavens appeared to contain ; his calculations give
12,1 48 stars for the space between 30° south and 90° north declination ;
and consequently, if we conjecture that the proportion of stars is the
same from 30° S. D. to the South Pole, we should have 16,200 stars of
the above-named magnitudes throughout the whole firmament. 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,
Catalogvs Sldlarum duplicium, p. xxxiv. ; Argelander, Banner Zonen,
s. xxvi.) I have given in my Uranometria 1441 stars of the sixth mag-
nitude 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 sixth, if
only entire classes were admitted into the calculation. 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 sixth, and 12 000
for the seventh, or 18,000 for the first to the seventh inclusive. From
other considerations on the number of the stars of the seventh magni-
tude, as given in my zones — namely, 2257 (p. xxvi.), and allowing for
those which have been twice or oftener observed, and for those which
have probably been overlooked, I approximated somewhat more nearly
to the truth. By this method I found 2340 stars of the seventh magni-
tude between 45° and 80° N. D., and, therefore, nearly 17,000 for the
whole heavens. Struve, in his Description de V Observatoire de Paul-
kova, p. 268, gives 13,400 for the number of stars down to the seventh
magnitude in the region of the heavens explored by him (from — 15°
E 2

106 COSMOS.

bution of the fixed stars according to difference of magnitude,
down to the ninth, in about the following proportion .

to +90°), whence we should obtain 21,300 for the whole firmament.
According to the introduction to Weisse's Catal. e Zonis Regiomonta-
nit, dcd., p. xxxii., Struve found in the zone extending from — 15° to
-{-15° by the calculus of probabilities, 3903 stars from the first to the
seventh, and therefore 15,050 for the entire heavens. This number is
lower than mine, because Bessel estimated the brighter stars nearly
half a magnitude lower than I did. We can here only arrive at a mean
result, which would be about 18,000 from the first to the seventh mag-
nitudes inclusive. Sir John Herschel, in the passage of the Outlines of
Astronomy, p. 521, to which you allude, speaks only of ' the whole num-
ber of stars already registered, down to the seventh magnitude inclu-
sive, amounting to from 12,000 to 15,000.' As regards the fainter stars,
Struve finds within the above-named zone (from — 15° to +15°), for
the faint stars of the eighth magnitude, ] 0,557 ; for those of the ninth,
37,739 ; and, consequently, 40,800 stars of the eighth, and 145,800 of the
ninth magnitude for the whole heavens. Hence, according to Struve,
we have, from the first to the ninth magnitude inclusive, 15,100+
40,800+145,800=201,700 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 com-
mon to, or different in, each zone. As the calculation was made from
a very large number of stars, it is deserving of great confidence. Bes-
sel has enumerated about 61,000 different stars from the first to the
ninth 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 contains about 101,500 stars of the above-named magni-
tudes. My zones between -j-45° and -|-80° contain about 22,000 stars
(Durchmu sterung des ndrdl. Himmels, s. xxv.), which would leave about
19,000 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
130,000 stars to the ninth magnitude inclusive, between — 15° and
-J-800. This space is, however, only 0-62181 of the whole heavens,
and we therefore obtain 209,000 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 improbably exceed it to a considerable ttent, since Struve reck-
oned stars of the 9-10 magnitude among thosrof the ninth. The num-
bers which, according to my view, may be ashamed for the whole firm-
ament, are therefore as follows : first mag., 20 ; second, 65 ; third, 190 ;
fourth, 425; fifth, 1100; sixth, 3200; seventh, 13,000; eighth, 40,000;
ninth, 142,000 ; and 200,000 for the entire number of stars from the
first to the ninth magnitude inclusive.

If you would contend that Lalande {Hist. Celeste, p. iv.) has given
the number of stars observed by himself with the naked eye at 6000, I
would simply remark that this estimate contains very many that have
been repeatedly observed, and that after deducting these, we obtain
only about 3800 stars for the portion of the heavens between — 26° 30*

NUMBER OF THH FIXED STARS. 107

1st Mag. SdMag. 3d Mag. 4th Mag. 5th Mag.

20 65 190 425 1100

6th Mag. 7th Mag. 8th Mag. 9th Mag.

3200 13,000 40,000 142,000
The number of stars distinctly visible to the naked eye
(amounting in the horizon of Berlin to 4022, and in that of
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
uniformly distributed, and reckon in round numbers 200,000
stars from the first to the ninth magnitude, we shall have
nearly a single star for each full-moon surface. This result
explains why, also, at any given latitude, the moon does not
more frequently conceal stars visible to the naked eye. If the
calculation of occultations of the stars were extended to those
of the ninth 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 un-
doubtedly acquainted with Hipparchus's catalogue of stars,

and +90° observed by Lalande. As this space is 0 723 1 0 of the whole
heavens, we should again have for this zone 5255 stars visible to the
naked eye. An examination of Bode's Uranography (containing 17,240
stars), which is composed of the most heterogeneous elements, does not
give more than 5600 stars from the first to the sixth magnitude inclusive,
after deducting the nebulous spots and smaller stars, as well as those
of the G-7th magnitude, which have been raised to the sixth. A simi-
lar estimate of the stars registered by La Caille between the south pole
and the tropic of Capricorn, and varying from the first to the sixth mag-
nitude, 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 endeavored to fulfill your wish for a more thor-
ough 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 observ
er gifted with keener sight than myself, I find 2836 stars from the first
to the sixth magnitude inclusive for the northern hemisphere, and there-
fore, on the presupposition of equal distribution, 5672 as the number
of stars visible throughout the whole firmament to the keenest unaided
vision." {From the Manuscripts of Professor Argelander, March, 1850.)
* Schubert reckons the number of stare, from the first to the sixth
magnitude, at 7000 for the whole heavens (which closely approximates
to the calculation made by myself in Cosmos, vol. i., p. 150), and up-
ward of 5000 for the horizon of Paris. He gives 70,000 for the whole
sphere, including stars of the ninth magnitude. (Astronomic, th. in., s.
54.) These numbers are all much too high. Argelander finds only
58,000 from the first to the eighth magnitude.

108 COSMOS.

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 fifth, while half a century later Ptolemy indicated only
1025 stars down to the sixth 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 relations to 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 construction of instruments. No catalogues
of the stars compiled 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 sev-
enth book of the Almagest (cap. 3, p. xv., Halma), their ob-
servations were conducted in a very rough manner (navv
oAoo^epoif), there can be no doubt that they both determ-
ined the declination of many stars, and that these determin-
ations 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 endeavor 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 invented
tradition.! It does indeed seem remarkable that Ptolemy
should not refer to the circumstance, but yet it must be ad-
mitted that the sudden appearance of a brightly luminous

* " Patrocinatur vastitas cceli, immensa discreta altitudine, in duo at-
que septuaginta signa. Haec sunt rerum et animantium effigies, in quas
digessere ccelum periti. In his quidem mille sexcentas adnotavere stel-
las, iusignes videlicet effectu visuve" .... Plin., ii., 41. "Hipparchus
nunquam satis laudatus, ut quo nemo magis approbaverit cognationera
cum homine siderum animasque nostras partem esse coeli, novam stel
lam et aliam in aevo suo genitam deprehendit, ejusque motu, qua die
fulsit, ad dubitationem est adductus, anne hoc saepius fieret moveren-
turque et ese quas putamus affixas ; itemque ausus rem etiam Deo im-
probam, adnumerare posteris Stellas ac sidera ad nomen expungere, or-
ganis excogitatis, per quse singularum loca atque magnitudines signaret,
ut facile discerni posset ex eo, non modo an obirent nascerenturve, sed
an omnino aliqua transirent moverenturve, item an crescerent minue-
renturque, coelo in hereditate cunctis relicto, si quisquam qvi cretioneru
earn caperet inventus esset." — Plin., ii., 26.

t Delambre, Hist, de VAstr. Anc., torn, i., p. 290, and Hist, de VAstr.
Mod., torn, ii., p. 186.

NUMBER OF THE FIXED STARS. 109

star in Cassiopeia (November, 1572) led Tycho Brahe to
compose his catalogue of the stars. According to an ingen-
ious 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 investiga-
tions, Hipparchus compiled his catalogue of the stars. Ed-
ward Biot, whose early death proved so great a loss to science,
found a record of this celestial phenomenon in the celebra-
ted collection of Ma-tuan-lin, which contains an account of
all the comets and remarkable stars observed between the
years B.C. 613 and A.D. 1222.

The tripartite didactic poem of Aratus,t 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
Eratosthenes, Timocharis, and Aristyllus. The astronomical
non-meteorological portion of the poem is based on the ura-
nography of Eudoxus of Cnidos. The catalogue compiled by
Hipparchus is unfortunately not extant ; but, according to
Ideler,f 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 de-
terminations of position for the year B.C. 128. In Hippar-
chus's other Commentary on Aratus, the positions of the stars,
which are determined more by equatorial armillse 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 entirely copied from that of Hip-
parchus, and which gives 1025 stars, together with five so-
called nebulae, they are referred by longitudes and latitudes

* Outlines, $ 831 ; Edward Biot, Sur les Etoilet Extraordinaire* ob-
servles en Chine, in the Connaissance des temps pour 1846.

t It is worthy of remark that Aratus was mentioned with approba-
tion almost simultaneously by Ovid (Amor., i., 15) and by the Apostle
Paul at Athens, in an earnest discourse directed against the Epicureans
•and Stoics. Paul (Acts, ch. xvii., v. 28), although he does not mention
Aratus by name, undoubtedly refers to a verse composed by him (Phccn.,
v. 5) on the close communion of mortals with the Deity.

\ Ideler, Untersuchungen fiber den Unsprung der Stemnamen, s. xxx.—
xxxv. Daily, in the Mem. of the Astron. Soc., vol. xiii., 1843, p. 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 com-
piled by Hipparchus (128. and not 140, B.C.) and by Ptolemy (138
AD.).

110 COSMOS.

to the ecliptic.* On comparing the number of fixed stars m
the Hipparcho-Ptolemaic Catalogue, Almagest, ed. Halma,
t. ii., p. 83 (namely, for the first mag., 15 stars ; second, 45 ;
third, 208 ; fourth, 474 ; fifth, 217 ; sixth, 49), with the
numbers of Argelander as already given, we find, as might
be expected, a great paucity of stars of the fifth and sixth
magnitudes, and also an extraordinarily large number of
those belonging to the third and fourth. The vagueness in
the determinations of the intensity of light in ancient and
modern times renders direct comparisons of magnitude ex-
tremely uncertain.

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 re-
ductions 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),

* Compare Delambre, Hist, de I'Astr. Anc., torn, i., p. 184; torn, ii.,
p. 260. The assertion that Hipparchus, in addition to the right ascen-
sion and declination of the stars, also indicated 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 Alma-
gest, book vii., cap. 4, where this reference to the ecliptic is noticed as
something 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 Ptole-
my was imperfectly acquainted with the amount of the retrogression of
the equinoctial and solstitial points (Almag., vii., c. 2, p. 13, Halma),
and assumed it about T^ too slow, the catalogue which he determined
for the beginning of tne reign of Antoninus (Ideler, op. cit., B. xxxiv.)
indicates the positions of the stars at a much earlier epoch (for the year
63 A.D.). (Regarding the improvements for reducing stars to the time
of Hipparchus, see the observations and tables as given by Encke in
Schumacher's Astron. Nachr., No. 608, s. 113-126.) The earlier epoch
to which Ptolemy unconsciously reduced the stars in his catalogue cor-
responds 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 connec-
tion with the poem of Hermes by the true Eratosthenes. (Eratostheni-
ea, ed. Bernhardy, 1822, p. 114, 116, 129.) These Pseudo-Eratosthe-
nian Catasterisms contain, moreover, scarcely 700 individual stars dis-
tributed among the mythical constellations.

EARLY CATALOGUES. -Ill

that of Tycho Brahe (1600), and that of Hevelius (1660).
During the short intervals of repose which, amid tumultuous
revolutions and devastations of war, occurred between the
ninth and fifteenth centuries, practical astronomy, under
Arabs, Persians, and Moguls (from Al-Mamun, the son of the
great Haroun Al-Raschid, to the Timurite, Mohammed Tar-
aghi Ulugh Beg, the son of Shah Rokh), attained an emi-
nence till then unknown. The astronomical tables of Ebn-
Junis (1007), called the Hakemitic tables, in honor of the
Fatimite calif, Aziz Ben-Hakem Biamrilla, afford evidence,
as do also the Ilkhanic 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 mul-
tiplication of more accurate methods differing from those em-
ployed by Ptolemy. In addition to clepsydras,f pendulum-
oscillationsj were already at this period employed in the
measurement of time.

The Arabs had the great merit of showing how tables
might be gradually amended by a comparison with observa-
tions. 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, 4

* Cosmos, vol. ii., p. 222, 223. The Paris Library contains a manu-
script of the Ilkhanic Tables by the hand of the son of Nassir-Eddin.
They derive their name from the title " Ilkhan," assumed by the Tar-
tar princes who held rule in Persia. — Reinaud, Introd. de la Gfogr.
d'Aboulfeda, 1848, p. cxxxix.

t [For an account of clepsydras, see Beckmann's Inventions, voL i.,
341, et seq. (Bohn's edition).]— Ed.

t Sedillot fils, Prolegomenes des Tables Astr. d' Oloug-Beg, 1847, p.
cxxxiv., note 2. Delambre, Hist, de I' Astr. du May en Age, p. 8.

$ In my investigations on the relative value of astronomical determ-
inations of position in Central Asia (Asie Centrale, t. iii., p. 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', while 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 as-
tronomical 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,
therefore, 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 Ren-
nell, whoso combinations are generally so successful, made an error of

112 COSMOS.

and not visible in 39° 52' lat. (?) It contains only 1019
positions of stars, which are reduced to the year 1437. A
subsequent commentary gives 300 other stars, observed by
Abu-Bekri Altizini in 1533. Thus we pass from Arabs, Per-
sians, 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 appli-
cation 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 splendor of the
southern sky, and the descriptions given by Vicente Yanez
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 much exaggerated that the intelligent Polyhistor Cardanus
indicated in this region 10,000 bright stars which were said
to have been seen by Vespucius with the naked eye.f

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
distances 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 in-
dustry were inserted in Tycho Brahe' s Rudolphine tables.

Scarcely half a century had elapsed from the time of Ma-
gellan's circumnavigation 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

about 19' in determining the latitude of Bokhara. (Humboldt, A fie
Centrale, t. iii., p. 592, and Sedillot, in the Proligorllenes d' Olov.g-Beg,
p. cxxiii.-cxxv.)

* Cosmos, vol. ii., p. 285-29C ; Humboldt, Examen Crit. de VHisloirt
de la Gtogr., t. iv., p. 321-336 : t. v., p. 226-238.

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

PROGRESS OP ASTRONOMY. 113

the laborious 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 most belong to the sixth magnitude. This cata-
logue, and that of Hevelius, which was less frequently em-
ployed, and contained 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 tele-
scopic 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 i • nervation, but they have also (what is still more import-
ant) indirectly exercised an essential influence on our knowl-
edge of the structure and configuration of the universe, on
tiiv.- discovery of new planets, and on the more rapid determ-
ination 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 discov-
ered 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 position 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 cosmic al
bodies which change their positions, moving, as it were, be-
tween fixed boundaries. Another circumstance proves even
more distinctly the importance of very complete catalogues
of the stars. If a new planet be once discovered in the
vault of heaven, its notification in an older catalogue of po-

» Cosmos, vol. i., p. 87-89.

114 COSMOS.

eitions will materially facilitate the difficult calculation of
its orbit. The indication of a new star which has subse-
quently been lost sight of, frequently affords us more assist-
ance 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 im-
portance for the determination of Uranus, and the star num-
bered 26,266 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 al-
ready 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 plan-
etary 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
eleventh magnitude), 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 that of the southern
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
sixth magnitude.! Flamstead had, indeed, begun his great
Star Atlas at an earlier period ; but the work of this cele-
brated observer did not appear till 1712. It was succeeded
by Bradley's observations (from 1750 to 1762), which led to
the discovery of aberration and nutation, and have been ren-
dered celebrated by the Fundamenta Astronomice of our
countryman Bessel (1818),^ and by the stellar catalogues of

* Bally, Cat. of those stars in the "Histoire Celeste" of Jerome de
Lalande,for which tables of reduction to the epoch 1800 have been pub-
lished 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 disappeared, Schumacher, Astr. Nachr., No. 624, and Bode, Jahrb.
fur 1817, s 249.

t Memoirs of the Royal Astron. Soc., vol. xiii., 1843, p. 33 and 168.

t Bessel, Fundamenta Astronomies pro anno 1755, deducta ex observa-
tionibus viri incomparabilis James Bradley in Specula astronomica Ore-
novicensi, 1818. Compare also Bessel, Tabula Regiomontancn reduclio-
num observationum astronomicarum ab anno 1750 usque ad annum 1850
computatoE (1830).

STAR CATALOGUES. 115

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 seventh to the
tenth magnitude which occupy the realms of space. The
catalogue known under the name of Jerome de Lalandt'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 appre-
ciated. After having been carefully revised by Francis Baily,
under the direction of the " British Association for the Ad-
vancement of Science" (in 1847), it now contains 47,390
stars, many of which are of the ninth, and some even below
that magnitude. Harding, the discoverer of Juno, catalogued
above 50,000 stars in twenty-seven maps. Bessel's great
work on the exploration of the celestial zones, which comprises
75,000 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 far as +80°
decl., by Argelander at Bonn. Weisse of Cracow, under the
auspices of the Academy of St. Petersburgh, has reduced
31,895 stars for the year 1825 (of which 19,738 belonged to
the ninth magnitude) from Bessol's zones, between — 15° and
+ 15° decl. ;t and Argelander' s exploration of the northern
heavens from +45° to +80° decl. contains about 22,000
well-determined positions of stars.

* I here compress into a note the numerical data taken from star cat-
alogues, 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
instruments magnifying only eight times, observed 9766 southern stars,
to the seventh magnitude inclusive, which were reduced to the year
1750 by Henderson ; Tobias Mayer, 998 stars to 1756 ; Flamstead, orig-
inally only 2866, to which 564 were added by Daily's care (Mem. of the
Astr. Soc., vol. iv., p. 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 Rflmker,
7385 stars, observed in New Holland in the years 1822-1828 ; Airy, 2156
stars, reduced to the year 1845 ; Riimker, 12,000 on the Hamburg hori-
zon; Argelander (Cat. of Abo), 560; Taylor (Madras), 11,015. The
British Association Catalogue of Stars (1845), drawn up under Baily's
superintendence, contains 8377 stars from the first to 7i magnitudes.
For the southern stars we have the rich catalogues of Henderson, Fal-
lows, Maclear, and Johnson at St. Helena.

t Weisse, Positiones media stellarum fixarum in Zonis Regiomontanit
a Bessclio inter — 15° ct -J-15° decl. observatanim ad annum 1825 re
dvcla (1846); with an important Preface by Struve.

116 COSMOS.

I can not, I think, make mere honorable 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 un-
dertaking, in his oration to the memory of Bessel : '' With
the completeness of catalogues is connected the hope that,
by a careful comparison of the different aspects of the heav-
ens 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 faint-
ness of their light, be noted by the unaided eye, and that
we may in this manner complete our knowledge of the so-
lar system. While Harding's admirable atlas gives a per-
fect representation of the starry heavens — as far as Lalande's
Histoire Celeste, on which it is founded, was capable of af-
fording such a picture — Bessel, in 1824, after the comple-
tion 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 as-
tronomers, by the completeness of his tables, at once to rec-
ognize every new celestial phenomenon. Although the star
maps of the Berlin Academy of Sciences, sketched in ac-
cordance 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 principal, 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 con-
tributed sixteen. These contain, as far as possible, all stars
down to the ninth magnitude, and many of the tenth.

The present would seem a fitting place to refer to the
average estimates which have been hazarded on the num-
ber of stars throughout the whole heavens, visible to us by
the aid of our colossal space-penetrating telescopes. Struve
assumes for Herschel's twenty-feet reflector, which was em-
ployed in making the celebrated star-gauges or sweeps, that
a magnifying power of 180 would give 5.800,000 for the
number of stars lying within the zones extending 30° on ei-
ther side of the equator, and 20,374,000 for the whole heav-
ens. Sir Wilh'am Herschel conjectured that eighteen mill-

* Encke, Geddchtnissrede auf Bessel, s. 13.

DISTRIBUTION OF THE FIXED STARS. 117

ions 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, wheth-
er visible to the naked eye or merely telescopic, whose po-
sitions are determined, and which are recorded in catalogues,
we turn to their distribution and grouping in the vault of
neaven.

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 precession 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 bod-
ies that move among them with a greater velocity or in an
opposite direction — consequently, all which are allied to tel-
escopic comets and planets. The first and predominating
interest excited by the contemplation of the heavens is di-
rected to the fixed stars, owing to the multiplicity and over-
whelming 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 astron-
omy.

Amid the innumerable multitude of great and small stare,
which seem scattered, as it were by chance, throughout the
vault of heaven, even the rudest nations separate single
(and almost invariably the same) groups, among which cer-
tain bright stars catch the observer's eye, either by their
proximity to each other, their juxtaposition, or, in some cases,
by a kind of isolation. This fact has been confirmed by re-
cent 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 ob-
jects. 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

* Compare Struve, Etudes d'Astr. Sttllaire, 1847, p. 66 and 72 ; Cot-
mo$, vol. i., p. 100; ami Madlec Astr., 4te Aufl., $ 417.

118 COSMOS

belt of Orion (Jacob's stafT), Cassiopeia, the Swan, the Soor
pion, the Southern Cross (owing to the striking difference
in its direction before and after its culmination), the South-
ern 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
attentive consideration, and have gradually led to a symbol-
izing connection of ideas. Men thus became familiarized
with the aspect of the heavens before the development of
measuring astronomy. They soon perceived that besides
the daily movement from east to west, which is common to
all celestial bodies, the sun has a far slower proper motion in
an opposite direction. The stars which shine in the even-
ing 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 which were shining in the morning sky
before the rising of the sun, recede further and further from
it. In the ever-changing aspect of the starry heavens, suc-
cessive constellations are always coming to view. A slight
degree of attention suffices 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 Hipparchus, Hellenic literature
abounds in metaphoric allusions to the disappearance of the
stars amid the sun's rays, and their appearance in the morn-
ing twilight — their heliacal setting and rising. An atten-
tive observation of these phenomena yielded the earliest ele-
ments of chronology, which were simply expressed in num-
bers, while mythology, in accordance with the more cheerful
or gloomy tone of national character, continued simultane-
ously to rule the heavens with arbitrary despotism.

The primitive Greek sphere (I here again, as in the his-
tory of the physical contemplation of the universe,* follow
the investigations of my intellectual friend Letronne) had be-
come gradually filled with constellations, without being in
any degree considered with relation to the ecliptic. Thus
Homer and Hesiod designate by name individual stars and

* Cosmos, vol. ii., j>. 167

ZODIACAL SIGNS. 119

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 constella-
tions of Draco, Cepheus, and Ursa Minor, which likewise do
not set. The statement does not prove a want of acquaint-
ance with the existence of the separate stars forming these
three catasterisms, but simply an ignorance of their arrange
ment into constellations. A long and frequently misunder-
stood passage of Strabo (lib. i., p. 3, Casaub.) on Homer, II.,
xviii., 485-489, specially proves a fact — important to the
question — that in the Greek sphere the stars were only grad-
ually 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 not yet been arranged in a separate group, and that the
name did not reach the Hellenes until after the Phoanicians
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 introduction to
Thales. In the Pseudo-Eratosthenian work to which we
have already referred, the lesser Bear is called <&otviKTj (or,
as it were, the Phoenician guiding star). A century later
(01. 71), Cleostratus of Tenedos enriched the sphere with the
constellations of Sagittarius, TO^OTT/C, and Aries, K.pi6$.

The introduction of the Zodiac into the ancient Greek
sphere coincides, according to Letronne, with this period of
the domination of the Pisistratidae. Eudemus of Rhodes, one
of the most distinguished pupils of Aristotle, and author of a
"History of Astronomy," ascribes the introduction of this zo-
diacal belt (TI TOV fadiaicov dia^dxrig, also £wt Jio^ /cvwAof) to
(Enopides of Chios, a cotemporary of Anaxagoras.f The

* Ideler, Unters. uber die Sternnamen, s. xi., 47, 139, 144, 2 13 • Le-
tronne, Sur V Origins du Zodiaque Grec, 1340, p. 25.

t Letronne, op. cit., p. 25 ; and Carteron, Analyse de» Rechercn.es de
tl. Letronne sur les Representations Zodiacales, 1843, p. 119. "It ia
Yery doubtful whether Eudoxus (Ol. 103) ever made use of the word
Cudianof. We first meet with it in Euclid, and in the Commentary of
Hipparchus on Aratus (Ol. 160). The name ecliptic, eKfautTiicdf, is
also very recent." Compare Martin in the Commentary to Thconi*
Smyrn<ri Plalonici Liber de Aslronotnia, 1849, p. 50, GO.

120 COSMOS.

idea of the relation of the planets and fixed stars to the sun'*
course, 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 prim-
itive sphere those which were nearest to the ecliptic, and
could be used as signs of the zodiac. If the Greeks had bor-
rowed from another nation any thing 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 con-
stellations. The Scorpion would not have been divided into
two groups ; nor would zodiacal constellations have been in-
troduced (some of which, like Taurus, Leo, Pisces, and Virgo,
extend over a space of 35° to 48°, while others, as Cancer,
Aries, and Capricornus, occupy only from 19° to 23°), which
are inconveniently grouped to the north and south of the
ecliptic, either at great distances from each other, or, like Tau-
rus and Aries, Aquarius and Capricornus, so closely crowded
together as almost to encroach on each other. These cir-
cumstances 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, Hipparchus. 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

* Letronne, Orig. du Zod., p. 25 ; and Analyse Crit. des Reprtt.
Zod., 1846, p. 15. Ideler and Lepsius also consider it probable " that
the knowledge of the Chaldean zodiac, as well in reference to its divi-
sions as to the names of the latter, had reached the Greeks in the sev-
enth century before our era, although the adoption of the separate signs
of the zodiac in Greek astronomical literature was gradual and of a sub-
sequent d*te." (Lepsius, Chronologic der ^Egypter, 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 belong-
ing to the Chaldean Dodecatomeria ? If they introduced the twelve
signs, they are hardly likely to hava removed one in order to replace it
at a subseq :en* period.

ZODIACAL SIGNS. 121

passage, probably falsified by a copyist).* The earliest no-
tice of this new constellation occurs in Geminus and Varro
scarcely half a century before our era ; and as the Romans,
from the time of Augustus to Antoninus, became more strong-
ly imbued with a predilection for astrological inquiry, those
constellations which " lay in the celestial path of the sun"
acquired an exaggerated and fanciful importance The Egyp-
tian zodiacal 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 nec-
essary materials for the decision of the question had not been
collected, and the wildest hypothesis still prevailed regard-
ing 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.!

