UCrNRLF

UNIVERSITY OF CALIFORNIA.

FROM THE LIBRARY OF

DR. JOSEPH LECONTE.

GIFT OF MRS. LECONTE.
No.

COSMOS:

SKETCH

OF A

PHYSICAL DESCRIPTION OF THE UNIVERSE.

BY

ALEXANDER VON HUMBOLDT.

VOL. Ill— PART I.

Natures vero rerum vts atqtie majestas in omnibus momentisfide caret, si quit modo partet </'««
ae non totam complectatur animo.— PLIN. H. N. lib. vii. c. 1.

TRANSLATED UNDER THE SUPERINTENDENCE OF

LIEUT.-COL. EDWARD SABINE, E.A., Y.P.&TRBAS. R.S.

LONDON:

PRINTED FOR

LONGMAN, BROWN, GREEN, AND LONGMANS,

PATERNOSTER ROW J AMI)

JOHN MURRAY. ALBEMARLE STREET.

. 1851.
UNIVERSITY

QM

LONDOK :

VTitsoN AMD OOILTT, 57, SKIHNEB STKBBT,
SNOWHIU..

CONTENTS.

Page
INTKODTJCTION.

Historical Eeview of the attempts which had for their object
the consideration of the phenomena of the Universe re-
garded as a whole ..... 3—25

SPECIAL RESULTS OF OBSEKVATION IN
COSMICAL PHENOMENA.

A. UEAFOLOGICAI POETION of the physical description of
the universe.
a. ASTEOGWOSY ....... 26—29

I. Cosmical space, and conjectures respecting what
appears to occupy the intervals between the hea-
venly bodies . . . . . . . 30 — 42

n. Natural and telescopic vision, p. 43 — 67 ; Scin-
tillation of stars, p. 67—71 ; Velocity of light,
p. 71—78 ; Photometric results, p. 78—85 . 42—85

HI. Number, distribution, and colour of the fixed
stars, p. 86—118 ; Clusters of stars, p. 119—123 ;
Milky way, p. 124—131 ..... 86—131

IV. Newly appeared and vanished stars, p. 132 —
147 ; Variable stars with recurring and mea-
sured periods, p. 147 — 171 ; Variation of light
in celestial bodies of which the periodicity has
not yet been investigated, p. 171—177 . . 132— 177

98831

11

CONTENTS.

Page

V. Proper motion of the fixed stars, p. 178—182 ;

Problemetical existence of dark bodies, p. 182 —
185 ; Parallax and measured distances of some
of the fixed stars, p. 185 — 192 ; Motion of the
solar system, and doubts concerning the assump-
tion of a central body for the whole sidereal
heavens, p. 192—198 . . . . . 178—198

VI. Double or multiple stars ; their number and
distances apart, and periods of revolution around

a common centre of gravity .... 199—214-

NOTES.

To Introduction . i — ix

To special results of observation ix

To section I. x — xiv

To section II. . xiv — xlv

To section III. xlvi— kvi

To section IV ... kvi— kx

To section V. kx— kxiv

To section VI kxiv — kxviii

TABLES.

Clusters of stars .... . 120—123

New stars . 138—147

Variable stars . . 163—171

Parallaxas ... 190

Elements of the orbits of double stars . . . 214

Photometric tables of stars . xlii — xl

COSMOS,

VOL. III.

COSMOS:

A PHISICAL DESCRIPTION OF THE UNIVEBSE.

SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN OF
COSMICAL PHENOMENA.

INTRODUCTION.

IN pursuance of the aim which I had proposed to myself,
as attainable in a degree commensurate with my own powers
and with the present state of knowledge, I have consi-
dered Nature, in the two volumes of the Cosmos which
have already appeared, in a twofold point of view. I have
sought to represent her, first, in the pure objectivity of
external phsenomena, and, next, as the reflex of the image
received through the senses on the mirror of man's inner
being, his ideas and feelings.

The external world of phsenomena has been described
under the scientific form of a general picture of Nature in
her two great spheres, uranologic and telluric ; beginning
with the stars which glimmer amidst nebulae in the most
distant regions of space, and descending through our plane-

4 SPECIAL RESULTS OF OBSEIIVATION IN THE DOMAIN

tary system to the vegetable covering with which the earth
is invested, and to the minutest organisms often floating in
the air, which escape our unassisted vision. In order to
allow us to contemplate with greater clearness the existence
of a common bond comprehending the whole of the material
universe, the government of never changing laws, and the
causal connection of entire groups of phenomena so far as
is yet known to us, it was necessary to avoid the accumula-
tion of detached facts. Such care appeared more particu-
larly requisite where, in the telluric sphere of the Cosmos,
by the side of the dynamic actions of moving forces, we
find manifested the powerful influence of the specific hetero-
geneity of matter. In the sidereal or uranological part of
the Cosmos, the problems, in all that can be reached by
observation, are in their nature of admirable simplicity ;
being by the theory of motion susceptible of rigid calcula-
tion, according to the attracting force of matter and the
quantity of its mass. If, as I believe, we are justified in
regarding the aerolites, or meteoric asteroids, as parts of
our planetary system, they, but they only, by falling upon
our globe, enable us to recognise diversity of substance in
bodies belonging to cosmical space external to our own
planet. (l) We have here the reason why terrestrial phse-
nomena have hitherto been less generally, and less success-
fully, subjected to mathematical development and treatment,
than have the movements of the heavenly bodies, with their
mutual perturbations and periodical returns, governed, so
far as our perceptions extend, only by the one fundamental
force of homogeneous matter.

My endeavours in the telluric portion of the description
of Nature were directed to the arrangement of the phseno-

OF THE COSMOS. — INTRODUCTION. 5

mena in significant order, suggestive of their causal connec-
tion. The terrestrial globe was described in its form, its
mean density, the gradations of its temperature increasing
with increasing depth, its electro-magnetic currents and
evolution of polar light. On the reaction of the interior of
the planet upon its external crust depend all the phsenomena
of volcanic activity ; comprising those of earthquakes in
more or less complete circles of waves, as well as their
simply dynamic effects, eruptions of gas, hot springs, and
mud. The most powerful manifestation of internal terres-
trial activity is the elevation of fire-emitting mountains. We
have described volcanoes, both central and forming chains,
not only as destructive agents, but also as producing or
emitting various substances, and still forming under our eyes,
for the most part periodically, those classes of rock which
we term eruptive rocks ; while, in contrast with this forma-
tion, we have also shewn the precipitation, likewise still
going on, of sedimentary rocks from fluids containing their
minute constituent particles in solution or suspension.
Such a comparison of that which is still in process of elab6-
ration, with those strata of the crust of the globe which have
long since been solidified, conducts to the distinction of
geological epochs, and to a secure determination of the
successive age of formations, in which lie enveloped, in
successive series chronologically recognisable, the remains of
extinct races of plants and animals, forming the Moras and
Eaunas of an earlier world. The modes of formation, altera-
tion, and upheaving of the strata, varying at different geo-
logical epochs, are conditions on which all the particular
features of the surface of the globe depend : on them depend
the distribution of land and water, and the configuration and

6 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

extent of the continental masses in the vertical as well as in
the horizontal direction. These features of the earth's
surface constitute, in their turn, conditions on which depend
the thermic state of oceanic currents, the meteorological

J O

processes of the aerial covering of our planet, and the geo-
graphical and typical distribution and extension of animal
and vegetable forms. This brief allusion to the order and
manner in which the various telluric phenomena are pre-
sented, in the view or picture of Nature in the first volume
of my work, is, I think, sufficient to shew that the mere
bringing together of great and apparently complicated
results of observation, may promote insight into their causal
connection. On the other hand, the interpretation of
Nature is obscured when the description languishes under
too great an accumulation of insulated facts.

If, in a carefully designed objective representation of the
world of phsenomena, completeness in the enumeration of par-
ticulars ought not to be desired, neither should it be sought
for in the description of the reflex of external nature on the
human mind. Here it was needful to draw the limits still
closer. The measureless domain of human thought, fer-
tilised for thousands of years by the impulses and powers
of mental activity, presents in different races, and at dif-
ferent stages of civilisation, at one time a cheerful, and at
another a melancholy, aspect ; (2) a delicate appreciation of
the beautiful in nature, or a dull insensibility to all that
she can display. At an early period we see the human
mind directed to the deification of natural forces or powers,
and of certain objects of the material universe ; at a later
period it followed religious impulses of a higher and more
purely spiritual character. (3) The internal reflex of external

OF THE COSMOS. — INTRODUCTION. 7

phenomena influences in a variety of ways the mysterious
process of the formation of language, (4) a process in which
original physical temperament, and the impressions received
from surrounding nature, both act as powerful concurrent
elements. Man elaborates within himself the rough mate-
rials supplied through the senses ; and the results or pro-
ducts of such mental processes belong as essentially to the
domain of the Cosmos, as do the external phenomena which
are reflected in the internal mirror of the mind.

As the image of nature reflected under the influence of
excited creative imagination cannot be preserved pure and
true, there arises, by the side of what we call the actual
or external world, an ideal or internal world, tilled with
fantastic and partly symbolical myths, and animated
by creatures of fabulous shape, whose different parts are
borrowed either from various animals of the present crea-
tion, or even from the remains of extinct species. (5) Mar-
vellous and fabulous flowers and trees spring from the
mythical soil, as in the songs of the Edda, the giant ash,
the world-tree, Ygdrasil, whose branches rise above the
heavens, while one of its triple roots reaches down to the
raging fountains of the lower world. (6) Thus the cloud-land
of physical myths is filled, according to the particular cha-
racter of the race and climate, either with pleasing images
or shapes of terror, and these enter into the circles of ideas
of later generations, to whom they are bequeathed.

If my published work does not correspond sufficiently to
the title, of which I have often acknowledged the imprudent
boldness, the reproach of incompleteness must especially
attach to that portion which touches on the spiritual life in
the Cosmos, or the reflex image of external nature in the

8 SPECIAL RESULTS OF OBSERVATION Iff THE DOMAIN

domain of human thought and feeling. In this part of my
undertaking I have more particularly contented myself with
dwelling on the subjects which lay most in the direction of
my previously long-cherished studies : on the manifestations
of the more or less vivid feeling of nature in classical
antiquity, and in modern times; — on the fragments of
poetic description of nature, whose tone of colouring has
been so materially influenced by individuality of national
character, and by the religious monotheistic view of crea-
tion ; — on the pleasing magic of landscape painting ; — and
on the history of the physical contemplation of the Uni-
verse ; i. e. the history of the gradual development, in the
course of two thousand years, of the recognition of the
unity of phsenomena, and of the Universe as a Whole.

In a work so comprehensive, and at once scientific and
literary in its aim, all that a first and imperfect attempt can
aspire to accomplish is, to influence rather by what it may call
forth than by what it can itself supply. A book of Nature,
which may be worthy of so exalted a title, can only be looked
for when the natural sciences, notwithstanding their inherent
incapability of absolute completion, shall yet, by continued
progress and extension, have reached a higher standing
point ; and when thus a new and clearer light shall have
been thrown alike on the two spheres of the one Cosmos, —
the external world perceived by the senses, and its internal
reflection in the mind.

I think I have sufficiently indicated the reasons which
have determined me not to give to the general picture of
Nature a wider extension. It remains for the third and
last volume of my work to supply some of the deficiencies
of the earlier ones, and to put forward those results of

OF THE COSMOS. — INTRODUCTION. 9

observation which form the principal basis of present
scientific opinion. The order of succession in which these
results are presented will again be that which, in confor-
mity with previously enounced principles, was followed
by me in the general view of Nature. Before, however, pro-
ceeding to particular results in the several sciences, I desire
still to add a few more general elucidatory considerations.
The unexpected favour with which my undertaking has
been received, both in my own and in other countries,
makes me doubly feel the need of expressing myself once
more as distinctly as possible in reference to the fundamen-
tal idea of the entire work ; and respecting -requirements
which I have never even attempted to fulfil, because, accord-
ing to my individual view of our experimental knowledge,
their fulfilment could not be contemplated by me. With
these considerations, to which I am led by the desire of
justifying my manner of proceeding, there are naturally
associated historical reminiscences of earlier attempts to
discover the idea of the Universe, which should so compre-
hend its structure as to reduce all phsenomena, in their
causal connection, to a single principle.

The fundamental principle (7) of my work on the Cosmos,
as developed by me more than twenty years ago in lectures
delivered in the French and German languages, at Paris
and at Berlin, consists in the constant tendency or endea-
vour to embrace the phsenomena of the universe as a natural
Whole ; to shew how, in particular groups of the phsenomena,
those conditions which are common to the entire group, —
i. e. the government of great and comprehensive laws, — have
been discovered and recognised, and by what means we
ascend from the knowledge of these laws to that of their

10 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

causal connection. Such a tendency to advance continu-
ally towards the comprehension of the plan of the Universe,
or the order of Nature, commences with the combination
and generalisation of particular facts ; — with the recognition
of the conditions under which phenomena, i. e. the mani-
festations of physical alterations, are always reproduced in a
similar manner : it conducts to the thoughtful consideration
of the materials supplied by observation and experiment ;
but it does not conduct to a " view of the Universe derived
from speculation and the development of thought alone, or
to a science or doctrine of the unity of Nature apart
from experience." We are, I here repeat it, still far
from the time, when it may be thought possible to concen-
trate all the perceptions of our senses into the unity of
one comprehensive idea embracing the whole of Nature.
The safe path was perceived a full century before "Francis
Bacon, by Leonardo da Yinci, and indicated by him in a
few words : — " Comminciare dalF esperienza, e per mezzo di
questa, scoprirne la ragione." (8) In many groups of phse-
nomeria we must, indeed, still content ourselves with a
deduction of empirical laws ; but the highest object of all
investigation into nature, though seldom attained, is the
discovery of physical causes. (9) This is most satisfac-
torily and conclusively accomplished, when it is possible
to connect the laws of phenomena with the causes which
explain them, by the intervention of mathematical rea-
soning. It is, however, only in some particularly fa-
voured parts of natural science that the "physical descrip-
tion" coincides with the "physical explanation of the
universe." The two expressions cannot yet be regarded
as identical. The inherent grandeur and solemnity of that

OF THE COSMOS. — INTRODUCTION. 11

mental labour, the boundaries of which are hereby marked,
consist in the elevating consciousness of the infinite nature of
the object of its efforts, — the comprehension of the unknown
and inexhaustible fulness of creation, whether formed or in
process of formation, whether existing or to be hereafter
developed.

Such efforts, acting throughout all ages, must have led
often, and under many various forms, to the illusory
hope of having attained the goal, and found the prin-
ciple by which all that is variable in the material
universe, the totality of all the phsenomena which are cog-
nizable by the senses, might be explained. After a long
period in which, in conformity with the early fundamental
mode of contemplation of the Hellenic national mind, the
forming, transforming, and destroying forces of nature had
been honoured as divine or spiritual powers, clothed in
human forms, (10) there became developed amidst the phy-
siological fancies of the Ionic school the germ of a scientific
contemplation of Nature. The first cause of all phenomena
was explained in two different directions (n), sometimes ac-
cording to mechanical, and sometimes according to dynamic
views, — from the assumption of concrete corporeal princi-
ples called " elements of nature," or from processes of
rarefaction and condensation. The hypothesis, primarily
perhaps of Indian origin, of four or five substantially dif-
ferent elements, has continued, from the didactic poem of
Empedocles to the most recent times, to mingle itself with
all systems of natural philosophy, forming an evidence and
monument of high antiquity of man's desire to seek for the
generalisation and simplification of ideas, not only in forces,
but also in the qualitative essences of substances.

In the later development of the Ionic physiology, An ax-

12 SPECIAL RESULTS OP OBSERVATION IN THE DOMAIN

agoras of Clazomene passed from the assumption of ma-
terial forces to the idea of a Spirit, distinct from all matter
but intermixed with all its homogeneous ultimate particles.
He spoke of the world-regulating Mind (vovg) governing the
continually progressive formation of the Universe, and being
the original cause of all motion, and thus of all physical
phenomena. It is by the assumption of a centrifugal re-
volving movement (12), by whose intermission, previously
noticed, he accounts for the fall of meteoric stones, that
Anaxagoras explains the apparent motion of the celestial
sphere from East to West. This hypothesis indicates the
commencement of vortex- theories, which more than two
thousand years afterwards became of much cosmical im-
portance by the writings of Descartes, Huygens, and Hooke.
This work is not the place in winch to enquire whether
Anaxagoras means by the " world-regulating Mind" the
Godhead itself, or whether he only means to speak pan-
theistically of a spiritual principle in the general life of
Nature. (13)

In marked contrast with the two divisions of the Ionic
School, though likewise embracing the whole Universe, is
the mathematical symbolism of the Pythagoreans. In the
phenomena of the Universe, their regards were fixed ex-
clusively on the dominion of law in the determination of
form (the five fundamental forms) ; and on the ideas of
number, measure, harmony, and antithesis. To them,
things were mirrored in numbers, which are as it were an
" imitative representation"" (/u/^o-tc) thereof. They saw in
the illimitability of numbers, inasmuch as they can be
endlessly repeated and increased, the character of eternity,
and of the infinitude of Nature. They considered that the

OF THE COSMOS. — INTRODUCTION. 13

essence of things may be known by ratios of numbers, and
their alterations and transformations by combinations of
numbers. Plato's Physics also contain attempts to reduce
all the essences of substances in the universe, and their
gradations of changes, to corporeal forms ; and these to the
simplest (triangular) plane figures. (14) But what the ulti-
mate principles (as it were the elements of the elements), may
be, "this," said Plato, with modest diffidence, "is known to
God alone, and to whomso is beloved by Him among men."
This mathematical treatment of physical phenomena, the
formation of atomic doctrines, the philosophy of measure
and of harmony, have continued to a late period to influ-
ence the development of the natural sciences : they have
also contributed to lead fanciful discoverers astray from the
true road, into by-paths which it may be requisite to notice
in the history of the physical contemplation of the Universe.
" There dwells a peculiar and fascinating charm recognised
by all antiquity in the simple relations of time and space
as manifested in tones, numbers, and lines."" (15)

The idea of the order and government of the Universe shines
forth pure and exalted in the writings of Aristotle. All the
phenomena of Nature are described in the "Auscultationes
Physicse" as moving vital activities of a Universal Power.
On the " unmoved Motor of the World depend Heaven and
Nature," (16) — Nature being the terrestrial sphere of phse-
nomena. The " Orderer," and the final cause of all alte-
rations which can be perceived, must be regarded as imper-
ceptible to sense, as distinct from all matter. (17) Unity
in the different manifestations of force in substances is raised
by Aristotle to the rank of a leading principle, and these
manifestations of force are themselves always reduced to

14 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

motions. Thus we even findin»the book "De Anima" (18)
the germ of the undulatory theory of light. The sensation
of seeing follows from a movement or vibration of the medium
between the sight and the object seen, not from effluxes either
from the object or from the eye. Hearing is compared
with seeing, as sound is also a consequence of concussion of
the air.

In inculcating the exercise of thoughtful reason in the
search after that which is general or universal amidst the
particular facts perceived by the senses, Aristotle always com-
prehends the whole of Nature, and the internal connection
not only of forces but also of organic forms. In the book
which treats of the parts (organs,) of animals, he clearly
enounces his belief in the gradual chain of beings ascending
from lower to higher forms. Nature proceeds in uninter-
rupted progressive development from the inanimate (ele-
mentary,) through plants to animals : advancing first to
" what indeed is not properly an animal, but so nearly allied
thereto that it is on the whole but little distinguished from
one."" (19) In the transition of forms " the intermediate
steps are almost insensible/'' (20) The unity of Nature is to
the Stagirite the great problem of the Cosmos. He says,
with singular vivacity of expression, "In Nature nothing
is isolated; there is no want of connection as in a bad
tragedy." (21)

In all the physical writings of this profound, sage, and
accurate observer of nature, we cannot fail to recognise
the philosophical tendency to subordinate all the pheno-
mena of the one Cosmos to a single principle of expla-
nation ; but the defective state of knowledge, and ignorance
of the method of experimenting, (i. e.} of calling forth
phenomena under definite conditions), prevented even small

OP THE COSMOS. INTRODUCTION. 15

groups of physical processes from being comprehended in
their causal connection. All was reduced to ever recurring
antitheses of cold and heat, moisture and drought, primitive
density and rarity ; and even to the effecting of alterations
in the material world by means of a kind of internal antago-
nism (antiperistasis), which reminds us of our present
hypotheses of opposite polarities and the contrasts of -f
and — . (22) Aristotle's supposed solutions of problems do
but reproduce the facts themselves in disguise; and in
explaining meteorological and optical processes, his elsewhere
ever powerful and concise style often passes into self com-
placent diffuseness or Hellenic verbal redundancy. As the
mind of Aristotle was but little directed to diversity of sub-
stances, but chiefly to the consideration of motion, we see
the fundamenal idea of ascribing all telluric natural phse-
nomena to the impulse of the motion of the heavens, (i. e.
the revolution of the celestial sphere), recurring continually,
always indicated and cherished with special partiality, but
not presented with definiteness or precision. (23) The
impulse here spoken of imports only the communication
of motion as the ground of all terrestrial phaenomena. Pan-
theistic views are excluded : the Godhead is the highest
" presiding Unity, regulating all things, revealing Himself in
all spheres of the entire Universe, giving to each creature its
destination, and hoi ding all together by His absolute power ,"(24)
The ideas of purpose and adaptation are not so much ap-
plied to the subordinate processes of nature, (those of in-
organic elementary nature), as by preference to the higher
organisations (25) of the animal and vegetable worlds. It
is remarkably striking that in the teaching of Aristotle, as
if he had been aware of the distribution of masses and the

16 SPECIAL RESULTS OF OBSEKVATION IX THE DOMAIN

existence of perturbations, the Deity employs a number of
astral Spirits to maintain the planets in their eternal ap-
pointed courses. (26) The stars display the image of the
Divinity in the visible world. The small pseudo- Aristotelian
book of the Cosmos, which is certainly of Stoic origin, is
not mentioned here, notwithstanding its name. It presents,
it is true, in a descriptive manner, and often with animated
rhetoric and vivacity of colouring, both the heavens and the
earth, mid the currents of the ocean and of the atmosphere ;
but it manifests no tendency to reduce the phenomena of
the Cosmos to general physical principles, i. e., to principles
founded in the properties of matter.

I have dwelt the longer on the most brilliant epoch of
antiquity, as respects views of Nature, in order to place in
opposition the earliest and the more recent attempts at
generalisation. In the intellectual movement which has
taken place in the course of centuries, and which in reference
to the enlargement of the domain of cosmical contemplation
was described in another portion (27) of the present work,
the end of the 13th and beginning of the 14th centuries
were particularly distinguished; but the Opus Majus of
Eoger Bacon, the Mirror of Nature of Vincentius of Beau-
vais, the Physical Geography (Liber Cosmographicus) of
Albertus Magnus, the Picture of the World (Imago Muiidi)
of Cardinal Petrus de Alliaco, (Pierre d'Ailly), are works
which, however powerfully they may have influenced their
cotemporaries, do not correspond in their contents to the
titles which they bear. Among the Italian opposers of
Aristotle's Physics, Bernardino Telesio of Cosenza was the
founder of a "Rational" system of natural science, in which
he regarded all the phaenomena of matter, itself passive, as

OF THE COSMOS. INTRODUCTION. 17

the effects of two incorporeal principles, (activities, forces,
or powers,) heat and cold. Even the whole of organic life,
("animated" plants and animals) is the production of these
two eternally-divided forces, one of which, heat, belongs to
the celestial, and the other, cold, to the terrestrial sphere.

With fancy still more unregulated, but gifted with a pro-
found spirit of research, Giordano Bruno of Nola attempts in
three works entitled " De la Causa Principio e Uno," " Con-
templationi circa lo Infinito, Universe e Moudi innumerabili,"
and " De Minirno et Maximo," to embrace the entire Uni-
verse. (2S) In the " Natural Philosophy'' of Telesio, a cotem-
porary of Copernicus, we perceive at least the endeavour to
reduce the variations of matterto two of its fundamental forces,
" which are indeed imagined as acting from without," yet are
similar to the fundamental forces of attraction and repulsion
in the dynamic doctrines of Boscovich and Kant. The cosmi-
cal views of Giordano Bruno are purely metaphysical; they do
not seek the causes of sensible phenomena in matter itself,
but touch on ee the infinity of space filled with self luminous
worlds, the animation of these worlds by souls, and the
relations of the highest Intelligence, God, to the universe."
Although himself but scantily furnished with mathematical
knowledge, Giordano Bruno was, nevertheless, up to the
time of his dreadful martyrdom, (29) an enthusiastic admirer
of Copernicus, Tycho Brahe, and Kepler. Although a co-
temporary of Galileo, he died before the invention of the
telescope by Hans Lippershey and Zacharias Jansen, and
could not therefore witness the discovery of Jupiter's satel-
lites, the phases of Yenus, and the nebulse. With daring
confidence in what he termed "lume interno, ragione natn-
rale, altezza dell' intelleto," he gave himself up to happy

vor.. m. C

18 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

conjectures respecting the movement of the fixed stars,
the planetary nature of comets, and the deviation of the
figure of the Earth from that of a perfect sphere. (30) Gre-
cian antiquity is also full of such uranological divinations,
which have been subsequently realised.

In the development of thought respecting cosmical relations
of which the leading forms and epochs have been here enume-
rated, it was Kepler who, fully 78 years before the publication
of Newton's immortal work of the " Principia Philosophise
naturalis," came nearest to a mathematical application of
the doctrine of gravitation. Although the Eclectic Sim-
plicius expressed in a general manner that " the non-falling
of the heavenly bodies was caused by the centrifugal force
having the upper hand of the proper falling force, the down-
ward traction;" — although John Philoponus, a disciple of
Ammonius, the son of Hermeas, ascribed the movements of
the heavenly bodies " to a primitive impetus and to the con-
tinued tendency to fall •" — and although Copernicus, as was
noticed in an earlier part of the present work, describes the
merely general idea of gravitation, as it acts in the Sun as
the centre of the planetary world, and in the Earth and
Moon, in these remarkable words : " Gravitatem non aliud
esse quam appetentiam quandam naturalem partibus inditam
a divina providentia opificis universorum, ut in unitatem
integritatemque suam sese conferant, in formam globi co-
euntes ;" yet it is ' in Kepler, in the Introduction to the
book "De Stella Martis," (31) that we first find numerical
quantities assigned to the attracting forces which the Earth
and the Moon exercise upon each other in the ratio of their
masses. It distinctly adduces the ebb and flow of the sea
(32) as a proof that the attracting power of the Moon, (virtus

OF THE COSMOS. — INTRODUCTION. 19

tractoria) extends as far as the Earth ; and he even says
that this force, " similar to that which the magnet exercises
upon iron/' would deprive the Earth of water, if the Earth
itself ceased to attract the water. Unfortunately, ten years
later, in 1619, this great man, perhaps out of deference to
Galileo, who ascribed the ebb and flow to the rotation of the
Earth, gave up the true explanation, and in the Harmonice
Mundi described the Earth as a living animal whose whale-
like respirations, in periodical alternations of sleeping and
waking dependent on the solar time, cause the swelling and
sinking of the ocean. The profound mathematical genius,
recognised by IJaplace, which shiiies forth in one of Kepler's
writings (33), makes us regret that the discoverer of the three
great laws of all planetary movement did not persevere in
the path, in which his views respecting the attraction of
masses had led him to enter.

Descartes, furnished with a greater variety of knowledge
in the natural sciences than Kepler, and himself the founder
of several parts of a mathematical system of physics, under-
took to embrace the whole world of phsenomena, the ce-
lestial sphere, and all that he knew of animate and inanimate
terrestrial Nature, in a work to which he gave the names of
"Traite du Monde" and "Summa Philosophise." The
organization of animals, and particularly that of man, for
the understanding of which he pursued for eleven years a
systematic course of anatomical study, (34) was to form the
concluding portion of the work. In his correspondence
with Father Mersenne, we find many complaints of the
slow progress of the undertaking, and of the difficulty of
arranging and combining such numerous materials. This
Cosmos, which. Descartes always called his World (son.

20 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

Monde), was finally to have been sent to press at the con-
clusion of 1633 ; but the report of the sentence passed upon
Galileo in the Inquisition at Rome (which was only made
known four months later, in October, 1633, by Gassendi
and Bouillaud), arrested its progress, and deprived the
world of a great work, executed with so much labour and
care. The motives for its non-publication were the love of
a quiet and peaceful life in his retirement at Dev enter, and
a pious anxiety not to shew himself disrespectful to the
Pope's decree against the Earth's planetary motion. (35)
It was not until 1664, fourteen years after the philosopher's
death, that some fragments of the work were printed
under the strange title of " Le Monde, ou Traite de la Lu-
miere." (36) The three chapters which treat of Light hardly
form a fourth part of the whole. On the other hand the
sections which belonged originally to Descartes' Cosmos,
and contained considerations on the motion and.solar distance
of the planets, on terrestrial magnetism, on tides, and on
earthquakes and volcanoes, were transferred to the third
and fourth parts of the celebrated work entitled " Principes
de la Philosophic."

The " Kosmotheoros" of Huygens, which was not pub-
lished until after his death, notwithstanding its high-sound-
ing and significant name, hardly deserves to be mentioned
in this enumeration of cosmical essays. It contains the
dreams and conjectures of a great man on the vegetable and
animal worlds of distant heavenly bodies, and especially on
the altered forms under which mankind may appear there.
One seems to be reading Kepler's " Somnium Astronomi-
cum/' or Kircher's " Ecstatic Journey." As Huygens al-
ready, like the astronomers of the present day, allowed to

OF THE COSMOS. — INTRODUCTION. 21

the Moon neither air nor water, (37) he finds the supposed
existence of lunar men present to him still greater diffi-
culties than that of the inhabitants of the remoter planets
" rich in clouds and vapour."

The immortal author of the Philosophise Naturalis Prin-
cipia Mathernatica, succeeded, by the assumption of a single
all- governing fundamental moving force, in embracing the
whole uranological portion of the Cosmos in the causal
connection of its phenomena. Newton first raised physical
astronomy to a mathematical science, and made it the solu-
tion of a great problem of mechanics. The quantity of
matter in each heavenly body gives the measure of its at-
tracting force, a force which acts in the inverse ratio of the
square of the distance, and determines the magnitude of the
perturbing actions which not only the planets, but all the
heavenly bodies in space, exert upon each other. But the
Newtonian theorem of gravitation, so admirable for simpli-
city and generality, is not limited in its cosmical application
to the sphere of uranology ; it governs also terrestrial phse-
nomena in directions still partly uninvestigated ; it gives
the key to periodic movements in the ocean and in the
atmosphere, (3S) to the solution of problems of capillarity,
endosmose, and many chemical electro -magnetic and organic
processes. Newton himself (39) already distinguished the
" attraction of mass," as it manifests itself in all celestial
bodies and in the phaenomena of the tides, from " molecular
attraction," which acts at infinitely small distances and in
the closest contact.

Thus among all human efforts to reduce all variations
taking place in the world known to us through our senses
to a single fundamental principle, the doctrine of gravita-

Z'Z SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

tioii shews itself the most comprehensive and the most rich
in cosmical promise. It is indeed true, notwithstanding
the brilliant progress made in modern times in Stoechiornetry
(calculation of chemical elements and of the ratios of volume
in compound gases), we are not yet able to reduce all
theories of substances to a mathematical explanation. Em-
pirical laws have been discovered, and in following the
widely extended views of the atomic or of the corpuscular
philosophy, many things have been rendered more accessible
to mathematical treatment ; but from the boundless hetero-
geneity of matter, and the multifarious conditions of aggre-
gation of what are called the particles of mass, the demon-
strations of these empirical laws can as yet by no means be
derived from the theory of " contact attraction," with the
same certainty as is effected by the establishment of
Kepler's three great laws on the basis of the theory of
" mass attraction" or gravitation.

Yet, after Newton had recognised all the motions of the
heavenly bodies as consequences of one single force, he did
not, with Kant, regard gravitation itself as an essential pro-
perty of matter, (40) but as either derived from a higher
force still unknown to him, or as the result of a "revolving
of the Ether which fills all space, and is more rare in the
intervals between the particles of mass, and increases in
density outwards." The latter view is developed in detail
in a letter to Robert Boyle, (41) dated 28th February, 1678,
which ends with the words, " I seek in the Ether the cause
of gravitation." Eight years later, as may be seen from a
letter to Halley, Newton gave up this hypothesis of denser
and rarer Ether altogether. (42) It is a striking circumstance
that, in 1717, nine years before his death, in the extremely

OF THE COSMOS. INTRODUCTION. 23

short preface to the second edition of his Optics, he thought
it necessary to declare explicitly that he by no means re-
garded gravitation as an " essential property of bodies" : (43)
while more than a century before, in 1600, Gilbert had
viewed magnetism as a force inherent in all matter. So
much did the most profound of thinkers, Newton himself,
who ever leaned so strongly to experience, hesitate in respect
to the " ultimate mechanical cause" of motion.

The establishment of a science of Nature, from the laws
of gravity up to the formative impulse in animated bodies,
as one organic Whole, is no doubt a brilliant problem, and
one worthy of the human intellect ; but the imperfect state
of so many parts of our knowledge places insuperable diffi-
culties in the way of its solution. The impossibility of
complete experimental knowledge, in a boundless sphere of
observation, renders the problem of explaining all the
changes of matter from the powers of matter itself an " in-
determinate problem.'" What is perceived is far from
exhausting what is perceivable. If, to recall only the pro-
gress of the time nearest to our own, we compare the
imperfect knowledge of nature possessed by Gilbert, Eobert
Boyle, and Hales with the present, and if we remember
that the rate of progress is a rapidly increasing one, we may
have some idea of the periodical endless transformations
which still await all the physical sciences. New substances
and new powers will be discovered. Even though many
natural processes, as those of light, heat, and electro-mag-
netism, being reduced to movement (undulations), have
become accessible to mathematical treatment, yet there
remain the often referred to, and perhaps unconquerable,
problems of the cause of chemical diversity of substance,

24 • SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

and of the order and proportion s, seemingly not reducible to
any laws, of the magnitudes, densities, inclinations of axis,
and eccentricities of orbit of the planets, the numbers and
distances of their satellites, the form of continents, and the
position of their loftiest mountain chains. All these cir-
cumstances (having reference to space geographical or celes-
tial), which are here instanced merely as examples, can as
yet only be regarded as natural facts, of which we know the
existence but not the explanation. But although neither
the causes nor the connection of these facts are yet known
to us, I (Jo not therefore term them in any sense accidental.
They are doubtless the results of events or occurrences in
space at the time of the formation of our planetary system,
and of geological phenomena which accompanied or pre-
ceded the elevation of the outermost strata of our globe
into continents and mountain chains. Our knowledge of
the early period of the physical history of the Universe does
not reach back far enough to enable us to describe that
which exists in its process of formation. (44)

But although it has not yet been possible in all cases
fully to recognise the causal connection between phenomena,
no part of the domain of the natural sciences can be ex-
cluded from the study of the Cosmos, or the physical de-
scription of the Universe. Bather that study comprehends
the whole of such domain, the phenomena of both spheres,
celestial and telluric ; but it does so only under the single
point of view of the tendency towards the recognition
of the Universe as a Whole. (45) As, in the description
of what has taken place in the moral and political
sphere, the historian (46) cannot directly discern, accord-
ing to man's view, the plan of the government of the world,

OF THE COSMOS. — INTRODUCTION. 25

but can only divine it through the ideas by which it
manifests itself; so the investigator of nature, in seeking
to present cosmical relations, is penetrated by the convic-
tion that the number of impelling, forming, and producing
powers or forces of the material universe, is far indeed
from having been exhausted by the results hitherto ob-
tained, either by immediate observation, or by the analysis
of phenomena.

SPECIAL RESULTS IN THE URANOLOGICAL

A.

RESULTS OF OBSERVATION IN THE URANOLOGICAL PORTION
OF THE PHYSICAL DESCRIPTION OF THE UNIVERSE.

WE commence afresh with the depths of space and with the
remote sporadically-scattered clusters of stars which present
themselves to telescopic vision as faintly shining nebulae.
We descend step by step to the double stars, often of two
different colours, which revolve around a common centre of
gravity ; to the nearer strata of stars, one of which appears
to, include our planetary system ; and lastly, through this
planetary system to the air- and sea-surrounded spheroid
which we inhabit. I have noticed in an earlier volume, in
the introduction to the general picture of Nature, (47) that this
order is the only one which is suitable to the particular
character of a work which treats of the Cosmos ; in contradis-
tinction to an arrangement more directly accordant with the
immediate perceptions of sense, which should begin with our
terrestrial dwelling-place and the organic creation by which
its surface is enlivened, and should proceed from the appa-
rent to the real motions of the heavenly bodies.

The uranological domain, as opposed to the telluric, di-
vides itself conveniently into two portions : one of which

PORTION OF THE COSMOS. — ASTROGNOSY. 27

includes Astrognosy, or the heaven of the fixed stars ; and
the other, our solar and planetary system. The imperfect
and unsatisfactory character of this nomenclature and these
definitions need not be again dwelt on here. Names were
introduced into the natural sciences before the true dif-
ferences and distinctions between objects were sufficiently
known. (48) Such questions are, however, of less importance
than the connection of ideas, and the order in which the
objects are to be treated ; whilst novelties in the names of
groups, and the diversion of names in frequent use from the
signification they have hitherto borne, are objectionable, as
tending to perplexity and confusion.

a. Astrognosy (heaven of the fixed stars).

Nothing in space is in repose ; not even what are called
the fixed stars, as Halley(49) first attempted to shew in the
case of Sirius, Arcturus, and Aldebaran, and as has been
proved incontestably in modern times in the case of many
other stars. In the course of 2100 years of observation
(since Aristillus and Hipparchus), the bright star Arcturus
has altered its place, relatively to the neighbouring fainter
stars, as much as two and a half times the diameter of the
moon. Encke remarks that the star p in Cassiopea would
appear to have moved three and a half times, and the star 61
Cygni six times, the diameter of the moon from their respec-
tive places, if we regard the old observations as sufficiently
exact to justify the conclusion. Inferences based on analogies
support the conjecture that progressive, and probably also
rotatory, motion exists everywhere. The name " fixed star"
leads to erroneous suppositions ; whether it be taken in its

28 SPECIAL RESULTS IN THE URANOLOGICAL

first signification among the Greeks of set or fixed in the
crystal firmament, or according to the later and more Roman
interpretation of steadfast, resting, and immoveable. One
of these ideas necessarily implied and led to the other. In
Grecian antiquity (at least going back as far as Anaxi-
menes, who belonged to the Ionic school, or as the
Pythagorean Alcmseon), all the stars or heavenly bodies were
divided into moving (uarpa TrXavw/^va or TrXav^ra) and non-
moving stars (dTrXave'ig aartpeg or cnr\avij affrpa). (50)
Besides this latter generally employed term, which Macrobius
latinises in the Somnium Scipionis by Sphsera aplanes,(51)
we find in Aristotle repeatedly (as if he wished to in-
troduce a new technical term) the name of ej^e^eVa aorpa,
instead of airXavij. (52) From this form of expression there
followed, with Cicero, sidera irifixa ccelo ; with Pliny, stellas
quas putamus affixas ; and with Manilius, even astra fixa,
just like our " fixed stars." (53) The idea of being fixed or
set in the solid sky, led to the secondary implied idea of
immobility, or ' { remaining fixed in one place •" and thus, in
Latin versions, throughout the whole middle ages, the original
meaning of the word infixum or affixum sidus, was gradually
set aside, and the idea of immobility alone retained. We
find the impulse to this already given in the highly rhe-
torical passage of Seneca (Nat. Qusest. vii., 24), on the
possibility of discovering new planets : " credis autem in
hoc maximo et pulcherrimo corpore inter innumerabiles
stellas, qua? noctem decore vario distinguunt, quse aera
minime vacuum et inertem esse patiuntur, quinque solas
esse, quibus exercere se liceat ; ceteras stare Jixum et im-
mobilem populum ?" This "quiet^ immoveable people" is
nowhere to be found.

PORTION OF THE COSMOS. ASTEOGN03Y. 29

In order to divide conveniently into groups the principal
results of actual observation,, and the conclusions or con^
jectures to which they lead, I propose to distinguish, in the
astrognostic portion of the description of the Universe, the
following heads : —

I. Considerations on space, and on what is supposed to
occupy it.

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

III. The number, distribution, and colour of stars; clusters
of stars ; and the milky way, in which are only a few nebulae.

IY. Newly appeared stars; vanished stars; and stars
which vary periodically.

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

VI. Double stars, and their periods of revolution round a
common centre of gravity.

VII. Nebulae, which in the Magellanic clouds are inter-
mixed with many clusters of stars ; and the black spots or
patches in the sky (" coal-bags").

30 SPECIAL RESULTS IN THE URANOT,OGICAL

I.

COSMICAL SPACE, AND CONJECTURES RESPECTING WHAT

APPEARS TO OCCUPY THE INTERVALS BETWEEN THE

HEAVENLY BODIES.

WE may in some respects view a commencement of the phy-
sical description of the Universe, by the consideration of
what fills the intervals between the stars in the remote re-
gions of space and remains inaccessible to our organs, in
the same light as mythical commencements of the world's
history. In infinite space, as in infinite time, everything
appears in uncertain and often illusive twilight. Imagi-
nation is then doubly stimulated to draw from her own
abundance, and to give to the indeterminate and varying
forms outline and duration. (54) Such an avowal may, I
hope, suffice to shield me from the reproach of having
confounded what direct observation or measurement have
raised to mathematical certainty, with what rests only
on very imperfect induction. Wild reveries belong to
the romance of physical astronomy : nevertheless, minds
exercised in scientific labour may dwell, not without
pleasure, on questions which, in connection with the present
state of our knowledge and the hope winch this state excites,
have been deemed by some of the most distinguished

PORTION OF THE COSMOS. — COSMICAL SPACE. 31

astronomers of the present day worthy of serious exami-
nation.

It may be assumed with great probability that we are in
communication, through the influence of gravitation and
through light and radiant heat,(55) not only with our own
sun, but also with all the other shining suns of the firmament.
The important discovery of the measurable resistance opposed
by a space-filling fluid to a comet of a five years' period of
revolution, has been completely confirmed by exact numerical
accordances. Inferences founded on analogies may serve to
fill a part of the wide chasm which separates the assured re-
sults of a mathematical natural philosophy, from conjectures
directed to the extreme, and therefore obscure and desert,
boundaries of all scientific development of thought.

l^rom the infinity of Space, which indeed was doubted by
Aristotle, (56) follows its immeasurability. Only separate
parts have been accessible to measurement ; and the results,
which surpass all our powers of realisation, are brought to-
gether with complacency by those who take a childish plea-
sure in large numbers, and even imagine that, by means of
images of physical magnitude creating astonishment, they
peculiarly enhance the sublimity of astronomical studies.
The distance of the star 61 Cygni from the sun is 657000
semi-diameters of the earth's orbit, — a distance which light
takes rather more than ten years to traverse, whilst it comes
from the sun to the earth in 8 minutes 17*78 seconds. Sir
John Herschel conjectured, from an ingenious combination
of photometric estimations, (57) that, supposing stars of
the milky way which he saw glimmer in his twenty-foot
telescope to be newly formed luminous bodies, they would
have required 2000 years thus to have sent us their

32 SPECIAL RESULTS IN THE DRANOLOGICAL

first ray of light. All attempts to bring such numerical re-
lations home to our imaginations fail, either from the vast-
ness of the unit of measure employed, or from the vastness
of the number of its repetitions. Bessel said very truly (58)
"that the distance which light travels in one year can no more
be rendered sensible to us than the distance which it tra-
verses in ten years : no endeavours to bring home to our ima-
gination a magnitude far exceeding all magnitudes accessible
on the earth are ever successful." We find the oppressive
power of numbers exceeding what our conceptions can grasp,
alike in the smallest organized beings of animal life, and in
the galaxy of self-luminous suns which we term fixed stars.
What a mass of Polythalamia are contained, according to
Ehrenberg, in a thin stratum of chalk ! Of the microscopic
Gaillonella distans, according to the same great inquirer into
nature, a cubic inch of the Bilin polishing slate, which forms
a dome 40 feet high, contains 41000 millions of individuals.
Of Gaillonella ferruginea, one cubic inch contains upwards of
1 billion 750000 millions. (59) Such estimations remind
us of the Arenarius (\lsappiTijc) of Archimedes, of the grains
of sand which might fill Space ! If, in considering the
starry heavens,, impressions of vast magnitudes in space and
time, which numbers convey but imperfectly, remind man of
liis smallness of stature, his physical weakness, and the ephe-
meral duration of his earthly existence, — he is, on the other
hand, cheered and invigorated by the consciousness, that the
application and development of the human intellect have
already made known to him such important portions of the
subjection of nature to definite laws, and so much of the
sidereal order of the universe

If we assume that the spaces between the heavenly bodies

PORTION OF THE COSMOS. — COSMICAL SPACE. 33

are not a vacuum, (60) but are filled with some kind of matter,
— as not only the propagation of light, but also a particular
effect of its enfeeblement, as well as'-the influence of a resisting
medium on the period of revolution of Encke's comet, and the
dissolution of many vast tails of comets, appear to shew, — it
is necessary to take the precaution of reminding the reader
that the term " ether" now employed, and which has come
to us from the earliest south and west Asiatic antiquity, has
not during so many centuries always conveyed the same
ideas. With the Indian philosophers the aether (aka'sa) is
one of the " pantschata" or five elements, a fluid of infinite
rarity pervading the entire universe, and the exciter of life,
as well as the medium of the propagation of sound. (61)
Etymologically, "aka'sa" signifies, according to Bopp,
" shining," and therefore in its original meaning ap-
proaches the aether of the Greeks as nearly as " shining"
does "burning/'

This aether (aidrjp), according to the dogmas of the
Ionian philosophy, and according to Anaxagoras and Empe-
docles, was altogether different from the thicker (denser),
vapour-filled, true air (a*7p), which surrounds the earth " and
perhaps extends to the moon." It was "of a fiery nature,
a pure fiery atmosphere, bright beaming (62), of great tenuity
(rarity) and eternal serenity." The etymological de-
rivation from " burning" (cufeiv) accords perfectly with
this definition. Singularly enough, out of predilection for
mechanical views, and referring to the constant revolving
motion, it was subsequently changed by Plato and Aristotle,
by a play upon words, into another derivation, aei 0eu/.(63)
The idea of the rarity and thinness of this upper air, the
sether, does not appear to have been a consequence of the

VOL. III. D

34 SPECIAL RESULTS IN THE URANOLOGICAL

knowledge of the purer mountain air, comparatively free
from heavy terrestrial vapours ; or of the diminishing density
of the strata of air with increasing height. As the " elements"
of the ancients signify not so much diversity, or even sim-
plicity or indecomposability of substance, as " states of
matter/' the idea of the upper sether (the fiery celestial
atmosphere) had its root in the first and normal antitheses
of "heavy" and "light," "under" and "upper," "earth"
and " fire." Between these two extremes are two " middle
elementary states :" water, more 'nearly akin to the heavy
earth ; and air, nearer to the light fire. (64)

As a space-filling medium, the aether of Empedocles has no
analogy, excepting by its tenuity and rarity, with the ether
by whose transverse vibrations modern physical science has
succeeded so happily in explaining, by pure mathematical de-
duction, the propagation of light and all its properties
(double refraction, polarisation, and interference). In the
natural philosophy of Aristotle it was also taught that the
sethereal substance pervaded and penetrated all organic beings,
plants, and animals ; that it became in them the principle of
vital heat, and even the germ of a psychical principle, which,
preserving itself distinct from the body, awakened men to
self-activity. (65) These imaginations draw down the aether
from upper space into the terrestrial sphere ; they present it
as an exceedingly fine substance constantly pervading and
penetrating both the atmosphere and solid bodies, as does
the ether in the undulatory theory of light, according to the
views of Huygens, Hooke, and our present physicists. But
that which most directly distinguishes the two hypotheses, the
ancient Ionian aether and the modern ether, from each other,
is the original assumption (not altogether shared, however,

PORTION OF THE COSMOS. COSMICAL SPACE. 35

by Aristotle), in regard to the former, of self-luminosity.
The upper fiery atmosphere of Empedocles is expressly
called "bright beaming" (irapQavAiav) , and in certain pheno-
mena was supposed to be seen by the inhabitants of the
earth as the brightness of fire through clefts and rents
(xaff/^ara) opened in the firmament. (66)

In the intimate relations between light, heat, electricity,
and magnetism, now so much examined, it is deemed pro-
bable that, as the transverse undulations of the space-filling
ether produce the phenomena of light, so thermic and electro-
magnetic phenomena depend on analogous kinds of motion
(currents). Great discoveries on these subjects are no
doubt reserved to future times. Light, and radiant heat in-
separable from light, are, to the non-luminous cosmical
bodies, and to the surface of our own planet, a principal source
of motion and of all organic life. (67) Even remote from
the surface, in the interior of the crust of the earth, the heat
which penetrates inwards calls forth electro-magnetic cur-
rents, which exercise their exciting influence on combina-
tions and decompositions of substances, upon all formative
activity in the mineral kingdom, and on the disturbance of
equilibrium in the atmosphere, as well as on the functions of
vegetable and animal organisms. If electricity moving in cur-
rents developes magnetic forces, — if, according to an earlier
hypothesis of Sir William Herschel, (68) the sun itself is in
the condition " of a perpetual Aurora" (I should say of an
electro-magnetic storm), it would not appear an inappropriate
conjecture to suppose that in space also, the light of the sun,
propagated by vibrations of the ether, may be accompanied
by electro-magnetic currents.

It is true that in terrestrial magnetism direct observation

36 SPECIAL RESULTS IN THE URANOLOGICAL

of the periodical variations of declination, inclination, and
force, has not as yet disclosed with certainty any influence
from the different positions either of the sun or of the nearer
moon.* The magnetic polarity of the earth does not shew
oppositions which relate to the sun, and are sensibly affected
by the precession of the equinoxes. (69) Only the re-
markable varying direction of the cone of light which
streamed from Halley's comet, and which Bessel observed
from the 12th to the 22d October, 1835, and sought to
interpret, had persuaded that great astronomer of the exis-
tence of a polar force, — " of the action of a force differing
materially from gravitation or the ordinary attracting power
of the sun, since those portions of the comet which form
the tail experience the effect of a repelling force from the
body of the sun."(70) The fine comet of 1744, which was
described by Heinsius, had also given occasion to similar
conjectures on the part of my deceased friend.

The action of radiant heat is regarded as less problematical
than electro-magnetic agencies in space. According to
Fourier and Poisson, the temperature of space is the result of
the radiation of heat from the sun and all the heavenly
bodies, diminished by the absorption which the heat suffers
in traversing space filled with " ether." p1) The " heat of the
stars" was spoken of on many occasions by the ancients
(the Greeks and Romans) ; (72) not merely because, accord-

* [Since this passage was printed in the German original, the Philoso-
phical Transactions for 1849 have reached M. de Humboldt, containing a
memoir in which it is shown that the magnetic observations made in different
hemispheres, (at Toronto in Canada, and at Hobarton in Van Diernen Island),
concur in indicating that the terrestrial magnetism does undergo an annual
variation connected with the sun's position relatively to the earth. — ED.]

PORTION OF THE COSMOS. — COSMICAL SPACE. 37

ing to a widely prevalent opinion, the stars belonged to the
region of the fiery aether, but because they are themselves of
a fiery nature :{73) and Aristarchus, of Samos, even taught
that the fixed stars and the sun are of the same nature. In
very recent times, through the influence of the two great
French mathematicians who have just been named, the in-
terest of an approximate determination of the temperature of
space has been more strongly felt, as it has at length been
perceived how important, on account of the radiation of heat
from the earth's surface to the heavens, was this deter-
mination in respect to all thermic relations, and, one might
even say, to the habitability of our planet. According to
Fourier's analytical theory of heat, the temperature of space
(des espaces planetaires ou celestes) is somewhat below the
mean temperature of the Pole, or perhaps even somewhat
below the lowest temperature hitherto observed in the Polar
regions. Fourier estimates it accordingly at from — 50° to
-60° Cent. (-58°to-76°Fah.) The point of greatest cold
(pole glacial) no more coincides with the pole of the earth
than does the "thermal equator" (which connects the warmest
points on all meridians) with the geographical equator.
Arago concluded the temperature of the north pole, from
the gradual decrease of mean temperatures, to be — 25° Cent.
( — 13° F.) ; the maximum cold observed by Captain Back,
in January 1834, at Port Reliance (lat. 62° 46'), was
— 56°-6' C. (-69°-88 P.) (?4) The lowest known tempera-
ture is, I believe, that which Neveroff observed on the 21st
of January, 1838, at Jakutsk (lat. 62° 2'). The accurate
Middendorff had compared the observer's instruments with
his own. Neveroff found the temperature on the day in
question, -60° Cent, (-76° P.)

38 SPECIAL RESULTS IN THE UKANOLOGICAL

Among the many grounds of uncertainty in respect to a
numerical result for the thermic condition of space, is the
circumstance, that we cannot yet obtain a mean of the points
of greatest cold of the two hemispheres, as we are still so
little acquainted with the meteorology of the southern hemi-
sphere, which must bear its part in determining the mean
annual temperature. Poisson's view, that, owing to the un-
equal distribution of heat-radiating stars, different regions of
space must have a very different temperature, and that, from
the movement of the whole solar system, our globe in tra-
versing warm and cold regions has received its internal heat
from without, (75) appears to me to have a very low degree
of physical probability.

The question whether the thermal condition of space,
or the climates of its several regions, are exposed in the
course of long periods of time to great changes of tem-
perature, depends principally on the solution of a question
proposed and discussed with great animation by Sir William
Herschel : viz. are the nebnlse subject to progressive processes
of formation, by condensation taking place according to the
laws of attraction around one or several nuclei ? If such a
condensation of cosmical nebulous matter take place, there
must be, in every transition of gaseous or fluid substances to
solids, disengagement of heat. (76) If, according to the latest
views, and from the important observations of theEarl of Eosse
and Mr. Bond, it becomes probable that all nebulae, even those
which have not yet been entirely resolved by the greatest
power of optical instruments, are thickly crowded clusters of
stars, the belief in this perpetually-arising production of heat
will indeed be somewhat shaken. But even small solid bo-
dies, seen in telescopes as distinguishable shining points, may

PORTION OF THE COSMOS. — COSMICAL SPACE. 39

also alter their density in combining into larger masses ; and
many phenomena which our own planetary system presents
lead to the supposition that the planets have been condensed
from a state of vapour, and that their internal heat is owing
to this process.

At first sight it seems hazardous to assert that a tempe-
rature of space so very low as between the freezing
points of mercury and of spirits of wine, can be deemed, even
indirectly, beneficial to the habitable climates of the globe,
and to the life of plants and animals ; but in order to be sa-
tisfied of the correctness of the expression it is sufficient to
reflect on the influence of the radiation of heat from the
earth. The surface of our globe warmed by the solar heat,
and the atmosphere up to its outermost stratum, radiate freely
towards space. The loss of heat which they suffer arises
from the difference of temperature between the air and space,
and the feebleness of the return which they receive. How
enormous would be the loss (77) if space, instead of the tem-
perature which we express by —60° Cent. (—76° F.), had,
for example, a temperature of -800° Cent. (-1408° P.),
or even several thousand degrees lower !

There still remain to be developed two more considerations
in reference to the existence of a fluid throughout space :
one, less well-established, relates to a " limit to the trans-
parency of space ;" the other, based on direct observation,
and affording numerical results, to the regular diminution
of the period of revolution of Encke's comet. Olbers of
Bremen, and, as Struve has remarked, Loys de Cheseaux
at Geneva, eighty years before, (78) called attention to the
dilemma, — that as in infinite space no point can be imagined

40 SPECIAL RESULTS IN THE URANOLOGICAL

which should not present a fixed star (i. e. a sun), either the
entire vault of heaven, if light arrived to us quite un enfeebled,
must appear as luminous as our sun ; or, if this be not so,
that we must assume an enfeeblement of light in its passage
through space, or a decrease of the intensity of ]ight greater
than in the inverse ratio of the square of the distance.
Now, since we do not see such an almost uniform brightness
covering the heavens (to which Halley (79) also alludes in
reference to an hypothesis which he rejects), therefore, in
the view of Cheseaux, Olbers, and Struve, we must assume
that space is not absolutely and perfectly transparent.
Results which Sir William Herschel derived from his star
gaugings, (80) and from ingenious investigations on the
space-penetrating power of his great telescope, appear to
establish that, if the light of Sirius lost only ^^ on its way
to us in passing through a gaseous or ethereal fluid, this
loss, which would give the measure of the density of a light-
enfeebling fluid, would suffice to explain phenomena as they
present themselves. Amongst the grounds of doubt which
the illustrious author of the new " Outlines of Astronomy"
opposes to the supposition of Olbers and Struve, one of the
most important is, that in the greater part of the milky way,
in both hemispheres, his twenty-foot telescope shews him
the smallest stars projected on a black ground. (81)

A better proof of the existence of a resisting fluid, (82)
and one, as I have already said, founded on direct observation,
is furnished by Encke's comet, and by the ingenious and
highly important conclusions to which it has conducted its
discoverer. The impeding medium must, however, be con-
ceived to be different from the all -penetrating ether whose

PORTION OF THE COSMOS. — COSMICAL SPACE. 41

undulations propagate light, because resistance implies non-
penetration of what is solid. The observations require for
the explanation of the diminished period of revolution, (the
diminished major axis of the ellipse), a tangential force ;
and this is supplied in the most direct manner by the as-
sumption of a resisting fluid. (83) The greatest effect shows
itself in the twenty-five days next before the passage of the
comet through its perihelion, and in the twenty-five days
which follow the passage. Thus the value of the constants
is somewhat different, because near the sun, the so rare,
but yet gravitating, strata of the resisting fluid are denser.
Olbers (s4) was of opinion that the fluid could not be in
repose, but must rotate from right to left round the sun ;
and, therefore, the resistance to retrograde comets, like
Halley's, must be quite different from the resistance to a
comet whose motion is direct, as Encke's. The calcu-
lation of perturbations in comets of long period, and
the differences of, masses and magnitudes of the comets,
complicate the results, and mask what may be due to par-
ticular causes.

The nebulous or vaporous matter which forms the ring
of zodiacal light, may be, perhaps, as Sir John Herschel ex-
presses it, only the denser part of the comet-resisting medium
itself. (85) Even supposing it were already proved that all
nebulae are only imperfectly- seen crowded clusters of stars,
there yet remains the fact, that innumerable comets, by
the dissolution of their tails of more than fifty millions of
miles in length, fill space with a material* substance.
Arago has ingeniously shown from optical considerations, (86)
that the variable stars which in their periodical phases
always show white light, without any trace of colour, might

42 SPECIAL RESULTS IN THE URANOLOGICAL

furnish a means of determining the superior limit of the
density ascribable to the ether, if we assume it to resemble
terrestrial gaseous fluids in its powers of refraction.

Connected with the question of the existence of a space-
filling ethereal fluid, is the one proposed with so much ani-
mation by Wollaston, (87) of the limit of the atmosphere, —
a limit which must exist at the height where the specific
elasticity of the air and the attraction of gravitation are in
equilibrium. Faraday's ingeniously devised experiments
upon the limit of an atmosphere of mercury, — on the height
which vapour of mercury tested by amalgamation with
gold-leaf scarcely appears to reach in air, — have given
increased weight to the hypothesis of a definite surface of
the atmosphere, " similar to the surface of the sea." May
gaseous substances from space mix with our atmosphere and
produce meteorological changes ? Newton (88) has touched
this question, leaning to the affirmative side. If shooting
stars and meteoric stones are regarded as planetary asteroids,
we may well hazard the conjecture that, with the streams of
myriads of shooting stars which traversed the sky in the
month of November, (89) in the years 1799, 1833, and
1834, and when Auroras were observed at the same time, —
the atmosphere received from space something which was
extraneous to itself, and which might excite electro-magnetic
processes.

PORTION OF THE COSMOS.— VISUAL POWER. 43

II.

NATURAL AND TELESCOPIC VISION SCINTILLATION OF STARS

VELOCITY OF LIGHT RESULTS OF PHOTOMETRY.