* On the passage referred to in the text, and interpolated by a copy
ist of Hipparchus, see Letronne, Orie. 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
antiquity, in which the Balance occurs as a sign of the zodiac) to that
passage in Hipparchus (Comment, in Aratum, lib. iii., cap. 2) which re-
fers to the tiripiov 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 KOTO

f , and is opposed to the pincers of the Scorpion in an observ-
ation, which was undoubtedly not made at Babylon, but by some of
the astrological Chaldeans, dispersed throughout Syria and Alexandria.
( Vues des Cordilleret et Monument des Peuples Indigenes de I'Amerique,
t. ii., p. 380.) Buttman maintained, what is very improbable, that the
£7/A<u originally signi6ed the two scales of the Balance, and were sub-
sequently by some misconception converted into the pincers of a scor-
pion. (Compare Ideler, Untersuchungen uber die astronomischen Beo-
bachtungen der Alien., 8. 374, and Ueber die Sternnamen, s. 174-177,
with Carteron, Recherches de M. Letronne, p. 113.) It is a remarkable
circumstance connected with the analogy between 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. ( Vites des Cordilleres, t. ii., p. 6-12.)

t Compare A. W. von Schlegel, Ueber Sternbilder des Thierkreises im
alien Indien, in the Zeitschrift fur die Kunde det Morgenlandes, bd. i.,
Heft 3, 1837, and his Commentatio de Zodiari Antiquitate et Origins,
1839, with Adolph Holtzmaun, Ueber den Griechtichen Ursprung det In

Vo*. III.— F

122 COSMOS.

The artifical grouping of the stars into constellations,
which arose incidentally during the lapse of ages — the fre-
quently inconvenient extent and indefinite outline — the com-
plicated designations of individual stars in the different con-
stellations— the various alphabets which have been required
to distinguish them, as in Argo — together with the tasteless
blending of mythical personages with the sober prose of philo-
sophical instruments, chemical 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 haz-
ardous in respect to the southern hemisphere, where Scorpio,
Sagittarius, Centaurus, Argo, and Eridanus alone possess any
poetic interest.*

The heavens of the fixed stars (orbis inerrans of Apule-
ius), and the inappropriate expression of fixed stars (astro,
fixa of Manilius), reminds us, as we have already observed
in the introduction to the Astrognosy,f of the connection, or,
rather, confusion of the ideas of insertion, and of absolute im-
mobility or fixity. When Aristotle calls the non-wandering
celestial bodies (dnXavrj darpa) riveted (ivdede^iva), when
Ptolemy designates them as ingrafted (TrpoanefivKorec;), these
terms refer specially to the idea entertained by Anaximenes
of the crystalline sphere of heaven. The apparent motion
of all the fixed stars from east to west, while their relative
distances remained unchanged, had given rise to this hypoth-
esis. " The fixed stars (drrAavr/ aarpa) belong to the higher
and more distant regions, in which they are riveted, like nails,

dischcn Thierkreises, 1841, s. 9, 16, 23. " The passages quoted from
Amorakoscha and Ramayana," says the latter writer, "admit of un-
doubted interpretation, 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."

* Compare Buttman, in Berlin Astron. Jahrbuchfur 1822, s. 93, Ol-
bers on the more recent constellations in Schumacher's Jahrbuch fur
1840, s. 283-251, and Sir John Herschel, Revision and Rearrangement
of the Constellations, with special reference to those^ of the Southern Hem-
uphere, in the Memoirs of the Astr. Soc., vol. xii., p. 201-224 (with a
very exact distribution of the southern stars from the first to the fourth
magnitude). On the occasion of Lalande's formal discussion with Bode
on the introduction of his domestic cat and of a reaper (Messier!), Ol-
bers complains that in order " to find space in the firmament for Kirg
Frederic's glory, Andromeda must lay her right arm in a different place
from that which it had occupied for 3000 years !"

t Vide supra, p. 26-28, and note.

THE FIXED STARS. 123

to the crystalline heavens ; the planets (aarpa
or TrAavT/rd), 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 Stella fixa was
substituted for infixa or affiza, it may be assumed that the
schools of Rome attached thereto at first only the original
signification of riveted ; but as the word Jixus also embraced
the idea of immobility, and might even be regarded as sy-
nonymous with immotus and immobilis, we may readily con-
ceive 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 fixum et immobilem populum.

Although, according to Stobseus, and the collector of the
" Views of the Philosophers," the designation " crystal vault
of heaven" dates as far back as the early period of Anax-
imenes, the first clearly-defined signification of the idea on
which the term is based occurs in Empedocles. This phi-
losopher regarded the heaven of the fixed stars as a solid
mass, formed from the ether which had been rendered crys-
talline and rigid by the action of fire.f According to his

* According to Democritus and his disciple Metrodorus, Stob., Eclog.
Phys., p. 582.

t Plut., De plac. Phil., ii., 11; Diog. Laert., viii., 77; Achilles Tat.,
ad. Arat., cap. 5, EMTT, Kpvara^un TOVTOV (TOV ovpavbv) elvai (fujaiv, ix
TOV KayeTudovc. ffv/.AeyevTO ; in like manner, we only meet with the
expression crystal-likti in Diog. Laert., viii., 77, and Galenus, Hist. Phil.,
I'-i (Sturz, Empedocles Agrigent., t. i., p. 321). Lactautius, De Opificio
Dei, c. 17 : " An, si milii quispiam dixerit tcncum esse ccelum, aut vi-
treum, aut, ut Empedocles ait, aCrem glacialum, statimne assentiat quia
cajliim 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 incontinently assent thereto, for I am ignorant of
what substance the heavens are composed." We have no early Hel-
lenic testimony of the use of this expression of a glass-like or vitreous
heaven (cesium vitreum'), 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 reflection of the sun's light from the body of the
moon (supposed to be consolidated in the same manner as hailstones),
is frequently noticed by Plutarch, apud Euseb. Prtep. Evangel., 1, p.
24, D, and De Facie in Orbe Lunte, cap. 5.) Where Uranos is described
as xaZiceof and otdrjpeof by Homer and Pindar, the expression refers
only to the idea of steadfast, permanent, and imperishable, as in speak-
ing of brazen hearts and brazen voices. V61cker uber Homerische Geo-
graphie, 1830. s. 5. The earliest mention, before Pliny, of the word
Kov<Tra/lAof when applied to ice-like, transparent rock-crystal, occurs in
Uionysius Periegetes, 781, Lilian, xv., 8, and Strabo, xv., p. 717 Ca-

124 COSMOS.

theory, the moon is a body conglomerated (like hail) by the
action of fire, and receives its light from the sun. The original

saub. The opinion that the idea of the crystalline heavens being a gla-
cial vault (atr glacintvs of Lactantius) arose among 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 Casio, 11, 7, p. 289.) In speaking of the
music of the spheres (Aristot., De Casio, 11, p. 290), which, according
to the views of the Pythagoreans, is not perceived by men, because it
is continuous, whereas tones can only be heard when they are inter-
rupted by silence, Aristotle singularly enough maintains that the move-
ment of the spheres generates heat in the air below them, while they
are themselves not heated. Their vibrations produce heat, but no sound.
" The motion of the sphere of the fixed stars is the most rapid (Aristot.,
De Caelo, ii., 10, p. 291) ; as ths sphere and the bodies attached to it are
impelled in a circle, the subjacent space is heated by this movement,
aud 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 expression, " riveted stars" (kv6ede[ieva aarpa), which he uses, in-
dicates a general idea of solid spheres, without, however, specifying the
nature of the substance. We do riot meet with any allusion to the sub-
ject in Cicero, but we find in his commentator, Macrobius (Cic. Som-
nium Scipionis, 1, c. 20, p. 99, ed. Bip.), traces of freer ideas on the dim-
inution of temperature with the increase of height. According to him,
eternal cold prevails in the outermost zones of heaven. " Ita enim not
solum ten-am sed ipsum quoque coelum, quod vere mundus vocatur,
temperari a sole certissimum est, ut extremitates ejus, quae via solis
longissime recesserunt, omni careant 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 confines, which
are most distant from the sun, are deprived of the benefits of heat, and
languish in a state of perjpetual cold." These confines of heaven (ex-
tremitates cceli), in which the Bishop of Hippo (Augustinus, ed. Antv.,
1700, i., 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 a somewhat earlier expression of Macrobius (1, c. 19,
p. 93), the fiery ether which enigmatically enough does not prevent this
eternal cold: " Stellte supra coalum locate, in ipso purissimo asthere suut,
in quo omne quidquid est, lux naturalis et sua est, quae tota cum igne
suo its sphasrae solis incumbit, ut cceli zonas, quas procul a sole suut,
perpetno frigore oppressae sint." " The stars above the heavens are
situated in the pure ether, in which all things, whatever they may be,
have a natural and proper light of their own" (the region of self-lumin-
ous 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 oppress-
ed by perpetual cold." My reason for entering so circumstantially into
the physical and meteorological ideas of the Greeks and Romans is sim-
ply because these subjects, except in the works of Ukert, Henri Martin,

THB FIXED STARS. 125

idea of transparency, congelation, and solidity would not, ac-
cording to the physics of the ancients,* and their ideas of the
solidification of fluids, have referred directly to cold and ice :
but the affinity between jcpvaroAAof, fpuoc, and *pwrr<uv&>.
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 Lac-
tantius : " Ccelum aerem glaciatum esse" and " vitreum coe-
lum." Empedocles undoubtedly did not refer to the glass of
the Phoenicians, but to air, which was supposed to be con-
densed into a transparent solid body by the action of the fiery
ether. In this comparison with ice (cpvoTaAAof), 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 commentator of Aratus) lim-
ited themselves to the expression crystalline or crystal-like,
Kpvo-a/J.o£i6fi$. In like manner, Trayoc (from tr^ywaBfu,
to become solid) signifies a piece of ice — its condensation be
ing 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 seven to ten glassy
strata, incasing one another like the different coatings of an
onion. This supposition still keeps its ground in some of the
monasteries of Southern Europe, where I was greatly sur-
prised to hear a venerable prelate express an opinion in ref-
erence to the fall of aerolites at Aigle, which at that time
formed a subject of considerable interest, that the bodies we
called meteoric stones with vitrified crusts were not portions
of the fallen stone itself, but simply fragments of the crys-

and the admirable fragment of the Meteorologia Vetenm of Julias Ide-
ler. have hitherto been very imperfectly, and, for the most part, super
ficially considered.

* The ideas that fire has the power of making rigid (Aristot., ProbL,
xiv.. 11). and that the formation of ice itself may be promoted by beat,
are deeply rooted in the physics of the ancients, and based on a fanci-
ful theory of contraries (AnJiperittatit) — on obscure conceptions of po-
larity (of exciting opposite qualities or conditions). ( Vide mpra, p.
14, and note.) The quantity of hail produced was considered to be
proportional to the degree of heat of the atmospheric strata. (Aristot.,
Meteor., i.. 12.) In the winter fishery on the shores of the Euxin-s
warm water was used to increase the ice formed in the neighborhood
of an upright tube. (Alex. Aphrodu., foL 86, and Plat, De\
do, c. 12.)

126 COSMOS.

tal vault shattered by it in its fall. Kepler, from his con-
siderations of comets which intersect the orbits of all the
planets,* boasted, nearly two hundred and fifty years ago,
that he had destroyed the seventy-seven concentric spheres
of the celebrated Girolamo Fracastoro, as well as all tki?
more ancient retrograde epicycles. The ideas entertained
by such great thinkers as Eudoxus, Mensechmus, Aristotle,
and Apollonius Pergaeus, respecting the possible mechanism
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
representation, or intellectual fancies, by means of which diffi-
cult problems of the planetary orbits might be solved or de-
termined approximately, are subjects of which I have already
treated in another place,t and which are not devoid of interest
in our endeavors to distinguish the different periods of devel-
opment which have characterized the history of astronomy.
Before we pass from the very ancient, but artificial zodi-
acal grouping of the fixed stars, as regards their supposed
insertion into solid spheres, to their natural and actual ar-
rangement, and to the known laws of their relative distri-
bution, it will be necessary more fully to consider some of
the sensuous phenomena of the individual cosmical bodies —
their extending rays, their apparent, spurious disk, and their
differences of color. In the note referring to the invisibility
of Jupiter's satellites,^: I have already spoken of the influ-
ence of the so-called tails of the stars, which vary in num-
ber, position, and length in different individuals. Indistinct-
ness of vision (la vue indistincte) arises from numerous or-
ganic causes, depending on aberration of the sphericity of

* Kepler expressly says, in his Stella Mortis, fol. 9 : " Solidos orbes
rejeci." "I have rejected the idea of solid orbs;" and in the Stella
Nova, 1606, cap. 2, p. 8: " Planetse in puro aethere, perinde atque
aves in aftre cursus suos conficiunt." " The planets perform their
course in the pure ether as birds pass through the air." Compare also
p. 122. He inclined, 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 riveted to the crystal
heavens, but that the planets were free and unrestrained" (roif Se Trhav-
•firae avtiadai). (Plut., plac. Phil., ii., 13; Eraped., 1, p. 335, Sturz;
Euseb., Preep. Evang., xv., 30, col. 1688, p. 839.) It is difficult to con-
ceive how, according to Plato in the Titnueus ( Tim., p. 40, B ; see Bohn's
edition of Plato, vol. ii., p. 344; but not according to Aristotle), the fixed
stars, riveted as they are to solid spheres, could rotate independently.

t Cosmos, vol. ii., p 315, 316. t Vide supra, p. 51, and note.

VELOCITY OF LIGHT.

tne eye, diffraction at the margins of the pupil, or at the
eyelashes, and on the more or less widely-diffused irritabili-
ty of the retina from the excited point.* I see very regu-

* "Le3 principales causes de la vue iudistincte sont: aberration de
sphericite de 1'oeil, diffraction sur les bords de la pupille, communica-
tion d'irritabilite 4 des points voisius sur la retine. La vue confuse est
celle ou le foyer ne tombe pas exactement sur la retine, mais tombe
au-clevant ou derriere la retine. Les queues des etoiles sont 1'effet de
la vision iudistincte, autant qu'elle depend de la constitution du cristal-
lin. D'apres un tres ancien m^moire de Hassenfratz (1809) ' les queues
au nombre de 4 ou 8 qu'offrent les etoiles ou une bougie vue 4 25 me-
tres de distance, sont les caustiques du cristallin formees par 1'interseo
tiou des rayons refractes.' Ces caustiques se meuvent a mesure que
nous iuclinons la tete. La propriete de la lunette de terminer 1'image
lait qu'elle concentre dans un petit espace la lumiere qui sans cela en
aurait occupe uu plus grand. Cela est vrai pour les etoiles fixes el
pour les disques des planetes. La lumiere des etoiles qui n'ont pas de
disque reels, conserve la me me intensite, quel que soil le grossissement.
Le foud de 1'air duquel se detache 1'etoile dans la lunette, devient plus
noir par le grossisseraent qui dilate les molecules de 1'air qu'embrasse
le champ de la lunette. Les planetes a vrais disques deviennent elles-
m^mes plus pales par cet effet de dilatation. Quand la peinture focale
est uette, quand les rayons partis <fun point de 1'objet se sont concen-
tr6s en un seul point dans 1'image, 1'oculaire donne des resultats satis-
faisants. Si au contraire les rayons emanes d'un point ne se reiinissent
pas au foyer en un seul point, s'ils y forment un petit cercle, les images
de deux points contigus de 1'objet empietent necessairement 1'une sur
1'autre; leurs rayons se confondeut. Cette confusion la lentille ocu-
laire ue saurait la faire disparaitre. L'office qu'elle remplit exclusive-
ment, c'est de grossir ; elle grossit tout ce qui est dans 1'image, les de-
fauts comme le reste. Les etoiles n'ayant pas de diametres angulaires
sensibles, ceux qu'elles conservent toujours, tiennent pour la plus grande
partie au manque de perfection des instrumens (£. la courbure moins
reguliere donnee aux deux faces de la lentille objective) et & quelques
defauts et aberrations de notre ceil. Plus une 6toile semble petite,
tout etant egal quant au diametre de 1'objectif, au grossiasement em-
ploy6 et A 1'eclat de Petoile observee, et plus la lunette a de perfection.
Or le meilleur moyen de juger si les etoiles sont tres petites, si des
points sont representes au foyer par des simples points, c'est evidem-
ment de viser ^. des etoiles excessivement rapproch6es entr'elles et de
voir si dans les etoiles doubles connues les images se confondent, si
elles empietent 1'une sur 1'autre, ou bien si on les apercoit bien nette-
ment separees."

" The pi-incipal causes of indistinct vision are, aberration of the sphe-
ricity 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 ou the retina, but either somewhat
before or behind it. The tails of the stars are the result of indistinct-
ness of vision, as far as it depends on the constitution of the crystalline
lens. According to a very old paper of Hassenfratz (1809), ' the four
or eight tails which surround the stars or a candle seen at a distance
of 25 metres [82 feet], are the caustics formed on the crystalline lens
by the intersection ofrefracted rays.' These caustics follow the move*

128 COSMOS.

laxly eight rays at angles of 45° in stars from the first to the
third magnitude. As, according to Hassenfratz, these radi-
ations are caustics intersecting one another on the crystal-
line lens, they necessarily move according to the direction
in which the head is inclined.* Some of my astronomical
friends see three, or, at most, four rays ahove, and none be-
IOAV 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 hieroglyphics signifies, according to Hora-
pollo, the number five.f

The rays of the stars disappear when the image of the
radiating star is seen through a very small aperture made

ments of the head. The property of the telescope, in giving a definite
outline to images, causes it to concentrate in a small space the light
which would otherwise be more widely diffused. This obtains for the
fixed stars and for the disks of planets. The light of stars having no
actual disks, 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 included in
the field of view are expanded. Planets having actual disks 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
concentrated into one point in the image, the ocular focus affords satis-
factory results. But if, on the contrary, the rays emanating 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 im-
pinge upon each other, and their rays will be confused. This confusion
can not be removed by the ocular, since the only part it performs is
that of magnifying. It magnifies every thing comprised in the image,
including its defects. As the stars have no sensible angular diameters,
those which they present are principally owing to the imperfect con-
struction 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
instrument, 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 distinct." (Arago, MS. of 1834 and 1847.)

* Hassenfratz, Sur les rayons divergens des Etoiles in Delam6therie,
Journal de Physique, torn. Ixix., 1809, p. 324.

t Horapollinis Niloi Hieroglyphica, ed. Con. Leemans, 1835, cap. 13,
p. 20. The learned editor notices, however, in refutation of Jomard's
assertion (Descr. de VEgypte, torn, vii., p. 423), that a star, as the nu-
merical hieroglyphic for 5, has not yet been discovered on any monu-
ment or papyrus-roll. (Horap., p. 194.)

RAYS OF THE STARS. 129

with a needle in a card, and I have myself frequently ob-
served both Canopus and Sirius in this manner. The same
thing occurs in telescopic vision through powerful instru-
ments, when the stars appear either as intensely luminous
points, or as exceedingly small disks. Although the fainter
scintillation of the fixed stars in the tropics conveys a cer-
tain impression of repose, a total absence of stellar radiation
would, in my opinion, impart a desolate aspect to the firma-
ment, as seen by the naked eye. Illusion of the senses, op-
tical illusion, and indistinct vision, probably tend to augment
the splendor of the luminous canopy of heaven. Arago long
since proposed the question why fixed stars of the first mag-
nitude, notwithstanding their great intensity of light, can
not be seen when rising above the- horizon in the same man-
ner as under similar circumstances we see the outer margin
of the moon's disk.*

Even the most perfect optical instruments, and those hav-
ing the highest magnifying powers, give to the fixed stars
spurious disks (diametres factices) ; " the greater aperture,"
according to Sir John Herschel, " even with the same mag-
nifying power, giving the smaller disk."t Occultations of
the stars by the moon's disk show that the period occupied
in the immersion and emersion is so transient that it can not
be estimated at a fraction of a second of time. The frequent
occurrence of the so-called adhesion of the immersed star to
the moon's disk is a phenomenon depending on inflection of
light in no way connected with the question of the spurious
diameter of the star. We have already seen that Sir Will-
iam Herschel, with a magnifying power of 6500, found the
diameter of Vega 0"'36. The image of Arcturus was so di-
minished in a dense mist that the disk was below 0"'2. It
is worthy of notice that, in consequence of the illusion occa-
sioned by stellar radiation, Kepler and Tycho, before the in-
vention of the telescope, respectively ascribed to Sirius| a
diameter of 4' and of 2' 20".

of the Pacific, that the age of the moonTmight be determinecl before
first quarter by looking at it through a piece of silk and counting the
multiplied images. Here we have a phenomenon of diffraction ob-
served through fiue slits.

t Outlines, $ 816. Arago has caused the spurious diameter of Alde-
baran to increase from 4" to 15" in the instrument by diminishing the
object-glass.

t Delambre, Hist, de I'Astr. Moderne, torn, i., p. 193 ; Arago,
mre, 1842, p. 366.

F2

130 COSMOS.

The alternating light and dark rings which surround the
email spurious disks 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 observ-
ations of Arago and Airy. The smallest objects which can
be distinctly seen in the telescope as luminous points, may
be employed as a test of the perfection in construction and
illuminating power of optical instruments, whether refractors
or reflectors. Among these we may reckon multiple stars,
such as e Lyrse, and the fifth and sixth star discovered by
Struve in 1826, and by Sir John Herschel in 1832, in the
trapezium of the great nebula of Orion,* forming the quad-
ruple star 6 of that constellation.

A difference of color in the proper light of the fixed stars,
as well as in the reflected light of the planets, was recog-
nized at a very early period ; but our knowledge of this re-
markable 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 color which, as already observed, ac-
companies scintillation even in the whitest stars, and still
less to the transient and generally red color exhibited by
stellar light near the horizon (a phenomenon owing to the
character of the atmospheric medium through which we see
it), but to the white or colored stellar light radiated from
each cosmic al 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 tele-

* " Two excessively minute and very close companions, to perceive
loth of which is one of the severest tests which can be applied to a tel-
escope." (Outlines, § 837. Compare also Sir John Herschel, Observ-
ations at the Cape, p. 29 ; and Arago, in the Annuaire pour 1834, p.
302-305.) Among the different planetary cosmical bodies by which
the illuminating power of a strongly magnifying optical instrument may
be tested, we may mention the first and fourth satellites of Uranus, re-
discovered by Lassell and Otto Struve in 1847, the two innermost and
the seventh satellite of Saturn (Mimas, Enceladus, and Bond's Hyperi-
on), and Neptune's satellite discovered by Lassell. The power of pen-
etrating into celestial space occasioned Bacon, in an eloquent passage
in praise of Galileo, to whom he erroneously ascribes the invention of
telescopes, to compare these instruments to ships which cany men upon
an unknown ocean : " Ut propriora exercere possiut cum ccelestibus
commercia." ( Works of Francis Bacon, 1740, vol. i., Novum Orga-
num, p. 361.)

COLOR OF THE STABS. 131

Biope, in the radiant fields of the starry heaven, as in the
blossoms of the phanerogamia, and in the metallic oxyds,
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
(vnoictppoi) fiery red stars, viz. :* Arcturus, Aldebaran, Pol-
lux, Antares, a Orionis (in the right shoulder), and Sirius.
Cleomedes even compares Antares in Scorpio with the fiery
red Mars,f which is called both Trvppdf and nvpoeidfj^.

Of the six above-named stars, five still retain a red or red-
dish light. Pollux is still indicated as a reddish, but Castor
as a greenish star.J Sirius therefore affords the only ex-
ample of an historically proved change of color, for it has at
present a perfectly white light. A great physical revolu-
tion§ must therefore have occurred at the surface or in the
photosphere of this fixed star (or remote sun, as Aristarchus

* The expression vnonififtof, which Ptolemy employs indiscriminate-
ly 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 color. He seems to attach the gen-
eral predicate £av66f, fiery yellow, to all the other fixed stars. (Almag.,
viii., 3d ed., Halma, torn, ii., p. 94.) ~K.if>f>6( 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.
Quasi., i., 1) to be redder than Mars, and belongs to the stars called in
the Almagest vnoKifipoi, there can be no doubt that the word implies
the predominance, or, at all events, a certain proportion of red rays.
The assertion that the affix 7roi*c/^of , which Aratus, v. 327, attaches to
Sirius, has been translated by Cicero as " rutilus," is erroneous. Cicero
says, indeed, v. 348:

" Namque pedes subter rutilo cum lumine claret,
Fervidus ille Canis stellarum luce refulgena ;"

but " rutilo cum lumine" is not a translation of iroiK&of, but the mere
addition of a free translation. (From letters addressed to me by Pro-
fessor 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 rec-
ognized the reddish character of the light of Sirius."

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

t Madler, Aslr., 1849, s. 391.

$ Sir John Herschel, in the Edinb. Review, vol. 87, 1848, p. 189, and
in Schum., A$tr. Nachr., 1839, No. 372: " It seems much more likely
that in Sirius a red color should be the effect of a medium interfered,
than that in the short space of 2000 years so vast a body should have
actually undergone such a material change in its physical constitution.
It may be supposed owing to the existence of some sort of cosmical
cloudiness, subject to internal movements, depending on causes of which
we are ignorant." (Compare Arago, in the Annuaire pour 1842. p. 350-
353.)

132 COSMOS.

of Samos called the fixed ttars) 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 rays, either in the pho-
tosphere 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 color of Sirius had been re-
corded 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 undoubtedly 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 color to a reddish
hue, and again became white in January, 1574, the red ap-
pearance of the star was compared to the color of Mars and
Aldebaran, but not to that of Sirius. M. Sedillot, or other
philologists conversant with Arabic and Persian astronomy,
may perhaps some day succeed in discovering evidence of
the earlier color of Sirius, in the periods intervening from
El-Batani (Albategnius) and El-Fergani (Alfraganus) to Ab-
durrahman 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, in-
dicates as red stars (stellcn ruffce, 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 mention Sirius. If at this period Sirius had been no
longer red, it would certainly be a striking fact that El-Fer

* In Muhamedis Alfragani Chronologica et Astronomica Elementa, ed.
Jacobus Christmannus, 1590, cap. 22, p. 97, we read, " Stella ruffa in
Tauro Aldebaran ; Stella ruffa in Geminit quse appellatur Hajok, hoc
est Capra." Alhajoc, Aijuk are, however, the ordinary names for Ca-
pella Aurigae, in the Arabic and Latin Almagest. Argelander justly ob-
serves, in reference to this subject, that Ptolemy, in the astrological
work (Tcrpu&CAof cvvTagif), 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 color, and has thus connected Mar
tis stella, Quce urit slcut congruit igneo ipsius colori, with Auriga? stella
or Capella. (Compare Ptol., Quadripart. Construct., libri iv., Basil,
1551, p. 383.) Riccioli (Almageslum Novum, ed. 1650, torn, i., pars i.
lib. 6, cap. 2, p. 394) also reckons Capella, together with Antares, Aide
baran, and Arcturus, among red stars.

SIRIUS. 133

gani, who invariably follows Ptolemy, should not here indi-
cate the change of color 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 color
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 development
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 arrange-
ments of the Egyptian calendar into those ancient epochs, in-
cluding 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 accept-
able to those who, from love for the history of astronomy, seek
in languages and their affinities monuments of the earlier
conditions of knowledge. t

10-195, 3. e compete arrangement o te gyptan caen
referred to the earlier part of the year 3285 before our era, i. e.,
a century and a half after the building of the great pyramid of Ch
Chufu, and 940 years before the period generally assigned to the D

See Chronologie der^Egypter, by Richard Lepsius, bd. i., 1849, s.
190-195, 213. The complete arrangement of the Egyptian calendar is

i. e., about
f Cheops-
the Deluge.

(Compare Cosmos, vol. ii., p. 114, 115, 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 pyr-
amid very nearly corresponded to the angle 26° 15', which in the time
of Cheops (Chufu) was attained by the star a 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 diflerence
of 540 years tends to strengthen the assumption that a Drac. was re-
garded as the pole star, as in 3970 it was still at a distance of 3° 44' from
the pole.

t I have extracted the following observations from letters addressed
to me by Professor Lepsius (February, 1850). "The Egyptian name
of Sirius is Sothis, designated as a female star ; hence q Hudif is identi-
fied in Greek with the goddess Sole (more frequently Sit in hieroglyph-
ics), and in the temple of the great Ramses at Thebes with Isis-Sothis
(Lepsius, Ckron. der ^gypter,bd. i., s. 119, 136). The signification of
the root is found in Coptic, and is allied with a numerous family of words,

134 . COSMOS.

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

the members of which, although they apparently differ very widely from
each other, admit of being arranged somewhat in the following order.
By the three-fold transference of the verbal signification, we obtain from
the original meaning, to throw out — -projicere (sagittam, telurn) — first,
seminare, to sow; next, eztendere, to extend or spread (as spun threads);
and, lastly, what is hero most important, to radiate light and to shine
(as stars and fire). From this series of ideas we may deduce the names
of the divinities, Satis (the female archer); Sothis, the radiating, and
Seth, the fiery. We may also hieroglyphically explain sit or seti, the
arrows as well as the ray ; seta, to spin ; setu, scattered seeds. Sothit
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 arranged in numerous triple rows issuing in a down-
ward direction from the sun's disk. Seth is the fiery scorching god, ia
contradistinction to the warming, fructifying water of the Nile, the god-
dess Satis who inundates the soil. She is also the goddess of the cat-
aracts, 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 2i?0 instead of Sothis ; but neither the name nor the
subject admits of our identifying Thoth with Seth or Sothis, as Ideler
has done. (Handbuch der Chronologic, bd. i., 8. 126.)" (Lepsius, bd.
i., s. 136.)

I will close these observations taken from the early Egyptian periods
with some Hellenic, Zend, and Sanscrit etymologies : " Se/p, the sun,"
says Professor Franz, " is an old root, differing only in pronunciation
from tfep, &£pog, heat, summer, in which we meet with the same change
in the vowel sound as in relpof and repof or repaf. The correctness of
these assigned relations of the radicals aelp and &ep, depof, is proved
not only by the employment of tfepetTarof in Aratus, v. 149 (Ideler,
Sternnamen, s. 241), but also by the later use of the forms aeipof, aei-
piof, and asipivof, hot, burning, derived from oeip. It is worthy of no-
tice that oeipd or deipiva Ifiana is used the same as tiepiva iftdria, light
summer clothing. The form oelpiof seems*, however, to have had a wider
application, for it constitutes the ordinary term appended to all stars in-
fluencing the summer heat: hence, according to the version of the poet
Archilochus, the sun was aeipioc aarrip, while Ibycus calls the stars gen-
erally adpia, luminous. It can not be doubted that it is the sun to which
Archilochus refers in the words iroJUoiif /*£v avrov aeipioe Karavavel 6£i>f
kXXufiTruv. According to Hesychius and Suidas, Set'ptof does indeed
signify both the sun and the Dog-star; but I fully coincide with M. Mar-
tin, 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 oei-
piof, which has established itself as the ' epilheton perpetuum' of the
Dog-star, we derive the verb aeipidv, which may be translated ' to
sparkle.' Aratus, v. 331, says of Sirius, bt-£a aeipiuei, ' it sparkles strong-
ly.' When standing alone, the word Setpjyv, the Siren, has a totally dif-
ferent 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 Smyrna^us
(Liber de Astronomia, 1850, p. 202), derive 'Zeipfjv from oeipid&iv (a

THE COLOR OF THE STARS 135

stars, Struve enumerates about 300 in which both stars are
•white.* Procyon, Atair, the Pole Star, and more especially
ft Ursae Min. have a more or less decided yellow light. "We
have already enumerated among the larger red or reddish stars
Betelgeux, Arcturus, Aldebaran, Antares, and Pollux. Rum
ker finds y Crucis of a fine red color, and my old friend, Cap
tain Berard, who is an admirable observer, wrote from Mada
gascar in 1847 that he had for some years seen a Crucis grow
ing red. The star 77 Argus, which has been rendered cele-
brated by Sir John Herschel's observations, and to which 1
shall soon refer more circumstantially, is undergoing a change
in color as well as in intensity of light. In the year 1843,
Mr. Mackay noticed at Calcutta that this star was similar in
color to Arcturus, and was therefore reddish yellow ;t but in
letters from Santiago de Chili, in Feb., 1850, Lieutenant Gil-
liss speaks of it as being of a darker color than Mars. Sir
John Herschel, at the conclusion of his Observations at the
Cape, gives a list of seventy-six ruby-colored small stars, of
the seventh to the ninth magnitude, some of which appear
in the telescope like drops of blood. The majority of the vari-
able stars are also described as red and reddish, f the excep-

moreover unaccredited form of acipiav'), is likewise entirely erroneous.
While the motion of heat and light is implied by the expression aeipiof,
the radical of the word Zeipijv represents the flowing tones of this phe
nomenon of nature. It appears to me probable that "Zeipriv is connect-
ed with elpeiv (Plato, Cratyl., 398, D, TO yap slpetv hiyeiv kar'C), in which
the original sharp aspiration passed into a hissing sound." (From let
ters of Prof. Franz to me, January, 1850.)

The Greek 2e<p, the sun, easily admits, according to Bopp, " of be-
ing associated with the Sanscrit word star, which does not indeed sig-
nify the sun itself, but the heavens (as something shining'). The ordi-
nary Sanscrit denomination for the sun is surya, a contraction of svdrya,
which is not used. The root svar signifies in general to shine. The
Zend designation for the sun is hvare, with the h instead of the s. The
Greek $fp, $^pof, and i?ep//6f comes from the Sanscrit word gharma
(N7om. gharmas'), warmth, heat."

The acute editor of the Rigveda, Max MQller, observes, that " the
special Indian astronomical name of the Dog-star, Lubdkaka, which sig-
nifies a hunter, when considered in reference to the neighboring con-
stellation Orion, seems to indicate an ancient Arian community of ideas
regarding these groups of stars." He is, moreover, principally inclined
" to derive Zetptof from the Veda word rira (whence the adjective sair-
ya) and the root tri, to go, to wander ; so that the sun and the bright-
est of the stars, Sirius, were originally called wandering stars." (Com.
pare also Pott, Etymologische Forschungen, 1833, s. 130.)

* Stvuve, Stellarum compositarum Mensuree Micrometricts, 1837, ]X
Ixxiv. et Ixxxiii.

t Sir John Herschel, Observation! at (he Cape, p. 34.

t Madler's Attronomie, s. 436.

136 SOSMOS.

tions being Algol in Caput Medusae, ft Lyraj and e Auriga,
which have a pure white light. Mira Ceti, in which a pe-
riodical change of light was first recognized, has a strong red-
dish light ;* but the variability observed in Algol and ft Lyrse
proves that this red color is not a necessary condition of a
change of light, since many red stars are not variable. The
faintest stars in which colors can be distinguished belong, ac-
cording to Struve, to the ninth and tenth magnitudes. Blue
stars were first mentioned by Mariotte,t 1686, in his Traite
des Couleurs. The light of a Lyrse is bluish ; and a smaller
stellar mass of 3^- minutes in diameter in the southern hem-
isphere consists, according to Dunlop, of blue stars alone.
Among the double stars there are many in which the princi-
pal star is white, and the companion blue ; and some in which
both stars have a blue lightj (as 6 Serp. and 59 Androm.).
Occasionally, as in the stellar swarm near « of the Southern
Cross, which was mistaken by Lacaille for a nebulous spot,
more than a hundred variously-colored red, green, blue, and
bluish-green stars are so closely thronged together that they
appear in a powerful telescope " like a superb piece of fancy
jewelry. "§

The ancients believed they could recognize a remarkable
symmetry in the arrangement of certain stars of the first
magnitude. Thus their attention was especially directed to
the four so-called regal stars, which are situated at oppo-
site points of the sphere, Aldebaran and Antares, Regulus
and Fomalhaut. We find this regular arrangement, of
which I have already elsewhere treated, II specially referred
to in a late Roman writer, Julius Firmicus Maternus,1T who
belonged to the age of Constantine. The differences of
right ascension in these regal stars, stellce regales, are llh.
57m. and 12h. 49m. The importance formerly attached to
this subject is probably owing to opinions transmitted from
the East, which gained a footing in the Roman empire un-
der the Caesars, together with a itrong national predilection
for astrology. The leg, or north star of the Great Bear (the
celebrated star of the Bull's leg in the astronomical repre-

* Cosmos, vol. ii., p. 330. t Arago, Annuaire pour 1842, p. 348.

t Struve, Stella comp., p. Lxxxii.

$ Sir John Herschel, Observations at the Cape, p. 17, 102. (" Nebula
and Clusters, No. 3435.")

II Humboldt, Vues des CordUleres et Monument des Peuples Indigenes
de VAmerique, torn, ii., p. 55.

IT Julii Firmici Maierni Astron., libri viii., Basil, 1551, lib. vi., cap
i., p. 150.

SOUTHERN STARS. 137

sentations of Dendera, 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 Plei-
ades are contrasted with " the chambers of the south," and
in which the four quarters of the heavens in like manner are
indicated by these four groups.*

"While a large and splendid portion of the southern heav-
ens beyond stars having 53° S. Decl. were unknown in an-
cient times, and even in the earlier part of the Middle Ages,
the knowledge of the southern hemisphere was gradually
completed about a century before the invention and appli-
cation 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 Cen-
taur, and, according to Pliny, also called Ccesaris Thronus,
in honor of Augustus,! and Canopus (Canobus) in Argo,
which is called Ptolemceon by the scholiast to Germanicus.J

* Lepsius, Chronol. der ^Egypter, 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 Septua-
gint ^ives : 6 iroiuv 'EAetd<5a /cat 'Ecmepov Kal 'ApKrovpov /cat ra^eta
vorov.

The early English translators, like the Germans and Dutch, under-
go >d 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.)

t Ideler, Sternnamen, s. 295.

t Martianus Capella changes Ptolemceon into Ptolemceus; 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), Canopus ingens et niger of the Latin translation ; most
probably one of the black coal-sacks. (Humboldt, Examen Crit. de
la Geogr., torn, v., p. 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. Catharine,
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 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 northwest to the coun
tries 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 toward Ceylon. In accordance with ancient practice,
they combined these stars into new constellations. A bold fiction rep-
resented the later-seen stars as having been subsequently created by
the miraculous power of Visvamitra, who threatened " the ancient gods
that he would overcome the northern hemisphere with his more richly-

138 COSMOS.

In the catalogue of the Almagest, Achernar, a star of the
first magnitude, the last in Eridanus (Achir el-nahr, in
Arabic), is also given, although it was 9° below the hori-
zon. A report of the 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 be-
tween Ocelis and the Malabar emporium, Muziris.* Though
improvements in the art of navigation led Diego Cam, to-
gether with Martin Behaim, along the western coasts of Af-
rica, as early as 1484, and carried Bartholomew 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 large 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 Mediterranean," be-
long to the epoch of Vicente Yanez Pinzon, Amerigo Ves-
pucci, and Andrea Corsali, between 1500 and 1515. The
distances of the stars of the southern hemisphere were meas-
ured at the close of the sixteenth and the beginning of the
seventeenth century. t

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

starred southern hemisphere." (A. W. von Schlegel, in the Zeilschrift
fur die Kunde des Morgcnlandes, bd. i., B. 240.) While this Indian
myth figuratively depicts the astonishment excited in wandering na-
' , by the aspect of i

tions by the aspect of a new heaven (as the celebrated Spanish poet,
Garcilaso de la Vega, says of travelers, " they change at once their coun-
try and stars," mttdan de pays y de estrellas), we are powerfully re-
minded of the impression that must have been excited, even in the
rudest nations, when, at a certain part of the earth's surface, they ob-
served large, hitherto unseen stars appear in the horizon, as those in
the feet of the Centaur, in the Southern Cross, in Eridauus or in Argo,
while those with which they had been long familiar at home wholly
disappeared. The fixed stars advance toward 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
Cosmog, vol. i., p. 149, and vol. ii., p. 282.) " Cauopus, 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
a distance of 1° more to bring it within the limits of visibility for our
horizon." * Cosmos, vol. ii., p. 571, 572.

t Olbers, in Schumacher's Jahrb.f&r 1840, s.249, and Cosmos, vol. i.,
p. 51.

DISTRIBUTION OF STARS. 139

at different heights and in various directions over the field
of view, of 15' in diameter, of his twenty-feet reflecting tel-
escope. Frequent reference has already been made in the
present work to his laborious process of " gauging the heav-
ens." The field of view each time embraced only ^^TV^?tn
of the whole heavens ; and it would therefore require, ac-
cording to Struve, eighty-three years to gauge the whole
sphere by a similar process.* In investigations of the par-
tial distribution of stars, we must specially consider the class
of magnitude to which they photometrically belong. If we
limit our attention to the bright stars of the first three or
four classes of magnitudes, we shall find them distributed on
the whole with tolerable uniformity, t although in the south-
ern 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
travelers on the relative beauty of the northern and south-
ern 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 por-
tion of the constellations culminate in the daytime. It fol-
lows, from the gaugings of the two Herschels in the north-
ern and southern hemispheres, that the fixed stars from the
fifth and sixth to the tenth and fifteenth magnitudes (par-
ticularly, therefore, telescopic stars) increase regularly in
density as we approach the galactic circle (6 yaAafmf KV-
/cAof) ; 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 increases in all directions, at first slowly, and then rap-
idly, 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 tunes (nearly 30 times) as many stars in the
center of the Milky Way as in regions surrounding the ga-
lactic poles. In northern galactic polar distances of 0°, 30°,
60°, 75°, and 90°, the relative numbers of the stars in a tel-
escopic field of vision of 15' diameter are 4-15, 6-52, 17'68,
30-30, and 122-00. Notwithstanding the great similarity
in the law of increase in the abundance of the stars, we
again find in the comparison of these zones an absolute pre-

* Etudes tfAstr. Stellaire, note 74, p. 31.
t Outlines of Astr., § 785

140 COSMOS.

ponderance* on the side of the more beautiful southern
heavens.

When in 1843 I requested Captain Schwinck (of the En-
gineers) to communicate to me the distribution according to
right ascension of the 12,148 stars (from the first to the sev-
enth inclusive), which, at Bessel's suggestion, he had noted
in his Mappa Caslestis, he found in four groups —
Right Ascension, 50° to 140° 3147 stars.
140° 230° 2627 "
230° 320° 3523 "
320° 50° 2851 "

These groups correspond with the more exact results of the
Etudes Stellaires, according to which the maxima of stars
of the first to the ninth magnitude occur in the right ascen-
sion 6h. 40m. and. I8h. 40m., and the minima in the right
ascension of Ih. 30m. and 13h. 30m. t

It is essential that, in reference to the conjectural struc-
ture 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 dusters or swarms, which
frequently contain thousands of telescopic stars in recogniza-
ble relations to each other, and which appear to the unaided
eye as round nebulae, shining like comets. These are, the
nebulous stars of EratosthenesJ and Ptolemy, the nebulosce
of the Alphonsine Tables in 1483, and the same of which
Galileo said in the Nuncius Sidereus, " Sicut areolee spar-
sim per sethera 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
clusters, and the most important in reference to the config-
uration of the galactic circle, occurs in a region of the south-
ern heavens^ between Corona Australis, Sagittarius, the

* Op. cit., § 795, 796 ; Struve, Eludes cTAstr. Stell., p. 66, 73 (and
note 75).

t Struve, p. 59. Schwinck finds in his maps, R. A. 0°-90°, 2858
stars; R. A. 9QO-1800, 3011 stars; R. A. 180°-270°, 2688 stars; R. A
270°-360°, 3591 stars ; sura total, 12,148 stars to the seventh magnitude

t On the nebula in the right hand of Perseus (near the hilt of his
sword), see Eratosth., Catant., c. 22, p. 51, Schaubach.

$ John Herschel's Observations at the Cape, $ 105, p. 136.

CLUSTERS OF STARS. 141

tail of Scorpio, and the Altar (R. A. 16h. 45m.-l9h.). 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 center. In many globular
clusters the stars are uniform in magnitude, in others they
vary. In some few cases they exhibit a fine reddish cen-
tral star* (R. A. 2h. 10m. ; N Decl. 56° 21'). It is a dif-
ficult problem in dynamics to understand how such island-
worlds, with their multitude of suns, can rotate free and un
disturbed. Nebulous spots and clusters of stars appear sub-
ject 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 heav-
ens." It is, moreover, worthy of notice, that, with an in-
strument of equal aperture and magnifying power, round
nebulous spots are more easily resolved into clusters of stars
than oval ones.f

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, and rov
rrAetv (from TrAetv, 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 rrAeof,
plenty. The navigation of the Mediterranean lasted from
May to the beginning of November, from the early rising to
the early setting of the Pbiades.

Prsesepe in Cancer : according to Pliny, nubecula quam
Prczsepia vacant inter Asellos, a ve</>eA*ov of the Pseudo^
Eratosthenes.

The cluster of stars on the sword-hilt of Perseus, frequent-
ly 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. I3h. 34m. 12s., N. Decl. 29° 14' ; more than a thousand
stars from the tenth to the twelfth magnitude.

Cluster of stars between 77 and £ Herculis, visible to the
naked eye in clear nights. A magnificent object in the tel-
escope (No. 1968), with a singular radiating margin ; R. A.

» Outlines, $ 864-869, p. 591-596; Madler's Astr., s. 764.
t Observation at the Cape, $ 29, p. 19.

142 COSMOS.

16h. 35m. 37s., N. Dccl. 36° 47' ; first described by Halley
in 1714.

A cluster of stars near w 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 fourth or fifth magni-
tude ; in powerful instruments it appears composed of count-
less stars of the thirteenth to the fifteenth magnitude, crowd-
ed together and most dense toward the center; R. A. 13h.
16m. 38s., S. Decl. 46° 35' ; No. 3504 in Sir John Herschel's
catalogue of the clusters of the southern hemisphere, 15' in
diameter. (Observations at the Cape, p. 21, 105 ; Outlines
ofAstr., p. 595.)

Cluster of stars near K of the Southern Cross (No. 3435),
composed of many-colored small stars from the twelfth to the
sixteenth magnitude, distributed over an area of Jj-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, p. 17, 102, pi. i., 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 sev-
eral evenings, imagining it to be a comet, when, on my ar-
rival at Peru, I saw it in 12° south lat. rise high above the
horizon. The visibility of this cluster to the naked eye is in-
creased by the circumstance that, although in the vicinity
of the lesser Magellanic cloud, it is situated in a part of the
heavens containing no stars, and is from 15' to 20' in diam-
eter. It is of a pale rose color in the interior, concentrically
inclosed by a white margin composed of small stars (four-
teenth to sixteenth magnitude) of about the same magnitude,
and presenting all the characteristics of the globular form.*

A cluster of stars in Andromeda's girdle, near v of this con-
stellation. The resolution of this celebrated nebula into small
stars, upward of 1500 of which have been vecognized, apper-
tains to the most remarkable discoveries in the observing as-
tronomy of the present day. The merit of this discovery is due
to Mr. George Bond, assistant astronomerf at the Observatory

* " A stupendous object — a most magnificent glolular cluster," says
Sir John Herschel, " completely insulated, upon a ground of the sky per-
fectly black throughout the whole breadth of the sweep." — Observations
at the Cape, p. 18 and 51, PI. iii., fig. 1 ; Outlines, $ 895, p. 615.

t Bond, in the Memoirs of the American Academy of Arts and Sciences,
iiew series, vol. iii., p. 75.

CLUSTERS 9F STARS. 143

of Cambridge, United States (March, 1848), and testifies to
the admirable illuminating power of the refractor of that Ob-
servatory, which has an object-glass fifteen inches in diam-
eter ; since even a reflector with a speculum of eighteen inch
es in diameter did not reveal " a trace of the presence of a
star."* Although it is probable that the cluster in Adrom-
eda was, at the close of the tenth century, already recorded
as a nebula of oval form, it is more certain that Simon Ma-
rius (Mayer of Guntzenhausen), the same who first observed
the change of color in scintillation,! perceived it on the 1 5th
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, Bouil-
laud, the author of Astronomia Philolaica, occupied himself
with the same subject. This cluster of stars, which is 2^-°
in length and more than 1° in breath, is specially distinguish-
ed by two remarkable very narrow black streaks, parallel to
each other, and to the longer axis of the cluster, which, ac-
cording to Bond's investigations, traverse the whole length
like fissures. This configuration vividly reminds us of the
singular longitudinal fissure in an unresolved nebula of the
southern hemisphere, No. 3501, which has been described
and figured by Sir John Herschel. (Observations at the
Cape, p. 20, 105, pi. 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 Orion's belt in this selection
of remarkable clusters of stars, as it appeared to me more ap-
propriate to consider those portions of it which have been re-
solved in the section on Nebulae.

The greatest accumulation of clusters of stars, although
by no means of nebulas, occurs in the Milky WayJ (Galaxias,

* Outlines, $ 874, p. 601.

t Delambre, Hist, de VAstr. Moderne, t. i., p. 697.

t We are indebted for the first and only complete description 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
Cosmos which treats of the directions, ramifications, and various con-
tents of the Milky Way, I have exclusively followed the above-named
astronomer and physicist. (Compare also Struve, Etudes d'Astr. Stel-
laire, p. 35-79 ; Madler, Ast., 1849, § 213 ; Cosmos, vol. i., p. 103, 150.)
I need scarcely here remark that in my description of the Milky Way,
in order not to confuse certainties with uncertainties, I have not refer-
red to what I had myself observed with instruments of a very inferior

144 COSMOS.

the celestial river of the Arabs*), which forms almost a great
circle of the sphere, and is inclined to the equator at an an-
gle of 63°. 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 Phoenix and Cetus.
While all planetary local relations are referred to the eclip-
tic— the great circle in which the plane of the sun's path in-
tersects 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 world
of our solar system. The Milky Way cuts the equator in
Monoceros, between Procyon and Sinus, R. A. Gh. 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.f 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, be-
tween 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

illuminating power, in reference to the very great inequality of the
light of the whole zone, during my long residence iu the southern hem-
isphere, 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 constellation 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. (Ide-
ler, Untersuchungen uber den Ursprung und die Dedeutung der Sternna*
men, § 78, 183, and 187 ; Niebuhr, Beschreibung von Arabien, e. 112.)

t Outlines, p. 529; Schubert, Ast., th. iii., s. 71.

t Struve, Etudes d'Astr. Stellaire, p. 41.

$ Cosmos, vol. L, p. 150.

MILKY WAY. 145

be ascribed to irresolvable nebulosity. A more careful ap-
plication of reflecting telescopes of great dimensions and pow-
er of light has since proved, with more certainty, the cor
rectness of the conjectures advanced by Democritus and Ma-
nilius, in reference to the ancient path of Phaeton, that this
milky glimmering light was solely owing to the accumu
lated strata of small stars, and not to the scantily inter
spersed nebulae. 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 nebulous vapor.* It is a remarkable feature of
the Milky "Way that it should so rarely exhibit any globular
clusters and nebulous spots of a regular or oval form ;t 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 condensa-
tion, and nebulous spots of a definite oval or a wholly irreg-
ular form, are intermingled. A remarkable exception to
the rarity of globular clusters in the Milky Way occurs in a
region between R. A. 16h. 45m. and 18h. 44m., between the
Altar, the Southern Crown, the head and body of Sagitta-
rius, and the tail of the Scorpion.^ We even find between
£ and 6 of the latter one of those annular nebulae, which are
of such extremely rare occurrence in the southern hemi-
sphere.

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

* "Stars standing on a clear black ground." (Observations at the
Cape, p. 391.) " This remarkable belt (the Milky Way, when exam-
ined through powerful telescopes) is found (wonderful to relate !) to
consist entirely of stars scattered by millions, like glittering dust on the
)lack ground of the general heavens." — Outlines, p. 182, 537, and 539.

t " Globular clusters, excepting in one region of small extent (be-
tween 16h. 45m. and 19h. in R. A.), and pebulce of regular elliptic
forms, are comparatively rare in the Milky Way, and are found con-
gregated in the greatest abundance in a part of the heavens the most
remote possible from that circle." (Outlines, p. 614.) Huygens him-
self, 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 th 3 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 in vol. h., p. 330, 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 Hugenii Opera varia, 1724, p. 540.

t Observations at the Cape, $ 105, 107, and 328. On the annular nel>
ulsB, No. 3686, see p. 114.

VOL. Ill— ?

146 . COSMOS.

Herschel, a twenty-feet instrument penetrates 900, and a
forty-feet one 2800 distances of Sinus), the Milky Way ap-
pears as diversified in its sidereal contents as it is irregular
and indefinite in its outlines and limits when seen by the
unaided 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 in-
terrupted by granular or reticular darker* intervals contain-
ing but few stars ; and in some of these intervals in the in-
terior 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 oc-
cur in the midst of the most minute telescopic stars, while
all the intermediate classes are absent. Perhaps those stars
which we regard as belonging to the lowest order of mag-
nitudes do not always appear as such, solely on account of
their enormous distance, but also because they actually have
a smaller volume and less considerable development of light.
In order rightly to comprehend the contrast presented by
the greater brilliancy, abundance, or paucity of stars, it will
be necessary to compare regions most widely separated from
each other. The maximum of the accumulation and the
greatest luster 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 Sagit-
tarius, and the right foot of Ophiuchus. " No region of the
heavens is fuller of objects, beautiful and remarkable in
themselves, and rendered still more so by their mode of as-
sociation" and grouping. t Next in brightness to this por-

* " Intervals absolutely dark and completely void of any ttar of the
smallest telescopic magnitude." — Outlines, p. 536.

t " No region of the heavens is fuller of objects, beautiful and re-
markable in themselves, and rendered still more so by their mode of
association, and by the peculiar features assumed by the Milky Way,
which are without a parallel in any other part of its course."— '•Observ-
ations at the Cape, p. 386. This vivid description of Sir John Hersche]
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, remarks
with striking truth, " Such is the general blaze of starlight near the
Cross from that part of the sky, that a person is immediately made

MILKY WAY. 147

tion of the southern heavens is the pleasing and richly-star-
red region of our northern hemisphere in Aquila and Cyg-
nus, where the Milky Way branches off in different direc-
tions. 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 naighborhood of Monoceros and Perseus.

The magnificent effulgence of the Milky Way in the south-
ern hemisphere is still further increased by the circumstance
that between the star r\ Argus, which has become so cele-
brated in consequence of its variability, and a Crucis, undei
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 constella-
tions Orion, Canis Major, Scorpio, Centaurus, and the South-
ern Cross. The direction of this remarkable zone is indi-
cated by a great circle passing through e Orionis and the
foot of the Cross. The picturesque 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. According to Sir John Herschel's
observations, the branches separate in the great bifurcation
at a Centauri,* and not at )3 Cent., as given in our maps of
the stars, or, as was asserted by Ptolemy,t in the constella-
tion 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 e Cassiopeiae, the
Milky Way sends forth toward e 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 e, £, rj, the Hsedi of
that constellation, preceding Capell a, between the feet of Gem-
ini and the horns of the Bull (where it intersects the eclip-

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 atmosphere, resembling the effect of the young moon." (See
Piazzi Smyth, On the Orbit of a Centauri, in the Transact, of the Royal
Soc. of Edinburgh, vol. xvi., p. 445.)