IT is only within the last two centuries and a half that the
artificial telescopic enhancement of the visual power of the
eye, — the organ by which we contemplate the Universe, —
has afforded the grandest of all aids and instruments for the
recognition of the contents of space, and for the discovery
of the form, physical constitution, and mass of the planets
and of their satellites. The first telescope was constructed
in 1608, seven years after the death of the great observer
Tycho Brahe. Jupiter's satellites, the solar spots, the
phases of Yenus, Saturn's ring, telescopic clusters of stars,
and the nebula in Andromeda, (90) had already been suc-
cessively discovered by means of the telescope, when, in
1634, the French astronomer Morin (worthy of honourable
mention in reference to observations of longitude), thought
of attaching a telescope to the alidade of a measuring in-
strument, and looking for Arcturus in the day-time. (91)
The improvement of the graduation of the limbs of instru-
ments would have failed, either wholly or in great part, in
attaining its principal object, viz. greater precision in obser-

44 SPECIAL EESULTS IN THE URANOLOGICAL

vation, if optical means had not been adopted for augment-
ing the exactness of the reading commensurately with that
of the measurement. The construction of micrometers with
fine threads stretched in the focus of the telescope, the ap-
plication of which first gave to more exact graduation its
peculiar and indeed inestimable value, was devised six years
afterwards, in 1640, by the young and talented Gas-
coigne. (92)

While, therefore, in astronomical researches, telescopic
observation and measurement include only 240 years, we may
reckon, (without reference to the Chaldeans, Egyptians, and
Chinese, and counting only from Timochares and Aristillus(93)
to the discoveries of Galileo), more than nineteen centuries
in which the position and movements of the heavenly bodies
were observed with the naked eye. Seeing the numerous
interruptions to which the progress of civilisation and know-
ledge among the nations surrounding the Mediterranean was
exposed during that long period, we must regard with surprise
and admiration the recognition by Hipparchus and Ptolemy
of the intricate movements of the planets, of the two principal
lunar inequalities, and of the places of the stars; the per-
ception, by Copernicus, of the true system of the universe ;
and the improvement, by Tycho Brahe, of practical astro-
nomy and its methods, — all antecedent to the invention of
the telescope. Exactness of observation may doubtless have
been somewhat increased by the employment of long tubes,
used most probably by the ancients and certainly by the Arabs,
and arranged so that the object was seen through dioptra or
narrow apertures. Abul Hassan speaks decidedly of tubes
having eye and object dioptra attached to the extremities; and
this arrangement was also employed at the observatory esta-

PORTION OF THE COSMOS. — VISUAL POWER. 45

blished by Hulagu at Meragha. If looking through tubes
facilitates the finding of stars in the twilight,, — in other
words, if, in the evening twilight/ stars are earlier visible to
the naked eye with tubes than without, — the reason, as Arago
has remarked, is, that the tube, when the eye is kept close to
it, cuts off a large portion of the disturbing diffused light
(rayons perturbateurs) of the atmospheric strata which in-
tervene between the star and the eye. In like manner, even
in a dark night, the tube is useful in preventing the lateral
impression of the faint light which the particles of air re-
ceive from all the other stars in the sky ; the intensity of the
luminous image and the size of the star thus appear increased.
In a much amended, and often contested, passage of Strabo, in
which there is a reference to looking through tubes, the en-
larged appearance of the stars, or heavenly bodies, is expressly
mentioned, although erroneously attributed to refraction.(94}
Light, from whatever source it may proceed, — whether
from the sun, as solar light, or as reflected by the planets ;
from the fixed stars ; from rotten wood ; or as the product
of vital activity in glow-worms and other luminous animals, —
always shows the same refractive properties. (95) But the
prismatic coloured images, or spectra, from different sources
of light, (from the sun and from the fixed stars), show a
difference in the position of the dark lines, which were first
discovered by Wollaston in 1808, and of which Fraunhofer
determined the position with great exactness twelve years
later. Fraunhofer had counted 600 dark lines (properly
speaking, interruptions, or defective parts, of the coloured
image or spectrum) : in the fine experiments of Sir David
Brewster with nitrous acid gas, in 1833, their number rose to
above 2000. It had been remarked that, at certain seasons

46 SPECIAL RESULTS IN THE URANOLOGICAL

of the year, particular lines were wanting ; but Brewstet
has shewn that this is a consequence of the different heighr
of the sun, and the different absorption of the rays of light
in their passage through the atmosphere. In the coloured
spectra given by the reflected light of the Moon, Yenus,
Mars, and the Clouds, we find, as would no doubt have
been expected, all the characteristics of the solar spectrum.
On the other hand, the dark lines of the spectrum of Sirius
differ from those of Castor or of other fixed stars. Castor
himself shows other lines than those shown by Pollux and
Procyon. Arnici has confirmed these differences, which
had already been indicated by Fraunhofer, and has called
attention to the fact that, in fixed stars of at present equal
and perfectly -white light, the dark lines are not the same.
There still remains here a wide and important field for
future research, (96) in order to separate what is certain
from what is rather to be termed accidental— dependent on
the absorbing effect of the atmosphere.

There is another phenomenon deserving to be here noticed,
in which the specific character of the source of light has a
powerful influence. The light of glowing solid bodies and
that of the electric spark show great variety in the number
and position of Wollaston's dark lines. According to Wheat-
stone's remarkable experiments with revolving mirrors, the
light of friction-electricity appears also to have a velocity
greater than that of solar light, in the ratio of at least 3 to 2
(or fully 83920 geographical miles in a second of time).

A new life has animated all departments of optics from
the time when (in 1808) the reflection of the light of the
setting sun from the windows of the Palais du Luxembourg
accidentally led the acute Malus to the important dis-

PORTION OF THE COSMOS. VISUAL POWER. 47

covery of polarisation. (97) Since that event, the more deeply-
examined phsenomena of double refraction, ordinary (Huyge-
nian) polarisation and coloured polarisation, interference, and
diffraction, have furnished the investigator with unexpected
means of distinguishing between direct and reflected light (98),
of penetrating the secret of the constitution of the Solar
orb and his luminous envelopes ("), of measuring the pres-
sure and the minutest aqueous contents of the atmosphere,
of discerning the bottom of the sea and its shoals by the
aid of a plate of tourmaline (10°), and even of comparing,
according to Newton's example, the chemical (101) composi-
tion of several substances (102) with their optical effects. It
is sufficient to mention the names of Airy, Arago, Biot,
Brewster, Cauchy, Faraday, Fresnel, John Herschel, Lloyd,

Malus, Neumann, Plateau, Seebeck to recall to

the recollection of the scientific reader a series of brilliant
discoveries, and of the happiest applications of each newly-
discovered step. The great works of Thomas Young,
marked with the stamp of genius, more than prepared the
way for these important labours. Arago's polariscope, and
the observed position of coloured diffraction -fringes (conse-
quences of interference), have become of great and varied
use in the investigation. Meteorology has profited no less
than physical astronomy by the opening of this new path
of research.

Different as is the power of vision with the naked eye in
different men, yet here also there is a certain mean degree of
organic capability, which was the same among the ancient
Greeks and Romans as in the present day. The Pleiades
furnish the proof of this, showing that some thousand years
ago, as now, stars which astronomers call of the 7th magnitude

48 SPECIAL RESULTS IN THE URANOLOGICAL

are not visible to the naked eye in persons of ordinary powers
of vision. The group of the Pleiades consists of a star of
the 3rd magnitude, Alcyone; two of the 4th magnitude,
Electra and Atlas ; three of the 5th, Merope, Maia, and
Taygeta ; two between the 6th and 7th, Pleione and Celseno ;
one between the 7th and 8th, Asterope ; and several very
small telescopic stars. I employ the present denominations
and oi-'ler of magnitudes, for among the ancients some of these
names were assigned to other stars. It was only the six first-
named stars, of the 3rd, 4th, and 5th magnitudes respectively,
that could be easily seen. (103) Ovid says (Past. iv. 170) :
" Quse septem dici, sex tamen esse solent." It was supposed
that one of the daughters of Atlas, Merope, the only one
who had married a mortal, remained veiled through bashful-
ness, or even that she had entirely disappeared. She was
probably the star of almost the 7th magnitude, which we
now call Celseno ; for Hipparchus remarks, in the commen-
tary to Aratus, that in clear moonless nights seven stars
could really be perceived. It was then Celseno which was
seen as the seventh Pleiad ; Pleione, which is of equal
brightness, being too near Atlas (a star of the 4th magni-
tude) to be distinguished.

The small star Alcor (which, according to Priesnecker, is
at a distance of 11' 48" from Mizar, in the tail of the Great
Bear) is, according to Argelander, of the 5th magnitude, but
overpowered by the brightness of Mizar. It was called by
the Arabs " Saidak," " the tester ;" because it was the cus-
tom, as the Persian astronomer Kazwini(104) informs us,
" to test a man's power of sight by it." Notwithstanding
the low altitude of the constellation of the Great Bear within
the tropics, I have seen Alcor with the naked eye with

PORTION OF THE COSMOS. — VISUAL POWER. 49

great distinctness every evening on the rainless coast of
Cumana, and on the high plateaus of the Cordilleras at
elevations of twelve thousand feet ; but I have recognised
it only rarely and uncertainly in Europe, and in the dry
air of the steppes of Northern Asia. The limit within
which it is possible, with the naked eye, to separate two
objects very near to each other in the heavens, depends, as
Madler has very justly remarked, on their relative bright-
ness. The two stars of the 3d and 4th magnitudes, marked
a Capricorni, which are six and a half minutes apart, are
separated without difficulty. Galle thinks it possible, in a
very clear atmosphere, to separate with the naked eye e and
5 Lyrse, though only three and a half minutes apart, because
they are both of the 4th magnitude.

The too great comparative brightness of the neighbouring
planet is also the principal reason why Jupiter's satellites,
(one of which, and not all, as is often erroneously stated,
is equal in its light to stars of the 5th magnitude), remain
invisible to the naked eye. According to recent estimations
and comparisons with neighbouring stars by my friend,
Dr. Galle, the third satellite, which is the brightest, may
correspond to stars from the 5th to the 6th magnitude ;
whilst the others correspond, as their light varies, to stars
from the 6th to the 7th magnitude. Only occasional in-
stances have been cited of persons of extraordinary keenness
of vision, (persons who could perceive distinctly with the
naked eye stars below the 6th magnitude), having seen
any of Jupiter's satellites without a telescope. The angular
distance of the third and brightest satellite from the centre
of the planet is 4' 42" ; that of the fourth, which is only
l-6th smaller than the largest, 8' 16"; and all Jupiter's

VOL. III. E

50 SPECIAL IlESULTS IN THE ITRANOLOGICAL

satellites have at times., as Arago states, (105) an intenser
light, on equal surfaces, than the planet : at times, on the
other hand, they appear on the face of Jupiter, as recent
observations inform us, as gray spots.

The rays, which appear to our eyes to issue from the planets
and from the fixed stars, — and which from the earliest times
have been employed in pictorial representations, particularly
among the Egyptians, to designate the shining heavenly
bodies, — have a length of at least five or six minutes. Has-
senfratz declares them to be focal lines, " intersections de
deux caustiques," on the crystalline lens. " The image of
stars seen by us with the naked eye is enlarged by diverging
rays : by reason of this extension it occupies a larger space
on the retina than if it were concentrated in a single point.
The impression on the nerve is weaker. A very dense clus-
ter of stars, in which all the single stars hardly attain the
7th magnitude, may, on the other hand, become visible to
the naked eye, because the images of the many single stars
overlap each other on the retina ; so that, as in the case of
a concentrated image, every sensible point of the latter is
more strongly excited." (106).

Telescopes, unfortunately, also give, though in a much
less degree, an untrue or spurious diameter to stars : from the
examinations of William Herschel,(107) however, these diame-
ters decrease with increased magnifying power. This acute
observer, with the enormous magnifying power of 6500,
still estimated the apparent diameter of a Lyrse at 0"'36.
In terrestrial objects, besides the illumination, the form of
the object helps to determine the smallest visual angle
under which it can be seen by the naked eye. Adams re-
marked very justly, that a long thin rod can be seen at a
much greater distance than could a square, whose side should

PORTION OF THE COSMOS. — VISUAL POWER. 51

be equal to the thickness of the rod. A line is seen much
further than a point, even if the breadths of the two are
equal. Arago examined the influence of form in this
respect by angular measurements of the lightning conductors
visible from the Paris Observatory. Determinations of the
smallest optical angle of vision under which terrestrial
objects can be recognised by the naked eye have always
continued to advance progressively to smaller and smaller
quantities ; — from Robert Hook, who declared a full minute
to be absolutely necessary, to Tobias Mayer, who required
34" for a black spot on white paper, and further to Leuwen-
hoek's spiders' threads, which can be seen by persons of
very ordinary powers of vision under an angle of 4"' 7. In
the most recent and very exact experiments of Hueck on
the motion of the crystalline lens, it was barely possible to
see white lines on a black ground at an angle of 1"% a
spider's thread at 0"-6, and a fine shining wire at 0"'2.
The problem does not admit of a strict numerical solution,
as the result depends on the shape of the objects, their
illumination, their contrast with the back ground from
which they detacli themselves, and the movement or still-
ness, as well as the nature, of the intervening atmospheric
strata.

I was much impressed by a circumstance which occurred
during my stay at a beautiful country-seat belonging to the
Marques de Selvalegre, at Chillo (not far from Quito), from
whence the long extended ridge of the Volcano of Pichincha
was seen at a horizontal distance, trigonometrically measured,
of 85000 Paris (90590 Eng.) feet. My fellow-traveller
Bonpland, who was then engaged alone on an expedition to
the Volcano, was recognised by the Indians standing near
me as a white point moving alon^ the face of a black ba-

52 SPECIAL RESULTS IN THE URANOLOGICAL

saltic precipice, before we, who were looking for him with
telescopes, discovered him. In a short time my companion
(the ill-fated son of the Marques, Carlos Montufar, who
afterwards fell a victim in the civil war) and myself were
also able to distinguish the white moving figure with the
naked eye. Bonpland was wrapped in a white cotton
mantle, the poncho of the country. Allowing from 3 to 5
feet for the breadth of the shoulders, as the mantle some-
times clung close, and sometimes seemed to fly loosely in
the wind, and taking the known distance, we have from
7" to 12" as the angle under which the moving, object was
distinctly seen. "White objects on a black ground are seen,
according to Hueck's repeated experiments, at a greater dis-
tance than black objects on a white ground. The weather
was clear, and the ray passed through the stratum of thin
air, proper to an elevation of 14412 Trench (15360 Eng.)
feet above the level of the sea, to our station at Chillo, itself
8046 (8575 Eng.) feet high. The distance from the eye
to the object was 85596 (91225 Eng.) feet, or 14'8 geo-
graphical miles. The heights of the barometer and ther-
mometer at the two stations were very different: at the
upper, probably, 194 lines (17*23 English inches), and 8°
Cent. (46°.4 Eahr.) ; and at the lower, by exact observation,
250-2 lines (22'22 English inches), and 1S'7 Cent. (65'66
Eahr.) Gauss's heliotropic light, which has become so
important an auxiliary in our German trigonometrical
measurements, reflected from the Brocken to the Hohen-
hagen, was seen there at a distance of 213000 French feet
(227008 Eng.), — more than 36 geographical miles; and
often at points at which the angle subtended by a three-inch
mirror only amounted to. 0'H3.

The visibility of distant objects is modified by the absorp-

PORTION OF THE COSMOS. — VISUAL POWER. 53

tion of the rays proceeding from the terrestrial object, and
arriving at the unassisted eye at different distances, through
strata of air more or less dense, and more or less charged
with aqueous vapour ; by the intensity of the diffused light
radiated from the particles of air ; and by many still im-
perfectly explained meteorological circumstances. According
to old experiments of the accurate Bouguer, a difference of
1-6 Oth in the intensity of the light is necessary for visibility.
We see, as he expresses it, only in a negative manner, hill
and mountain summits which radiate but little light, and
detach themselves as dark masses against the sky. We see
them only by the difference of the thickness of the atmos-
pheric strata, which extend in the one instance to the
object, and in the other to the extremest horizon. On the
other hand, bright or shining objects, as snowy mountains,
white limestone rocks, and cones covered with pumice, are
seen in a positive manner. The distance at which high
mountain summits can be recognised at sea is not without
interest in navigation, when exact astronomical determinations
of the ship's place are wanting. I have treated this subject
in detail in another place, (108) when discussing the distance
at which the Peak of Teneriffe may be visible.

The power of seeing stars with the naked eye in the day-
time from the shafts of mines, or on \«ry lofty mountains,
has been a subject of examination with me from early youth.
I was aware (109) that Aristotle had affirmed that stars could
sometimes be seen from vaults and reservoirs, as well as through
tubes. Pliny, also, mentions this, and notices at the same
time the circumstance that stars can be clearly distinguished
in the day-time during solar eclipses. In the course of my
professional engagements as a mining engineer, I for some

t7OOT»o nooeaH o lovrva nstvfanvi f\T cmnT'V rlov llTlflPT*

54 SPECIAL RESULTS IN THE URANOLOGICAL

.looking up from the bottom of deep shafts to the zenith,
but without ever seeing a star ; nor have I since found an
individual in Mexican, Peruvian, or Siberian mines, who
had ever heard of stars being seen in the day-time, although
in such different latitudes as those embraced by my inquiries
and experience in both hemispheres, a sufficient number of
zenith stars must have presented themselves advantageously.
This entirely negative evidence renders very remarkable the
highly credible testimony of a celebrated optician who, in
early youth, saw the stars during bright day -light through a
chimney. (no) Phenomena whose visibility depends on an
accidental concurrence of favourable circumstances must
not be denied because they are of rare occurrence.

This principle also applies, I think, to the statement of
the always careful and accurate Saussure, in reference to
stars being seen with the naked eye on the ascent of Mont
Blanc, at a height of 11970 (12757 Eng.) feet. He says,
t( Quelques-uris des guides m'ont assure avoir vu des etoiles
en plein jour ; pour moi je n'y songeois pas, en sorte que
je n'ai point ete le temoin de ce phenomeiie ; mais I' asser-
tion uniforme des guides ne me laisse aucun doute sur
la realite. (1H) II faut d'ailleurs etre entierement a Fombre,
et avoir meme au-dessus de la tete une masse d'ombre d'une
epaisseur considerable, sans quoi Fair trop fortement eclaire
fait evanouir la foible clarte des etoiles." The conditions
are, therefore, almost entirely the same as those presented by
the reservoirs of the ancients and the chimney before referred
to. I have not found this remarkable statement (bearing
date the morning of the 2nd of August, 1787) repeated in
any subsequent journey in the Swiss mountains. Two highly
informed and excellent observers, the brothers Hermann
and Adolph Schlagintweit, who have recently explored the

POETION OF THE COSMOS. — VISUAL POWER. 55

eastern Alps to the summit of the Grosglockner (12213
Fr., or 13016 Eng. feet*), were never able to see stars in
the day-time, nor did they hear any statement to that effect
among the herdsmen and chamois hunters. T spent several
years in the Cordilleras of Mexico, Quito, and Peru, and
was very often, together with my friend Bonpland, in clear
weather on heights of upwards of fifteen or sixteen thousand
(English) feet ; and neither we, nor subsequently Boussin-
gault, could ever recognise stars in the day-time, although
the azure of the sky was so deep and dark, that with the same
cyanometer of Paul of Geneva with which Saussure had
read 39° on Mont Blanc, I should have found under the
tropics, at elevations between 16000 and 18000 (17052
and 19184 Eng.) feet, 46° at the zenith. (112) Under the
magnificent, ethereally pure and serene sky of Cumana, on
the plain of the sea-shore, after the observation of occulta-
tions of Jupiter's satellites, I have several times with ease
found the planet again with the naked eye,, and seen him
most distinctly whilst the sun's disk was 18° or 20° above
the horizon.

This is the proper place in which to notice, at least in a
cursory manner, another optical phsenomenon which, among
my many ascents of mountains, was only observed by me
once — viz. on the 22nd of June, 1799, before sunrise, on
the declivity of the Peak of Teneriffe. Being in the Mai-
pays, 10700 (11404 Eng.) feet above the sea, I saw with
the naked eye stars low down near the horizon in strange

[* Since given more correctly by Messrs. H. and A. Schlagintweit
12158 French or 12958 English feet, in their Physicalische Geographic der
Alpen.— ED.]

56 SPECIAL RESULTS IN THE URANOLOGICAL

fluctuating movement. Luminous points rose upwards,
moved sideways, and fell back to their former places. The
phenomenon lasted only seven or eight minutes, and ceased
long before the edge of the sun appeared above the sea ho-
rizon : it was seen equally through a telescope, and there
was no doubt that the apparent movement was that of the
stars themselves. (113) Did this change of place belong to
the much contested question of the lateral refraction of rays?
Does the undulation of the rising solar disk, small as it is
found by measurement, present, in the lateral alteration and
motion of the sun's limb, any analogy to what has been de-
scribed ? We know, apart from this question, that the dis-
turbance of the sun's disk would appear larger from being
near the horizon. Almost half a century later this same
phsenomenon has been observed, both with the naked eye
and through a telescope, in exactly the same spot in the
Malpays, and similarly before sunrise, by a well-informed
and very attentive observer, Prince Adalbert of Prussia. I
found the observation entered in his manuscript journal
without his having been aware, before his return from the
River Amazon, that an entirely similar appearance had been
seen by me. (114) Neither on the ridges of the Andes, nor
in the frequent mirage of the hot plains (Llanos) of South
America, notwithstanding the excessive variety of admixture
of unequally heated strata of air, could T ever find any trace
of lateral refraction. As the Peak of Teneriffe is so near to
us, and is often visited before sunrise by scientific travellers
provided with instruments, I may hope that my renewed
request for the observation of the lateral fluctuation of stars
may not be without effect.

I have already drawn attention to the fact, that long
before the great epoch of the invention of telescopes and

POETION OF THE COSMOS. — VISUAL POWER. 57

their application to celestial observation, — before therefore
the memorable years 1608 and 1610, — an exceedingly im-
portant part of the astronomy of our planetary system was
already established. The inherited treasures of Greek and
Arabian knowledge were augmented by the careful and ex-
tensive labours of George Purbach, Regiomontanus ( Johann
Muller), and Bernhard Walther of Nuremberg. Their efforts
were followed by the bold and comprehensive intellectual de-
velopment of the Copernican system ; and to this succeeded
an abundant mass of exact observations by Tycho Brahe,
and the acuteness in combination, and indomitable perseve-
rance in calculation, of Kepler. Two great men, Kepler
and Galileo, stand at the most important epoch which the
history of practical astronomy presents, — that which separates
observation with the naked eye, but with greatly improved
measuring instruments, from telescopic vision. Galileo was
then 44, and Kepler 37 years old; Tycho Brahe, the most
exact practical astronomer of that great period, had been
dead seven years. I have already remarked in the 2nd
volume of Cosmos (English edition, p. 324), that Kepler's
three great laws, which have made his name for ever illus-
trious, did not receive the praise of any one of his cotempo-
raries, — not even of Galileo. Discovered by a purely em-
pirical path, but more rich in consequences to science at
large than the isolated discovery of previously unseen celes-
tial bodies, they belong entirely to the period of natural
vision,— to the period of Tycho Brahe, and even to the Ty-
chonian observations ; although the printing of the " Astro-
nomia nova, seu Physica coelestis de Motibus Stellse Martis"
was not completed until 1609, and the third law; according
to which the squares of the periodic revolutions of two

58 SPECIAL RESULTS IN THE URANOLOGICAL

planets are in the ratio of the cubes of their mean distances,
was first developed in the " Harmonice Mundi," in 1619.

The transition from natural to telescopic vision, which
marks the first ten years of the seventeenth century, — and
forms an epoch in astronomy, or the knowledge of celestial
space, even more important than 1492 had been to the
knowledge of terrestrial space, — not only enlarged indefinitely
our view into creation, but also, by proposing for solution
new and intricate problems, became the means of raising
mathematical knowledge to a degree of brilliancy never
before attained. Thus the strengthening of the organs of
sense reacted upon the world of thought, leading to the
invigoration of the intellectual power, and to the ennoble-
ment of humanity. We owe to the telescope alone,
within the space of two centuries and a half, the knowledge
of 1 3 new planets, and 4 new systems of satellites (4 belong-
ing to Jupiter, 8 to Saturn, 4, perhaps 6, to Uranus, and 1
to Neptune) ; of the solar spots and faculse ; of the phases
of Venus ; of the form and elevation of the mountains in the
moon ; of the winter polar zones of Mars ; of the belts of
Jupiter and Saturn; the ring of Saturn; the interior (plane-
tary) comets of short periods of revolution ; and of many
other phsenomena which, like these, escape the perception
of the unassisted eye. If our solar system, which was so long
limited to 6 planets and 1 satellite, has been thus enriched
within the last 240 years, what is called the " heaven of the
fixed stars" has, during the same period, received a still more
unexpected extension. Thousands of nebulae, clusters of
stars, and double stars, have been catalogued. The variable
position of the double stars which revolve around a common
centre of gravity, as well as the proper motion of all the

PORTION OF THE COSMOS. VISUAL POWER. 59

fixed stars, show that gravitating forces prevail in those dis-
tant regions of space, as well as in the narrower sphere of the
mutually perturbing orbits of the planets of our system.
From the time that Morin and Gascoigne combined optical
powers with measuring apparatus (which was not> how-
ever, until twenty-five or thirty years after the invention of
the telescope), it has been possible to obtain more delicate
and precise determinations of the alterations of place of the
heavenly bodies. In this manner it has become possible to
measure with the greatest precision the present position of a
heavenly body, the aberration-ellipses of the fixed stars and
their parallaxes, and the distances apart of the double stars,
though only amounting to a few tenths of a second of arc.
The astronomical knowledge of the solar system has gra-
dually expanded into that of the system of the Universe.

We know that Galileo made his discoveries of Jupiter's
satellites with a magnifying power of 7, and that he was never
able to employ a higher power than 32. One hundred and
seventy years afterwards, we see Sir William Herschel em-
ploy, in his investigations on the magnitude of the apparent
diameters of Arcturus and a Lyra3, magnifying powers of
6500. From the middle of the 17th century men vied
with each other in attempting telescopes of great length.
Although as late as 1655 Christian Huygens discovered the
first of Saturn's satellites, (Titan, the sixth in distance from
the centre of the planet), with a telescope of only 1 2 feet,
he subsequently employed in astronomical observations tele-
scopes of 122 feet; but the three of 123, 170, and 210
feet focal distance, in the possession of the Royal Society of
London, which had been made by his brother Crnstantine
Huygens, were tried by Christian, as he himself expressly

60 SPECIAL RESULTS IN THE URANOLOGICAL

says, (115) on terrestrial objects. Auzout, who as early as
1663 constructed colossal telescopes without tubes, and,
therefore, without a solid or rigid connection between the
object-glass and the eye-piece, completed an objective which,
with a focal length of 300 feet, would bear a magnifying
power of 600. (116) Dominic Cassini made great use of such
object-glasses attached to poles, in the successive discovery,
between 1671 and 1684, of the eighth, fifth, fourth, and third
of the satellites of Saturn He employed the object-glasses
which Borelli, Campani, and Hartsoeker had ground : the
latter were of 250 feet focal length. Those of Campani, which
enjoyed the highest reputation under the reign of Louis XIV.,
have been often in my hands at the Paris Observatory during
my long residence in that city. If we remember the faint
light of the satellites of Saturn, and the difficulty of
managing such apparatus, (117) which could only be moved
by the aid of cords, we cannot sufficiently admire the skill
and perseverance of the observer.

The advantages which were then supposed to be attainable
exclusively by means of gigantic lengths, led great minds,
as is often the case, to form extravagant hopes. Auzout
thought it necessary to refute Hooke, who, in order to see
animals in the moon, had proposed telescopes 10000 feet,
or almost 2 geographical miles, in length. (118) The
practical inconvenience of optical instruments of more than
100 feet focal length, gradually led to the introduction, in
England especially, and through Newton himself (according
to the precedents set by Mersenne and by James Gregory of
Aberdeen), of the shorter reflecting instruments. Bradley' s
and Pound's careful comparison of 5 -feet Hadleyian re-
flectors with the refractor already noticed of Constantiiie

PORTION OF THE COSMOS. VISUAL POWER. 61

Huygens of 123 feet focal length, proved entirely to the
advantage of the former. Short's costly reflectors were
now everywhere adopted, until the successful practical solu-
tion, (1759), by John Dollond, of the problem of achro-
matism proposed by Leonhard Euler and Klingenstierna,
again turned the scale in favour of refractors. The appa-
rently incontestable rights of priority of the mysterious
Chester More Hall, of Essex (1729), were first made known
to the public when John Dollond obtained a patent for his
achromatic telescopes. (119)

But this victory of the refracting instruments was not
of long duration : eighteen or twenty years after the
publication of John Dollond' s accomplishment of achro-
matism by a combination of crown and flint glass, new
fluctuations of opinion were induced by the merited tri-
bute of admiration paid, both in England and elsewhere,
to the ever memorable labours of a German, William
Herschel. The construction of his numerous 7 -feet and
20 -feet telescopes, to which magnifying powers of 2200
to 6000 could be successfully applied, was followed by the
construction of his 40-feet reflector, by means of which
were discovered, in August and September 1789, the two in-
nermost of the satellites of Saturn, — the second, Enceladus ;
and soon after Mimas, the first or nearest to the ring. The
discovery of the planet Uranus (1781) was made with the
7 -feet telescope of Herschel. The satellites of Uranus,
which have such feeble light, were first seen by him, in 1787,
in his 20-feet instrument arranged for the " front view/' (12°)
The previously unattained degree of perfection which this
great man was able to impart to his reflecting telescopes, in
which the light was reflected only once, led, by the unin-

62 SPECIAL RESULTS IN THE URANOLOGICAL

terrupted labours of more than forty years, to the most
important extension of all parts of physical astronomy, in the
planetary system as well as in the nebulae and double stars.
A long reign of reflectors was again followed, in the first
twenty years of the nineteenth century, by a happy emula-
tion in the construction of achromatic refractors and helio-
meters, moved equatorially by clock-work. Eor object-
glasses of extraordinary size, a homogeneous flint glass, free
from striae, was supplied in Germany by the Munich esta-
blishment of Utzschneider and Praunhofer, subsequently
of Merz and Mahler; and in Switzerland and France (for
Lerebours and Cauchoix), in the manufactories of Guinaud
and Bontems. It is sufficient for the purpose of this
historical review, to name here, as instances, the great refrac-
tors made, under Fraunhofer's superintendence, for the ob-
servatories of Dorpat and Berlin, having 9 Parisian inches
free aperture, with a focal length of 13 J (14 Engish) feet j
the refractors of Merz and Mahler, in the observatories of
Pulkova, and Cambridge in the United States of North
America, (121) both furnished with object-glasses of 14
Parisian inches aperture, and 21 feet focal length (14*9
English inches, and 22 English ieet 4'6 inches).* The
heliometer of the Konigsberg Observatory, which was for a
long time the largest in existence, has 6 Parisian inches aper-
ture, and has become celebrated by the memorable labours
of Bessel. The short dialytic refractors, advantageous in
respect of light, which Plosl, in Vienna, was the first to
execute, the merits of which were recognised almost at the

* [The exact focal length of the refractor at Cambridge, U.S. is 22 English
feet 6 inches.— ED.]

PORTION OF THE COSMOS. VISUAL POWER. 63

same time by Eogers in England, deserve to be constructed
of larger dimensions.

During the same period in which these endeavours
were made, — to which I have thus referred because they
have so materially influenced the enlargement of cosmical
views, — mechanical improvements in measuring-instruments
(zenith sectors, meridian circles, and micrometers) did not
remain behind the progress made in optical instruments,
and in those employed for measuring time. Amongst the
many distinguished names of the present or recent times, I
will mention only the following : — for measuring instru-
ments, those of Eamsden, Troughton, Fortin, Eeichenbach,
Gambey, Ertel, Steinheil, Eepsold, Pistor, Oertling; for
chronometers and astronomical clocks — Mudge, Arnold,
Emery, Earnshaw, Breguet, Jiirgensen, Kessels, Winnerl,
Tiede. In the valuable and extensive investigations into
the distances apart and the periodic movements of double
stars, which we owe to William and John Herschel, South,
Struve, Bessel, and Dawes, we specially remark this pro-
portionate and simultaneous advance in the perfection at
once of sight and of measurement. Stmve's classification
of double stars contains, of those which are less than 1' apart,
about 100, and of those between 1' and 2" apart, 336, —
all by frequently repeated measurements. (122)

Within the last few years, two men who, by station and
circumstances, were far removed from such occupations with
a view to pecuniary profit, the Earl of Eosse, at Parsonstown
(fifty miles west of Dublin), and Mr. Lassell, at Starfield,
near Liverpool, animated by a noble love of astronomy,
have, with devoted liberality and under their own immediate
direction and superintendence, accomplished the completion

64 SPECIAL RESULTS IN THE URANOLOGICAL

of two reflecting telescopes which have raised to the highest
degree the expectation of astronomers. (123) With LasselFs
telescope, which has only 2 feet aperture and 20 feet focal
length, there have been already discovered a satellite of
Neptune and an eighth satellite of Saturn, besides the redis-
covery of two satellites of Uranus. Lord Rosse's new colossal
telescope has 6 feet clear aperture and 53 feet focal length.
It is placed in the meridian between two piers, each 12 feet
distant from the tube, and from 47 to 54 feet in height.
Many nebulae which no previous instrument could resolve,
have, by this magnificent telescope, been resolved into clusters
of stars, and the forms of other nebulae have now for the first
time been shown in their true outlines. The quantity of light
reflected from the surface of the mirror is truly wonderful.

Morin, who, with Gascoigne, and before Picard and Auzout,
first combined the telescope with measuring instruments, con-
ceived, about 1638, the idea of observing stars telescopically
in full daylight. He says himself (124) that he " was led to
a discovery which may become important for the determina-
tion of longitudes at sea, not by Tycho Brahe's great labours
on the positions of the fixed stars, — as, in 1582, and there-
fore twenty-eight years before the invention of the telescope,
he compared Venus with the sun in the day-time and with
the stars at night, — but merely by the simple thought that it
might be possible, as with Yenus so also with Arcturus and
other fixed stars, once having them in the field of view of
the telescope before sunrise, to continue to follow them in
the heavens after sunrise." No one, he said, before him
" had been able to find the fixed stars in the broad daylight."
Since the establishment of great meridian telescopes by Romer
in 1691, day observations of the heavenly bodies have been

PORTION OF THE COSMOS. VISUAL POWER. 65

frequent and highly serviceable : they are sometimes usefully
applied even to the measurement of double stars. Struve (125)
remarks, that with the Dorpat refractor, employing a magni-
fying power of 320, he had determined the smallest distances
apart of exceedingly faint double stars during a twilight so
bright that one could read conveniently at midnight. The
Pole star has a companion of the 9th magnitude only 18"
from itself ; in the Dorpat refractor Struve and "Wrangel
have seen this companion in the day-time, (126) as have also
(once) Encke and Argelander.

The reason of the powerful effect of telescopes at a time
when, by multiplied reflection, the diffused light (127) of the
atmosphere is injurious, has given occasion to a variety of
doubts. As an optical problem it was regarded with the
most lively interest by Bessel. In his long correspondence
with me he often returned to the subject, and acknowledged
that he could find no solution which was entirely satisfactory
to him. I think I may reckon on the thanks of my readers
for the introduction in a note (128) of the views of Arago, as
contained in one of the many manuscripts which I was per-
mitted to use when at Paris. According to his ingenious
explanation, high magnifying powers facilitate the finding
and recognition of the fixed stars, because, without sensibly
enlarging their image, they conduct a greater quantity of in-
tense light to the eye, whilst they act according to a different
law on the aerial field from which the star detaches itself.
The telescope, by magnifying the distance between the illu-
minated particles of air, darkens the field of view, or dimi-
nishes the intensity of its illumination; and it is to be
remembered that we see only by the difference between the
light of the star and that of the aerial field, i. e. the mass of

VOL. III. F

66 SPECIAL RESULTS IN THE TJRANOLOGICAL

air which surrounds it, in the telescope. The case of the
simple ray of the image of a fixed star differs from that of
planetary discs ; the latter, under the magnifying power of
the telescope, losing in intensity of light by dilatation
equally with the aerial field from which they detach them-
selves. It is also to be noticed that high magnifying
powers increase the apparent rapidity of motion in the fixed
stars as well as in the planets. In instruments which are
not mounted equatorially, and made to follow the movement
of the heavens by means of clock-work, this circumstance
may facilitate the recognition of objects in the day-time.
New points on the retina are successively stimulated. Yery
faint shadows, as Arago has remarked elsewhere, first become
visible by being put in motion.

Under the serene sky of the tropics in the driest season
of the year, I have often been able to find the pale disc of
Jupiter, in a Dollond's telescope, with the low magnifying
power of 95, when the sun was already 15° or 18° above;
the horizon. The f'aintness of the light of Jupiter and Sa-
turn seen in the day-time in the large Berlin refractor, and
contrasted with the brighter, though equally reflected, light
of the planets nearer to the sun, Mercury and Yenus, has
repeatedly surprised Dr. Galle. Occupations of Jupiter's
satellites have sometimes been observed in the day-time with
powerful telescopes (by Plaugergues, 1792; and Struve,
1820). Argelander, at Bonn (7th December, 1849), saw
very clearly three of Jupiter's satellites a quarter of an hour
after sunrise with a 5 -feet IVaunhofer. He could not
recognise the fourth satellite. His assistant, Herr Schmidt,
saw still later the emersion from behind the dark limb of
the moon of all the satellites including the fourth, in the

PORTION OP THE COSMOS. — SCINTILLATION OF STARS. 67

8 -feet heliometer. The determination of the limits of teles-
copic visibility of small stars during daylight, in different
climates and at different elevations above the level of the sea,
has both an optical and a meteorological interest.

Among the phenomena belonging to natural and tele-
scopic vision which are remarkable in themselves, and of
which the causes are much contested, is the nocturnal
sparkling (twinkling or scintillation) of the stars. According
to Arago,(129) there are two things to be essentially distin-
guished in the scintillation : 1. alteration in the intensity of
the light by a sudden decrease, amounting even to extinc-
tion, and rekindling ; 2. alteration of colour. Both altera-
tions are even stronger in reality than they appear to the
naked eye; for when the several points of the retina are
once excited, they retain the impression of light which they
have received; so that the disappearance of the star, its
obscuration, and its change of colour, are not felt by us in
their full measure. Still more striking is the phenomenon
of scintillation seen through a telescope, if the latter is
shaken. Fresh and fresh points of the retina are excited,
and there appear coloured and often interrupted circles. In
an atmosphere composed of constantly varying strata of dif-
ferent temperature, moisture, and density, the principle of
interference explains how, after a momentary coloured flash,
there follows an equally momentary disappearance or obscu-
ration. The undulation theory teaches in general that two
rays of light (two systems of waves) proceeding from one
source (one centre of vibration) by the inequality of their
paths destroy each other; that the light of one ray, added
to that of the other ray, produces darkness. When one sys-

68 SPECIAL RESULTS IN THE URANOLOGICAL

tern of waves is so far behind the other as amounts to an
uneven number of semi-undulations, the two systems of
waves strive to impart to the same molecule of ether, at the
same instant, equal but opposite velocities ; so that the effect
of their union is the repose of the molecule, or darkness.
In some cases it is 'rather the refrangibility of the different
atmospheric strata traversed by the rays of light, than the
different length of their paths, which performs the principal
part in the phenomenon. (13°)

The degree of scintillation is strikingly different in dif-
ferent fixed stars; not dependent solely on their altitude or
their apparent magnitudes, but also, it would seem, on the
nature of their particular light. Some, for example a Lyrse,
twinkle less than Arcturus and Procyon. The absence of
scintillation in the planets with the largest discs is to be
ascribed to compensation, and to the mixture of the colours
proceeding from different points of the disc. The disc is
to be regarded as an aggregation of stars, which mutually
restore the light neutralised by interference, and recombine
the coloured rays into white light. Thus traces of scintil-
lation are most rare in Jupiter and Saturn, but are seen in
Mercury and Yenus, whose diameters diminish to 4/'*4 and
9"'5. The diameter of Mars, at the time of conjunction,
may be as small as 3"*3. In the clear cold winter nights
of the temperate zone, the scintillation of the stars enhances
the impression of the lustre of the starry heavens from the
circumstance that, as we see stars of the 6th and 7th
magnitudes shine forth suddenly here and there, we are led
to imagine that we perceive more shining points than the
unassisted eye can really distinguish. Hence arises the
popular surprise at the few thousands of stars noted in

PORTION OF THE COSMOS. SCINTILLATION OF STARS. 69

accurate catalogues as visible to the naked eye. That the
trembling light of the fixed stars distinguishes them from
the planets, was early known to the Grecian astronomers ;
but Aristotle, in accordance with the emanation and tangen-
tial theory of vision to which he adhered, singularly enough
ascribed the trembling and twinkling of the fixed stars
merely to an effort or straining of the eye. " The fixed
stars," said he,(131) "sparkle, but the planets do not : for
the planets are near, so that the sight is able to reach them ;
but in the fixed stars (irpbg tie TOVQ ^ivovrao) the eye, by
reason of the distance and the effort, falls into a tremulous
movement."

In Galileo's time, between 1572 and 1604, — in an epoch
of great events in cosmical space, and when three new
stars(132), brighter than stars of the first magnitude, ap-
peared suddenly, and one of them, in Cygnus, continued to
shine for twenty -one years, — Kepler's attention was parti-
cularly drawn to scintillation as the probable criterion of
a non-planetary body ; but the state of optics at that period
did not permit him to rise above the ordinary ideas of va-
pours in motion. (133) Also, among the newly-appeared
stars mentioned in the Chinese annals, according to the
great collection of Ma-tuan-lin, the strong degree of scintil-
lation is sometimes noticed.

In and near the tropical zone, from the more uniform
character of the atmospheric strata, the comparative or
entire absence of scintillation in the fixed stars to within
twelve or fifteen degrees of the horizon, gives to the vault
of heaven a peculiar character of repose and tranquil bril-
liancy. In several of my descriptions of nature, I have
spoken of this characteristic of the tropics, which had not

70 SPECIAL RESULTS IN THE URANOLOGICAL

escaped the observation of La Condamine and Bouguer in
the Peruvian plains, and of Garcin (134) in Arabia, India,
and on the coasts of the Persian Gulf, near Bender Abassi.

As the aspect of the starry heavens at the season of per-
petually clear and perfectly cloudless tropical nights had for
me a peculiar charm, I took the pains of always noting in
my journals the altitude above the horizon at which the
scintillation ceased with different hygrometrical readings.
Cumana, and the rainless part of the Peruvian sea-coast,
before the season of Garua or fog, were particularly suited
for such observations. According to the mean results of
my observations, the larger fixed stars would appear for the
most part to scintillate only when below 10° or 12° from
the horizon. At greater altitudes they shed a mild and
planetary light. The difference is best recognised by fol-
lowing the same star in its gradual ascent or descent, mea-
suring at the same time its angle of altitude, or calculating
it, if the latitude of the place and the time be known.
Sometimes, in equally clear and equally calm nights, the
region of scintillation extends to 20° and even 25° of alti*
tude ; yet there could hardly ever be traced any connection
between these differences, and the state of the thermometer
and hygrometer as observed in the lowest, and only accessi-
ble, atmospheric stratum. I have seen in successive nights,
after considerable scintillation of stars between 60° and 70°
high, with Saussure's hair hygrometer at 85°, the scintilla-
tion cease entirely at 15° above the horizon, although the
humidity of the air had so much increased that the hygrometer
had advanced to 93°. It is not the quantity of aqueous
vapour which the atmosphere holds in solution, but the
unequal distribution of vapour in the superimposed strata,

PORTION OF THE COSMOS. — VELOCITY OF LIGHT. 7 1

and the upper currents of cold and warm air, not perceptible
iii the lower regions, which modify the intricate compensa-
tory movement of the interferences of the luminous rays.
The presence of a very thin orange-coloured mist, which
tinged the sky a short time before earthquake shocks, in-
creased the scintillation of the stars at high altitudes in a
striking manner. All these remarks apply to the perfectly
clear, cloudless, and rainless season of the tropical zone 10
or 12 degrees north and south of the equator. The changes
which take place in the phenomena of the light of the stars
at the commencement of the rainy season, during the passage
of the sun through the zenith, depend on very general and
almost tempestuous meteorological causes. The sudden
slackening of the north-east trade wind, and the inter-
ruption of the regular upper currents from the equator to
the poles, and of the lower currents from the poles to the
equator, produce the formation of clouds, and the daily
occurrence, at certain hours, of thunder and heavy rain.
I have remarked in several successive years, in places where
the scintillation of stars is at other times a rare occurrence,
that the approach of the rainy season is announced many
days beforehand by the tremulous light of stars high in the
heavens. Sheet lightning, and single flashes in the distant
horizon, without visible cloud, or in narrow perpendicularly
rising columns of cloud, are accompanying signs. In seve-
ral of my works I have tried to describe these changes in
the physiognomy of the heavens, which are the characteristic
precursors of the rainy season.

On the subject of the velocity of light, and the probability
that it requires a certain time for its propagation, we find

72 SPECIAL RESULTS IN THE TJKANOLOGICAL

the earliest view expressed by Francis Bacon, in the second
book of the Novum Organum. He speaks of the time re-
quired by a ray of light to traverse the immensity of space,
and throws out the question whether the stars still exist
which we now see sparkle. (136) One is astonished at find-
ing so happy a conjecture in a work whose celebrated author
was so far below some of his cotemporaries in mathematical,
astronomical, and physical knowledge. The velocity of the
reflected solar light was measured by Homer (November
1675) by comparison of the times of occultation of Jupiter's
satellites ; and the velocity of the direct light of the fixed
stars by Bradley' s great discovery of the aberration of light
(made in the autumn of 1727), — that demonstration to our
senses of the earth' s movement of translation in its orbit ;
viz. of the truth of the Copernican system. In very recent
times a third method of measurement has been proposed by
Arago, by the phenomena of the light of a variable star ; for
example, Algol in Perseus. (137) We have to add to these
astronomical methods a terrestrial measurement, which has
very recently been executed with great ingenuity and suc-
cess by M. Fizeau, in the neighbourhood of Paris. It recals
to recollection an attempt of Galileo's with two lanterns,
which did not lead to any result.

Erom Eomer's first observations of Jupiter's satellites,
Horrebow and Du Hamel estimated the time occupied in
the passage of light from the sun to the earth, at their
mean distance apart, at 14' 7"; Cassini, at 14' 10"; New-
ton (138), which is very striking, much nearer to the truth,
at 7' 30". Delambre,(139) by taking into account, among
the observations of his time, only those of the first satellite,
found 8' 13"*2. Encke has very justly remarked how

PORTION OF THE COSMOS. VELOCITY OF LIGHT. 73

important it would be, with the certainty of obtaining the
more accordant results which the present perfection of tele-
scopes would afford, to undertake a series of occupations
of Jupiter' s satellites, for the express purpose of deducing
the velocity of light.

From Bradley' s observations of aberration, recently re-
discovered by Rigaud of Oxford, there follows, accord-
ing to the investigation of Dr. Busch (14°) of Konigs-
berg, for the passage of light from the sun to the earth,
8' 12"-14 ; for the velocity of the light of the stars 167976
geographical miles in a second ; and for the constant of
aberration, 20"'2116 : but, from the more recent aberration-
observations of Struve, made for eighteen months with the
large transit instrument at Pulkova,(141) it appears that the
first of these numbers must be considerably increased. The
result of Struve's great investigation is 8' 17"' 78; whence,
with the aberration-constant, 20". 4451, with Encke's cor-
rection of the sun's parallax made in 1835, and with the
value of the earth's semi-diameter given by him in the
Jahrbuch for 1852, we have for the velocity of light 166196
geographical miles in a second. The probable error of the
velocity scarcely amounts to eight geographical miles.
Struve' s result for the time which light requires to reach
the earth from the sun differs -—-^ from that of De-
lambre (8' 13"'2), which latter was employed by Bessel in
the Tabulae Eegiomontanse, and has been used hitherto in
the Berlin Astronomical Almanack. The discussion of
this subject cannot be regarded as completely terminated ;
but the earlier entertained supposition, that the velocity of
the light of the Pole-star was less than that of its companion
in the ratio of 133 : 134, remains subject to great doubts.

74 SPECIAL RESULTS IN THE URANOLOGICAL

A physicist distinguished for his knowledge as well as for
his great delicacy in experimenting, M. Fizeau, lias succeeded
in executing a terrestrial measurement of the velocity of
light, by means of an ingeniously devised apparatus, in which
the artificial star-like light of oxygen and hydrogen is returned
to the point from whence it came, by a mirror placed at a
distance of 8633 metres (28324 English feet), between
Suresne and La Butte Montmartre. A disc, furnished with
720 teeth, which made L2'6 revolutions in a second, alter-
nately stopped the ray of light, and allowed it to pass freely
between the teeth of the limb. Prom the indications of a
counter (compteur) it was inferred, that the artificial light
traversed 17266 metres (56648 Eng. feet), or twice the
distance between the stations, in 1 6^00 of a second of time ;
whence there results a velocity of 167528 geographical miles
in a second. (142) This result comes nearest to that of
Delambre derived from Jupiter's satellites, which is 167976
geographical miles in a second.

Direct observations, and ingenious considerations on the
absence of any alteration of colour during the change of light
of variable stars, (a subject to which I shall presently re-
turn), have led Arago to the conclusion that, (in the language
of the undulatory theory), rays of light which have different
colours, and therefore very different lengths and rapidities of
transverse vibration, move through space with equal velo-
cities ; but that in the interior of the different bodies through
which the coloured rays pass, their rates of propagation and
their refractions are different. (143) Arago' s observations
have shown that in the prism the refraction is not altered
by the relation which the velocity of light bears to that of
the Earth's motion. All the measurements accord in the

PORTION OF THE COSMOS. VELOCITY OF LIGHT. 75

result, that the light of the stars towards which the Earth is
advancing has the same index of refraction, as the light of
the stars from which the Earth is receding. Speaking in the
language of the emission hypothesis, the celebrated observer
we have just named said, that bodies send forth rays of all
velocities, but that among these different velocities there is
only one which can awaken the sensation of light. (144)

If we compare the velocities of solar, sidereal, and terres-
trial light, which all comport themselves exactly in the same
manner in the prism, with the velocity of the current of
friction-electricity, we are inclined to assign to the latter,
according to the experiments devised with admirable in-
genuity by Wheatstone, a velocity superior to the former
in the ratio of at least 3 to 2. According to the lowest
results of Wheatstone' s optical rotating apparatus, the elec-
tric current traverses 288000 English statute miles, or
250000 geographical miles, in a second. (145) If, then, we
reckon with Struve for sidereal light in the aberration-
observations 166196 geographical miles in a second, we get
a difference of 83804 geographical miles in a second for the
greater velocity of the electric current.

This result appears to contradict the previously mentioned
view of William Herschel, which regarded the light of the
sun and of the fixed stars as perhaps the effect of an electro-
magnetic process, — a perpetual Aurora. I say appears to
contradict ; for it cannot be deemed impossible that, in the
different luminous bodies of space, there may be several
magneto-electric processes very different in kind, and in
which the light produced by the process may have a different
rate of propagation. To this possible conjecture must be
added the uncertainty of the numerical result obtained with

76 SPECIAL RESULTS IN THE URANOLOGICAL

Wheatstone's apparatus, which result he himself regards as
"not sufficiently established, and as requiring fresh confir-
mation" in order to be compared satisfactorily with the de-
ductions from aberration- and satellite- observations.

Later experiments made by Walker in the United States
of North America on the velocity of the propagation of elec-
tricity, on the occasion of his telegraphic determinations of
the longitudes of Washington, Philadelphia, New York, and
Cambridge, have excited a lively interest in the minds of
physical enquirers. According to Steiuheil's description of
these experiments, the astronomical clock of the Observatory
at Philadelphia was connected with Morse's writing appa-
ratus on the line of telegraph in such manner, that the clock's
march noted itself by points on the endless strip of paper of
the apparatus. The electric telegraph carries each of these
points instantaneously to the other stations, and gives them
the Philadelphia time by similar points on their moving strips
of paper. Arbitrary signals, or the instant of the passage of
a star, may be noted in the same manner by the observer, by
merely touching or pressing an index with his finger. The
material advantage of this American method consists, as
Steinheil expresses it, " in its making the determination of
time independent of the connection of the two senses,
sight and hearing ; as the clock's march notes itself, and the
instant of the star's passage is given direct (to within a mean
error of the 70th part of a second, as Walker states) by the
movement of the observer's finger. A constant difference
between the compared clock-marks of Philadelphia and
Cambridge is produced by the time which the electric cur-
rent requires to traverse twice the closed circuit between the
two stations/'

PORTION OF THE COSMOS. — VELOCITY OF LIGHT. 77

Measurements made with conductors 1050 Eng. statute
miles, or 968 geographical miles, in length, gave, from 18
equations of condition, the rate of "propagation of the hydro-
galvanic current at only 18700 statute or 16240 geogra-
phical miles in a second ; (146) i. e. fifteen times slower than
the electric current in Wheatstone's rotating disc apparatus !
As in Walker's remarkable experiments two wires were not
used, but half the conduction, according to the common ex-
pression, took place through the moist body of the earth, it
might seem a justifiable supposition that the velocity of the
propagation of electricity is dependent on the-nature as well as
on the dimensions (147) of the medium. In the voltaic circuit
bad conductors become more heated than good conductors,
and electric discharges are very variously complicated phe-
nomena, as appears by the latest experiments of Eiess. (148)
The now prevailing views respecting what is commonly called
" connection through the Earth" are opposed to the view of
linear molecular conduction between the two ends of the wire,
and to the conjectures of impediments to conduction, and of
accumulation and discharges in a current ; as that which was
once regarded as intermediate conduction in the Earth is now
supposed to belong only to an equalisation or to a restora-
tion of electric tension.

Although, according to the present limits of exactness in
this kind of observation, it is probable that the aberration-
constant, and therefore the velocity of light, of all the fixed
stars, is the same, yet the possibility has more than once
been spoken of, that there may be luminous bodies in space
whose light does not reach us because, from their enormous
mass, gravitation constrains the luminous particles to return.
The emission theory gives to such fancies a scientific

78 SPECIAL RESULTS IN THE URANOLOGICAL

form : (149) I only allude to them here, because T shall sub-
sequently have to notice certain peculiarities of motion
ascribed to the star Procyon, which appear to point to a
perturbation by dark bodies. It is the object of this part of
my work to touch on matters which, during the time in
which it has been in progress, have influenced the direction
which science has pursued, and thus to mark the individual
character of the epoch in regard to the study of Nature,
whether in the sidereal or the telluric sphere.

The photometrical relations, or relative brightness, of the
self-luminous bodies which fill space, have formed a subject
of scientific observation and estimation for more than two
thousand years. The description of the starry heavens in-
cluded not only the determinations of place, the measure-
ment of the angular distances of the heavenly bodies, and of
their paths relatively to the apparent course of the sun and
the diurnal movement of the celestial vault, but also the
relative intensity of light in different stars. It was no
doubt the subject which earliest drew the attention of men ;
single stars received names before they were combined
with others into imaginary groups or constellations. Among
the small savage tribes inhabiting the densely wooded
districts of the Upper Orinoco and Atabapo, in places where
the impenetrable thickness of the forest usually obliged me
to observe only high culminating stars for determinations of
latitude, I often found single individuals, especially old men,
who gave particular names to Canopus, Achernar, the feet
of the Centaur, and the principal star in the Southern Cross.
Supposing the list of constellations which we have under the
name of the Catasterisms of Eratosthenes really to possess the

PORTION OF THE COSMOS. — PHOTOMETRY. 79

high antiquity so long ascribed to it, (between Autolycus of
Pitane and Timocharis, almost a century and a half, therefore,
before Hipparchus), we should possess in the astronomy
of the Greeks an indication of the time when the fixed stars
were not yet classed according to their relative brightness.
In the Catasterisms, in speaking of the stars which make
up a constellation, there is often a notice of the number of
those which are " brightest" or " largest" among them, while
others are said to be dark or little noticeable, (15°) but
nothing is said of the stars in one constellation relatively to
those in another. According to Bernhardy, Baehr, and
Letronne, the Catasterisms are two centuries more modern
than the Catalogue of Hipparchus, and are a mere compila-
tion made without much care, an extract from the Poeticum
astronomicum ascribed to Julius Hyginus, if not from the
'E^ftj/e of the ancient Eratosthenes. The Catalogue of
Hipparchus, which we possess in the form given to it in the
Almagest, contains the first and important determination of
the classes of magnitude (degrees of brightness) of 1022
stars, or about l-5th of all the stars visible to the naked
eye in the whole heavens between the 1st and 6th magni-
tudes inclusive. Whether the estimations are exclusively
Hipparchus' s own, or whether they do not rather belong in
part to the observations of Timocharis or Aristyllus which
Hipparchus so often used, remains uncertain.

This work formed the foundation on which the Arabians
and the whole of the middle ages continued to build ; and
even the habit which has been carried on into the 19th
century, of limiting the number of stars of the 1st magnitude
to 15 (Madler counts 18, and Rumker, after a careful exami-
nation of the southern heavens, above 20), is derived from

80 SPECIAL RESULTS IN THE UEA.KOLOGICAL

the classification of the Almagest at the close of the Table of
Stars in the 8th book. Ptolemy, with reference to unas-
sisted vision, called all stars " dark" which were fainter than
his 8th class, of which class singularly enough he gives
only 49, almost equally distributed in the two hemispheres.
Considering that the table includes about a fifth part of the
stars visible to the naked eye, it ought, according to Arge-
lander's investigations, to have given 640 stars of the 6th
magnitude. The nebulous stars (veQeXoethlQ) of Ptolemy,
and of the Catasterisms of the Pseudo-Erastosthenes, are
mostly small clusters of stars (151) which, in the purer air of
southern skies, appear as nebulae. I rest this conjecture
more particularly on the mention of a nebula in the right
hand of Perseus. Galileo, to whom, as well as to the Greek and
Arabian astronomers, the nebula in Andromeda, although
visible to the naked eye, was unknown, said, in the Nuncius
sidereus, that " stellse nebulosse" are no other than clusters
of stars, which as " areola? sparsim per sethera fulgent." (152)
The expression "order of magnitude" (T&V /ueyaXwv rafe),
although referring only to brilliancy, yet led, as early
as the 9th century, to hypotheses respecting the diameters of
stars of different degrees of brightness ; (153) as if the in-
tensity of the light did not depend on the distance, the
volume, the mass, and the peculiar nature or character of
the surface of the body, as more or less favourable to the
luminous process or production of light.

At the time of the Mogul Power in the 15th century,
when, under Ulugh Beig, the descendant of Timour,
astronomy flourished in the highest degree at Samarcand,
photometric determinations received such an impulse, that
each of the six classes or orders of magnitude of Hipparchus and

PORTION OF THE COSMOS. — PHOTOMETRY. 81

Ptolemy were divided into three subdivisions; distinguishing,
for example, small, middling, and large, of the second mag-
nitude ; reminding us of the attempts of Struve and
Argelander, in our own day, to introduce decimal grada-
tions^154) In the tables of Ulugh Beig, this photometric
advance, or more exact determination of different degrees of
light, is ascribed to Abdurrahman Sufi, who had published a
work specially " on the knowledge of the fixed," or fixed
stars, and who first noticed the existence of one of the ma-
gellanic clouds under the name of the " White Ox." Since
the introduction of telescopic vision, and its gradual improve-
ment, estimations of successive gradations of light have ex-
tended far beyond six classes or magnitudes. The desire of
comparing with the light of other stars the newly-appeared
stars in Cygnus and Ophiuchus, (the first of which continued
to shine for 21 years), at successive stages of their increasing
and decreasing light, gave a stimulus to photometric con-
siderations. The so-called " dark" stars of Ptolemy, or those
below the 6th magnitude, received numerical denominations
corresponding to the relative intensity of their light. " As-
tronomers," says Sir John Herschel, "who are accustomed
to the use of powerful space-penetrating telescopes, pursue the
descending gradations of light from the 8th down to the 16th
magnitude." (155) But with such faint degrees of light, the
denominations of the different classes of magnitude some-
times become very uncertain; and Struve occasionally
reckons as belonging to the 12th or 13th magnitude stars
which John Herschel calls of the 18th or even 20th.

This is not the place for examining in a critical manner
the very different methods which have been applied to
photometric determinations, during the last century and a half,

VOL. III. G

82 SPECIAL RESULTS IN THE URANOLOGICAL

from Auzout and Huygens to Bouguer and Lambert ; and
from William Herschel, Rumford, and Wollaston, to Stein-
heil and John Herschel. It is sufficient, according to the
object of this work, to notice them in a brief and general
manner. They include comparison with the shadows of
artificial lights differing in number and distance ; diaphragms ;
plane glasses of different thicknesses and colours ; artificial
stars formed by reflection on glass globes ; two 7 feet
telescopes so placed that the observer could pass from
one to the other in scarcely more than a second of time ;
reflecting instruments, in which two stars which were to be
compared could be seen at once, after the telescope had
been so arranged that the star which was seen direct had
given two images of equal intensity ;(156) apparatuses with
a mirror adapted to the objective, and with shades, the
degree of intensity being measurable on a ring ; tele-
scopes with divided object-glasses, each half of which
received the star's light through a prism; and astro-
meters, (157) in which the image of the Moon, or of Jupiter,
is reflected by a prism, and this image is concentrated by a
lens, at different distances, into a brighter or fainter star.
The distinguished astronomer, who in modern times has
most zealously pursued in both hemispheres the numerical
determination of the intensity of light in different stars,
Sir John Herschel, owns, notwithstanding what he has him-
self accomplished, that the practical application of exact
photometric methods must still be regarded as a " deside-
ratum in astronomy," and that " photometry or the measure-
ment of light is still in its infancy." The increasing inte-
rest taken in variable stars, and a new cosmical event in
the extraordinary augmentation of light in a star of the ship

PORTION OP THE COSMOS. — PHOTOMETRY. 83

Argo, in 1837, have made the want of better photometric
processes more than ever felt.

It is material to distinguish between the mere successive
arrangement of stars in the order of their brilliancy, but with-
out numerical estimations of the intensity of light, (the
Scientific Manual for Naval Officers, published by the British
Admiralty, contains such a list), and classifications with num-
bers appended expressing the intensity of light, either under
the form of so-called relations of magnitude, or by the more
hazardous assignment of the quantities of radiated light. (158)
The first numerical series, founded on estimations with the
naked eye, but progressively improved by a careful revision
of the materials, (159) probably deserves, in the present very
imperfect stateof photometric apparatus, the preference among
the different approximate methods ; although the exactness
of the estimations is no doubt impaired by differences in the
individual powers and habits of different observers, — the
clearness of the atmosphere, — the different altitudes of the
stars which are to be compared, and which can only be so
by means of many intermediate links, — and, above all, by
inequalities of colour. Yery bright stars of the 1st magni-
tude, Sirius and Canopus, a Centauri and Achernar, Deneb
and a Lyrse, though they have all white light, are much
more difficult to compare with each other by estimation with
the naked eye, than are stars of fainter light, — as, for ex-
ample, those below the 6th and 7th magnitudes. But the
difficulty is still greater with stars of very intense light,
when yellow stars like Procyon, Capella, or Atair, are to
be compared with red ones like Aldebaran, Arcturus, and
Betelgeuze.(160)

Sir John Herschel, by means of a photometric comparison

84 SPECIAL RESULTS IN THE URANOLOGICAL

of the Moon with the double star a Oentauri in the southern
heavens, the third in brightness of all the fixed stars, has
attempted to determine the ratio between the intensity of the
solar light, and the light of a star of the 1st magnitude ; ful-
filling thereby (as had been earlier done by Wollaston) a
wish expressed by John Michell (161) in 1767. From the
mean of 11 measurements made with a prismatic apparatus,
Sir John Herschel found the full moon 27408 times brighter
than a Centauri. Now the light of the Sun is, according
to Wollaston, (l62) 801072 times greater than that of the
full moon ; whence it follows that the light which the Sun
sends to us is to that, which we receive from a Centauri
about as 22000 millions to 1. Hence it would follow with
great probability that, if we take into account the distance
of a Centauri according to its parallax, its inherent (absolute)
|ight would be 2' 3 times as great as that of our Sun.
"Wollaston found the brightness of Sirius 20000 million
times less than that of the Sun; and according to what
is now supposed to be known in respect to the parallax
of Sirius, (0"'230), its actual (absolute) .light would be
63 times greater than that of the Sun. (163) Our Sun
would thus be, in regard to the intensity of its light,
one of the fainter of the fixed stars. Sir John Herschel
estimates the light of Sirius as equal to that of nearly two
hundred stars of the 6th magnitude. As from analogy with
what we already know it is very probable that all cosmical
bodies change their place in space, as well as the strength
of their light, — though it may be only in very long and un-
measured periods of time, — and remembering the dependence
of all .organic life on temperature and the strength of the
Sun's light, the improvement of photometry appears deserving

PORTION OF THE COSMOS. PHOTOMETRY. 85

of being regarded as a great and serious object of scientific
investigation. This improvement can alone render it possi-
ble to leave to future generations numerical determinations
respecting the light of the heavenly bodies. Many geolo-
gical phsenomena which connect themselves with the thermic
state of our atmosphere, and relate to the former distribution
of plants and animals on the surface of our globe, may be
elucidated thereby. More than half a century ago such
considerations had not escaped the great investigator William
Herschel, who before the close connection between electricity
and magnetism had been discovered, compared the ever
luminous cloud-envelopes of the solar orb, to the Polar Light
of the terrestrial globe. (l64)

Arago recognised in the complementary condition of co-
loured rings seen by transmission and reflection, the most pro-
mising means of a direct measure of the intensity of light. I
give in a note(165) in my friend's own words a statement of
his photometric method, to which he has also added the
optical principle on which his cyanometer rests.

The so-called relative magnitudes of the fixed stars now
given in our Catalogues and Star Maps are partly belonging
to the same epoch, and partly include alterations of light
belonging to different epochs. We cannot, however, as was
long assumed, take as a safe criterion of such changes, the
succession of the letters of the alphabet appended to the
stars in the Uranometria Bayeri, which has been in such
extensive use since the beginning of the 17th century.
Argelander has shewn that we cannot infer relative bright-
ness from alphabetical order, and that Bayer allowed himself
to be guided in the choice of letters by the shape and
direction of the constellations. (166)

86 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

III.

NUMBER, DISTRIBUTION, AND COLOUR OF THE FIXED STARS

CLUSTERS OF STARS. MILKY WAY, IN WHICH A FEW

NEBULA ARE INTERSPERSED.

I HAVE already alluded, in the first section of this frag-
mentary Astrognosy, to a consideration which was first pro-
posed by Olbers. (167) If the whole vault of heaven were
covered with a countless succession of starry strata one
behind another, forming an unbroken starry canopy, then, sup-
posing also their light to be unenfeebled in traversing space,
no single constellation could be recognised amidst the uni-
versal brightness. The Moon would be seen as a dark disk,
and the Sun would be known only by his spots. I have been
forcibly reminded of a state of the heavens which, totally op-
posite in its cause, would be equally disadvantageous to human
knowledge, by what takes place during a portion of the year
on thePeruvian plain between the shores of the Pacific and the
chain of the Andes. A thick mist covers the sky for several
months during the season called " el tiempo de la garua."
No planet, not one even of the brightest stars of the Southern
Hemisphere, neither Canopus, nor the Southern Cross, nor
the two bright stars of the Centaur, are visible. Often one
can hardly conjecture the place of the Moon. If, occasion-

OF THE COSMOS. NUMBER OP THE FIXED STAHS. 87

ally during the day-time it is possible to distinguish the
outline of the Sun's disk, it appears rayless ; shorn of its
beams, as if viewed through a coloured glass ; usually of a
yellowish red or orange colour ; now and then white, or most
rarely bluish green. Navigators, driven by the cold oceanic
current flowing from south to north, and unable to obtain
observations for latitude, sail past the harbour which they
desire to enter. It is only, as I have shown elsewhere,
by the use of the dipping needle (168) that, thanks to the
direction of the magnetic lines in that part of the globe,
they may be enabled to avoid error.

Bouguer and his coadjutor, Don Jorge Juan, complained
long before me of the " uuastronomical sky of Peru." A
grave consideration is suggested by the character of this atmo-
spheric stratum, which is so unfavourable to the transmission
of light, and so unfitted for electric discharges, that thunder
and lightning are unknown there, and which veils the
plains in constant mist, while above, the Cordilleras raise
aloft, free and unclouded, their elevated plains and snowy
summits. According to the conjectures which modern
geology leads us to form respecting the ancient history
of our atmosphere, its primitive state, in respect to com-
position and density, must have been but little favour-
able to the passage of light. If, then, we think of the many
processes which may have been in operation in the early
state of the crust of the globe, in the separation of solid, liquid,
and gaseous substances, we are impressed with a view of how
possible it must have been, that we should have been subjected
to conditions and circumstances very different from those
which we actually enjoy. We might have been sur-
rounded by an untransparent atmosphere, which, while but

88 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

little unfavourable to the growth of several kinds of vegeta-
tion, would have veiled from us the whole starry firmament.
Man's investigating spirit would then have been deprived of
all knowledge of the structure of the Universe. Creation
would have appeared to us limited either solely to our own
Globe, or comprising, at the utmost, the Sun and Moon be-
sides. Universal space would have seemed to us to be occu-
pied only by a triple star, consisting of Sun, Earth, and Moon.
Deprived of a great, and, indeed, of the most sublime part
of his ideas of the Cosmos, Man would have been without
the inducements, which have unceasingly stimulated him
during thousands of years to the solution of difficult and im-
portant problems, and have exercised so beneficial an influence
on the most brilliant advances in the higher departments of
mathematics. Before proceeding to the enumeration of
that which we have already attained, it may be permitted
to us thus briefly to glance at a danger from which we
have been preserved, and which might have opposed impass-
able physical barriers to the full intellectual development of
our race.

In the consideration of the number of heavenly bodies
which fill space, three questions are to be distinguished : —
How many fixed stars are seen with the naked eye ? how
many of these have been progressively catalogued, together
with the determination of their places (in latitude and longi-
tude, or in declination and right ascension) ? and what is
the number of stars, from the 1st to the 9th and 10th
magnitudes, ,which have been seen through telescopes in all
parts of the heavens ? These three questions admit of being
answered, approximately at least, according to the materials
already supplied by observation. Of a different class are

OF THE COSMOS.— NUMBER OF THE FIXED STARS. 89

the conjectures which, founded on the "star-gaugings" of
particular parts of the Milky Way, touch the theoretical
solution of the question — How many stars would be distin-
guished over the whole heavens by Herschers 20 -foot
telescope, comprehending all those stars whose light is be-
lieved(169) to have required 2000 years to reach the Earth?
The numerical data which I here publish on this subject
are chiefly taken from the final results obtained by my highly
esteemed friend Argelander, Director of the Astronomical
Observatory at Bonn. The author of the " Beview of the
Northern Heavens" has carefully examined for me afresh,
at my request, the data supplied by Star-catalogues up to
the present time. In the lowest class of stars visible to the
naked eye some uncertainty is occasioned by the difference
of estimation caused by organic differences in individual ob-
servers, stars between the 6th and 7th magnitudes being found
among those of the 6th magnitude. By a variety of com-
binations we obtain, as a mean number, from 5000 to 5800
as the number of stars visible to the unassisted eye, through-
out the entire heavens. The distribution of the fixed stars
in descending magnitudes down to the 9th, is given by
Argelander(170) approximately as follows : —

1st magnitude. 2nd magnitude. 3rd magnitude. 4th magnitude. 5th magnitude.

20 65 190 425 1100

6th magnitude. 7th magnitude. 8th magnitude. 9th magnitude.

3200 13000 40000 142000

The number of stars which can be clearly distinguished by
the naked eye (4022 above the horizon of Berlin, 4638
above that of Alexandria), appears at first sight astonishingly

90 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

small. (171) If we take the mean semi-diameter of the
moon at 15' 3 3 ".5., 195291 surfaces of the full moon
would cover the whole heavens. Assuming an equable dis-
tribution, and taking the entire number of stars of all classes
from the 1st to the 9th in round numbers at 200000,, we
should have about one such star for every full-moon surface.
This result explains to us why in any given latitude stars
visible to the naked eye are not oftener occulted by the
moon. If the calculation of occultations was extended to
stars of the 9th magnitude, there would be, according to
Galle, on the average an occultation every 44J minutes ;
as in this time the moon passes over a fresh piece of the
heavens equal to its own area. Pliny (who was certainly ac-
quainted with Hipparchus' s list of stars, and who calls it a
bold undertaking in Hipparchus to seek to " bequeath to
posterity the starry heavens as an inheritance") reckoned in
the fine sky of Italy 1600 stars, (172) having descended in
this estimation to stars of the 5th magnitude ; half a cen-
tury later, Ptolemy recorded only 1025 stars, down to the
6th magnitude.

Since the fixed stars ceased to be distinguished merely in
respect to the constellations to which they belonged, but have
been tabulated according to their relations to the great circles
of the Equator or the Ecliptic, and therefore according to
determinations of their places, the number as well as the
exactness of such entries have constantly increased with the
progress of science and the increased perfection of instruments.
No catalogue has come down to us from Timocharis and
Aristyllus (283 B. c.) ; but even though their observations,
as Hipparchus says in his fragments " upon the length of
the year/' quoted in the 7th book of the Almagest (cap. 3,

OP THE COSMOS. NUMBER OF THE FIXED STARS. 91

p. 15, Halma), were very incomplete (iraw 6Xoo-x£f>£c), yet
there can be no doubt that they both determined the decli-
nation of many stars, and that these determinations preceded
by almost a century and a half Hipparchus' s Table of Fixed
Stars. It is known (although we have only Pliny's statement
of the fact) that Hipparchus was stimulated by the appear-
ance of a new star to pass the heavens in review and to
determine the places of the stars. This statement has, how-
ever, more than once been regarded as merely the echo of a
tale invented after the period to which it relates; (173) and
it is certainly remarkable that Ptolemy does not allude to it
in the slightest degree. It is, however, incontestably true
that it was the sudden appearance of a bright star in Cassio-
peia (November, 1572) that occasioned Tycho Brahe to under-
take his great star-catalogue. According to an ingenious con-
jecture of Sir John Herschel,(174) a star which appeared in
the constellation of Scorpio in the month of July, 134
years before our Era (according to the Chinese annals under
the reign of Wou-ti, of the Han Dynasty), may very well be
the same which Pliny mentions. Its appearance falls six
years before the epoch at which (according to Ideler's re-
searches) Hipparchus prepared his catalogue. Edouard
Biot, of whom science has been too early deprived, dis-
covered the notice of this cosmical event in the celebrated
collection of Ma-tuan-lin, which contains all the appearances
of comets and unusual stars between the years 613 B.C.,
and A.D. 1222.

The tripartite didactic poem of Aratus, (175) to which we
owe the only writing of Hipparchus which has come down
to us, belongs to about the period of Eratosthenes, Timo-
charis, and Aristyllus. The astronomical (not meteorological)

92 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

part of the poem is founded on the description of the heavens
given by Eudoxus of Cnidos. The star- table of Hipparclms
has unhappily not been preserved to us : according to
Ideler(176) it probably formed the principal part of the
treatise, cited by Suidas, on the arrangement of the heaven
of the fixed stars and the other heavenly bodies, and con-
tained 1080 positions for the year 128 before our Era. In
Hipparchus's Commentary, all the positions, determined
probably by equatorial armillae rather than by the astrolabe,
are referred to the equator by right ascension and declina-
tion ; in the star-table of Ptolemy, which is supposed to be
altogether imitated from Hipparchus, and which, including
five so-called nebulse, contains 1025 stars, they are referred
to the Ecliptic (177) by assigned longitudes and latitudes.
If we compare the number of fixed stars in the Almagest,
(ed. Halma, T. ii. p. 83),

1st mag. 2nd mag1. 3rd mag. 4th mag. 5th mag. 6th mag.

15 45 208 474 217 49

with the numbers of Argelander in a previous page, we see
(with a neglect of stars of the 5th and 6th magnitudes which
was to be expected,) a remarkable fulness in the 3rd and
4th magnitudes. The indeterminateness of estimations of
the degree of light in ancient and modern times does, indeed,
throw great uncertainty on every direct comparison.

If the catalogue of the fixed stars, which bears the name
of Ptolemy, only comprises a fourth part of the stars visible
to the naked eye at Rhodes and Alexandria, — and if, from
the erroneous reduction for precession, it gives positions as
if they had been determined in the year 63 of our Era, — we
have in the next sixteen centuries only three original, and

OP THE COSMOS. NUMBER OF THE FIXED STARS. 93

for their epoch complete, star-catalogues : that of Ulugh
Beig (1437), of Tycho Brahe (1600), and of Hevelius
(1660). In the short intervals of repose which inter-
vened between the devastations of war and wild intestine
revolutions, practical astronomy flourished among the
Arabians, Persians, and Moguls, from the middle of the
9th to that of the ] 5th centuries, — from Al-Mamun, son
of the great Harun Al-Raschid, to the Timuride, Mohammed
Teraghi Ulugh Beig, son of the Shah Eokh, — in a degree
never before witnessed. The astronomical tables of Ebn-
Junis (1007), called the Hakemite Tables in honour of the
Patimite Caliph Aziz Ben-Hakem Biamrilla, testify, — as do
also the Ilkhanic Tables O?8) of Nassir-Eddin Tusi, the
builder of the great observatory of Meragha, not far from
Tauris (1259), — to the more advanced knowledge of the
planetary movements, the improvement of measuring instru-
ments, and the multiplication of methods differing from
those of Ptolemy, and superior to them in exactness. In
addition to Clepsydras, Pendulum oscillations (179) now
began to be used as a measure of time.

The Arabians have the great merit of having shewn how
by the intercomparison of observations and tables the latter
might be greatly improved. The star-catalogue of Ulugh
Beig (originally written in Persian), with the exception of
a part of the southern stars of Ptolemy not visible (18°) in
the latitude of 39° 52' (?), was prepared in the Gymnasium at
Samarcand from original observations. It contained at first
only 1019 positions of stars, which are reduced to the year
1437. A later commentary furnishes 300 additional stars
observed by Abu-Bekri Altizini in 1533. Thus we
come, through Arabians, Persians, and Moguls, down to

94 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

the great epoch of Copernicus,, and almost to that of Tycho
Brahe.

Since the beginning of the 16th century the extension of
navigation in tropical seas and high southern latitudes
has operated powerfully in enlarging the knowledge of
the firmament, though it has done so in a less degree than
has the employment of telescopes, began a century later.
By both, new regions of space before unknown have been
opened to our view. I have noticed in a previous volume
(181) what was related of the magnificence of the Southern
Hemisphere, first by Amerigo Yespucci, and next by
Magellan and by Elcano's companion Pigafetta, and how
the black patches (Coal sacks) were described by Yicente
Yanez, and the Magellauic Clouds by Anghiera and Andrea
Corsali. Here, also, contemplative astronomy preceded
measuring astronomy. The riches of the firmament near
the South Pole, — a region which is really, as is now well
known, comparatively poor in stars, — were described with
such exaggeration, that Cardauus Polyhistor said that Yes-
pucci saw there 10000 stars with his unassisted eyes. (182)
The first persons who seriously began the task of observing
the stars of the Southern Hemisphere were Eriedrich Hout-
mann and Petrus Theodori of Ernden (who, according to
Olbers, was the same person as Dircksz Keyser) . They mea-
sured distances of stars at Java and Sumatra, and the most
southern stars were now entered in the celestial maps of
Bartsch, Hondius, and Bayer, as well as, by the diligent care
of Kepler, in the Eudolphine star-catalogue of Tycho Brahe.

Scarcely half a century after Magellan's circumnavigation
of the globe, Tycho Brahe began his admirable examination
of the position of the fixed stars, — a work surpassing in

Or THE COSMOS. — NUMBEK OF THE FIXED STARS. 95

exactness anything which, practical astronomy had yet fur-
nished, even the careful observations of -the fixed stars by
the Landgrave Wilhelm IV. at Cassel. Tycho Brahe's
Catalogue, revised by Kepler, contains, however, only 1000
stars, of which -^ih a^ the utmost are of the 6th magni-'
tude. This catalogue, and the less used one of Hevelius,
having 1564 determinations of places of stars for the
year 1660, are the last which (owing in the latter case to
the obstinate aversion o^ the Dantzig astronomer to the
application of telescopes to measuring instruments) were
drawn up from observations made with the unassisted eye.

The combination of the telescope with measuring in-
struments made it at length possible to determine the places
of stars below the 6th magnitude, and especially^ between the
7th and 12th magnitudes. Astronomers now first began to
approach the time when they might be said to take possession
of the world of fixed stars. But the enumeration of the
feebler telescopic stars, and the determination of their places,
have not only, by extending the horizon of the field of ob-
servation, given us to know more of the contents of the re-
moter regions of space, — but they have also, which is yet more
important, exercised indirectly a material influence on our
knowledge of the structure of the Universe and of its form,
on the discovery of new planets, and on the more rapid de-
termination of their paths. WhenWilliain Herschel conceived
the happy thought of, as it were, casting the sounding lead
into the depths of space, and in his star gaugings (183)
counting the stars which passed through the field of his
great telescope at different distances from the Milky Way, —
the law of the increasing quantity of stars in approaching
the Milky Way was discovered, and brought with it the idea

yo SPECIAL RESULTS IN THE TJRANOLOGICAL PORTION

of the existence of great concentric rings filled with millions
of stars, forming the Galaxy. The knowledge of the num-
ber and relative position of the fainter stars, as has been
shown by Galleys prompt and happy discovery of Neptune,
and by that of several of the smaller planets, facilitates
the discovery of planetary bodies which change their place,
moving amidst fixed points. Another circumstance shows,
in a still clearer light, the importance of very complete star-
catalogues. When once a new pk.net has been discovered
in the celestial vault, the difficult calculation of its path is
aided by its rediscovery in a catalogue of older date. The
fact of a star having been formerly registered, and being
now missing in the position assigned to it, has thus often
effected more, than, from the slowness of the planet's motion,
could be gained by the most carefully-repeated measure-
ment during several successive years. Thus for Uranus,
the star "No. 964 in the Catalogue of Tobias Mayer,
and for Neptune, the star 26266 in the Catalogue of
Lalande, (184) have been of great importance. "We now
know that Uranus was observed 21 times before it was
known to be a planet : once by Tobias Mayer, 7 times by
Elamsteed, once by Bradley, and 12 times by Le Monnier.
We may say, that the increasing hope of future discoveries of
planetary bodies rests partly on the excellence of our present
telescopes (Hebe, when discovered in July 1847, was equal
to a star of between the 8th and 9th magnitudes, but in May
1849 was only of the llth magnitude), and partly, and
perhaps still more, on the completeness of our catalogues
and the care of our observers.

Subsequent to the epoch when Morin and Gascoigne com-
bined telescopes with measuring instruments, the first star-

OF THE COSMOS. NUMBER OF THE FIXED STARS. 97

catalogue which was published was that of Halley's
southern stars. It was the fruit of a short visit to Saint
Helena in 1677 and 1678, but it contained no determina-
tion of any star below the 6th magnitude. (185) It is true
that Flamsteed had previously undertaken his great Star
Atlas, but the work of that celebrated man was not published
until 1712. It was followed by the observations of Bradley
(1750 to 1762), which led to the discovery of aberration and
nutation, and received a further lustre from our Bessel, in his
Fundamenta Astronomise (1818) ; (186) and by the star
catalogues of Lacaille, Tobias Mayer, Cagnoli, Piazzi, Zach,
Pond, Taylor, Groombridge, Argelander, Airy, Brisbane, and
Eiiniker.

We cite here only works which embrace large masses, (187)
and present to us an important part of the contents of
space in stars between the 7th and 10th magnitudes. The
catalogue which is known under the name of Jerome de
Lalande, but which is founded on observations made by his
nephew, Le Francois de Lalande, and Burckhardt, between
1789 and 1800, has lately, though for the first time, received a
great acknowledgment. In the state to which it has been
brought by the careful reduction, editorship, and publication,
for which astronomy is indebted to Francis Baily and the
British Association for the Advancement of Science, it
contains 47390 stars, many of which are of the 9th, and
several rather below the 9th magnitude.* Harding, the dis-

[* The star-catalogues of Lalande and Lacaille, the first containing upwards
of 47000 stars (as stated in the text), and the second above 10000 stars,
were reduced, catalogued, and prepared for publication at the cost of the
British Association for the Advancement of Science, the first under the
superintendence of Mr. Francis Baily, and the second under that of Professor

98 SPECIAL RESULTS IN THE URANOLO3ICAL PORTION

coverer of Juno, has entered above 50000 stars in 27 sheets.
Bessel's great work of the observations of Zones of the
Heavens, comprising 75000 observations, and which extended,
in the years 1825— 1833, from —15° to + 45° of declination,
has been continued by Argelander of Bonn, from 1841
to 1844, with a care deserving of the highest praise, and has
been carried by him to + 80° of declination. Prom Bessel's
Zones, between — 15° and +15° of declination, Weisse of
Cracow, at the request of the Academy of St. Petersburg,
has reduced 31895 stars (of which 19738 are of the 9th
magnitude) to the year 1825. (188) Argelander' s "Review
of the Northern Heavens from + 45° to +80° of declina-
tion," contains 22000 well-determined places of stars.

I think that I cannot refer to the great work of the star
maps of the Berlin Academy more worthily than by intro-
ducing, in Encke's own words, an extract on the subject
of this undertaking from his comprehensive discourse in
memory of Bessel. " With the completion of catalogues
is connected the hope that, by continued careful comparison
of the stars marked as fixed points with the aspect of the
heavens at the time of observation, we shall be enabled to

Henderson. But the expense of printing these two catalogues was defrayed
by Her Majesty's Government, in consequence of a representation of their
importance to the purposes of practical Astronomy made by the British
Association to the late Sir Robert Peel.

The catalogues of Lelande and Lacaille are distinct from the " British
Association Catalogue," not noticed in this part of the text of Cosmos,
but frequently referred to in the course of the volume. The " British
Association Catalogue" was also prepared under the superintendence of
Mr. Francis Baily, but in its case the cost of printing, as well as that of
preparing for publication, was defrayed by the contributions of the members
of the British Association. — ED.]

OF THE COSMOS. NUMBER OF THE FIXED STARS. 99

note all heavenly bodies which change their place, but whose
movements, from the faintness of their light, it would be
scarcely possible to perceive directly by the eye ; and in
this manner we may anticipate the discovery of all that
still remains unknown to us in our solar system. As
Harding' s excellent Atlas offers a complete picture of the
heavens, so far as Lalaude's Histoire Celeste, on which
it is founded, is capable of affording such a picture, so
Bessel, in 1824, after finishing the first section of his Zones,
formed the plan of founding thereupon a still more detailed
representation of the sidereal heavens, which should have for
its object, not merely the reproduction of observation, but
the systematic attainment of a degree of completeness which
should permit every new phenomenon to be immediately
recognised. The star maps of the Berlin Academy of
Sciences, sketched upon Bessel's plan, although they have
not yet completed the first proposed cycle, have already
attained their object in the discovery of new planets in the
most brilliant manner, as up to the present time (1850)
they have been the principal, though not the exclusive,
means of the discovery of seven new planets. (189) Of the
24 sheets which are to represent the heavens within
15 degrees on either side of the Equator, our Academy has
now published 16. They contain, as nearly as possible, all
stars clown to the 9th, and partially down to the 10th
magnitudes."

I may here introduce a notice of the approximate estima-
tions which have been hazarded respecting the number of
stars in all parts of the heavens which may be visible to
human eyes, aided by our present powerful space-penetrating
telescopes. For Herschel's 20-feet reflector, which was

100 SPECIAL RESULTS IN THE URANOLOG1CAL PORTION

used in the celebrated star-gaugings or sweeps, with a
magnifying power of 1 80, Struve takes for the zones within
30° on either side of the Equator, 5800000 stars; and, for the
whole heavens, 20374000 stars. With a still more powerful
instrument, the 40-feet reflector, Sir William Herschel sup-
posed that 18 millions of stars would be visible in the Milky
Way alone. (™°)

Having considered the number of fixed stars, whether
telescopic or visible to the naked eye, which have been
entered in catalogues, together with the determination
of their places, we now turn to their distribution and grouping
on the celestial vault. We have seen that, from their small
and exceedingly slow (apparent and real) change of place,
due partly to precession and the unequal influence of the
progressive movement of our solar system, and partly to their
own proper motion, they may be regarded in the light of
fixed marks in space, enabling the attentive observer to
recognise all bodies moving amongst them, either at a morfc
rapid rate or in a different direction, as planets and tele-
scopic comets. In gazing on the vault of heaven, our first
and leading interest is attracted by the bodies which by
their multitude and mass fill space, — it is the fixed stars
which claim and receive the homage of our admiration :
but the orbits of the moving planetary bodies speak more to
the investigating reason, to which they present complicated
problems, whose study promotes and accelerates intellectual
development in the domain of astronomy.

From the multitude of stars, large and small, which
appear intermingled, as it were by accident, on the celestial
vault, the rudest tribes of men (as several now carefully-

OF THE COSMOS. — GROUPING OF THE FIXED STARS. 101

examined languages of what are called savage nations testify)
single out particular, and almost everywhere the same, groups,
in which bright stars attract the eye, either by their proxi-
mity to each other, by peculiarities in their arrangement and
relative position, or by a certain degree of isolation. Such
groups awaken obscurely the idea of a relation of parts to
each other; and, each being regarded as a whole, receive par-
ticular names, differing in different tribes, and most often
taken from organic beings with which imagination peoples
the silent regions of space. Thus there were early distin-
guished the Pleiades (called by some the brood of chickens),
the seven star's of the Great Bear or Wain (the lesser Bear
or Wain was remarked later, and only on account of the re-
petition of the form), Orion's Belt (Jacob's Staff), Cassiopeia/,
the constellations of the Swan, the Scorpion, the Southern
Cross (on account of the striking change of direction before
and after culmination), the Southern Crown, the Eeet of the
Centaur (as it were the Twins of the Southern Hemi-
sphere), &c.

Where steppes, grassy prairies, or sandy deserts, present a
wide horizon, the rising and setting of the constellations,
varying with the seasons of the year, and associated thereby
with the requirements of pastoral and agricultural life, become
• the subject of diligent attention, and are also gradually
connected with symbolical combinations of ideas. Contem-
plative, not measuring, astronomy then begins to be more
developed. Besides the diurnal movement common to all
heavenly bodies from morning to evening, it is soon per-
ceived that the sun has a movement of its own, much slower,
and in the opposite direction. The stars which, when night
comes on, are seen high in the evening sky, sink daily more

1 02 SPECIAL RESULTS IN THE TJRANOLOGICAL PORTION

and more towards the setting sun, until at last they are losf; in
his beams, and disappear in the twilight ; on the other hand,
the stars which shone in the morning sky before sunrise
recede more and more from the Sun. In the constantly
changing spectacle of the starry heavens, fresh and fresh
constellations show themselves. With some degree of
attention it is easily recognised that they were the same
which had before become invisible in the West ; and that,
in the course of about half a year, those stars, which before
were seen near the Sun, are now opposite to it, setting when
it rises, and rising when it sets. From Hesiod to Eudoxus,
and from Eudoxus to Aratus and Hipparchus, the literature
of the Greeks is full of allusions to the disappearance of
stars in the Sun's rays (their heliacal setting), and their
becoming visible in the morning twilight (their heliacal
rising). The accurate observation of these phenomena
presented the first elements of chronology — elements which
were simply expressed in numbers; while at the same time,
mythology, varying in its imaginations with the gay or
gloomy dispositions of the national mind, exercised without
restraint its capricious sway in the fictions connected with
the bright bodies of space.

The primitive Greek sphere (I here follow again, as in the
history of the Physical Contemplation of the Universe, (191) •
the researches of my too early departed friend, the illus-
trious Letronne) became gradually filled with constellations,
without their having been in the commencement referred in
any way to the Ecliptic. Thus Homer and Hesiod dis-
tinguish different groups of stars, as well as single stars, by
particular names : Homer notices the She Bear (" else called
the Wain of Heaven, and which alone never descends to

OF THE COSMOS. GROUPING OF THE FIXED STA11S. 103

bathe in the ocean"), Bootes, and the Dog of Orion ; and
Hesiod names Sirius and Arcturus ; both speak of the Plei-
ades, the Hyades, and Orion. (192). If Homer twice says that
the Bear alone never plunges into the ocean, this merely
implies that in his time the constellations of the Dragon,
Cepheus, and the Little Bear, which also never set, had not
yet been placed in the Greek Celestial Sphere. It by no
means implies that the existence of the stars forming these
three catasterisins was not known, but only that they had
not yet been arranged in figures. A long and often mis-
understood passage of Strabo (lib. i. p. 3, Casaub.) on Homer
(II. xviii. 485 — 489) proves rather than anything else that
which is here important — viz., the gradual acceptance of
figures or constellations in the Grecian Sphere. "It is
unjustly," says Strabo, " that Homer is accused of ignorance,
as if he knew only of one Bear instead of two. Perhaps the
second was not yet constellated, and that it was only after
the Phoenicians had marked out this constellation, and used
it in navigation, that it came to the Greeks." All the
scholiasts on Homer, Hygin, and Diogenes Laertius, ascribe
the introduction to Thales. The Pseudo-Eratosthenes calls
the Little Bear QOIVIKTI (as it were the Phoenician Lode-
star). One hundred years later (01. 71), Cleostratus of
Tenedos enriched the Sphere with Sagittarius, TO^OT^C, and
the Earn, jcpioc.

It is to this epoch, that of the tyranny of the Pisistratides,
that we are to ascribe, according to Letronne, the introduc-
tion of the Zodiac in the ancient Greek Sphere. Eudemus
of Rhodes, one of the most distinguished disciples of AnV-
totle, author of a "History of Astronomy," ascribes the
introduction of the Zodiacal Zone (*/ rov

1 04 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

also faifiioQ KVK\OQ) to (Enopides of Chios, a cotemporary of
Anaxagoras. (193) The idea of referring the planets and
fixed stars to the Sun's path, and the division of the Ecliptic
into twelve equal parts (Dodecatoraeria), are ancient Chal-
dean, and it is highly probable that they reached the Greeks
from Chaldea itself, and not from the Yalley of the Nile,
and, at earliest, at the beginning of the 5th or in the 6th
century before our Era. (194) The Greeks only selected from
the constellations already marked in their primitive Sphere
those which were nearest to the Ecliptic, and which could
be employed as Signs of the Zodiac. If anything more than
the idea and the number of divisions of a zodiac, — if the
zodiac itself, with its signs, — had been borrowed by the Greeks
from another nation, 11 signs would not have been thought
sufficient originally ; nor would the Scorpion have been
applied to two divisions ; nor would zodiacal figures have
been formed, — some of which, as Taurus, Leo, Pisces, and
"Virgo, cover, with their outlines, 35° to 48°; while others, as
Cancer, Aries, and Capricornus, occupy only 19° to 23°, —
which deviate inconveniently to the North and South of the
Ecliptic, — which sometimes are widely separated, and some-
times, like Taurus and Aries, Aquarius and Capricornus,
are closely crowded and almost overlap. All these circum-
stances prove that earlier-formed catasterisms were made
into zodiacal signs.

According to Letronne's conjecture, the sign Libra was
introduced in the time of Hipparchus, — perhaps by himself.
Eudoxus, Archimedes, Autolycus, and even Hipparchus,
in the few remains of theirs which we possess (with the
exception of one passage, probably falsified by a copyist), (195)
never mention it. We first find a notice of the new sign

OF THE COSMOS. — GROUPING OF THE FIXED STARS. 105

in Geminus and Yarro, hardly half a century before our
Era ; and as the Romans soon after this date, from Augustus
to Antoninus, became vehemently attached to astrology,
those constellations " which lay along the Sun's celestial
path" grew into a heightened fanciful importance. To the
first half of this period of the Roman Empire belong the
Egyptian zodiacal figures of Dendera, Esne, the Propylon of
Panopolis, and some mnmmy cases, — as was asserted by
Yisconti and Testa at a time when all the materials for the
decision of the question had not yet been collected, and
when wild hypotheses prevailed respecting the signification
of those symbolical zodiacal signs, and their dependence on
the precession of the equinoxes. Prom Adolph Holtzmann's
acute researches, the high antiquity which, from passages in
Menu's Institutes, Yalmiki's Ramayana, and Amarasinha's
Dictionary, August Wilhelm von Schlegel had attributed to
zodiacs found in India, has become very doubtful. (196)

The artificial grouping of stars in constellations which,
in the course of centuries, has taken place in so accidental
a manner, — the often inconvenient magnitude and uncertain
outlines of these figures, — the confused nomenclature of
separate stars in the constellations, with the exhaustion of
several alphabets, as in the Ship Argo, — the incongruous
mixture of mythical personages with the plain prose of
physical instruments, chemical furnaces, and pendulum
clocks, in the southern hemisphere, — have several times led
to proposals for a new division of the celestial sphere, which
should be entirely without imaginary figures. Por the
southern hemisphere, where only Scorpio, Sagittarius, Cen-
taurus, Argo, and Eridanus, have ancient poetic possession,
the enterprise would seem less hazardous. (1.97)

106 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

The heaven of the fixed stars (or bis inerrans of Apuleius),
and the improper expression "fixed stars" (astra fixa of
Manilius), remind us, as I have already remarked in the
Introduction to the portion of this volume which treats of
Astrognosy, (198) of the combination and even confusion
which has taken place between the two ideas of " being set
or fastened in the sky," and of " absolute immobility or
fixity." When Aristotle terms the non-wandering orbs
(aTrXarrj &<rrpa) fastened (frfoftpfrfe), and when Ptolemy calls
them attached (wpo**<B^Nfdri*)r, these expressions have a
direct reference to Anaximenes' supposition of a crystal
sphere. The apparent motion of all the fixed stars from
East to West, while their distances from each other remained
the same, had given rise to this hypothesis. "The fixed
stars (air\avri aorpa) belong to the upper or more remote
region, in which they are fastened as if nailed to the crystal
heaven; the planets (aorpa TrXaj/wjueva or TrXav^ra), which
have an opposite motion, belong to the lower or nearer
region." (199) If, in Manilius, as early as the times of the
first Csesars, " stella fixa" is used instead of " infixa" or
" affixa," we may still assume that the school of Home kept
only at first to the original meaning of being fastened; but
that, as the word *' fixus" also included the signification of
" immobility," and might even be taken as synonymous with
"immotus" and " immobilis," it might easily happen that
popular opinion, or rather the usage of language, should
gradually connect with " stella fixa" the idea of immobility,
without remembering the sphere in which the stars had been
supposed to be fastened : and thus Seneca might term the
world of fixed stars "fixum et immobilem populum."

If, following Stoba3us and the collector of the " Views of

OF THE COSMOS.— GROUPING OF THE FIXED STARS. 107

Philosophers," we carry back the expression of " crystal
heaven" to the early time of Anaximenes, we find, however,
the idea which forms the groundwork of such an appellation
first developed with precision by Empedocles. He regards
the heaven of the fixed stars as a solid mass, formed from
the aether which has been solidified into a crystalline substance
by heat. (20°) The Moon is regarded by him as a body which
has been molten as by the action of fire, and subsequently
consolidated like hail. The original idea of transparent
solidified substances would not, according to the physics of
the Ancients, (201) and their ideas of the solidification of
fluids, have led directly to cold and ice ; but the affinity of
Kpv<TTa\\oQ with Kpvog and Kpvaraiv^, as well as comparison
with the most transparent of all bodies, gave occasion to the
more definite statements, that the vault of heaven consisted
of ice or of glass. Thus we find in Lactantius " coelum
aerem glaciatum esse," and " vitreum cesium." Empedocles
was certainly not thinking of Phoenician glass, but of air
which, by the action of the fiery aether, had been run together
into a transparent solid body. In the comparison with ice
(KpvaraXXoQ), the prevailing idea was that of transparency :
the origin of ice by the action of cold was not regarded,
all that was directly considered being the case of a fluid
which had become solid and was transparent. If the poets
used the word crystal, in prose (as is testified by the
passage of Achilles Tatius, the commentator of Aratus, cited
in Note 200,) the expression employed is only crystalline, or
similar to crystal (irpvorraAXoet&ye). So also TTUJOQ (from
irhyvvoSai, to solidify) signifies a piece of ice, in which the
solidification is the only thing considered.

Through the Fathers of the Church, who, in allusions

108 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

to the subject, assume from seven to ten glass heaveis suc-
cessively placed over each other like the coats of an onion, this
view of the crystal vault passed to the Middle Ages : it has
even been preserved to recent times in some of the convents
of the south of Europe, where, to my astonishment, a vene-
rable dignitary of the Church, in reference to the fall of
aerolites at Aigle which excited so much attention, expressed
the opinion that what we called meteoric stones, and which
were covered with a vitrified crust, were not parts of the
fallen stone itself, but pieces of the crystal heaven which it
had broken through in falling. Kepler first, two centuries
and a half earlier, induced by the consideration of comets
cutting through all the planetary orbits, had boasted (202)
of having destroyed the 77 homocentric spheres of the cele-
brated Girolamo Fracastoro, as well as all the more ancient
retrograding epicycles. How such great minds as Eudoxus,
Mensechmus, Aristotle, and Apollonius of Perga, had con-
ceived to themselves the possible mechanism and motion of
spheres intercalated with each other, and carrying with them
the planets, — or whether they regarded these spherical
systems as ideal contemplations — fictions of the intellect — by
the aid of which the difficult problems of the courses of the
planets might be explained and approximately computed, —
are questions which I have touched on elsewhere, (203) and
which are not without importance in the history of astronomy,
when that history attempts to distinguish periods of deve-
lopment.

Before we pass from the very ancient but artificial zodiacal
grouping of the fixed stars (as imagined to be set in a
solid sphere) to their natural or real grouping, and to such

OF THE COSMOS. — RAYS AND SPU1UOUS DISCS. 109

laws in respect to their relative distribution as have hitherto
been recognised, we have still to consider some particular
appearances presented by them to our sense of vision ; viz.
their rays, their apparent unreal diameters, and the di-
versities of colour of different stars. Of the apparent rays,
which differ in number, position, and length, as seen by
every individual, I have already spoken when treating of the
subject of Jupiter's satellites. (204) Indistinct vision (la
vue indistincte) arises from various organic causes, dependent
on the spherical aberration of the eye, on diffraction at
the margins of the pupils or at the eye-lashes, and on the
irritability of the retina spreading more or less widely from a
stimulated point. (205) I see very regularly, in stars from
the 1st to the 3d magnitude, eight rays, at angles of 45°.
As, according to Hassenfratz, these rays are caustics on the
crystalline, formed by the intersection of the refracted rays,
they move according as the spectator inclines his head to
either side. (206) Some of my astronomical friends see three
or at most four upward, and no downward rays. It has always
appeared to me remarkable that the ancient Egyptians inva-
riably give to stars five rays only (at every 72°) ; so much so,
that, according to Horapollo, a star signifies in hieroglyphics
the number 5. (2°7)

These rays disappear if the star is viewed through a small
hole made in paper with a needle (I have often observed
Canopus, as well as Sirius, in this manner) . The rays appear
in telescopic vision with high magnifying powers, when the
stars present themselves either as luminous points of more
intense light, or as extremely small discs. Although the less
degree of scintillation between the tropics gives a certain im-
pression of repose, yet the entire absence of rays, in viewing.

110 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

the heavens with the naked eye, would appear to me a pri-
vation. Illusion of the senses, and indistinctness of vision,
may perhaps augment the magnificence of the shining canopy
of heaven. Arago long ago proposed the question — Why is
it that, notwithstanding the strong light of the fixed stars, we
do not perceive them when rising above the horizon, whilst
yet we see the extreme margin of the moon's disc under
similar circumstances ? (208)

Even the most perfect optical instruments, with the highest
magnifying powers, give to the fixed stars false diameters
(spurious discs, diametres factices), which, according to Sir
John HerscheFs remark, (209) "with equal magnifying powers
diminish as the aperture of the telescope increases." Occul-
tations of stars by the Moon's disc show that immersion and
emersion are sensibly instantaneous, — so much so, that no
fraction of a second can be assigned for the time occupied
in disappearance or reappearance, The frequent observation
of stars in their immersion adhering to the disc of the moon,
is a phenomenon of the inflection of light which has no con-
nection with the question of the star's diameter. I have
already noticed elsewhere, that Sir William Herschel, with a
magnifying power of 6500, still found the diameter of
a Lyrse 0"'36. The image of Arcturus was so lessened in a
thick mist as to be even below 0"'2. It is remarkable that, from
the illusion produced by irradiation, Kepler and Tycho
Brahe, before the invention of telescopes, ascribed to Sirius a
diameter, the one of 4', the other of 2' 20". (21°) The alter-
nating light and dark rings which surround the factitious
discs of stars, viewed with magnifying powers of two or three
hundred, and which, when diaphragms of different shapes are
applied, show prismatic colours, are the consequences at once

OF THE COSMOS. COLOUR OF THE FIXED STARS. Ill

of interference and of diffraction, as we learn from Arago's
and Airy's observations. The smallest objects which can
still be distinctly seen (telescopically) as luminous points
(multiple stars such as « Lyrse, and the 5th and 6th star
discovered by Struve in 1826 and by Sir John Herschel in
the trapezium, (2n) formed by the quadruple star 0 Oriouis)
may be employed to test the quantity of light and merits in
other respects of optical instruments, whether refractors or
reflectors.

A difference of colour in the proper light of the fixed stars,
as well as in the reflected light of the planets, has been re-
cognised from very early times ; but the knowledge of this
remarkable phenomenon has been wonderfully enlarged
since tbe period of telescopic vision, and especially since
double stars have become an object of lively interest and
diligent observation. We do not here refer to the change
of colour which, as has been already remarked, acccompanies
scintillation even in the whitest heavenly bodies, — still less
the transitory and most frequently reddish tinge which the
light of stars receives in the vicinity of the horizon from the
medium (/. e. the atmospheric strata) through which we
view them ; but we speak of the white or of the coloured
light which radiates from stars as the result of peculiar lu-
minous processes and the particular character of the surface
of each. The Grecian astronomers knew only red stars ;
while, by the aid of the telescope, the moderns have
discovered in the starry vault, — in the celestial fields which
light traverses, as in the corollas of our flowering plants, and
in the metallic oxides, — almost every gradation of prismatic
colour between the two extremes of refrangibility, or

112 SPECIAL RESULTS EN THE URANOLOGICAL PORTION

between the violet and the red rays. Ptolemy, in his cata-
logue of the fixed stars, calls six stars vxoKippot, fiery red, (212)
viz. — Arcturus, Aldebaran, Pollux, Antares, Betelgueze, and
Sirius. Cleomedese ven compares Antares with the red hue (213)
of Mars, which is itself called sometimes wppos, and some-
times 7TVpO£l(ti)Q.

Of the six stars above enumerated, five have still, in our
days, a red or reddish light : Pollux is still marked in our cata-
logues as reddish, whereas Castor is said to be greenish. (214)
Sirius, on the other hand, offers the solitary example of an
historically -proved alteration of colour, for it has at present
a perfectly white light. Some great revolution of nature (215)
must doubtless have taken place on the surface or in the pho-
tosphere of such a fixed star, — such a distant sun, as already
Aristarchus of Sarnos would have called the fixed stars, — to
disturb the process by which, through the absorption of other
complementary rays (whether in the photosphere of the star
itself, or in wandering cosmical clouds), the less refrangible
red rays had once been the prevailing ones. Now that, from
the modern advances in optics, this subject has become one
of great and lively interest, it would be very desirable to be
able to assign some fixed limits in point of time to the epoch
of such an event in Nature as that of the disappearance of
the red colour of Sirius. In the time of Tycho Brahe the
light of Sirius must certainly have been already white; for
when the new star which appeared in Cassiopeia in 1572, and
which was at first of dazzling whiteness, was seen to assume,
in March 1 573, a red tinge, and, in January 1574, to become
once more white, — the astonished observers who witnessed
these changes compared the red star to Mars and Aldebaran,
but not to Sirius. Perhaps Sedillot, or other philologists

OF THE COSMOS. — COLOUR OF THE FIXED STARS. L13

conversant with Arabian and Persian astronomy, may
succeed in discovering in the intervals from El-Batani
(Albategnius) and El-Fergani (Alfraganus) to Abdurrahman
Sufi, arid Ebn-Junis (from 880 to 1007), and from Ebn-
J unis to Nassir-Eddin andlllugh Beig (from 1007 to 1437)
some evidence respecting the colour of Sirius at that time.
El-Fergani (properly called Mohammed Ebn-Kethir El-
Fergani), who, as early as the middle of the 10th century,
observed at Rakka ( Aracte) on the Euphrates, names as " red
stars" (" stellse ruffse" in the old Latin version of 1590)
Aldebaran, and, perplexingly enough, (216) the now yellow,
or at the utmost reddish-yellow, Capella, but not Sirius.
On the other hand, if we suppose that Sirius had then ceased
to be a red star, it would seem strange that El-Fergani, who
follows Ptolemy throughout, should not have pointed out the
change of colour in a star of such note. Negative reasons
are, however, seldom conclusive ; and it should be remarked
that, in the same passage, El-Fergani does not mention the
colour of Betelgeuze (a Orionis), which is now, as in Ptolemy's
time, a red star.

It has long been recognised, that among all the brightly-
shining fixed stars in the heavens, Sirius occupies the first
and most important place in chronological respects, and in
its historical connection with the earliest development of
human civilization in the Yalley of the Nile. According to
the most recent researches of Lepsius, (21?) the Sothic period,
and the heliacal rising of Sothis (Sirius),— on which subject
Biot has furnished an excellent memoir, — remove the complete
construction of the Egyptian calendar to the highly ancient
epoch of almost 33 centuries before our Era, when not only
the summer solstice, and consequently the commencement

VOL III. I

114 SPECIAL RESULTS IN THE UllAXOLOGICAL PORTION

of the rising of the Nile, but also the heliacal rising of Sothis,
fell upon the day of the first water-month (on the first
Pachon). The most recent and hitherto unpublished re-
searches on the etymology of Sothis and Sirius in the Coptic,
the Zend, the Sanscrit, and the Greek, have been brought to-
gether by me in a note(218), which cannot be otherwise than
welcome to those who, from interest in the history of astro-
nomy, are led to recognise, in languages and their affinities,
monuments of earlier knowledge.

At the present time, besides Sirius ; Yega,Deneb, Eegulus,
and Spica, are decidedly white stars ; and among the small
double stars, Struve counts 300 in which both stars are
white. (219) Procyon, Atair, Polaris, and especially /3 Ursse
Minoris, have a yellow or yellowish light. Of red or
reddish large stars, we have already named Betelgeuze,
Arcturus, Aldebaran, Antares and Pollux. Eiimker finds y
Crucis to have a fine red colour ; and my old friend Captain
Berard, who is an excellent observer, wrote from Madagascar
in 1847, that he had for some years perceived a Crucis to be
reddening. The star ri Argus, which has acquired celebrity
from Sir John HerscheFs observations, and of which I shall
soon have occasion to speak in more detail, is changing the
colour as well as the intensity of its light. In 1843, at
Calcutta, Mr. Mackay found this star like Arcturus in colour,
—therefore of a reddish yellow; (22°) but in February 1850,
Lieutenant Gilliss, in letters from Santiago de Chile, calls it
" of a darker colour than Mars/' Sir John Herschel, at the
conclusion of his Cape observations, gives a list of 76 ruby-
coloured small slars, from the 7th to the 9th magnitude.
The appearance of some of them in the telescope is like drops
of blood. The majority of " variable" stars are described

OF THE COSMOS. DISTRIBUTION OF THE FIXED STARS. 115

as red or reddish. (221) I may name as exceptions — Algol
in the head of Medusa, /3 Lyrse, and e Aurigse, which have
a pure white light. Mira Ceti, whose periodic variation of
light was the first recognised, (222) has a strongly reddish
light ; but the variability of Algol and /3 Lyrse shows that
the red colour is not a necessary condition of variability of
light ; and we know, moreover, that there are several reddish
stars which are not included among the variable stars.
According to Struve, the faintest stars in which colours can
still be distinguished are of the 9th and 10th magnitudes.
We find the first mention of blue stars (223) in Mariotte's
" Traite des Couleurs/' in 1686. The star n Lyrse is bluish.
A small cluster of 3 J minutes' diameter in the southern he-
misphere consists, according to Dunlop, exclusively of small
blue stars. Among the double stars there are many in
which the, principal star is white, and the companion blue ;
and some in which both the principal star and the companion
have a blue light, (224) as £ Serp. and 59 Androm. Some-
times, as in the cluster of stars near K of the Southern
Cross, which was taken by Lacaille for a nebula, above a
hundred small stars of different colours (red, green, blue,
and bluish-green) are so crowded together, that they appear,
in large telescopes, like gems of \nany colours ("like a
superb piece of fancy jewellery)." (^5)

The ancients thought they recognised a remarkable sym-
metrical arrangement in the position of certain stars of the
1st magnitude. Thus their attention was particularly
directed to what they call ed the " four royal stars," which
are opposite to each ot'ner on the sphere— Aldebaran and
Antares, Eegulus and 'Eomalhaut. This regular arrange

116 SPECIAL RESULTS IN THE UllANOLOGICAL PORTION

ment, which I have noticed elsewhere, (226) is discussed at
length by a Eoman writer of the age of Constantino, Julius
Firmicus Maternus.(227) The differences in right ascen-
sion of the "royal stars/' "stellse regales," are llh. 57m.
and 12h. 49m. The importance which was attached to
this subject was probably founded on opinions derived from
the East, which, under the Caesars, made their way into the
Eoman empire, together with a great predilection for astro-
logy. An obscure passage in the book of Job (ch. ix. v. 9),
in which the te chambers of the south" are opposed to u the
Leg/' i. e. the North Star in the Great Bear (the celebrated
Bull's Leg in the astronomical representations at Dendera,
and in the Egyptian " Book of the Dead"), seems also in-
tended to allude to the four quarters of the heavens, marked
by four constellations. (228)

If a large and fine portion of the southern heavens, — viz.
all stars beyond 53° of south declination, — remained con-
cealed from the ancients, and even until the latter part of the
Middle Ages, yet the knowledge of the southern celestial
hemisphere had gradually become complete about one hun-
dred years before the invention and employment of telescopes.
In the time of Ptolemy, the Altar, the feet of the Centaur,
the Southern Cross then included in the Centaur, or other-
wise (according to Pliny) called Csesaris Thronus in honour
of Augustus, (229) and lastly Canopus (Canobus), which the
scholiast to Germanicus (23°) calls the Ptolemaeon, — were all
visible above the horizon of Alexandria. In the catalogue of
the Almagest, Achernar, a star of the 1st magnitude, the last
in the constellation of the Biver Eridanus (in Arabic, Achir-
el-nahr), is also mentioned, although it was 9° below the
horizon. Intelligence of the existence of this star must

OF THE COSMOS. DISTRIBUTION OF THE FIXED STARS. 117

have been brought to Ptolemy from voyages to the southern
part of the Eed Sea, or between Ocelis and the commercial
entrepot of Muziris (231) on the Malabar coast. No doubt
Diego Cam in company with Martin Behaim, in 1484, on
the West Coast of Africa, Bartholomew Diaz in 148 1, and
Vasco de Gama in 1497 on the voyage to India, passed far
beyond the Equator, and into the Southern Ocean as far as
35° S. latitude ; but the first particular notice of the large
stars and nebulae, the description of the Magellanic clouds
and the ee coal sacks," and even the fame of the " wonders
of the heavens not seen in the Mediterranean/' belong to
the epoch of Vincent Yanez Pinzon, Amerigo Vespucci, and
Andrea Corsali, between 1500 and 1515. Star-distances
were measured in the southern heavens at the end of the
16th and the beginning of the 17th century. (232)

Laws of relative density in the distribution of the fixed
stars on the celestial vault began to be recognised when
William Herschel, in 1785, conceived the happy thought
of estimating the number of stars visible in the field of view,
15' in diameter, of his 20 -feet reflector, at different altitudes
and in different directions. This laborious process of
" gauging the heavens" has been already repeatedly referred
to in the present work. The field of view embraced each
time only 8d ^op-p-th of the whole heavens ; and, according to
a remark of Struve's, 83 years would be required for the
completion of such gaugiugs over the entire sphere. (233)
In inquiries respecting the equal or unequal distribution of
stars, their photometric magnitudes must be particularly
taken into account. If we confine our attention to the
bright stars of the first three or four classes of magnitude,
we find them pretty uniformly distributed (234) on the whole ;

118 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

but locally, in the southern hemisphere, from e Orionis to
a Crucis, rather crowded together in a superb zone in the
direction of a great circle. The disagreement in the judg-
ments pronounced by different travellers, as to the relative
beauty of the northern and southern hemispheres, has often
I believe, depended only on the circumstance, that some of
he observers had visited the southern regions at a time when
the finest constellations culminate in the day-time. Prom the
gaugings of the two Herschels in the northern and southern
celestial hemispheres, it follows that the fixed stars, from the
5th and 6th magnitudes down to the 10th and 15th mag-
nitudes, (particularly, therefore, telescopic stars), increase
regularly in density as the Milky Way (6 ya\a£tag KVK\OQ) is
approached ; and thus that there may be said to be poles of
abundance or richness, and poles of scarcity or poverty,
in respect to stars, — the latter being at right angles to
the principal axis of the Milky "Way. The density of stars is
least at the poles of the galactic circle, and increases in all
directions, — at first slowly, and then more and more rapidly
as the galactic polar distance increases.

By an ingenious and careful consideration of the results
of the star-gaugings which we possess, Struve finds that, on
the average, there are, in the central pprts of the Milky Way,
29-4 times (almost 30 times) as many stars as in the
regions around the poles of the Milky Way ; and in northern
galactic polar distances of 0°, 30°, 60°, 75°, and 90°, the
ratios of the numbers of stars in the field of view of 15
diameter are 4-15, 6-52, 17'68, 30'30, and 122*00. In
the comparison of opposite zones, notwithstanding the great
similarity in the law of increase in the number of stars, we
again find an absolute preponderance f235) on the side of the
richer and more beautiful southern heavens.

OF THE COSMOS. — CLUSTERS OF STARS. 119

When,, in the year 1 843, I asked Captain Schwink to be
so kind as to communicate to me the distribution, in right
ascension, of the 12148 stars (1st to 7th magnitude inclu-
sive), which, at Bessel's instance, he had entered in his
•" Mappa ccelestis," he found, in four groups-
Eight ascension, 50°- 140°; 3147 stars
140°- 230° j 2627 "
230°-320°; 3523 "
" 320°- 50°; 2851 "

These groups agree with the still more exact results of the
" Etudes stellaires •" according to which, the maxima of stars
from the 1st to the 9th magnitude fall in the right ascen-
sions of 6h. 40m. and 18h. 40m., and the minima in those
of Hi. 30m. and 13h. 30m. (236)

In reference to conjectures respecting the structure of
the Universe, and the position or depth of the sidereal
strata, it is essential to distinguish, among the countless
multitude of stars, those which are scattered sporadically,
from those which we find crowded in detached independent
groups. The latter are the " clusters of stars" which have
been spoken of : they often contain many thousands of
telescopic stars in recognisable relation to each other,
and are seen by the naked eye as round or oval nebulse,
appearing like comets. These are the "nebulous stars"
of Eratosthenes (23?) and Ptolemy ; the " nebulosa3" of the
Alphonsine Tables of 1252, and those of Galileo, which (as
it is said in the Nuncius sidereus) sicut areolse sparsirn per
sethera subfulgent.

120 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

The clusters of stars, again, are either placed solitarily in
the heavens, or else are closely and unequally crowded, as it
were in strata, in the Milky Way and in the two Magellanic
clouds. The most numerous, and, in respect to the annular
configuration of the Milky Way, the most important assem-
blage of " globular clusters," is in a region of the southern
heavens, (238) between the Corona australis, Sagittarius, the
tail of the Scorpion, and the constellation of the Altar
(E. A. 16h. 45m. — 19h.) But all the clusters of stars which
are in or near the Milky Way are not round or globular :
there are several of irregular outline, less rich in stars,
and with not very dense centres. In many round groups
the individual stars are of equal, and in others of unequal,
magnitudes. In some rare cases they show a fine reddish
central star (239) ; (E. A. £h. 10m., N. Bed. 56° 21').
How such world-islands, with their multiplicity of suns, can
rotate free and undisturbed, is a difficult problem in dynamics.
Clusters of stars and nebulae, even though it be now very gene-
rally assumed respecting the latter that they also consist of
very small but still more distant stars, yet appear to be
subject to different laws in respect to their local distribution.
The recognition of these laws will have a prominent in-
fluence in modifying conjectures respecting what has been
adventurously termed the " structure of the heavens." It
is also a very remarkable fact of observation, that, with the
same aperture and magnifying power of the telescope, round
nebulae are more easily resolved into clusters of stars than
oval ones. (24°)

Of the clusters of stars which form, as it were, detached
systems, I content myself with naming the following : —
The Pleiades : doubtless recognised from the earliest

OF THE COSMOS. — CLUSTERS OF STARS. 121

times by the rudest nations ; the constellation of naviga-
tion, Pleias, airo TOV TT\EII> , according to the etymology of
the old scholiast of Aratus, which is probably more correct
than that of later writers, who derive the name from
TrXt'oe, abundance. The navigation of the Mediterranean
lasted from May to the beginning of November, — from
the early rising to the early setting of the Pleiades.

The Bee-hive in Cancer : according to Pliny, nubecu-la
quam Prsesepia vocant inter Asellos ; a veyiKiov of the
Pseudo-Eratosthenes.

The cluster of stars in the hilt of the sword in Perseus,
often mentioned by the Greek astronomers.

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

Cluster of stars near Arcturus (No. 1663), telescopic;
E. A. 13h. 34m. 12s., N. declination, 29° 14'; more than
a thousand small stars of the 10th to the 12th magni-
tude.

Cluster of stars between r? and £ Herculis : in very fine
nights visible to the naked eye ; a magnificent object in
the telescope (No. 1968), with singular ray-shaped out-
lines ; K A. 16h. 35m. 37s.; N. Decl. 36° 47'; first
described by Halley in 1714.

Cluster of stars near w Centauri : described as early as
1677 by Halley; appears to the naked eye as a round
comet-like patch, shining almost like a star of the 4.5
magnitude ; when seen in powerful telescopes it appears
to be composed of a countless multitude of small stars of
the 13th to the 15th magnitude, which are more densely
crowded towards the centre; E. A. 13h. 16m. 38s.,
S. Declination 46° 35'; No. 3504 in Sir John HerscheFs

122 SPECIAL RESULTS JN THE URANOLOGICAL PORTION

catalogue of the clusters of stars in the Southern Heavens,
15' in diameter. (Cape Observ. pp. 21 and 105, Outl. of
Astr. p. 595).

Cluster of stars near K of the Southern Cross (No.
34-35) : composed of many-coloured stars of the 12th to
the 16th magnitude, distributed over an area of -^th of a
square degree; a nebulous star according to Lacaille, but
so completely resolved by Sir John Herschel that no ne-
bulous appearance remained : the central star deep red.
(Cape Observ. pp. 17 and 102, PL 1, fig. 2).

Cluster of stars 47 Toucani, Bode ; No. 2322 of Sir
John Herschel's catalogue, one of the most remarkable
objects of the Southern heavens. I was myself deceived
by it for some nights, taking it for a comet, when, on my
first arrival in Peru, in 12° South latitude, I saw it rise
high above the horizon. Its visibility to the naked eye
is so much the greater because, although near the smaller
Magellanic Cloud, it is in a place wholly devoid of stars,
and has a diameter of 15' to 20'. It is of a pale
roseate colour in the inside, surrounded concentrically by
a white border, and composed of small stars all about the
same magnitude (14m. to 16m.), presenting all the cha-
racteristics of bodies of a globular form. (241)

Cluster of stars in the girdle of Andromeda, near the
star v of that constellation. The resolution of this cele-
brated nebula into stars, above 1500 of which have been
distinctly made out, is one of the most remarkable dis-
coveries of this department of astronomy in our time.
Its merit belongs to George Bond, (142) assistant at the
Observatory of Cambridge in, the United States (March
1848) ; and it also evidences the excellence and abun-

OF THE COSMOS.— CLUSTERS OF STARS. 123

dance of light of the refracting telescope of that Obser-
vatory (which has an object glass of 14 Parisian inches
diameter), since even a reflecting telescope, in which the
mirror has 1 8 inches diameter, does not shew the faintest
trace by which the presence of a star can be divined. (243)
The cluster of stars in Andromeda may perhaps have been
known as a nebula of oval form as early as the end of the
tenth century ; but it is more certain that on the 1 oth of
December,1612, Simon Marius( Mayer of Guntzenhauseu,
the same who first remarked the change of colour in
scintillation (244) ), distinguished it as anew and wonderful
starless cosmical body which had not been named by Tycho
Brahe, and it was he who first gave a detailed description
of it. Half a century later, Bouillaud, the author of the
Astronomia philolaica, occupied himself with the same
subject. This cluster of stars, which is 2J° long and
above 1° broad, is particularly characterised by two re-
markable very narrow black streaks, nearly parallel to each
other and to the longer axis of the cluster, and, according
to Bond's examination, traversing the whole like fissures.
This arrangement reminds us strongly of the remarkable
longitudinal fissure in an unresolved nebula of the
Southern hemisphere, No. 3501, which has been described
and figured by Sir John Herschel. (Cape Observ. pp.
20 and 105, PL IY. fig. 2.)