* Outlines, $ 789. 791 ; Observations at the Cape, $ 325.

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

148 COSMOS.

tic 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 Argus, 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 Argus. It begins again in a similar
fan-like expansion, but contracts at the hind feet of the Cen-
taur and before its entrance into the Southern Cross, where
it is at its narrowest part, and is only 3° or 4° in width.
Soon after this the Milky Way again expands into a bright
and broad mass, which incloses /3 Centauri as well as o and
ft Crucis, and in the midst of which lies the black pear-
shaped coal-sack, to which I shall more specially refer in the
seventh 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
northward in the direction of the constellation Lupus, where
it seems gradually lost ; a division next shows itself at y
Normse. 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 Scorpion, in the direction of the bow of Sagittarius,
where it intersects the ecliptic in 276° long. It next runs
in an irregular patchy and winding stream through Aquila,
Sagitta, and Vulpecula up to Cygnus ; between e, a, and y,
of which constellation a broad dark vacuity appears, which,
as Sir John Herschel says, is not unlike the southern coal-
sack, and serves as a kind of center for the divergence of
three great streams.* One of these, which is very vivid and
conspicuous, may be traced running backward, as it were,
through j3 Cygni and f Aquilae, without, however, blending
with the stream already noticed, which extends to the foot
of Ophiuchus. A considerable offset or protuberant append-
age is also thrown off by the northern stream from the head

* Outlines, p. 531. The strikingly dark spot between a and y Cas-
siopeia; is also ascribed to the contrast with the brightness by which it
is surrounded. See Struve, Eludes Stell., note 58.

MILKY WAY. 149

of Cepheus, and therefore near Cassiopeia (from which con-
stellation we began our description of the Milky Way), to-
ward Ursa Minor and the pole.

From the extraordinary advancement which the applica-
tion of large telescopes has gradually effected in our knowl
edge of the sidereal contents and of the differences in the
concentration 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 Wilky 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 hy-
pothesis 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 favor 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 favored 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 undoubt-
edly situated at very differentjiltitudes, i. e., at very unequal
distances from us ; but the relative brightness of the sep-
arate stars which we estimate as of the tenth to the six-
teenth magnitude, can not be regarded as affording sufficient
data to enable us in a satisfactory manner to deduce numer-
ically 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 points projected
on the dark, starless ground of the heavens. We here act-

* 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 Philot. Magazine, ser. iii., No. 32. Thomas Wright, to whose
researches the attention of astronomers has been so permanently di
reeled since the beginning of the present century, through the ingen
ions speculations of Kant and William Herschel, observed only with a
reflector of one foot focal length.

t Pfaff, in Will. HertchePi sdmmtl. Schriften, bd. i. (1826), a. 78-8l ;
Struve, Etvdet Stell., p. 35-44.

$ Encke, in Schumacher's Attr. Nochr., No. 622, 1847 « 341-34C

150 COSMOS.

ually look through as into free space. " It leads us," says
Sir John Herschel, " irresistibly to the conclusion that in
these regions we see fairly through the starry stratum."*
In other regions we see, as it were, through openings and
fissures, remote world-islands, or outhranching portions of the
annular system ; in other parts, again, the Milky Way has
hitherto been, fathomless, even with the forty-feet telescope. f
Investigations on the different intensity of light in the Milky
Way, as well as on the magnitudes of the stars, which regu-
larly increase in number from the galactic poles to the circle
itself (an increase especially observable for 30° on either side
of the Milky Way in stars below the eleventh magnitude, J
and therefore in |^ths of all the stars), have led the most
recent investigator of the southern hemisphere to remarkable
views and probable results in reference to the form of the
galactic annular system, and what has been boldly called
the sun'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 two sheets, § in one of those desert re-
gions lying nearer to the Southern Cross than to the oppo-
site node of the Milky Way.ll "The depth at which our
system is plunged in the sidereal stratum constituting the
galaxy, reckoning from the southern surface or limit of that

* Outlines, p. 536, 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."

t Struve, Etudes Stell., p. 63. Sometimes the largest instruments
reach a portion of the heavens, in which the existence of a starry stra-
tum, shining at a remote distance, is only announced by " a 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 tele-
scopic branches of the Milky Way, or of an independent sidereal sys-
tem or systems bearing a resemblance to such branches."

t Observations at the Cape, § 314.

$ 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, p. 267-271.

|| " I 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 stra-
tum, 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 eccen-
trically, so as to be much nearer to the region about the Cross than to
that diametrically opposite to it." (Mary Somerville, On the Connec-
*ion of the Physical Sciences, 1846, p. 419.)

NEW STARS. 151

stratum, is about equal to that distance which, on a general
average, corresponds to the light of a star of the ninth or
tenth magnitude, and certainly does not exceed that corre
spending to the eleventh."* Where, from the peculiar nature
of individual problems, measurements and the direct evi-
dence 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.

IV.

NEW STARS AND STARS THAT HAVE VANISHED.— VARIABLE STARS,
WHOSE RECURRING PERIODS HAVE BEEN DETERMINED.— VARIA-
TIONS IN THE INTENSITY OF THE LIGHT OF STARS WHOSE PERI-
ODICITY IS AS YET UNINVESTIGATED.

NEW STARS. — 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 oc-
currence in the realms of space which has ever excited as-
tonishment. This astonishment is the greater, in proportion
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 phenomena 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 becomes 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 visi-
ble comets is estimated at about sixty-three, while that of
new stars does not amount to more than nine. Consequent-
ly, 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 to seven. We shall pres-
ently show that if from the tailless comets we separate the
new stars which, according to the records of Ma-tuan-lin,
* Observations at the Cape, $ 315.

152 COSMOS.

have been observed in China, and go back to the middle o"
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 Germa-
ny," says Tycho Brahe, " I resided for some time with my
uncle, Steno Bille (ut aulicse vitae fastidium lenirem), in the
old and pleasantly situated monastery of Herritzwadt ; and
here I made it a practice not to leave my chemical labora-
tory until the evening. Raising my eyes, as usual, during
one of my walks, to the well-known vault of heaven, I ob-
served, with indescribable astonishment, near the zenith, in
Cassiopeia, a radiant fixed star, of a magnitude never be-
fore seen. In my amazement, I doubted the evidence of my
senses. However, to convince myself that it was no illusion,
and to have the testimony of others, I summoned my assist-
ants from the laboratory, 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. I subsequently
heard that, in Germany, wagoners and other common peo-
ple first called the attention of astronomers to this great phe-
nomenon 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
without a tail, not surrounded by any nebula, and perfectly
like all other fixed stars, with the exception that it scintil-
lated more strongly than stars of the first magnitude. Its
brightness was greater than that of Sirius, a Lyrse, or Jupi-
ter. For splendor, it was only comparable to Venus when
nearest to the earth (that is, when only a quarter of her
disk is illuminated). Those gifted with keen sight could,
when the air was clear, discern the new star in the daytime,
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 admo-
dum densas). Its distances from the nearest stars of Cassi-
opeia, which, throughout the whole of the following year, I
measured with great care, convinced me of its perfect immo-
bility. Already, in December, 1572, its brilliancy began to

NiJW STARS. 153

diminish, and the star gradually resettled Jupiter ; but by
January, 1573, it had become less bright than that planet.
Successive photometric estimates gave the following results :
for February and March, equality with stars of the first mag-
nitude (stellarum affixarum primi honoris — for Tycho Brahe
seems to have disliked using Manilius's expression of stellse
fixae) ; for April and May, with stars of the second magni-
tude ; for July and August, with those of the third ; for Oc-
tober and November, those of the fourth magnitude. To-
ward the month of November, the new star was not bright-
er 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 fol-
lowing 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 afterward.)

The gradual diminution of the star's luminosity was, more-
over, invariably regular ; it was not (as is the case in the
present day with 77 Argus, though indeed that is not to be
called a new star) interrupted by several periods of rekind-
ling or by increased intensity of light. Its color also changed
with its brightness (a fact which subsequently gave rise to
many erroneous conclusions as to the velocity of colored 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 ; afterward he thought that it nearly resembled Be-
telgeux, the star in the right shoulder of Orion. Its color,
for the most part, was like the red tint of Aldebaran. In
the spring of 1573, and especially in May, its white color re-
turned (albedinem quandam sublividam induebat, qualis Sa-
turni stellse subesse videtur). So it remained 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 faintness.

The circumstantial minuteness of these statements* is of

* De admiranda Nova Stella, anno 1572, exorta in, Tychonis Brahe
AttronomicE instauratce Progymnatmata, 1603, p. 298-304, and 578. In
the text I have closely followed the account which Tycho Brahe him-
self gives. The very doubtful statement (which is, however, repeated
in several astronomical treatises) that his attention was first called to

154 COSMOS.

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 astronomy.
For (notwithstanding the general rarity of the appearance of
new stars) similar phenomena, accidentally crowded togeth-
er within the short space of thirty-two years, were thrice re-
peated within the observation of European astronomers, and
consequently served to heighten the excitement. The im-
portance of star catalogues, for ascertaining the date of the
sudden appearance of any star, was more and more recog-
nized ; the periodicity* (their reappearance after many cen-
turies) was discussed ; and Tycho Brahe himself boldly ad-
vanced a theory of the process by which stars might be
formed and molded out of cosmical vapor, which presents
many points of resemblance to that of the great William
Herschel. He was of opinion that the vapory celestial mat-
ter, which becomes luminous as it condenses, conglomerates
into fixed stars : " Coeli materiam tenuissimam, ubique nostro
visui et planetarum circuitibus perviam, in unum globum con-
densatam, 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 brightness. Accordingly, the
place of the new star, as well as of those which became sud-
denly visible in 945 and 1264, was on the very edge of the
Milky Way (quo factum est quod nova stella in ipso galaxise
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.f All this reminds one of the theories of

the phenomenon of the new star by a concourse of country people,
need not, therefore, be here noticed.

* 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 Kep-
ler on the appearance of the new star in Ophiucus in 1604, supposes
that the star of the Magi, through a confusion of atnrjp with uarpnv,
which is so frequent, was not a single great star, but a remarkable con-
junction of stars — the close approximation of two brightly-shining plan-
ets at a distance of less than a diameter of the moon. — Tychonis Pro-
gymnasmata, p. 324-330; contrast with Ideler, Handbuch der Malhe-
matischen nnd Technischen Chronologic, bd. ii., s. 399-407.

t Progymn., p. 324-330. Tycho Brahe, in his theory of the forma-
tion of new stars from the Cosmical vapor of the Milky Way, builds
much on the remarkable passages of Aristotle on the connection of the

TEMPORARY STARS.

155

transition of the cosmical vapor into clusters 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 century, but which at pres-
ent, 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.

(b) 123 A.D.

.... in Ophiuchus.

(c) 173 "

.... in Centaurus

(d) 369 "

7

(e) 386 "

.... in Sagittarius.

[f) 389 "

. in Aquila.

(s\ 393 "

in Scorpio.

\O /

ft) 827 "

in Scorpio.

(i) 945 «

.... between Cepheus and Cassiopeia.

A) 1012 "

in Aries.

Z) 1203

'

in Scorpio.

m) 1230

•

in Ophiuchus.

n) 1264

•

between Cepheus and Cassiopeia.

(o) 1572

1

in Cassiopeia.

(p) 1578

•

(o) 1584

'

in Scorpio.

r) 1600

'

in Cygnus.

s) 1604
t) 1609

'

in Ophiuchus.

u) 1670

•

in Vulpes.

v) 1848 '

in Ophiuchus.

EXPLANATORY REMARKS.

(<z) This star first appeared in July, 134 years before our era. We
have taken it from the Chinese Records of Ma-tuan-lin, for the transla-
tion of which we are indebted to the learned linguist Edward Biot
( Connaistance des Temps pour Van 1846, p. 6 1). Its place was between
P and p of Scorpio. Among the extraordinary foreign-looking stars of
these records, called also guest-stars (etoiles hdtes, " Ke-sing," strangers
of a singular aspect), which are distinguished by the observers from
comets with tails, fixed new stars and advancing tailless comets are cer-
tainly sometimes mixed up. But in the record of their motion (Ke-sing

tails of comets (the vapory radiation from their nuclei) with the galaxy
to which I have already alluded. (Cotmos, vol. i., p. 103.)

156 COSMOS.

of 1092, 1181, and 1458), and in the absence of any si ch 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 nucleus of all comets, wheth-
er with or without tails, is dull, never scintillates, and exhibits only a
mild radiance, while the luminous intensity of what the Chinese call
extraordinary (stranger) stars has been compared to that of Venus — a
circumstance totally at variance with the nature of .comets in general,
and especially of those without 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 state-
ment of Pliny, induced him to commence his catalogue of the stars.
Delambre twice calls this statement a fiction, " une historiette." (Hist,
de VAstr. Anc., torn, i., p. 290; and Hist, de VAstr. Mod., torn, i., p. 186.)
Since, according to the express statement of Ptolemy (Almag., vii., p. 2,
13, Halmd), the catalogue of Hipparchus belongs to the year 128 B.C.,
and Hipparchus (as I have already remarked elsewhere) carried on his
observations in Rhodes (and perhaps also in Alexandria) from 162 to
127 B.C., there is nothing irreconcilable with this conjecture. It is very
probable that the great Nicean astronomer had pursued his observations
For a considerable period before he conceived the idea of forming a reg-
ular catalogue. The words of Pliny, " suo sevo 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., p. 319-325). The words " ejus-
que motn addubitationem adcluctus" may undoubtedly lead to the sup-
position of a faint, or altogether tailless comet; but Pliny's rhetorical
style admitted of such vagueness of expression.

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

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

Jt appeared on the 10th of December, 173, between a and /? Centauri
and at the end of eight months disappeared, after exhibiting the five
colors one after another. " Successivement" is the term employed by
Ed. Biot in his translation. Such an expression would almost tend to
suggest a series of colors similar to those in the above-described star
of Tycho Brahe ; but Sir John Herschel more correctly takes it to mean
a colored scintillation (Ozttlines, 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 <j> Sagittarii. In the Chinese Record it is expressly
observed, " where the star remained (i. e., without movement) from
April to July, 386.

(/) A new star, close to a Aquilso. In the year 389, in the reign of
the Emperor Honorius, it shone forth with the brilliancy of Venus, ac-
cording to the statement of Cuspinianus, who had himself seen it. It
totally disappeared in about three weeks.*

* Other accounts place the appearance in the year 388 or 398
Jacques Cassini, Element d'Astronomie, 1740 (Etottes Nouvelles), p. 59.

TEMPORARY STARS. 157

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

(h) 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
Calif Al-Mamun, the two famous Arabian astronomers, Haly and Gia-
far Ben Mohammed Albumazar, observed at Babylon a new star, whose
light, according to their report, "equaled that of the moon in her quar-
ters." This natural phenomenon likewise occurred in Scorpio. The
atar disappeared after a period of four months.

(t) 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 Leovi-
tius, 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 con-
stellations of Cepheus and Cassiopeia, close to the Milky Way, and near
the spot where Tycho Brahe's star appeared in 1572. Tycho Brahe
(Progym., p. 331 and 709) defends the credibility of Cyprianus Leovi-
tius against the attacks of Pontanus and Camerarius, who conjectured
that the statements arose from a confusion of new stars with long-tailed
comets.

(&) According to the statement of Hepidannus, the monk of St. Gall
(who died A.D. 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 insolitae magnitudinis,
aspectu fulgurans et oculos verberans non sine terrore. Qua? mirum in
modum aliquando contractior, aliquando diffusior, etiam extinguebatur
interdum. Visa est autem per tres menses in intimis finibus Austri, ul-
tra omnia signa qute videntur in ccelo." (See Hepidanni, Annales bre-
ves, in Duchesne, Histories Francorum Scriptores, t. iii., 1641, p. 477.
Compare also Schnurrer, Chronik der Seuchen, th. i., s. 201.) To the
manuscript made use of by Duchesne and Goldast, which assigns the
phenomenon to the year 1012, modern historical criticism has, howev-
er, 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 Annales San-
gallenses majores, in Pertz, Afonumenta Germanise historica Scriptorum,
t. i., 1826, p. 81.) Even the authenticity of the writings of Hepidannus
has been called into question by modern critics. The singular phenom-
enon of variability has been termed by Chladni the conflagration and
extinction of a fixed star. Hind (Notices of the Asfron. 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 a and <p 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.

(A Toward the end of July, 1203, in the tail of Scorpio. According
to the Chinese Record, this new star was "of a bluish-white color,
without luminous vapor, and resembled Saturn." (Edouard Biot, in the
Connaissance des Temps pour 1846, p. 68.)

(TO) Another Chinese observation, from Ma-tuan-lin, whose astronom-
ical records, containing an accurate account of the positions «f comet*

158 COSMOS.

and fixed stars, go back to the year 613 B.C., to the times of Thalea
and the expedition of Golaeus of Samoa. This new star appeared in the
middle of December, 1230, between Ophiuchus and the Serpent. It
dissolved toward the end of March, 1231.

(») This is the star mentioned by the Bohemian astronomer, Gypri-
anus Leovitius (and referred to under the ninth star, in the year 945).
About the same time (July, 1264), a great comet appeared, whose tail
swept over one half of the heavens, and which, therefore, could not be
mistaken for a new star suddenly appearing between Cepheus and Gas-
siopeia.

(o) This is Tycho Brahe's star of the llth 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 constellation ia
not given, but the intensity and radiation of the light must have been
extraordinary, since the Chinese Record appends the remark, " a star
as large as the sun !"

(?) On the 1st of July, 1584, not far from TT 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 celes-
tial globe testifies, to draw attention 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 ob-
serve it till two years later, and, indeed (what is the more surprising,
since the star was of the third magnitude), then first heard of its exist-
ence. He thus writes : " Cum mense Maio, anni 1602, primum litteris
monerer de novo Cygni phffinomeno." (Kepler, De Stella Nova tertii

honoris in Cygno, 1606, which is appended to the work De Stella Nova
in Serpent., p. 152, 154, 164, and 167.) In Kepler's treatise it is no-
where said (as we often find asserted in modern works) that this star

of Cygnus upon its first appearance was of the first magnitude. Kep-
ler even calls it " parva Cygni stella," and speaks of it throughout as
one of the third magnitude. He determines its position in R. A. 300°
46' ; Decl. 36° 52' (therefore for 1800 : R. A. 302° 36' ; Decl. -f 37° 27').
The star decreased in brilliancy, especially after the year 1619, and van-
ished in 1621. Dominique Cassini (see Jacques Cassini, Ellmens d'Astr.,
p. 69) saw it, in 1655, again attain to the third magnitude, and then dis-
appear. Hevelius observed it again in November, 1665, at first ex-
tremely small, then larger, but never attaining to the third magnitude.
Between 1677 and 1682 it decreased to the sixth 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.

(«) 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 1 Oth
of October, 1604, not by Kepler himself, but by his pupil, the Bohemian
astronomer, John Bronowski. It was larger than all stars of the first
order, greater than Jupiter and Saturn, but smaller than Venus. Her-
licias 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 daytime. But its scintillation was considerably greater, and espe-

TEMPORARY STARS. 159

cially excited the astonishment of all who saw it. As scintillation is
always accompanied with dispersion of color, much has been said of
its colored and continually-changing light. Arago (Annuaire pour 1834,
p. 209-301, and Ann. pour 1842, p. 345-347) has already called atten-
tion to the fact that the star of Kepler did not by any means, like that
of Tycho Brahe, assume, at certain long intervals, different colors, 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 colors of the rainbow, it is to convey a clear
idea of its colored scintillation. His words are: " Exemplo adamantis
multanguli, qui solis radios inter convertendum ad spectantium oculos
variabili fulgore revibraret, colores Iridis (stella nova in Ophiucho) sue-
sessive vibratu continue reciprocabat." (De Nova Stella Serpent., p. 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 being of the third magnitude. Its
proximity to the sun prevented all observation for four months. Be-
tween February and March, 1606, it totally disappeared. The inaccu-
rate 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, Elemens d'Astr., p. 65, long since observed) deserv-
ing 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 of
September, 1604, there was seen in China a reddish-yellow (" ball-
like?") star, not far from TT of Scorpio. It shone in the southwest till
November of the same year, when it became invisible. It reappeared
on the 14th of January, 16t)5, in the southeast; but its light became
slightly duller by March, 1606. (Connaissance des Temps pour 1846,
p. 59.) The locality, TT of the Scorpion, might easily be confounded
with the foot of Ophiuchus ; but the expressions southwest and south-
east, its reappearance, and the circumstance that its ultimate total dis
appearance is not mentioned, leave some doubts as to its identity.

(£) This also is a new star of considerable magnitude, and seen in the
southwest. It is mentioned in Ma-tuau-lin. No further particulars are
recorded.

(M) This is the new star discovered by the Carthusian monk Anthel-
mus on the 20th of June, 1670, in the head of Vulpes (R. A. 294° 27';
Decl. 26° 47'), and not far from /? Cygni. At its first appearance it was
not of the first, but merely of the third magnitude, and on the 10th of
August it diminished to the fifth. It disappeared after three months,
but showed itself again on the 17th of March, 1671, when it was of the
fourth 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 splendor after ten months, but in Februa-
ry, 1672, it was looked for in vain. It did not reappear until the 29th
of March in the same year, and then only as a star of the sixth magni-
tude ; since that time it has never been observed. (Jacques Cassini,
Element d'Astr., p. 69—71.) These phenomena induced Dominique
Cassini to search for stars never before seen (by him !). He main
tained that he had discovered fourteen such stars of the fourth, fifth,
and sixth magnitudes (eight in Cassiopeia, two ir 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

160 COSMOS.

discovered by Maraldi between 1694 and 1709, their existence is more
than questionable, they can not be introduced in our present list.
(Jacques Cassini, Elimens tfAstron., p. 73-77 ; Delambre, Hist, de
VAstr. Mod., t. ii., p. 780.)

(t?) One hundred and seventy-eight years elapsed after the appear-
ance of the new star in Vulpes without a similar phenomenon having
occurred, although in this long interval the heavens were most care-
fully explored, and its stars counted, by the aid of a more diligent use
of telescopes and by comparison with more correct catalogues of the
stars. On the 28. h of April, 1848, at Mr. Bishop's private observatory
(South Villa, Regent's Park), Hind made the important discovery of a
new reddish-yellow star of the fifth 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 po-
sition been demonstrated with greater precision. At the present time
(1850) it is scarcely of the eleventh magnitude, and, according to Lich
tenberger's accurate observations, it will most likely soon disappear.
(Notices of the Astr.Soc.,vo\. viii., p. 146 and 155-158.)

The above list of new stars, which, within the last two
thousand years, have suddenly appeared and again disap-
peared, 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 77 Argus* which suddenly exhib-
it an unusual increase of brilliancy, the variations of which
are still undetermined. All these phenomena are, most prob-
ably, intrinsically related to each other. 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 sixth magnitude, leads us to infer the affinity of the two
first kinds of celestial phenomena. The celebrated star dis-
covered by Tycho Brahe in Cassiopeia in 1572 was consid-
ered, 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 phenom-
ena, 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 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-mag-

* Arago, Annuaire pour 1842, p. 332.

NEW STARS 161

netic 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 regu-
larly or 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, frequent-
ly observed in the formation for several consecutive days,
during perfectly 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 first mag-
nitude, 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 pecul-
iarity, and one well deserving of consideration. Kepler* at-
tached such weight to this criterion, that he refuted the idle
pretension of Antonius Laurentinus Politianus to having seen
tiio 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 lu-
mine 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 first
magnitude ; viz., the star which appeared in Cygnus in
1600, and that in Vulpes in 1670, which were both of the
third, and Hind's ne tar in Ophiuchus in 1848, which is
of the fifth magnitude.

It is much to be regretted, as we have already observed,
that after the invention of the telescope in the long period
of 178 years, only two new stars have been seen, whereas
these phenomena have sometimes occurred in such rapid suc-
cession, that at the end of the fourth century four were ob-
served 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 sev-
enteenth centuries, no less than six were observed within a

* Kepler, De Stella Nova in pede Serp., p. 3.

162 COSMOS.

period of thirty-seven years. Throughout this examination I
have kept in view the Chinese observations 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 probability recorded in the rec-
ords 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 phenomenon which was observed in China
in February, 1578. The difference of longitude (1 14°) could
only, HI 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 phenomena, either upon the earth or in the heav-
ens, is not invariably a proof of their never having taken
place ; and on comparing together the three different cata-
logues which are given in Ma-tuan-lin, we actually find com-
ets (those, for instance, of 1385 and 1495) mentioned in one
but omitted in the others.

Even 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 Eu-
rope and China have appeared in the neighborhood 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, Tycho Brahe's hypothesis, which wo
have already mentioned, of the formation of new, suddenly-
shining fixed stars, by the globular condensation of celestial
vapor, falls at once to the ground. What the influence of
gravitation may be among the crowded strata and clusters
of stars, supposing them to revolve round certain central nu-
clei, 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, 393,
827, 1203, and 158 1) appeared in Scorpio, three in Cassi-
opeia and Cepheus (945, 1264, 1572), and four in Ophiu-
chus (123, 1230, 1604, 1848). Once, however (1012), one
was seen in Aries at a great distance from the Milky Way
(ths star seen by the monk of St. Gall). Kepler himself
who, however, considers as a new star that described by Fa

VANISHED STARS. 163

bricius as suddenly shining in the neck of Cetus in the year
1596, and as disappearing in October of the same year, like-
wise advances this position as a proof to the contrary. (Kep-
ler, De Stella Nova Serp., p. 112.) Is it allowable to in-
fer, from the frequent lighting up of such stars in the same
constellations, that in certain regions of space — those, name-
ly, where Cassiopeia and Scorpio are to be seen — the condi-
tions of their illuminations are favored by certain local re-
lations ? Do such stars as are peculiarly fitted for the ex-
plosive temporary processes of light especially lie in those
directions ?

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
third magnitude, as at its first appearance, and afterward
dwindled down to the sixth magnitude, without, however
(according to Argelander's observations), being entitled to
rank among periodically 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 prob-
ably 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 convic-
tion 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,*

* On instances of stars which have not disappeared, see Argelander,
in Schumacher's Astronom. Nachr., No. 624, e. 371. To adduce an ex-
ample from antiquity, I may point to the fact that the carelessness with
which Aratus compiled his poetical catalogue of the stars has led to the
often-renewed question whether Vega Lyrze is a new star, or one which
varies in long periods. For instance, Aratus asserts that the constella-
tion of Lyra consists wholly of small stars. It is singular that Hippar-
chus, 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 ac-
cidental and not demonstrative ; for when Aratus also ascribes to Cyg-
nus none but stars " of moderate brilliancy," Hipparchus expressly re-
futes this error, and adds the remark that the bright star in the Swan

164 COSMOS.

often disfigure the very best catalogues. The disappearance
of a heavenly body from the place in which it had before
been distinctly seen, may be the result of its own nution as
much as of any such diminution of its photometric process
(whether on its surface or in its photosphere), as would ren-
der the 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 Hipparchus, makes
i a question : Stellae an obirent nascerenturve ? The ap-
parent eternal cosmical alternation of existence and destruc-
tion is not annihilation ; it is merely the transition of matter
into new forms, into combinations which are subject 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 every thing is variable both in space
and time, we are led by analogy to infer that as the fixed
stars universally have not merely an apparent, but also a
proper motion of their own, so their surfaces or luminous at-
mospheres are generally subject to those changes which re-
cur, in the great majority, in extremely long, 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 in-
stance 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 as-
certained. It is of importance here to make a distinction
between three great sidereal phenomena, whose connection
has not as yet been demonstrated ; namely, variable stars of
known periodicity ; the instantaneous lighting up in the heav-
ens of so-called new stars ; and sudden changes in the lu-
minosity of long-known fixed stars, which previously shone

(Deneb) is little inferior in brilliancy to Lyra (Vega Lyra;). Ptolemy
classes Vega among stars of the first magnitude, and in the Cataster
isms of Eratosthenes (cap. 25), Vega is caEed Tievnov KOI TiOfnrpnv. Con
sidering 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., i. e., between the times
of Aratus and Hipparchus, that the star Vega Lyrae (Fidicula of Pliny,
xviii., 25) became a star of the first magnitude.