In this selection of remarkable clusters of stars, I have
not included the great nebula in Orion's belt, notwith-
standing the important discoveries for which we are in-
debted to the Earl of Eosse and his colossal telescope, as
I prefer reserving it for the section on Nebula3, although
portions have thus been already resolved.

124 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

We find the greatest accumulation of clusters of stars
(but by no means of nebulae) in the Milky Way (245) (the
Galaxy, the Celestial River (246) of the Arabians), which
forms almost a great circle of the sphere, and is inclined to
the equator at an angle of 63°. The poles of the Milky
Way are situated in E. A. 14h. 47m., North Decl. 27° ; and
E. A. Oh. 47m., South Decl. 27°: therefore that which may be
called the North pole is near Coma Berenices, and the South
pole between Phoenix and Cetus. If all planetary relations
of place are referred to the Ecliptic, i. e. to the great circle
in which the plane of the sun's path cuts the sphere,
we may with equal convenience refer many relations in
space of the fixed stars, (for example their accumulation or
grouping) to the approximate great circle of the Milky
Way. In this sense, the latter is to the sidereal universe
what the ecliptic is to the planetary world of our solar
system. The Milky Way cuts the equator in the constellation
of the Unicorn between Procyon and Sirius, E. A. 6h.
54ra. (for 1800), and in the left hand of Antinous, E. A.
19h. 15m. Tims the Milky Way divides the celestial sphere
into two rather unequal portions, whose areas are to each
other in the proportion of about 8 to 9. The vernal point
is situated in the smaller portion. The breadth of the
Milky • Way varies very much in different parts of its
course. (247) Where it is narrowest, and at the same time
brightest (between the prow of the Ship and the Cross, and
nearest to the Southern Pole), its width is barely from 3° to
4°: at other points it is 16°, and in the divided part,
between Ophiuchus and Antinous, (248) it is as much as 22°.
William Herschel has remarked, that, judging by his star-
gauging, the Milky Way is in many regions 6 or 7

OF THE COSMOS. — MILKY WAY. 125

degrees broader than the brightness visible to the naked
eye. (™)

Huygens, who examined the Milky Way with his 23 feet
refractor, had denied, as early as 1656, that its milky
whiteness was to be attributed to unresolvable nebulae. A
more careful application of reflecting telescopes of the
largest dimensions and greatest power of light, have subse-
quently proved wifh still more certainty, what Democritus
and Manilius had already conjectured respecting the ancient
path of Phaeton, viz. that the milky brightness was to be
ascribed solely to the crowded strata of small stars, and not
to the scantily interspersed nebulae. The general white or shin-
ing appearance is the same in points where all can be perfectly
resolved into stars, and even where these stars, thus viewed
through the telescope, are seen to be projected on a black
ground, entirely without any nebulous light. (25°) It is in
general a remarkable characteristic of the Milky Way, that
globular clusters of stars, and nebulous patches of a regular
oval shape, are equally rare in it, (251) whereas at a great
distance from it both are congregated in large numbers ;
and in the Magellanic clouds we even find isolated stars,
globular clusters in all states of condensation, and nebulae
both of definite oval and of wholly irregular form, inter-
mingled. A remarkable exception to this rarity of globular
clusters in the Milky Way occurs in a region of it which is
situated between E. A. 16h. 45m. and 18h. 44m. ; between
the Altar, the Southern Crown, the head and body of
Sagittarius, and the tail of the Scorpion. Between the
stars e and 6 of the Scorpion, there is even one of those
annular nebula which are so exceedingly rare in the
southern celestial hemisphere. (252) In the field of view of

126 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

powerful telescopes (and we must remember that, according
to the estimations of Sir William Herschel, a 20-feet in-
strument penetrates space to 900, and a 40 -feet instrument
to 2800 distances of Sirius), the Milky Way appears in
different parts as varied in its sidereal contents, as it seems
irregular and indeterminate in its outlines arid boundary
when viewed by the naked eye. If in some parts of the
Milky Way large spaces exhibit great uniformity, both in
respect to light and to the apparent magnitude of the stars
of which it consists, in other parts the brightest patches of
closely-crowded luminous points are interrupted in a
granular, and even in a reticular manner, by darker inter-
vals (253) which are poor in stars : indeed, in some of these
intervals, quite in the interior of the galaxy, not even the
smallest star (18th or 20th magnitude) can be discovered.
One can hardly refrain from thinking, that in such places
we really see through the whole sidereal stratum of the
Milky Way. When gauging with a field of view of the
telescope of 15' diameter, the change is almost immediate
from fields containing 40 or 50 stars on an average, to others
having between 400 and 500 stars. Often, stars of the higher
orders of magnitude occur in the midst of the finest " star
dust," while all the intermediate magnitudes are wanting.
Perhaps those stars which we call of the lower orders of
magnitude do not always appear to us such solely on ac-
count of their enormous distance : it is also possible that they
may really have less volume and less development of light.

In order to represent to ourselves the greatest contrast,
in respect to abundance or paucity of stars, we must take
regions widely removed from each other. The maximum of
accumulation and the greatest brilliancy are to be found

OF THE COSMOS. — MILKY WAY. 127

between the prow of the Ship and Sagittarius ; or, to speak
more exactly, between the Altar, the tail of the Scorpion, the
hand and bow of Sagittarius, and the right foot of Ophiuchus.
" No region of the heavens is fuller of objects, beautiful and
remarkable in themselves, and rendered still more so by
their association and grouping." (254) Next in richness to
this beautiful part of the southern celestial vault, is the
pleasing and well-starred region in our northern heavens in
Aquila and Cygnus, where the Milky Way divides into
branches. As the Milky Way is most narrow below the
foot of the Southern Cross, so, on the other hand, the region
of minimum brightness (where the galaxy is comparatively
desert) is in the vicinity of the Unicorn and of Perseus.

The magnificent effect of the Milky Way in the southern
hemisphere is enhanced by the circumstance, that between
the star 17 Argus, which has become so celebrated on account
of its variability, and a Crucis, it is intersected, in the
parallels of 59° and 60° S. Latitude, at an angle of 20°, by
the remarkable zone of very large and probably' very near
stars, to which the constellations of Orion, Canis Major,
Scorpio, Centaurus, and Crux belong. A great circle,
passing through e Orionis and the foot of the Cross, indicates
the direction of this remarkable zone. The (I might almost
say) picturesque effect of the Milky Way is heightened in
both hemispheres by its repeated divisions or branchings.
For about two-fifths of its length it remains undivided. In
the greatest bifurcation the branches divide, according to Sir
John Hefschel, at a Ceritauri, (255) not at 0 Centauri as
our star-maps represent, nor at the Altar as was stated by
Ptolemy (256) : they reunite in Cygnus.

In order to afford a general view of the course and di-

128 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

rection of the Milky Way, together with its subordinate
branches, I subjoin a very brief and compressed account of
its parts, following their order of Eight Ascension. Passing
through y and £ Cassiopeiae, the Milky Way sends out to the
southward, towards e Persei, a branch, which loses itself
near the Pleiades and Hyades. The main stream, which is
here very faint, passes over the three remarkable stars called
the Hcedi, in Auriga, between the feet of Gemini and the
horns of Taurus, — where it intersects the Ecliptic nearly at
the summer solstice, — and thence over the club of Orion,
cutting the equinoctial (in 1800), at 6h. 54m. E. A., in the
neck of Monoceros : — from this place it increases considerably
in brightness. At the after-part of the Ship a branch
detaches itself towards the south, proceeding as far as
y Argus, where it breaks off suddenly. The main course
continues to 33° South Declination, where, having opened
out into a fan-like shape 20° wide, it breaks off ; so that,
in the line between y and X Argus, there is a wide gap
in the Milky Way. After this it resumes its course, at first
with a similar expansion in breadth ; but near the hind
feet of the Centaur it narrows again, and before entering the
constellation of the Cross it reaches its narrowest part,
which is only 3° or 4° wide. Soon afterwards the shining
Way spreads out into a bright and broad mass, which
includes $ Centauri as well as a and /3 Crucis, and in the
middle of which the black pear-shaped coal-bag or coal-
sack, which I have spoken of more particularly in the 7th
section, is situated. It is in this remarkable region, a little
below the coal- sack, that the Milky Way approaches nearest
to the South Pole.

The principal division of the Milky Way, alluded to

OF THE COSMOS. MILKY WAY. 129

above., takes place at a Centauri : it is a bifurcation
which, according to older views, continues to the constel-
lation of Cygnus. Proceeding from a Centauri, a narrow
branch goes northwards towards the constellation Lupus,
where it loses itself: then a division shows itself at
y Normse. The northern branch runs into irregular
shapes until near the feet of Ophiuchus, where it entirely
disappears ; the southern branch now becomes the main
stream, and passes through the Altar and the tail of
the Scorpion to the bow of Sagittarius, where it cuts the
Ecliptic iii 276° longitude. Further on we recognise it
still, but in an interrupted patchy form, passing through
Aquila, Sagitta, and Vulpecula, to Cygnus. Here begins a
very irregular district, where, between e, a, and y Cygni,
there is a broad dark space, which Sir John Herschel (257)
compares to the coal-sack in the Southern Cross, and which
forms, as it were, a centre whence three partial streams
diverge. One of these, which has most strength of light,
may be pursued in, as it were, a retrograde course past
jg Cygni and s Aquilse : it does not however unite with the
branch before spoken of, which goes to the foot of Ophiuchus.
There is still a considerable additional piece of the Milky
Way, which extends from the head of Cepheus, and therefore
in the vicinity of Cassiopeia, from which constellation we
began our description, to Ursus Minor and the North Pole.
Prom the extraordinary improvement which, by the applica-
tion of large telescopes, has gradually been made in the know-
ledge of the sidereal contents, and the differences in respect to
concentration of light, in different parts of the Milky Way,
views of merely optical projection have been replaced by
what may rather be deemed views of physical character and

VOL. III. K

130 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

formation . Thomas "Wright of Durham, (258) Kant., Lambert,
and at first also William Herschel, were inclined to regard
the form of the Milky Way, and the apparent accumulation
of stars in it, as consequences of the flattened form and
unequal dimensions of the " world-island" (sidereal stratum)
in which our solar system is included. The hypothesis of
equal magnitude and equable distribution of fixed stars has
recently been shaken on many sides. The bold and able
investigator of the heavens, William Herschel, declared
himself, in his last work, (259) decidedly in favour of the
assumption of a ring or annulus of stars, — which assumption
he had combated in a treatise in the year 178 k. Recent
observations have favoured the hypothesis of a system of
detached concentric rings. The thickness of these rings
appears to be very unequal, and the several strata whose
united stronger or fainter light we receive, are doubtless
situated at very different heights, i. e. very different distances
from us : but the relative brightness of the several stars,
which we estimate as being from the 10th to the 16th mag-
nitude, cannot be regarded as such a measure of their relative
distances, as could enable us to derive from thence a satis-
factory numerical (26°) determination of the radii of the
respective spheres of distance.

In many parts of the Milky Way, the space-penetrating
power of instruments is sufficient to resolve the star- clouds,
and to enable us to see single luminous points projected
on the dark starless regions of celestial space. In such case
we really look through into free and open space. " It leads us/'
says Sir John Hersthel, " irresistibly to the conclusion, that in
these regions we see, fairly through the starry stratum." (261)
In other regions we see, as through openings and fissures,

OF THE COSMOS. — MILKY WAY. 131

either distant world-islands, or out-branching parts of the
annular system; in others, again, the Milky Way has
hitherto remained "fathomless," even to the 40 -feet teles-
cope. (262) Investigations respecting differences in the
intensity of light in the Milky Way, as well respecting the
magnitudes of stars, and their regular increase in numbers
from the poles of the galaxy to the galactic circle itself,
(an increase which is particularly remarked for 30° on either
side of the Milky Way in stars below the llth magni-
tude, (263) and therefore in -j-f-ths of the whole number),
have conducted those who have been engaged in the most
recent researches in the southern heavens, to remarkable
views and probable results in regard to the form of the
galactic annular system, and to what has been boldly called
the place of our Sun in the world-island to which that
annular system belongs. The place assigned to the Sun is
excentric, and conjectured to be where a subordinate stratum
branches off from the principal ring, (264) in one of the
comparatively desert regions, and nearer to the Southern
Cross than to the opposite galactic node. (265) The depth
to which our system is immersed in the star-stratum which
forms the Milky Way (reckoned from the southern limit) is
supposed to be equal to the distance, (or to the light-path) of
stars of the 9th and 10th, but not of the 11 th magnitude. (266)
Where, from the peculiar nature of particular problems,
measurements and immediate cognizance by the senses fail,
we view, as it were by an imperfect twilight, the results
which intellectual contemplation aspires to attain.

132 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

IV.

NEWLY- APPEARED AND VANISHED STARS. — VARIABLE STARS,

WHICH HAVE MEASURED AND RECURRING PERIODS.

VARIATIONS OF THE INTENSITY OF LIGHT IN CELESTIAL
BODIES OF WHICH THE PERIODICITY HAS NOT YET BEEN
INVESTIGATED.

THE appearance of previously unseen stars in the celestial
vault, especially the sudden appearance of strongly scin
tillating stars of the 1st magnitude, is an event in the
regions of space of which the occurrence has ever ex-
cited the astonishment of men. This astonishment is so
much the greater, as such an event in Nature as the
sudden visibility of an object which, though previously
unseen, we yet believe to have existed previously, is one of
the rarest of all phsenomena. In the course of the three
centuries from 1500 to 1800, there have appeared to the
inhabitants of the northern hemisphere 42 comets visible
to the naked eye, — being, on an average, 14 in a century ;
while, during the same three hundred years, only 8 new stars
have been observed. The rarity of the latter occurrence
becomes still more striking when we embrace yet longer
periods. From the important epoch in the history of
astronomy of the completion of the Alphonsine Tables, to
the time of William Herschel, or from 1252 to 1800, we

OF THE COSMOS. NEW STARS. 133

reckon, of comets visible to the naked eye, about 63, and
of new stars only 9 ; thus, for the period within which, in
European civilised countries, we can count on a tolerably
accurate enumeration, we find the proportion of new stars to
comets, both being visible to the naked eye, as 1 to 1 * We
shall soon show, that if in the Chinese registers of Ma-
tuan-lin, we carefully distinguish the observations of newly-
appeared stars from those of tail-less comets, — and if we. go
back to a century and a half before the Christian era, — we
find that, in the course of almost 2000 years, 20 or 22 of
such phsenomena are the utmost that can be adduced with
any degree of certainty.

Before proceeding to general considerations, I prefer, by
dwelling on a single example, and by the narration of an
eye- witness, to attempt to convey to my readers a just idea
of the vividness of the impression produced by the appearance
of a new star. " When," says Tycho Brahe, " I was returning
to the Danish Islands, after travelling in Germany, I
remained awhile (ut aulicse vitse fastidium lenirem) with my
uncle, Steno Bille, at the pleasantly- situated former convent
of Herritzwadt, where I was in the habit of only quitting my
chemical laboratory in the evening. On coming forth into
the open air, and raising my eyes as usual to the well-known
heavenly vault, I saw, with indescribable astonishment, near
the zenith, in Cassiopeia, a radiant fixed star of a magnitude
never before seen. In the excitement, I thought I could
not trust my senses. In order to convince myself that it
was no illusion, and to collect the testimony of others, I
called my workman from the laboratory, and asked all the
country people who were passing by, whether they saw the
new suddenly-outshining bright star as I did. Subsequently

134 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

I learned that in Germany, waggoners, and ( other common
people/ first called the attention of astronomers to this great
celestial phsenomenon, which (as in the case of comets
appearing without having been predicted) renewed the usual
scoffs at learned men."

" I found this new star," Tycho Brahe continues, " with-
out any tail, not surrounded by any nebulous appearance,
and perfectly similar in all respects to all the other fixed
stars, but sparkling still more brightly than those of the
1st magnitude. It exceeded in brilliancy Sirius, a Lyrse,
and Jupiter, and could only be paralleled by the brightness
of Venus when she is nearest the Earth, (at which time only
her fourth part is illuminated). When the atmosphere was
clear, men gifted with keen sight could distinguish the new
star in the day-time, and even at noon. At night, when the
sky has been so far covered that all other stars were veiled,
it has repeatedly been seen through clouds of moderate
density (nubes non admodum densas). Distances from
other neighbouring stars in Cassiopeia, which I measured
with great care throughout the whole of the following year,
convinced me of its perfect immobility. In December 157&,
the light of the star began to diminish: it soon became
equal to Jupiter; and in January 1573 it was less bright
than that planet. Continued photometric estimations gave,
in February and March, an equality with the stars of the
1 st magnitude (stellarum afnxamm primi honoris ; for Tycho
Brahe seems determined never to use the expression of
Manilius, stellse fixse) ; for April and May, light equal to
stars of the 2d; for July and August, of the 3d; and
for October and November, of the 4th magnitude. About
the month of November, the new star was no brighter than

OF THE COSMOS. — NEW STARS. 135

the eleventh star in the lower part of Cassiopeia's chair.
From December 1573 to February 1574, it diminished
successively to the 5th and 6th magnitudes,, In the
following month, after shining for seventeen months, the
new star disappeared altogether, leaving no trace visible
to the naked eye." (The telescope was invented thirty-seven
years later.)

It appears, then, that the loss of light in this star was
exceedingly gradual and regular, and not interrupted by
periods of renewed or fresh increase of light, (as has been
several times the case in our own days with TI Argus, which,
indeed, is not to be called a new star). In the star
in Cassiopeia, of which we have been speaking, there was
alteration of colour as well as of light, — a circumstance
which has since given occasion to many erroneous conclu-
sions respecting the velocity of coloured rays in traversing
space. When it first appeared, and as long as it equalled
first Venus and then Jupiter in brightness, its light was,
during two months, white; after which it passed through
yellow into red. In the spring of 1573, Tycho Brahe com-
pared it to Mars ; he next found it almost comparable to
the star in the right shoulder of Orion (Betelgeuze) . Its
colour resembled most nearly the red colour of Aldebaran.
In the spring of 1573, particularly in the month of May,
the whiteness returned (albedinem quandam sublividam
induebat, qualis Saturni stellse subesse videtur). In
January 1574 it still continued to be of the 5th magnitude
and white, but of a duller white, and with a degree of
scintillation strikingly great in proportion to its feeble light,
until its entire gradual disappearance in the month of
March, 1574.

136 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

The detailed character of these statements (267) would of
itself suffice to show how great a stimulus to the considera-
tion of highly important questions must have been afforded,
by the occurrence of such a phenomenon at a period so
brilliant in the history of astronomy. The stimulus was the
stronger, because, notwithstanding the above^deseribed
general rarity of the appearance of new stars, it happened
that European astronomers witnessed phsenomena of this
kind three times within the short period of thirty-two years.
The importance of star-catalogues, determining with cer-
tainty the novelty of such stars, was more and more
recognised ; their periodical character, i. e. their reappear-
ance after the lapse of several centuries, was discussed ; (268)
and Tycho Brahe even boldly put forth a theory respecting
the process of formation of stars from cosmical vapour or
nebulosity, which had much analogy with that of the great
William HerscheL He believed that the nebulous celestial
matter, luminous in the course of its condensation, solidified
into fixed stars : — " Cceli materiem tenuissimam, ubique
nostro visui et planetarum circuitibus perviam, in unum
globum condensatain, stellam effingere." He conceived this
everywhere-diffused celestial matter to have already a certain
degree of condensation in the Milky Way, where its dawning
luminosity produced a mild silvery brightness, — and this he
thought the reason why the new star, like those of 945 and
1264, shone forth on the edge of the Milky Way itself (quo
factum est quod nova stella in ipso Galaxise margine
constiterit) ; and it even seemed possible to recognise the
place (the opening, hiatus) from whence the nebulous matter
of the Milky Way had been taken. (269) All this reminds us
of the transition of. cosmical vapour into clusters of stars, —

OF THE COSMOS. — NEW STARS. 137

of the concentration to a central nucleus, — and of the hypo-
theses respecting the gradual development of solid celestial
bodies from a vaporous fluid, — which gained acceptance at
the commencement of the present century ; but which now,
according to the ever-varying fluctuations of the world of
thought, have become subject to fresh doubts.

We may, with more or less certainty, reckon among the
new ' ' temporary" stars the following, which I have arranged
in the order of their first shining forth : —

a 134 B.C.

in Scorpio.

!> 123 A.D.

in Ophiuchus.

c 173 —

in Centaurus.

d 369?—

e 386 —

in Sagittarius.

/ 389 —

in Aquila.

g 393 —

in Scorpio.

h 827? —

in Scorpio.

i 945 —

between Cepheus

and Cassiopeia.

k 1012 -

in Aries.

1 1203 —

in Scorpio.

m 1230 —

in Ophiuchus .

n 1264 —

between Cepheus

and Cassiopeia.

o 1572 -

in Cassiopeia.

p 1578 —

q 1584 —

in Scorpio.

r 1600 —

in Cygnus.

* 1604 —

in Ophiuchus.

t 1609 —

u 1670 —

in Vulpes.

v 1848 —

in Ophiuchus.

138 SPECIAL RESULTS IN THE URANOLCGICAL PORTION

Elucidatory Notices of the above Temporary Stars.

a. "Which first appeared between /3 and p Scorpii, in
the month of July, 134 years before our Era, is recorded
in the Chinese Notices of Ma-tuan-lin, for the knowledge
of which we are indebted to the philological learning of
Edouard Biot (Connaissance des Temps pour Fan 1846,
p. 61). The "extraordinary" stars of "strange or
foreign appearance" of these Chinese Notices, — called also
"guest-stars" ("etoiles notes," "ke-sing," as it were
foreigners of strange physiognomy), and from which the ob-
servers themselves had distinguished and separated comets
with tails, — included, it is true, some tail-less comets, as
well as non-moving new stars, properly so-called ; but an
important though not infallible criterion was implied
by the assignment of motion in some cases (ke-sing of
1092, 1181, and 1458), and its non-assignment in others,
as well as in the occasional addition of the remark —
"the Ke-sing dissolved" (disappeared). We may also
recal here the faint, never sparkling, always mild light of
the heads of comets, ^whether with or without tails,
whereas the Chinese " extraordinary stars" are compared,
in respect to the intensity of their light, to Yenus, which
does not at all suit the character of comets, and more
especially of tail-less comets. The star we are now
speaking of (a, 134 B.C.), which appeared under the old
dynasty of Han, may, as Sir John Herschel remarks, have
been the new star of Hipparchus, which, according to
Pliny's account, induced him to draw up his list of stars.
Delambre twice calls this account " a fable," — " une
historiette" (Hist, de 1'Astr. anc. T. i. p. 290 ; and Hist.

OF THE COSMOS. — NEW STARS. 139

de FAstr. mod. T. i. p. 186). As, however, according
to Ptolemy's express statement (Almag. vii. 2, p. 13,
Halina), Hipparchus's star-list is connected with the
year 128 B.C. ; and Hipparchus, as I have already said
elsewhere, observed in Ehodes, and perhaps also at
Alexandria, between 162 and 127 B.C., there is at least
nothing to contradict the conjecture : it is very con-
ceivable that the great astronomer of Nicea might have
observed much before the time when he may have been
led to propose to himself the preparation of an actual
catalogue. Pliny's expression — " suo sevo genita," refers
to his whole life. When Tycho Brahe's star appeared, in
1572, the question was much debated whether it should
be regarded as belonging to the class of new stars or to
that of comets without tails. Tycho Brahe himself was
of the first opinion (Progymn. p. 319 — 325). The
words " ej usque motu ad dubitationem adductus" might,
indeed, lead us to think of a faint or tail-less comet, but
the rhetorical style of Pliny permits every degree of
indefiniteness in expression.

b. Appeared between a Herculis and a Ophiuchi, in
December, A.D. 123, according to the Chinese notice,
extracted by Edouard Biot from Ma-tuan-lin. (A new
star is also said to have appeared under Hadrian, in
130. A.D.)

c. A singular very large star. The notices of this and
of the three following stars are also taken from Ma-tuan-
lin. It appeared on the 10th of December, A.D. 173,
between a and j8 Centauri, and disappeared at the end of
eight months, having shown the five different colours one
after another; — Edouard Biot says, in his translation,

140 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

"successively" (" successivernent") . Such an expression
might almost lead us to infer a series of colours like those
of the Tychonian Star before spoken of; but Sir John
Herschel (I believe more correctly) regards it us a
description of coloured scintillation (Outlines, p. 563), as
Arago has interpreted an almost similar expression of
Kepler's, relatively to the new star, in 1604, in Ophiuchus
(Annuaire pour 1842, p. 847).

d. Shone from March to August, 369.

e. Between X and 0 in Sagittarius. In the Chinese
Notices it is expressly remarked — " where the star
remained without motion from April to July, 386."

f. A new star near a Aquilse shone forth in the
time of the Emperor Honorius in 389, with the bright-
ness of Yenus, as is related by Cuspinianus : three
weeks afterwards it disappeared without leaving any
trace. (27<>)

g. March, 393 in the tail of the Scorpion; from
Ma-tuan-lin's notices.

h. The year 827 is doubtful ; what is more certain is the
epoch of the first half of the 9th century, in which, under
the government of the Caliph Al-Mamun, the two cele-
brated Arabian Astronomers Haly, and Giafar Ben-
Mohammed Albumazar, observed at Babylon a new star
whose light is said " to have equalled that of the moon- in
her quarters !" This cosmical event also belongs to the
constellation of Scorpio. The star disappeared after an
interval of only four months.

i. The appearance of this star, which is said to have
shone forth in the reign of the Emperor Otho the Great
in the year 945, as well as that of the star of 1264, both

OF THE COSMOS. NEW STARS. 141

rest solely on the testimony of the Bohemian astronomer
Cyprianus Leovitius , who declares that he took the in-
formation from a manuscript chronicle, and who calls
attention to the circumstance that both phenomena • (in
the years 945 and 1264) took place between the con-
stellations of Cepheus and Cassiopeia, quite close to the
Milky Way, and at the very place where the Tychonian
star appeared in 1572. Tycho Brahe (Progymn. p. 381
and 709), defends the trustworthiness of Cyprianus
Leovitius against Pontanus and Camerarius, who surmised
.a confusion with long-tailed comets.

k. According to the testimony of the monk of St. Galle,
Hepidannus, (who died in the year 1088, and whose
annals extend from 709 to 1044), a new star, of unusual
magnitude and dazzling brightness (oculos verberans),
was seen in the most southern part of the heavens in the
sign of Aries : it appeared near the end of the month of
May 1012, and contiuued to shine for three months.
It varied in a wonderful manner, sometimes appearing
larger, sometimes smaller, and sometimes not being seen
at all. "Nova stella apparuit insolitse magnitudinis,
aspectu fulgurans, et oculos verberans non sine terror e.
Qua? mirum in modum aliquando contractior, aliquando
diffusior, etiam extinguebatur interdum. Yisa est autem
per tres menses in intimis finibus Austri, ultra omnia
signa quse videntur in ccelo;" (see Hepidanni, Annales
breves, in Duchesne, Historic Francorum Scriptores, T. iii.
1641, p. 477 ; compare also Schnurrer, Chronik der
Seuchen, Th. I. S. 201. More recent historical criticism
has, however, preferred to the manuscript used by Duchesne
and Goldast, which places the phenomenon in 1012,

142 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

another which gives a difference of dates, placing it six
years earlier, or in 1006, (see Annales Sangallenses
majores in Perfcz, Monumenta Germanise historica
Scriptorum, T. i. 1826, p. 81). The authorship of the
supposed writings of Hepidannus has also been rendered
doubtful by recent investigations. The strange pheno-
menon of variability has been called by Chladni the
" conflagration and destruction of a fixed star." Hind,
(Notices of the Astron. Soc. Yol. viii. 1848, p. 156)
conjectures, that the star of Hepidannus may be identical
with the star which Ma-tuan-lin marks as having been
seen in China in February 1011, in Sagittarius, between
a and (j>. But in such case Ma-tuan-lin must have been
mistaken not only in the year, but also in the constellation
in which the star appeared.

/. End of July 1203, in the tail of the Scorpion.
According to the Chinese notice, " a new star of a blueish
white light, without any luminous nebulosity, resembling
Saturn (Edouard Biot, in the Connaissance des temps
pour 1846, p. 68).

m. Another Chinese observation from Ma-tuan-lin,
whose astronomical Notices, with the exact indication of
the positions of the comets and fixed stars, reascend to
613 years B. c.f or to the time of Thales and the
Expedition of Colseus of'Samos. The new star appeared
in the middle of December, 1230, between Ophiuchus
and the serpent. It " dissolved away" at the end' of
March 1231.

n. Is the star whose appearance in 1264 is mentioned
by the Bohemian astronomer, Cyprianus Leovitius, (see
the star previously referred to, i, 945). At the same

OF THE COSMOS. — NEW STARS. 143

time (July 1264) there appeared a great comet, whose
tail extended over half the sky, and which therefore could
not be confounded with the star described as having shone
forth between Cepheus and Cassiopeia.

o. The star of Tycho Brahe, of the llth of November
1572, in Cassiopeia's chair; B. A. 3° 26'; Decl. 63° 3'
(for 1800).

p. February 1578, from Ma-tuan-iin. The con-
stellation in which the star appeared is not given ; but
the intensity and radiation of its light must have been ex-
traordinary, since the Chinese notice has appended to it a
note, saying " a star as great as the sun \"

q. ] st of July 1 584, not far from IT Scorpii ; a Chinese
observation.

r. The star 34 Cygni, according to Bayer. Wilhelm
Janson, the distinguished geographer, who for some time
observed with Tycho Brahe, first had his attention arrested
by the new star in the breast of the Swan, (at the com-
mencement of the neck), as an inscription upon his
celestial globe testifies. Kepler being prevented, both by
his journeys and by the want of instruments after Tycho
Brahe's death, did not begin to observe it until two
years later, and (which is the more surprising, as the star
was of the 3rd magnitude) he even was not until then
aware of its existence. He says : " Cum mense Majo anni
1902 primum litteris monerer de novo Cygni phse-
nomeno ..." (Kepler de Stella nova tertii honoris in
Cygno 1606, appended to the work de stella nova in
Serpent, p. 152, 154, 164, and 167). In Kepler's me-
moir it is never said (as it has often been in more modern
writings) that the star in the Swan, on its first appearance,

144 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

was of the 1st magnitude. Kepler even calls it parva
Cygni stella, and everywhere describes it us of the 3rd
magnitude. He determines its position in E. A. 300°46' ;
Decl. 36°52': (therefore for 1800) E. A. 302°36';
Decl. + 37°27'). The star decreased in brightness, espe-
cially after 1619, and disappeared in 1621. Dominique
Cassini (see Jacques Cassini, Elemens d'Astr. p. 69) saw
it again attain the 3rd magnitude in 1655, and then dis-
appear. Revelius observed it again in November 1665 :
at first very small, then larger, but without reattaining
the 3rd magnitude. Between 1677 and 1682 it was
already only of the 6th magnitude, and so it has re-
mained. Sir John Herschel places it in the list of
" variable" stars, but Argelander does not.

«. Next to the star in Cassiopeia, in 1572, the new star
which has gained the greatest celebrity is that which ap-
peared in Ophiuchus in 1604. (E. A. 259° 42', and South
Decl. 21° 15' for 1800). With each of these two stars
a great name is connected. The star in the right foot of
Ophiuchus was first seen, not by Kepler himself but by
his pupil, the Bohemian John Bruno w ski, on the 10th
of October 1604 ; being then " brighter than any star of
the first magnitude, larger than Jupiter and Saturn, but
not so large as Venus." Herlicius claims to have
observed it on the 27th of September. Its brightness
was inferior to that of the Tychonian star of 1572, nor
was it seen, like the latter, in the day-time ; but its scin-
tillation was much stronger, and especially excited the
astonishment of all observers. As sparkling is always
connected with dispersion of colour, much is said of its
coloured and continually changing light. Arago ( Annuaire

PORTION OF THE COSMOS. — NEW STARS. 145

pour 1834, p. 299-301 ; and Ann. pour 1842, p. 345-
347), has already called attention to the fact, that Kepler's
star did not change colour after long intervals like the
Tychonian star, which was first white, then yellow, red,
and again white. Kepler says decidedly, that his star, as
soon as it had risen above terrestrial vapours, was white.
If he speaks of the colours of the rainbow, it is in order to
give a clear idea of the coloured scintillation, — " exemplo
adamantis multanguli, qui Solis radios inter convertendum
ad spectantium oculos variabili fulgore revibraret, colores
Iridis(stella nova inOphiucho) successive vibratu continue
reciprocabat." (De Nova Stella Serpent., p. 5 and 125.)
In the beginning of January 1605, the star was still
brighter than Antares, but not so bright as Arcturus.
At the end of March of the same year it was described as
of the 3rd magnitude. The proximity of the sun prevented
all observations for four months. Between February and
March 1606 it disappeared, without leaving any trace.
The inaccurate observations of the "great changes of
position of the new star" of Scipio Claramontius and the
geographer Blaeu or Blaew, as Jacques Cassini has already
remarked (Elem. d'Astron. p. 65), scarcely deserve to be
mentioned, as they have been refuted by the more certain
observations of Kepler. The Chinese notices of Ma-tuan-lin
speak of a phenomenon which, in point of time and of
position, has some resemblance to the appearance of the
new star in O^hiuchus. On the 30th of September, 1604,
there was seen in China, not far from TT Scorpii, a reddish
yellow (globe-large) star. It shone in the South West
until November of the same year, when it became in-
visible. It appeared on the 14th of January, 1605, in the

VOL. III. L

146 SPECIAL RESULTS IN THE URANOLOGICAL

South East, but "darkened" a little in March 1606.
(Connaissance des temps pour 1846, p. 59) . The locality,
TT Scorpii, might easily have been confounded with the
foot of Ophiuchus, but the expressions South West and
South East, the reappearance, and the circumstance of
no mention being made of the final complete disappearance
of the star, leave the identity doubtful.

/. Also from Ma-tuan-lin's notices: a star of con-
siderable magnitude, seen in the South West ; all more
circumstantial details are wanting.

u. Discovered by the Carthusian Monk Anthelme, on
the 20th of June, 1670, in the head of Vulpes (R A.
294° 27'; Decl. 26° 47'), not far from 0 Cygni. When
it first shone out it was not of the 1st but of the 3rd
magnitude. It disappeared at the end of three months,
but shewed itself on the 17th of March, 1671, being then
of the 4th magnitude. Dominique Cassini observed it
diligently in April 1671, and found its light very variable.
The new star was expected to have returned to its
original brightness at the end of about ten months, but
it was sought in vain in February 1672, and did not
appear until the 29th of March in that year, and then
only of the 6th magnitude, and has never been seen since.
(Jacques Cassini, Elemens d' Astronomic, p. 69-71.)
These phenomena induced Dominique Cassini to seek for
stars never before seen (by him !). He states that he
found 14 such stars, of the 4th, 5th, and 6th magnitudes
(8 in Cassiopeia, 2 in Eridanus, and 4 near the North
Pole) . From the absence of precisely assigned positions,
and as, moreover, like those found by Maraldi between
1694 and 1709, they are in other respects more than

PORTION OP THE COSMOS. — NEW STARS. 147

doubtful, I do not include them in the present list.
(Jacques Cassini, Elem. d'Astron. p. 73-77; Delambre,
Hist, de 1'Astr. mod. T. ii. p. 780.)

v. Since the appearance of the new star in Vulpes,
178 years had passed without any similar phenomenon
having presented itself, although in this long interval the
heavens had been most carefully examined by the combi-
nation of a more diligent use of telescopes, and comparison
with improved star-catalogues. On the 28th of April,
184»8, in the private Observatory of Mr. Bishop (South
Villa, Regent's Park), Mr. Hind made the important
discovery of a new star of the 5th magnitude in Ophiuchus,
of a reddish yellow colour : E. A. 16h. 50m. 59s. ; South
Decl. 12° 39' 16" for 1848. In the case of no other
newly-appeared star have the novelty of the phenomenon
and the invariability of position been more certainly and
accurately shown. It is now (1850) barely of the llth
magnitude, and, according to Lichtenberg's diligent ob-
servation, is probably near its time of vanishing. (Notices
of the Astr. Soc. Vol. viii. pp. 146 and 155-158.)

The above enumeration and description of new stars
which have appeared and disappeared within the last 2000
years are perhaps somewhat more complete than any which
have been given previously. It may justify some genera)
considerations. We distinguish three kinds of phenomena :
— new stars, which suddenly shine forth, and vanish again
after a greater or less interval of time; — stars whose brightness
is subject to an already determinable periodical variability ; —
and stars which, like r\ Argus, show at once an extraordinarily
increasing and an irregularly varying brightness. All these

148 SPECIAL RESULTS IN THE URANOLOGICAL

three phenomena are probably intimately allied. The new
star in Cygnus (1600), which, after entirely disappearing,
(to the unassisted eye, it must be remembered), reappeared
and remained as a star of the 6th magnitude, leads us to
recognise the affinity between the two first kinds of celestial
phenomena. The celebrated Tychonian star of 1572 was
believed, while its light still shone, to be identical with the
new star of 945 and ]264. The period of 300 years sur-
mised by Goodricke (the intervals between the epochs of the
phenomena, which are perhaps not very certain, are 319 and
308 years), is reduced by Keill and Pigott to 150 years.
Arago (271) has shewn how improbable it is that Tycho Brahe's
star (1572) should belong to the class of periodically varying
stars. Nothing as yet would appear to justify our regarding
all newly appeared stars as variable in periods of long, and
therefore unknown, duration. If, for example, we regard the
self-luminosity of all the suns in the firmament as the
results of electro-magnetic processes in their respective
photospheres, we may (without assuming local and tem-
porary condensations of the " celestial air," or the intervention
of cosmical clouds) imagine this luminous process to take
place in various manners, either once only or periodically,
and either regularly or irregularly in respect to the time of
recurrence. The electric luminous processes of our ter-
restrial globe, whether presenting themselves to us as thunder-
storms in the atmosphere, or as polar effluxes, with much
seemingly irregular variability, do yet often shew also a
certain periodicity dependent on the seasons of the year and
the hours of the day. We may even often trace this peri-
odicity in the formation, for several successive days, and in
an otherwise perfectly serene sky, of small clouds at the same

PORTION OF THE COSMOS. NEW STARS. 149

part of the heavens, as is shewn by the frequently recurring
failure in observations of the culmination of particular stars.

The circumstance that almost all have shone forth at first
with great intensity of light as stars of the first magnitude,
and even scintillating more brilliantly, and that they are
not seen (by the naked eye at least) to increase gradually in
brightness, appear to me peculiarities well deserving of
regard. Kepler (272) attended so much to this as a crite-
rion, that he confuted the vain pretension of Antonius Lau-
rentinus Politianus, who claimed to have seen the star ill
Ophiuchus (1604) before it had been seen by Brunowski, by
the fact of Laurentinus having said — " Apparuit nova stella
parva, et postea de die in diem crescendo apparuit lumine
flon multo inferior Venere, superior Jove." Only three
stars are known (and these may be viewed, therefore, as ex-
ceptional instances) which did not shine forth at first as
stars of the first magnitude : viz. two of the 3rd magnitude,
one in Cygnus in 1600, and one in Vulpes in 1670 ; and
Hind's new star of the 5th magnitude in Ophiuchus in 1848.

It is much to be regretted, as we have already remarked,
that in the long interval of 178 years which have elapsed
since the invention of the telescope, only 2 new stars have
been seen ; whereas these phenomena have been sometimes
so comparatively frequent, that at the close of the fourth
century 4 took place in 24 years, in the thirteenth century
8 in 61 years, and at the end of the sixteenth and beginning
of the seventeenth centuries (in the period of Kepler and
Tycho Brahe), 6 were observed in 37 years. In all these
numerical statements I take into account the Chinese obser-
vations of " extraordinary stars," the greater part of which
are regarded by our most distinguished astronomers as

150 SPECIAL RESULTS IN THE URANOLOGICAL

worthy of confidence. If the question be asked why, among
the new stars which have been seen in Europe, that of Kep-
ler in Ophiucus may possibly be indicated in Ma-tuan-lin's
notices, but that of Tycho Brahe in Cassiopeia (1572)
certainly is not so, I can no more explain the reason of
such a circumstance as an isolated fact, than I can explain,
for example, why the great luminous phenomenon seen in
China in February 1578 is not mentioned by European ob-
servers of that period. The difference of longitude (114°)
could only explain invisibility in a few cases. Those who
have occupied themselves with similar inquiries know ths
the circumstance of events, either in politics or in nature,
either on the earth or in the skies, not being noticed, is not
always a proof of their not having occurred ; and if we com-
pare together the three different Chinese lists of stars ii
Ma-tuan-lin, we shall also find that comets (ex. gr. those
1385 and 1495) which are contained in the one list
wanting in the others.

Older astronomers, Tycho Brahe and Kepler, as well as
modern ones, Sir John Herschel and Mr. Hind, have called
attention to the circumstance, that by far the greater num-
ber (I find four-fifths) of all the new stars which have been
described either in Europe or in China have appeared in or
near the Milky Way. If, as is more than probable, the
mild nebulous light of the annular sidereal strata of the
galaxy proceeds solely from a simple aggregation of tele-
scopic stars, Tycho Brahe's hypothesis of the formation of
new fixed stars by a globular condensation of the celestial
vapour falls to the ground. What may be effected by forces
or powers of attraction in crowded sidereal strata or star-
clusters, supposing them to rotate round central nuclei,

PORTION OF THE COSMOS. — NEW STARS. 151

cannot be here determined, and belongs rather to the my-
thical department of Astrognosy. Of the 21 new stars
enumerated in the list above given, 5 (those of 134, 393,
827, 1203, and!584) appeared in the constellation Scorpius ;
3 (those of 945, 1264, and 1572) in Cassiopeia and
Cepheus; and 4 (those of 123, 1230, 1604, and 1848) in
Ophiuchus. On one occasion, however, a new star (that of
the Monk of St. Galle in 1012) appeared very far from the
Milky Way, or in Aries. Kepler himself, who considered
the star which Fabricius described as shining forth in the
neck of the Whale in 1596, and as having disappeared from
view in October of the same year, to be really a new star,
yet gives i\s position as a reason to the contrary. (Kepler
de Stella Nova Serp. p. 112.) Ought the comparative fre-
quency of these phenomena in the same constellations to
lead us to infer that, in certain directions in space, for ex-
ample, in those in which we see the stars of Scorpius and
Cassiopeia, the conditions of this kindling or beaming forth
are peculiarly favoured by local conditions or relations?
Are there situated in these directions rather than in any
others such celestial bodies as are peculiarly adapted for
explosive luminous processes of short duration ?

The luminosity was briefest in the stars of the years
389, 827, and 1 0 1 2. In the star corresponding to the first
of these dates it lasted 3 weeks, in the second 4 weeks, and
in the third 3 months. On the other hand, Tycho Brahe's
star in Cassiopeia shone for 17 months, and Kepler's in
Cygnus (1600) was fully 21 years before it disappeared. It
reappeared in 1655, being then, as on its first appearance,
of the 3rd magnitude, whence it declined to the 6th; but,

152 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

according to Argelander's observations, it is not to be ranked
in the class of periodically variable stars.

The careful consideration and enumeration of vanished
stars, or stars which are supposed to have disappeared, are
important in respect to the research for the great number of
small planets which are probably belonging to our solar
system ; but notwithstanding the exactness of the modern
registration of telescopic fixed stars, and of our modern star-
maps, very great care is still required for the attainment of
full certainty and conviction, that any particular star has
actually disappeared from the heavens within any definite
period. Errors of observation, of reduction, or of the
press, (273) often disfigure the best catalogues. The disap-
pearance of a celestial body from the place where it had
certainly been seen before, may be occasioned either by its
having moved from thence, or by the luminous process on
its surface or in its photosphere being so far enfeebled, that
the luminous undulations no longer sufficiently stimulate our
visual organs. What we no longer see has not on that
account ceased to exist. The idea of the " destruction" or
the " burning out" of stars which are gradually becoming
invisible, belongs to the Tychonian period., Pliny also, in
the fine passage upon Hipparchus, asks : " Stellse an obirent
nascerenturve ?" The continual apparent change in the
Universe, such as the disappearance of what was before seen,
is not annihilation, but only the transition of material sub-
stances into new forms, or into compositions dependent on
new processes. Dark cosmical bodies may suddenly shine
forth afresh by a renewed luminous process.

OF THE COSMOS. — PERIODICALLY VARIABLE STARS. 153

Since all is in motion in the celestial canopy, and all
things are variable in space and in time, we are led by ana-
logy to conjecture, that as the fixed stars have all not merely
an apparent motion, but also a proper motion of their own, —
so also their surfaces or luminous atmospheres may be gene-
rally subject to changes, which, in the case of the greater
number of these cosmical bodies, may occur in exceedingly
long, and therefore unmeasured, and perhaps indeterminable,
periods ; while, in the case of a few, they may take place
without being periodical, as by a sudden revolution, and for
a longer or shorter continuance. The latter class of phae-
nomena, of which a remarkable example is presented in our
own days by a large star in the Ship (rj Argus), will not be
discussed in this place, where we are about to consider only
stars variable within periods which have already been inves-
tigated and measured. It is important to distinguish from
each other three great sidereal phenomena, of which the
connection has not yet been recognised : viz. variable stars
of known periodicity ; the blazing forth of what are called
new stars ; and sudden changes of light in long-known fixed
stars, which had previously always shewn a uniform inten-
sity. I propose at present to dwell exclusively on the firsts
named form of variability, of which the earliest accurately
observed example (1638) is furnished by Mira Ceti, a star
in the neck of the Whale. David Fabricius, a minister of
the church in East Friesland, and the father of the disco-
verer of the solar spots, had, it is true, already observed this
star as of the 3rd magnitude, on the 13th of August, 1596,
and had noticed its disappearance in October of the same
year. But the alternately recurring change of light, or the
periodical variability of the star, was not discovered until

154 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

forty-two years later, by a Professor of Praneker, Johann
Phocylides Holwarda. This discovery was followed in the
same century by that of two other variable stars : /3 Persei
(1669), described by Montanari, and x Cygrii (1687), de-
scribed by Kirch.

The increased number of stars of this class which have
been observed since the beginning of the present century,
and the irregularities which have been remarked in their
periods, have excited in the highest degree the interest which
is taken in this very complicated group of phsenomena.
Erom the difficulty of the subject, and my earnest desire that
in this work the numerical elements, as the most important
fruit of all observation, should be given as they are afforded
by the most recent investigation, and according to the actual
state of our knowledge, I have requested the kind aid of
the astronomer who, among our cotemporaries, has devoted
himself with the greatest activity and the most brilliant suc-
cess to the study of periodically varying stars. I laid before
my kind friend Argelander, Director of the Astronomical
Observatory at Bonn, in the fullest confidence, the doubts
and questions to which my own inquiries had given occa-
sion ; and I am indebted solely to his manuscript commu-
nications for what follows, great part of which has not yet
been otherwise published.

The greater number of variable stars are red or reddish,
but by no means all. So, for example, besides 0 Persei
(Algol in the head of Medusa), 0 Lyrse and e Aurigae have
also white light. 77 Aquilse is somewhat yellowish; and so,
in a still less degree, is £ Geminorum. The statement for-
merly made, that some variable stars, and particularly Mira
Ceti, were redder while their brightness was diminishing than

OF THE COSMOS. — PERIODICALLY VARIABLE STARS. 155

while it was increasing, appears unfounded. Whether in the
double star a Herculis, in which Sir William Hershchel calls
the large star red, and Struve calls it yellow and its compa-
nion dark-blue, this small companion which is estimated from
the 5th to the 7th magnitude, be itself also variable, appears
very problematical. Struve (274) himself says only "suspicor
minorem esse variabilem." Variability is by no means
attached to redness of colour. There are many red, and
some very red, stars, as Arcturus and Aldebaran, in which,
hitherto, no variation has ever been observed ; and the ex-
istence of any variability in a star in Cepheus (No. 7582 of
the Catalogue of the British Association), — which, on account
of its extraordinary redness, was called by William Herschel,
in 1782, the Garnet — is more than doubtful.

It is difficult to say exactly what ought to be regarded
as the whole known number of periodically variable stars,
because the periods which have already been deduced are of
very unequal degrees of certainty. The two variable stars
in Pegasus, as well « Hydrse, e Aurigas, and a Cassiopeise,
have not the same certainty as Mira Ceti, Algol, and
£ Cephei. In drawing up a table, therefore, the question
arises, what degree of certainty is to be regarded as suffi-
cient. As will be seen in the general table at the close of
this investigation, Argelander reckons the number of satis-
factorily determined periods at only 24. (275)

We have seen that the phsenomenon of variability belongs
to some white stars as well as to red ones, and it is also
found to exist in stars of very different magnitudes : for
example, in one star of the 1st magnitude, a Orionis; in
Mira Ceti, a Hydrse, a Cassiopeise, and # Pegasi, all of the
2nd magnitude ; 0 Persei, 2' 3 magnitude ; and in rj Aquilse
and £ Lyrse, 3*4 magnitude. There are also, and in much

156 SPECIAL RESULTS IN THE URANOLOGJCAL PORTION

greater number, variable stars of the 6th to the 9th mag-
nitudes, as the Variabiles, Coronse, Yirgiuis, Cancri, and
Aquarii. The maximum of the star x Cygni undergoes
great fluctuations.

That variable stars are very irregular in their periods had
long been known ; but that in the midst of tin's apparent ir-
regularity their variations are yet subject to definite laws,
has for the first time been made out by Argelander. He
hopes to demonstrate the truth of his views in this respect
in detail in an extensive treatise devoted expressly to the
subject. He now considers that two perturbations in the
period of ^ Cygni, one of 100 and the other of 8' 5 single
periods, are more probable than one of 108. Whether such
disturbances originate in alterations in the luminous process
going on in the atmosphere of the star, or in the period of
revolution of a planet revolving round the fixed star or sun
X Cygni, and affecting the form of its photosphere by at-
traction, remains indeed still uncertain. The greatest ir-
regularities in the variation of lustre are certainly presented
by the star " Variabilis Scuti" in Sobieski's Shield, as this
star sometimes diminishes from 5*4m. down to 9m. and
once, according to Pigott, disappeared entirely at the end of
the last century. At other times its fluctuations have only
been between 6 -5m. and 6m. The maximum brightness
observed in % Cygni has varied between 6*7m. and 4m.,
and that of Mira, between 4m. and 2*lm. On the
other hand, 3 Cephei has shewn in the length of its periods
an extraordinary degree of regularity, greater than in any
other variable star, as has appeared by 87 minima observed
between the 10th of October, 1840, and the 8th of January,
1848, and others still more recent. In e Aurigae the alte-
ration of brightness, (276) as found by an indefatigable ob-

OF THE COSMOS. — PERIODICALLY VARIABLE STARS. 157

server, Heis at Aix la Chapelle, is only from the 3'4m. to
the 4*5 magnitude.

Mira Ceti shews great differences of maximum brightness :
for example, on the 6th of November, 1779, it was only a
little inferior to Aldebaran, and it has not infrequently been
brighter than stars of the 2nd magnitude ; whilst at other
times it has not even attained the brightness of S Ceti, which
is of the 4th magnitude. Its mean brightness is equal • to
that of y Ceti (3rd magnitude). If we represent the light
of the faintest star visible to the naked eye by 0, and that of
Aldebaran by 50, then Mira has fluctuated, in its maximum,
between 20 and 47. Its probable brightness would be ex-
pressed by 30, and it is oftener below than above this limit :
when it exceeds it, however, the excess is much greater in
amount than is the defect when it falls below it. No de-
cided period in these oscillations has yet been discovered, but
there are indications of a period of 40, and of one of 1 60 years.

The periods of variation differ in different stars as much
1 : 250. The period of ft Persei of 68 hours 49 minutes is
unquestionably the shortest, supposing that of Polaris, of
less than 2 days, not to be confirmed. Next to ft Persei
follow successively $ Cephei (5d. 8h. 49m.), 77 Aquilae
(7d. 4h. 14m.), and £ Geminorum (lOd. 3h. 85m.) The
variable stars of which the period has the longest duration are :
30 Hydrse Hevelii, 495 days ; x Cygni, 406 days ; Yariabilis
Aquarii, 388 days ; Serpentis S. 367 days ; and Mira Ceti,
332 days. In several variable stars it is certain that the
light increases more rapidly than it decreases : this phe-
nomenon shews itself in the most striking manner in
£ Cephei. Other stars have equal times of increasing and
decreasing light (ex. gr. ft Lyrse) . A difference in this
respect is sometimes found in the same star. As a general

158 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

rule, Mira Ceti (like 8 Cephei) increases faster 'than it
decreases ; but the contrary has also been observed.

In regard to periods which are themselves subject to a
periodical variation, we find such decidedly in Algol,
Mira Ceti, and p Lyrse, and with much probability in
x Cygni. The decrease of the period of Algol is now
undoubted. Goodricke did not find it, but Argelander has
done so, having in 1842 been able to compare above 100
well-assured observations, of which the extremes are above
58 years apart, comprising 7600 periods. (Schumacher's
Astr. Nachr. No 472 and 624.) The decrease of duration
becomes more and more sensible. (277) For the periods of
maximum in Mira (taking in the maximum of brightness
observed by Fabricius in 1596), Argelander has given a
formula (278) by which all the maxima can be so deduced
that the probable error in a mean period of 33 Id. 8h. does
not exceed 7 days, whereas on the assumption of a uniform
period it would be 15 days.

The double maximum and minimum of /3 Lyrae, in each
of its periods of almost 1 3 days, were already very correctly
recognised in 1784 by the discoverer Goodricke, but have
been placed still more beyond doubt by the most recent ob-
servations. (279) It is worthy of notice, that this star attains
the same degree of brightness in both its maxima, but at its
principal minimum it is half a magnitude less than at its
secondary minimum. From the earliest discovery of the
variability of ft Lyrse its period was probably lengthening,
but more and more slowly, until, between 1840 and 1844,
the period ceased to increase, and has since decreased. We
find something similar to the double maximum of ft Lyrse in
3 Cephei ; it has so far an inclination to a second maximum
that the decrease of light does not proceed uniformly, but,

OF THE COSMOS. — PERIODICALLY VARIABLE STARS. 159

after having been at first rapid, comes after some time to a
stand, or at least to a very inconsiderable degree of diminution ;
after which the decrease suddenly resumes a most rapid rate.
It is as if the attainment of a second maximum was inter-
fered with.

The question of whether there is, on the whole, more re-
gularity iu variable stars of very long than in those of very
short periods, is one difficult to answer. The deviations
from a uniform period can only be taken relatively, i. e. in
parts of the period itself. In order to begin with long
periods, x Cygni, Mira Ceti, and 30 Hydrse, must be first
considered. In x Cygni, the deviations from the most pro-
bable period, on the assumption of a uniform variability
(406-0634 days), is as great as 39'4 days. Even though a
part of this may be ascribed to errors of observation, yet
there will still certainly remain from 29 to 30 days, or -^th
of the whole period. In Mira Ceti, (28°) in a period of
331*340 days, the deviations extend to 55'5 days, even if we
leave out of the account the observations of David Fabricius.
If, on account of errors of observation, we reduce the esti-
mation to 40 days, we obtain a quotient of -|-th, or, as com-
pared with x Cygni, a deviation almost twice as great. In
30 Hydrse, which has a period of 495 days, the deviation is
certainly still greater, perhaps amounting to £th. It is only
within a few years, since 1840 and still later, that the
variable stars with very short periods have been observed
perseveringly and with due precision ; so that, in regard to
them, the question we are speaking of is still more difficult
of solution. As far, however, as experience hitherto can en-
lighten us, the deviations would appear to be less considerable.
In 17 Aquilse (Period 7d.4h.) they are only -^ or -p^-th of the
whole period j in £ Lyra (Period 12d. 21h.) only -^ or

160 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

but as yet this investigation is still subject to many uncer-
tainties in the comparison of long and short periods. Of
#Lyrse, from 1700 to 1800 periods have been observed; of
Mira Ceti, 279 ; of x Cygni, only 145.

The question which has been asked, whether stars which
have long shewn themselves variable in regular periods
cease to be so, would appear to require to be answered in
the negative. If among the persistently varying stars there
are some which shew sometimes a very great and sometimes
a very slight degree of variability (for example, variabilis
Scuti), there would also appear to be others whose variability
is at certain times so small, that, with our limited means, we
cannot detect it. The star variabilis Coronse bor. (No.
5236 in the British Association Catalogue), of ' which
Pigott recognised the variability, and which he observed for
some time, belongs to this class. In the winter 1795-
3 7 9 6, this star was quite invisible : subsequently it reappeared,
and its alterations of light were observed by Koch. Harding
and Westphal, in 1817, found its brightness almost constant;
but, in 1824, Olbers was again able to observe its change.
Afterwards the constancy of light returned, and from August
1843 to September 1845 was observed by Argelander. At
the end of the month of September, 1845, a fresh decrease
began to take place. In October, the star was no longer
visible in the Comet- seeker : it reappeared in February 1846,
and in the beginning of June it had again attained its usual
magnitude (the 6th), which it has since retained, if we omit
the consideration of small and not very well assured fluc-
tuations. To this perplexing class of stars the one called
variabilis Aquarii also belongs, as does perhaps Janson's and
Kepler's star in Cygnus, which appeared in 1600, and which
we have already noticed among " New stars/'

OF THE COSMOS. — PERIODICALLY VARIABLE STARS. 161

_

ooo

-<-> -M **

rjl I>if5

cb

oooo

•** -^ -^ •**

VO t> O5 00

cb

tion of
eriod.

o «j. xco i-3 PCQ.*0 « O 02 t><! 02 02 G 8 « 8 *J-oqiP4Q

VOL. III.

M

162 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

Remarks : by Fr. Argelander.

Zero, in the column of minimum, denotes that the star
is then fainter than the 10th magnitude. For the sake of
indicating, in a convenient and simple manner, the smaller
variable stars, which for the most part have neither names
nor other designations, I have permitted myself to attach
letters to them ; and as the greater part of the Greek and
small Latin alphabets have been already employed by
Bayer, I have taken capital letters.

Besides the stars given in the table, there is an almost
equal number which are surmised to be variable because
different observers have assigned to them different mag-
nitudes. But as such estimations were only occasional,
and not made with great precision, and as different ob-
servers follow different principles in the estimation of
magnitudes, it seems safer not to include such stars until
a decided variation in them at different times shall have
been found by the same observer. This is the case with
all the stars given in the above table, and the fact of their
change of light is well assured, even where no determination
of its period has yet been possible. The periods assigned
rest, for the most part, on my own investigations and ex-
aminations, both of older published observations, and of
those made by myself and still unprinted which extend
over more than ten years. The exceptions will be stated
in the following notices.

In these notices the positions are for 1850, and are ex-
pressed in Eight Ascension and Declination. The often-
employed expression, gradation, signifies such a difference
of brightness as can be securely recognised, either with the

OF THE COSMOS. PERIODICALLY VARIABLE STARS. 163

naked eye, or, in stars not visible to the naked eye, with
a Fraunhofer's Comet-seeker of 24 Parisian inches focal
length. For the brighter stars above the 6th magnitude,
a gradation is about the 10th part of the difference
between two successive orders of magnitude ; for the
smaller stars, the magnitudes in ordinary use are con-
siderably closer together.

1. o Ceti, E. A. 32° 57', Decl.-3° 40'; also called
Mira, on account of its wonderful change of light, the
phenomenon having been first observed in this star. The
periodicity of the change was already recognised in the
second half of the 17th century, and Bouillaud determined
the duration of the period at 333 days ; it was also found
at the same time that this duration was sometimes longer
and sometimes shorter, as well as that the light of the
star, when at the greatest, was sometimes brighter and
sometimes fainter. This has since been perfectly confirmed.
Whether the star ever becomes quite invisible has not yet
been decided; it has sometimes been seen of the llth or
12th magnitude at the time of the minimum, and at other
times it has not been possible to see it with 3 and 4 feet
telescopes. Thus much is certain, that it is for a long
time fainter than the 10th magnitude. There are, however,
few existing observations of it at this stage ; most obser-
vations commencing only when, being of the 6th mag-
nitude, it begins to shew itself to the naked eye. From
that moment the star increases in brightness, at first ra-
pidly, then more slowly, and afterwards more rapidly.
On the mean, the time occupied by the increase of light,
from the 6th magnitude upwards, is 50 days, and by the
decrease of light, down to the same degree of brightness,

164 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

69 days; so that the star is visible to the naked eye for
an interval of about four months. This is, however, only the
mean duration of the star's visibility, which has sometimes
been augmented to five, and sometimes diminished to only
three months. So, also, the relative duration of the increase
and decrease of light is subject to great fluctuations, the
former being sometimes slower than the latter : as was
the case in 1840, when the star took 62 days to arrive at
its greatest brightness, and in 49 days decreased from
thence to invisibility to the naked eye. The shortest ob-
served duration of the increase was SO days, in 1679 ; the
longest, 67 days, in 1709. The decrease lasted longest
in 1839, when it extended over 91 days, and was shortest
in 1660, when it was only 52 days. Sometimes, at the
time of its greatest brightness, the light of the star
scarcely undergoes any sensible change in the course of
an entire month ; at other times an alteration is distinctly
perceptible at the end of a few days. Sometimes, after
the star has decreased in brightness for some weeks, a
suspension of change for several days ensues, or at least
the decrease becomes scarcely sensible : this was the case
in the years 1678 and 1847.

As already noticed, the maximum brightness is by no
means always the same. If we represent the light of th
faintest star visible to the naked eye by 0, and that of
Aldebaran, a star of the first magnitude, by 50, then the
observed maximum brightness of Mira has fluctuated
between 20 and 47, i. e. between the brightness of stars
of the 4th and of the 1st to the 2nd magnitudes : the
mean brightness is 28, or that of the star y Ceti. The
duration of the period has been almost even more irregular :

Of THE COSMOS. PERIODICALLY VARIABLE STARS, 165

in the mean it is 331 days 20 hours, but its fluctuations
are as great as a month ; for the shortest time which has
been known to elapse from one maximum to the next was
only 306, and the longest was 367 days. These ir-
regularities become still more striking if we compare the
epochs of the actually observed maxima of light with the
results which would be obtained by calculating them upon
the assumption of a uniform period. The differences
between calculation and observation amount to 50 days ;
tind these differences are found to be nearly the same and
on the same side for several successive years. This cir-
cumstance clearly indicates that the luminous phenomena
are affected by a perturbation of long period. More exact
•calculation has proved, however, that one perturbation does
not suffice, and 'that we must assume several, wLi-eh may
indeed proceed from the same cause, one returning after
1 1, a second after 88, a third after 176, and a fourth
after 264 single periods. According to these assumptions
we may derive a formula of sines (278) with which the se-
veral maxima now shew a very near accordance, although
there still remain deviations which cannot be explained
by errors of observation.

2. ft Persei, Algol; E, A, 44° 36'; DecL + 400 22'.
Although Geminiano Montanari first remarked the varia-
bility of this star in 1667, and although it was also ob-
served by Maraldi, yet it was Goodricke who, in 1782,
first made out the regularity of the variations. The
reason of this may very probably be, that this star does
not increase and decrease gradually, as do most of the
other variable stars, but for 2 days and 13 hours shines
constantly with the same brightness (2'8 m,), and only

166 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

shews a less degree of light for between 7 and 8 hours,
in the course of which it descends to the 4th magnitude.
The decrease and increase of brightness are not quite
regular, but, proceeding more rapidly near the minimum,
enable the moment of least brightness to be determined
to within 10 or 15 minutes. It is remarkable that, after
increasing in light for the space of an hour, it remains for
about the same time at almost exactly the same degree of
brightness, after which it again begins to increase sensibly.
Hitherto the length of the period has been supposed to
be perfectly uniform, and Wunn was able to represent all
the observations well, by taking it at 2d. 21h. 48m. 58*5s.
A more exact calculation, with an interval almost twice as
great as that which Wurm had at his command, has,
however, shewn that the period is becoming gradually
shorter. In 1784 it was 2d. 20h. 48m. 59'4s., and in
1842 only 2d. 20h. 48m. 55'2s. The latest observations
render it very probable, also, that this decrease of the
period is taking place more rapidly than before, so that,
for this star also, there will in time be derived a formula
of sines for the perturbation of the period. The present
shortening of the period might be explained by the as-
sumption, that Algol either approaches us nearer every
year by about 2000 geographical miles, or recedes from us
that quantity less each year than the preceding ; as in
such case the light would reach us each year as much
sooner as the diminution of the period requires, i. e.
about 12 thousandth parts of a second. Should this be
the true reason, there would naturally be deduced in time,
a formula of sines.

3. x Cygni, E. A. 269° 12'] DecL + 320to 32'. This

OF THE COSMOS.— PERIODICALLY VARIABLE STARS. 167

star also shews nearly the same irregularities as Mira :
the deviations of the observed maxima from the results
calculated on the supposition of a uniform period are as
rrluch as 40 days, but are very greatly diminished by the
introduction of a perturbation of 8 J single periods, and
another of 100 such periods. At its maximum, of
brightness, this star reaches, on the mean, a faint 5m., or
one gradation brighter than the star 17 Cygni. But
here also the fluctuations are very considerable, and have
been observed from 13 gradations below the mean to 10
above it. If the star never exceeded the weaker maximum,
it would be altogether invisible to the naked eye, whereas,
in 1847, it could be seen for fully 97 days without a
telescope ; the mean duration of its visibility is 52 days,
of which 20 days in the mean are occupied by the increase,
and 32 by the decrease.

4. 30 Hydra Hevelii, E. A. 200° 23' ; Decl. 22° 30'.
Of this star, which from its position in the heavens can
only be seen for a short time in each year, all that can yet
be said is, that both its period and its maximum brightness
are subject to great irregularities.

5. Leonis E=420 Mayeri; E. A. 144° 52', Ded.+
12° 1'. This star has often been confounded with the
neighbouring stars 18 and 19 Leonis, and has on that
account been very little observed ; it has, however, been
sufficiently so, to shew that the period is rather irregular.
The maximum brightness also appears to fluctuate through
some gradations.

6. n Aquilae, also called 77 Antinoi; E. A. 296° 12';
Decl-f 0° 37'. The period of this star is tolerably
uniform, 7d. 4h. 53m. 53s.; but yet the observations

168 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

shew, that in longer intervals of time small fluctuations
occur ; not, however, exceeding about 20 seconds. The
change of light even proceeds with so much regularity, that
hitherto no deviations have been perceptible which may
not be explained by errors of observation. At its minimum
this star is a gradation fainter than t Aquilae ; it then
increases, at first slowly, then more rapidly, and then
more slowly ; and 2d. 9h. after the minimum it attains its
greatest brightness, when it is almost three gradations
brighter than /3,but still 2 gradations fainter than 3 Aquilae.
The decrease from the maximum is less regular, for when
the star has declined to the brightness of /3, which it
reaches 1 day and 10 hours after the maximum, it alters
more slowly than before or afterwards.

7. 0 Lyra, K. A. 281° 8', Decl.-f 33° 11'; a remark-
able star, in having two maxima and two minima. At its
lowest minimum it is Jrd of a gradation fainter than
£ Lyrse ; it then rises in 3d. 5h. to its first maximum, in
which it continues to be f ths of a gradation fainter than
y Lyrse. It then sinks in 3d. 3h. to its secondary mi-
nimum, in which its brightness exceeds that of £ by 5
gradations. After 3d. 2h. more, it reaches its second
maximum, when it has again the same brightness as in the
first, and then sinks again in 3d. 12h. to its lowest mi-
nimum ; so that it passes through its whole variation of
light in 12d. 21h. 46m. 40s. This duration, however,
only holds good for the years 1840 to ]844 : before that
time the period was less; in 1784 by 2J hours, in 1817
and 1818 by more than an hour, and now there is
evidently again a shortening of the period. No doubt,
therefore, it will be possible, in the case of this star also,

OF THE COSMOS. — PERIODICALLY VARIABLE STARS. 169

to express the perturbation of the period by a formula of
sines.

8. a Cephei, E. A. 335° 54', Decl. + 57° 39'. Is of all
known stars the one which shews the greatest regularity
in all respects. The period of 5d. 8h. 47m. 39'5s. re-
presents all observations from 1784 to the present time,
to within the limits of errors of observation, which errors
may also suffice for the explanation of the small differences
which shew themselves in the march of the variations of
light. At its minimum the star is -f-th of a gradation
brighter than e Cephei, and at its maximum it is equal to e
of the same constellation ; it takes Id. 15h. to rise from
the minimum to the maximum, and more than double that
time, i.e. 3d. 18h. to return to the minimum ; after which,
however, it scarcely alters at all for eight hours, and only
quite inconsiderably for an entire day.

9. a Herculis, K A. 256° 57', Decl. + 14° 84'. A very
red double star, whose variation of light is irregular in
every respect. Often it scarcely alters at all for months,
at other times it is five gradations brighter at its maximum
than at its minimum, and hence the period is also still
very uncertain. The discoverer assumed it at 63 days ;
I began by taking it at 95, until a careful calculation of
all my observations during seven years gave me the period
assigned in the text. Heis thinks that he can represent
the observations by a period of 184d. 9h., having two
maxima and two minima.

10. CoromeK, E. A. 235° 36', Decl. + 28° 37'. This
star is only occasionally variable ; the assigned period was
calculated by Koch from his own observations, which are
unfortunately lost.

170 SPECIAL RESULTS IN THE TJRANOLOGICAL PORTION

11. Scuti E., A. E. 279° 52', Bed.— 5° 5V. Sometimes
the fluctuations of the light of this star are comprised
within a few gradations, whilst at other times it sinks from
the 5th to the 9th magnitude. It has been still too little
observed to permit us to decide whether any determinate
rule prevails in these alterations. The length of the
period is also subject to considerable fluctuations.

12. Virginis E., E. A. 187° 43', Ded. + 7° 49'. Its
period and maximum brightness are tolerably regular, yet
deviations occur which appear to me too large to be as-
cribed solely to errors of observation.

13. Aquarii E, E. A. 354° 11', Decl.-16° 6'.

14. Serpentis E, E. A. 235° 57'] Ded. + l5° 36'.

15. Serpentis S, E. A. 228° 40', Decl.-f 14° 52'.

16. Cancri E, E. A. 122° 6', Bed. + 12° 9'.
Eespecting these four stars, observations of which are

exceedingly scanty, there is little more to be said than is
given in the table.

17. a Cassiopeia, E. A. 8° 0', Decl. + 55° 43'. This
star is very difficult to observe ; the difference between
maximum and minimum only amounts to a few gradations,
and is moreover as variable as is the length of the period.
The very different results assigned for it are attributable
to this circumstance. The result which I have given re-
presents sufficiently well the observations from 1782 to
1849, and appears to me the most probable.

18. a Orionis, E. A. 86° 46', Decl. + 7° 22'. The
variation in the light of this star from the minimum to the
maximum only amounts to four gradations ; it increases
in brightness during 91 J days, and decreases during 104£:
its decrease from the 20th to the 70th day after the maxi-

OP THE COSMOS. PERIODICALLY VARIABLE STARS. 171

mum is quite insensible. Sometimes its variation of
light is still less, and scarcely noticeable. It is very red.

19. a Hydra, R. A. 140° 3', DecL-8° 1'. Is of all
variable stars the most difficult to observe, and the period
is still quite unassured. Sir John Herschel gives it at
29 or 30 days.

20. e Auriga, R. A. 72° 48', Decl. + 43° 36'. Either
the changes of light in this star are very irregular, or in
a period of several years there are several maxima and
minima : this can only be determined after a lapse of many
years.

21. fGeminorum, A. R. 103° 48', Decl.-f 20° 47'.
Hitherto this star has shewn an entirely regular
course in its changes of light. At the minimum its
brightness is half way between v and v of the same con-
stellation, and at the maximum not quite equal to A ; it
occupies 4d. 21h. in increasing, and 5d. 6h. in decreasing.

22. j3 Pegasi, R. A. 344° 7', Decl. + 27° 16'. The
period is already pretty well determined, but there is as
yet nothing to be said about the regularity or otherwise
of the variation of its light.

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

24. Cancri S, R. A. 128° 50', Decl. + 19° 34'.
There is as yet nothing to be said respecting these two

stars.

FR. ARGELANDER.
Bonn, August 1850.

In the scientific investigation of important natural phe-
nomena, whether in the telluric or in the sidereal sphere of
the Cosmos, prudence commands us not to be too hasty in

172 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

linking together phenomena whose immediate causes are
still veiled in obscurity. For this reason we willingly dis-
tinguish between newly appeared stars which have again
entirely disappeared (as the star in Cassiopeia in 1572) ;
newly appeared stars which have not disappeared again
(as the star in Cygnus, 1600) ; variable stars whose periods
have been investigated (as Mira Ceti, Algol, &c.) ; and
stars whose luminous intensity varies without our having as
yet discovered any periodicity in the variation, (as r\ Argus) .
It is not at all improbable, but it also by no means necessarily
follows, that these four kinds of phenomena (281) arise from
similar causes belonging to the photospheres of those dis-
tant suns, or to the nature of their surfaces.

As we began the description of the new stars with the
most remarkable instance of this class of celestial events, i. e.
the sudden appearance of the star of TychoBrahe, — so, guided
by the same reasons, we will begin the description of the
alteration of the light of stars, in which the periodicity of the
variation has not yet been investigated, by the still proceeding
unperiodic fluctuations of luminous intensity in the star
q Argus. This star is situated in the great and magnificent
constellation of the Ship, which is the " glory of the southern
heavens/' As early as ] 677, Halley, on his return from his
voyage to St. Helena, expressed many doubts respecting
change of light in the stars of the Ship Argo, particularly
on the shield of the prow and on the deck (aainSioK.?! and
icard<rrpwjua), whose relative order of magnitude had been
given by Ptolemy (282) ; but from the uncertainty of the star
positions of the Ancients, the many variations in the manu-
scripts of the Almagest, and the uncertain estimations of
luminous intensity, these doubts could not lead to any results.

OF THE COSMOS. VARIABLE STA11S. 173

In 1677 Halley had found r\ Argus of the 4th magnitude ;
in 1751 Lacaille found it already of the 2d. Afterwards the
star returned to its earlier fainter intensity, for Burchell,
during his residence in Southern Africa in 1811 — 1815
found it of the 4th magnitude. From 1822 to 1826
Tallows and Brisbane saw it of the 2nd magnitude ; and in
February 1827, Burchell, who was then at St. Paul in Brazil,
found it of the 1 st magnitude, and quite equal to a Crucis.
After a year it returned to the 2nd magnitude; it was
found so by Burchell in the Brazilian town of Goyaz on the
29th February, 1828, and was so entered by Johnson and
Taylor in their registers from 1829 to 1833. Sir John
Herschel at the Cape of Good Hope also estimated it from
1834 to 1837 at between the 2nd and 1st magnitude.

But on the 16th of December, 1837, when the last named
celebrated astronomer was preparing to make photometric
measurements of the numberless telescopic stars of the llth
to the 16th magnitudes which fill the fine nebula around
i) Argus, he was astonished at finding this often observed
star increased to such an intensity of light, that it almost
equalled the brightness of a Centauri, and surpassed that of
all other stars of the first magnitude except Canopus and
Sirius. It had attained the maximum of its brightness on
that occasion on the 2nd of January, 1838. It soon became
fainter than Arcturus, but still surpassed Aldebaran in the
middle of April 1838. It went on decreasing until March
1843, always continuing, however, to be a star of the 1st
magnitude, but we then find, particularly in April of the same
year, that the light began to increase again to such a degree,
that according to the observations of Mackay at Calcutta, and
of Maclear at the Cape, TI Argus became brighter than Canopus,

174 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

and even almost equal to Sirius. (283) It has retained this
degree of brightness very nearly to the commencement of the
present year. A distinguished observer, Lieutenant Gilliss,
who has the command of the Astronomical Expedition which
the Government of the United States has sent to the coast of
Chili, writes from Santiago in February 1850 : "n Argus with
its yellowish red light, which is darker than that of Mars, now
comes next to Canopus in brightness, and is brighter than
the united light of a Centauri." (284) Since the ap-
pearance of the new star in Ophiuchus in 1604, no
fixed star has brightened to such an intensity of light, and
for a continuance of now already seven years. In the 173
years (from 1677 to 1850) during which we have ac-
counts of the magnitude of this fine star, it has under-
gone eight or nine oscillations of increase and decrease.
It was a fortunate circumstance, and one which has
stimulated the persevering attention of astronomers to
the phenomenon of a great but unperiodic variability in
this star, that it should have manifested itself in the most-
striking manner during the memorable five years' expedi-
tion of Sir John Herschel to the Cape of Good Hope.

Similar variations of light which have not yet been re-
cognised as periodical have been remarked in several other
instances, both in isolated fixed stars and in double stars
observed by Struve (Stellarum compos. Mensurse microm.
p. Ixxi. — Ixxiii.) The examples which it may suffice to
cite here are founded on actual photometric estimations
and measurements made at different times by the same as-
tronomers, and not at all upon the alphabetical series in
Bayer's Uranometry. Argelander, in the treatise " de fide
Uranometrise Bayerianse," 1842, in p. 15, has shown very

OF THE COSMOS. VARIABLE STARS. 175

convincingly that Bayer did not follow the principle of
always indicating the brightest stars by the first letters ; but
that, oil the contrary, in the same star-magnitude he distri-
buted the letters in the order of position in such manner
as to pass usually from the head of the figure, in each con-
stellation, to its feet. The alphabetical order of the letters
employed in Bayer's Uranometry has long given prevalence
to a belief in changes having taken place in the light of a
Aquilse, of Castor, and of Alphard.

Struve (1838) and Sir John Herschel saw Capella increase
in light. Sir John Herschel now estimates Capella as
much brighter than Vega, whereas he formerly always
considered it fainter (285). Galle and Heis form the same
judgment from a present comparison of Capella and Vega :
Heis considers the latter star to be between five and six
gradations, or more than half a magnitude, fainter than
Capella.

The alterations in the light of some stars in the constella-
tions of the Great and Little Bear, are deserving of particular
attention. "The star »/ Ursae majoris," says Sir John
Herschel, " is now certainly the brightest of the seven bright
stars in the Great Bear, whilst in 1837 the first rank belonged
incontestably to e" This remark occasioned me to make
inquiries from Heis, who occupies himself with so much
ardour, and so extensively, with the variability of the light
of stars. He wrote to me in reply to the following effect : —
" From the mean of the observations made by me at Aix-la-
Chapelle from 1842 to 1850, I find the order of succession
thus : 1. e Ursse maj., or Alioth ; 2. « or Dubhe; 3. rj or
Benetnasch; 4. <T or Mizar; 5. |3; 6. y; 7. 3. In respect
to the differences of brightness between these seven stars, E,

176 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

a and y are nearly equal to each other ; so that, when the
atmosphere is not quite clear, their order of succession may
appear doubtful : £ is decidedly fainter than t, a, and i?.
The two stars |3 and y, both sensibly fainter than '(, are almost
equal to each other. Lastly, 3, which in old maps is given
as equal with /3 and y, is more than an entire order of magni-
tude fainter than those stars, e is certainly variable : although
usually brighter than a, I have five times in three years seen
it decidedly fainter than a. I also regard |3 Ursa3 majoris
as variable, but without being able to assign any determinate
period. Sir John Herschel, in 1840 and 1841, found /3
Ursse min. much brighter than Polaris ; whereas, in May
1846, the contrary was observed by him. He surmises
variability in /3 (286). Since 1843, I have usually found
Polaris fainter than ]3 Ursse min. ; but between October 1843
and July 1849 my registers show that, on fourteen occasions,
Polaris was seen to exceed /3 in brightness. I have repeatedly
had an opportunity of convincing myself that the last-named
star is not always equally reddish : it is sometimes more or
less yellow, and sometimes very decidedly red" (287). All
laborious investigations of the relative brightness of stars
will gain essentially in certainty, when successive arrangement
according to mere estimation shall be finally superseded by
methods of measurement founded on the progress of modern
optical science (288), and astronomers and physicists ought
not to doubt the possibility of attaining such an object.

From the probably great physical similarity of the luminous
process in all self-luminous celestial bodies (in the central
body of our own planetary system, and in the remoter suns
or fixed stars), it has long been justly pointed out, (289) how
important a bearing the periodical or non-periodical variation

OF THE COSMOS. VARIABLE STARS. 177

of light in stars may possibly have on climatology in general,
— on the history of the terrestrial atmosphere, i. e. on the
varying quantity of heat received in the course of ages by our
planet from solar radiation, — and on the condition of organic
life, and its forms of development, in different latitudes. The
variable star, Mira Ceti, changes from the 2d to the llth
magnitude, and even to entire disappearance ; and we have
just seen that 77 Argus has increased from the 4th to the
1st magnitude, and even to the brightness of Canopus, and
almost to that of Sirius. If only a very small part of such
alterations of luminous intensity and radiant heat, either in
the ascending or descending scale, should have taken place
in our Sun (and why should it be different from other suns ?),
they would have produced more powerful and even more
fearful consequences to our planet, than are required for the
explanation of all geological relations and ancient telluric
revolutions. William Herschel and Laplace were the first
who called attention to these considerations. If I thus notice
them in this place, however, it is not because I would seek
exclusively in them for the solution of the great problem of
the alterations of temperature upon our globe. It may also
have been that the primitive high temperature of the planet
due to the manner of its formation and to its consolidation, —
the radiation of heat through deep fissures or open clefts, and
veins not yet filled with metallic ores, — more powerful elec-
tric currents, — and a very different distribution of land and
sea, — may, in the earlier ages of our planet, have rendered
the distribution of temperature independent of latitude, i. e.
of position relatively to the Sun. Cosmical contemplation
ought not to limit itself by too partial a view to astrognostic
relations only.

VOL. in. N

178 SPECIAL EESULTS IN THE URANOLOGICAL PORTION

V.

PROPER MOTION OF THE FIXED STARS. — PROBLEMATICAL

EXISTENCE OF DARK BODIES. — PARALLAX. MEASURED

DISTANCE OF SOME FIXED STARS. DOUBTS CONCERNING

THE ASSUMPTION OF A CENTRAL BODY FOR THE WHOLE
SIDEREAL HEAVENS.

BESIDES variations of luminous intensity, the heaven of the
fixed Stars, in contradiction to its name, also undergoes
variation from the perpetually progressive motion of the
several stars. It has already been recalled how, without
the general equilibrium of the sidereal system being dis-
turbed thereby, no point in the entire heavens has remained
fixed, — how, of the bright stars observed by the most
ancient of the Greek astronomers, none has maintained its
position in space unaltered. In two thousand years, the
change of place, by the accumulated effects of annual proper
motion, has amounted in Arcturus, /j. Cassiopeise, arid a
double star in Cygnus to spaces corresponding to 2£, 3J,
and 6 diameters of the moon. At the end of three
thousand years, about 20 fixed stars will have altered their
place 1° arid upwards. (e9°) As the proper motions of fixed
stars which have been measured vary from ^th or '05 of a
second to 7 '7 seconds, (differing, therefore, at least in the

OF THE COSMOS. PROPER MOTION OF STARS. 179

proportion of ] : 154), it follows that the relative distances
of the fixed stars, inter se, and the configuration of the con-
stellations does not remain the same for long periods. The
Southern Cross will not always shine in the heavens in the
same form which that constellation now presents, as the four
stars of which it is composed move with unequal velocities
in different paths. How many thousand years may be re-
quired for the entire dissolution of the constellation is not
to be calculated. In relations of space and time, there is
no absolute great or small. If we would embrace in a
general view the changes which take place in the heavens,
modifying in the course of ages the " physionomic character"
of the celestial canopy, or the aspect of the firmament as
seen at a determinate point of the earth's surface, we must
enumerate, as efficient causes of such alteration, (1) the
precession of the equinoxes and the nutation of the earth's
axis, by the joint influence of which new stars arise above
the horizon, and others become invisible ; (2) the periodic
and non-periodic variations of luminous intensity in many
fixed stars \ (3) the shining forth of new stars, some few
of which have remained ; (4) the revolution of telescopic
double stars round a common centre of gravity. Amongst
these so-called fixed stars, which vary slowly and unequally
in intensity of light and in position, 20 planets, and 20
satellites belonging to five of these planets, complete their
more rapid course. Thus, besides the countless hosts of
(also, without doubt, revolving) fixed stars, there are dis-
covered up to the present time (October 1850), 40 planetary
bodies. In the time of Copernicus, and of the great improver
of the art of observation, Tycho Brahe, only 7 were known.
We might also have named here as planetary bodies almost

180 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

200 calculated comets, of which 5 are of short periods of
revolution, and interior, i. e. their paths are entirely com-
prised between those of the principal planets. During
their mostly short appearance, they, or rather those amongst
them which are visible to the naked eye, as well as the true
planets, and those bodies which have suddenly shone forth
as new stars of the first magnitude, animate, in the most
attractive manner, the already rich picture of the sidereal
heavens.

The knowledge of the proper motion of the fixed stars is
wholly connected, historically, with the advances which have
been made in the art of observing by the improvement of
instruments and of methods. It first became possible to
discover these motions when telescopes were combined with
graduated instruments, — when astronomers were able pro-
gressively to advance from certainty in respect to a minute of
arc (which Tycho Brahe first succeeded, by the most strenu-
ous endeavours, in giving to his observations in the Island
of Huen), to certainty in respect to seconds and parts of
seconds, — and when it was possible to compare together re-
sults separated by a long series of years. Such a comparison
was made by Halley, who employed in it the positions of
Sirius, Arcturus, and Aldebaran, as entered by Ptolemy in
his Hipparchian Catalogue, 1847 years before. He thought
himself justified by this comparison (1717) in announcing
the existence of a proper motion in the three above named
fixed stars. (291) The great and deserved regard which, even
long after Flamsteed's and Bradley* s observations, was paid
to the Eight Ascensions contained in Burner's Triduum,
incited Tobias Mayer (1756), Maskelyne (1770), and Piazzi
(180(1), to compare Homer's observations with later ones.(292)

OF THE COSMOS. PROPER MOTION OF STARS. 181

These comparisons led, as early as the middle of the last
century, to the recognition of the proper motion of the fixed
stars generally; but we are indebted for more exact and
numerical determinations of this class of phenomena, first to
the great work of William Herschel in 1783, founded on
Flamsteed's observations (293), and since in a far higher de-
gree to Bessel's and Argelander's comparison of Bradley' s
Star Positions for 1755 with later catalogues.

The discovery of the proper motion of the fixed stars, is
of so much the higher importance to physical astronomy,
since it has led to the recognition of the movement of
our own solar system through star-filled space, and even to
the exact knowledge of the direction of this movement.
This is a fact of which we could never have become aware,
if the progressive proper motion of the fixed stars had been
so small as altogether to escape our measurement. The
zealous endeavour to investigate the quantity and direction
of this movement, together with the parallax of the fixed
stars and their distance, by stimulating the improvement of
arc- graduation and micrometric apparatus combined with
optical instruments, has eminently contributed to the ad-
vance of observing astronomy to the point to which, (espe-
cially since 1830), it has been raised by the judicious
employment of large meridian-circles, refractors, and helio-
meters.

The quantity of proper motion which has been measured
in different stars varies, as I have remarked in the beginning
of this section, from the 20th part of a second to almost 8
seconds. The brighter stars have in many cases a less
motion than stars of the 5th, 6th, and 7th magnitudes. (294)
The 7 stars which have shewn unusually great proper

182 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

motion, are, Arcturus (1st magnitude) which has an annual
proper motion of 2"'25 ; a Centauri (1st m.), 3'x'58 (29°) ;
ju Cassiopeiee (6th m.), 3"'74; the double star Sin Eridanus
(5-4 m.) 4"-08; the double star 61 Cygni (5'6 m.), 5"-123,
the motion being recognised by Bessel in 1812 by compa-
rison with Bradley' s observations ; a star on the borders of
the constellations Cam's Yenaticus (296) and Ursus Major, No.
1830 of Groombridge's catalogue of circum polar stars (7th
m.), according to Argelander 6/7<974 ; c Indi, 7/x*74 accord-
ing to D' Arrest (297) ; 2151 PuppisN(6th m.) 7y-871. The
arithmetical mean (298) of the several proper motions of fixed
stars, taken from all the zones into which Madler has di-
vided the celestial sphere, would hardly exceed 0"'102.

An important investigation into the variability of the
proper motions of Procyon and Sirius, had in 1844 (a
short time before the commencement of his painful and
fatal illness), impressed the mind of the greatest astronomer
of our time, Bessel, with the conviction, "that stars,
whose variable motions become sensible when examined
with the most perfect instruments, are parts of systems
which are limited to spaces small in comparison with
the great distances of the fixed stars from each other."
This belief in the existence of double stars, of which one
member of the pair is supposed to be non-luminous, was so
strong in BesseFs mind (as his long correspondence with
myself testified), as to add greatly to the general interest
excited by whatever promises to enlarge our knowledge
of the physical constitution of the sidereal heavens. " The
attracting body," said he, "must be situated either very
near the star which shews the observed change of place,

OF THE COSMOS. PROBLEMATICAL DARK STARS. 183

or very near the sun. But since nothing in the motions
of our planetary system betrays the presence of an attract-
ing body of considerable mass at a very small distance, from
the sun, we are conducted back to the supposition of the
existence of such a body at a very small distance from a star.

€/ t/ «/

as the only valid explanation of an alteration in the propel
motion of the latter becoming visible in the course of
century." (299) In a letter to myself, in July 1844, (I had
sportively expressed some uneasiness at the idea of such a
ghost-world of dark stars), he said, "I do, indeed, con-
tinue in the belief, that Procyon and Sirius are both true
double stars, each consisting of one visible and one invisible
star. There is no a priori reason for regarding luminosity
as an essential property of bodies. The countless host of
visible stars clearly proves nothing against the possible
existence of an equally countless host of invisible stars.
The physical difficulty of a variation in the proper motion,
is satisfactorily met by the hypothesis of dark stars. The
simple supposition cannot be blamed, that an alteration of
velocity only takes place in obedience to a force, and that
forces act according to the Newtonian laws."

A year after BesseFs death, Fuss, at Struve's instance,
renewed the investigation of the anomalies of Procyoii and
Sirius, partly by new observations with ErteFs Meridian
Telescope at Pulkova, arid partly by reductions and com-
parison with earlier observations. Struve and Fuss (30°)
consider the result to be against BesseFs opinion. On the
other hand, a laborious inquiry, just completed by Peters
at Konigsberg, and a similar one by Schubert, the calcu-
lator employed on the North American Nautical Almanac,
support Bessel.

184 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

The belief in the existence of non-luminous stars was
already prevalent in Grecian antiquity, and especially in the
early times of Christianity. It was assumed that " among
the fiery stars which are nourished by vapours, there move
other earthy bodies which remain invisible to us." (301) The
entire extinction of new stars, particularly of those in Cas-
siopeia and Ophiuchus, so carefully observed by Tycho Brahe
and Kepler, appeared to afford a firmer support to this
notion. As it was then supposed that the first-named of
these two stars had already shone forth twice before, at
intervals of about 300 years, the idea of annihilation or
complete dissolution was not likely to find acceptance. The
illustrious author of the "Mecanique Celeste" founds his
persuasion of the existence of non-luminous masses in the
Universe on the same phenomena of 1572 and 1604.
"Ces astres devenus invisibles apres avoir surpasse Feclat
de Jupiter m£me, n'ont point change de place durant leur
apparition." (Only the luminous process in them has
ceased.) "II existe done dans 1'espace celeste des corps
opaques aussi considerables et peut-£tre en aussi grands
n ombres que les 6toiles". (302) So also Madler, in his
" Untersuchungen iiber die Fixstern-Systeme" (303) says,
" A dark body might be a central body ; it might, like our
sun, be only surrounded in its immediate vicinity by dark
bodies such as are our planets. The movements of Procyon
and Sirius pointed out by Bessel constrain (?) the assump-
tion that there are cases in which luminous bodies are
satellites to dark masses." I have already noticed that
some adherents of the emanation-theory of light supposed
such masses to be light-radiating, though at the same time
invisible from being of such enormous dimensions that the

OF THE COSMOS. — PAEALLAX OF STARS. 185

rays of light sent forth (luminous molecules) are so held
back by the force of attraction, that they cannot pass
beyond a certain limit. (304) If, as may well be assumed,
there are dark invisible bodies in space in which the process
of light-producing undulations does not take place, they
must either not fall within the circumference of our planetary
and cometary system, or they must be of very small mass,
since their presence does not manifest itself by any percep-
tible perturbations.

The investigation of the motion of the fixed stars in
amount and direction (meaning thereby both their true
proper motion, and the merely apparent motion due to the
change in the observer's place caused by the earth's motion
in her orbit), — the determination of the distance of the fixed
stars from the Sun by investigations of their parallax, — and
conjectures as to the part of space towards which our plane-
tary system is moving ; — are three problems in Astronomy
which, in respect to the means of observation which have
been successfully employed in their partial solution, are
nearly allied to each other. Every improvement, either of
instruments or of methods, applied to the advancement of
one of these difficult and complicated inquiries, has been
productive of benefit to the others. I prefer commencing
with the parallaxes, and with the determination of the
distances of some of the fixed stars, in order to complete the
account of the present state of our knowledge in reference
to single fixed stars.

As early as the beginning of the 17th century, Galileo put
forward the idea of " measuring the, doubtless very unequal,
distances of the fixed stars from the solar system" ; and even

186 SPECIAL RESULTS IN THE TJRANOLOGICAL PORTION

with great acuteness, proposed the means of finding the
parallax, not by the determination of the distance of a star
from the zenith or the pole, but " by the careful com-
parison of one star with another very near to it." Although
expressed in very general terms, this is the micrometric
method subsequently employed by William Herschel
(1781), Struve and Bessel. « Perche io non credo/'
said Galileo (305) in his third discourse (Giornata terza),
"che tutte le stelle siano sparse in una sferica superficie
egualmente distanti da un centra ; ma stimo, che le loro
lontananze da noi siano talmente varie, che alcune ve ne
possano esser 2 e 3 volte piu remote di alcune altre; talche
quando sitrovasse col Telescopic qualche picciolissima steMa
vicinissima ad alcuna delle maggiori, e che pero quella fusse
altissima, potrebbe accadere, che qualche sensibile mutazione
succedesse tra di low" The promulgation of the Coper-
nican system carried with it the grounds for requiring the
numerical assignment by measurement of the change of
direction, which the half-yearly change of place of the Earth,
in her orbit round the Sun, must produce in the apparent
position of the fixed stars. But as the angular determina-
tions of Tycho Brahe, so happily employed by Kepler,
(although, as I have already said, they might be considered
certain to one minute of arc), still did not shew any such
change arising from parallax, the Copernicans long satis-
fied themselves by replying to such requirements, that the
diameter of the Earth's orbit, (41-J- German, 165£ English
millions of geographical miles), was too small in proportion
to the exceedingly great distance of the fixed stars.

The hope of being able to discover by observation the ex-
istence of parallax, must therefore have been seen to be de-

OF THE COSMOS. — PABALLAX OF STARS. 187

pendent on the improvement of optical and measuring in-
struments, and on the possibility of determining very small
angles with certainty. So long as such certainty was only
equal to one minute, the non-detection of parallax only proved
that the fixed stars must be more distant than 3438 semi-dia-
meters of the Earth's orbit. (306) Certainty to a second in
the observations of the great Astronomer, James Bradley,
raised this lower limit to 206265 semi-diameters; and in the
brilliant epoch of the Fraunhofer instruments, it was raised,
by the direct measurement of nearly the tenth part of a
second of arc, to 2062648 semi-diameters of the Earth's
orbit. The efforts, and ingeniously devised Zenith apparatus,
of Newton's great cotemporary, Robert Hooke, in 1669, did
not conduct to the desired aim. Picard, Horrebow who
worked out Homer's rescued observations, and Elamsteed
thought they had found parallaxes of several seconds, be-
cause they confounded the proper motions of the Stars with
the effects of parallax. On the other hand, the sagacious
John Michell (Phil. Trans. 1767, Vol. Ivii. pp. 234-264),
was of opinion that the parallaxes of the nearest fixed stars
must be less than 0/x'02, and therefore " could only be recog-
nised by a magnifying power of 12000." From the very pre-
valent idea that the superior brightness of a star must always
indicate its greater proximity, stars of the first magnitude,
Yega, Aldebaran, Sirius, and Procyon, were first studied,
and were the subjects of the unsuccessful observations of
Calandrelli, and of the meritorious Piazzi. (1805) To these
observations, we must add those which were published (1815)
in Dublin by Brinkley, and which, ten years later, were re-
futed by Pond, and especially by Airy. A sure and satis-
factory knowledge of parallaxes, founded on micrometric

188 SPECIAL RESULTS IN THE TJRANOLOG1CAL PORTION

measurements, only commenced between the years 1832
and 1838.

Although Peters, (3°7) in his important work on the dis-
tances of fixed stars (1846), gives the number of cases of
parallax already discovered at 33, I will content myself with
citing nine, which deserve, though in very unequal degrees,
the greatest amount of confidence, giving them nearly in the
order of time of their determinations.

The first place belongs to the Star 61 Cygni, which Bessel
has rendered so celebrated. As early as 1812, the Konigs-
berg astronomer determined the large proper motion of this
double star (below the sixth magnitude) ; but it was only
in 1838, that he ascertained its parallax by the employment
of the heliometer. My friends Arago and Mathieu made a
series of numerous observations, from August 1812 to No-
vember 1813, for ascertaining the parallax of 61 Cygui by
measuring its Zenith distance. They arrived at the very just
conjecture, that the parallax of the Star must be less than
half a second.(308) As late as 1815 and 1816, Bessel, as
he himself expresses it, " had not arrived at any admissible
result." (309) Observations from August 1837 to October
1838, in which he availed himself of the large heliometer
established in 1829, first led him to infer a parallax of
0"-3483, corresponding to a distance of 592200 semi-
diameters of the Earth's orbit, and to a passage of light of
9| years. Peters, in 1842, confirmed this result, by find-
ing 0'x'3490 ; subsequently, however, Bessel's result was con-
verted by a temperature correction into 0"*3744. (31°)

The parallax of the finest double Star in the Southern
Heavens, a Centauri, has been determined by observations
at the Cape of Good Hope, by Henderson in 1832, and by

OF THE COSMOS. — PARALLAX OF STARS. 189

Maclear in 1839, at 0"-9128. (311) This would make it the
nearest of all the fixed Stars whose parallaxes have yet been
measured, and three times nearer than 61 Cygni.

The parallax of a Lyrse, has long been the subject of
Struve's observations. The earlier observations (1836) gave
(312) between 0"-07 and 0"-I8 ; later ones gave 0/7-2613, and
a distance of 771400 semi-diameters of the Earth's orbit,
with a light passage of 1 2 years ; (313) but Peters has found
the distance of this bright Star still greater, since he gives
its parallax at only 0"'103. This result contrasts with
another Star of the first magnitude (a Centauri), and with a
Star of the sixth magnitude (61 Cygni).

The parallax of Polaris was determined by Peters, by
many comparisons made in the years 1818 — 1838, at
Oy<106, and the more satisfactorily as the same comparisons
give the aberration 20'H55. (314)

The parallax of Arcturus is, according to Peters, 0/x*127
(Rumker's earlier observations with the Hamburgh Meridian
Circle had given it much larger). The parallax of another
star of the 1st magnitude, Capella, is still less, being,
according to Peters, 0"'046.

The Star 1830 of Groombridge's Catalogue, which, ac-
cording to Argelander, has shown the greatest proper
motion of any star yet observed, has a parallax of 0/7>226,
as inferred from 48 very exactly observed Zenith distances
by Peters in 1842 and 1843. Paye had believed it to be
5 times greater, viz., 1"'08, or more considerable than the
parallax of a Centauri. (3l5)

The following table contains the parallaxes of the nine
stars which deserve the greatest amount of confidence, with
the names of the observers, and the probable errors of the
determinations.

190 SPECIAL RESULTS IN THE TJRANOLOGICAL PORTION

FIXED STARS.

PARAL-
LAXES.

PROBABLE
ERRORS.

NAMES OF
OBSERVERS.

0''913

O'.OTO

Henderson & Maclear.

61 Cvgni...

0".3744

0"-020

Bessel.

Sirius

0'-230

Henderson.

1830 Groombridge ...

0'-226

0"'141

Peters.

i Ursse maj

0'-133

0"-106

Peters.

0*-127

o"-o73

Peters.

0*-207

0"'038

Peters.

Polaris

0'-106

0*'012

Peters.

Capella

0*-046

0"-200

Peters.

The results hitherto obtained by no means show gene-
rally that the brightest stars are also the nearest. Although
the parallax of a Centauri is indeed the largest hitherto
known, yet, on the other hand, a Lyrse, Arcturus, and
especially Capella, have parallaxes from 3 to 8 times less
than a star of the 6th magnitude in Cygnus. It is also
to be remarked that the two stars which, next to 2151
Puppis and e Indi, show the most rapid proper motion,
i. e., the Star in Cygnus which has just been named
(having an annual motion of 5//*123), and No. 1830 of
Groombridge, called in France Argelander^s Star (annual

OF THE COSMOS. DISTANCE OF FIXED STARS. 191

motion 6V*974*), are, the one 3, and the other 4 times as far
from the Sun as a Centauri, which has a proper motion
of 3'x*58. Yolume, mass, intensity of light, proper motion
(316), and distance from our solar system, are certainly in
very various and complicated relations to each other. Al-
though, therefore, it may be generally probable that the
brightest stars are the nearest, yet there may be individual
cases of very remote small stars whose photospheres and
surfaces may, from the nature of their physical constitution,
support a very intense luminous process. Stars, which on
account of their brightness we reckon as belonging to the
1st magnitude, may thus be really more distant from us
than stars which we call of the 4th, 5th, or 6th magni-
tudes. If we descend from the consideration of the great
sidereal stratum, of which our solar system is a part, to the
subordinate particular system of our planetary world, and
step by step, still lower, to the systems of Jupiter and
Saturn with their respective satellites, we see central bodies
surrounded by masses in which the succession of magni-
tudes and of intensities of reflected light does not appear
to depend at all on distance. The immediate connection
subsisting between our direct knowledge, still so slight, of
the parallaxes of stars, and our knowledge of the entire
structural form of the universe, gives a peculiar interest
and charm to considerations which relate to the distance
of the fixed stars.

Human ingenuity has devised for this class of investiga-
tions a method quite different from those usually employed ;
it is founded on the velocity of light, and deserves to be
briefly noticed in this place. Savary, of whom the physical
sciences have been too early deprived, has shown how, in

192 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

double stars, the aberration of light may be used for deter-
mining the parallax. If the plane of the orbit, which the
secondary star describes round the central body, is not per-
pendicular to the line of sight from the earth to the double
star, but, on the contrary, nearly coincides with it, then the
course of the secondary star will appear to be in a right
line, and the points on the half of its orbit which is turned
towards the earth will all be nearer the observer, than the
corresponding points of the other half Which is turned from
the earth. Such a division into two halves produces, not
a really, but to the observer an apparently, unequal velocity
according as the smaller star is approaching or receding
from him. If, then, the semi-diameter of the orbit is so
large that light requires several days or weeks to traverse it,
then the time of the semi-revolution on the farther side will
be greater than on the side turned towards the observer.
The sum of the two unequal numbers which express the
duration of the two semi-revolutions, is still equal to the
true period of entire revolution, since the inequalities occa-
sioned by the cause referred to mutually destroy each other.
In Savary's ingenious method, by converting days and parts
of days into a standard of length (light traverses 14356
millions of geographical miles in 24 hours), it is possible
to deduce from these ratios of duration the absolute magni-
tude of the semi-diameter of the orbit, and by the simple
determination of the angle under which the semi-diameter
presents itself to the observer, the distance of the central
body and its parallax. (317)

As the determination of the parallaxes informs us con-
cerning the distances of a small number of fixed stars anil

OF THE COSMOS. — MOTION OF THE SOLA.R SYSTEM. 193

the position in space to be assigned to them, so the know-
ledge of the measure and direction of their proper motion
(i. e. of the changes experienced by the relative positions
of self-luminous bodies) conducts us to two problems depen-
dent on each other ; viz., the motion of our solar system,
(318) and the situation of the centre of gravity of the whole
heaven of the fixed stars. What can as yet only be reduced
in so very incomplete a manner to numerical relations, must
for that very reason be ill adapted for the clear mani-
festation of casual connection. Of the two last named pro-
blems, the first only has received a solution, in particular by
Argelander's excellent investigation, which can be viewed as
in some degree of a satisfactory defmiteness ; the second, in
which so many opposing and mutually compensating forces
are concerned, has been treated with great ingenuity by
Madler : but, according to that astronomers own avowal, (319)
the attempted solution is deficient in " all the evidences of a
complete and scientifically adequate demonstration/''

After carefully separating and deducting all that belongs
to the precession of the equinoxes, the nutation of the
earth's axis, the aberration of light, and the parallactic change
occasioned by the earth's revolution round the Sun, the
remaining annual motion of the fixed stars still includes
both the effects of the movement of translation of the en-
tire solar system in space, and those of the true proper
motion of the fixed stars themselves. In Bradley's ad-
mirable investigation of nutation in his great work in 1748,
we find the first expressed anticipation of the translation of
the solar system, and also an indication of the method of
observation most desirable to be pursued for its discovery.
" If/' says he, (32°) " it should be found that our planetary

VOL. III. 0

1 94 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

system changes its situation in absolute space, there may
thence arise, in course of time, an apparent variation in the
angular distance of the fixed stars. Now, as in such case
the position of the stars nearest to us would be more
affected than that of the more distant ones, the position of
these two classes of stars would appear altered relatively to
each other, although in themselves they might all have re-
mained unmoved. If, on the other hand, our solar system
is in repose, and some stars actually move, then their appa-
rent positions will also be altered ; and this the more as the
motions are more rapid, the stars in a favourable position,
and the distance from the earth less. The alteration in
their relative positions may be dependent on so great a
number of causes that, perhaps, many centuries may be
required before the laws can be discovered/'

After Bradley, sometimes the mere possibility, and sometimes
the greater or less probability of the movement in space of
the solar system, were discussed in the writings of Tobias
Mayer, Lambert, and Lalande ; but William Herschel had
first the merit of supporting the opinion by actual observa-
tion (1783, 1805, and 1806). He found, what many later
and more exact investigations have confirmed and deter-
mined within narrower limits of uncertainty, that our solar
system is moving towards a point near the constellation of
Hercules in E.A. 260° 44', and North Declination 26° 16'
(reduced to 1800). Argelander, by a comparison of 319
Stars, and taking into account LundahFs investigations,
found for the situation of this point, for 1800; E.A. 257°
54'-l ; Decl. + 28° 49''2 ; and for 1850 ; E.A. 258°
28'-5 ; Decl. + 28° 45'-6 ; and Otto Struve (from 392
Stars) found it for 1800, E.A. 261° 26'*9, Decl. + 37°

Or THE COSMOS. — MOTION OF THE SOLAE, SYSTEM. 195

35'-5, and for 1850, E.A. 261° 52'-6 and Dec. 37° 33'-0.
According to Gauss, (321) the place sought for is situated
within a quadrangle whose angular points are in

E.A. 258° 40' and Bed. + 30° 40'
„ 258° 42' „ 30° 57'
„ 259° 13' „ 31° 9'
„ 260° 4' „ 30° 32'

It still remained to examine what result would be ob-
tained by employing stars of the Southern Hemisphere,
which never rise above the horizon in Europe. Galloway
has devoted himself with great diligence to this research.
He Has compared very recent determinations (1830) by John-
son at St. Helena, and by Henderson at the Cape of Good
Hope, with determinations of older date, (1750 and 1757)
of Bradley and Lacaille. The result (322) has been, for 1790,
E.A. 260° 0', Decl. + 34° 23', and therefore for 1800
E.A. 260° 5', Decl. + 34° 22' ; and for 1850, 260° 33'
and + 34° 20'. This agreement with the results obtained
from Northern Stars is extremely satisfactory.

Ifa then, we may consider the direction of the progressive
movement of our solar system to be determined within
moderate limits, the questions very naturally arise, — Is the
world of the fixed stars distributed into groups, each con-
sisting only of neighbouring partial systems ? — or must we
imagine a general relation, i.e. that all self-luminous celes-
tial bodies (suns) revolve around a common centre of gra-
vity, either occupied ly a mass of matter, or void, i.e. not so
occupied ? "We are here entering on the domain of mere
conjecture, to which a scientific form may indeed be given,
but which, from the insufficiency of the data at our com-

196 SPECIAL RESULTS IN THE URANOLOGICAL PORTION

mand, either as the results of observation or of analogy, are
not capable of leading to such evidence as other parts of
Astronomy enjoy.

One reason which especially opposes a thorough mathe-
matical treatment of problems so difficult of solution, con-
sists in our ignorance of the proper motion of a countless
host of very small stars (10th to 14th magnitude), which
appear scattered amongst brighter ones, and most abundantly
in what is so important a part of our sidereal stratum, the
rings of the Milky Way. The consideration of our plane-
tary sphere, in which we ascend from the small partial sys-
tems of Jupiter, Saturn, and Uranus with their respective
satellites, to the general solar system, easily led to the Belief
that the fixed stars might be imagined to be in an analogous
manner divided into many single groups, which, though se-
parated by wide intervals, might yet (in the higher relation
of such groups to each other) be all subjected to the pre-
ponderating attracting force of a great central body, which
might be regarded, as it were, as the one central Sun of the
Universe. (323) But the series of consequences here alluded
to as having been based on the analogy of our solar system,
is opposed by the facts of observation as known to us up to
the present time. In the " Multiple Stars," two or more
self-luminous heavenly bodies or suns do not revolve around
each other, but around a centre of gravity situated far out-
side of them. It is true that in our planetary system,
something similar takes place, inasmuch as the planets re-
volve, not around the centre of the body of the solar orb
itself, but around the centre of gravity of all the masses
of the system. This common centre of gravity falls, accord-
ing to the relative position of the larger planets, Jupiter

OF THE COSMOS. — MOTION OF THE SOLAR SYSTEM. 197

and Saturn, sometimes within the corporeal circumference
of the Sun, and sometimes (and this is the more frequent
case) on the outside of that circumference. (324) Thus the
centre of gravity, which in the double stars is void, is in
the solar system sometimes void, and sometimes occupied
by matter. All that has been said respecting the possi-
bility of the assumption of a dark central body in the centre
of gravity of the double stars, or of planets originally dark
but faintly illuminated by foreign light revolving around
them, belongs to the wide domain of mythical hypothesis.

It is a graver consideration, and one more deserving of a
thorough examination, that, if we assume a movement of
revolution, both for our own entire solar system, and for
all the proper motions of the fixed stars situated at such
widely different distances from us, the centrum of this re-
volving motion must be 90° from the point (325) towards
which our solar system is moving. In reference to the
combination of ideas which is here introduced, the situation
of the stars, which have, on the one hand, a very consider-
able, or, on the other hand, a very slight proper motion,
becomes of great moment. Argelander has cautiously,
and with his own peculiar sagacity, tested the degree of
probability with which, in our own sidereal stratum, a
general centrum of attraction might be sought for in the
sidereal constellation of Perseus. (326) M'adler, rejecting the
hypothesis of a central body occupying the place of the
general centre of gravity, and being itself of preponderating
mass, seeks the centre of gravity in the group of the
Pleiades, and in the middle of the group, in or near(327)
the bright star r\ Tauri (Alcyone). This work is not the
place for examining the degree of probability, on the one

198 SPECIAL RESULTS IN THE URANOLOGICAL

hand, or, on the other, the insufficiency of the founda-
tion, (328) of this last supposition. With the distinguished
and active director of the Observatory at Dorpat, rests the
merit of having in his laborious investigation examined the
position and proper motion of upwards of 800 fixed stars,
and of having at the same time given activity to researches,
which, if they do not conduct to a satisfactory resolution of
the great problem itself, are yet suited to throw light on
kindred subjects in physical astronomy.

PORTION OF THE COSMOS. MULTIPLE STARS. 199

VI.

MULTIPLE, OR DOUBLE STARS. THEIR NUMBER AND DI3

TANCES APART. PERIOD OP REVOLUTION OF TWO

SUNS ROUND A COMMON CENTRE OF GRAVITY.

IF, in considerations on the subject of the fixed stars, we descend
from conjectural, higher and more general relations, to such as
are more special, we find ourselves on ground firmer and better
adapted for direct observation. In multiple stars, to which
class Unary or double stars belong, several self-luminous
cosmical bodies (Suns) are connected with each other by
mutual attraction, and this attraction necessarily calls forth
motion in re-entering curved lines. Previous to the recog-
nition, by actual observation, of the revolutions of double
stars, (329) our knowledge of the existence of motion in re-
entering curved lines was limited entirely to our own planetary
solar system. On this apparent analogy hasty inferences
were based, which led aside from the true path. As the
name of double-star was applied in all cases where proxi-
mity prevented separation by the unassisted eye (as in
Castor, a Lyrae, /3 Orionis, and a Centauri), the term very
naturally came to include two classes of multiple stars;
those whose proximity might be occasioned solely by their
accidental position in relation to the observer, while they

200 SPECIAL RESULTS IN THE TJRANOLOGICAL

might really be situated at very different distances, and might
belong to altogether different sidereal strata, — and those
which, being actually and truly near to each other, and
being connected by mutual dependence or reciprocal attrac-
tion, form a particular system of their own. It is now the
custom to call the first class optically, and the second
physically, double stars. Yery great distance and slowness
of elliptic motion, may possibly cause several of. the latter
class to be confounded with the former. To cite here a
well-known object, the small star Alcor, (which received
much attention from Arabian astronomers, because visible
to the naked eye in very clear atmosphere and to persons
whose visual organs are very perfect,) forms, in the widest
sense of the term, such an optical combination as has been
spoken of, with % in the tail of the Great Bear. I have
already noticed in Sections II. and III. the difficulty of
separating with the unassisted eye adjacent stars of very
unequal intensity of light, — the influence generally of such
inequality of light, — the rays which appear to issue from
stars, — and the organic defects which produce indistinctness
of vision. (33°)

Galileo, without making double stars a particular subject
of his telescope observations, (for which, indeed, the mag-
nifying powers employed by him would have been quite
inadequate), yet in a celebrated passage of the Giornata
terza of his Discourses, pointed out by Arago, mentions the
use which astronomers might make of optically double stars
(quando si trovasse nel telescopic qualche picciolissima stella,
vicinissima ad alcuna delle maggiori), for discovering parallax
in the fixed stars, f831) Until the middle of the last century,
star- catalogues scarcely contained notices of as many as 20

PORTION OF THE COSMOS. MULTIPLE STARS. 201

double stars, exclusive of such as are more than 32/x apart ;
now, a hundred years later (thanks principally to the great
labours of the two Herschels and Struve), there have been
discovered in both hemispheres about 6000. Among the
earliest described double stars, (332) are £ Ursse maj. (7th
Sept. 1700, by Gottfried Kirch), a Centauri (1709, by
Eeuillee), y Virginia (1718), a Geminorum (1719), 61
Cygni (1753, the distances and angles of direction were
observed in this and the two preceding cases by Bradley),
p Ophiuchi, and % Cancri. The number of double stars
enumerated gradually augmented, from Plamsteed who
employed a micrometer, to the Star Catalogue of Tobias
Mayer, which appeared in 1756. Two men, sagacious in
conjecture and apt in combination of thought, Lambert
(" Photometria," 1760 ; and " Cosmological Letters on the
Arrangement of the Structure of the Universe/' 1761), and
John Michell (1767), although they did not themselves
observe double stars, were the first who promulgated just
views respecting the relations of attraction of stars in partial
binary systems. Lambert, like Kepler, ventured to suppose
the distant suns (fixed stars), to be, like our own sun, sur-
rounded by dark bodies, as planets and comets, but respect-
ing fixed stars in near proximity to each other, (although he
otherwise seems inclined to entertain the supposition also of
dark central bodies), his belief was, (333) that they performed
within a moderate time a revolution around their common
centre of gravity. Michell, (334) who had no knowledge of
Kant's and Lambert's ideas, was the first who, with much
sagacity, applied the calculus of probabilities to close groups
of stars, especially to multiple stars, binary and quaternary.
He showed the probabilities to be 500,000 to 1 against the

202 SPECIAL RESULTS IN THE URANOLOGICAL

juxtaposition of the six principal stars in the Pleiades being
accidental, and thence inferred that their grouping must
rather be supposed to be founded on some peculiar relation
existing between them. He felt so certain of the existence
of luminous stars which move round each other, that he
proposed to apply these partial star-systems to the ingenious
solution of some astronomical problems. (335)

The Manheim astronomer, Christian Mayer, has the great
merit of having first (1778) made the double stars a special
object of research by the sure path of actual observation.
The name which he unfortunately selected of " fixed-star
satellites," and the relations which he thought he recognised
between stars 2^° and 2° 55' distant from Arcturus, ex-
posed him to the bitter attacks of his cotemporaries, and
among the number to the censure of the great and acute
mathematician, Nicolaus Puss. That dark bodies should
become visible by reflected light at such enormous distances
was indeed improbable. The results of observations care-
fully planned and executed were unfortunately disregarded,
because the proposed systematic explanation of the pheno-
mena was rejected ; and yet, in a paper written in his own
defence against Maximilian Hell, Director of the Imperial
Astronomical Observatory at Vienna, Mayer had expressly
said, "that the small stars which are so near large ones may
be either planets dark in themselves, but illuminated by
reflected light, or, that both bodies, i. e., the principal star
and its companion, may loth be self-luminous suns revolving
round each other/' Long after Mayer's death, that which is
important in his works has been gratefully and publicly
acknowledged by Struve and M'adler. In his two Memoirs,
entitled, ' ' Vertheidigung neuer Beobach-tungen von Fix-

PORTION OF THE COSMOS. MULTIPLE STARS. 203

stern-trabanten (1778), and Diss. de novis in Coelo sidereo
Phseriomenis (17 79)," 80 multiple stars observed by him are
described, among which 67 are less than 32" apart. The
greater number were new discoveries of his own made with
the excellent eight-feet telescope of the Manheim Mural
quadrant ; " some are still amongst the most difficult objects,
and which can only be shown by powerful instruments ; as
p and 71 Herculis, f Lyrse, and w Piscinca." Mayer, in-
deed (as, however, was still done long after his time), only
measured distances in Eight Ascension and Declination by
his meridian instrument; -and from his own observations,
and those of earlier astronomers, showed changes of position,
from the numerical values of which he erroneously did not
deduct what (in particular cases) belonged to the proper
motions of the stars (336).

These slight but memorable beginnings were followed by
William HerscheFs colossal work on multiple stars. It em-
braces a period of more than 25 years ; for although the first
table of HerscheFs double stars was published 4 years after
Mayer's Memoir on the same subject, yet HerscheFs obser-
vations go back to 1779, or even, if we include his investi-
gations on the trapezium in the great nebula in Orion, to
1776. Almost all that we now know relative to the several
classes of double stars has its origin in Sir William HerscheFs
work. He not only gave in the catalogues of 1782, 1783,
and 1804, the positions and angular distances apart of
846 double stars (337), the majority of which were discovered
exclusively by himself ; but what is much more important than
the increase of number, he exercised his acute sagacity and
true spirit of observation on all that relates to the paths,
supposed periods of revolution, luminous intensity, contrast

204 SPECIAL RESULTS IN THE URA.NOLOGICAL

of colours, and classification according to the degree of
distance apart, of the double stars. Imaginative, and yet
always advancing with caution, he expressed himself, in the
year 1794, when distinguishing between optically and
physically double stars, in a brief and preliminary manner
respecting the nature of the relation subsisting between the
larger star and its smaller companion. Nine years after-
wards, he first developed the entire connection and mutual
dependence of the phenomena, in the 93rd volume of the
Philosophical Transactions. The idea of partial star-systems,
in which two or more suns revolve around a common centre
of gravity, was now firmly established. The powerful
dominion of attracting forces, which, in our solar system,
extends to Neptune, at a mean solar distance 30 times
greater than that of the Earth (or 2488 millions of
geographical miles), and even constrained the great comet
of 1680 to return when at a distance equal to 28 distances
of Neptune, or 70,800 millions of geographical miles, — also,
reveals itself in the motion of the double star 61 Cygni,
which, in correspondence with a parallax of 0/x>3744, is
18,240 distances of Neptune, or 550,900 semi-diameters
of the Earth's orbit, or 11,394,000 German or 45,576,000
English millions of geographical miles from our sun. If,
however, the causes and the general connection of the
phenomena were very distinctly recognised by "William
Herschel, yet in the first ten years of the 19th century, the
angles of position derived from his own observations, and
from older star-catalogues employed without sufficient care,
belonged to epochs too close together, to admit of the periods
of revolution or the elements of the orbits being derived
with due certainty from the several numerical values. Sir

PORTION OF THE COSMOS. — MULTIPLE STARS. 205

John Herschel himself notices the very uncertain assign-
ments of the periods of a Geminorum (334 years instead of
according to Madler, 520), (338); of 7 Virginias (70,8 year?
instead of 169); and of y Leonis (1424 of Struve's great
catalogue), a superb pair of stars, golden yellow and reddish-
green (1200 years).

After William Herschel, the foundations of this impor-
tant branch of astronomy were laid in a more thorough and
special manner by Struve (Senior), 1813 — 1842, and Sir
John Herschel, ]819 — 1838, with admirable activity and
by the aid of highly improved instruments (more particu-
larly in micrometric apparatus). Struve published his first
Dorpat Table of double stars (796 in number) in 1820.
This was followed in 1824 by a second, containing 3112
double stars down to the 9th magnitude at distances apart
less than 32/x, only about one-sixth of which had been pre-
viously seen. Tor the execution of this work, 120000 fixed
stars had been examined in the great Fraunhofer refractor.
Struve' s third Table was published in 1837, and forms the
important work entitled, " Stellarum Compositarum Men-
surse imcrometricse." (339) It contains, (several insecurely
observed objects being carefully excluded,) 2787 multiple
stars.

During Sir John Herschel's four years' residence at Feld-
hausen, at the Cape of Good Hope, a residence which
constitutes an epoch in respect to the more exact topogra-
phical knowledge of the southern heavens, his perseverance
enriched the department of astronomy which we are now
considering by upwards of 2100 double stars, which, with
a few exceptions, had never been observed before. (34C) All
these African observations were made with a twenty-feet

206 SPECIAL RESULTS IN THE URANOLOGICAL

reflector; they are reduced to 1830, and are arranged in
6 Catalogues, which contain 3346 double stars, and were
presented by Sir John Herschcl to the Royal Astronomical
Society of London, for the 6th and 9th parts of their
valuable memoirs. (341) In the European portion of these
catalogues, there are included 380 double stars which were
observed in 1825 by the above-named celebrated astro-
nomer, conjointly with Sir James South.