PERIODICAL STARS. 165

with uniform intensity. We shall first of all dwell exclu-
sively on the first kind of variability ; of this, the earliest in-
stance accurately observed is furnished (1638) by Mira, a
star in the neck 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 third magnitude, and in October of
the same year he saw it disappear. But it was not until for-
ty-two years afterward that the alternating, recurring vari-
ability of its light, and its periodic changes, were discovered
by the Professor Johann Phocylides Holwarda, Professor of
Franeker. This discovery was further followed in the same
century by that of two other variable stars, ft Persei (1669),
described by Montanari, and % 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, have, since the beginning of the
nineteenth 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 (as
being the most important result of all observations), so far as
in the present state of the science they have been ascertain-
ed, I have availed myself of the friendly aid of that astrono-
mer who of all our cotemporaries has devoted himself 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 labors I confidently
laid before my worthy friend Argelander, the director of the
Observatory at Bonn, and it is to his manuscript communi
cations 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 color. Thus, for instance, besides /3
Persei (Algol in the head of Medusa), /3 Lyrae and e Aurigse
have also a white light. The star 77 Aquilae is rather yellow-
ish ; so also, in a still less degree, is £ Geminorum. 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 fifth to the seventh magnitude, ia

166 COSMOS.

itself also variable, appears very problematical. Struve*
himself merely says, Suspicor minorem esse variabilem,
Variability is by no means a necessary concomitant of red-
ness. There are many red stars : some of them very red —
as Arcturus and Aldebaran — in which, however, no variabil-
ity 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 determ-
ined are all irregular and uncertain, even if there were no
other reasons. The two variable stars of Pegasus, as well
as a Hydra, s Aurigse, and a Cassiopeise, have not the cer-
tainty that belongs to Mira Ceti, Algol, and 6 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 investigation, reckons the number of satisfactorily de-
termined periods at only twenty-four.t

The phenomenon of variability is found not only both in
red and in some white stars, but also in stars of the most di-
versified magnitude ; as, for example, in a star of the first
magnitude, a Orionis ; by Mira Ceti, a Hydra, a Cassiopeiae,
and (3 Pegasi, of the second magnitude ; ft Persei, of the 2'3d
magnitude ; and in 77 Aquilse, and (3 Lyrse, of the 3'4th mag-
nitude. There are also variable stars, and, indeed, in far
greater numbers, of the sixth to the ninth magnitude, such
as the variabiles Coronae, Virginis, Cancri, et Aquarii. The
star % Cygni likewise presents very great fluctuations at its
maximum.

* Compare Madler, Astr., s. 438, note 12, with Struve, Stellarum,
compos. Mensurce Microm., p. 97 and 98, star 2140. "I believe," says
Argelander, "it is extremely difficult with a 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; or, during my
many observations in the daytime with the telescopes of the 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 fifth or 5-6th magnitude."

t Madler's Table (Astron., s. 435) contains eighteen stars, with widely
differing numerical elements. Sir John Herschel enumerates more than
forty-five, including those mentioned in the notes. — Outlines, § 819-826.

VARIABLE STARS. 167

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. In the case of % Cygni, he considers that two perturb-
ations in the period — the one of 100, the other of 8^ — 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 % 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 ninth magnitude ;
and, moreover, according to Pigott, it once totally disappeared
at the end of the last century. At other times the fluctua-
tions in its brightness have been only from the 6-5th to the
sixth magnitude. The maximum of the variations of% Cygni
have been between the 6'7th and fourth magnitude ; of Mira,
from the fourth to the 2- 1st magnitude. On the other hand,
in the duration of its periods 6 Cephei shows an extraordi-
nary, 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 Aurigse, the variation of its brilliancy, dis-
covered by that indefatigable observer, Heis, of Aix-la-Cha
pelle,* extends only from the 3'4th to the 4'5th magnitude.

A great difference in the maximum of brightness is exhib-
ited by Mira Ceti. In the year 1779, for instance (on the
6th of November), Mira was only a little dimmer than Alde-
baran, and, indeed, not unfrequently brighter than stars of
the second magnitude ; whereas at other times this variable
star scarcely attained to the intensity of the light of 6 Ceti,
which is of the fourth magnitude. Its mean brightness is
equal to that of y Ceti (third magnitude). If we designate
by 0 the brightness of the faintest star visible to the naked
eye, and that of Aldebaran by 50, then Mira has varied in
its maximum from 20 to 47. Its probable brightness may be
expressed by 30 : it is oftener below than above this limit.
The measure of its excess, however, when it does occur, ia

* Argelander, in Schumacher's Aslron. Nachr., bd. xxvi. (1848), No,
624, s. 369.

168 COSMOS.

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 va nation in different stars vary as 1:250.
The shortest period is unquestionably that exhibited by (3
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 ft Persei come 6 Cephei (5d. 8h. 49m.), 77 Aquilaa
(7d. 4h. 14m.), and $ Geminorum (lOd. 3h. 35m.). The
longest periods are those of 30 Hydrae Hevelii, 495 days ;
X Cygni, 406 days ; Variabilis Aquarii, 388 days ; Serpentis
S., 367 days ; and Mira Ceti, 332 days. In several of the
variable stars it is well established that they increase in brill-
iancy more rapidly than they diminish. This phenomenon
is the most remarkable in 6 Cephei. Others, as, for instance,
ft Lyrse, have an equal period of augmentation and diminu-
tion 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 Ceti (as also 6 Ce-
phei) is more rapid in its augmentation than in its diminu
tion ; but in the former the contrary has also been observed

Periods within periods have been distinctly observed in
the case of Algol, of Mira Ceti, of ft Lyrao, and with great
probability also in % 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 ob-
servations (comprising 7600 periods), of which the extremes
differed from each other more than 58 years. (Schumacher's
Astron. Nachr., Nos. 472 and 624.) The decrease in the
period is becoming more and more observable.* For the

* " If," says Argelander, " I take for the 0 epoch the minimum bright-
ness of Algol, in 1800, on the 1st of January, at 18h. 1m. mean Paris
time, I obtain the duration of the periods for

—1987, 2d. 20h. 48m., or 59s.-416iOs.-316
—1406, " 58s.-737iOs.-094

58s.-393JtOs.-175
58s.-154-tOs.-039
58s.-193-tOs.-096
57s.-971iOs.-045
558.-182-j-Os.-348
" In this table the numbers have the following signification : if we
designate the minimum epoch of the 1st of Jan., 1800, by 0, that im-
mediately preceding by — 1, and that immediately following by -^-1, and
BO on, then the duration between — 1987 and — 1986 would be exactly
2d. 20h. 48m. 59s -416. but *Jie duration between -f-5441 and +5442

VARIABLE STARS. 169

periods of the maximum of Mira (including the maximum of
brightness observed by Fabricius in 1596), a formula* has
been established by Argelander, from which all the maxima
can be so deduced that the probable error in a long period of
variability, extending to 33 Id. 8h., does not in the mean ex-
ceed 7 days, while, on the hypothesis of a uniform period, it
would be 15 days.

The double maximum and minimum of (3 Lyrae, 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 doubtf by very recent observ-
ations. 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 (3 Lyrae, 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
the years 1840 and 1844. During that time its period was
nearly invariable ; at present it is again decidedly on the de-
crease. Something similar to the double maximum of (3 Lyrse
occurs in 6 Cephei. There is a tendency to a second maxi-

would be 2d. 20h. 48m. 55s. -182 ; 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."

* Argelander's formula for representing all observations of the maxima
of Mira Ceti is, as communicated by himself, as follows :

1751, Sep., 9-76 -f331d.-3363 E.

+10d.-5, sin. (3T6T°° E. +86° 23') +18d.-2, sin. (ff° E. +231° 42')
+33d.-9, sin. (ff° E. +170° 19') -f 65d.-3, sin. (fp E. -j-6° 37')
where E. represents the number of maxima which have occurred 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+36115d.-G5-|-8d.-44— 12d.-24.

4-18d.-59+27d.-34=1850, Sep., 8d.-54.

" The strongest evidence in favor of this formula is, that it represents
even the maximum of 1596 {Cosmos, vol. ii., p. 330), 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 particular cases — e. g., for the accurately observed
maximum of 1840 — the formula was wrong by many days (nearly twen-
ty-five)."

t Compare Argelander's essay, written on the occasion of the cen-
tenary jubilee of the KOnigsberg University, and entitled De Stella
8 Lyra; Variabili, 1844.

VOL. III.— H

170 COSMOS.

uaum, in so far as its diminution of light does not \ •£&/
uniformly ; but, after having been for some time tolerably
rapid, it comes to a stand, or at least exhibits a very Incon-
siderable diminution, which suddenly becomes rapicj again.
In some stars it would almost appear as though th,j light
were prevented from fully attaining a second maximum. In
% Cygni it is very probable that two periods of variability
prevail — a longer one of 100 years, and a shorter on; of 8£.
The question whether, on the whole, there is greater reg-
ularity in variable stars of very short than in those of very
long periods, is difficult to answer. The variations from a
uniform period can only be taken relatively ; i. e., in parts
of the period itself. To commence with long periods, ^ Cygni,
Mira Ceti, and 30 Hydrse must first of all be consideied. In
X Cygni, on the supposition of a uniform variability, the devi-
ations from a period of 406-0634 days (which is the most
probable period) amount to 39-4 days. Even though a por-
tion of these deviations may be owing to errors of observa-
tion, still at least 29 or 30 days remain beyond doubt ; i. 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 ; conse-
quently, as compared with % Cygni, nearly twice as great a
deviation. In the case of 30 Hydrse, which has a period of
495 days, it is still 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 solu-
tion. From the observations, however, which have as yet
been taken, less considerable deviations seem to occur. In
the case of 77 Aquilse (with a period of 7d. 4h.) they only
amount to one sixteenth or one seventeenth of the whole pe-
riod ; in that of ft Lyrse (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 j3 Lyra between 1700 and 1800 periods have
been observed ; of Mira Ceti, 279 ; of % Cygni, only 145.
The question that has been mooted, whether stars which

* The work of Jacques Cassini (Eltmens £ Astronomic, 1740, p. 66-
69) belongs to the earliest systematic attempts to investigate tb? mean
duration of the period of the variation of Mira Ceti.

VARIABLE STARS. 171

have long appeared to be variable in regular periods ever
cease to be so, must apparently be answered in the nega-
tive. As among the constantly variable stars there are
some which at one time exhibit a very great, and at anoth-
er a very small degree of variability (as, for instance, vari-
abilis Scuti), so, it seems, there are also others whose vari-
ability is at certain times so very slight, that, with our lim-
ited means, we are unable to detect it. To such belongs
variabilis Coronae 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 1 8 1 7 , Harding and Westphal found that its bright-
ness was nearly constant, while in 1824 Olbers was again
enabled to perceive a variation in its luminosity. Its con-
stancy now again returned, and from August, 1843, to Sep-
tember, 1845, was established by Argelander. At the end
of September, a fresh diminution of its light commenced.
By October, the star was no longer visible in the comet-seek-
er ; but it appeared again in February, 1846, and by the be-
ginning of June had reached its usual magnitude (the sixth).
Since then it has maintained this magnitude, if we overlook
some small fluctuations whose very existence has not been
established with certainty. To this enigmatical class of stars
belong also variabilis Aquarii, and probably Janson and Kep-
ler's star in Cygnus of 1600, which we have already men-
tioned among the new stars.

172

TABLE OP THE VARIABLE STARS, BY F. ARGELANDEE.

No.! Name of tli* Star.

Length of
Period.

Brigbtnes

s in the
Minimum.

NameofniscoTeraraod
Date of DiKjorery.

1 o Ceti

J). H. M.

331 20

Magnit.
4to2-l
23
6-7 to 4
5 to 4
5
34
3-4
43
3
6
6 5 to 5-4
7to6'7
9 to 6 7
67
8 to 7-8
7
2
1
2
34
4-3
2
8
7-8

Magnit.
0
4
0
0
0
5-4
45
5-4
34
0
9 to 6
0
0
0
0
0
3-2
1-2
23
4-5
5-4
2*3

Holwarda, 1639.
Montanari, 1669.
Gottfr. Kirch, 1687.
Maraldi, 1704.
Koch, 1782.
E. Pigott, 1784.
Goodricke, 1784.
Ditto, 1784.
Wm. Herschel 1795.
E. Pigott, 1795.
Ditto, 1795.
Harding, 1809.
Ditto, 1810.
Ditto, 1826.
Ditto, 1828.
Schwerd, 1829.
Birt, 1831.
John Herschel, 1836.
Ditto, 1837.
Heis, 1846.
Schmidt, 1847.
Ditto, 1848.
Hind, 1848.
Ditto, 1848.

210 Perse i

22049
406 1 30
495
31218 —
7-414
122145
5 849
66 8 —
323
71 17 —
145 21 —
388 13 —
359
367 5 —
380
79 3 —
196
55
i

10 335
4023 —
350

i

3 \x Cygni

430 Hydra He v. .
5LeonisR.,420M.

6 17 A(| u il;i-

7/3 Lyra

8 6 Cephei .

9 a Herculis
10 Coronje R.

11 Scuti R.

12 Virginia R
13Aquarii R

14Serpentis R
ISSerpentis S
l6Cancri R

17 a Cassiopeiae ...
18 a Orionis

19 o Hydra

20eAurigae

21 f Geminorum ...
22 {3 Pegasi

23PegasiR
24CancriS

EXPLANATORY REMARKS.

The 0 in the column of the minima indicates that the star is then
fainter than the tenth magnitude. For the purpose of clearly and con-
veniently designating the smaller variable stars, which for the most part
have neither names nor other designations, I have allowed myself to ap-

C,d to them capitals, since the letters of the Greek and the smaller
in 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 pre-
cision, and as different astronomers have different principles in estima-
ting magnitudes, it seems the safer course not to notice any euch 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 ob-
servations within the last ten years, which have not as yet been pub-
lished. 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

VARIABLE STARS. 173

right ascension and declination. The frequently-repeated term grada-
tion indicates a difference of brightness, which may be distinctly recog-
nized even by the naked eye, or, in the case of those stars which are
invisible to the unaided sight, by a Frauenhofer's comet-seeker of twen-
ty-five and a half inches focal length. For the brighter stars above the
sixth magnitude, a gradation indicates about the tenth part of the dif-
ference by which the successive orders of magnitude differ from one an-
other ; for the smaller stars the usual classifications of magnitude are
considerably closer.

(l)o Ceti, R. A. 32° 57', Decl. —3° 40' ; also 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 recognized, and Bouillaud fixed the duration of its period
at 333 days ; it was found, however, at the same time, that this dura-
tion was sometimes longer and sometimes shorter, and that the star, at
its greatest brilliancy, appeared sometimes brighter and sometimes faint-
er. 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 eleventh or twelfth
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 tenth magnitude. But few observations 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 sixth
magnitude. From this period the star increases in brightness at first
with great rapidity, afterward more slowly, and at last with a scarcely
perceptible augmentation ; then, again, it diminishes at first slowly, aft-
erward rapidly. On a mean, the period of augmentation of light from
the sixth magnitude extends to fifty days ; that of its decrease down to
the same degree of brightness takes sixty-nine 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 diminution 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 bright-
ness, and then in forty-nine days became visible 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) oc-
curred 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 com-
pleted 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 fe w days. On some occasions, after the star had decreased in bright-
ness for several weeks, there was a period of perfect cessation, or, at
least, a scarcely perceptible diminution of light during several days ; this
was the case in 1678 and in 1847.

The maximum brightness, as already remarked, is by no means al-
ways 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 first magnitude, by fifty, then the maximum of light of Mira fluc-
tuates between 20 and 47, i. e., between the brightness of a star of the
fourth, and of the first or second magnitude : the mean brightness is 28

174 COSMOS.

or that of the star y Ceti. But the duration of its periods is still more
irregular: its mean is 33 Id. 20h., while its fluctuations have extended
to a month ; for the shortest time that ever elapsed from one maximum
to the next was only 306 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 a uni-
form period. The difference between calculation and observation then
amounts to 50 days, and it appears that, for several years in succession,
those differences 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 calculations, however, have prov-
ed that the supposition of one disturbance is not sufficient, and that sev-
eral must be assumed, which may, however, all arise from the same
cause ; one of these recurs after 1 1 single periods ; a second after 88 ;
a third after 176 ; and a fourth after 264. From hence arises the form-
ula of sines (given at p. 169, note *), with which, indeed, the several
maxima very nearly accord, although deviations still exist which can
not be explained by errors of observation.

(2) (3 Persei, Algol ; R. A. 44° 36', Decl. 4-40° 22'. Although Gemi-
niano Montanari observed the variability or this star in 1667, and Ma-
raldi 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 di-
minish in brightness, but for 2d. 13h. shines uniformly as a star of the
2-3d magnitude, and only appears less bright for seven or eight hours,
when it sinks to the fourth magnitude. The augmentation and dimi-
nution 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 be accurately calculated to within ten to fifteen
minutes. It is moreover remarkable that this star, after having increased
in light for about an hour, remains for nearly the same period at the
same brightness, and then begins once more perceptibly 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. 58is. However, a more ai curate cal-
culation, 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 re-
cent 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 diminution will be accounted for if we as-
sume 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 decrease of the
period requires; *. e., about the twelve thousandth 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 calculated for a uniform period amount to forty days,
but are considerably diminished by the introduction of a disturbance
of 8J^ single periods, and of another of 100 such periods. In its maxi-
mum this star reaches the mean brightness of a faint fifth magnitude, or

VARIABLE STARS. 175

one gradat/on brighter than the star 17 Cygni. The fluctuations, how
ever, are in this case also very considerable, and have been observed
from thirteen gradations below the mean to ten above it. At this low-
est maximum the star would 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 ninety-seven days ; its mean visibility
extends to fifty-two days, of which, on the mean, it is twenty days on
the increase, and thirty-two on the decrease.

(4) 30 Hydras Hevetii, E. A. 200° 23', Decl. —22° 30'. Of this star,
which, from its position in the heavens, is only visible for a short time
during every year, all that can be said is, that both its period and its
maximum brightness are subject to very great irregularities.

(5) Leonis R. =420 Mayeri; R. A. 144° 52', Decl. -f 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, how-
ever, to show that the period is somewhat irregular. Its brightness at
the maximum seems also to fluctuate through some gradations.

(6) n Aquilss, called also y Antinoi ; R. A. 296° 12', Decl. +0° 37'.
The period of this star is tolerably uniform, 7d. 4h. 13m. 53s. ; observa-
tions, 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 deviations
have been discovered which could not be accounted for by errors of ob-
servation. In its minimum, this star is one gradation fainter than i
Aquilis ; at first it increases slowly, then more rapidly, and afterward
again more slowly ; and in 2d. 9h. from its minimum, attains to its great-
est brightness, in which it is nearly three gradations brighter than /?,
but two fainter than 6 Aquilse. From the maximum its brightness does
not diminish quite so regularly; for when the star has reached the bright-
ness of (3 (*. e., in Id. lOh. after the maximum), it changes more slowly
than either before or afterward.

(7) /3 Lyra;, R. A. 281° 8', Decl. -f-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 f Lyrse, it rises
in 3d. 5h. to its first maximum, in which it remains three fourths of a
gradation fainter than y Lyrse. It then sinks in 3d. 3h. to its second
minimum, in which its light is about five gradations greater than that of
f. After 3d. 2h. more, it again reaches, in its second maximum, to the
brightness of the first ; and afterward, in 3d. 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 2^h ; in 1817 and 1818, by more than an hour ;
and at present, a shortening of it is again clearly perceptible. There
is, therefore, no doubt that in the case of this star the disturbance of its
period may be expressed by a formula of sines.

(8) 6 Cephei, R. A. 335° 54', Decl. +57° 39'. Of all the known va-
riable stars, this exhibits in every respect the greatest regularity. The
period of 5d. 8h. 47m. 39is. is given by all the observations from 1784
to the present day, allowing for errors of observation, which will ac-
count for all the slight differences exhibited in the course of the altern
ations of light. This star is in its minimum three quarters of a gradation
brighter than e ; in its maximum it resembles i of the same constellation
(Cepheus). It takes Id. 15h. to pass from the former to the latter ; but,
on the other hand, more than double that time, viz., 3d. 18h., to change

176 COSMOS.

again to its minimum during eight hours of the latter period, however
it scarcely changes at all, and very inconsiderably for a whole day.

(9) a Herculis, R. A. 256° 57', Decl. +14° 34'; an extremely red
double star, the variation of whose light is in every respect very irreg-
ular. 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 discoverer 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
iny observations, made during seven years, at length gave me the peri-
od assigned in the text. Heis believes that he can represent all the ob-
servations by assuming a period of 184-9 days, with two maxima and

(10) Corona; R., R. A. 235° 36', Decl. +28° 37'. This star is varia-
ble only at times ; the period set down has been calculated by Koch
from his own observations, which unfortunately have been lost.

(11) Scuti R., R. A. 279° 52', Decl. —5° 51'. The variations of bright-
ness of this star are at times confined within a very few gradations,
whereas at others it diminishes from the fifth to the ninth magnitude. It
has been too little observed to determine when any fixed rule prevails
in these deviations. The duration of the period is also subject to con-
siderable fluctuations.

(12) Virginis R., R. A. 187° 43', Decl. +7° 49'. It maintains its pe-
riod and its maximum brightness •with tolerable regularity ; some devi-
ations, however, do occur, which appear to me too considerable to be
ascribed merely to errors of observation.

(13) Aquarii R., R. A. 354° 11', Decl. —16° 6'.

(14) Serpentis R., R. A. 235° 57', Decl. -f 15° 3.T.

(15) Serpentis S., R. A. 228° 40', Decl. -f 14° o^'.

(16) Cancri R., R. A. 122° 6', Decl. 4-12° 9'.

Of these four stars, which have been but very slightly observed, little
more can be said than what is given in the table.

(17) a Cassiopeia, R. A. 8° 0', Decl. +55° 43'. This star is very diffi-
cult 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 state-
ments on this head. That which I have given, which satisfactorily rep-
resents the observations from 1782 to 1849, appears to me the most prob-
able one.

(18) a Orionis, R. A. 86° 46', Decl. +7° 22'. The variation in the
light of this star likewise amounts to only four gradations from the min-
imum to the maximum. For 91^ days it increases in brightness, while
its diminution extends over 104-fc, and is imperceptible from the twen-
tieth to the seventieth day after the maximum. Occasionally its varia
bility is scarcely noticeable. It is a very red star.

(19) a Hydras, 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 un-
certain. Sir John Herschel sets it down at from twenty-nine to thirty

§1) e Aurigae, R. A. 72° 48', Decl. -f 43° 36'. The alternation of
in this star is either extremely irregular, or else, in a period of sev-
eral years, there are several maxima and minima — a question which can
not be decided for many years.

(21) f Geminorum, R. A. 103° 48', Decl. +20° 47'. This star has
hitherto exhibited a perfectly regular course in the variations of its ligbt

VARIABLE STARS. 177

Ita brightness at its minimum keeps the mean between v 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 diminu-
tion.

(22) 0 Pegasi, R. A. 344° 7', Decl. -j-27° 16'. Its period is pretty
well ascertained, but as to the course of its variation of light nothing can
as yet be asserted.

(23) Pegasi R., R. A. 344° 47'. Decl. +9° 43'.

(24) Cancri 8., R. A. 128° 50', Decl. +19° 34'.
Of these two stars nothing at present can be said.

FK. ARGELANDBR.

Bonn, August, 1850.

VARIATION OF LIGHT IN STARS WHOSE PERIODICITY is
UNASCERTAINED. — In the scientific investigation of important
natural phenomena, either in the terrestrial or in the sidereal
sphere of the Cosmos, it is imprudent to connect together,
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 ap-
pe^red 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 pe-
riodicity is as yet unascertained (as i\ 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
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 concerning the
variable stars whose periods have not yet been ascertained,
with the unperiodical fluctuations in the light of 77 Argus,
which to the present day are still observable. This star is
situated in the great and magnificent constellation of the

* Newton (Philos. Nat. Principia Mathem., ed. Le Seur et Jacquier,
1760, torn, iii., p. 671) distinguishes only two kinds of these sidereal
phenomena. " Stella? fixse quae per vices apparent et evanescunt, quae-
quo paulatim crescunt, videntur revolvendo partem lucidam et partem
obscuram per vices ostendere." The fixed stars, which alternately ap.
pear and 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 Riccioli. With respect to the
caution necessary in predicating periodicity, see the valuable remarks
of Sir John Herschel, in his Observations at the Cape, $ 261.

K2

178 COSMOS.

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 (damdiaKT] and KardoTpufid), whose relative or-
ders 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 intensity of light, these doubts failed
to lead to any result. According to Halley's observation in
1677, r) Argus was of the fourth magnitude ; and by 1751
it was already of the second, as observed by Lacaille. The
star must have afterward returned to its fainter light, for
Burchell, during his residence in Southern Africa, from 1811
to 1815, found it of the fourth magnitude ; from 1822 to 1826
it was of the second, 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 first magnitude, per-
fectly equal to a Crucis. After a year the star returned to
the second magnitude. It was of this magnitude when Bur-
chell saw it on the 29th of February, 1828, in the Brazilian
town of Goyaz ; and it is thus set down by- Johnson and Tay-
lor, in their catalogues for the period between 1829 and 1833.
Sir John Herschel also, at the Cape of Good Hope, estimated
it as being between the second and first magnitude, from
1834 to 1837.

When, on the 16th of December, 1837, this famous astron-
omer was preparing to take the photometric measurements
of the innumerable telescopic stars, between the eleventh
and sixteenth magnitudes, which compose the splendid neb-
ula around 77 Argus, he was astonished to find this star, which
had so often before been observed, increase to such intensity
of light that it almost equaled the brightness of a Centauri,
and exceeded that of all other stars of the first magnitude,
except Canopus and Sirius. By the 2d of January, 1838, it
had for that time reached the maximum of its brightness.
It soon became fainter than Arcturus ; but in the middle of
April, 1838, it still surpassed Aldebaran. Up to March,
1843, it continued to diminish, but was even then a star of
the first magnitude ; after that time, and especially in April,
1843, it began to increase so much in light, that, according

* Delambre, Hist, de VAstron. Ancicnne, torn, ii., p. 280, arid Hist, de
I'Attron. au IScme Siecle, p. 119.