We see by this historical account, how, in the course
of half a century, science has gradually arrived at an
extensive and accurate knowledge of partial, and more
particularly of binary, star systems existing in space. The
number of double stars (including those both optically and
physically double) may now be estimated with some degree
of security at 6000, including those observed by Bessel
with the fine Praunhofer heliometer, by Argelander (342)
at Abo (1827—1835), by Encke and Galle at Berlin
(1836 and 1839), by Preuss and Otto Struve at Pulkova
(since the Catalogue of 1837), by Madler at Dorpat, and
by Mitchell at Cincinnati in Ohio with a 17 feet Munich
Refractor. In how many of these cases the stars seen in
close proximity in the telescope are really connected with
each other by immediate relations of attraction, forming par-
ticular systems and revolving in closed orbits, — i. e. how
many are what are called physically double stars, — is an
important question, but one difficult to answer. More and
more revolving companions are gradually being discovered.
Extraordinary slowness of motion, or the circumstance of
the direction of the plane of the orbit, as it presents itself
to our eyes, being such that the position of the moving star
is unfavourable for observation, may long cause physically

PORTION OF THE COSMOS. — MULTIPLE STARS. 207

double stars to be included by us among optically double
stars in which the proximity is only apparent. But a dis-
tinctly recognised measurable motion, such as we have been
speaking of, is not the only criterion; Argelander and
Bessel have shown, in a considerable number of multiple
stars, a perfectly equal proper motion in space (i. e. a com-
mon progressive movement, such as that of our own solar
system, including, together with the Sun, all its planets and
satellites), which testifies in favour of the principal stars and
their companions being respectively connected with each
other by a true and actual relation, forming separate partial
systems. Madler has made the interesting remark that, —
whereas in 1836, among 2640 catalogued double stars,
there were only 58 in which a difference of relative position
had been observed with certainty, and 105 in which such
a difference could be regarded as indicated with a greater or
less degree of probability, — the proportion of physical to
optical double stars is now so changed in favour of the
first, that among 6000 multiple stars there are, according
to a Table published in 1849, six hundred and fifty (343)
in which an alteration of relative position can be demon-
strated. The earlier ratio gave 1 in 16, the latter one
already gives 1 in 9, for the proportion of cases in which
the motions of the principal star and its companion show
these celestial bodies to be physically double.

The relative distribution of binary star-systems, not only
in the celestial spaces generally, but even simply on the ap-
parent heavenly vault, has as yet been but little examined
numerically. In the Northern Hemisphere, double stars are
most frequent in the direction of certain constellations (An-
dromeda, Bootes, the Great Bear, the Lynx, and Orion),

£08 SPECIAL RESULTS IN THE URANOLOGICAL

In the Southern Hemisphere, we have from Sir John Her-
schel, the unexpected result that, "in the extra-tropical
parts, the number of multiple stars is much less than in the
corresponding parts of the Northern Hemisphere/'' And yet
these fair southern regions were examined with an excellent
20 -feet reflector, which separated stars of the 8th magnitude
in distances of only three-fourths of a second apart, under the
most favourable atmospheric conditions, and by a most prac-
tised observer. (344)

An exceedingly remarkable peculiarity of multiple stars,
consists in the occurrence among them of contrasted co-
lours. Struve, in his great work published in 1837, gave
the following results in respect to colours, derived from
600 of the brightest double stars. (845) In 375 cases, the
colour of the principal star and the companion was the
same, and equally intense. In 101, the colour was the same,
but a difference of intensity was perceived. The cases of
double or multiple stars having entirely different colours,
were 120 in number, or one-fifth of the whole ; whereas
uniformity of colour between the principal stars and their
companions, extended to four-fifths of the entire carefully
examined mass. In almost half the 600 cases, both the
principal star and the companion are white. Among those
in which the colours are different, combinations of yellow
and blue (as in t Cancri), and of reddish-yellow and green (as
in the ternary star y Andromedse), (346) are very frequent.

It was Arago who in 1825 first called attention to the
circumstance, that in most, or at least in very many cases,
the diversity of colour in binary systems appeared to have
reference to complementary colours (i. e. to the subjective re-
lation between colours, the union of which forms white). (347)

PORTION OF THE COSMOS. — MULTIPLE STARS. 209

It is a well-known optical phenomenon, that a faint white
light appears green, when a strong (intense) red light is
brought near to it ; and that white light becomes blue, when
the surrounding stronger light is yellowish. Arago, however,
cautiously and justly remarked, that, although the green or
the blue colour of the companion may sometimes be the result
of contrast with the brighter star, yet that the actual existence
of green or of blue stars is by no means to be denied. (348)
He gives instances in which a bright white star (1527
Leonis, 1768 Can. ven.) is accompanied by a small blue
star; cites a double star (b Serp.), in which both the prin-
cipal star and its companion are blue; (349) and proposes
a mode of examining whether the contrasted colour is merely
subjective, by covering the principal star in the telescope,
when the distance permits, by a wire, or by a diaphragm.
Usually it is the smallest star only which is blue; it
is otherwise, however, in the double star 23 Orionis
(696 of Struve's catalogue, p. Ixxx), in which the principal
star is bluish, and the companion pure white. If, in the
multiple stars, the different coloured suns are often sur-
rounded by planets invisible to us, such planets must be
variously illuminated, having their white and blue, or their
red and green days.(350)

As we have already seen (351) in a preceding section, that
the periodical variability is not necessarily associated with a
red or reddish colour, so also neither is colour in general,
nor a contrasted diversity of colour in the principal star and
its companion in particular, a characteristic of double stars.
Circumstances, which we find to be frequent, are not there-
fore general and necessary conditions of the phenomena,
whether of the periodical variation of the light of stars, or

VOL. III. P

210 SPECIAL RESULTS IN THE URANOLOGICAL

of the revolution of sidereal bodies in partial systems round
a common centre of gravity. A careful examination of the
brighter double stars (colour is still determinable in stars of
the 9th magnitude), teaches us that,, besides pure white, all
the colours of the solar spectrum are to be found in double
stars ; but that the principal star, when not white, generally
approximates to the red extreme, namely, that of the least
refrangible rays, and the companion to the violet extreme,
or that of the most refrangible rays. The reddish stars
are twice as frequent as the blue and bluish, and the
white are about twice and a half as numerous as the red and
reddish. It is also to be remarked, that usually a great
difference of colour is combined with a considerable differ-
ence in the intensity of the light. In two pairs of stars,
which, from their great brightness, can be easily measured
in the daytime with powerful telescopes, — £ Bob'tis and y
Leonis, — the first-named pair consists of two white stars of
the 3rd and 4th magnitudes, and the latter of a principal star
of the 2m., and a companion of the 3 '5m. This last-named
star (y Leonis) is said to be the finest double star of the
Northern Hemisphere, but a Centauri (352) and a Crucis, of
the Southern Heavens, surpass all other double stars in
brilliancy. As in ? Bobtis, so also in a Centauri and y
Virginis, we remark the rare combination of two large stars
having but little inequality of light.

Eespecting variability of brightness in multiple stars, and
especially respecting variability in the companion, unanimity
and certainty do not yet prevail. '"We have already spoken
more than once (353) of the somewhat irregular variability of
the brightness of the principal star of a yellowish-red colour,
in aHerculis. Also the variation of brightness, observed by

PORTION OF THE COSMOS. — MULTIPLE STARS. 211

Struve (1831-1833), in the nearly equally bright yellowish
stars (3rd magnitude) of the double star y Virginis and
Anon. 2718, may perhaps indicate a very slow rotation
around the axes of those two suns. (354) "Whether any actual
change of colour has ever taken place in double stars (y
Leonis and y Delphini ?), whether white light ever becomes
coloured in them, — as we know that inversely in Sirius,
which is a single star, coloured light has become white, — is
still undecided ; (3'5) when the differences in question only
have reference to faint shades of colour, organic indivi-
duality in the observers, and when refractors are not
employed, the often reddening influence of the metallic
speculum in telescopes, are to be taken into account.

Among the multiple stars, or systems, I may cite : —
ternary; £ Librae, £ Cancri, 12 Lyncis, 11 Monoceritis : —
quaternary; 102 and 2681 of Struve's catalogue, a Andro-
medae and e Lyrae : — and a six-fold combination in 0 Oripnis,
the celebrated trapezium in the great nebula in Orion, pro-
bably forming a single physical system united by laws of mu-
tual attraction, since the five smaller stars (6 '3m.; 7m.; 8m.;
ll'3m. ; and 12m.) follow the proper motion of the principal
star (4'7m). As yet, however, no change in their relative
positions has been observed. (356) In two ternary multiple
stars, ? Librae and £ Cancri, the movement of revolution of
both companions has been recognised with great certainty ;
£ Cancri consists of three stars differing but little in bright-
ness, being all of the 3rd magnitude, and the nearer com-
panion appears to have a ten times quicker motion than
the more distant one.

The number of double stars, in which it has been possible
to compute the elements of the orbits, is given at present

212 SPECIAL RESULTS IN THE URA.NOLOGICAL

as from 14 to 16. (357) Of these £ Herculis, since its first
discovery, has already twice completed its circuit of revolu-
tion ; and in so doing has presented (in 1802 and 1831)
the phenomenon of the apparent occultation of one fixed
star by another. We are indebted for the earliest calcula-
tions of the orbits of double stars to the industry of Savary
(in the case of £ Ursse majoris), Encke (70 Ophiuchi), and
Sir John Herschel ; and they have been since followed by
Bessel, Struve, Madler, Hind, Smyth, and Captain Jacob.
Savary's and Encke's methods require four complete observa-
tions sufficiently distant from each other. .The shortest
periods of revolution yet known are of 30, 42, 58, and 77
years, intermediate, therefore, between those of the planets
Saturn and Uranus; the longest periods yet determined
with any degree of certainty exceed 500 years, or are about
three times as long as that of Le Terrier's planet Neptune.
According to the investigations hitherto made, the excen-
tricity of the orbits of double stars appears to be extremely
considerable, resembling that of comets ; in the case of <r
Coronse it is 0'62, in that of a Centauri 0*95. The least ex-
centric internal comet, that of Paye,has an excentricity of 0'55,
or less than that of the orbits of the two double stars just
named ; excentricities much smaller are presented, according
to Madler's and Hind's calculations, by r\ Coronse and Castor,
being 0'29 in the former, and 0'22 or 0*24 in the latter.
In these double stars, therefore, the suns describe ellipses,
which approximate closely to those of two of the smaller
planets of our solar system, as the orbit of Pallas has an
excentricity of 0'24, and that of Juno 0*25.

If with Encke we regard the brighter of the two stars in
a binary system as being in repose, and accordingly refer to

PORTION OF THE COSMOS. — MULTIPLE STARS. 213

it the motions of its companion, we find, from the observa-
tions hitherto made, that the companion describes round
the principal star a conic section in the focus of which the
latter is placed ; or an ellipse in which the radius vector
of the revolving body passes over equal areas in equal
times. Exact measurements of angles of position and of
distances, adapted for determinations of orbits, have already
shewn, in the case of a considerable number of double stars,
that the companion moves round the principal star con-
sidered as a body at rest, in obedience to the same gravi-
tating forces which prevail in our solar system. This well-
established conviction, gained within scarcely a quarter of
a century, marks one of the great epochs in the history of
the development of the higher cosmical knowledge. Celes-
tial bodies, to which the name of fixed stars (assigned by
ancient usage) is still given, although they are neither
affixed to the heavenly vault nor motionless, have been seen
to occult each other. The knowledge of the existence of
partial systems, the several parts of which have motions
referable to and dependent on each other, extends our
views the more- widely as those motions are again sub-
ordinated to more general ones.

The table on the next page contains the Elements of the
orbits of six double stars, the determinations of which ap-
pear entitled to principal confidence.

ELEMENTS OF THE ORBITS OF DOUBLE STAES.

NAME.

SEMI
MAJOR Axis.

ECCENTRI-
CITY.

PERIOD OF
REVOLUTION
IN YEARS.

COMPUTER.

1. SUrsseMaj. ...

3*-857

0-4164

58-262

Savary, in 1830.

ii

3"-278

0-3^77

60-720

John Herschel,
Table of 1849.

»

2"-295

0-4037

61-300

Madler, 1847.

2. p Ophiuchi

4"-328

0-4300

73-862

Encke, 1832.

3. SHerculis

1*208

0-4320

30-22

Madler, 1847.

4. Castor

8fl<086

0'7582

252-66

John Herschel,

Table of 1 849.

••

5//-692

0-2194

519-77

Madler, 1847.

»

6*300

0-2405

632-27

Hind, 1849.

5. y Virginis

37/t580

0-8795

182-12

John Herschel,
Table of 1849.

M

3/7-863

0-8806

169-44

Madler, 1847.

6. a Centauri

15*-500

0-9500

77-00

Captain Jacob, 1848.

NOTES.

(1) p. 4. — Kosmos, Bd. i. S. 56 — 59 and 141 (English edition, Vol. i.
p. 50—53 and 126).

(2) p. 6. — Kosmos, Bd. i. S. 6 — 8 ; Bd. ii. S. 10 — 12 and 92 (English
edition, Vol. i. p. 6 — 7 ; Vol. ii. p. 9 — 11 and 89).

(3) p. 6.— Kosmos, Bd. ii. S. 26—31 and 44—49 (English edition,
Vol. ii. p. 24—30 and 43 — 48).

(4) p. 7.— Kosmos, Bd. i. S. 383—386 ; Bd. ii. S. 141—144 (English
edition, Vol. i. p. 354—357; Vol. ii. p. 10?).

(5) p. 7. — M. von Olfers, On the Remains of Animals of Gigantic Size
belonging to the Ancient World, in connection with Legends of Eastern Asia,
in the Abh. der Berl. Akad. 1839, S. 51. On the opinion of Empedocles
respecting the cause of the destruction of the more ancient forms of animal
life, vide Hegel's Geschichte der Philosophic, Bd. ii. S. 344.

(6) P- 7- — Respecting the world-tree, Ygdrasil, and the raging fountain,
Hvergelmir, see Jacob Grimm's Deutsche Mythologie, 1844, S. 530 and 756 ;
and Mallet's Northern Antiquities, 1847, p. 410, 489, and 492.

(') p. 9.— Kosmos, Bd. i. S. 30—33 and 62—70 (English edition,
p. 30—33 and 56—64).

(8) p. 10.— Kosmos, Bd. ii. S. 484 (English edition, p. 285 and xciv.)

(9) p. 10. — In the introductory Contemplations in the first volume of
Cosmos (p. 33), it should not have been said generally and without exception
that " the discovery of laws, and their progressive generalisation, are the
objects of the experimental sciences :" a more limited sense should have been
given by the introduction of the words " in many groups of phenomena."
The manner in which I expressed myself in the second volume respecting the

VOL. in. a

11 NOTES.

relation subsisting between the achievements of Newton and Kepler, must, I
think, show without doubt that I do not confound together the discovery
of natural laws, and the interpretation, i. e. the explanation, of phenomena.
I say of Kepler (p. 310) — "The rich supply of exact observations which were
furnished by Tycho Brahe, laid the foundation of the discovery of those uu-
changing laws of the planetary movements which prepared for Kepler
imperishable fame, and which, when interpreted by Newton, and shown by
him to be theoretically necessary, were transferred to the bright domain of
thought, and became the intelligent recognition of Nature" — of Newton
(p. 351) — "We terminate with the figure of the Earth as then recognised
from theoretical considerations. Newton attained to the explanation of the
system of the Universe, because he succeeded in discovering the Force of whose
operation the Keplerian laws are the necessary consequences." See on this
subject the excellent remarks " On Laws and Causes," contained in Sir Johu
Herschel's Address at the Fifteenth Meeting of the British Association, held
at Cambridge, 1845, p. xlii. ; and the Edinburgh Review, Vol. Ixxxvii. 1848,
p. 180—183.

( °) p. 11. — In the remarkable passage in which Aristotle (Metaph. xii. 8,
p. 1074, Bekker) speaks of the " fragments of an early knowledge orice
discovered and subsequently lost," there occurs a passage of much im-
port, indicating freedom from the Deification of natural forces or powers,
personified under the forms of various divinities resembling human beings :
he says — "Much has been added mythically for the sake of persuading the
multitude, as well as for the support of the laws and other useful objects."

(u) p. 11. — The important difference between these directions, Tgdiroi, in
Natural Philosophy, is clearly indicated in Aristot. Phys. Auscult. i. 4, p. 187,
Bekker. Comp. Brandis, in the Rhein. Museum fur Philologie, Jahr. iii.
S. 105.

(is) p. 12.— Kosmos, Bd. i. S. 139 and 405, Note 59 ; Bd. ii. S. 348 and
501, Note 27 (English edition, Vol. i. p. 124, and Note 89; Vol. ii. p. 308,
and Note 467). A remarkable passage of Sirnplicius (p. 491) opposes in
the clearest manner the centripetal force to the centrifugal force : it speaks of
" the heavenly bodies not falling where the centrifugal force preponderate
over the proper falling force — that which draws them downwards." On the
same account, in Plutarch de Facie in Orbe Lunse, p. 923, the moon is com-
pared, in respect to its not falling towards the Earth, to " the stone in the
sling." Respecting the proper signification of the irepix^pfifis of Anax'agoras,
vide Schaubach, in Auaxag. Clazom. IVagm. 1827, p. 107—109.

NOTES. Ill

(15) p. 12.— Scbaubach, in Anaxag. Clazom. Fragrn. p. 151—156 and
185 — 189. Plants were also supposed to be animated by the vovs, or mind
(Aristot. de Plant, i. 1, p. 1815, Bekk.)

(14) p. 13. — On this part of the mathematical physics of Plato, compare
Bockh de Platonico Syst. coelestium globorum, 1810 etlSll ; Martin, Etudes
sur le Timee, T. ii. p. 234—242; and Braudis, in the Geschichte der
Griechisch-Romischen Philosophic, Th. ii. Abth. i. 1844, S. 375.

(ls) p. 13.— Kosmos, Bd. ii. S. 520, Note 4 (English edition, Vol. ii.
Note 544). Compare Gruppe iiber die Fragmente des Archytas, 1840, S. 33.

(16) p. 13.— Aristot. Polit. vii. 4, p. 1326 ; and Metaph. xii. 7, p. 1072,
10, Bekk., and xii. 10, p. 1074, 5. The pseudo- Aristotelian book.De
Mundo, which Osann ascribes to Chrysippus (Kosmos, Bd. ii. S. 14 and 106),
contains also (cap. 6, p. 807) a very eloquent passage on the " Orderer and
Upholder of the Universe."

(17) p. 13. — The passages which prove this are collected in Ritter's Gesch.
der Philosophic, Th. iii. S. 185—191.

(ls) p. 14. — Compare Aristot. de Anima, ii. p. 419. The analogy with
sound is most clearly expressed in this passage ; but in other parts of his
writings Aristotle modified his theory of vision in various ways. Thus he
says, in De Insomniis, cap. ii. p. 459, Bekker — "It is evident that vision is
active as well as passive, — that the sight not only suffers, or receives as a
passive recipient, something fron> the air (the medium of vision), but that it
also acts upon the medium." He alleges as proof that, " under particular
circumstances, a new and very pure metallic mirror, being looked upon by a
woman, has its surface dimmed by clouded spots difficult to efface." (Compare
therewith Martin, Etudes sur le Timee de Platon, T. ii. p. 159—163.)

(19) p. 14. — Aristot. de Partibus Anim., Lib. iv. cap. 5, p. 681, liu. 12,
Bekker.

(20) p. 14.— Aristot. Hist. Anim., Lib. ix. cap. 1, p. 588, lin. 10—24,
Bekker. " If in the animal kingdom some of the representatives of the four
elements, — those, for instance, corresponding to the element of the purest
fire, — are wanting upon our Earth, these intermediate steps may perhaps be
present in the moon." (Biese, Die Phil, des Aristoteles, Bd. ii. S. 186).
The Stagirite sought in another celestial body absent links in the chain : we
find such missing intermediate gradations among ancient terrestrial forms
of plants and animals which have perished.

(21) p. 14.— Aristot. Metaph. lib. xiii. cap. 3, p. 1090, lin. 20, Bekker.
(^ p. 15. — The dvTiirepHrracris of Aristotle especially plays a great part

IV NOTES.

in all explanations of meteorological processes, as in the works — De generatione
et interitu, Lib. ii. cap. 3, p. 330; 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 least drawn up
according to Aristotelian principles. In the ancient hypothesis of polarity,
/car' dvTnrfpKrraa-tv, similar conditions attract each other, and dissimilar
conditions ( + and — ) repel each other (compare Ideler, Meteorol. veterum
Grsec. et Rom. 1832, p. 10). " Opposite conditions, instead of neutralising
tension by their combination, on the contrary increase it. The
tyvXP^v heightens the &epiJ.6v ; so also, inversely, in the formation of hail,
while the cloud sinks into warmer strata of air, the surrounding warmth
makes the cold body still colder." Aristotle explains by his antiperi static
process, by polarity of heat, what modern physical science explains by con-
duction, radiation, evaporation, and change of capacity for heat. See ingenious
considerations by Paul Erman, in the Abhandl. der Berliner Akademie auf
das J. 1825, S. 128.

f23) p. 15. — "All variation in natural bodies, all terrestrial phsenomena,
are called forth by the motion of the celestial sphere." — Aristot. Meteor, i. 2,
p. 339 ; and De gener. et corrupt, ii. 10, p. 336.

(24) p. 15.— Aristot. de Ccelo, Lib.i. cap. 9, p. 279 ; Lib. ii. cap. 3, p. 286 ;
Lib. ii. cap. 13, p. 292, Bekker. (Compare Biese, Bd. i. S. 352—357.)

P) p. 15.— Aristot. phys. Auscult. Lib. ii. cap. 8, p. 199 ; De Anima,
Lib. iii. cap. 12, p. 434 ; De Animal, generat. Lib. v. cap. 1, p. 778, Bekker.

(M) p. 16.— Aristot. Meteor, xii. 8, p. 1074 ; of which passage a remark-
able elucidation is contained in the Commentary of Alexander Aphrodisiensis.
The heavenly bodies are not soul-less matter, they are rather to be regarded as
acting and living beings (Aristot. de Coelo, Lib. ii. cap. 12, p. 292). They are
the divinest of phenomena, TO, &eiJrepa TWV Qavep&v (Aristot. de Ccelo,
Lib. i. cap. 9, p. 278 ; and Lib. ii. cap. 1, p. 284) . In the little pseudo-
Aristotelian writing, De Mundo, in which a religious tone (respecting the
preserving omnipotence of God, cap. 6, p. 400) is often seen to prevail, the
upper aether is also termed divine (cap. 2, p. 392). What Kepler, in the
Mysterium cosmographicum (cap. 20, p. 71), fancifully terms "moving
spirits" — "animae motrices" — is the confused idea of a force (virtus) which
has its principal seat in the sun (anima mundi), diminishes by distance
according to the laws of light, and impels the planets in their elliptic paths.
Comp. Apelt, Epochen der Ge?ch. d<T Meuscheit (Epochs in the History of
Mankind), Bd. i. S. 274.

NOTES. V

(27) p. 16.— Kosmos, Bd. ii. S. 280—291 (English edition, Vol. ii.
p. 243—254).

(2S) p. 17- — See the ingenious and learned account of the writings of the
philosopher of Nola, in the work entitled — Jordano Bruno, par Christian
Bartholmess, T. ii. 1847, p. 129, 149, and 201.

(-19) p. 17.— He was burnt at Rome on the 17th of February, 1600,
according to the sentence — "ut quam clementissime et citra sanguinis
effusionem puniretur." Bruno was a prisoner sis years under the leads at
Venice, and two years in the inquisition at Rome. Undaunted and unbroken
in spirit when the sentence of death was announced to him, he replied —
" Majori forsitan cum timore sententiam in me fertis quam ego accipiam."
When a fugitive from Italy (in 1580), he taught in Geneva, Lyons,
Toulouse, Paris, Oxford, Marburg, Wittenberg (which he called the Athens
of Germany), Prague, Helmstedt, where in 1589 he completed the scientific
education of Duke Henry Julius, of Brunswick- Wolfenbiittel (Bartholmess,
T. i. p, 167—178), and from 1592 in Padua.

I30) p. 18.— Bartholmess, T. ii. pp. 219, 232, and 370. Bruno collected
with care the several observations respecting the great cosmical event (1572)
of the sudden shining forth of a new star in Cassiopeia. The relations of
his natural philosophy to that of two of his Calabrian countrymen — Bernardino
Telesio and Thomas Campanella, and to the platonisiug Cardinal Nicolaus Krebs
of Cusa (vide Kosmos, Bd. ii. S. 503 ; English edition, Vol. ii. p. 109), — have
been much examined in modern times.

(31) p. 18. — " Si duo lapides in aliquo loco muudi collocarentur propinqui
invicem, extra orbem virtutis tertii coguati corporis ; illi japides ad simili-
tudinem duorum magueticorum corporum coirent loco intermedio, quilibet
accedens ad alterum tanto iutervallo, quanta est alterius moles in compara-
tione. Si Luna et Terra non retinerentur vi animali (!) aut alia aliqua sequi-
pollente, qxisclibet in suo circuitu, Terra adscenderet ad Lunam quiuquagesima
quarta parte iutervalli, Luna descenderet ad Terram quinquaginta tribus circiter
partibus intervalli ; ibi jungereutur, posito tamen quod substantia utri usque
sit unius et ejusdem densitatis." Kepler, Astronomia nova seu Physica
coelestis de Motibus Stellse Martis, 1609, Introd. fol. v. On the older views
of gravitation, see Kosmos, Bd. ii. S. 348, 501, and 502 (English edition,
Vol. ii. pp. 308, cvii. aud cviii.

t32) p. 18. — " Si Terra cessaret attrahere ad se aquas suas, aquse rnarinee
omnes elevarentur et in corpus Lunse influerent. Orbis virtutis tractoria3, quse
est in Luna, porrigitur usque ad terras, et prolectat aquas quacunqueinverticeiu

VI NOTES.

loci incidit sub zonam torridam, quippe in.occursum suum quacunque in
verticein loci incidit, insensibiliter in maribus inclusis, seusibiliter ibi ubi
sunt latissimi alvei oceani propinqui, aquisque spaciosa reciprocationis

libertas" (Kepler, 1. c.) " Undas a Luna trahi ut ferrum a magnete "

Kepleri Harmonices Mundi libri quinque, 1619, lib. iv. cap. 7, p. 162.
This same work, which contains so much that is admirable, and even the
basis of the important " third law " (according to which the squares of the
periods of revolution of two planets are to each other as the cubes of the
mean distances), is disfigured by the wildest fancies : respiration, nutrition,
and vital heat of the Earth as an animal ; on a soul possessed by this animal ;
its memory (memoria animse Terrse) ; and even its imaginative powers
(animse Telluris imaginatio). Kepler was so much attached to these reveries
that he even had a serious dispute with the mystic author of the Macrocosmos —
Robert Fludd. of Oxford, — (said to have had a share in the invention of the
thermometer) — respecting the right of priority in these views of the Earth as
a living creature (Harm. Mundi, p. 252). The attraction of mass is often
confounded in Kepler's writings with magnetic attraction. " Corpus Solis
esse magneticum. Virtutem, quse planetas niovet, residere in corpore Solis,"
(Stella Martis, Pars iii. cap. 32 and 34). He gives to every planet a mag-
netic axis, which is always directed to the same quarter of the heavens (Apelt,
Joh. Keppler's a*tron. Weltansicht, 1849, S. 73).

P) p. 19.— Comp. Kosmos, Bd. ii. S. 364 and 512, Note 55 (English
edition, Vol. ii. p. 323, and Note 495).

(34) p i9._La Vie de M. Des-Cartes (par Baillet), 1691, P. i. p. 197 ;
and (Euvres de Descartes publiees par Victor Cousin, T. i. 1824, p. 101.

(35) IK 20.— Lettres de Descartes au P. Mersenne du 19 Nov. 1633 et du
5 Janvier 1634 (Baillet, P. i. p. 244—247).

(36) p. 20. — The Latin translation is entitled, Mundus, sive Dissertatio de
Lumine ut et de aliis Sensuum Objectis primariis. See R. Descartes, Opuscula
posthurna physica et mathematica, Amst. 1704.

(ST) p. 21. — "Lunam aquis carere et acre : marium similitudinem in Luna
nullam reperio. Nam regiones planas quse montosis multo obscuriores sunt,
quasque vulgo pro maribus haberi video et oceanorum nominibus insiguiri, in
his ipsis, longiore telescopic inspectis, cavitates exiguas inesse comperio
rotundas, urnbris intus cadentibus ; quod maris superficiei convenire nequit
turn ipsi campi illi latiores non prorsus sequabilem superficiem prseferunt, cum
diligentius eas intuemur. Quodcirca maria esse non possuut, sed materia
constare debent minus candicante, quam quse est partibus asperioribus, in

NOTES. Vll

quibus rursus qufedam viridiori lumine cseteras preecellunt" (Hugeni
Cosmotheoros, ed. alt. 1699, Lib. ii. p. 114). Huygens supposes, however,
that there is much storm aud rain in Jupiter, for " ventorum flatus ex ilia
nubium Jovialium mutabili facie cognoscitur" (Lib. i. p. 69). The reveries
of Huygens respecting the inhabitants of the distant planets, which were not
worthy of a severe mathematician, have been renewed unfortunately by
Immanuel Kant in his excellent work, Allgemeine Naturgeschichte und
Theorie des Himmels, 1755 (S. 173—192).

(^) p. 21. — Laplace, (des Oscillations de 1' Atmosphere, du Flux solaire et
lunaire,) in the Mecanique celeste, Livre iv. ; and in the Exposition du Syst.
du Monde, 1824, p. 291—296.

(39) p. 21. — "Adjicere jam licet de spiritu quodam subtilissimo corpora
crassa pervadente et in iisdem latente, cujus vi et actionibus particulae
corpornm ad minimas distanlias se mutuo attrahunt et contiguse factse
cohserent" (Newton, Principia Phil. nat. ed. Le Seur et Jacquier, 1760 ;
Schol. ge'n. T. iii. p. 676). Compare also Newton, Opticks (ed. 1718),
Query 31, p. 305, 353, 367, and 372. (Laplace, Syst. du Monde, p. 384 ;
Kosmos, Bd. i. S. 56 and 74 (English edit. Vol. i. pp. 60 and x. Note 22).

(40) p. 22. — " Hactenus phsenomena coslorum et maris nostri per vim gravi-
tatis exposui, sed eausam gravitatis uondum assignavi. Oritur utique hsec
vis a causa aliqua, quse penetrat ad usque centra solis et planetarum, sine
virtutis diminutione ; quseque agit non pro quantitate superficierum parti-
cularum, in quas agit (ut solent causae mechanicse), sed pro quantitate
materise solidse. — Rationem harum gravitatis proprietatum ex phseno-
menis nondura 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 species of things is
endowed with an occult specifick quality, by which it acts and produces mani-
fest effects, is to tell us nothing ; but to derire two or three general principles
of motion from phenomena, and afterwards to tell us how the properties and
actions of all corporeal things follow from those manifest principles, would be
a very great step in philosophy, though the causes of those principles were
not yet discovered, and therefore I scruple not to propose the principles
of motion, and leave their causes to be found out" (Newton, Opticks,
p. 377). In an earlier place (Query 31, p. 351) it is said — " Bodies act one
upon another by the attraction of gravity, magnetism, and electricity ; and it
is not improbable that there may be more attractive powers than these. How
these attractions may be performed, I do not here consider. What I call

Vlll NOTES.

attraction, may be performed by impulse, or by some other means unknown
to me. I use that word here to signify any force by which bodies tend
towards one another, whatsoever be the cause."

(41) p. 22. — " I suppose the rarer sether within bodies, and the denser
without them." Operum Newtoui, Tomus iv. (ed. 1782, Sam. Horsley),
p. 386 ; with application to the explanation of diffraction or bending of light
discovered by Grimaldi. At the conclusion of Newton's letter to Robert
Boyle, written in February 1678, p. 394, he says, " I shall set down one
conjecture more which came into my mind : it is about the cause of gravity."
Newton's correspondence with Oldenburg, in December 1675, also shows
that he was not, at that period, disinclined to the hypothesis of an aether.
According to it the impulse of material light would put the sether in vibration;
the vibrations of the sether, which is akin to a nervous fluid, not by themselves
producing light. See, respecting the controversy with Hook, Horsley, T. iv.
p. 378—380.

(4-) p. 22.— Brewster, Life of Sir Isaac Newton, p. 303—305.

(43) p. 23. — The precautionary explanation, " not to take gravity for an
essential property of matter," given by Newton in the " Second Advertise-
ment," contrasts with the forces of attraction and repulsion which he attri-
butes to all molecules, in order to explain, in a manner accordant with the
theory of emission, the phsenomena of refraction and reflection of rays of light
from mirror surfaces " before actual contact." (Newton, Opticks, Book ii.
Prop. 8, p. 241; and Brewster's Life of Newton, p. 301.) According to
Kant (Die metaphysischen Anfangsgriinde der Naturwissenschaft, 1800,
S. 28), the existence of matter, without these forces of attraction and
repulsion, cannot be imagined. According to him, therefore, as according to
the earlier Goodwin Knight (Phil. Trans. 1748, p. 264), all physical pheno-
mena are to be traced back to the conflict of these two fundamental forces.
In the atomic systems, which are diametrically opposed to Kant's dynamic
views, and according to an assumption which was widely diffused, especially
through the influence of Lavoisier, the attractive force is attributed to the
ultimate particles or molecules of which all bodies consist, and the repulsive
force to the atmospheres of caloric which surround the molecules. In this
hypothesis, which regards the so-called caloric as matter in a constant state
of expansion, there are assumed two different kinds of matter; i. e. two
different elementary substances, as in the myth of two kinds of sether.
(Newton, Opt. Query 28, p. 399.) Oue then asks, What is it which again
expands this caloric matter ? Considerations on the density of the molecules

NOTES. IX

in comparison with the density of their aggregates (the entire body), lead, in
following atomic hypotheses, to the result, that the distance of the mole-
cules from each other is much greater than their diameters.

(41) p. 24.— Kosmos, Bd. i. S. 98—102 (English edit. Vol.i. p. 85—89).

(45) p> 24 —Id. Bd. i. S. 39 and 50— 5G (English, edit. Vol. i. p. 40 and
42—50).

(46) p 24— Wilhelm von Humboldt, Gesamrnelte Werke, Bd. i. S. 23.

(47) p. 26.— Kosmos, Bd. i. S. 80 and 81 (English edition, Vol. i.
p, 68 and 69).

(43) p 27.— Id. S. 51 (English edition, p. 44).

(49) p. 27.— Halley, in the Phil. Trans, for 1717, Vol. xxx. p. 736.

(50) p. 28.— Pseudo-Plut. de plac. Philos. ii. 15—16; Stob. Eclog. phys.
p. 582 ; Plato, in Tim. p. 40.

(51) p. 28. — Macrob. Somn. Scip. i. 9 — 10 ; " stellee inerrantes," in Cicero
de Nat. Deorum, iii. 20.

(52) p. 28. — The principal passage in which the technical expression,
evSeSe^eW ito-rpa, occurs, is Aristot. de Ccelo, ii. 8, p. 289, lin. 34 ; p. 290,
lin. 19, Bekker. This alteration of the nomenclature had previously arrested
my attention when engaged in examinations respecting Ptolemy's optics, and
his experiments on the refraction of rays. Professor Franz, of whose philo-
logical learning I have often been glad to avail myself, remarks that
Ptolemy (Syntax, vii. 1) also says of the fixed stars — #arep 7rpo(nre<j>u/c($Tes-§
as if fastened to the sky. Ptolemy blames the expression ff&aipa dirAavvis
(orbis inerrans), remarking that, "inasmuch as the stars always preserve
their distances from each other, we may justly term them dirhave'is ; but
inasmuch as the whole sphere to which they are attached is in motion, the
name air^av^s seems but little suited thereto."

(53) p. 28.— Cicero de Nat. Deor. i. 13; Plin. ii. 6 and 24; Manilius,
ii. 33.

(54) p. 30.— Kosmos, Bd. i. S. 91 (English edition, Vol. i. p. 78).
Compare Encke's excellent considerations on the Arrangement of the
Sidereal System, 1844, S. 7.

(M) p. 31.— Kosmos, Bd. i. S. 162 (English edition, Vol. i. p. 145).
(5G) p. 31.— Aristot. de Ccelo, i. 7, p. 276, Bekker.
(57) p. 31.— Sir John Hersehel, Outlines of Astronomy, 1849, § 803,
p. 541.

X NOTES.

(58) p. 32.— Bessel, in Schumacher's Jahrbuch fur 1839, S. 50.

(59) p. 32.— Ehrenberg, in the Abhaudl. der Berl. Akad. 1838, S. 59 ; in
his " Infusionsthieren," S. 170.

(m) p. 33. — Aristotle, at that early period, argued against Leucippus and
Democrites that there can be no unoccupied space — no void in the Universe
(Phys. Auscult. iv. 6 to 10, p. 213-217, Bekker).

(61) p. 33. — "Aka'sa, according to Wilson's Sanscrit Dictionary, is 'the
subtle and ethereal fluid supposed to fill and pervade the Universe, and to be the
peculiar vehicle of light and sound.' The word aka'sa (shining) comes
from the root ka's, to shine, combined with the preposition a. The five
elements collectively are called pantschata or pantschatra ; and a dead man is,
singularly enough, called one who has attained the five elements (prapta-
pantschatra), i. e. one who has been dissolved into the five elements So in
the text of the Amarakoscha, Amarasinha's Dictionary" (Bopp). Colebrook's
excellent Memoir on the Sankhya-Philosophy treats of the five elements
(Transactions of the Asiatic Society, Vol. i. Lond. 1827, p. 31). Strabo
(xv. § 59, p. 713, Gas.) notices, from Megasthenes, the fifth all-fashioning
element of the Indians, without, however, naming it.

(62) p. 33. — Empedocles (v. 216) terms the sether -rra/j.<pav6wv, bright-
beaming, therefore self-luminous.

(63) p> 33._plato, Cratyl. 410, B, where &«&c^> is found. Aristot. de
Coslo, i. 3, p. 270, Bekk.,in opposition to Anaxagoras — a&fpa Trpo<r<mv6fjia(Ta.v

irov, diro TOV 3-e?v oet r6v 6'iStov ^p6vov Sep-evai Tr\v firu-
O.VTW. Aval-aybpas Se KaraKe'xpTjTat rw vvo^ari rovrca 6v Ka\ws
yap a&fpa ai/n irvpos. In Aristot. Meteor, i. 3, p. 339,
lin. 21 — 34, Bekk., it is said more in detail — " The so-called aether has an
ancient appellation, which Anaxagoras appears to identify with fire ; for the
upper region, he says, is full of fire, arid that upper region he looked upon as
aether : and herein he was also right, for the bodies which move eternally in
their courses appear to have been regarded by the ancients as having in their
nature something divine, and therefore were called ather, as a substance to
which there is nothing comparable on earth. Those, however, who regard
surrounding space, and not merely the bodies which move in it, as fire, and
all between the Earth and the stars as air, would surely give up their childish
dream if they would accurately consider the results of the latest researches of
mathematicians." (The same etymology of the word, from rapid revolution,
is repeated by the author of the book De Mundo, cap. 2, p. 392, Bekk.)
Professor Franz has justly remarked, "that the play upon words of bodies

NOTES. XI

engaged in an 'eternal course' (o-w/ua oet d-e'o?) and 'divine' (i^eTov), alluded
to in the Meteorologica, is strikingly indicative of Greek fancy, and gives an
additional evidence of the far from happy treatment of etymologies by the
ancients." Professor Buschmann calls attention to a Sanscrit word, aschtra,
for sether, atmosphere, which resembles much in appearance the Greek a&np,
and had been compared with it by Vans Kennedy, in his " Researches into
the Origin and Affinity of the principal Languages of Asia and Europe," 1828,
p. 279. There may be assigned to this word, also, a root (as, asch), to which
the Indians attached the idea of " shilling."

(M) p. 34.— Aristot. de Coelo, iv. 1 and 3—4, p. 308 and 311—312,
Bekk. If Aristotle refused to the sether the name of a fifth element— which,
indeed, Hitter and Martin deny (vide Hitter, Geschichte der Philosophic,
Th. iii. S. 259 ; and Martin, Etudes sur le Time'e de Platon, T.ii. p. 150)—
it was only because the sether, as a state of matter, appeared to him to want
a counterpart (compare Biese, Philosophic des Aristoteles, Bd. ii. S. 66).
With the Pythagoreans, aether as a fifth element was represented by the fifth
of the regularly-formed bodies, the dodecahedron, composed of twelve penta-
gons (Martin, T. ii. p. 245—250).

(65) p. 34. — See on this subject the passages collected by Biese, Bd. ii.
S. 93.

(6G) p. 35.— Kosmos, Bd. i. S. 159 and 416, Note 88 (English edition,
Vol. i. p. 143, Note 118).

(67) p. 35. — Compare the fine passage on the rays of the sun in Sir John
Herschel's Outlines of Astronomy, p. 237 : — By the vivifying action of the
sun's rays vegetables are enabled to draw support from inorganic matter, and
become, in their turn, the support of animals and of man, and the sources of
those great, deposits of dynamical efficiency which are laid up for human use
in our coal strata. By them the waters of the sea are made to circulate in
vapour through the air, and irrigate the laud, 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."

(68J p. 35.— Phil. Trans, for 1795, Vol. Ixxxv. p. 318; John Herschel,
Outlines of Astronomy, p. 238 ; Kosmos, Bd. i. S. 195 and 436, Note 33
(English edition, Vol. i. p. 177 and Note 163).

(69) p. 36.— Bessel, in Schumacher's Astr. Nachr. Bd. xiii. 1836,
No. 300, S. 201.

(70) p. 36.— Bessel, in the same, S. 186—192 aud 229.

Xll NOTES.

(71) p. 36.— Fourier, Theorie analytique de la Chaleur, 1822, p. ix.
(Annales de Chimie et de Physique, T. iii. 1816, p. 350 ; T. iv. 1817, p. 128 ;
T. vi. 1817, p. 259 ; T. xiii. 1820, p. 418.) Numerical estimations of the
loss which the heat of the stars (chaleur stellaire) suffers in passing through
space, by absorption in the ether, are attempted by Poisson, in his Theorie
mathematique de la Chaleur, § 196, p. 436; § 200, p. 447 ; and § 228, p. 521.

(72) p. 36. — On the warming power of the stars, see Aristot. Meteor, i. 3,
p. 340, lin. 28 ; and Seneca, on the height of the strata of the atmosphere
which have the minimum of heat, in Nat, Qusest. ii. 10 — "superiora enim
aeris calorem vicinorum siderum seutiunt "

P) p. 36.— Piut. de plac. Philos. ii. 13.

(74) p. 37. — Arago sur la temperature du Pole et des espaces celestes,
in the Annuau-e du Bureau des Long, pour 1825, p. 189, and pour 1834,
p. 192 ; Saigey, Physique du Globe, 1832, p. 60 — 78. From discussions on
the refraction of rays, Svanberg finds, for the temperature of space, — 50°.3
Cent., or -58°.5 F. (Berzelius, Jahresbericht fiir 1830, S. 54) ; Arago makes
it, from polar observations, -56°.7 Cent. (-70° F.) ; Peclet, -60° Cent.
(— ?6° F.) ; Saigey, by the diminution of heat in the atmosphere from 367
of my determinations in the Andes and in Mexico, — 65° Cent. ( — 85° F.), and
by thermometric observations on Mont Blanc and in Gay-Lussac's aerostatic
voyage, -77° Cent. (-106°.6 F.) ; Sir John Herschel (Edinburgh Review,
Vol. Ixxxvii. 1848, p. 223) makes it- 132° F. That Poisson, (the mean tempe-
rature of Melville Island, lat. 74° 47', being already - 18°.7 Cent.or— 1°.7 F.),
could deduce for the temperature of space, from purely theoretical grounds —
[according to which space would be warmer than the extreme limit of the
atmosphere (§ 227, p. 520)] —a temperature no lower than - 13° or + 8°.6 F.,
— while, on the other hand, Pouillet (Comptes rendus de 1'Acad. des Sc.T. vii.
1838, p. 25-65) makes it —142° C. (223°.6 F),— must excite our astonish-
ment, and diminish our confidence in the methods of inquiry hitherto pursued
in these interesting speculations.

(~5) p. 38. — Poisson, Theorie mathem. de la Chaleur, p. 438. According
to him, the consolidation of the terrestrial strata oegan from the centre, and
proceeded gradually from, thence to the surface (§ 193, p. 429). Compare
also Kosmos, Bd. i. S. 184 (English edition, Vol. i. p. 166).

(76) p. 38.— Kosmos, Bd. i. S. 86 and 149 (English edition, Vol. i. p. 74
and 133).

(77) p. 39. — " Were there no atmosphere, a thermometer, freely exposed
(at sunset) to the heating influence of the earth's radiation, and the cooling

NOTES. Xlll

power of its own iuto space, would indicate a medium temperature between
that of the celestial spaces ( — 132° F.) and that of the earth's surface below
it (82° F. at the equator, -3°.5 F. in the Polar Sea). Under the equator,
then, it would stand, on the average, at —25° F., and in the Polar Sea at
— 68° F. The presence of the atmosphere tends to prevent the thermometer
so exposed from attaining these extreme low temperatures — first, by imparting
heat by conduction ; secondly, by impeding radiation outwards" (Sir John
Herschel, in the Edinburgh Review, Vol. Ixxxvii. 1848, p. 223). " Si la
chaleur des espaces planetaires n'existoit point, notre atmosphere eprouverait
un refroidissement, dont on ne peut fixer la limite. Probablement, la vie des
plantes et des animaux seroit impossible a la surface du globe, ou releguee
dans une etroite zone de cette surface" (Saigey, Physique du Globe, p. 77).

(7S) p. 39. — Traite de la Comete de 1743, avec une Addition sur la Force
de la Lumiere et sa Propagation dans 1'Ether, et sur la Distance des Etoiles
fixes, par Loys de Cheseaux (1744). On the transparency of space, see
Gibers, in Bode's Jahrbuch fur 1826, S. 110—121 ; Struve, Etudes d'Astr.
stellaire, 1847, p. 83—93, and Note 95. Compare also Sir John Herschel,
Outlines of Astr. § 798 ; and Kosmos, Bd. i. S.158 (English edit. vol. i. p. 142).

(79) p. 40. — Halley on the Infinity of the Sphere of Fixed Stars, in the
Phil. Trans. Vol. xxxi. for the year 1720, p. 22—26.

(8°) p. 40.— Kosmos, Bd. i. S. 92 (English Edition, Vol. i. p. 80).

(81) p. 40. — "Throughout by far the larger portion of the extent of the
Milky Way in both hemispheres, the general blackness of the ground of the

heavens on which its stars are projected," &c "In those regions where

that 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 Astronomy, p. 537 and 539).

(82) p. 40.— Kosmos, Bd, i. S. 89, 113, and 393, Note 23 (English edition,
p. 77, 99, and Note 53) ; Laplace, Essai philosophique sur les Probabilites,
1825, p. 133 ; Arago, in the Annuaire du Bureau des Long, pour 1832,p. 188,
pour 1836, p. 216; John Herschel, Outlines of Astronomy, § 577.

(M) p. 40.— The vibratory motion of the effluxes at the head of some
coitnets — such as was observed in the comet of 1744, and by Bessel in Halley's
comet between the 12th and 22d October, 1835 (Schumacher, Astron. Nachr.
No. 300— 302, S. 185— 232)— "may, indeed, in particular individuals of this
class of bodies, influence the translatory motion and the rotation, and even
leaius to infer polar forces (S. 201 and 229) different from the ordinary attract-
ing power of the Sun ;" but the acceleration of the three and a half yearly period

XIV NOTES.

of revolution of Encke's comet, which has already manifested itself with such
great regularity for sixty-three years, cannot well be conceived to be depen-
dent on a sum of accidental effluxes. Compare, respecting this cosmically
important subject, Bessel, in Schumacher's Astr. Nachr. No. 289, S. 6, and
No. 310, S. 345—350, with Encke's Memoir on the Hypothesis of a
Resisting Medium, in Schum. No. 305, S. 265—274.

(**) p. 41.— Olbcrs, in Schum. Astr. Nachr. No. 268, S. 58.

(*) p. 41.— Outlines of Astronomy, § 556 and 597.

(86) p. 41. — " En assimilant la matiere tres rare qui remplit les espaces
celestes quant a ses proprietes refringentes aux gas terrestres, la densite de cette
matiere ne saurait depasser une certaine limite doiit les observations des
etoiles changeantes, p. e. celles d' Algol ou de £ de Persee, peuvent assignor
la valeur (Arago, Annuaire pour 1842, p. 336 — 345).

(80 p. 41.— Wollaston, in the Phil. Trans, for 1822, p. 89 ; Sir John
Herschel, Outl. of Astr. § 34 and 36.

t88) p. 42.— Newton, Princ. mathem. T. iii. (1760), p. 671 :— " Vapores,
qai ex sole et stellis fixis et caudis cometarum oriuntur, incidere possunt in
atmospheeras planetarum."

(89) p. 42.— Kosmos, Bd. i. S. 129 and 141 (English edition, Vol. i. p. 114
and 126).

(*") p. 43.— Kosmos, Bd. ii. S. 355—373 and 507—515 (English edition,
Vol. ii. p. 314—330, Note 482—503).

(91) p. 43.— Delambre, Hist, de 1'Astronomie moderne, T. ii. p. 255, 269,
and 272. Morin says himself, in his Scientia Longitudinum, published in
1634 — "Applicatio tubi optici ad alhidadam pro stellis fixis prompte et
accurate mensurandis a me excogitata est." Picard used no telescope with his
mural quadrant up to 1667 ; and Hevelius, when Halley visited him in 1679,
at Dantzic, and admired the exactness of his measurements of altitude (Baily,
Catal. of Stars, p. 38), observed through improved apertures for unassisted
vision.

(92) p. 44. — The unfortunate Gascoigue, whose merits were long unac-
knowledged, met his death, when hardly 23 years of age, at the battle of
Marston Moor, between Cromwell and the King's troops (see Derham, in the
Phil. Trans. Vol. xxx. for 1717—1719, p. 603—610). To him belong
inventions or adaptations which were long attributed to Picard and Anzout,
and which gave to " Observing Astronomy," — which has for its chief object

NOTES. XV

the determination of place in the heavens, — an extension and success never
before attained.

(93) p. 44.— Kosmos, Bd. ii. S. 209 (English edition, Vol. ii. p. 175).

(94) p. 45. — The passage in which Strabo (Lib. iii. p. 138, Casaub.) seeks
to refute the views of Posidonius, runs, according to the manuscript, as
follows : — " The image of the sun, both at sunrise and sunset, is enlarged
over the sea, because there the vapours ascend most abundantly from the
humid element ; for the eye, when it sees through vapours, as when it looks
through tubes, receives the images refracted and enlarged : and the same thing
happens when it sees the sun or moon set behind a thin dry cloud, in which
case they also appear of a red colour." This passage has, quite lately, been
supposed to be corrupt (Kramer, in Strabouis Geogr. 1844, Vol. i. p. 211) ;
and it has been proposed to read in lieu of 81 ouAwz/, St va.\tav (through
glass globes) (Schneider, Eclog. phys. Vol. ii. p. 273). The magnifying
power of hollow glass globes filled with water (Seneca, i. 6) was, indeed,
known to the ancients, as well as the effects of burning glasses, or " burning
crystals" (Aristoph. Nub. v. 765), and of Nero's emerald (Pliu. xxxvii. 5) ;
but certainly such globes could not serve for astronomical measuring instru-
ments (compare Kosmos, Bd. ii. S. 464, Note 44 ; English edition, Vol. ii,
Note 384). Altitudes of the Sun, taken through thin light clouds, or through
volcanic vapours, show no trace of the influence of refraction (Humboldt,
Recueil d'Observ. astr. Vol. i. p 123). Colonel Baeyer has been unable to
find any angular alteration of the heliotrope light when streaks of inist were
passing, or even with vapours purposely called forth, — thus confirming
Arago's experiments. Peters, in Pulkova, in comparing groups of star-
altitudes measured when the sky was clear with others observed through
light clouds, finds no difference amounting to 0".017 (see his Recherches sur
la Parallaxe des Etoiles, 1848, p. 80 and 140—143 ; Struve, Etudes stellaires
p. 98). On the employment of tubes in Arabian instruments, see Jourdain
sur 1'Observatoire de Meragah, p. 27 ; and A. Sedillot, Mem. sur les Instru-
ments astrpnomiques des Arabes, 1841, p. 198. Arabian astronomers have
also the merit of having first introduced large gnomons with small circular
openings. In the colossal sextants of Abu Mohammed al-Chokandi, the
limb, graduated to 5 minutes, received the image of the Sun itself. " A midi
les rayous du Soleil passaieut par une ouverture pratiquee dans la voute de
1'Observatoire qui couvrait 1'instrument, suivaieut le tuyau, et formaient sur la
concavite du sextant une image circulaire, dont le centre donnait, sur 1'arc
gradue, le complement de la hauteur du Soleil. Get instrument ne differe de

XVI >'OTES.

notre Mural qu'en ce qn'il etait garni d'un simple tuyau an lieu d'une lunette"
Sedillot, p. 37, 202, and 205. Pierced Sight-vanes (Diopters, Pinnule,)
were employed by the Greeks and Arabians for the determination of the
diameter of the Moon in such manner, that the circular opening in the
moveable object-diopter was larger than that of the eye-diopter, which did not
move ; and the former was moved until the disc of the Moon seen through the
eye-aperture filled up the object-aperture (Delambre, Hist, de 1'Astr. du moyen
Age, p. 201 ; Sedillot, p. 198). The sight-vanes, with round or longitudinal
openings of Archimedes, who made use of the direction of the shadows of two
small cylinders attached to the same alidade, appear to be an arrangement
first introduced by Hipparchus (Bailly, Hist, de 1'Astr. mod. 2de edit. 1785,
T. i. p. 480). Compare also Theon Alexandrin. Bas. 1538, p. 257 and 262 ;
Les Hypotyp. de Proclus Diadochus, ed. Halma, 1820, p. 107 and 110; and
Ptolem. Almag. ed. Halma, T. i. Par. 1813, p. Ivii.

(M) p. 45. — According to Arago. See Moigno, Repert. d'Optique moderne,
1847, p. 153.

(^ p. 46. — Respecting the comportment of the dark streaks of the Sun's
image in the Daguerreotype, see the Comptes rendus des Seances de P Academic
des Sciences, T. xiv. 1842, p. 902—904; and T. xvi. 1843, p. 402—407.

(97) p. 47.— Kosmos, Bd. ii. S. 370 (English edition, Vol. ii. p. 329).

(S8) p. 47. — For the important distinction of proper and reflected light
I may adduce, as an example, Arago's investigation of the light of comets.
By the employment of chromatic polarisation, discovered by him in 1811,
the production of the complementary colours, red and green, showed that the
light of Halley's comet (1835) contained reflected solar light. I was myself
present at his earlier attempts to compare, by means of the equal or unequal
intensities of the images in the polariscope, the proper light of Capella with
the light of the bright comet which emerged suddenly from amidst the rays of
the Sun in the beginning of July 1819. Annuaire du Bureau des Long,
pour 1836, p. 232 ; Kosmos, Bd. i. S. Ill and 392 (English edition, p. 97
and p. xix. Note 51) ; and Bessel, in Schumacher's Jahrbuch fiir 1837,
S. 169.

(99) p> 47._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), que la lumiere de tous les corps terrestres incandescents, solides ou
liquides, est de la lumiere naturelle, tant qu'elle emane du corps sous des
incidences perpendiculaires. La lumiere, an contraire, qui sort de la surface
incandescente sous un angle aigu, offre des marques manifestes de polarisation.

NOTES. XV 11

Je ne m'arrete pas a te rappeler 19! comment je deduisis de ce fait la conse-
quence curieuse que la lumiere ne s'engendre pas seulement a la surface des
corps : qu'uue portion nait dans leur substance meme, cette substance fut-elle
du platine. J'ai seulement besoin de dire qu'en repetant la mcrne serie
d'epreuves, et avec les memes instruments, sur la lumiere que lance une sub-
stance gazeuse enflammee, on ne lui trouve, sous quelque inclinaison que ce
soit, aucun des caracteres 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 011 la soumet a
des reflexions ou a des refractions convenables. De la une methode tres
simple pour decouvrir a 40 millions de lieues de distance la nature dn Soleil.
La lumiere provenant du lord de cet astre, la lumiere emanee de la rnatiere
solaire sous un angle aigu, et nous arrivant sans avoir eprouve en route des
reflexions ou des refractions sensibles, oflre-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 partie 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." (On
the envelopes of the Sun, see Arago, in the Annuaire pour 1846, p. 464.)
I give all the detailed optical explanations which I borrow from the writings
of my friend (whether manuscript or printed) in his own words, in order to
avoid mistakes to which the fluctuations of scientific terminology might give
rise in either retranslating into French or in translating into the several other
languages in which Cosmos appears.

(I0°) p. 47. — Sur Met d'une lame de tourmaline taillee parallelement aux
arretes du prisme servant, lorsqu'elle est convenablement situee, a elimiuer
en totalite les rayons reflechis par la surface de la mer et meles a la lumiere
provenant de 1'ecueil : vide Arago, Instructions de la Bonite, in the Anuuaire
pour 1836, p. 339—343.

(101) p. 47. — De la possibilite de determiner les pouvoirs refringents des
corps d'apres leur composition chimique (applied to the proportions of oxygen
and nitrogen in atmospheric air ; to the quantity of hydrogen contained in
ammonia and in water ; to carbonic acid, alcohol, and the diamond), see Biot
et Arago, Memoire sur les Affinite's des Corps pour la Lumiere, March 1806 ;
also, Memoires mathe'm. et phys. de 1'Institut, T. vii. p. 327—346 ; and my
Memoire sur les Refractions astronomiques dans la Zone torride, in the Recueil
d'Observ. astron. Vol. i. p. 115 and 122.

(102) p. 47.— Experiences de M. Arago sur la puissance refractive des
VOL. III. b

XV111 NOTES.

corps diaphanes (de 1'air sec et de 1'air humide) par le deplacement des
franges, in Moigno, Repertoire d'Optique mod. 1847, p. 159 — 162.

(103) p. 48. — In order to refute the statement of Aratus, that in the
Pleiades there are only six stars visible, Hipparchus says, (Ad Arati Phsen. i.
p. 190, in Uranologio Petavii) "A star has escaped A.ratus ; for if, in a clear and
moonless light, one gazes steadfastly and keenly upon the constellation of the
Pleiades, there appear in it seven stars : it seems, therefore, surprising that
Attalus, in his description of the Pleiades, allows the oversight of Aratus to
pass unuoticed, as if his statement had been correct." In the Catasterisma
(xxiii.)attributed to Eratosthenes,Merope is termed "the invisible," Trava^av^s.
On a conjectured connection between the name of the veiled daughter of
Atlas with geographical myths in the Meropis of Theopompus, as well as with
the great Saturnian continent of Plutarch, and the Atlantis, see my Examen.
crit. de 1'Hist. de la Geographic, T. i. p. 1?0. Compare also Ideler,
Untersuchungen tiber den Ursprung und die Bedeutung der Sternnamen,
1809, S. 145 ; and in reference to the determination of astronomical place,
see Madler, Untersuch. iiber die Fixstem-Systeme, Th. ii. 1848, S. 36 und
166, as well as Baily, in the Mem. of the Astr. Soc. Vol. xiii. p. 33.

(104) p. 48.— Ideler, Sternnamen, S. 19 und 25. " On observe," says Arago,
"qu'une lumiere forte fait disparaitre une lumiere faible placee dans le
voisinage. Uuelle peut en etre la cause ? II est possible physiologiquemeut
que 1'ebranlement communique a la retine par la lumiere forte s'etend au
dela des points que la lumiere forte a frappes, et que cet ebranlement secondaire
absorbe et neutralise en quelque sorte 1'ebranlement provenant de la seconde et
faible lumiere. Mais sans entrer dans ces causes physioiogiques, il y a une
cause directe qu'on peut indiquer pour la disparition de la faible lumiere :
c'est que les rayons provenant de la grande n'ont pas seulemeut forme une
image nette sur la retine, mais se sont disperses aussi sur toutes les parties de
cet organe a cause des imperfections de transparence de la cornee. Les
rayons du corps plus brillant, a, en traversant la cornee se comportent comme
en traversant un corps legerement depoli. Une partie de ces rayons refractes
regulierement forme 1'image meme 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 Pobjet voisin b, Cette derniere image doit done ou disparaitre ou etre
affaiblie. De jour deux causes contribuent a 1'affaiblissement des etoiles :
1'une de ces causes, c'est 1'image distincte de cette portion de 1'atmosphere,
comprise dans la direction de 1'etoile (de la portion aerienne placee entre 1'ojil
et 1'etoile), et sur laquelle 1'image de 1'etoile vient de se peiudre ; 1'autre cause,

NOTES. XIX

c'est la lumiere diffuse provenant de la dispersion que les defauts de la
cornee impriment aux rayons emauants de tous les points de 1'atmosphere
visible. De nuit les couches atmospheriques 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 diaphanite de la cornee. Le meme raisonnement s'applique a
une deuxieme, troisieme .... millieme etoile. La retine se trouve done
eclairee en totalite par une lumiere diffuse proportionelle au nombre de ces
etoiles et a leur eclat. On con9oit par la que cette somme de lumiere diffuse
affaiblisse ou fasse entierement disparaitre 1'image de 1'etoile vers laquelle on
dirige la vue" (Arago, Manuscript, 1847).

(lft5) p. 50. — Arago, in the Annuaire for 1842, p. 284, and in the Comptes
rendus, T. xv. 1842, p. 750; Schum. Astr. Nachr. No. 702. Dr. Galle
writes to me — "With reference to your conjectures on the visibility of
Jupiter's satellites, I have made some estimations of their magnitude, and,
contrary to my own expectation, have found that they are not of the 5th, but
only of the 7th, or at the utmost of the 6th magnitude. It was only the
brightest of the satellites, the third, which showed itself at all equal to a
neighbouring star of the 6th magnitude, which 1 could only recognise with
the naked eye at some little distance from Jupiter : so that, making allowance
for the brightness of Jupiter, this satellite might, perhaps, be estimated at
from the 5th to the 6th magnitude if it stood alone. The fourth satellite was
at its greatest elongation, but I could only estimate it at the 7th magnitude.
The rays of Jupiter would not prevent this satellite from being visible if it
were itself brighter. After comparisons of Aldebaran with the neighbouring
clearly -recognisable double star, & Tauri (with 5§ minutes of distance), I
estimate, for an ordinary eye, the radiation from Jupiter at from 5 to 6
minutes at least." These estimations agree with those of Arago ; the latter
even believes that the false rays may amount in some persons to double the
quantity. The mean distances of the four satellites from the centre of the
planet are, as is well known, 1' 51", 2' 57", 4' 42", and S' 16". " Si
nous supposons que 1'image de Jupiter, dans certains yeux exceptionnels,
s'epanouisse seulement par des rayons d'une ou deux minutes d'arnplitude, il
ne semblera pas impossible que les satellites soient de terns en terns apei^us
sans avoir besoin de recourir a 1'artifice de I'amplification. Pour verifier
cette conjecture, j'ai fait construire une petite lunette dans laquelle 1'objectif
et 1'oculaire ont a peu pres le meme foyer, et qui des lors ne grossit point,
Cette lunette ne detruit pas entierement les rayons divergents, mais elle en

XX o , NOTES.

reduit considerablement la longueur. Cela a suffi pour qu'un satellite con-
veuablement ecarte de la planete soit devenu visible. Le fait a etc constate
par tous les jeunes astronomes de PObsejvatoire" (Arago, in the Comptes
reudus, T. xv. p. 751). I may instance, as a remarkable example of the
keen sight and great sensibility of the retina in particular individuals
who s<je Jupiter's satellites with the naked eye, a deceased master tailor of the
name of Sehon, in Breslau, respecting whom the learned and active Director
of the Observatory of that place, Herr von Boguslawski, has given ma
interesting communications. " After being assured by repeated trials, since
1820, that in clear moonless nights Schon, with the naked eye, could assign
correctly the position of Jupiter's satellites, even of more than one at a time,
— on speaking to him of the rays and tails of light which seemed to prevent
others from doing the same, he expressed his astonishment at it ; and from
the animated discussion which arose between him and the bystanders
respecting the difficulty of seeing the satellites with the naked eye, I could
not but infer that the planets and the fixed stars always appeared to him as
luminous points, free from rays. He saw the third satellite best, and he could
also see the first at its widest elongation ; but he never saw the second or
fourth. "When the atmosphere was not quite favourable, the satellites
appeared to him only as faint streaks of light. Small fixed stars, perhaps on
account of their scintillating and less tranquil light, were never confounded by
him with the satellites. Some years before his death, Schon complained to
me that his eyes, as they grew older, could no longer reach Jupiter's satellites,
and that now, even when the atmosphere was quite clear, their place was
only marked to him by faint streaks." The above account agrees perfectly
with what has long been known respecting the relative brightness of Jupiter's
satellites ; for, in individuals whose organs have so high a degree of perfection
and sensibility, probably brightness and the quality of light are more
influential than distance from the central planet. Schon never saw the second
and fourth satellites : the second is the smallest of all ; the fourth is, indeed,
next to the third, the largest, and also the most distant, but periodically it is dark
in colour, and at ordinary times it has the faintest light of any of the satellites.
Of the third and first, which have been seen best and most often with the
unassisted eye, the third is the largest of all, usually the brightest, and of a
very decided yellow colour ; but the first sometimes exceeds in the intensity of
its bright yellow light the brightness of the third, which is much larger
(Miidler, Astron. 1846, S. 231—234 und 439). How, by relations of
refraction in the visual organ itself, distant luminous points may appear as

NOTES. XXI

lines or streaks of light, has been shown by Sturm and Airy in the Comptes
rendus, T. xx. p. 764—766.

(10fi) p. 50. — "L'image epanouie d'une etoile de 7eme grandeur n'cibranle
pas suffisamraent la re'tine : elle n'y fait pas naitre uue sensation appreciable
de lumiere. Si 1'image n'etait point epanouie (par des rayons divergents),
la sensation aurait plus de force et 1'etoile se verrait. La premiere classe
d'etoiles invisibles a 1'oeil nu ne serait plus alors la 7eme : pour la trouver,
il faudrait peut-etre descendre alors jusqu'a la 12eme. Cousiderons un gronpe
d'etoiles de 7eme grandeur tellement rapprochees les uues des autres que les
intervalles echappent necessairement a roeil. Si la vision avait de la
nettete, — si I'image de chaque etoile etait tres petite et bien terminee, 1'obser-
vateur apercevrait nu champ de lumiere dont cliaque point aurait V eclat con-
centre d'une etoile de 7«ne grandeur. Ij eclat concentre d'une etoile de
7eme grandeur suffit a la vision a 1'oeil nu. Le groupe serait done visible a
1'oeil na. Dilatons maintenant sur la retine 1'image de chaque etoile du
groupe; remplacons chaque point de 1'ancienne image generale par un petit
cercle : ces cercles empieteront les uns sur les autres, et les divers points de
la retine se trouveront eclaires par de la lumiere venant simultanement de
plusieurs etoiles. Pour pen qu'on y reflechisse, il restera evident qu'excepte
sur les bords de 1'image geuerale 1'aire lumineuse ainsi eclairee a precisement,
a cause de la superposition des cercles, la mcme intensite que dans le cas oil
chaque etoile n'eclaire qu'un seul point an fond de 1'oeil ; mais si chacun do ces
points re9oit une lumiere egale en intensite a la lumiere concentree d'une
etoile de 7e grandeur, il est clair que I'epauouissement des images individuelles
des etoiles coutigiies ne doit pas empecher la visibilite de 1'ensernble. Les
instruments telescopiques ont, quoiqu'a un beaucoup moindre degre, le defaut
de donner aussi aux etoiles un diametre sensible et factice. Avec ces instru-
ments, comme a 1'oeil nu, on doit done apercevoir des groupes, composes
d'etoiles inferieures en intensite a celles que les memes lunettes ou telescopes
feraient apercevoir isolement" (Arago, in the Anuuaire du Bureau des
Longitudes pour 1'an 1842, p. 284).

(10?) p. 50.— Sir William Herschel, in the Phil. Trans, for 1803, Vol. xciii.
p. 225 ; and for 1805, Vol. xcv. p. 184. Compare Arago, in the Annuaire
pour 1842, p. 360—374.

(10S) p. 53. — Humboldt, Relation hist, du Voyage aux Regions equinox.
T. i. p. 92 — 97 ; and Bouguer, Traite d'Optique, p. 360 and 365. Compare
also Captain Beechey, in the Manual for Scientific Enquiry for the use of the
Royal Navy, 1849, p. 71.

XX11 NOTES.

(109) p. 53.— The passage of Aristotle referred to by Buffon is in a book
where one would least have looked for it — in the De generat. animal, v. 1,
p. 780, Bekker. Closely translated, it is as follows : — " Keen sight means,
on one side, the power of seeing far ; and, on the other, an exact recognition of
the differences between the things seen. Both are not the case at the same
time in the same person ; for a man holding his hand above his eyes, or
looking through a tube, is not more or less able to judge of the difference
Between colours, but he will be able to see objects at a greater distance.
Thus also it happens that those who are in vaults or cisterns sometimes see
stars from them." Qp\ry(j.a.ra, and especially <ppeara, are subterranean cisterns
or well-chambers, which, in Greece, are so constructed (as an eye-witness,
Professor Franz, remarks) as to communicate with the air and light by a
perpendicular shaft, widening below like the neck of a bottle. Pliny (Lib. ii.
cap. 14) says — " Altitude cogit minores videri stellas j affixas coelo Solis
fulgor interdiu non cerni, quum acque ac noctn luceant : idque manifestnm
fiat defectu Soils et prcealtis puteis" Cleomedes (CycL Theor. p. 83, Bake)
does not speak of stars being seen in the day-time, but he states "that the
Sun, seen from deep cisterns, appears larger by reason of the darkness and the
damp air."

(no) p. 54. — " We have ourselves heard it stated by a celebrated optician,
that the earliest circumstance which drew his attention to astronomy, was
the regular appearance, at a certain hour, for several successive days, of a
considerable star through the shaft of a chimney" (John Herschel, Outlines
of Astronomy, f 61). The chimney-sweepers from whom I have inquired,
say pretty uniformly, " that they never see stars in the day-time ; but that
at night the sky seen through tall chimneys looks quite near, and the stars
seem larger." I forbear from any consideration of the connection between
these two illusions.

^iii) p. 54.— Saussure, Voyage dans les Alpes (Neuchatel, 1779, 4to.) T. iv.
$ 2007, p. 199.

(112) p. 55. — Humboldt, Essai sur la Geographic des Plantes, p. 103.
Compare also my Voy. aux Regions equinox. T. i. p. 143 and 248.

(113) p. 56. — Humboldt, in Baron Zach's Monatlicher Correspondenz zur
Erd- und Himmels-kunde, Bd. i. 1800, S. 396 ; and in Voy. anx Regions
equin. T. i. p. 125. " On croyoit voir de petites fusees lancees dans Fair. Des
points lumineux, eleves de 7 a 8 degres, paroissoient d'abordsemouvoir dans
le sens vertical, mais puis se convertir en une veritable oscillation horizontale.
Ces points lumineux etoient des images de plusieurs etoiles agrandies (en

NOTES. xxir

apparence) par les vapeurs et revenant au meme point d'ou elles etoiem
parties."

(m) p. 56. — Prinz Adalbert von Preussen, Aus meinem Tagebuche, 1847,
S. 213. May the phenomenon described by me be connected with that
which Carlini observed at the passage of the Pole star, and its oscillations of
10 — 12 seconds, with the strongly-magnifying meridian telescope at Milan ?
(See Zach, Correspondance astronomique et geogr. Vol. ii. 1819, p. 84).
Brandes (Gehler's umgearb. phys. Worterb. Bd. iv. S. 549) is disposed to
refer them to mirage. The star-like light of the heliotrope has also been seen
by an excellent and practised observer, Colonel Baeyer, often uctuating hori-
zontally to and fro.

(115) p. 60. — The distinguished merit as an artist of Constantino Huygens,
who was secretary to King William III., has only recently been placed in its
true light by Uptenbrock, in the Oratio de fratribus Christiano atque Con-
stantino Hugenio, artis dioptricse cultoribus, 1838 ; and by the learned
Director of the Leydeu Observatory, Professor Kaiser, in Schumacher's Astr.
Nachr. No. 592, S. 246.

(116) p. 60.— Arago, in the Annuaire for 1844, p. 381.

(117) p. 60. — " Nous avons place ces grands verres," says Dominique
Cassini, " tantot sur un grand mat, tantot sur la tourde bois venue de Marty ;
enfin nous les. avons mis dans un tuyau monte sur un support en forme
d'echelle a trois faces, ce qui a eu (dans la decouverte des satellites de Saturne)
le succes que nous en avions espere." (Delambre, Hist, de 1'Astr. moderne,
T. ii. p. 785.) These excessive lengths of optical instruments remind us of
the Arabian quadrants of about 190 feet radius, in the divided limb of which the
image of the sun fell, as in a gnomon, through a small round aperture. There
was such a quadrant at Samarcand, probably imitated from an earlier-con-
structed sextant of Al-Chokandi, about 60 feet high. Compare Sedillot,
Prolegomenes des Tables d'Oloug Beigh, 1847, p. Ivii. and cxxix.

(118) p. 60.— Delambre, Hist, de 1'Astr. mod. T. ii. p. 594. The Capuchin
Monk, Schyrle von Rheita, a mystic, but highly experienced in optical matters,
had previously spoken, in his Oculus Enoch et Elise (Antv. 1645), of the
expected possibility of soon obtaining magnifying powers of 4000 for tele-
scopes, in order to give accurate maps of the Moon. Compare Kosmos, Bd.
ii. S. 511, Note 48 (English edition, p. cxvi. Note 488).

(119) p. 61.— Edinb. Encyclopedia, Vol. xx. p. 479.

(1JO) p. 61.— Struve, Etudes d'Astr. stellaire, 1847, Note 59, p. 24. I
have preserved in the text the denominations of Herschel's reflectors of 40,

XXIV NOTES.

20, and 7 English feet (though I use French measures everywhere else), not
only as more convenient, but also because the great labours of the father and
son in England and at Feldhausen, at the Cape of Good Hope, have given to
the names of these instruments an historical interest. [The French measures
are converted into English throughout this translation ; retaining, hovrever,
the original measures in addition wherever precision seems important, and
there could be room for doubt. But in the cases of the focal length by
which the telescopes severally referred to in pp. 59 and 60 of the text are
designated, the lengths specified by M. de Humboldt are left unchanged, for
reasons similar to those adduced by himself in the case of the Herschelian
telescopes.— ED.]

(121) p. 62.— Schumacher's Astr. Nachr., No. 371 and 611. Canchoix
and Lerebours have also sent out object-glasses of more than 12| (12'61 Eng.)
Paris inches, and 23 £ (24£ Eng.) feet focal length.

(122) p. 63. — Strove, Stellarum dupliciumet multiplicium Mensurse micro-
metricse, p. 2—41.

(123) p. 64. — Mr. Airy has recently given a comparative description of the
methods of construction of these telescopes, — the casting of the mirrors and
mixing of the metal, the polishing and the mounting (Abstr. of the Astr. Soc.
Vol. ix. No. 5, March 1849). Of the effect of the 6-foot metallic mirror of the
Earl of Rosse,it is there said (p. 120) : — "The Astronomer-Royal (Mr. Air)')
alluded to the impression made by the enormous light of the telescope : partly
by the modifications produced in the appearances of nebulse already figured,
partly by the great number of stars seen even at a distance from the Milky
Way, and partly from the prodigious brilliancy of Saturn. The account given
by another astronomer of the appearance of Jupiter was, that it resembled a
coach-lamp in the telescope; and this well expresses the blaze of light which
is seen in the instrument." Compare also Sir John Herschel, Outlines of
Astronomy, § 870 : — "The sublimity of the spectacle afforded by the magni-
ficent reflecting telescope constructed by Lord Rosse of some of the larger
globular and other clusters, is declared by all who have witnessed it to be such
as no words can express. This telescope has resolved or rendered resolvable
multitudes of nebulse which had resisted all inferior powers."

(124) p. 64.— Delambre, Hist, de 1'Astr. moderne, T. ii. p. 255.

(125) p. 65. — Struve, Mens. microm. p. xliv.

O25) p. 65.— Schumacher's Jabrbuch fur 1839, S. 100.
(127) p. 65. — "La lumiere atmospherique diffuse ne peut s'expliquer par le
reflet des rayons solaires sur la surface de separation des couches de differeute

NOTES. XXV

densites dont on suppose 1'atmosphere composee. En effet supposons le
Soleil place a 1'horizon, les surfaces de separation dans la direction du zenith
seraient horizoutales ; par consequent la reflexion serait horizontale aussi, et
nous ne verrions aucune lumiere au zenith. Dans 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 Fatmosphere composee de molecules
(spheriques, par example) dont chacune donne une image du soleil a peu pres
comme les boules de verres que nous pla9ons dans nos jardins. L'air pur est
bleu, parce que d'apres Newton les molecules de 1'air ont Ytpaisseur qui con-
vient a a reflexion des rayons bleus. II est done naturel que les petites
images du soleil que de tous cotes reflechissent les molecules spheriques de
1'air, et qui sont la lumiere diffuse, aient une teinte bleue ; mais ce bleu n'est
pas du bleu pur, c'est un blanc dans lequel le bleu predomine. Lorsque le
ciel n'est pas dans toute sa purete, et que Fair est mele de vapeurs visibles,
la lumiere diffuse re9oit 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 debleuetde
jaune." (Arago, Manuscript, 1847.)

(128) p. 65. — D'un des Effets des Lunettes sur la visibilite des etoiles
(Lettre de M. Arago a M. de Humboldt, en Dec. 1847) : — " L'oeil n'est doue
que d'une sensibilite circonscrite, bornee. Quand la lumiere qui frappe la
retine n'a pas assez d'intensite, 1'ceil ne sent rien. C'est par un manque
d'intensite que beaucoup A'etoiles, meme dans les nuits les plus profondes,
echappent a nos observations. Les lunettes ont pour effet, quant aux etoiles
d'augmenter 1'intensite de Fimage. Le faisceau cylindrique de rayons paral-
leles venaut d'une etoile, qui s'appuie sur la surface de la lentille objective, et
qui a cette surface circulaire pour base, se trouve considerablement resserre a
la sortie de la lentille oculaire. Le diametre du premier cylindre est au dia-
metre du second comme la distance focale de 1'objectif est a la distance focale
de P oculaire, ou bien comme le diametre de 1'objectif est au diametre de la
portion d'oculaire qu'occupe le faisceau emergent. Les inteusites de lumiere
dans les deux cylindres en question (dans les deux cylindres incident et
emergent) doivent etre entr'elles comme les etendues superficielles des bases.
Aiusi la lumiere ernergente sera plus condensee, plus 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 yrossit, etant plus etroit que le faisceau cylindrique qui
tombe sur 1'objectif, il est evident que la pupille, quelle que soit son ouverture,

XXVI NOTES.

recueillera plus de rayons par 1'intennediaire de la lunette que sans elle. La
lunette augmentera done toujours 1'intensite de la lumiere des etoihs.

" Le cas le plus favorable, quant a 1'effet des lunettes, est evidemment
celui ou 1'oeil re9oit la totalite du faisceau emergent, le cas ou ce faisceau a
moms de diametre que la pupille. Alors toute la, lumiere que 1'objectif em-
brasse, concourt, par 1'entremise du telescope, a la formation de 1'image. A
Trail nu, au contraire, une portion seule de cette meme lumiere est mise a
profit : c'est la petite portion que la surface de la pupille decoupe dans le
faisceau incident naturel. L'intensite de 1'image telescopique d'une etoile est
done a 1'intensite de 1'image a 1'oeil nu, comm'e la surface de 1'objectif est a
celle de la pvpille.

" Ce qui precede est relatif a la visibilite d'un seul point — d'une seule etoile.
Venons a 1'observation d'un objet ayant des dimensions angulaires sensibles, —
a 1'observation d'une planete. Dans les cas les plus favorables, c'est-a-dire
lorsque la pupille re9oit la totalite du pinceau emergent, 1'intensite de 1'image
de chaque point de la planete se calculera par la proportion que nous venons
de donner. La quantite totale de lumiere concourant a former V ensemble de
1'image a 1'ceil nu, sera done aussi a la quantite totale de lumiere qui forme
1'image de la planete, a 1'aide d'une lunette, comme la surface de la pupille
est a la surface de 1'objectif. Les intensites comparatives, non plus de points
isoles, mais des deux images d'une planete, qui se forment sur la retine a 1'ceil
nu, et par 1'intermediare d'une lunette, doivent evidemment diminuer
proportionnellement aux etendues superficielles de ces deux images. Les
dimensions lineaircs des deux images sont entr'elles comme le diametre de
1'objectif est au diametre du faisceau emergent. Le nombre de fois que la
surface de 1'image amplifiee surpasse la surface de 1'image a 1'oeil nn, s'ob-
tiendra done en divisant le carre du diametre de 1'objectif par le carre du
diametre du faisceau emergent, ou bien la surface de Vobjectifpar la surface
de la base circulaire du faisceau emergent.

" Nous avous deja obtenu le rapport des quantites totales de lumiere qui
engendrent les deux images d'une planefe, eu divisant la surface de 1'objectif
par la surface de la pupille. Ce nombre est plus petit que le quotient auquel
on arrive en divisaut la surface de Vobjectif par la surface du faisceau emer-
gent. II en resulte, quant aux planetes, qu'une lunette fait moins gagner en
intensite de lumiere qu'elle ne fait perdre en agrandissant la surface des
images sur la retine: 1'intensite de ces images doit doncallercontinuellement
en s'affaiblissant a mesure que le pouvcir amplificatif de la lunette ou du tele-
scope s'accroit.

NOTES. XXV11

" L'atmosphere peut etre considered comme une planete a dimensions in-
defmies. La portion qu'on en verra dans une lunette subira done aussi la loi
d'affaiblissement que nous venons d'indiquer. Le rapport entre 1'intensite de
la lumiere d'une planete et le champ de lumiere atmospherique a travers
lequel on la verra, sera le meme a 1'oeil nu et dans les lunettes de tous les
grossissementSj de toutes les dimensions. Les lunettes, sous le rapport de
1'intensite, ne favorisent done pas la visibilite des planetes.

" II n'en est point ainsi des etoiles. L'intensite de 1'image d'une etoile est
plus forte avec une lunette qu'a 1'ceil nu ; au contraire, le champ de la vision,
uniformement eclaire dans les deux cas par la lumiere atmospherique, est plus
clair a Pceil nu que dans la lunette. II y a done deux raisons, sans sortir des
considerations d'intensite, pour que dans une lunette 1'image de 1'etoile pre-
domine sur celle de 1'atmosphere notablement plus qu'a Fceil nu.

"Cette predominence doit aller graduellement en augmentant avec le
grossissement. En effet, abstraction faite de certaine augmentation du dia-
metre de 1'etoile, consequence de divers effets de diffraction ou d 'interferences ;
abstraction faite aussi d'une plus forte reflexion que la lumiere subit sur les
surfaces plus obliques des oculaires de tres courts foyers, 1'intensite de la
lumiere de V etoile est constante tant que 1'ouverture de 1'objectif ne varie pas.
Comme on 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 cir-
con stances rest ant egales, uue etoile sera d'autaut plus visible — sa predomi-
nence sur la lumiere du champ du telescope sera d'autant plus tranchee — qu'on
fera usage d'un grossissement plus fort." (Arago, Manuscript, 1847.) I add
from the Annuaire du Bureau des Long, pour 1846 (Notices scient. par M.
Arago), p. 381 : — " L'experience a montre que pour le commun des homines,
deux espaces eclaires et contigus ne se distinguent pas 1'un de 1'autre ; a
moms que leurs intensites comparatives ne presentent, au minimum, une
difference de -£$. Quand une lunette est tournee vers le firmament, son
champ semble uniformement eclaire : c'est qu'alors il existe, dans un plan
passant par le foyer et perpendiculaire a 1'axe de I'objectif, wtimageinclefinie
de la region atmospherique vers laquelle la lunette est dirigee. Supposons
qu'un astre, c'est-a-dire un objet situe bien au dela de I'atmosphere, se trouve
dans la direction de la lunette : sou image ne sera visible qu'autant qu'elle
augmentera de ^, au moins, 1'intensite de la portion de 1'image focale inde-
finie de I'atmosphere sur laquelle sa propre image limitee ira se placer. Sans
cela, le champ visuel continuera Kparaltre partout de la meme intensite."

(129) p. 67. — The earliest publication of Arago's explanation of the phscno-

XXV111 NOTES.

menon of scintillation was in the Appendix to the 4th hook of my Voyage aux
Regions equinoxiales, T. i. p. 623. I have great pleasure in being enabled to
enrich the section upon natural and telescopic vision with the following
extracts from the MSS. of my friend, which, for reasons already given, I
print in the original : — Des Causes de la Scintillation des Etoiles : " Ce qu'il
y a de plus remarquable dans le phenomene de la scintillation, c'est le change-
ment de couleur. Ce changement est beaucoup plus frequent que 1'observation
ordinaire ne 1'indique. En effet, en agitant la lunette on trausforme 1'image
dans une ligne on un cercle, et tons les points de cette ligne ou de ce cercle
paraissent de couleurs differentes. C'est la resultante de la superposition de
toutes ces images que Ton voit lorsqu'on laisse la lunette immobile. Les
rayons qui se reunissent au foyer d'uue lentille, vibreut d'accord ou en des-
accord, s'ajoutent ou se detruisent, suivant que les couches qu'ils ont traverse,
out telle ou telle refringence. L'ensemble des rayons rouges peut se detruire
seul si ceux de droite et de gauche, et ceux de haut et de has, out traverse des
milieux inegalement refringents. Nous avons dit seul, parce que la difference
de refringence qui correspond a la destruction du rayon rouge n'est pas la meme
que celle qui amene la destruction du rayon vert, et reciproquement. Main-
tenant si des rayons rouges 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,
'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 pen, il faut
se rappeller que le disque peut etre considere comme une aggregation d'etoiles
ou de petite points qui scintillent isolement ; mais les images de differentes
couleurs que chacun de ces points pris isolement dounerait, empietant les
unes sur les autres, formeraient du blanc. Lorsqu'on place un diaphragme
ou un bouchon perce d'un trou sur 1'objectif d'une lunette, les etoiles acqui-
erent un disque entoure d,'une serie d'anneaux lumiueux. Si Ton eufouce
1'oculaire, le disque de 1'etoile augmente de diametre, et il se produit dans son
centre un trou obscur ; si Ton enfonce davantage, un point lumineux se sub-
stitue au point noir : un nouvel enfoucemeut donne naissance a un centre
noir, etc. Prenons la lunette lorsque le centre de 1'image est noir, et visons
a une etoile qui ne scintille pas : le centre restera noir, comme il 1'etait
auparavant. Si, au contraire, on dirige la lunette a une etoile qui scintille, on
verra le centre de 1'image lumineux et obscur par intermittence. Dans la
position ou le centre de 1'image est occupe par un point lumineux, on verra ce
point disparaitre et renaitre successivemeiit. Cette disparition ou rcapparition
du point central est la preuve directe de Y interference variable des rayons.

NOTES. XXIX

Pour bien concevoir 1'absence de lumiere au centre de ces images dilatees, il
faut se rappeler que les rayons regulierement refractes par 1'objectif ne se
reuuissent et ne peuvent par consequent interfere qu'au foyer : par conse-
quent les images dilatees que ces rayons peuvent produire resteraient toujours
pleines (sans trou). Si dans une certaine position de 1'oculaire un trou se
presente au centre de 1'image, c'est que les rayons regulierement refractes
interferent avec des rayons diffractes sur les bords du diaphragme circulaire.
Le phenomene n'est pas constant, parce que les rayons qui interferent dans
un certain moment n'interferent pas un instant apres, lorsqu'ils ont traverse
des couches atmospheriques dont le pouvoir refringent a varie. On trouve
dans cette experience la preuve mauifeste du role que joue dans le phenomene
de la scintillation 1'inegale refrangibilite des couches atmospheriques traver-
sees par les rayons dont le faisceau est tres etroit.

" II resulte de ces considerations que 1'explication des scintillations ne pent
e'tre rattachee qu'au phenomenes des interferences lumineuses. Les rayons
des etoiles, apres avoir traverse une atmosphere ou il existe des couches
iue'ualement chaudes, inegalement dcnses, inegalement humides, vont se
reunir au foyer d'une lentille, pour y former des images d'intensite et de cou-
leurs perpetuellernent changeantes, c'est-a-dire des images telles que la scin-
tillation les presente. II y a aussi scintillation hors du foyer des lunettes.
Les explications proposees par Galilei, Scaliger, Kepler, Descartes, Hooke,
Huygens, Newton et John Michell, que j'ai examinees dans un memoire
presente a 1'Institut en 1840 (Comptesrendus, T.x.p. 83), sont inadmissibles.
Thomas Young, auquel nous devons les premieres lois des interferences, a cru
inexplicable le phenomene de la scintillation. La faussete de I'ancienue
explication par des vapeurs qui voltigent et deplacent, est deja prouvee par la
circonstance que nous voyons la scintillation 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 pieces qni manquent, done encore effet de 1'interfereuce
des rayons." (Extracted from MSS. of Arago, 1847.)

(13°) p. 68.— Arago, in the Annuaire for 1831, p. 168.

(131) p. 69.— Aristot. de Coelo, ii. 8, p. 290, Bekker.

(132) p. 69.— Kosmos, Bd. ii. S. 363 (English edition, p. 322).

(133) p. 69.— Causa Scintillationis, in Kepler de Stella nova in pede Ser-
pentarii, 1606, cap. 18, p. 92—9?.

(134) p. 70. — Lettre de M. Garcin, Dr. en Med., a M. de Reaumur, in the
Hist, de 1'Academie Royale des Sciences, Annee 1743, p. 28—32.

(135) p. 71.— See Voyage aux Regions equin. T. i. p. 511 and 512, T. ii.

XXX NOTES.

p. 202—208; also my Ansichten der Natur, 3te Ausg. Bd. i. S. 29
and 225. "En Arabie," says Garcin, "de merae qu'a Bender-Abassi,
port fameux du Golfe Persique, 1'air est parfaitemeut serein presque toute
1'annee. Le printemps, 1'ete et 1'automme se passent, saus qu'on y voie
la moindre rosee. Dans ces memes temps tout le monde couche dehors
sur le haut des maisons. Q,uaud on est aiasi couche, il n'est pas possible
d'exprimer le plaisir qu'on prend a contempler la beaute du ciel, 1'eclat
des etoiles. C'est une lumiere pure, ferme et eclatante, sans etincille-
ment. Ce n'est qu'au milieu de 1'hiver que la scintillation, quoique
tres-foible, s'y fait apercevoir." (Garcin, in Hist, de 1'Acad. des Sciences,
1743, p. 30.)

(136) p. 72. — Speaking of the illusions occasioned by the different velocities
of sight and sound, Bacon says — " Atque hoc cum similibus nobis quandoque
dubitationem peperit plane monstrosam; videlicet, utrum coeli sereni et
stellati facies ad idem tempus cernatur, quando vere existit, an potius aliquanto
post ; et utrum non sit (quatenus ad visum coelostium) non minus lempns
verum et tempus visum, quam locus verus et locus visus, qui notatur ab
astronomis in parallaxibus. Adeo incredibile nobis videbatur, species sive
radios corporum coelestium, per tarn immensa spatia milliarium, subito deferri
posse ad visurn; sed potius debere eas in tempore aliquo notabili delabi.
Verum ilia dubitatio (quoad majus aliquod intervallum tempo ris inter tempus
verum et visum) postea plane evanuit, reputantibus nobis." (The Works of
Francis Bacon, Vol. i. Lond. 1740 — (Novum Organum), p. 371.) He then,
quite in the manner of the Ancients, recalls a true view just expressed. Com-
pare Somerville, The Connexion of the Physical Sciences, p. 36 ; and Kosmos,
Bd. i. S. 161 (English rdition, Vol. i. p. 144—145).

(137) p. 72. — See Arago's development of his method, in the Annuaire du
Bureau des Longitudes pour 1842, p. 337 — 343: " L'obsermtion attentive
des phases d' Algol a six mois d'intervalle servira a determiner directement la
vitesse de la lumiere de cette etoile. Pres du maximum et du minimum le
changemeut d'intensite s'opere lentement ; il est, au contraire, rapide a cer-
taines epoques iutermediaires entre celles qui correspondent aux deux etats
extremes, quand Algol, soit en diminuant, soit en augmeutanc d'eclat, passe
par la troisieme grandeur."

(138) p. 72.— Newton, Opticks, 2d edit. (Lond. 1718), p. 325: "Light
moves from the Sun to us in seven or eight minutes of time." Newton
compares the velocity of sound (" 1140 feet in one second") with that of
light. Reckoning for the latter, according to the occultations of Jupiter's

NOTES. XXXI

satellites (Newton died about half a year before Bradley's discovery of aberra-
tion), 7' 30" from the Sun to the Earth, and assuming a distance of 70
millions of English (statute) miles, — light traverses, in every second of time,
155555^ English miles, the reduction of which to geographical miles
would vary according to the assumption of the figure of the Earth. Accord-
ing to Encke's exact assumptions in the Jahrbuch for 1852 (taking, with
Dove, 1 English mile = 5280 English feet=4954'206 Paris feet), there are
691637 English statute miles to an equatorial degree. Newton's result would
thus be 33736 German geographical miles 15 to a degree, (or 134944 English
geographical miles 60 to a degree, which are generally used throughout
this translation under the name of " geographical miles"). But Newton took
the Sun's parallax at 12" : if it is 8"'57116, as given by Encke's calculation
of the transit of Venus, the distance is greater, and we should have for the
velocity of light (taking 7i' from the Sun) 47232 German, or 188928
English geographical miles for a second of time, — too much, therefore, instead
of, as before, too little. It is certainly very remarkable, though it was not
noticed by Delambre (Hist, de 1' Astronomic moderne, T. ii. p. 653), that
whereas, from Homer's discovery in 1675 to the beginning of the 18th
century, the times assigned for the passage of light over half the major axis
of the Earth's orbit fluctuated between 11' and 14' 10", — being always much
too high, — Newton, supported perhaps by more recent English observations of
the first satellite, came within about 47" of the truth (or, at least, of the now
accepted result of Struve). The oldest memoir in which Romer, who was
Picard's pupil, presented his discovery to the Academy, bears date Nov. 22,
1675. He found, by forty emersions aud immersions of Jupiter's satellites,
" un retardement de lumiere de 22 minutes par 1'intervalle qui est le double
de celui qu'il y a d'ici au Soleil" (Memoires de 1'Acad. de 1666—1699, T. x.
1730, p. 400). Cassini did not contest the fact of the retardation, but he
contested the assigned amount of time, because (he very erroneously supposed)
different satellites gave different results. Du Ham el, the Secretary of the
Paris Academy (Regise Scieutiarum Academies Historia, 1698, p. 145),
seventeen years after Romer had left Paris, but still referring to him, gives
from 10' to 11'; but we know, by Peter Horrebow (Basis Astronomies, sive
Triduum Roemerianum, 1735, p. 122 — 129), that in 1704 — six years,
therefore, before his death — when about to publish his own work on the
velocity of light, Romer kept steadily to the result of 11' : so, also, did
Huygens (Tract, de Lumine, cap. 1, p. 7). Cassini proceeded quite diffe-»
rently : he found for the first satellite 7' 5", for the second 14' 12"; and he

XXX11 NOTKS.

lays down, as the basis of his tables of Jupiter, 14' 10" " pro peregramlo
diametri semissi." The error was therefore on the increase. (Compare
Horrebow, Trid-uum, p. 129; Cassini, Hypotheses et Satellites de Jupiter, in
the Mem. de 1'Acad. 1666—1699, T. viii. p. 435 and 475 ; Delambre, Hist,
de 1'Astr. moderne, T. ii. p. 751 and 782 ; Du Harael, Physica, p. 435.)
(139) p. 72.— Delambre, Hist, de 1'Astr. mod. T. ii. p. 653.
(14°) p. 73. — Reduction of Bradley's Observations at Kew and Wansted,
1836, p. 22 ; Schumacher's Astr. Nachr. Bd. xiii. 1836, No. 309. (Com-
pare Miscellaneous Works and Correspondence of the. Rev. James Bradley, by
Professor Rigaud, Oxford, 1832.) Ou the attempts hitherto made to ex-
plain the aberration of light on the uudulatory theory, see Doppler, in the
Abhandl. der kon. bohmischen Gesellschaft der "Wiss. 5te Folge, Bd. iii. S.
745 — 765. It is a circumstance deserving of particular attention in the
history of great astronomical discoveries, that more than half a century before
Bradley's actual discovery and explanation of the cause of aberration (probably
from 1667), Picard remarked a periodical movement of the Pole-star of about
20", which " can neither be the effect of parallax or of refraction, and is very
regular in the opposite seasons of the year" (Delambre, Hist, de 1'Astr.
moderne, T. ii. p. 616). Picard was on the path which might have led to the
discovery of the velocity of direct light, half a century before his disciple
Homer made known the velocity of reflected light.

(M1) p. 73.— Schum. Astr. Nachr. Bd. xxi. 1844, No. 484; Struve,
Etudes d'Astr. stellaire, p. 103 and 107 (compare Kosmos, Bd. i. S. 160;
English edition, p. 144). In the Annuaire pour 1842, p. 287, the velocity
of light is given at 308000 kilometres, or 77000 lieues (each 4000 metres),
in a second : this result comes nearest to the present one of Struve. It gives
41507 German, or 166028 English geographical miles, in a second; that of
the Pulkova Observatory being 41549 German, or 166196 English geo-
graphical miles in a second. On the difference between the aberration of the
Pole-star and that of its companion, and on Struve's own recently-conceived
doubts, see Madler, Astronomic, 1849, S. 393. A still larger result for the
passage of light from the Sun to the Earth is given by "William Richardson,
viz. 8' 19"'28, to which belongs a velocity of 165688 geographical miles
(Mem. of the Astron. Soc. Vol. iv. Pt. 1, p. 68).

(142) p. 74.— Fizeau gives his result in leagues, 25 to an equatorial degree,
70000 such leagues in a .second (168000 English geographical miles) . On
earlier experiments of Fizeau, see Comptes rendus, T. xxix. p. 92. In
Moigno, Repert. d'Optique moderne, P. iii. p. 1162, the result is given at

NOTES. XX Xlll

70843 (25 = 1°) : therefore 42506 German, or 170024 English geographical
miles, which comes nearest to Bradley's result, according to Buscli.

(143) p. 74. — D'apres la theorie mathematique dans le systeme des ondes,
les rayons de differentes couleurs, les rayons dont les ondulations soiit inegales,
doivent neanmoins se propager dans 1'Ether avec la meme vitesse. II n'y a
pas de difference a cet egard entre la propagation des ondes sonores, lesquelles
se propagent dans 1'air avec la meme rapidite. Cette egalite de propagation,
des ondes sonores est bieu etablie experimentalement par la similitude d'effet
que produit une musique donnee a toutes distances du lieu ou Ton 1'execute.
La principale difficulte, je dirai 1'unique difficulte qu'on eut elevee coutre le
systeme des ondes, consistait done a expliquer comment la vitesse de propaga-
tion des rayons de differentes couleurs dans des corps differents pouvait etre
dissemblable et servir a reudre compte de Finegalite de refraction de ces
rayons ou de la dispersion. On a montre recemment que cette difficulte n'est;
pas insurmontable ; qu'on peut constituer 1'Ether dans les corps inegalement
denses de maniere que des rayons a ondulations dissemblables 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 experimentalement d'une serie de faits relatifs aux
interferences : —

Millimetres.

Violet 0-000423

Jaime 0'000551

Rouge 0-000620

La vitesse de transmission des rayons de differentes couleurs dans les espaces
celestes est la meme dans le systeme des ondes, et tout-a-fait independante de
1'etendue ou de la vitesse des ondulations" (Arago, MSS. 1849). Compare
also Annuaire pour 1842, p. 333 — 336. The length of the luminous wave of
the ether and the rapidity of the vibrations determine the character of the
coloured rays. The violet, which is the most refrangible ray, has 662, and
red, which (with the greatest length of wave) is the least refrangible ray, has
only 451, billions of vibrations in a second.

(144) p. 75. — " J'ai prouve, il y a bien des annees, par des observations
directes, que les rayons des etoiles vers lesquelles la Terre marche, et Jes rayons
des etoiles dont la Terre s'e'loigne, se refractent exactementde la meme quan-
tite. Un tel resnltat ne peut se concilier avec la theorie de V emission qu'a
1'aide d'une addition importante a faire a cette theorie : il faut admettre quo
les corps lumineux e'mettent des rayons de toutes les vitesses, et que les seuls

VOL. III. d

XXXI V NOTES.

rayons d'une vitesse determined sont visibles, qu'eux seuls produisent daus
1'eeil la sensation de lumiere. Dans la theorie de 1'emission, le rouge, le
jauue, le vert, le bleu, le violet. solaires sont respectivement accompagnes de
rayons pareils, mais obscurs par defaut ou par exces de vitesse. A plus de
vitesse correspond une moindre refraction, comme 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 uus plus, les autres
inoins que lui : ainsi il existe des rayons dans les stries noires de la portion
rouge du spectre; la meme chose doit etre admise des stries situees dans les
portions jaunes, vertes, bleues et violettes" — Arago, in the Comp'tes rendus
de 1'Acad. des Sciences, T. xvi. 1843, p. 404. (Compare also T. viii. 1839,
p. 326; and Poisson, Traite de Me'canique, ed. 2, 1833, T. i. § 168.)
According to the undulatory theory, the heavenly bodies send out waves of
infinitely different velocities of transverse vibration.

(145) p. 75.— Wheatstone, in the Phil. Trans, of the Royal Society for
1834, p. 589 and 591. From the experiments described in this memoir, it
appears to follow that the human eye is capable of receiving impressions
from luminous phenomena, of which the duration is limited to one-millionth
part of a second (p. 591). On the hypothesis alluded to in the text, according
to which the Sun's light is analogous to the Earth's polar light, see Sir John
Herschel, Results of Astron. Observ. at the Cape of Good Hope, 1847, p.
351. The ingenious application of Wheatstone's revolving apparatus, im-
proved by Breguet, to a critical experiment in the decision between the emis-
sion and undulatory theories, — as, according to the former, light should pass
quicker, and according to the latter slower, through water than through air, —
has already been spoken of by Arago in the Comptes rendus, T. vii. 1838, p.
956. (Compare Comptes rendus pour 1850, T. xxx. p. 489 — 495 and 556.)

(146) p. 77.— Steinheil, in Schumacher's Astr. Nachr. No. 679 (1849), S.
97 — 100 ; Walker, in the Proceedings of the American Philosophical Society,
Vol. v. p. 128 (compare older propositions of Pouillet, in the Comptes rendus,
T. xix. p. 1386). Still later ingenious experiments of Mitchel, Director of the
Observatory of Cincinnati (Gould's Astron. Journal, Dec. 1849, p. 3, on the
Velocity of the Electric Wave), and of Fizeau and Gounelle at Paris (April
1850), differ from Wheatstone's and Walker's results. Striking differences
between iron and copper, in respect to conduction, are shown by experi-
ments given in the Comptes rendus, T. xxx. p. 439.

(M7) p. 77- — See Poggendorff, in his Anualen, Bd. Ixxiii. 1848, S. 337;
and Pouillet, Comptes rendus, T. xxx. p. 501.

NOTES. XXXV

(148) p. 77.— Riess, in Poggen. Ann. Bd. 78, S. 433. On the non-con-
duction through the earth, see the important experiments of Guillemin
" sur le courant dans une pile isolee, et sans communication entre les poles,"
in the Comptes rendus, T. xxix. p. 521. " Quand on remplace un fil par la
terre dans les telegraphes electriques, la terre sert plutot de reservoir commun
que de moyen d'union entre les deux extremites du fil."

(149) p. 78.— Madler, Astr. S. 380. Laplace, according to Moigno, Re-
pertoire d'Optique moderne, 1847, T. i. p. 72: — "Selon la theorie de 1'emis-
sion, on croit pouvoir demontrer que si le diametre d'une etoile fixe serait
250 fois plus grand que celui du soleil, sa densite restant la meme, 1'attraction
exercee a sa surface detruirait la quantite de mouvement de la molecule
lumineuse einise, de sorte qu'elle serait invisible a de grandes distances."
If, with William Herschel, we ascribe to Arcturus an apparent diameter of
0"'l, it would follow from this assumption that the actual diameter of
this star is only 11 times greater than that of our Sun (Kosrnos, Bd. i.
S. 153 and 415; English edition, p. 137—138, and Note 107). According
to the above view of one of the causes of non-luminosity, it would follow that,
with very different dimensions of the heavenly bodies, the velocity of their light
would be also very different, which hitherto has by no means been confirmed
by observation. (Arago, in the Comptes rendus, T. viii. p. 326, says : —
" Les experiences sur 1'egale deviation prismatique des etoiles vers lesquelles
la terre marche ou dont elle s'eloigne, rend compte de 1'egalite de vitesse
apparente des rayons de toutes les etoiles.")

(15°) p. 79. — Eratosthenes, Catasterismi, ed. Schaubach, 1795 ; and Era-
tosthenica, ed. God. Bernhardy, 1822, p. 110—116. The description dis-
tinguishes among stars \afj.Trpovs (^yaXovs) and apavpovs (cap. 2, 11, 41).
So also Ptolemy : with whom ol a.u.6p<bwroi relate only to stars which are not
included formally in a constellation.

(151) p. 80.— Ptol. Almag. ed. Halma, T. ii. p. 40 ; and in Eratosth.
Catast. cap. 22, p. 18 : •{] Se Ke<J>aA.}; /col f) Hp-jry &vairTos oparai, 8i£ Se
vf<t>e\<a8ovs ffva-TpoQTJs So/ce? TKTIV 6pa<rQou. So also Geminus, Phsen.
(ed. Hilder. 1590), p. 46.

(152) p. 80.— Kosmos, Bd. ii. S. 369 and 514 (Anm. 63) ; English edi-
tion, p. 328 and cxviii. (Note 503).

(ls3) p. 80.— Muhamedis Alfragani Chronologica et Astr. Elements, 1590,
cap. xxiv. p. 118.

(U4) p. 81.— Some manuscripts of the Almagest point to such sub-divisions
or intermediate classes, as they add to the determinations of magnitude the

XXXVI NOTES.

words peifav or fhaffo-wv (Cod. Par. N° 2389). Tycho Brahe expressed this
increasing or diminishing by points.

(155) p. 81.— Sir John Herschel, Outl. of Astr. p. 520—527.

(lo6) p. 82. — This was the application of mirror sextants to the determina-
tion of the light of stars which I employed in the tropics still more than
diaphragms, which had been recommended to me by Borda. T began the
work under the fine sky of Cumana, and continued it subsequently up to 1803,
undei less favourable circumstances, on the high plains of the Andes, and on
the coast of the Pacific at Guayaquil. I had formed for myself an arbitrary
scale, in which I made Sirius, as the brightest of all the fixed stars, = 100 ;
stars of the 1st magnitude-between 100 and 80 ; 2d magnitude between 80
and 60 ; 3d magnitude between 60 and 45 ; 4th between 45 and 30 ; and
5th between 30 and 20. I passed in review more particularly the constella-
tions of Argo and Grus, in which I believed I should find alterations
since Lacaille's time. It appeared to me, after careful combinations of esti-
mation, and employing other stars as intermediate gradations, that Sirius is
as much superior in the strength of its light to Canopus, as a Centauri is to
Achernar. On account of the above-mentioned mode of classification, my
numbers do not admit of direct comparison with those given since 1838 by
Sir John Herschel. (See my Recueil d'Observ. astr. Vol. i. p. Ixxi. ; and
Relat. hist, du Voy. 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.
N° 374.) In this letter I say : — "M. Arago, qui possede desmoyens phoco-
metriques entierement differents de ceux qui ont ete publics jusqu'ici, m'avait
rassure sur la partie des erreurs qui pouvaient provenir dn changement d'in-
clinaison d'un miroir entame sur la face interieure. II blame d'ailleurs le
principe de ma methode, et le regarde comme peu susceptible de perfectionne-
ment, non-seulement a cause de la difference des angles entre Tetoile vue
directement et celle qui est amenee par reflexion, mais surtout parce que le
resultat de la mesure d'intensite depend de la partie de 1'ceil qui se trouve en
face de 1'oculaire. II y a erreur lorsque la pnpille n'est pas tres-exactement
a la hauteur de la limite inferieure de la portion non entamee du petit
niiroir."

(157) p. 82.— Compare Steinheil, Elemente der Helligkeit's-Messungen am
Sternenhimmel Munchen, 1836 (Schum. Astr. Nachr. No. 609) and John
Herschel, Results of Astronomical Observations made during the years 1834
—1838 at tbe Cape of Good Hope (Lond. 1847), p. 353—357. In 1846,

NOTES.

Seidel attempted to determine with SteinheiTs pftotometer the quantities of
light of several stars of the 1st magnitude which appear at sufficient altitudes in
our northern hemisphere. He makes a Lyrse = 1, and then finds Sirius ==
5'13; Rigel, whose brightness seems to be increasing, = 1'30; Arcttirus,
0-84 ; Capella, 0'83 ; Procyon, O'?l ; Spica, 0'49 ; Atair, 0'40 ; Aldebaraa
0'36; Deneb, 0-35; Regulus, 0'34 ; Pollux, 0'30 ; Betelgeuze is left out,
because it is variable, as appeared particularly between 1836 and 1839
(Outlines, p. 523).

(158) p. 83. — For the numerical bases of the photometric results, compare
four tables of Sir John Herschel, in his Cape Observations (a. p. 341 ; b.
p. 367 — 371 ; c. p. 440 ; and d. in his Outlines of Astronomy, p. 522
— 525, and 645 — 646). For a mere arrangement in order of magnitude
or brightness, but without any numbers being expressed, see the Manual of '
Scientific Enquiry prepared for the Use of the Navy, 1849, p. 12. In order
to render more complete the conventional language which has been hitherto
used (i. e, the old classification into magnitudes), Sir John Herschel, in the
Outlines of Astronomy, p. 645, has appended to the vulgar scale of magni-
tudes, a scale of photometric magnitudes obtained merely by the addition of
0*41, as is more fully explained in the Cape Observations, p. 370. I subjoin
such a table, combining in it the stars of the Northern and Southern Hemi-
spheres without distinction. See p. xlii. to p. xlv. at the close of the Notes
belonging to this section.

(159) p. 83. — Argelander, Durchmnsterung des nordl. Himrnels zwisehen
45° und 80° Decl. 1846, S. xxiv.— xxvi. ; Sir John Herschel, Ast, Obs. at
the Cape of Good Hope, p. 327, 340, and 365.

(16°) p. 83.— Same work, p. 304 ; and Outlines, p. 522.

(161) p. 84.— Phil. Trans. Vol. Ivii. for the year 1767, p. 234.

(162) p. 84. — Wollastou's comparison of the light of the Sun and of the
Moon was made in 1799, and was based on shadows cast by wax-lights, while
in the experiments with Sirius in 1826 and 1827 images reflected from a
glass-globe were employed. The earlier assigned ratios of the intensity of the
solar light as compared to that of the Moon differ very much from the results
here given. Michel! and Euler, proceeding from theoretical grounds, had
respectively concluded 450000 and 374000 to 1. Bouguer, from measurements
of the shadows of wax-lights, had even made it only 300000 to 1. Lambert
considers the light of Venus, when at the brightest, to be 3000 fainter than
that of the full Moon. According to Steinheil, the Sun would require to be
3286500 times further off than it is in order to appear to the inhabitants of

XXXV111 NOTES.

the Earth like Arcturus (Struve, Stellarum compositarum mensurse micromc-
tricse, p. clxiii.) ; and Arcturus, according to Sir John Herschel, has for us
only half the strength of light of Canopus (Herschel, Observations at the
Cape, p. 34). All these ratios of intensity, and particularly the important
comparison of the Sun, the full Moon, and the ashy light of our satellite, so
different according to its position in reference to the reflecting Earth, deserve
a final arid much more serious examination.

(163) p. 84— Outl. of Astr. p. 553 ; Astr. Observ. at the Cape, p. 363.

(164) p. 85.— William Herschel on the Nature of the Sun and Fixed Stars,
iu the Phil. Trans, for 1795, p. 62, and on the changes that happen to the
fixed stars, in the Phil. Trans, for 1796, p. 186. Compare also Sir John
Herschel, Observ. at the Cape, p. 350—352.

(165) p. 85.— Extrait d'une lettre de M. Arago a M. de Humboldt (Mai
1850) :—

" a. Mesures photometriques.

" II n'existe pas de photometre proprement dit, c'est-a-dire ^'instrument
donnant Pintensite d'une lumiere isolee ; le photometre de Leslie, a Paide
duquel il avait eu 1'audace de vouloir comparer la lumiere de la lune a la
lumiere du soleil, par des actions calorifiques, est completement defectueux,
J'ai prouve en effet, que ce pretendu photometre monte quand on Pexpose a
la lumiere du soleil, qu'il descend sous Paetion de la lumiere du feu ordinaire,
et qu'il reste completement 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 lumieres en presence, et cette comparaison n'est meme a 1'abri de toute
objection que lorsqu'on ramene ces deux lumieres a Pegalite par un affaiblisse-
ment graduel de la lumiere la plus forte. C'est comme criterium de cette
egalite que j'ai employe les anneaux colores. Si on place 1'une sur Pautre
deux lentilles d'un long foyer, il se forme autour de leur point de contact des
atmeaux colores tant par voie de reflexion que par voie de transmission. Les
anneaux reflechis sont complementaires en couleur des anneaux transmis ; ces
deux series d'anueaux se neutralisent mutuellement quand les deux lumieres
qui les forment 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'an-
neaux transmis, suivant que la lumiere qui forme les premiers, est plus forte
ou plus faible 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 auxquelle je me suis livre.

NOTES. XXXIX

" b. Cyanometre.

" Mon cyanometre est une extension de mon polariscope. Ce dernier
instrument, comme tu sais, se compose d'un tube ferme a 1'une de ses extre-
mites par une plaque de cristal de roche perpendiculaire a 1'axe, de 5 mille-
metres 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 hasard la nuance du bleu de ciel. Cette couleur bleue
fort affaiblie, c'est-a-dire tres melangee de blanc lorsque la lumiere est presque
neutre, augmente d'intensite — progressivement a mesure que les rayons qui
penetrent dans 1'instrument, renferment une plus grande proportion de
rayons polarises.

" Supposous done que le polariscope soit dirige sur une feuille de papier
blanc ; qu'entre -eette feuille et la lame de cristal de roche il existe une pile
de plaques de verre susceptible de changer d'inclinaison, ce qui rendra la
lumiere eclairante du papier plus ou moins polarisee ; la couleur bleue fournie
par l'instrument va en augmentant avec 1'inclinaison de la pile, et Ton s'ar-
rete lorsque cette couleur parait la meme que celle de la region de 1'atmo-
sphere dont on veut determiner la teinte cyanometrique, et qu'on regarde a
1'oeil nu immediatement a cote de Fiustrument. La mesure de cette teinte
est dounee par 1'inclinaison de la pile. Si cette derniere partie de l'instru-
ment se compose du merne nombre de plaques et d'une meme espece de verre,
les observations faites dans divers lieux seront parfaitement comparables
entr'elles."

(166) p. 85. — Argelander de fide Uranometrise Bayeri, 1842, p. 14 — 23 :
" in eadem classe l^ttera prior majorem splendorem nullo modo indicat" (§ 9).
According to this it is by no means proved by Bayer's authority that Castor
was brighter in 1603 than Pollux.

NOTES.

PHOTOMETRIC ARRANGEMENT OE THE FIXED STARS.

I CONCLUDE this section with a table taken from Sir John Herschel's Out-
lines of Astronomy (p. 645 and 646) : I am indebted for its arrangement
and lucid explanation to my learned friend, Dr. Galle, from whose letter to
myself, dated in March 1850, I subjoin the following extract : —

" The numbers in the Photometric Scale in the Outlines of Astronomy
are results obtained from the ' Vulgar Scale,' by an addition throughout of 0'41.
The author (Sir John Herschel) has arrived at these more exact determina-
tions of star-magnitudes by observed 'sequences' of brightness, and by the
combination of these observations with the average of the assigned magnitudes
in ordinary use (Cape Observations, p. 304 — 352), taking more particularly
the data in the Astronomical Society's Catalogue for 1827 as a basis. The
proper photometric results of several stars by means of the Astrometer (Cape
Observations, p. 353, et seq.) have not been employed directly in this table,
but have only served in a general way as a means of judging of the relation
or correspondence of the scale in common use (1st, 2d, 3d, &c. magnitudes),
to the real quantities of light in different stars. There has thus been found
the result (at all events remarkable), that the decrease of our ordinary star-
magnitudes (1, 2, 3 ) is approximately as if a star of the 1st magnitude

were placed successively at distances of 1, 2, 3, whereby, according to

photometric law, its brightness would have successively the values 1, £,

£, -Jg. (Cape Observations, p. 371, 372; Outlines, p. 521, 522) ; but in

order to make accordance still greater, it is only necessary to raise our star-
magnitudes, as hitherto employed, about half a magnitude (or more exactly
0'41) ; so that in future a star of the 2'00 magnitude should be called of the
2'41 magnitude; a star of 2'5 magnitude, 2'91, and so on. Sir John
Herschel has proposed this * photometric' (raised) scale for accept-
ance (Cape Obs. p. 372 ; Outl. p. 522), and his proposal will surely be
assented to : for, the difference from the Common or Vulgar Scale would
' hardly be felt' (Cape Obs. p. 372) ; and the table in the ' Outlines
of Astronomy,' p. 645, et seq., may already serve as a basis as far

NOTES. x

down as the 4th magnitude. The determination of magnitudes of stars

according to this rule — viz. that the brightnesses of stars of the 1, 2, 3, 4

magnitudes should be to each other in the ratio of 1, %, i, TTg- exactly, as

they already are approximately, — is thus already in part practicable'. Sir
John Herschel (Outlines, p. 523 ; Cape Obs. p. 372) takes a Centauri as a
normal star for the 1st magnitude of the Photometric Scale, and as the unit
for the quantity of light. If, therefore, we square the photometric magnitude
of a star, we have the inverse ratio of its quantity of light to that of a Cen-
tauri. So, for example, if K. Orionis is of photometric magnitude 3, it has
i of the light of a Centauri. At the same time, the number 3 would show
K Orionis to be 3 times as far from us as a Centauri, if we assume the two
stars to be bodies equal in real magnitude and brightness. If another star —
ex. gr. Sirius, which is four times as bright — had been chosen as the unit
of the photometric magnitudes indicating distances, the regular conformity to
law would not have been seen with so much simplicity. Nor is it without
interest that the distance of a Centauri is known with some probability, and
that among the distances of fixed stars which have yet been investigated it is
the least. The author treats in the Outlines, p. 521, of the inferiority, in
point of suitability, of other scales as compared with the photometric one,

which advances according to the squares 1, \, •£, -Jg- He also notices

geometrical progressions — as, for example, 1, i, \, ^ or 1, ^, -g, ^

The gradations which you selected in the Observations at the Equator in your
American Expedition follow an arithmetical progression (Recueil d'Observ.
astrou. Vol. 1, p. Ixxi. ; and Schumacher, Astron. Nachr. No. 3?4). All these
scales adapt themselves less well to the vulgar scale than to the photometric
(quadratic) progression." In the following table, the 190 stars of the " Out-
lines of Astronomy" are arranged solely according to their magnitudes,
without regard to South or North Declination.

xlii

NOTES.

List of 190 STABS of the First, Second, and Third Magnitudes,
arranged according to the determinations of Sir JOHN HERSCHEL,
and giving the ordinary or "vulgar" magnitudes with greater
exactness than usual ; as well as the photometric scale proposed
by him.

STABS OF THE FIRST MAGNITUDE.

Star.

Vulgar
Scale.

Photo.
Scale.

Star.

Vulgar
Scale.

Photo.
Scale.

Sirius . .

0.08

0.49

a Orionis . .

1.0:

1.43

il Argus (Var.)

—

• —

a Eridani . .

1.09

1.50

Canopus . .

0.29

0.70

Aldebaran .

1.1:

1.5:

a Centauri . .

0.59

1.00

/8 Centauri . .

1.17

1.58

Arcturus . .

0.77

1.18

a Crucis .

1.2

1.6

Kigel . . .

0.82

1.23

Antares . .

1.2

1.6

Capella . .

1.0:

1.4:

a Aquilse . .

1.28

1.69

a Lyrse . . .

1.0:

1.4:

Spica . . .

1.38

1.79

Procyon . .

1.0:

1.4:

STABS OP THE SECOND MAGNITUDE.

Star.

Vulgar
Scale.

Photo.
Scale.

Star. "

Vulgar
Scale.

Photo.
Scale.

Fomalhaut .

1.54

1.95

a Ursse (Var.) .

1.96

2.37

£ Crucis . .

1.57

1.98

£ Orionis . .

2.01

2.42

Pollux . .

1.6:

2.0:

ft Argus . . .

2,03

2.44

Regulus . .

1.6:

2.0:

a Persei . . .

2.07

2.48

a Gruis . . .

1.66

2.07

7 Argus . . .

2.08

2.49

7 Crucis . .

1.73

2.14

e Argus . . .

2.18

2.59

e Orionis . .

1.84

2.25

rj Urs«j (Var.) .

2.18

2.59

e Canis . . .

1.86

2.27

7 Orionis . .

2.18

2.59

A. Scorpii . .

1.87

2.28

a Triang. austr.

2.23

2.64

a Cygni . . .

1.90

2.31

e Sagittarii . .

2.26

2.67

Castor . .

1.94

2.35

/3 Tauri . . .

2.28

2.69

e Ursa? (Var.) .

1.95

2.36

Polaris . .

2.28

2.69

NOTES. xliii

STAES OP THE SECOND MAGNITUDE — continued.

Star.

Vulgar
Scale.

Photo.
Scale.

Star.

Vulgar
Scale.

Photo.
Scale.

3- Scorpii . .

2.29

2.70

5 Argus .

2.42

2.83

o Hydra? . .

2.30

2.71

£-Ursa? . . .

2.43

2.84

5 Canis . . .

2.32

2.73

j8 Andromeda? .

2.45

2.86

a Pavonis . .

2.33

2.74

0 Ceti . . .

2.46

2.87

7 Leonis . .

2.34

2.75

A Argus . . .

2.46

2.87

£ Grruis . . .

2.36

2.77

jS Auriga? . .

2.48

2.89

a Arietis . .

2.40

2.81

7 Andrornedse .

2.50

2.91

or Sagittarii . .