VARIABLE STARS. 179

to the observations of Mackay at Calcutta, and Maclear at
the Cape, 77 Argus became more brilliant than Canopus, and
almost equal to Sirius.* This intensity of light was contin-
ued almost up to the beginning of the present year (1850).
A distinguished observer, Lieutenant Gilliss, who commands
the astronomical expedition sent by the government of the
United States to the coast of Chili, writes from Santiago,
in February, 1850 : " rj Argus, with its yellowish-red light,
which is darker than that of Mars, is at present next in brill-
iancy to Canopus, and is brighter than the united light of
a Centauri."t Since the appearance of the new stars in
Ophiuchus in 1604, no fixed star has attained to such an in-
tensity of light, and for so long a period — now nearly seven
years. In the 173 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 phenom-
enon of a great but unperiodical variability in rj Argus, 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. Mensurce Microm.,
p. Ixxi.-lxxiii.), similar variations of light have been no-
ticed, which have not as yet been ascertained to be period-
ical. The instances which we shall content ourselves with
adducing are founded on actual photometrical estimations
and calculations made by the same astronomer at different
times, and not on the alphabetical series of Bayer's Uranom-
etry. In his treatise De fide Uranometricz Bayeriante,
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 desig-
nated stars of equal magnitude according to the positions of

* Compare Sir John Herschel's Observations at the Cape, $ 71-78;
and Outlines of Astron., $ 830 (Cosmos, vol. i., p. 153).

t Letter of Lieutenant Gilliss, astronomer of the Observatory at Wash-
ington, to Dr. Fid gel, consul of the United States of North America at
Leipsic (in manuscript). The cloudless purity and transparency of the
atmosphere, which last for eight months, at Santiago, in Chili, are so
great, that Lieutenant Gilliss (with the first great telescope ever con-
structed in America, having a diameter ol seven inches, constructed by
Henry Fitz, of New York, and William Young, of Philadelphia) wa»
able clearly to recognize the sixth star in the trapezium of Orion.

180 COSMOS.

the stars in a constellation, beginning usually at the head,
and proceeding, in regular order, down to the feet. The or-
der of letters in Bayer's Uranometria has long led to a be-
lief that a change of light has taken place in a Aquilae, in
Castor Geminorum, and in Alphard of Hydra.

Struve, in 1838, and Sir John Hersohel, observed Capella
increase in light. The latter now finds Capella much bright-
er than Vega, though he had always before considered it
fainter.* Galle and Heis come to the same conclusion, from
their present comparison of Capella and Vega. The latter
finds Vega between five and six gradations, consequently
more than half a magnitude, the fainter of the two.

The variations in the light of some stars in the constella-
tions of the Greater and of the Lesser Bear are deserving of
especial notice. " The star 77 Ursae majoris," says Sir John
Herschel, "is at present certainly the most brilliant of the
seven bright stars in the Great Bear, although, in 1837, e
unquestionably held the first place among them." This re-
mark induced me to consult Heis, who so zealously and care-
fully occupies himself with the variability of stellar light.
" The following," he writes, " is the order of magnitude which
results from my observations, carried on at Aix-la-Chapelle
between 1842 and 1850 : 1. £ Ursse majoris, or Alioth ; 2.
a, or Dubhe ; 3. r\, or Benetnasch ; 4. 6, or Mizar ; 5. /3 ; 6.
; 7. 6. The three stars, e, a, and rj, of this group, are near-
y equal in brightness, so that the slightest want of clearness
in the atmosphere might render their order doubtful ; £ is de-
cidedly fainter than the three before mentioned. The two
stars ft and y (both of which are decidedly duller than £) are
nearly equal to each other ; lastly, 6, which in ancient maps is
usually set down as of the same magnitude with ft and y, is
by more than a magnitude fainter than these ; e is decided-
ly 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 ft Ursre ma-
joris to be variable, though I am unable to give any fixed
periods. In the years 1840 and 1841, Sir John Herschel
found ft UrszB minoris much brighter than the Polar star ;
whereas still earlier, in May, 1846, the contrary was ob-

* Sir John Herschel ( Observations at the Cape, p. 334, 350, note 1, and
440). For older observations of Capella and Vega, see William Her-
schel, in the Philos. Transact., 1797, p. 307, 1799, p. 121 ; and Bode's
Jahrbuchfur 1810, B. 148. Argelander, on the other hand, advances
many doubts as to the variation of Capella and of the stars of the Bear.

r,

VARIABLE STARS. 181

served by him. He also conjectures (3 to be variable.* Since
1843, I have, as a rule, found Polaris fainter than ft Urssa
minoris ; but from October, 1843, to July, 1849, Polaris was,
according to my registers, fourteen times brighter than (3. I
have had frequent opportunities of convincing myself that the
color of the last-named star is not always equally red ; it is
at times more or less yellow, at others most decidedly red."f
All the pains and labor spent in determining the relative
brightness of the stars will never attain any certain result
until the arrangement of their magnitudes from mere esti-
mation shall have given place to methods of measurement
founded on the progress of modern optical science.J 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
light in all self-luminous stars (in the central body of our own
planetary system, and in the distant 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 climatology
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 dif-
ferent degrees of latitude. The variable star in the neck of
the Whale (Mira Ceti) changes from the second magnitude
to the eleventh, and sometimes vanishes altogether ; we have
seen that t\ Argus has increased from the fourth to the first
magnitude, and among the stars of this class has attained to
the brilliancy of Canopus, and almost to that of Sirius. Sup-
posing 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 augment-

* Observations at the Cape, $ 259, note 260.

t Heis, in his Manuscript Notices of May, 1 850 ; also Observations at
the Cape, p. 325 ; and P. von Boguslawski, Uranus for 1848, p. 186.
The asserted variation of n, a, and 6 Ursse majoris 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 12,000 years, Vega, the brightest of all possible
polar stars, will take their place. ; Vide supra, p. 96

$ William Herschel, On the Changes that happen to the Fixed Stars,
in the Philos. Transact, for 1796, p. 186. Sir John Herschel, in the
Observations at the Cape, p. 350-352 ; as also in Mrs. Somerviue's ex-
cellent work, Connection of the Physical Sciences, 1846, p. 407.

182 COSMOS.

ation of its light-process, 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 some-
what 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 formation, and the solidification of con-
glomerating matter ; the 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 differ-
ent 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 central body. Cosmical considerations must
not be limited merely to astrognostic relations.

V.

PROPER MOTION OF THE FIXED STARS. — PROBLEMATICAL EXIST-
ENCE OF DARK COSMICAL BODIES.— PARALLAX— MEASURED DIS-
TANCES OF SOME OF THE FIXED STARS.— DOUBTS AS TO THE AS-
SUMPTION OF A CENTRAL BODY FOR THE WHOLE SIDEREAL HEAV-
ENS.

THE 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 indi-
vidual 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/z Cassiopeise, and of a double star in Cyg-
nus, this change of position has, by the accumulation of their
annual proper motion during 2000 years, amounted respect-
ively to 2|, 3i, and 6 moon's diameters. In the course of
3000 years about twenty fixed stars will have changed their
places by 1° and upward.* Since the proper motions of the
fixed stars rise from •£$th of a second to 7-7 seconds (and

* Encke, Betrachtungen fiber die Anordnung des Stern-systems, B. 12.
Vidctupra, p. 27. Madler, Astr., s. 445.

PROPER MOTION OF THE STARS. 183

consequently differ, at the least, in the ratio of 1 : 154), the
relative distances also of the fixed stars from each other, and
the configuration of the constellations themselves, can not 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 veloc-
ity in different paths. How many thousand years will elapse
before its total dissolution can not be calculated. In the re-
lations of space and the duration of time, no absolute idea
can be attached to the terms great and small.

In order to comprehend under one general point of view
the changes that take place in the heavens, and all the mod-
ifications which in the course of centuries occur in the phys-
iognomic character of the vault of heaven, or in the aspect
of the firmament from any particular spot, we must reckon
as the active causes of this change: (1), the precession of
the equinoxes and the mutation of the earth's axis, by the
combined operation of which new stars appear above the
horizon, and others become invisible ; (2), the periodical and
non-periodical variations 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
center 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 undoubt-
edly 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. Near-
ly two hundred comets, five of which have short periods of
revolution and are interior, or, in other words, are inclosed
within those of the principal planets, still remain to be men-
tioned in our list of planetary bodies. Next to the actual
planets and the new cosmical bodies which shine forth sud-
denly as stars of the first magnitude, the comets, when, dur-
ing their usually brief appearance they are visible to the na
ked eye, contribute the most vivid animation to the rich^'c-
ture — 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 sci-

184 COSMOS.

ence of observation through the improvement of instruments
and methods. The discovery of this motion was first ren-
dered practicable when the telescope was combined with
graduated instruments ; when, from the accuracy of within
a minute of an arc (which after much pains Tycho Brahe
first succeeded in giving to his observations on the island of
Hven), astronomers gradually advanced to the accuracy of
a second and the parts of a second ; and when it became
possible to compare with one another results separated by a
long series of years. Such a comparison was made by Hal-
ley with respect to the positions of Sirius, Arcturus, and Al-
debaran, as determined by Ptolemy in his Hipparchian cat-
alogue, 1844 years before. By this comparison he consid-
ered himself justified (1717) in announcing the fact of a
proper motion in the three above-named fixed stars.* The
high and well-merited attention which, long subsequent even
to the observations of Flamstead and Bradley, was paid to
the table of right ascensions contained in the Triduum of
Romer, stimulated Tobias Mayer (1756), Maskelyne (1770),
and P;azzi (1800) to compare Homer's observations with
more recent ones.f The proper motion of the stars was in
some degree recognized as a general fact, even in the mid
die of the last century ; but for the more precise and numer-
ical determination of this class of phenomena we are in-
debted to the great work of William Herschel in 1783, found-
ed on the observations of Flamstead, $ and still more to Bes-
sel and Argelander's successful comparison of Bradley's "Po-
sitions 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 astron-
omy, as it has led to a knowledge of the motion of our own
solar system through the star-filled realms of space, and, in-
deed, to an accurate knowledge of the direction of this mo-
tion. 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 at-
tempts to investigate this motion, both in its quantity and
its direction, to determine the parallax of the fixed stars, and

* 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 variations in longitude. (Arago, ii the An-
Huairepour 1842, p. 387.)

t Delambre, Hist, de V Aslron. Moderne, t. ii., p. 658. Als , « £f&
de VAstron. au IMme Slide, p. 448.

t Philos. Transact., vol. Ixxiii., p. 138.

PROPER MOTION OP THE STARS. 185

their distances, have, by leading to the improvement and
perfection of arc-graduation and optical instruments in con-
nection with micrometric appliances, contributed more than
any thing else to raise the science of observation to the
height which, by the ingenious employment of great merid-
ian-circles, refractors, and heliometers, it has attained, espe-
cially since the year 1830.

The quantity of the measured proper motions of the stars
varies, as we intimated at the commencement of the present
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 fifth to the sixth and seventh mag-
nitudes.* Seven stars have revealed an unusually great
motion, namely : Arcturus, first magnitude (2"- 25) ; a Cen-
tauri, first magnitude (3//-58) ;t ft Cassiopeia?, sixth magni-
tude (3"-74) ; the double star, 6 Eridani, 5'4 magnitude
(4"-08) ; the double star 61 Cygni, 5'6 magnitude (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,J and the Great Bear, No. 1830 of the catalogue of
the circumpolar stars by Groombridge, seventh magnitude
(according to Argelander, 6"-974) ; e Indi (7"'74, according
to D'Ariest) ;§ 2151 Puppis, sixth magnitude (7"-&7l). The
uilihrn-oiicalll 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

* Bessel, in the Jahrbuch wn Schumacher fur 1839, s. 38. Arago
Annuaire pour 1842, p. 389.

t a Centauri, see Henderson and Maclear, in the Memoirs of the
Astron. Soc., vol. xi., p. 61 ; and Piazzi Smyth, in the Edinburgh
Transact., vol. xvi., p. 447. The proper motion of Arcturus, 2"-25
(Daily, in the same Memoirs, vol. v., p. 165), considered as that of a
very bright star, may be called very large in comparison with Aldeba
ran, 0"-185 (Madler, CentraUonne, a. 11), and o Lyra, 0"-400. Among
the stars of the first magnitude, a Centauri, with its great proper motion
of 3"-58, firms a very remarkable exception. The proper motion of
the binary system of Cygnus amounts, according to Bessel (Schum
Astr. Nochr., bd. xvi., s. 93), to 5"-123.

{ Schumacher's Astr. Nochr., No. 455.

$ Op. cit., No. 618, s. 276. D'Arest founds this result on comparisons
of LacaiDe (1750) with Brisbane (1825), and of Brisbane with Taylor
(1835). The star 2151, Puppis, has a proper motion of 7"-871, and ia
of the sixth magnitude. (Maclear, in Madler's Unlert. uber die Fix-
ttern-Sytteme, th. ii., s. 5.)

|| Schum., Aslr Nochr., No. 661, s. 201

186 COSMOS.

time, 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 appar-
ent 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 exist-
ence 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 per-
ceived 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, be-
comes appreciable."* In a letter (dated July, 1844) in an-
swer to one in which I had jocularly expressed my anxiety
regarding 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 essen-
tial property of these bodies. The fact that numberless stars
are visible is evidently no proof against the existence of an
equally incalculable 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
to the simple supposition that the change of 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 com-
parisons with, earlier observations. The result, in the opin-
ion of Struve and Fuss,t proved adverse to Bessel's assertion.

* Schuin., Attr. Nachr., Nos. 514-516.

t Struve, Etudes cCAstr. Stellaire, Texte, p. 47, Notes, p. 26, and 51-
57 ; Sir John Herschel, Outl., $ 859 and 860.

PROPER MOTION OP THE STARS. 187

A. laborious investigation which Peters has now completed
at Konigsberg, on the other hand, justifies it ; as does also a
similar one advanced by Schubert, the calculator for the
North American Nautical Almanac.

The belief in the existence of non-luminous stars was dif-
fused 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 vapcrs,
there revolve certain other earth-like 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 conjectured 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 Mecanique Celeste bases his convic-
tion 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 surpassed the brill-
iancy of Jupiter, have not changed their place during the
time of their being visible." (The luminous process in them
has simply ceased.) " There exist, therefore, in celestial
space dark bodies of equal magnitudes, and probably in as
great numbers as the stars, "t So also Madler, in his Un-
tersuchungen uber die Fixstern-Systeme, says :J "A dark
body might be a central body ; it might, like our own sun,
be surrounded in its immediate neighborhood 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. "§ It has been already remarked that the advocates
of the emanation theory consider these masses as both invis-
ible, 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 at-
traction, are unable to pass beyond a certain limit. H If, as

* Origen, in Gronov. Thesaur., t. x., p. 271.

t Laplace, Expos, du Syst. du Monde, 1824, p. 395. Lambert, in his
Kosmologische Brief e, shows remarkable tendency to adopt the hypoth-
esis of large dark bodies.

• \ Madler, Untersitch. tober die Fixstern-Systeme, th. ii. (1848), s. 3;
and his Astronomy, B. 416. $ Vide note t, p. 186

II Vide supra, p. 88, and note ; Laplace, in Zach's Alia. Geogr
Epkcm., bd. iv., B. 1 ; Madler, Astr., B. 393.

188 COSMOS.

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 can not 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 dis-
turbances.

The inquiry into the quality 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
the place of observation, as the earth moves in its orbit), the
determination of the distances of the fixed stars from the
sun by ascertaining their parallax, and the conjecture as to
the part in universal space toward which our planetary
system is moving, are three problems in astronomy which,
through the means of observation already successfully em-
ployed 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 par-
allaxes and the determination of the distances of certain fixed
stars, to complete that which especially relates to our pres
ent knowledge of isolated fixed stars.

As early as the beginning of the seventeenth century,
Galileo had suggested the idea of measuring the " certainly
very unequal distances of the fixed stars from the solar sys-
tem," and, indeed, with great ingenuity, was the first to
point out the means of discovering the parallax ; not by de-
termining the star's 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 mi-
crometrical method which William Herschel (1781), Struve,
and Bessel subsequently made use of. " Perche io non credo,"
says Galileo,* in his third dialogue (Giornata terza), " che
tutte le stella siano sparse in una sferica superficie egual-
tnente distanti da un centra; ma stimo, che le loro lonta-
nanze da noi siano talmente varie, che alcune ve ne possano
esser 2 e 3 volte piu remote di alcune altre ; talche quando
si trovasse col telescopic qualche picciolissima Stella vici-

* Opere di Galileo Galilei, vol. xii., Milano, 1811, p. 206. This re-
markable passage, which expresses the possibility and the project of
a measurement, was pointed out by Arago ; see his Annuaire pour 1842
p. 382.

DISTANCES OF THE STARS. 189

nissima ad alcuna delle maggiori, e che pero quella fussc al-
tissima, potrebbe accadere che qualche sensibil mutazione
succedes&e tra di loro." " \\Ther6fore I do not believe." says
Galileo, in liis third discourse (Giornata terza), <:that all the
stars are scattered over a spherical superficies at equal dis-
tances from a common center ; but I am 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 in-
troduction of the Copernican system imposed, as it were, the
necessity of numerically determining, by means of measure-
ment, 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 determina-
tions, of which Kepler so successfully availed himself, do not
manifest any perceptible change arising from parallax in
the apparent positions of the fixed stars, although, as I have
already stated, they are accurate to a minute of the arc.
For this the Copernicans long consoled themselves with the
reflection that the diameter of the earth's orbit (165£ mill-
ions 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 par-
allax 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 distance of the fixed stars must be more than 3438
times the earth's mean distance from the sun, or semi-di-
ameter of its orbit.* This lower limit of distances rose to
206,265 semi-diameters when certainty to a second was at-
tained in the observations of the great astronomer, James
Bradley ; and in the brilliant period of Frauenhofer's instru-
ments (by the direct measurement of about the tenth part
of a second of arc), it rose still higher, to 2,062,648 mean
distances of the earth. The labors and the ingeniously con-
trived zenith apparatus of Newton's great cotemporary , Rob-
ert Hooke (1669), did not lead to the desired end. Picard,
Horrebow (who worked out Romer's rescued observations)

* Bessel, in Schumacher's Jahrb. fur 1839, s. 511.

190 COSMOS

and Flamstead believed that they had discovered parallaxes
of several seconds, whereas they had confounded the proper
motions of the stars with the true changes from parallax.
On the other hand, the ingenious John Michell (Phil. Trans.
1767, vol. Ivii., p. 234-264) was of opinion that the paral-
laxes of the nearest fixed stars must be less than 0"'02, and
in that case could only "become perceptible when magnified
12,000 times." In consequence of the widely-diffused opin-
ion, that the superior brilliancy of a star must invariably in-
dicate a greater proximity, stars of the first 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 Jhose which Brinkley published in Dublin
(1815), and which, ten years afterward, were refuted by
Pond, and especially by Airy. An accurate and satisfactory
knowledge of parallaxes, founded on micrometric measure-
ments, dates only from between the years 1832 and 1838

Although Peters,* in his valuable work on the distance?
of the fixed stars (1846), estimates the number of parallaxes
hitherto discovered at 33, we shall content ourselves with re
ferring to 9, which deserve greater, although very different,
degrees of confidence, and which we shall consider in the
probable order of their determinations.

The first place is due to the star 61 Cygni, which Bessel
has rendered so celebrated. The astronomer of Kbnigsberg
determined, in 1812, the large proper motion of this double
star (below the sixth magnitude), but it was not until 1838
that, by means of the heliometer, he discovered its parallax.
Between the months of August, 1812, and November, 1813,
my friends Arago and Mathieu instituted a series of numer-
ous 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 labors they arrived at the very correct
conclusion that the parallax of this star was less than half a
second.f So late as 1815 and 1816, Bessel, to use his own

* Struve, Astr. Slell., p. 104.

t Arago, in the Connaissance des Temps pour 1834, p. 281 : " Nous
observames avec beaucoap de soin, M. Mathieu et moi, pendant le
mois d'Aout, 1812. et pendant le mois de Novembre suivant, In hauteur
angulaire de l'4toile audessus de 1'horizon de Paris. Cette hauteur, &
la seconde <§poque, ne surpasse la hauteur angulaire a la premiere quo
de 0"-66. Une parallaxe absolue d'une seule seconde aurait n&sessairo-
raent amend entre ces deux hauteurs une difference de l"-2. Nos ob-
servations u'indiqueut douc pas quo le rayon de 1'orbite terreste, que

DISTANCES OF THE STARS. 191

words, " had arrived at no available result."* The observa-
tions 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
592,200 mean distances of the earth, and a period of 9|
years for the transmission of its light. Peters confirmed this
result in 1842 by finding 0"'3490, but subsequently changed
Bessel's result into 0"-3744 by a correction for temperature. 1
The parallax of the finest double star of the southern hem-
isphere (a Centauri) has been calculated at 0"'9128 by the
observations of Henderson, at the Cape of Good Hope, in

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 sou-
tend un angle d'une demi-seconde quand on est eloigne de 412 mille
fois sa longueur. Done la 61e du Cygne est au moins a une distance
de la terre egale a 412 mille fois 39 millions de lieues." " During the
month of August, 1812, and also during the following 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 ex-
ceeded that of the former by 0"-66. An absolute parallax of only a
single second would necessarily have occasioned a difference of l"-2
between these heights. Our observations do not, therefore, show that
a semi-diameter of the earth's orbit, or thirty-nine millions of leagues,
are seeu from the star 61 of Cygnus, at an angle of more than 0"-5.
But a base viewed perpendicularly subtends an angle of 0"'5 only when
it is observed at a distance of 412,000 times its length. Therefore the
star 6 1 Cygni is situated at a distance from our earth at least equal to four
hundred and twelve thousand times thirty-nine millions of leagues."

* Bessel, in Schum., Jahrb. 1839, s. 39-49, and in the Astr. Nachr.,
No. 366, gave the result 0"-3136 as a first approximation. His later and
final result was 0"-3483. (Astr. Nachr., No. 402, in bd. xvii., s. 274.)
Peters obtained by his own observations the following, almost identical,
result of 0"-3490. (Struve, Astr. Slell, p. 99.) The alteration which,
after Bessel's death, was made by Peters in Bessel's calculations of the
angular measurements, obtained by the Konigsberg 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 Untersuch-
ungen, but he had not applied the corrections of temperature to the ob-
servations of parallax. This application was made by the eminent as-
tronomer Peters (Ergdnzungscheft zu den Astr. Nachr., 1849, s. 56),
and the result obtained, owing to the corrections of temperature, was
0"-3744 instead of 0"-3483.

t This result of 0"-3744 gives, according to Argelander, as the dis-
tance of the double star 61 Cygni from the sun, 550,900 mean distances
of the earth from the sun, or 45,576,000 miles, a distance which light
traverses in 3177 mean days. To judge from the three consecutive
statements of parallax given by Bessel, 0"-3136, 0"-3483, and 0"-3744,
this celebrated double star has apparently come gradually nearer to us
in light passages amounting respectively to 10, 9\, and 8T7ff yeara

192 COSMOS.

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 a Lyrse has long been the object of
Struve's observations. The earlier observations (1836)
gavet between 0"-07 and 0"-18 ; later ones gave 0"-2613,
and a distance of 771,400 mean distances of the earth, with
a period of twelve years for the transmission of its light. t
But Peters found the distance of this brilliant star to be
much greater, since he gives only 0"'103 as the parallax.
This result contrasts with another star of the first magni-
tude (a Centauri), and one of the sixth (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 sat-
isfactory, as the same comparisons give the aberration at
20"-455.§

The parallax of Arcturus, according to Peters, is 0"-127.
Riimker's earlier observations with the Hamburg meridian
circle had made it considerably larger. The parallax of an-
other star of the first 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 firm-
ament, has a 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 a Centauri. ||

* Sir John Herschel, Outlines, p. 545 and 551. Madler (Astr., s. 425)
gives in the case of a Centauri the parallax 0"-9213 instead of 0"-9128.

t Struve Stell. compos. Mens. Microm., p. clxix.-clxxii. Airy makes
the parallax of a Lyrse, which Peters had previously reduced to 0"-1,
still lower; indeed, too small to be measurable by our present instru-
ments. (Mem. of the Royal Astr. Soc., vol. x., p. 270.)

J Struve, On the Micrometrical Admeasurements by the Great Refract"
or at Dorpat (Oct., 1839), in Schum., Astr. Nachr., No. 396, s. 178.

$ Peters, in Struve, Aitr. Stell., p. 100. II Id., p. 101.

DISTANCES OF THE STARS.

19 j

Filed Star.

Parallax.

ProtabEi

Error.

Name of Observer.

a Centauri

0"- 913

0"-070

Henderson and Maclear.

61 Cygni

0"3744

0"-020

Bessel.

Sirius . .......

0"- 230

Henderson

1830, Groombridge.
i Ursse Maj.

0"- 226
0"- 133

0"-141
0"-106

Peters.
Peters.

Arcturus

0"- 127

0"073

Peters.

a Lyras

0"- 207

0"-038

Peters.

Polaris

0"- 106

0"-012

Peters.

Capella

0"- 046

0"-200

Peters.

It does not in general follow from the results hitherto ob-
tained that the brightest stars are likewise the nearest to us.
Although the parallax of a Centauri is the greatest of all at
present known, on the other hand, Vega Lyrte, Arcturus, and
especially Capella, have parallaxes from three to eight times
less than a star of the sixth magnitude in Cygnus. More-
over, the two stars which after 2151 Puppis and e Indi show
the most rapid proper motion, viz., the star just mentioned
in the Swan (with an annual motion of 5"- 123), and No.
1830 of Groombridge, which in France is called Argelander's
star (with an annual motion of 6"- 974), are three and four
times more distant from the sun than a 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. Al-
though, therefore, generally speaking, it may be probable that
the brightest stars are nearest to us, still there may be cer-
tain special very remote stars, whose photospheres and sur-
faces, from the nature of their physical constitution, maintain
a very intense luminous process. Stars which from their
brilliancy we reckon to be of the first magnitude, may be
further distant from us than others of the fourth, or even of
the sixth 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 systems 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 in-
tensity of the reflected light does not seem to depend on dis-
tance. The immediate connection subsisting between our
still imperfect knowledge of parallaxes, and our knowledge of

* On the proportion of the amount of proper motion to the proximity
of the brighter stars, see Struve, Stell, compot. Mensuree Aficrom., p
clxi?.

VOL. Ill -I

194 COSMOS.

the whole structural configuration of the universe, lends a pe-
culiar charm to those investigations which relate to the dis-
tances 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
parallaxes. If, for instance, the plane of the orbit which the
secondary star describes around the central 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 secondary 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 toward 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 tlio half revolution
through its more remote side will prove to be longer than the
time in the side turned toward the observer. The sum of
the two unequal times will always be equal to the true pe-
riodic time ; for the inequalities caused by the velocity of light
reciprocally destroy each other. From these relations of du-
ration, it is possible, according to Savary's ingenious method
of changing days and parts of days into a standard of length
(on the assumption that light traverses 14,356 millions of
geographical miles in twenty-four hours), to arrive at the
absolute magnitude 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
duration of proper motion, that is to say, of the changes which
take place in the positions of self-luminous stars,, throws some

* Savary, in the Connaissance des Temps pour 1830, p. 56-69, and
p. 163-171; and Struve, ibid., D. clxiv.

PROPER MOTION OF THE STARS. 195

light on two mutually dependent problems ; namely, the mo-
tion of the solar system,* and the position of the center of
gravity in the heaven of the fixed stars. 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 on such causal connection. Of the two prob-
lems just mentioned, the first alone (especially since Arge-
lander's admirable investigation) admits of being solved with
a certain degree of satisfactory precision ; the latter has been
considered with much acuteness by Madler, but, according
to the confession of this astronomer himself, t his attempted
solution is, in consequence of the many mutually compensa-
ting forces which enter into it, devoid " of any thing like evi-
dence amounting to a complete and scientifically certain
proof."

After carefully allowing for all that is due to the preces-
sion of the equinoxes, the nutation of the earth's axis, the
aberration of light, and the change of parallax caused by the
earth's revolution round the sun, the remaining annual mo-
tion of the fixed stars comprises at once that which is the
consequence of the translation in space of the whole sola?
system, and that also which is the result of the actual propel
motion -of the fixed stars. In Bradley's masterly labors 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.J " For if our own solar
system be conceived to change its place with respect to ab-
solute space, this might, in process of time, occasion an ap-
parent change in the angular distances of the fixed stars ;
and in such a case, the places of the nearest stars being more
affected than of those that are very remote, their relative
positions might seem to alter, though the stars themselves
were really immovable. 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 proper the direction of the motion is, to be ren-
dered perceptible by us. Since, then, the relative places of

• Cosmot, vol. i., p. 146. t Madler, Astronomic, B. 414.

t Arago, in his Annuaire pour 1842, p. 383, was the first to call at-
tention to this remarkable passage of Bradley's. See, in the same An-
nuaire, the section on the translation of the entire solar system, p. 389-
399.

i96 COSMOS.

the stars may be changed from such a variety of causes, con-
sidering that amazing distance at which it is certain some
of them are placed, it may require the observations of many
ages to determine 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 sys-
tem, were in turn advanced in the writings of Tobias Mayer,
Lambert, and Lalande ; but William Herschel had the great
merit of being the first to verify the conj ecture by actual ob-
servations (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 to-
ward 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 3 1 9 stars, and with a refer-
ence to Lundahl's investigations, found it for 1800: R.A.
257° 54'-l, Decl. +28° 49'-2 ; for 1850, R.A. 258° 23'-5,
Decl. +28° 45'-6. Otto Struve (from 392 stars) made it to
be for 1800 : R. A. 261° 26'-9, Decl. +37° 35'-5 ; for 1850,
261° 52'-6, Decl. 37° 33'-0. According to Gauss,* the point
in question falls within a quadrangle, whose extremes are,
R. A. 258° 40', and Decl. 30° 40' ; R. A. 258° 42', Decl.
+30° 57'; R.A. 259° 13', Decl. +31° 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 south-
ern hemisphere which never appear above the horizon in Eu-
rope. To this inquiry Galloway has devoted his especial
attention. He has compared the very recent calculations
(1830) 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 stars is extremely sat-
isfactory.

If, then, the progressive motion of our solar system may
be considered as determined within moderate limits, the

* In a letter addressed to me. See Sebum., Astr. Nachr., No. 622,
6. 348.

t Galloway, on the Motion of the Solar System, in the Phdot. Trant-
act. for 1847, p. 98.

MOTION OF THE STARS. 197

question naturally arises, Is the world of the fixed stars com-
oosed merely of a number of neighboring partial systems di-
vided into groups, or must we assume the existence of a uni-
versal relation, a rotation of all self-luminous celestial bodies
(suns) around one common center of gravity which is either
filed u-ith matter or void ? We here, however, enter the
domain of mere conjecture, to which, indeed, it is not im-
possible to give a scientific form, but which, owing to the
incompleteness of the materials of observation and analogy
which are at present 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 in-
finite number of very small stars from the tenth to the four-
teenth magnitude, which appear to be scattered among the
brighter ones, especially in the important part of the starry
stratum to which we belong, the annuli of the Milky Way,
is extremely prejudicial to the profound mathematical treat-
ment of problems so difficult of solution. The contempla-
tion 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 individual 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 universe).* The in-
ference here advanced, and founded on the analogy of our
own solar system, is, however, refuted 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 center of gravity. No doubt something
similar takes place in our own planetary system, inasmuch
as the planets do not properly move round the center of the
solar body, but around the common center of gravity of all
the masses in the system. But this common center of grav-
ity falls, according to the relative positions of the great plan-
ets Jupiter and Saturn, sometimes within the circumference
of the sun's body, but oftener out of it.f The center of
gravity, which in the case of the double stars is a void is

* Toe value or worthlessness of such views has been discussed by
Argelanderin his essay, " Ueber die eigene Bewegung des Sonnensysteott
kergelettet avs der eigenen Bewegwng der Sterne, 1837, s. 39.

t See Cosmot, vol. i., p. 145. (Madler, Attr., p. 400.)

accordingly, in the solar system, at one time void, at another
occupied by matter. All that has been advanced with re-
gard to the existence of a dark central body in the center
of gravity of double stars, or at least of one originally dark,
but faintly illuminated by the 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 planet-
ary system which changes its place, but also for the proper
motion of the fixed ^stars at their various distances, the cen-
ter of this revolving motion must be 90° distant* from the
point toward which our solar system is moving. In this con-
nection of ideas, the position of stars possessing a great or
very small proper motion becomes of considerable moment.
Argelander has examined, with his usual caution and acute-
ness, the degree of probability with which we may seek for
a general center of attraction for our starry stratum in the
constellation of Perseus. t Madler, rejecting the hypothesis
of the existence of a central body preponderating in mass,
as the universal center of gravity, seeks the center of grav-
ity in the Pleiades, in the very center of this group, in or
nearf to the bright star TJ Tauri (Alcyone). The present is

* Argelander, ibid., p. 42 ; Madler, CentraJsonne, s. 9, and Astr., s.
403.

t Argelauder, ibid., p. 43 ; and in Sebum., Astr. Nachr., No. 566.
Guided by no numerical investigations, but following 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,
Astr. Stell., p. 17, No. 19.)

t Madler, Astr., s. 380, 400, 407, and 414 ; in his Centraltonne, 1846,
p. 44-47 ; in Untersiickungen uber die Fixstern-Systeme, th. ii., s. 183-
185. Alcyone is in R. A. 54° 30', Decl. 23° 36', for the year 1840. If
Alcyone's parallax were really 0"-0065, its distance would be equal to
3H million semi-diameters of the earth's orbit, and thus it would be
fifty 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 sun in 8' 18"-2, would in that case take 500
years to pass from Alcyone to the earth. The fancy of the Greeks de-
lighted itself in wild visions of the height of falls. In Hesiod's Theo-
gonia, v. 722-725, it is said, speaking of the fall of the Titans into Tar-
tarus: " 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 777,600 seconds of time gives an equivalent in distance of
309,424 geographical miles (allowance being made, according to Galle's
calculation, for the considerable diminution in the force of attraction at
planetary distances), therefore 1 i times the distance of the moon from

DOUBLE STARS. 199

not the place to discuss the probability or improbability* of
such an hypothesis. Praise is, however, due to the eminent-
ly active director of the Observatory at Dorpat for having,
by his diligent labors, determined the positions and proper
motions of more than 800 stars, and at the same time ex-
cited investigations which, if they do not lead to the satis-
factory solution of the great problem itself, are nevertheless
calculated to throw light on kindred questions of physical
astronomy.

VI.

MULTIPLE OR DOUBLE STARS.— THEIR NUMBERS AND RECIPROCAL
DISTANCES.— PERIOD OF REVOLUTION OF TWO SUNS ROUND A COM-
MON CENTER OF GRAVITY.

WHEN, in contemplating the systems of the fixed stars, we
descend from hypothetical, higher, and more general consid-
erations 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 be-
long the binary or double stars, several self-luminous cosmic-
al bodies (suns) are connected by mutual attraction, which
necessarily gives rise to motions in closed curved lines. Be-
fore actual observation had established the fact of the revo-
lution of the double stars.t such movements in closed curves
were only known to exist in our own planetary 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

the earth. But, according to the Iliad, 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 (Il-
iad, 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 omnipo-
tence.

* Compare the doubts of Peters, in Schum., Astr. Nachr., 1849, s.
661, and Sir John Herschel, in the Outl. of Astr., p. 589 : " In the pres-
ent defective state of our knowledge respecting the proper motion of
the smaller stars, we can not but regard all attempts of the kind as to
a certain extent premature, though by no means to be discouraged as
forerunners of something more decisive."

t Compare Cosmos, vol. i., p. 146-149. (Struve, Ueber Dopplesternc
*ach Dorpater Micnmeter-Messungen von 1824 bis 1837, s. 11.)

200 COSMOS.

pair of stars, the close proximity of which precluded their
separation by the naked eye (as in the case of Castor, a
Lyrse, (3 Orionis, and a Centauri), this designation naturally
comprised two classes of multiple stars : firstly, those which,
from their incidental 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 in mutual attraction and reciprocal action,
and thus constitute a particular, isolated, sidereal system.
The former have long been called optically, the latter phys-
ically, double stars. By reason of their great distance, and
the slowness of their elliptical motion, many of the latter 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 of 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 optical combinations, without any closer physical con-
nection.* In sections II. and III. I have already treated of
the difficulty of separating by the naked eye adjacent stars,
with the very unequal intensity of light, of the influence of
the higher brilliancy and the star's tails, as well as of the
organic defects which produce indistinct vision.

Galileo, without making the double stars an especial ob-
ject of his telescopic observations (to which his low magni-
fying powers would have proved a serious obstacle), men-
tions (in a famous passage of the Giornata terza of his Dis-
courses, which has already been pointed out by Arago) the
use which astronomers might make of optically double stars
(quando si trovasse nel telescopic qualche picciolissima stella
vicinissima ad alcuna delle maggiori) for determining the
parallax of the fixed stars, t As late as the middle of the
last century, scarcely twenty double stars were set down in
the stellar catalogues, if we exclude all those at a greater

* Vide tupra. As a remarkable instance of acuteness of vision, we
may further mention that MSstlin, Kepler's teacher, discovered with the
naked eye fourteen, and some of the ancients nine, of the stars in the
Pleiades. (Madler, Untersuch. fiber die Fixslern-Systeme, th. ii., s. 36.)

t Vide supra. Dr. Gregory, of Edinburgh, also, in 1675 (consequent-
ly thirty-three years after Galileo's decease), recommended the samo
parallactic method. See Thomas Birch, Hist, of the Royal Soe., vol.
iii., 1757, p. 225. Bradley (1748) alludes to this method at the conclu-
sion of his celebrated treatise on Nutation.

DOUBLE STARS. 201

distance from each other than 32" ; at present, a hundred
yeais later (thanks chiefly to the great labors of Sir Will-
iam Herschel, Sir John Herschel, and Struve), about 60UO
have been discovered in the two hemispheres. To the ear-
liest described double stars* belong £ Ursae maj. (7th Sep-
tember, 1700, by Gottfried Kirch), a Centauri (1709, by Feu-
illee), y Virginis (1718), a Geminorum (1719), 61 Cygni
(1753) (which, with the two preceding, was observed by
Bradley, both in relation to distance and angle of direction),
p Ophiuclii 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 spec-
ulative thinkers, endowed with great powers of combination,
Lambert (Photometria, 1760 ; Kosmologische Briefe uber
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 binary 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 center of gravity." Michell,$
who was not acquainted with the ideas of Kant and Lam-
bert, was the first who applied the calculus of probabilities
to small groups of stars, which he did with great ingenuity,
especially to multiple stars, both binary and quaternary. He
showed that it was 500,000 chances to 1 that the colloca-
tion 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. $

* Miicller, Astr., s. 477. t Arago, in the Annuairepour 1842, p. 400.

t An Inquiry into the probable parallax and magnitude of the fixed
stars, from the quantity of light which they afford us, and the particu-
lar circumstances of their situation, by the Rev. John Michell; in the
Pkilos. Transact., vol. Ivii., p. 234-261.

$ John Michell, ibid., p. 238. " If it should hereafter be found that
any of the stars have others revolving about them (for 110 satellites bv

202 COSMOS.

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 cotemporaries, 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 carefully-conducted observations, because his theory of
the phenomena was rejected ; and yet Christian Mayer, in
his rejoinder to the attack of Father Maximilian Hell, Di-
rector of the Imperial Observatory at Vienna, expressly as-
serts " 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 compan-
ion— are self-luminous suns revolving round each other."

a borrowed light could possibly be visible"), we should then have the
means of discovering " Throughout the whole discussion he de-
nies that one of the two revolving stars can be a dark planet shining
with a reflected light, because both of them, notwithstanding their dis-
tance, 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 further says,
at p. 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 gravitation. It is high-
ly probable in particular, and next to a certainty in general, that such
double stars as appear to consist of two or more stars placed near to-
gether are under the influence of some general law, such, perhaps, as

gravity " (Consult also Arago, in the Annuaire pour 1834, p. 308,

and Ann. 1842, p. 400.) No great reliance can be placed on the indi-
vidual numerical results of the calculus of probabilities given by Michell,
as the hypotheses that there are 230 stars ir the heavens which, in in-
tensity of light, are equal to (3 Capricorn!, KJid 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. 320) 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 accompanied by a
change of color. " Besides their brightness, there is in the scintillation
of the fixed stars a change of color." ( Vide supra.)

DOUBLE STARS. 203

The importance of Christian Mayer's labors has, long after
his death, been thankfully and publicly acknowledged by
Struve and Madler. In his two treatises, Vertheidigung
neuer Beobachtungen von Fixstern-trabanten (1778), and
Dissertatio de novis in Ccdo sidereo Phcenomenis (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 him-
self, by means of the excellent eight-feet telescope of the Man
heim Mural Gluadrant ; " many even now constitute very
difficult objects of observation, which none but very power-
ful instruments are capable of representing, such as p and
71 Herculis, « 5 Lyrse, and GJ Piscium." Mayer, it is true
(as was the practice long after his time), only measured dis-
tances in right ascension and declination by meridian instru-
ments, 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 consider-
ation 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, 1783, and
1804, he has not only set down and determined the position
and distance of 846 double stars,! for the most part first dis-
covered by himself, but, what is far more important 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 colors, and classification according to the amount

* Struve, in the Recueil des Actes de la Stance publique de VAcad.
Imp. des Sciences de St. Petersbourg, le 29 Dec., 1832, p. 48-50. Mad-
ler, A*tr., s. 478.

t Philos. Transact, for the Year 1782, p. 40-126; for 1783, p. 112-
124 ; for 1804, p. 87. Regarding the observations on which Sir Will-
iam Herschel founded his views respecting the 846 double stars, see
Madler, in Schumacher's Jahrbuchfur 1839, s. 59, and his Untertuchun-
gen itler die Fixstern-Systeme, th. i., 18 17. s. 7.

204 COSMOS.

of their mutual distances. Full of imagination, yet alwayg
proceeding with great caution, it was not till the year 1794,
while distinguishing between optically and physically double
Btars, that he threw out his preliminary suggestions as to the
nature of the relation of the larger star to its smaller com-
panion. Nine years afterward, he first explained his views
of the whole system of these phenomena, in the 93d volume
of the Philosophical Transactions. The idea of partial
star-systems, in which several suns revolve round a common
center of gravity, was then firmly established. The stupen-
dous influence of attractive 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 com-
pelled the great comet of 1680 to return in its orbit, at the
distance of 28 of Neptune's semi-diameters (853 mean dis-
tances of the earth, or 70,800 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
18,240 semi-diameters of Neptune's orbit (i. e., 550,900
earth's mean distances, or 45,576,000 millions of geograph-
ical miles). But although Sir William Herschel so clearly
discerned the causes and general connection of the phenome-
na, still, in the first few years of the nineteenth century, the
angles of position 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 himself alludes to the doubts regarding the accu-
racy of the assigned periods of revolution of a Geminorum
(334 years instead of 520, according to Madler),* of y Vir-
ginis (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 1813 to
1842) and Sir John Herschel (from 1819 to 1838), availing
themselves of the great improvements in astronomical in-
struments, and especially in micrometrical applications, have,
with praiseworthy diligence, laid the proper and special foun-

* Madler, ibid., th. i., s. 255. For Castor we have two old observa-
tions 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 Virginia,
•ee Madler, Fixslern-Syst., th. ii., s. 234-40, 1848.

DOUBLE STARS 205

dation 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, con-
taining 3112 double stars, down to the ninth magnitude, in
distances under 32", of which only about one sixth had been
before observed. To accomplish this work, nearly 120,000
fixed stars were examined by means of the great Fraun-
hofer refractor. Struve's third table of multiple stars ap-
peared in the year 1837, and forms the important work Stel-
larum compositarum Mensurcs Micrometrices.* It contains
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 knowl-
edge of the southern hemisphere, constitutes an epoch in
astronomy,t has been the means of enriching this numbei
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
included in the six catalogues which contain 3346 double
stars, and were transmitted by Sir John Herschel to the As-
tronomical Society for the sixth and ninth parts of their val-
uable Memoirs.^. In these European catalogues are laid
down the 380 double stars which the above celebrated as-
tronomer had observed in 1825, conjointly with Sir James
South.

We trace in this historical sketch the gradual advance
made by the science of astronomy toward a thorough knowl-
edge 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 Bes-
sel with the excellent Fraunhofer heliometer, by Argelan-
der§ at Abo (1827-1835), by Encke and G-alle at Berlin

* Struve, Mensuree Microm., p. 40 and 234-248. On the whole,
26414-146, ». e., 2787 double stars have been observed. (Madler, in
Sebum., Jakrb., 1839, s. 64.)

t Sir John Herschel, Attron. Observ. at the Cape of Good Hope, p.
16.5-303. t Ibid., p. 167 and 242.

$ Argelander, in order carefully to investigate their proper motion,
examined a great number of fixed stars. See his essay, entitled "DLX.
Stellarum fixarum positionet media, ineunte anno 1830, ex observ. Aboa
habitit (Heltingfortia, 1825)." Madler (Astr., a. 625) estimates the

206 COSMOS.

(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 imme-
diate 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 re-
volving companions are gradually but constantly being dis-
covered. Extreme slowness of motion, or the direction of the
plane of the orbit as presented to the eye, being such as to
render the position of the revolving star unfavorable for ob-
servation, 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 (i. e., a com-
mon progressive movement, like that of our solar system, in-
cluding the earth and moon, Jupiter, Saturn, Uranus, and
Neptune, with their satellites), which in the case of a con-
siderable number of multiple stars has been proved by Arge-
lander and Bessel, bears evidence that the principal stars
and their companions stand in undoubted relation to each
other in separate partial systems. Madler has made the in-
teresting remark, that whereas, previous to 1836, among
2640 double 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 probable ; at present, the proportion of physically
double stars to optically double stars has changed so greatly
in favor of the former, that among the 6000 double stars,
according to a table published in 1849, 650 are known in
which a change of relative position can be incontestably
proved.* The earliest comparison gave one sixteenth, the

number of multiple stars in the northern hemisphere, discovered at
Pulkowa since 1837, at not less than 600.

* The number of fixed stars in which proper motion has been un-
doubtedly 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, Astr., s. 394, 490, and 520-540.)
Results obtained by the application of the Calculus of Probabilities, ac-
cording as the several reciprocal distances of the double stars are be-
tween 0" and 1", 2" and 8 , or 16" and 32", are given by Struve, in his
Mens. Microm., p. xciv. Distances less than 0"-8 have been taken, and

DOUBLE STARS. 207

most recent gives one ninth, as the proportion of the cosmic-
al bodies which, by an observed motion both of the primary
star and the companion, are manifestly proved to be phys-
ically 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 frequently occur in the direc-
tion of certain constellations (Andromeda, Bootes, the Great
Bear, the Lynx, and Orion). For the southern 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 correspond-
ing portion of the northern." And yet these beautiful south-
ern regions have been explored, under the most favorable
circumstances, by one of the most experienced of observers,
with a brilliant twenty-feet reflecting telescope, which sep-
arated stars of the eighth magnitude at distances even of
three quarters of a second.*

The frequent occurrence of contrasted colors constitutes an
extremely remarkable peculiarity of multiple stars. Struve,
in his great workf published in 1837, gave the following re-
sults with regard to the colors presented by six hundred of
the brighter double stars. In 375 of these, the color 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 colors were 120
in number, or one fifth of the whole ; and in the remaining
four fifths the principal and companion stars were uniform in
color. In nearly one half of these six hundred, the princi-
pal star and its companion were white. Among those of
different colors, combinations of yellow with blue (as in i
Cancri), and of orange with green (as in the ternary star y
Andromedae),t are of frequent occurrence.

Arago was the first to call attention to the fact that the
diversity of color in the binary systems principally, or at least,
in very many cases, has reference to the complementary col-
experiments with very complicated systems have confirmed the astron-
omer in the hope that these estimates are mostly correct within 0"'l
(Strnve, iiber Doppelsterne nach Dorpater Beob., B. 29.)

* Sir John Herschel, Observations al tht Cape, p. 166.

t Struve, Mensurte Microm., p. Ixxvii. to Ixxxiv.

t Sir John Herschel, Outlines of Aslr., p. 579.

208 COSMOS.

ors — the subjective colors, which, when united, form white.*
It is a well known optical phenomenon that a faint 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. t There are in-

* Two glasses, which exhibit complementary colors when placed one
upon the other, are used to exhibit white images of the sun. During
my long residence at the Observatory at Paris, my friend very success-
fully availed himself of this contrivance, instead of using shade glasses
to observe the sun's disk. The colors to be chosen are red and green,
yellow and blue, or green and violet. " Lorsqu'une lumiere forte ue
trouve aupres d'une lumiere faible, la derniere prend la teinte comple-
mentaire de la premiere. C'est la le contrast*; mais comme le rouge
n'est presque jamais pur, on peut tout aussi bien dire que le rouge est
complementaire du bleu. Les couleurs voisines du spectre solaire so
substitueut." " When a strong light is brought into contact with a
feeble one, the latter assumes the complementary color of the former.
This is the effect of contrast ; but as red is scarcely ever pure, it may
as correctly be said that red is the complementary of blue : the colors
nearest to the solar spectrum reciprocally change." (Arago, MS. of
1847.)

t Arago, in the Connaisance des Temps pour Van 1 828, p. 299-300 ;
and in the Annuaire pour 1834, p. 246-250; pour 1842, p. 347-350:
" Les exceptions que je cite, prouvent que j'avais bien raison en 1825
de n'introduire la notion physique du contraste dans la question des etoi-
les doubles qu'avec la plus grande reserve. Le bleu est la couleur re-
elle de certaines etoiles. II resulte des observations recueillies jusqu'ici
que le firmament est non seulement parseme de soleils rouges etjaunes,
comme le savaient les auciens, ma isencore de soleils Ileus et verts.
C'est au terns et a des observations futures & nous apprendre si les etoi-
les vertes et bleues ne sont pas des soleils deja en voie de decroissance ;
si les differentes nuances de ces astres n'indiquent pas que la combustion
s'y ope re 4 differens degres ; si la teinte, avec exces de rayons les plus
refrangibles, que presente souvent la petite etoile, ne tiendrait pas a la
force absorbante d'une atmosphere que developperait Faction de *' etoile,
ordinairement beaucoup plus brillante, qu'elle accompagne." " The
exceptions I have named proved that in 1825 I was quite right in the
cautious reservations with which I introduced the physical notion of
contrast in connection with double stars. Blue is the real color of cer
tain 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 blue and green suns.
Time and future observations must determine whether red and blue
stars are not suns, the brightness of which is already on the wane;
whether the varied appearances of these orbs do not indicate the de-
gree of combustion at work within them ; whether the color and the
excess of the most refrangible rays often presented by the smaller of
two stars be not owing to the absorbing force of an atmosphere devel

DOUBLE STARS. 209

stances in which a brilliant white star (1527 Leonis, 1768
Can. ven.) is accompanied by a small blue star ; others, where
in a double star (8 Serp.) both the principal and its companion
are blue.* In order to determine whether the contrast of
colors 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. Ixxx.), where the prin-
cipal star is bluish, and the companion pure white. If, in
the multiple stars, the differently colored suns are frequently
surrounded by planets invisible to us, the latter, being differ-
ently illuminated, must have their white, blue, red, and green
days.f

As the periodical variability^, of the stars is, as we have
already pointed out, by no means necessarily connected with
their red or reddish color, so also coloring in general, or a
contrasting difference of the tones of color between the prin-
cipal star and its companion, is far from being peculiar to
the multiple stars. Circumstances which we find to be fre-
quent are not, on that account, necessary conditions of the
phenomena, whether relating to a periodical change of light,
or to the revolution in partial systems round a common cen-
ter of gravity. A careful examination of the bright double
stars (and color can be determined even in those of the ninth
magnitude) teaches that, besides white, all the colors 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 fre-
quent as the blue and bluish ; the white are about 21 times
as numerous as the red and reddish. It is moreover remark-
able that a great difference of color is usually associated with

oped by the action of the accompanying star, -which is generally much
the more brilliant of the two." (Arago, in the Annuairepour 1834, p.
295-301.)

* Struve, Ueber Doppdtterne nach Dorpater Beobachtungen, 1837, a.
33-36, and Mensurce Microm., p. Ixxxiii., enumerates sixty-three double
Btarsin which both the principal and companion are blue or bluish, and
in which, therefore, the colcrs can not be the effect of contrast. When
\ve are forced to compare together the colors of double stars, as report-
ed by several astronomers, it is particularly striking to observe how fre-
quently the companion of a red or orange-colored star is reported by
some observers as blue, and by others as green.

t Arago, Annuain pour 1834, p. 302. t Vide tupra, p. 130-136.

210 COSMOS.

a corresponding difference in brightness. In two cases — in
£ Bootis and y Leonis — which, from their great brightness,
can easily be measured by powerful telescopes, even in the
daytime, the former consists of two white stars of the third
and fourth magnitudes, and the latter of a principal star of
the second, and of a companion of the 3 -5th magnitude.
This is usually called the brightest double star of the north-
ern hemisphere, whereas a Centauri* and a Crucis, in the
southern hemisphere, surpass all the other double stars in
brilliancy. As in £ Bootis, so also in a 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 t several times made mention
of the somewhat irregular variability of luster in the orange-
colored principal star in a Herculis. Moreover, the fluctua-
tion in the brightness of the nearly equal yellowish stars (of
the third 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.J
Whether any actual change of color has ever taken place
in double stars (as, for instance, in y Leonis and y Delphini) ;
whether their white light becomes colored, and, on the other
hand, whether the colored light of the isolated Sirius has be-
come white, still remain undecided questions. § Where the
disputed differences refer only to faint tones of color, we should
take into consideration the power of vision of the observer,
and, if refractors have not been employed, the frequently red-
dening influence of the metallic speculum.

Among the multiple systems we may cite as ternaries, £
Librae, £ Cancri, 12 Lyncis, 11 Monoc. ; as quaternaries,
102 and 2681 of Struve's Catalogue, a Andromedae, e Lyrae :
in 6 Orionis, the famous trapezium of the greater nebula of

* " This superb double star (a Cent.) is beyond all comparison the
most striking object of the kind in the heavens, and consists of two in-
dividuals, both of a high ruddy or orange color, though that of the
smaller is of a somewhat more somber and brownish cast." (Sir John
Herschel, Observations at the Cape of Good Hope, p. 300.) And, ac-
cording 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 first magnitude, and the satellite from the 2'5th to
the third magnitude. ( Transact, of tht Royal Soc. of Edinb., vol. X'vn
1849, p. 451.)

t Videtupra, p. 165, 166, and note.

t Struve, Ueber Doppeltt. nach Dorp Beob., s. 33. $ Ibid., s. 36

DOUBLE STARS. 211

Orion, we have a combination of six — probably a system sub-
ject to peculiar physical attraction, since the five smaller
stars (6'3m. ; 7m.; 8m.; ll'Sm. ; and 12m.) follow the prop-
er motion of the principal star, 4-7m. No change in their
relative positions has yet been observed.* In the ternary
combinations of £ Librae and £ Cancri, the periodical move-
ment of the two companions has been recognized with great
certainty. The latter system consists of three stars of the
third magnitude, differing very little in brightness, and the
nearer companion appears to have a motion ten times more
rapid than the remoter one.

Tho 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. t Of these, £ Herculis
has twice completed its orbit since the epoch of its first dis-
covery, 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 measurements of
the orbits of double stars, we are indebted to the industry of
Savary (£ Ursae Maj.), Encke (70 Ophiuchi), and Sir John
Herschel. These have been subsequently followed by Bes-
sel, Struve, Madler, Hind, Smyth, and Captain Jacob. Sa-
vary's and Encke's methods require four complete observa-
tions, taken at sufficient intervals from each other. The
shortest periods of revolution are thirty, forty- two, fifty-eight,
and seventy-seven years ; consequently, intermediate be-
tween 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, re-
sembling that of comets, increasing from 0'62 (a Coronae) up
to 0'95 (a Centauri). The least eccentric interior comet—-
that of Faye — has an eccentricity of 0-55, or less than that
of the orbits of the two double stars just mentioned. Ac-
cording to Midler's and Hind's calculations, i\ Coronas 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

* Madler, Astr., s. 517. Sir John Herschel, Ovtl., p. 568.

t Compare Madler, Untertuch. uber die Fixstcm-Systeme, th. i., s.
225-273 ; th. ii., s. 235-240 ; and his Astr., a. 541 Sir John HerscheL
Outl., p. 573.

212 COSMOS.

two of the smaller principal planets in our solar system, the
eccentricity of the orhit of Pallas being 0-24, and that of
Juno, 0-25.

If, with Encke, we consider one of the two stars in a bi-
nary system, the brighter, to be at rest, and on this supposi-
tion refer to it the motion of the companion, then it follows
from the observations hitherto made that the companion de-
scribes 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 su-
perficial areas in equal times. Accurate measurements of
the angles of position and of distances, adapted to the determ-
ination of orbits, have already shown, in a considerable num-
ber of double stars, that the companion revolves round the
principal star considered as stationary, impelled by the same
gravitating forces which prevail in our own solar system.
This firm conviction, which has only been thoroughly attain-
ed within the last quarter of a century, marks a great epoch
in the history of the development of higher cosmical knowl-
edge. Cosmical bodies, to which long use has still preserved
the name of fixed stars, although they are neither riveted
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 en-
large our view, by showing that these movements are them-
selves subordinate to more general movements animating th»
regions of space.

DOUBLE STARS.
ELEMENTS OF THE ORBITS OF DOUBLE STARS.

213

_t

Semi-Major
Axis.

Eccentricity.

Period of
Revolution
in yean.

Calculator.

(1) f UrsseMaj....

3"-857

0-4164

58-262

Savary, 1830.

3"-278
2"-295

0-3777
04037

60-720
61-300

John Herschel.
Tables of 1849.
Madler, 1847.

(2) pOphiuchi

4"-328

04300

73-862

Encke, 1832.

(3) fHerculis
(4) Castor

1"-208
8"-086

04320
0-7582

3022
252-66

Madler, 1847
John Herschel

5"-692

0-2194

519-77

Tables of 1849.
Madler, 1847.

6"-300

0-2405

632-27

Hind, 1849.

(5) y Virginia

3"-580
3"-863

0-8795
0-8806

182-12
169-44

John Herschel.
Tables of 1849.
Madler, 1847.

(6) oCentauri

15"-500

09500

7700

Captain Jacob,
1848.

INDEX TO VOL. III.

ACHROMATIC telescopes, 63.

Adalbert, Prince, of Prussia, his observa-
tions on the undulation of the stars, 59.

Alcor, a star of the constellation Ursa Ma-
jor, employed by the Persians as a test
of vision, 49, 50, 200.

Alcyone, one of the Pleiades, imagined
the center of gravity of the solar sys-
tem by Madler, 198.

Alphonsine Tables, date of their construc-
tion, 151.

Anaxagoras of Clazomense, his theory
of the world-arranging intelligence, 11 ;
origin of the modern theories of rota-
tory motion, 12.

Andromeda's girdle, nebula in, 142.

Arago, M., letters and communications of,
to M. Humboldt, 46, 49, 67, 68, 73, 96,
207-209 ; on the effect of telescopes on
the visibility of the stars, 69 ; on the
velocity of light, 80, 84 ; on photometry,
92, 90 ; his cyanometer, 97.

Aratus, a fragment of the work of Hip-
parchas preserved in, 109.

Archimedes, his " Arenarius," 30.

Avcturus, true diameter of, 89.

Argulander, his view of the number of
the fixed stars, 105, 106 ; his additions
to Bessel's Catalogue, 115 ; on period-
ically variable stars, 166.

ij Argus, changes in color and brilliancy
of, 135, 178, 179.

Aristotle, his distinct apprehension of the
unity of nature, 13-15; his defective
solution of the problem, 15; doubts the
infinity of space, 29, 30 ; his idea of the
generation of heat by the movement of
the spheres, 124.

aosy, the domain of the fixed stars,

Astronomy, the observation of groups of
fixed stars, the first step in, 118 ; very
bright single stars, the first named, 89.

Atmosphere, limits of the, 40, 41 ; effects
of an untransparent, 104.

Augustine, St., cosmical views of, 124.

Autolycus of Pitane, era of, 89, 90.

Auzout's object-glasses, 62.

Bacon, Lord, the earliest views on the ve-
locity of light found in his "Novum
Organum," 79.

Baily , Francis, his revision of De Lalande's
Catalogue, 115.

Bayer's lettering of the stars of any con-
stellation not an evidence of their rel-
ative brightness, 98.

Berard, Captain, on the change of color
of the star y Crucis, 135.

Berlin Academy, star maps of the, 11B.

Bessel, on repulsive force, 34, 35 ; his star
maps have been the principal means of
the recognition of seven new planets,
116 ; calculation of the orbits of double
stars by, 211.

Binary stars, 199.

Blue stars, 136 ; less frequent than red, 209.

Blue and green suns, the probable cause
of their color, 208.

Bond, of the Cambridge Observatory,
United States, his resolution of the neb-
ula in Andromeda's girdle into small
stars, 142.

Brewster, Sir David, on the dark lines of
the prismatic spectra, 44.

British Association, their edition of La-
lande's Catalogue, 115.

Bruno, Giordano, his cosmical views, 17 ;
his martyrdom, 17.

Busch, Dr., his estimate of the velocity of
light incorrect, 82.

Catalogues, astronomical, their great im-
portance, 113, 114 ; future discoveries
of planetary bodies mainly dependent
on their completeness, 114 ; list of, 114,
115 ; Halley's, Flamstead's, and others,
114 ; Lalande's, Harding's, Bessel's, 115

Catasterisma of Eratosthenes, 89, 90.

a Centauri, Piazzi Smyth on, 146, 147, 185;
the nearest of the fixed stars that have
yet been measured, 191, 192.

Central body for the whole sidereal heav-
ens, existence of, doubtful, 197.

Chinese record of extraordinary stars (of
Ma-tuan-lin), 109, 155-159; deserving of
confidence, 162.

Clusters of stars, or stellar swarms, 140 ;
list of the principal, 141-143.

Coal-sacks, a portion of the Milky Way in
the southern hemisphere so called, 137.

Colored rings afford a direct measure of
the intensity of light, 96.

Colored stars, 130; evidence of change
of color in some, 131, 132; Sir John
Herschel's hypothesis, 131 ; difference
of color usually accompanied by differ
ence of brightness, 209.

Comets, information regarding celestial
space, derived from observation on, 31,
39 ; number of visible ones, 151.

Concentric rings of stars, a view favored
by recent observation, 149.

Constellations, arrangement of stars into,
very gradual, 119.

Contrasted colors of double stars, 207.

Cosmical contemplation, extension of, la
the Middle Ages, 16.

Cosmical vapor, question as to condensa-
tion of, 37 ; Tycho Brahe's and Sir Will-
iam Herschel's theories, 154.

" Cosmos," a pseudo-Aristotelian work,
16.

Crystal vault of heaven, date of the desig-
nation, 133 ; its signification according
to Empedocles, 123 ; the idea favored
by the Fathers of the Church, 125.

Cyanometer, Arago's, 97.

Dark cosmical bodies, question of, 164,
187.

Dolambrc on the velocity of light, 82.

Descartes, his cosmical views, 19, 20 ; sup-
presses his work from deference to the
Inquisition, 20.

Dioptric tubes, the precursors of the tele-
scope, 43.

Direct and reflected light, 45.

Distribution of the fixed stars, according
to right ascension, 140.

Dorpat Table (Struve's) of multiple stars,
205.

Double stars, the name too indiscrimin-
ately applied, 199, 200 ; distribution into
optical and physical. 200 ; pointed out
by Galileo as useful in determining the
parallax, 200 ; vast increase in their ob-
served number, 201, 205; those earliest
described, 201; number in which a
change of position has been proved,
206 ; greater number of double stars in
the northern than in the southern hem-
isphere, 207 ; occurrence of contrasted
colors, 207 ; calculation of their orbits,
211 ; table of the elements, 213.

Earth-animal, Kepler and Fludd's fancies

regarding the, 19.
Edda-Songs, allusion to, 8.
Egypt, zodiacal constellations of, their

date, 121.
Egyptian calendar, period of the complete

arrangement of the, 133.
Ehrenberg on the incalculable number

of animal organisms, 30.
Electrical light, velocity of transmission

of, 86.
Electricity, transmission of, through the

Elements, Indian origin of the hypothesis
of four or five, 11.

Emanations from the head of some com-
ets, 39.

Encke, his accurate calculation of the
equivalent of an equatorial degree, 81 ;
on the star-maps of the Berlin Academy,
116 ; an early calculator of the orbits
of double stars, 2C \ ; his theory of their
motion, 212.

Encke's comet, considerations on space,
derived from periods of revolution of,
27; a resisting medium proved from
observation on, 39.

Ether, different meanings of, in the East
and the West, 31, 32.

Ether (Ak£ so, in Sanscrit), one of the In-
dian five elements, 31.

Ether, the, fiery, 35.

Euler's comparative estimate of the light
f the sun and moon, 95.

Fixed stars, the term erroneous, 27, 122 ;
scintillation of the, 73 ; variations in its
intensity, 76 ; our sun one of the fainter
fixed stars, 95; photometric arrange-
ment of, 99 ; their number, 105 ; num-
ber visible at Berlin with the naked eye,
107; at Alexandria, 107; Struve and
Herschel's estimates, 116; grouping of
the, 117 ; distribution of the, 140 ; prop-
er motion of the, 182 ; parallax, 188 ;
number of, in which proper motion has
been discovered, greater than of those
in which change of position has been
observed, 206, 207.

Fizeau, M., his experiments on the veloc-

ity of light, 80, 83.
Formula for

computing variation of light
of a star, by Argelander, :

Galactic circle, average number of stars
in, and beyond the, 139.

Galileo indicates the means of discover-
ing the parallax, 188.

Galle, Dr., on Jupiter's satellites, 50 ; on
the photometric arrangement of the
fixed stars, 99.

Garnet star, the, a star in Cepheus, so
called by William Hcrschel, 1G6.

Gascoigne applies micrometer threads to
the telescope, 42.

Gauging the heavens, by Sir William Her-
schel, 138, 139 ; length of time neces-
sary to complete the process, 139.

Gauss, on the point of translation in space
of the whole solar system, 196.

Gilliss, Lieutenant, on the change of color
of the star ij Argus, 135.

Gravitation, not an essential property of
bodies, but the result of some higher
and still unknown power, 22, 23.

Greek sphere, date of the, 119, 121.

Green and blue suns, 208.

Groups of fixed stars, recognized even
by the rudest nations, 117 ; usually the
same groups, as the Pleiades, the Great
Bear, the Southern Cross, &c., 117, 118.

Halley asserted the motion of Sinus and
other fixed stars, 26, 27.

Hassenfratz, his description of the rays
of stars as caustics on the crystalline
lens, 52, 127.

Heat, radiating, 35.

Hepidannus, monk of Saint Gall, a new
star recorded by, 157, 162.

Herschel, Sir William, on the vivifying
action of the sun's rays, 34 ; his estimate
of the number of the fixed stars, 116,
117 ; his " gauging the heavens," and its
result, 138, 139.

Herschel, Sir John, on the transmission
of light, 30 ; on the influence of the sun'g
rays, 34 ; compares the sun to a per-
petual northern light, 34 ; on the at-
mosphere, 37 ; on the blackness of the
ground of the. heavens, 39 ; on stars
seen in daylight^ 57; on photometry.

217

93 ; photometric arrangement of the
fixed stars, 99 ; on the number of stars

Lassell's telescope, discoveries made by
means of, 65.

actually registered. 106 ; on the cause
of the red color of Sirius, 131, 132 ; on

Lepsius, on the Egyptian name (Sothis)
of Sinus, 134.

fhe Milky Way, 145; on the sun's place,
150; on the determined periods of vari-

Leslie's photometer, defects of, 96.
Libra, the constellation, date of its intro-

able stars, 166; number of double stars

duction into the Greek sphere, 120.

the elements of whose orbits have been

Light, always refracted, 44 ; prismatic

determined, 211.

spectra differ in number of dark lines

Hieroglyphical signification of a star, ac-
cording to Horapollo, 128.

according to their source, 44, 45 ; polar-
ization of, 45 ; velocity of, 79 ; ratio of

Hind's discovery of a new reddish-yellow

solar, lunar, and stellar, 95 ; variation

star of the fifth magnitude, in Ophiu-

of, in stars of ascertained and unascer-

magnitude, 160 ; calculation of the or-

tained periodicity, 168, 177.
Light of the sun and moon, Euler's and

bits of double stars by, 211.
Hipparchus. on the number of the Plei-

Michelo's estimates of the comparative,
95.

ades, 48 ; his catalogue contains the

Limited transparency of the celestial re-

earliest determination of the classes of

gions. 38.

magnitude of the stars, 90 ; a fragment
of his work preserved to us in Aratus,

IftO

Macrobius, " Sphsera aplanes" of, 27.
Madler, on Jupiter's satellites. 52 ; on the

ioy.

Holtzmann, on the Indian zodiacs, 121.
Homer, not an authority on the state of
Greek astronomy in his day, 119, 123.
Humboldt, Alexander von, works of,
quoted in various notes:
Ansichten der Natur, 79.
Asie Centrale, 111, 112.
Essai sur la Geogr. des Plantes, 58.
Examen Critique de 1'Histoire de la

determined periods of variable stars,
166; on future polar stars, 181 ; on non-
luminous stars, 187 ; on the center of
gravity of the solar system, 198.
Magellanic clouds, known to the Arabs, 91.
Magnitude of the stars, classes of, 90, 91.
Mafus, his discoveries regarding light, 45.
'• Mappa ccelestis" of Schwinck, 140.
Ma-tuan-lin, a Chinese astronomical rec-
ord of 109

G6ographie, 49, 112, 137.
Lettre a M. Schumacher, 93.
Recueil d'Observations Astrono-
miques, 43. 47, 93.
Relation Historique du Voyage aux
Regions Equinoxiales, 56, 58. 79, 93.
Vue des Cordilleres et Monumens
des Peuples Indigenes de 1'Amer-

Mayer, Christian, the first special observer
of the fixed stars, 202.
Melville Island, temperature of, 36.
Michell, John, 95 ; applies the calculus of
probabilities to small groups of stars,
201 ; little reliance to be placed in its
individual numerical result?, 202.
Michelo's comparative estimate of the

ique, 121, 136.
Humboldt, Wiihelm von, quoted, 25.
Huygens, Christian, his ambitious but un-
satisfactory Cosmotheoros, 20; exam-
ined the Milky Way, 144.

light of the sun and moon, 95.
Milky Way, average number of stars in,
and beyond the, according to Struve,
139 ; intensity of its light in the vicinity
of the Southern Cross, 147 ; its course

Huygens, Constantin, his improvements

and direction, 147; most of the new

in the telescope, 02.
Hvergelmir, the caldron-spring of the Ed-

stars have appeared in its neighbor-
hood, 162.

da-Songs, 8.

Morin proposes the application of the tel-

Indian fiction regarding the stars of the
Southern hemisphere, 138.

escope to the discovery of the stars in
daylight, 41, 66.

Indian theory of the five elements (Pant-

Motion, proper, of the fixed stars, 182;

echota*), 31.

variability of, 185, 186.

Indian zodiacs, their high antiquity doubt-
ful, 121.

Multiple stars, 130, 199 ; variable bright-
ness of, difference of opinion regarding,
210.

Jacob, Capt, on the intensity of light in
the Milky Way. 146; calculation of the

Nebulas, probably closely crowded stellar

orbits of double stars, by, 211.
Joannes Philoponus, on gravitation, 18.
Jupiter's satellites, estimate of the magni-
tudes of, 50; case in which they were
visible by the naked eye, 52 ; occulta-
tious of, observed by daylight, 62.

swarms, 37.
Neptune, the planet, its orbit used as a
measure of distance of 61 Cygni, 204.
New stars, 151 ; their small number, 151 ;
Tycho Brahe's description of one, 152 ;
its disappearance, 153 ; speculations as
to their origin, 161 : most have appear-

Kepler, his approach to the mathematical
application of the theory of gravitation.
18; rejects the idea of solid orbs, 126.

ed near the Milky Way, 162.
Newton, embraces by his theory of gravi-
tation the whole uranological portion

of the Cosmos, 21.

Lalande, his Catalogue, revised by Baily,
115.

Non-luminous stars, problematical exist-
ence of, 187.

VOL III.— K

218 INI

Numerical results exceeding the grasp
of the comprehension, furnished alike
by the minutest organisms and the so-
called fixed stars, 30 ; encouraging views
on the subject, 31.

Optical and physical double stars, 200;
often confounded, 200.

Orbits of double stars, calculation of the,
211 ; their great eccentricity, 211 ; hy-
pothesis, that the brighter of the two
stars is at rest, and its companion re-
volves about it, probably correct, and a
great epoch in cosmical knowledge, 212.

Orion, the six stars of the trapezium of
the nebula of, probably subject to pe-
culiar physical attraction, 210, 211.

Pantschata or Pantschatra, the Indian the-

ory of the five elements, 31.
Parallax, means of discovering the, point-

ed out by Galileo, 183 ; number of par-

allaxes hitherto discovered, 190 ; detail

of nine of the best ascertained, 190.
Penetrating power of the telescope, 145,

146.

Periodically changeable stars, 164.
Periods within periods of variable stars,

168 ; Argelander on, 168.
Peru, climate of, unfavorable to astronom-

ical observations, 103.
Peters on parallax, 192.
Photometric relations of self-luminous

bodies, 89 ; scale, 99.
Photometry yet in its infancy, 94 ; first

numerical scale of, 94 ; Arago's meth-

od, 96.

Plato on ultimate principles, 12, 13.
Pleiades, one of the, invisible to the naked

eye of ordinary visual power, 48 ; de-

scribed, 141.
Pliny estimates the number of stars vis-

ible in Italy at only 1600, 108.
Poisson, his view of the consolidation of

the earth's strata, 36, 37.
Polarization of light, 45, 47.
Poles of greatest cold, 36.
Pouillet's estimate of the temperature of

space, 36.
Prismatic spectra, 44 ; difference of the

dark lines of, 45.
Ptolemy, his classification of the stars,

90 ; southern constellations known to,

137.
Pulkowa, number of multiple stars dis-

covered at, 205, 206.
Pythagoreans, mathematical symbolism

of tno, 12.

Quaternary systems of stars, 210.

Radiating heat, 35.

Ratio of various colors among the mul-

tiple and double stars, 209.
Rays of ftars, 52, 126-128 ; number of, in-

dicate distances, 128; disappear when

the star is viewed through a very sma

aperture, 138, 129.
Red stars, 131 ; varia

j Reflecting sextants applied to the determ-
I ination of the intensity of stellar light.

1.
variable stars mostly red,

Reflecting and refracting telescopes, 63.
i Regal stars of the ancients, 136.
j Resisting medium, proved by observa-
tions on Kncke's and other comets, 39.
Right ascension, distribution of stars ac-
cording to, by Schwinck, 140.
Rings, colored, measurement of the in-
tensity of light by, 96.
Rings, concentric, of stars, the hypothesis
of, favored by the most recent observa-
! tions, 149.
i Rosse's, Lord, his great telescope, 65 ; it*

services to astronomy, 66.
I Ruby-colored stars, 135.

Saint Gall, the monk of, observed a new
j star distant from the Milky Way, 162.

Saussure asserts that stars may be seen
in daylight on the Alps, 57 ; the asser-
tion not supported by other travelers'
j experience, 58.

Savary, on the application of the aberra-
tion of light to the determination of the
parallaxes, 194 ; an early calculator of
the orbits of double stars, 211.

Schlegel, A. W. von, probably mistaken
as to the high antiquity of the Indian
zodiacs, 121

Schwinck, distribution of the fixed stars
in his " Mappa coslestis," 140.

Scintillation of the stars, 73 ; variations
in its intensity, 76 ; mentioned in the
Chinese records, 77 ; little observed in
tropical regions, 77, 78 ; always accom-
panied by a change of color, 202.

Seidel, his attempt to determine the quan-
tities of light of certain stars of the first
magnitude, 93.

Self-luminous cosmical bodies, or suns,
199.

Seneca, on discovering new planets, 28.

Simplicius, the Eclectic, contrasts the cen-
tripetal and centrifugal forces, 12 ; his
vague view of gravitation, 18.

Sirius, its absolute intensity of light, 95 ;
historically proved to have changed its
color, 131 ; its association with the ear-
liest development of civilization in the
valley of the Nile, 133 ; etymological re-
searches concerning, 133, 134.

Smyth, Capt W. H., calculations of the
orbits of double stars by, 211.

Smyth, Piazzi, on the Milky Way, 146,
147 ; on a Centauri, 185.

Sothis, the Egyptian name of Sirius, 133,

South, Sir James, observation of 380 dou-
ble stars by, in conjunction with Sir
John Herschel, 205.

Southern constellations known to Ptol-
emy, 137.

Southern Cross, formerly visible on the
shores of the Baltic-, 138.

Southern hemisphere, in parts remark-
ably deficient in constellations, 112; dis-
tances of its stars, first measured about
the end of the sixteenth century, 138.

219

Space, conjectures regarding, 29 ; com- | its influence
pared to the mythic period of history, I 37.
29; fallacy of attempts at measurement , Temporary stars,

the climate of the earth,

t of, 155 ; notoe to,

of, 30 ; po'rtions between cosmical bod- I 155-160."
jes not void, 31 ; its probable low tem- Ternary stars, 210.

perature, 35.

Spectra, the prismatic, 44 ; difference of
the dark lines of, according to their
sources, 45.

" Sphtera aplanes" of Macrobiue, 27.

Spurious diameter of stars, 130.

Star of the Magi, Ideler's explanation of
the, 154.

Star of St. Catharine, 137.

Star systems, partial, in which several
suns revolve about a common center
of gravity, 204.

Stars, division into wandering and non-
wandering, dates at least from the early
Greek period, 27 ; magnitude and visi-

Timur Ulugh Beg, improvements in prac-
tical astronomy in the time of, 91.

Translation in space of the whole solar
system, 195; first hinted by Bradley,
195 ; verified by actual observation by
William Herschel, 196; Argelander.
Strove, and Gauss's views, 196.

Trapezium in the great nebula of Orion,
investigated by Sir Wm. Herschel, 203.

Tycho Brahe, his vivid description of the
appearance of a new star, 152 ; his the-
ory of the formation of such, 154.

Ultimate mechanical cause" of all mo-
tion, unknown, 24, 25.

bility of the, 48 ; seen through shafts I Undulation of the stars, 58, 59.

of chimneys, 57 ; undulation of the, 58, ' Undulations of rays of light, various

59 ; observation of, by daylight, 66 ; ! lengths of, 84.

scintillation of the, 73 ; variations in its Unity of nature distinctly taught by Aris-

intensity, 76 ; the brightest the earliest totle, 13-15.

named, 89; rays of, 52, 127, 128 ; color Uranological and telluric domain of the
Cosmos, 26.

of, 130 ; distribution of, 140 ; concentric
rings of, 149 ; variable, 161 ; vanished,
163 ; periodically changeable, 164 ; non-
luminous, of doubtful existence, 187 ;
ratio of colored stars, 209.

Steinheil's experiments on the velocity
of the transmission of electricity, 87 ;
his photometer, 93.

Stellar clusters or swarms, 140.

Struve on the velocity of light, 82 ; his
estimate of the number of tine fixed
stars, 1 17 ; on the Milky Way, 139 ; his
Dorpat Tables, 205 ; on the contrasted
colors of multiple stars, 207 ; calcula-
tion of the orbits of double stars by, 211.

Sun, the, described as " a perpetual north-
ern light" by Sir William Herschel, 34 ;
in intensity of light merely one of the
fainter fixed stars, 95 ; its place prob-
ably in a comparatively desert region
of the starry stratum, and eccentric, 150.

Suns, self-luminous cosmical bodies, 199.

Uranus observed as a star by Flamstead
and others, 114.

Vanished stars, 163; statements about
such to be received with great caution,
163.

Variable brightness of multiple and dou-
ble stars, 209.

Variable stars, 160-161 ; mostly of a red
color, 165; irregularity of their periods,
167 ; table of, 172.

Velocity of light, 79 ; methods of determ-
ining, 80 ; applied to the determination
of the parallax, 195.

Visibility of objects, 55 ; how modified, 56.

Vision, natural and telescopic. 41 ; aver-
age natural, 47, 48; remarkable in-
stances of acute natural, 52, 55.

Wheatstone's experiments with revolv-
mirrors,45; velocity of electrical

ing IT

light determined by, 86."
Table of photometric arrangement of 190 White Ox, name given to the nebula now
fixed stars, 100 ; of 17 stars of first mag- known as one of the Magellanic clouds,

nitude, 102; of the variable stars, by

91.

Argelander, 172, and explanatory re- Wollaston's photometric researches, 95.

marks, 172-177; of ascertained paral- Wright, of Durham, his view of the origin

laxes, 193 : of the elements of the or- of the form of the Milky Way, 149.
bits of double stars, 213.

Telescope, the principle of, known to the Yggdrasil, the World-tree of the Edda-

Arabs, and probably to the Greeks and Songs, 8.
Romans, 42, 43 ; di

:overies by its

means, 61 ; successive improvements ' Zodiac, period of its introduction into the
Greek sphere, 119; its origin among the
Chaldeans, 120 ; the Greeks borrowed
from them only the idea of the division,
and filled its signs with their own cataa-
toriems, 120; great antiquity of the In-

of the, 62; enormous focal lensrth of
som.', 63; Lord Rosse's, 65; Bacon's
comparison of, to discovery ships, 130;
penetrating power of the, 145, 146.
Telesio, Bernardino, of Cosenza, his v:

of the

iews
phenomena of inert matter, 16.

Temperature, low, of cclcstiiil
uncertainty of results "el obta

space, 35;
ained, 36 ;

dian ver

130; great
•y doubtful,

-ID.
THE END.

Zodiacal light, Sir John Herschel on the,

A

if 3

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