2.41

2.82

STAES OP THE THIED MAGNITUDE.

Star.

Vulgar
Scale.

Photo.
Scale.

Star.

Vulgar
Scale.

Photo.
Scale.

7 Cassiopeise .

2.52

2.93

e Scorpii . .

2.71

3.12

a Andromeda? .

2.54

2.95

£" Argus .

2.72

3.13

& Centauri .

2.54

2.95

jSUrsa? . . .

2.77

3.18

a Cassiopeia? .

2.57

2.98

a Phoenicia . .

2.78

3.19

)8 Canis . . .

2.58

2.99

t Argus . . .

2.80

3.21

X Orionis . .

2.59

3.00

« Bootis . .

2.80

3.21

7 Geminorum .

2.59

3.00

a Lupi . . .

2.82

3.23

8 Orionis . .

2.61

3*.02

e Centauri .

2.82

3.23

Algol (Var.) .

2.62

3.03

TJ Canis . . .

2.85

3.26

e Pegasi . .

2.62

3.03

)3 Aquarii . .

2.85

3.26

7 Draconis .

2.62

3.03

S Scorpii . .

2.86

3.27

j8 Leonis . .

2.63

3.04

e Cygni . . .

2.88

3.29

a Ophiuchi . .

2.63

3.04

77 Ophiuchi . .

2.89

3.30

£ Cassiopeia? .

2.63

3.04

7 Corvi . . .

2.90

3.31

7 Cygni . . .

2.63

3.04

o Cephei . .

2.90

3.31

a Pegasi . .

2.65

3.06

77 Centauri . .

2.91

3.32

0 Pegasi . .

2.65

3.06

a Serpentis . .

2.92

3.33

7 Centauri .

2.68

3.09

S Leonis . .

2.94

3.35

a Corona?

2.69

3.10

x Argus . . .

2.94

3.35

7 Ursa? . . .

2.71

3.12

)8 Corvi . . .

2.95

3.36

NOTES.
STABS OP THE THIRD MAGNITUDE— continued.

Star.

Vuljrar
Scale.

Photo.
Scale.

Star.

Vulgar
Scale.

Photo.
Scale.

£ Scorpii . .

2.96

3.37

1 & Argus . . .

3.26

3.67

f Centauri . .

2.96

3.37

ft Hydri . . .

3.27

3.68

f Ophiuchi . .

2.97

3.38

£• Persei . . .

3.27

3.68

a Aquarii . .

2.97

3.38

f Herculis . .

3.28

3.69

IT Argus . . .

.2.98

3.39

e Corvi . . .

3.28

3.69

7 Aquilae . .

2.98

3.39

i Aurigae . .

3.29

3.70

8 Cassiopeia .

2.99

3.40

7 Urs. min. . .

3.30

3.71

8 Centauri . .

2.99

3.40

77 Pegasi . .

3.31

3.72

a Leporis . .

3.00

3.41

ft Arse . . .

3.31

3.72

8 Ophiuchi . .

3.00

3.41

a Toucani . .

3.32

3.73

f Sagittarii . .

3.01

3.42

ft Capricorni .

3.32

3.73

TJ Botitis. . .

3.01

3.42

p Argus . . .

3.32

3.73

ij Draconis . .

3.02

3.43

£" Aquilse . .

3.32

3.73

ir Ophiuchi . .

3.05

3.46

ft Cygni . . .

3.33

3.74

ft Draconis . .

3.06

3.47

7 Persei . . .

3.34

3.75

0 Librae . . .

3.07

3.48

p. Ursae . . .

3.35

3.76

7 Virginia . .

3.08

3.49

ft Triang. bor. .

3.35

3.76

p. Argus . . .

3.08

3.49

•JT Scorpii . .

3.35

3.76

\ft Arietis . .

3.09

3.50

ft Leporis . .

3.35

3.76

•> Pegasi . .

3.11

3.52

7 Lupi . . ,

3.36

3.77

8 Sagittarii . .

3.11

3.52

8 Persei . . .

3.36

3.77

a Librae . . .

3.12

3.53

^ TJrsse . . .

3.36

3.77

A. Sagittarii . .

3.13

3.54

c Aurigae (Var.)

3.37

3.78

0 Lupi . . .

3.14

3.55

v Scorpii . .

3.37

3.78

e Virginia ? . .

3.14

3.55

i Orionis . .

3.37

3.78

a Columbee . .

3.15

3.56

7 Lyncis . .

3.39

3.80

& Aurigse . .

3.17

3.58

$ Draconis . .

3.40

3.81

£ Herculis . .

3.18

3.59

a Arae . . .

3.40

3.81

t Centauri . .

3.20

3.61

TT Sagittarii . .

3.40

3.81

8 Capricorai .

3.20

3.61

ir Herculis . ,

3.41

3.82

8 Corvi . '. ..

3.22

3.63

ft Can. min. ? .

3.41

3.82

a Can. ven. . .

3.22

3.63

f Tauri . . .

3.42

3.83

ft Ophiuchi . .

3.23

3.64

8 Draconis . .

3.42

3.83

8 Cygni . . .

3.24

3.65

p. Greminorum .

3.42

3.83

e Persei . . .

3.26

3.67

7 Bootis . .

3.43

3.84

rj Tauri ? . .

3.26

3.67

e Geininorum .

3.43

3.84

ft Eridani . .

3.26

3.67

a Muscae . .

3.43

3.84

NOTES.
STAES OF THE THIKD MAGNITUDE — continued.

xlv

—
Star.

Vulgar
Scale.

Photo.
Scale.

Star.

Vulgar
Scale.

Photo.
Scale.

a Hydri ? . .

3.44

3.85

i Ursse . . .

3.46

3.87

T Scorpii . .

3.44

3.85

i} Aurigse . .

3.46

3.87

5 Herculis . .

3.44

3.85

7Lyrse . . .

3.47

3.88

8 Geminorum .

3.44

3.85

•77 Greminorum .

3.48

3.89

q Orionis . .

3.45

3.86

7 Cephei . .

3.48

3.89

6 Cephei . .

3.45

3.86

K Ursse . . .

3.49

3.90

& Ursse . . .

3.45

3.86

e Cassiopeise .

3.49

3.90

£ Hydrse . .

3.45

3.86

& Aquilse . .

3.50

3.91

7 Hjdrge . .

3.46

3.87

<r Scorpii . .

3.50

3.91

& Triang. austr.

3.46

3.87

T Argus .

3.50

3.91

" The following statement of the Quantities of Light in 17 Stars
of the First Magnitude (as they follow from the photometric mag-
nitudes) may possess some interest :—

Sirius . . . . 4.165
•t) Argus .... —

Canopus .... 2.041

a Centauri .... 1.000

Arcturus .... 0.718

Eigel 0.661

Gapella .... 0.510

oLyrse 0.510

Procyon .... 0.510
as may also the Quantities of Light in Stars which are exactly of the
First to the Sixth Magnitudes :

Quantity of light.
1.00 0.500

2.00 0.172

3.00 0.086

4.00 0.051

5.00 0.034

6.00 0.024

the quantity of light in a Centauri being the unit throughout.'

a Orionis . .

. . 0.489

a Eridani . .

. . 0.444

Aldebaran

. . 0.444

j8 Centauri . .

. . 0.401

a Crucis . .

. . 0.391

Antares . .

. . 0.391

o Aquilse

. . 0.350

Spica

0312

Magnitude according to
the vulgar scale.

xlvi

NOTES.

(167) p. 86.— Kosmos, Bd. iii. S. 49 and 57, Anm. 32 and 33 (English
edition, p. 39, and Notes 78 and 79).

(168) p. 87.— Kosmos, Bd. i. S. 185 and 428, Anm. 14 (English edition,
p. 168, Note 144).

(169) p. 89.— On the Space- penetrating Power of Telescopes, in Sir John
Herschel's Outl. of Astr. § 803.

(17°) p. 89. — I cannot attempt to compress within the limits of a note all
the reasons upon which Argelander's views are founded. It will be sufficient
for me to insert the following extracts from some of his letters to myself: —
" A few years ago (] 843) you requested Captain Schwink to estimate for you
the number of stars visible on the whole celestial vault, from the 1st to the
7th magnitude inclusive, according to the proportion of those entered in his
Mappa coelestis. He finds 12148 stars between -30° and +90° Decl.;
consequently, assuming the same frequency of stars from — 30° Decl. to the
South Pole, there would be in the entire firmament 16200 stars of the above-
named magnitudes. This estimation seems to me also to come very near the
truth. We know that, if we only consider the general mass, each successive
class or magnitude contains about three times as many stars as the preceding
one (Struve, Catalogus Stellarum duplicium, p. xxxiv. ; Argelander, Bonner
Zonen, S. xxvi.) Now in my Uranometrie I have 1441 stars of the 6th
magnitude North of the Equator, whence there would follow, for the entire
heavens, about 3000; but this does not include stars of the 6*7 mag-
nitude, which yet, if whole classes only were counted, would be reckoned
as belonging to the 6th class. I think we might take these at 1000 : so that
we should have 4000 stars of the 6th magnitude ; and thus, according to the
above-mentioned rule, 12000 stars of the 7th magnitude,— or 18000 stars
from the 1st to the 7th magnitude inclusive. I arrive at a rather more
exact conclusion, by means of other considerations respecting the number of
stars of the 7th magnitude which I have marked in my zones, viz. 2251
(pag. xxvi.) ; having regard to stars which have been observed more than
once, and to those which have probably been overlooked. In this way I find,
between 45° and 80° North Decl., 2340 stars of the 7th magnitude, and thence,
over the whole heavens, about 17000 stars. Struve, in the Description de
1'Observatoire de Poulkova, p. 268, gives the number of stars down to the 7th
magnitude, in the region of the heavens examined by him (i. e. —15° to
4- 90°), 13400 ; whence there would follow, for the entire heavens, 21300.
According to the Introduction to "Weisse's Catal. e Zonis Regiomontanis ded.
p. xxxii., Struve finds, by the calculus of probabilities, 3903 stars from the

NOTES. xlvii

1st to the 7th magnitude in the zone from —15° to + 15° ; whence, in the
whole heavens, 15050 such stars. This number is less than mine, because
Bessel estimated the brighter stars about half a magnitude lower than 1 did.
It is only a mean number which we can look for here ; and this we might
take, therefore, at 18000 stars from the 1st to the 7th magnitude inclusive.
In the passage of the Outlines of Astronomy, p. 521, of which you remind
me, Sir John Herschel speaks only of the stars already registered : ' The
whole number of stars already registered, down to the 7th magnitude
inclusive, amounting to from 12000 to 15000.' As respects the fainter stars
of the 8th and 9th magnitudes, Struve finds, in the above-mentioned zone of
-15° to +15°, of stars of the 8th magnitude, 10557; and of stars of the
9th magnitude, 37739 : consequently, for the whole heavens, 40800 stars of
the 8th, and 145800 stars of the 9th magnitude. Thus we should have,
according to Struve, from the 1st to the 9th magnitude inclusive,
15100 + 40800+145800=201700 stars. These numbers were found by
Struve by carefully comparing those zones or parts of zones which included
the same parts of the heavens; and from the number of stars common to
them, and the number of those which were different, concluding, by the
calculus of probabilities, the number of stars actually existing. This calcu]a-
tion deserves very great confidence, as a large number of stars have contributed
to form its basis. Bessel has entered in the whole of his zones between
-15° and +45°, about 61000 different stars from the 1st to the 9th magni-
tude inclusive (after deducting stars observed more than once, and stars
of 9'10 magnitude) ; whence, taking into account those which have
been probably overlooked, there would follow, for the part of the heavens
which has been mentioned, about 101500 of the magnitudes in question. My
zones between +45° and + 80° contain about 22000 different stars (Durch-
musterung des nordl. Himmels, S. xxv.) : from this number we must deduct
about 3000 of the 9'10 magnitude; leaving 19000. My zones are
somewhat richer than Be&sel's, and I do not think I can assume more than
28500 as the number of actually existing stars within their limits (between
+ 45° and +80°) : so that we should have 130000, to the 9th magnitude
inclusive, between —15° and +80°. This is about 0'62181 of the entire
heavens ; so that, assuming a generally equable distribution, we should have
over the entire firmament 209000 stars, or thus again nearly the same number
as that assigned by Struve : perhaps even it may be one not inconsiderably
greater, as Struve has reckoned the stars of 9'10 magnitude as belonging to the
9th magnitude. The numbers which, according to my views, I should say

xlviii NOTES.

might be assumed for the entire heavens, would thus be — 1st mag. 20, 2d
mag. 65, 3d mag. 190, 4th mag. 425, 5th mag. 1100, 6th mag. 3200, 7th
mag. 13000, 8th mag. 40000, 9th mag. 142000 ; making together, from the
1st to the 9th magnitudes inclusive, 200000 stars. If you should object to
me, that Lalande (Hist, celeste, p. iv.) gives the number of stars visible to the
naked eye, observed by himself, at 6000, I should remark in reply that there
are amongst them very many observed more than once ; and that, omitting
these, we arrive approximately at only 3800 stars for the part of the heavens
comprised by Lalande's observations — i. e. between —26° 30' and +90°.
As this is 0'72310 of the entire heavens, the resulting number of stars visible
to the naked eye throughout the firmament would again be 5255. A review
of the Uranography of Bode, composed from very heterogeneous elements
(17240 stars), after deducting nebula and smaller stars, as well as stars of
6'7 magnitude raised to the 6th magnitude, gives not above 5600 stars from
the 1st to the 6th magnitude inclusive. A similar estimation for the whole
heavens, corresponding to the number of stars from the 1st to the 6tb magni-
tude inclusive, registered by Lacaille, between the South Pole and the
Tropic of Capricorn, confirms also the mean result previously given to you,
since it falls between the limits of 3960 and 5900. You see that I have
willingly endeavoured to fulfil your wish for a more thorough investigation of
the numbers. I may add that Heis, of Aix-la-Chapelle, has been for several
years engaged in an exceedingly careful revision' of my Uranometrie.
According to the portion of this work which is already completed, and accord-
ing to the considerable augmentations which have been made to my Urano-
metrie by an observer gifted with more acute vision, I find for the Northern
Hemisphere 2836 stars from the 1st to the 6th magnitude inclusive : and
hence, on the assumption of equal distribution over the whole firmament, we
have again 5672 stars visible to highly acute unassisted vision" (MS.
communication from Professor Argelander, March 1850).

(171) p. 90.— Of stars down to the 6th magnitude, Schubert reckoned the
number-for the whole heavens at 7000, — almost the same as the number
assumed by me in the first volume of Cosmos (English edition, p. 140), and
for the horizon of Paris above 5000 ; and down to the 9th magnitude inclusive
for the whole sphere, 70000 (Astronomic, Th. iii. S. 54). All these numbers
are considerably too high. Argelander finds, from the 1st to the 8th magni-
tude, only 58000.

(172) p. 90. — " Patrocinatur vastitas cocli, immensa discreta altitudine, in
duo atque septuaginta signa. Usec sunt rerum et auimantium effigies, in

NOTES. xx

quas digessere ccelum periti. la his quidem mille sexcentas adnotavere
stellas, insignes videlicet effectu vis uve." . . . (Plin. ii. 41.) "Hipparchus
nunquam satis laudatus, ut quo nemo magis approbaverit cognationem cum
homiue siderum aiiimasque nostras partem esse cceli, novam stellam et aliam
iu sevo suo genitam deprehendit, ej usque motu, qua die fulsit, ad dubitationem
est adductus, aune hoc ssepius fieret moverenturque et ese quas putamus
affixas ; itemque ausus rem etiam Deo improbain, adnumerare posteris stellas
ac sidera ad iiomen expuugere, organis excogitatis, per qnee 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 miauerenturque, coclo in hereditate cunctis relicto, si quisquam qui
cretionem earn caperet inventus esset" (Plin. ii. 26).

(173) p. 91.— Delambre, Hist, de 1'Astr. anc. T. i. p. 290 ; and Hist, de
I'Astr. mod. T. ii. p. 186.

(174) p. 91.— Outlines, § 831 ; Edonard Biot sur les Etoiles Extraordinaires
observees en Chine, in the Connaissance des Temps pour 1846.

(175) p. 91. — It is to Aratusthat the Apostle Paul refers with implied praise
in his discourse at Athens (Acts, ch. xvii., v. 28). The name is not, indeed,
mentioned, but it is impossible to mistake the allusion to a passage from
Aratus (Phsen. v. 5) on the community of mortals with the Deity. Aratus is
also singularly enough referred to at a not very different date by Ovid
(Amor. i. 15).

(176) p. 92. — Ideler, Uutersuchungen iiber den Ursprung der Sternnamen,
S. 30—35. Baily, in the Mem. of the Astron. Soc., Vol. xiii. 1843, pp. 12
and 15, also treats of the dates according to the Christian era, with which we
should connect the observations of Aristyllus, as well as the Star-tables of
Hipparchus (128, not 140, B.C.), and of Ptolemy A.D. 138.

(m) p. 92.— Compare Delambre, Hist, de I'Astr. anc. T. i. p. 1 84 ; T. ii. p.
260. The statement, that although Hipparchus always designates the stars
by their Right Ascension and Declination, yet that his Star-catalogue, like
that of Ptolemy, was arranged according to longitude and latitude, appears
to have little probability in its favour ; and is in contradiction to the Almagest,
book vii. cap. 4, where the relations to the Ecliptic are spoken of as some-
thing novel, tending to facilitate the knowledge of the movement of the fixed
stars round the pole of the Ecliptic. The Star-table with appended longitudes,
discovered by Petrus Victorius in a Medicean codex, and published with the
life of Aratus, at Florence, in 1567, is indeed attributed by him to Hipparchus
but without proof. It appears to be a mere transcript of Ptolemy's Table,

VOL. III. d

1 NOTES.

from an old manuscript of the Almagest, omitting all the latitudes. As
Ptolemy was but imperfectly acquainted with the amount of the retrogression
of the equinoctial and solstitial poiuts, (Almag. vii. c. 2, p. 13, Halma), and
had assumed it about 0'28 too slow, his table (Ideler, in the work above cited,
p. 34), which he intended to correspond to the beginning of the reign of
Antoninus, gives the places of the stars for a much earlier epoch (i. e. for the
year A.D. 63). Compare also considerations and tables for facilitating the
reduction of modern star places to the time of Hipparchus, given by Eucke in
Schumacher's Astr. Nachr., No. 608, S. 113 to 126. The earlier epoch for
which, unknown to its author, Ptolemy's table represents the firmament,
coincides very probably with the epoch to which we may refer the Catasterisms
of the Pseudo-Eratosthenes, which, as I have already remarked elsewhere, are
later than the Augustean Hyginus, appear to be taken from him, and are
unconnected with the poem of Hermes by the true Eratosthenes. (Eratos-
thenica, composuit God. Bernhardy, 1822, p. 114, 116, and 129.) These
Catasterisms of the Pseudo-Eratosthenes contain barely 700 separate stars
distributed among the mythical constellations.

(178) p. 93.— Kosmos, Bd. ii. S. 260 and 433; English edition, p. 224,
and Ldx. note 354. The Paris Library possesses a manuscript of the Ilkha-
nian Tables, written by the hand of the son of Nassir-Eddin. They take their
name from the title llkhan, assumed by the Tartar princes who reigned in
Persia. Keinaud Introd. de la Geogr. d'Aboulfeda, 1848, p. 139.

(179) p. 93.— Sedillot fils, Prolegomenes des Tables Astr. d'Olong-Beg,
1847, p. 134 ; Note 2 ; Delambre, Hist, de 1'Astr. du moyen age, p. 8.

(18°) p. 93. — In my examinations into the relative value of astronomical
determinations of geographical positions in the interior of Asia, (Asie Centrale,
T. iii. p. 581—596), I have given the latitudes of Samarcand and Bokhara
according to the different Arabian and Persian manuscripts in the Paris Li-
brary. T have shewn that the latitude of Samarcand is probably above 39° 52',
while the greater number and best MSS. of Ulugh Beig have 39° 37', and the
Kitab al-athual of Alfares, and the Kanun of Albyruni, 40°. I think it right
again to call attention to the importance to geography and to the history of
astronomy, of a new and trustworthy determination of the latitude and longi-
tude of Samarcand. We know the latitude of Bokhara by culminations of
stars from Burnes' Travels ; they make it 39° 43' 41*. This would give the
errors of the two fine Persian and Arabian MSS. (Nos. 164 and 2460) in the
Paris Library at only 7 to 8 minutes ; but Major Rennell, generally so happy
in his combinations, would have been in error 19' for the latitude of Bokhara.

NOTES. H

(Hnmboldt, Asie Centrale, T. iii. p. 592 ; and Sedillot in the Prolegomenes
d'Oloug-Beg, p. 123—125.)

(181) p< 94._Kosmos, Bd. ii. S. 327—332, and 485 Anm. 5—8 ; English
edition, p. 287—292, and notes 446—448 ; Humboldt, Examen Critique de
1'Histoire de la Geographic, T. iv. p. 321—336 ; T. v. p. 226—238.

(182) p. 94.— Cardani Paralipomenon, lib. viii. cap. 10; (Opp. T. is. ed.
Lugd. 1663, p. 508).

(183) p. 95.— Kosmos, Bd. i. S. 90-93 : Eng. edition, p. 78—80.

(184) p. 96.— Baily, Catalogue 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. 1395. On the benefits of complete
Star-catalogues, see the remarks of Sir John Herschel, Cat. of the British
Assoc., 1845, p. 4, S. 10. Compare also, respecting Missing Stars, Schu-
macher, Astr. Nachr., No. 624, and Bode's Jahrb.for 1817, S. 249.

(185) p. 97.— Memoirs of the Royal Astron. Soc., Vol. xiii. 1843, pp. 33
and 168.

(186) p. 97. — Bessel, Fundamenta Astronomise pro anno 1755, deducta ex
observationibus viri incomparabilis James Bradley in Specula astronomica
Grenovicensi, 1818. (Compare also Bessel, Tabulse Regiomoutanse reduc-
tionum observationum astronomiearum ab anno 1750 usque ad annum 1850
computatse, 1830.)

(18T) p. 97. — I compress into a note a brief list of Star-Catalogues contain-
ing lesser masses, or a smaller number of positions, adding the name of the
observer, and the number of the determinations of place. Lacaille (who
observed for barely ten months in 1751 and 1752, and with a magnifying
power of only eight times), 9766 southern stars to the 7th magnitude inclu-
sive, reduced to the year 1750 by Henderson ; Tobias Mayer, 998 stars for
1756; Flamsteed, originally 2866, but augmented by Baily's care by 564
additional (Mem. of the Astr. Soc. Vol. iv. p. 129—164); Bradley, 3222,
reduced by Bessel to the year 1755; Pond, 1112; Piazzi, 7646 stars for
1800; Groombridge, 4243, mostly circumpolar stars, for 1810; Brisbane
and Riimker, 7385 southern stars, observed in New Holland in the years
1822—1828 ; Airy, 2156 stars, reduced to the year 1845 ; Riimker, 12,000,
on the Hamburg horizon ; Argelander (Cat. of Abo), 560 ; Taylor (Ma-
dras), 11015. The British Association Catalogue, 1845, reduced under Mr.
Baily's superintendence, contains 8377 stars, from the 1st magnitude to the
7i. For the most southern stars, we have besides, the rich registers of
Henderson, Fallows, Maclear, and Johnson at St. Helena.

lii NOTES.

(188) p. 98. — Weisse, Positiones mediae stellarum fixarum in Zonis Regio-
moatanis a Besselio inter — 15° et -\- 15° decl. observatarum ad annum
1825, reductse (1846); with an important Preface by Struve.

O p. 99.— Encke, Gedachtniss rede auf Bessel, S. 13.

(I9°) p. 99.— Compare Struve, Etudes d'Astr. stellaire, 1847, p. 66 and
72 ; Kosmos, Bd. i. S. 156 (English edition, p. 140) ; and Madler Astr. 4th
Aufl. S. 417.

(191) p. 102.— Kosmos, Bd. ii. S. 197 and 432, Anm. 11 (English edition,
p. 163, and note 251).

(192) p. 102.— Ideler, Unters. iiber die Sternnamen, S. xi. 47, 139, 144,
and 243 ; Letronne sur 1'Origine du Zodiaque grec 1840, p. 25.

(193) p. 103. — Letronne, id. p. 25, and Carteron, Analyse des Recherches
de M. Letronne sur les Representations Zodiacales, 1843, p. 119 ; " II est
tres douteux qu'Eudoxe (01. 103) ait jamais employe le mot ZwSiaKog
On le trouve pour la premiere fois dans Euclide et dans le Commentaire
d'Hipparque sur Aratus (01. 160). Le nom d'ecliptique 6K\£t7rri/c6£ est
anssi fort recent." (Compare Martin in the Commentary to Theonis
Smyrnsei Platonici Liber de Astronomia, 1849, p. 50 and 60.)

(194) p. 103.— Letronne, Orig. du Zod. p. 25, and Analyse crit. des Repres.
Zod. 1846, p. 15. Ideler and Lepsius also consider it probable that " the
knowledge of the Chaldean zodiac, both as respects the division and the
name, had reached the Greeks as early as the 7th century before our era, but
that the reception of the several zodiacal figures into the Grecian astronomi-
cal literature was later, and only followed gradually" (Lepsius, Chronologic
der ^Bgypter, 1849, S. 65 and 124). Ideler is inclined to believe that the
Orientals had for their twelve divisions (Dodecatomery) names, but without
figures ; Lepsius thinks it natural to suppose " that the Greeks, at a time
when their sphere was in great part unoccupied, would add to their own
the Chaldean constellations from which the twelve divisions were named."
But, on this supposition, might we not ask why the Greeks should have had
at first only eleven signs, and not all the twelve signs of the Chaldean
Dodecatomery ? If they had received twelve figures, they would surely not
have cut out one to replace it subsequently.

(I9S) p. 1 04. — On the passage referred to in the text, and interpolated by a
transcriber as if belonging to Hipparchus, see Letronne, Orig. du Zod. 1840,
p. 20. As early as 1812, when I was myself still inclined to suppose that
the Greeks had been very early acquainted with the sign of the Balance, I
pointed out, in a carefully written memoir on the passages from Greek and

NOTES. liii

•

Roman Antiquity, in which the name of the Balance as a zodiacal sign
occurs, the passage of Hipparchus (Comment, in Araturn, lib. iii. cap. 2), in
which there is mention of the Srjpiov which holds the Centaur (by his fore-
foot), as well as the remarkable passage of Ptolemy, lib. ix. cap. 7 (Halma,
T. ii. p. 170). In this latter passage the southern Balance is named, with
the addition Kara XaXdaiovQ, and is opposed to the Pincers (Scheeren) of
the Scorpion, in an observation certainly not made in Babylon, but by the
astrological Chaldeans scattered in Syria and Alexandria (Vues des Cordilleres
et Monumens des peuples indigenes de 1'Amerique, T. ii. p. 380). Buttmann
was disposed to think, but which seems little probable, that the %»;Xat had
originally signified the two scales of the Balance, and were afterwards by a
misunderstanding converted into the pincers of a scorpion. (Compare Ideler
" Untersuchungen iiber die astronomischen Beobachtungen der Alien, "
S. 374, and the same writer, " iiber die Sternnamen," S. 174 — 177, with
Carteron, " Recherches de M. Letronne," p. 113). In the analogy between
many names of the twenty-seven " houses of the moon," and the Dodeca-
tomery of the zodiac, it has always appeared to me remarkable that we find
the sign of the Balance among the certainly very ancient Indian Nakschatras
(moon-houses). (Vues des Cordilleres, T. ii. p. 6—12.)

(196) p. 104.— Compare A. W. von Schlegel iiber Sternbilder des Thier-
kreises im alten Indien, in der Zeitschrift fur die Kunde des Morgenlandes,
Bd. i. Heft 3, 1837, and his Commentatio de Zodiaci antiquitate et origine,
1839, with Adolph Holtzmann iiber den griechischen Ursprung des indischen
Thierkreises, 1841, S. 9, 16, and 23. In the last-named work, it is said : —
The passages adduced from the Amarakoscha and the Ramayana are not of
doubtful interpretation — they speak in the clearest terms of the zodiacal circle
itself; but if the works which contain them were composed before the know-
ledge of the Greek Zodiac could have reached India, it ought to be closely
examined whether those passages are not more recent interpolations."

(197) p. 105 — Compare Buttmann in the Berlin Astron. Jahrbuch for
1822, S. 93; Olbers, on the more modern constellations, in Schumacher's
Jahrbuch for 1840, S. 238—251, and Sir John Herschel, Revision and Re-
arrangement of the Constellations with special reference to those of the
Southern Hemisphere, in the Memoirs of the Astr. Soc., Vol. xii. p. 201 —
224 (with a very exact distribution of the Southern Stars of the 1st to 4th
magnitudes). On the occasion of the formal discussion between Lalande and
Bode, respecting the introduction of Lalande's house-cat and of a harvest-
man (Messier!), Olbers complains, that in order to make room for new

llV NOTES.

figures, " Andromeda must lay her arm in another place than that which it
has occupied for 3000 years."

(198) p. 105.— Kosmos, Bd. iii. S. 37 and 53 (English edition, p. 28 and
note 52).

('") p. 105. — According to Democritus and his scholar Metrodorus, Stob
Eclog. phys. p. 582.

(20°) p. 106.— Plut. de Plac. Phil. ii. 11 ; Diog. Laert. viii. 77 ; Achilles.
Tat. ad Arat. cap. 5 ; Efjnr, /epvoraXXwdj; TOVTOV (TOV ovpavov) tival
(ftrjaiv, kit TOV 7ray£ra>£ou£ <rv\\fysvra ; so also we find only the expression
crystal-like or crystalline in Diog. Laert. viii. 77, and Galenus, Hist. phil. 12
(Sturz*, Empedocles Agrigent, T. i. p. 321). Lactantius de opificio Dei, c.
17 : an si mini quispiam dixerit ceneum esse coelum, aut vitreum, aut, ut
Empedocles ait, serem glaciatum, statimne assentiar, quia coelum ex qua ma-
teria sit ignorem? Respecting this cffilum vitreum, we have no earlier Hel-
lenic evidence ; for only one celestial body, the Sun, is termed by Philolaos a
glass-like or vitreous body, which receives and throws back to us the rays
from the central fire. The view of Empedocles, referred to in the text, of the
reflection of the solar light from the Moon, speaking of the latter as a body
which had consolidated in the manner of hail stones, is mentioned by Plu-
tarch, apud Euseb. Praep. Evangel, i. p. 21, D, and de facie in orbe Lunse,
cap. 5. When in Homer and Pindar the epithets xaXjeeog and ffiSnpeog are
applied to Uranos, it is only in a figurative sense, like hearts of brass, voice
of brass, as signifying stedfast, enduring, imperishable (Volcker u'ber Home-
rische Geographic, 1830, S. 5). The word icpvcrraXXog applied to the ice-
like, transparent substance of rock-crystal, first occurs before Pliny, in Dyo-
nisius Periegetes, 781, JElian, xv. 8, and in Strabo, xv. p. 717, Casaub.
The supposition that the idea of the crystal heavens, as a vault of ice (aer
glaciatus of Lactantius), had arisen among the ancients, from observing, when,
travelling among mountains, the increasing cold in ascending, and from the
sight of snow-capped mountains, is refuted by our knowing that they imagined
a fiery ether to exist at the limit of our atmosphere (Aristot. Meteorol. i. 3 ;
de Caelo, ii. 7, p. 289). In speaking of the music of the spheres, which,
" according to the Pythagoreans, is unheard by men because it never ceases,
and sounds are only heard if interrupted by silence," Aristotle (de Coelo, ii.
p. 290) affirms, singularly enough, that the motion of the spheres produces
heat in the air below, but without heating themselves. Their vibrations pro-
duce heat, not sound. " The motion of the sphere of the fixed stars is the
most rapid (Aristot. de Cselo, ii. 10, p. 291) j and while this sphere and the

NOTES. Iv

bodies attached to it revolve around, the space nearest thereto is continually
heated by this movement, and thus there is produced a warmth which extends
down to the surface of the earth" (Meteorol. i. 3, p. 340). I have always
been struck by the circumstance that Aristotle avoids the term " crystal
heaven," although the expression affixed to stars, IvStStukva aGrpa, seems
to indicate the general idea of solid spheres, but without specifying the kind
of material. Cicero is not very intelligible on this point, but in his com-
mentator (Macrobius in Cic. Somnium Scipionis, i. c. 20, p. 99, ed. Bip.)
we find traces of freer ideas respecting the decrease of heat in increasing
height. According to him, the extreme zones of the heavens are subject to
perpetual cold. " Ita enim non solum terram sed ipsura quoque coelum,
quod vere mundus vocatur, temperari a sole certissimum est, ut extremitates
ejus, quse a via solis longissime recesserunt, omni careant beneficio caloris et
una frigoris perpetuitate torpescaut." These " extreraitates cceli," in which
the Bishop of Hippo (Augustinus, ed. Antv. 1700, i. p. 102, and iii. p. 99)
placed, as in a region of ice-cold water, the uppermost and therefore the cold-
est of all planets, Saturn, still belong to the atmosphere, for it is only still
higher above this extreme limit that, according to an earlier statement of
Macrobius (i. c. 19, p. 93), is placed the fiery aether, which, strangely enough,
does not prevent that eternal cold. " Stellse supra coelum locatse, in ipso
purissimo eethere sunt, in quo omne, quidquid est, lux naturalis et sua est
(the seat of self-luminous heavenly bodies), quse tota cum igne suo ita sphserse
solis incumbit, ut cceli zonge, quse procul a sole sunt, perpetuo frigore op-
pressse sirit." If I enter into so much detail respecting the connection of
ideas in meteorology and physics entertained by the Greeks and Romans, it is
only because, excepting in the works of Ukert, Henri Martin, and the ex-
cellent fragment of Meteorologia Veterum by Julius Ideler, these subjects
have hitherto been treated only in a very incomplete, and, most often, super-
ficial manner.

(201) .p. 106.— That fire had the power of rigidifying (Aristot. Probl. xiv. 11),
and that the formation of ice itself is promoted by heat, were deeply-rooted
opinions in the Physics of the Ancients, resting on a fanciful antithetical
theory (Antiperistasis), or obscure ideas of polarity (a calling forth of opposite
qualities or states) ; Kosmos, Bd. iii. S. 15 and 29 (English edition, p. 15
and note 22). Hail, it is said, is formed in larger masses when the atmo-
spheric strata are warmer (Aristot. Meteor, i. 12). In winter fishing on the
shores of the Euxine, hot water was used to increase the formation of ice, in

Ivi NOTES.

the vicinity of an upright tube (Alex. Aphrodis. fol. 86, and Plut. de Primo
Frigido, c. 12).

(202) p. 107.— Kepler says expressly, in Stella Martis, fol. 9, " Solidos
orbes rejeci; and in Stella Nova, 1606, cap. 2, p. 8, "planet® in puro
sethere, perinde atque aves in aere, cursus suos conficiunt." (Compare also
p. 122.) Earlier, however, his opinion had been inclined in favour of a solid
icy celestial vault (orbis ex aqua factus gelu concreta propter solis absentiam).
Kepler, Epit. Astr. Copern. i. 2, p. 51. Two thousand years before Kepler,
Empedocles said that the fixed stars were fastened to the crystal heaven, but
that the planets were free and unrestrained (rovg dt TrXavrjTctQ dvuo&ai)..
(Plut. Plac. Phil. ii. 13 ; Emped. i. p. 335, Sturz ; Euseb. Praep. Evang. xv.
30, Col. 1688, p. 839.) It is difficult to conceive in what manner the fixed
stars were imagined to be attached to solid spheres, and yet to revolve singly,
as supposed by Plato in the Timseus (Tim. p. 40, B), but not by Aristotle.

(203) p. 108.— Kosmos, Bd. ii. S. 352 and 506 (English edition, p. 312,
and note 478).

(204) p. 108.— Kosmos, Bd. iii. S. 67 and 113 (English edition, p. 50, and
note 105).

(205) p. 108. — " Les principals causes de la vue indistincte sont : aberra-
tion de sphericite de 1'oeil, diffraction sur les bords de la pupille, communi-
cation d'irritabilite a des points voisins sur la retine. La vue confuse est celle
ou le foyer ne tombe pas exactement sur la retine, mais tombe ou devant ou
derriere la retine. Les queues des etoiles sont 1'effet de la vision indistincte
autant qu'elle depend de la constitution du cristallin. D'apres un tres ancien
memoire de Hassenfratz (1809), 'les queues an nombre de 4 ou 8 qu'offrent
les etoiles ou une bougie vue a 25 metres de distance, sont les caustiques du
cristallin formees par 1'intersection des rayons refractes.' Ces caustiques se
meuvent a mesure que nous inclinons la tete. La propriete de la lunette de
terminer 1'image fait qu'elle concentre dans un petit espace la lumiere qui
sans cela en aurait occupe un plus grand. Cela est vrai pour les etoiles fixes
et pour les disques des plauetes. La lumiere des etoiles qui n'ont pas de
disques reels, conserve la meme intensite quelque soit le grossissement. Le
fond de 1'air duquel se detache 1'etoile dans la lunette, devient plus noir par
le grossissement qui dilate les molecules de 1'air qn'embrasse le champ de
la lunette. Les planetes a vrais disques deviennent elles-memes plus pales
par cet effet de dilatation. — Quand la peinture focale est nette, quand les
rayons partis d'un. point de 1'objet se sont concentres en un seul 'point dans
1'image, 1'oculaire donne des resultants satisfaisants. Si au contraire les rayons

NOTES. Ivii

emanes d'uri point ne se reunissent pas au foyer en un seal point, s'ils y for-
ment un petit cercle, les images de deux points contigus de 1'objet empietent
"necessairement 1'une sur 1'autre; leurs rayons se confondent. Cette con-
fusion la lentille oculaire ne saurait la faire disparaitre. L'office qu'elle
remplit exclusivement, c'est de grossir; elle grossit tout ce qui est dans
1'image, les defauts comme le reste. Les etoiles n'ayant pas de diametres
angulaires sensibles, ceux qu'elles conservent toujours tiennent pour la plus
graude partie au manque de perfection des instrumens (a la courbure moins
reguliere donnee aux deux faces de la lentille objective) et a quelques defauts
et aberrations de notre O3il. Plus une etoile semble petite, tout etant egal
quant au diametre de 1'objectif, au grossisseraent employe et a 1'eclat de
1'etoile 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 de simples points, c'est evidemment de viser a des etoiles excessivement
rapprochees 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 aperf oit
bien nettement separe'es." Arago MSS. of 1834 and 1847.

(206) p. 108.— Hassenfratz sur les Rayons Divergens des Etoiles, in Dela-
metherie's Journal de Physique, T. Ixix. 1809, p. 324.

(207) p. 109. — Horapollinis Niloi Hieroglyphica, ed. Conr. Leemans, 1835,
cap. 13, p. 20. The learned editor, (Leemans) however, in opposition to
Jomard, (Descr. de 1'Egypte, T. vii. p. 423), remarks that neither on monu-
ments nor rolls of papyrus has the figure of a star been found employed as a
sign for the number 5 (Horap. p. 1 94).

(20S) p. 109. — On board Spanish ships in the Pacific I found a persuasion
prevailing among the sailors, that the moon's age could be determined, before
her first quarter, by looking at her face through a piece of silk, and counting
the number of images ; a phenomenon of diffraction through narrow longi-
tudinal apertures.

(209) p. 109. — Outlines, § 816. Arago made the diameter of the spurious
disk of Aldebaran, shewn by a telescope, increase from 4" to 15" by diminish-
ing the diameter of the object glass.

(21°) p. 110.— Delambre, Hist, de 1'Astr. Moderne, T. i. p. 193 ; Arago,
Annuaire 1842, p. 366.

(2n) p. 110. — "Minute and very close companions, the severest tests which
can be applied to a telescope." — Outlines, § 837. Compare also Sir John
Herschel, Cape Observations, p. 29, and Arago, in the Annuaire pour 1834,
p. 302 — 305. Of bodies belonging to our solar system, we may employ, for

Iviii

INOTES.

testing the power of light of a highly magnifying optical instrument, the 1st
and 4th satellites of Uranus, seen again by Lassel and Otto Struve in 184? ;
the two innermost and the 7th satellites of Saturn, (Mimas, Enceladus, and
Bond's Hyperion), and the satellite of Neptune, discovered by Lassel. The
power of penetrating the depths of celestial space, afforded by telescopes, led
Bacon, in an eloquent passage in praise of Galileo to whom he erroneously
ascribed their invention, to compare them to ships which conduct men into an
unknown ocean ; " ut propriora exercere possint cum ccelestibus commercia."
Works of Francis Bacon, 1740, Vol. i. Novum Organon, p. 361.

(212) p. 111. — " The expression v7r6Kippog) which Ptolemy uniformly em-
ploys in his catalogue for the six stars named by him, indicates a slight degree
of transition from fiery yellow to fiery red, thus, speaking precisely, it would
signify a fiery reddish colour. To the other fixed stars, he seems to apply
generally the epithet ZavSog, a fiery yellow. (Almag. viii. 3 ed. ; Halma,
T. ii. p. 94). Kippbs is, according to Galen, (Meth. med. 12) a pale fire red,
verging towards yellow. Gellius compares the word to melinus, which, according
to Servius, means the same as gilvus and fulvus. As Sirius is called by Seneca
(Nat. Qusest. i. 1) ' redder than Mars,' and as it is one of the stars called in
the Almagest vwoKippoi, there remains no doubt that the word indicates the
predominance, or at least the presence of a certain portion of red rays. The
assertion that the epithet TTOIK'L\OQ, applied to Sirius by Aratus, v. 327, is
ranslated by Cicero, rutilus, is erroneous. Cicero says, indeed, v. 348—

Namque pedes subter rutilo cum lumine claret
Fervidus ille Canis stellarum luce refulgens ;

but rutilo cum lumine is not a translation of TrouaXoc, but an addition made
by a free translator." (Extracts from letters to myself from Professor
Franz.) Arago in the Annuaire for 1842, p. 351, says, " Si en substituant
rutilus au terme grec d'Aratus, 1'orateur romain renonce a dessein a la
fidelite, il faut supposer que lui-meme avait reconnu les proprietes rutilantes
de la lumiere de Sirius."

(*13) p. 111.— Cleom.Cycl. Theor. i. 11. p. 59.

(214) p. 111.— Madler, Astr. 1849, S. 391.

(215) p. 111.— Sir John Herschel in the Edinb. Review, vol. Ixxxvii. 1848,
p. 189, and in Schum. Astr. Nachr. 1839, No. 372,—" It seems much more
likely that in Sirius a red colour should be the effect of a medium interfered,
than that in the short space of 2000 years, so vast a body should have actually
undergone such a material change in its physical constitution. It may be

NOTES. lix

supposed 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.)

(216) p. 112. — In Muhamedis Alfragani chroiiologica et astronbmica
elementa, ed. Jacohus Christmannus, 1590, cap. 22, p. 97, it is said, —
" stella ruffa in Tauro Aldebaran ; stella ruffa in Geminis quse appellatur
Hajok, hoc est Capra." But Alhajoc, Aijuk, are, in the Arabo-Latin
Almagest, the usual names of Capella. Argelander also remarks justly that
Ptolemy in the astrological work (T£rp«/3i/3\o£ triVra^ig), vouched as
genuine by style and ancient testimony, connects planets and stars according
to similarity of colour, and thus joins together Capella and Martis stella,
(quse urit sicut congruit igneo ipsius colori,) with Aurigee stella. (Compare
Ptol. quadripart. construct, libri iv. Basil 1551, p. 383). Riccioli (Almages-
tum novum ed. 1650, T. i. Pars 1, lib. 6, cap. 2, p. 394) also reckons
Capella, with Antares, Aldebaran, and Arcturus, among the red stars.

(217) p. 113.— See Chronologie der ^Egypter, by Richard Lepsius, Bd. i.
1849, S. 190—195, and 213. The complete construction of the Egyptian
calender is placed in the earliest part of the year 3285 before the Christian
era— z". e. about a century and a half before the building of the great pyramid
of Cheops- Chufu, and 940 years before the epoch usually assigned to the
Deluge. (Compare Kosmos, Bd. ii. S. 402, English edition, p. xxvii., Note
146). In the calculations which have been made in reference to the circum-
stance, that the inclination of the narrow subterranean passage leading into
the interior of the pyramid, measured by Colonel Vyse, corresponds very
nearly to the angle 26° 15', which, in the time of Cheops- Chufu, the star
a Draconis which marked the pole attained at its inferior culmination at
Gizeh,— the epoch of the building of the pyramid is taken, not at 3430 B.C.,
as given in Kosmos from Lepsius, but at 3970 B.C. as in the Outlines of Astr.
§ 319. This difference of 540 years is the less opposed to the assumption
of a Draconis having been the pole-star, as in 3970 its polar distance was
still 3° 44'.

(218) p. 113. — I have taken what follows from letters of Professor Lepsius
to myself (February 1850) : — " The Egyptian name of Sirius, marked as a
female star, is Sothis ; hence, in Greek, rj 2w3ie is identified with the goddess
Sote (oftener Sit in hieroglyphics), and in the temple of the great Ramses
at Thebes with Isis-Sothis. (Lepsius, Chronol. der JEgypter, Bd. i. S. 119
and 136). The signification of the root is found in Coptic, and allied with a
numerous family of words, the different members of which, though apparently

NOTES.

departing widely from each other, may, however, be arranged as follows :— By
a threefold transference of the verbal signification, we obtain from the original
meaning — to project, projicere (sagittam, telum) — 1st, seminare, to sow ; then
extendere, to extend or stretch (as spun threads) ; and lastly, what is here
most important, ' to radiate light,' 'to shine' (as do stars and fire). The
names of the divinities — Satis (the archer, female), Sothis (the radiant,
female), and Seth (the fiery, male}, may be connected with this series of
ideas. There may be pointed out hieroglyphically — sit or seti, the arrow or
dart, as well as the ray; seta, to spin; setu, scattered grains. Sothis is
especially the Irig Jit-learning star, regulating seasons and periods. The
small triangle, always painted yellow, which is a symbolical sign of Sothis,
is employed in the designation of the radiant sun, being placed in triple rows,
the triangles always pointing downwards from the sun. Seth is the fire-god,
the burning or scorching; in opposition to the warming and fertilizing waters
of the inundation of the Nile — the female divinity Satis. She is the goddess
of the Cataracts, because the swelling of the Nile began with the appearance
of the star Sothis, at the time of the summer solstice. In Vettius Valens, the
star itself is called SqB- instead of Sothis ; but we cannot by any means, as
Ideler has done (Handbuch der Chronologie, Bd. i. S. 126), identify Thoth
with Seth or Sothis, either as to name or person." (Lepsius, Bd. i. S. 136.)
To these considerations, taken from the earliest Egyptian antiquity, I sub.
join some Greek, Zend, and Sanscrit etymologies. " Scrp, the sun," says
Professor Franz, " is an ancient radical, differing only in pronunciation from
Sep, SepoQ, heat, summer, where the sound of the vowel is altered, as in
rtipog and rkpog, or rtpaQ. The correctness of the assigned relations
between the radicals fftlp, and &tp, 3-spoc, is confirmed, not only by the
application of Sepei'rarof in Aratus, v. 149 (Ideler, Sternnamen, S. 241),
but also by the later use of the forms derived from atip, <mpoe, atipiog,
ffsipivdg, hot, burning. It deserves remark that (mpa, or atipiva fytaria,
is pronounced quite like Srepiva J/zdrta, light summer clothing. But the
peculiar form (reiptoQ is of wider application, it is the epithet given to
all the heavenly bodies which influence the heat of summer : thus, according
to the poet Archilochus, the Sun was called crt iptoQ dvrrjp ; and Ibycus calls
the heavenly bodies adpia, ' the shining.' That it is really the sun which
is meant in the words of Archilochus, TTO\\OVQ piv avrov <ra'ptog
KaTavavti 6£vf i\\d[j.7nnv, cannot be doubted. It is true that, accord-
ing to Hesychius and Suidas, 2efpio£ signifies both the Sun and the
dog-star ; but I am as certain as is the new editor of Theon of Smyrna,

NOTES. 1x1

M. Martin, that the passage of Hesiod (Opera et Dies, v. 417) refers, as
Tzetzes and Proclus make it do, to the Sun, and not to the dog-star. The
verb vtipiav, which may be translated ' to sparkle,' comes from the adjective
a tiptoe, which has established itself as the epitheton perpetuum of the
dog-star. Aratus, v. 331, says of Sirius, blka aeipiaei, ' it sparkles strongly.
When standing alone, the word Seip^v, the Siren, has quite a different
etymology ; and your conjecture, that it is only a case of accidental similarity
of sound to the bright star Sirius, is perfectly well founded. They are
quite in error who, according to Theon Smyrneeus (Liber de Astrouomia
1850, p. 202), would derive "Seipt}v from aeipid&iv (a, moreover, quite
unaccredited form for <r«piaj>). While the motion of heat and light are
expressed in vtipioG, the word 5ap?)j> has a root which represents the flowing
tone of the natural phenomenon. It seems to me probable that Seiprjv is
connected with t'ipsiv ; (Plato, Cratyl. 398 D. TO yap hpeiv X&yeiv lerri ;)
the originally sharp aspiration passing into the hissing sound." Extracted
from letters to myself from Prof. Franz, January 1850.

According to Bopp, " the Greek Sap, the Sun, can be easily connected by
intermediate links with the Sanscrit word ' svar,' which indeed does not signify
the Sun, but the Heavens (as something bright or shining). The usual Sanscrit
name for the Sun is ' surya,' a contraction of ' svarya.' The root ' svar,1
signifies in general, to shine. The Zend name for the Sun is ' hvare,' with h
instead of s. The Greek Sep, 3-e'poe, and SepfJibg, comes from the Sanscrit
word, gharma (Nom. gharmas), warmth, heat."

The acute Max. Muller, who has edited the Rigveda, remarks "that the
Indian astronomical name for the dog-star, Lubdhaka, which signifies ' hun-
ter,' regarded in connection with the neighbouring constellation of Orion,
seems to point to a highly ancient Aric community of view in the contem-
plation of this group of stars." He is most inclined to derive Sa'pioe from
the Vedic word " sira" (whence the adjective sairya), and the root " sri," to
go, to walk ; so that the Sun and the brightest of stars, Sirius, would have had
the term moving or wandering star as their original name. (Compare also
Pott. Etymologische Foischungen, 1833, S. 130.)

(219) p. 113. — Struve, Stellarum compositarum Mensurse micrometricsc,
1837, p. Ixxiv. and Ixxxiii.

(22°) p. 114.— Sir John Herschel, Cape Observations, p. 34.

(*") p. 114.— Madler, Astronomic, S. 436.

C222) p. 114.— Kosmos, Bd. ii. S. 367 and 513, Anm. 63, English edition,
p. 327, and Note 503.

Ixii NOTES.

(223) p. 114.— Arago, Annuaire pour 1842, p. 348.
(»M p. 114.— Struve, Stellse comp. p. Ixxxii.

C225) p. 115.— Sir John Herschel, Cape Observations, pp. 17 and 102
(Nebulas and Clusters, No. 3435).

(226) p. 115. — Humboldt, Vues des Cordilleres et monumens des peuples
indigenes de 1'Amerique, T. ii. p. 55.

(227) p. 115.— Julii Firmici Materni Astron. libri viii. Basil, 1551, lib. vi.
cap. 1, p. 150.

(228) p. 115.— Lepsius, Chronol. der JEgypter, Bd. i. S. 143. "In the
Hebrew text they are called Asch, the Giant (Orion?), the 'many stars,'
(the Pleiades, Gemut ?), and the Chambers of the South. The Septuagint
version is : 6 iroiStv TLXtiada feat 'EffTrepoj/ Kai 'Apicroupov Kai rafitia
VOTOV."

C229) p. 116.— Ideler, Sternnamen, S. 295.

(23°) p. 116.— Martianus Capella changes Ptolemseon into Ptolemsetis.
Both names were given by the flatterers at the Egyptian Court. Amerigo
Vespucci believed he had seen three Canopuses, one of which was quite dark
(fosco), Canopus ingens et niger in the Latin translation : no doubt one of
the black coal sacks (Humboldt, Exaraen crit. de la Geogr. T. v. p. 227 —
229). In the Elem. Chronol. et Astron. of El-Fergani (p. 100), it is
related that the Christian pilgrims were wont to call the Sohel of the Arabs
(Canopus), the Star of St. Catherine, because they were accustomed to welcome
and admire it as their guiding star in journeying from Gaza to Mount Sinai.
In a fine episode in the oldest heroic poem of Indian antiquity, the Ramayana,
the stars near the southern pole are declared to be more recently created than
the more northern ones for a singular reason. "When the Brahminic In-
dians,— entering the lands of the Ganges from the north-west, advanced from
30° N. latitude farther into the tropics, subjecting the aborigines, — as they
approached Ceylon they saw stars before unknown rise above the horizon.
According to ancient custom, they combined these stars into new con-
stellations. By a bold fiction, the later-seen stars were said to have been
created later by the wonder-working power of Visvamitra, who " threatened
the old gods, that, with his more richly -starred southern hemisphere, he would
overpower the northern one" (A. W. von Schlegel, in the Zeitschrift fiir die
Kunde des Morgenlandes, Bd. i. S. 240). This Indian myth, expressive of
the astonishment of wandering nations at the aspect of regions of space before
unseen (as the celebrated Spanish poet, Garcilaso de la Vega, said of those
who travel, " they change at once their country and their stars," " mudan de

NOTES. Ixiii

pays y de estrellas"), reminds us vividly of the impression which must have
been made even on the rudest nations, when at the same part of the Earth's
surface they first saw rise above the horizon large stars such as those in the
feet of the Centaur, the Southern Cross, Eridanus, and the constellation of
the Ship, whilst others before familiar disappeared. By the precession of the
equinoxes, fixed stars approach and again recede from our view. I have al_
ready remarked, in another place, that 2900 years before our Era,— at a time,
therefore, when the great pyramid had already stood five hundred years, — the
constellation of the Southern Cross was 7° above the horizon of the countries
bordering on the Baltic Sea. (Compare Kosmos, Bd. i. S. 155, and Bd. ii.
S. 333. Eng. ed. Vol. i., p. 139. Vol. ii. p. 293). " Canopus, on the
other hand, can never have been visible in the locality of Berlin ; its distance
from the South Pole of the Ecliptic is only 14°, and it would have required
that the distance should have been 1° greater for the star to have ever reached
the limit of visibility in our horizon."

(23t) p. 116.— Kosmos, Bd. ii. S. 203 (English edition, p. 169—170).

C232) p. 116.— Olbers in Schumacher's Jahrb. fur 1840, S. 249; and
Kosmos, Bd. iii. S. 151.

(233) p. 117.— Etudes d'Astr. stellaire, Note 74, p. 31.

(234) p. 117.— Outlines of Astr. § 785.

(235) p. 118.— Id. § 795 and 796; Struve, Etudes d'Astr. stellaire, p. 66
—73 (also Note 75).

(2i6) p. 118.— Struve, p. 59. Schwink finds in his maps, R. A. 0°— 90°,
2858 stars; R. A. 90°— 180°, 3011 stars; R. A. 180°— 270°, 2688 stars;
R. A. 270°— 360°, 3591 stars; total 12,148 stars down to the 7th mag-
nitude.

(237) p. 119. — On the circular nebula in the right hand of Perseus (near
the sword handle), see Eratosth. Catast. c. 22, p. 51, Schaubach.

(238) p. 119.— Sir John Herschel's Cape Observations, § 105, p. 136.

(239) p. 119.— Outlines, § 864-869, p. 591—596; Madler, Astr. S. 764.
(24°) p. 120.— Cape Observations, § 29, p. 19.

(241) p. 122. — Sir John Herschel says: — "A stupendous object, a most
magnificent globular cluster completely insulated, upon a ground of the sky
perfectly black throughout the whole breadth of the sweep." (Cape, p. 18
and 51, PL iii. fig. 1 ; Outlines, § 895, p. 615.

(242) p. 122.— Bond, in the Memoirs of the American Academy of Arts and
Sciences, new series, Vol. iii. p. 75.

(243) p. 123.— Outlines, § 874, p. 601.

xv NOTES.

C") p. 123.— Delambre, Hist, de 1'Astr. Moderne, T. i. p. 697.

(245) p. 124. — We are indebted for the first and the only thoroughly com-
plete description of the Milky Way in both hemispheres to Sir John Her-
schel, 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 his Outlines of Astronomy, $ 787 — 799. I have followed him
throughout the entire section of Kosmos which is devoted to the direction,
branchings, and varied contents of the Milky Way. Compare also Struve,
Etudes d'Astr. stellaire, p. 35—79; Madler, Astr. 1849, § 213; Kosmos,
Bd. i. S. 109 and 156 (English edition, pp. 96 and 140). I need scarcely
remark here, that, in order not to mingle uncertainties with certainties, I
have not introduced into the description of the Milky Way, what I observed
and recorded respecting the very unequal light of the different parts of the
gallactic zone during my long sojourn in the Southern Hemisphere, where
the instruments with which I was provided commanded but little light.

(246) p. 124.— The comparison of the Milky Way to a Celestial River
caused the Arabs to give to parts of the constellation of Sagittarius, whose
bow falls in a region full of stars, the name of " cattle going to drink," and
even accompanying them by the ostrich, which requires so little water.
(Tdeler, Untersuchung iiber den Ursprung und die Bedeutung der Sternnamen,
S. 78, 183, and 187; Niebuhr, Beschreibung von Arabien, S. 112.)

(247) p. 124.— Outlines, p. 529 ; Schubert, Astr. Th. iii. S. 71.

(248) p. 124.— Struve, Etudes d'Astr. stellaire, p. 41.

(249) p. 125.— Kosmos, Bd. i. S. 156 and 415 Anm. 79 (English edition,
p. 140, and Note 109).

(^p. 125.— "Stars standing on a clear black ground" (Cape Ob-
servations, p. 391). This remarkable belt (the Milky Way, when examined
through powerful telescopes) is found (wonderful to relate!) to consist
entirely of stars scattered by millions, like glittering dust on the Hack
ground of the general heavens." Outlines, p. 182, 537, and 539.

(2SI) p. 125. — " Globular clusters, except in one region of small extent
(between 16h. 45m. and 19L in R. A.) w&nebula of regular elliptic forms,
are comparatively rare in the Milky Way, and are found congregated in the
greatest abundance in a part of the heavens the most remote possible from
that circle." Outlines, p. 614. Huygens, as early as 1656, had had his
attention drawn to the absence of nebulae and nebulous patches in the Milky
Way. In the same place in which he mentions the discovery and repre-
sentation of the great nebula in the belt of Orion, by means of a 28-feet

NOTES. 1XV

refractor (1656), he said (as I have already remarked in the 2nd Vol. of
Kosmos, S. 514, English edition, Note 503, p. cxviii): "viam lacteara per-
spicillis inspectara nullas habere nebulas "; and that the Milky Way, like all
that had been taken for nebulous stars, was a great cluster of stars. The
passage is printed in Hugenii Opera Varia, 1724, p. 593.

(252) p. 125.— Cape Observations, § 105, 107, and 328. On the annular
nebula, No. 3686, see p. 114.

(253) p. 126. — "Intervals absolutely dark and completely void of any star
of the smallest telescopic magnitude." Outlines, p. 536.

(254) p. 127. — "No region of the heavens is fuller of objects beautiful and
remarkable in themselves, and rendered still more so by their mode of asso-
ciation, and by the peculiar features assumed by the Milky Way, which are
without a parallel in any other part of its course" (Cape Observations, p. 386).
This animated expression of Sir John Herschel's agrees perfectly with the
impressions which I myself received. Captain Jacob (Bombay Engineers), in
speaking of the intensity of light of the Milky Way in the vicinity of the
Southern Cross, says, with striking truth, — " such is the general blaze of star-
light near the Cross from that part of the sky, that a person is immediately
made aware of its having risen above the horizon, though he should not be at
the time looking at the heavens, by the increase of general illumination of
the atmosphere, resembling the effect of the young moon." See Piazzi
Smyth on the orbit of a Cent, in the Transactions of the Royal Society of
Edinburgh (Vol. xvi. p. 445).

(253) p. 127.— Outlines § 789 and 791 ; Cape Observations, § 325.

t256) p. 127.— Almagest, lib. viii. cap. 2 (T. ii. p. 84 and 90, Halma)
Ptolemy's description is in particular parts excellent, especially compared with
Aristotle's treatment of the subject of the Milky Way. (Meteor, lib. 1.
pp. 29 and 34, according to Ideler's Edition.)

(257) p. 129.— Outlines, p. 531. Also between a and y Cassiopeia, a
strikingly dark spot or patch is ascribed to the contrast with the bright parts
by which it is surrounded. See Struve, Etudes stell. Note 58.

(258) p. 130.— An extract from the exceedingly rare work of Thomas
Wright of Durham (Theory of the Universe, London 1750), has been given by
de Morgan in the Philosophical Magazine (Series iii. No. 32, p. 241). Thomas
Wright, to whose writings the attention of astronomers has been permanently
directed since the beginning of the present century, by the influence of the
ingenious speculations of Kant and William Herschel on the form of our
sidereal stratum, observed only with a reflector of 1 foot focal length.

VOL. III. e

xv NOTES.

C59) p. 130.— Pfaff in W. Herschcl's sumratl. Schriften Bd. i. 1826, (S.
78—81 ; Struve, Etudes stell. p. 35—44).

(26°) p. 130.— Encke in Schumacher's Astr. Nachr. No. 622, (1847) S.
341-346.

(*l) p. 130. — Outlines, p. 536. On the next page it is said, on the same
subject, " In such cases it is equally impossible not to perceive that we are
looking through a sheet of stars of no great thickness compared with the
distance which separates them from us."

(262) p. 131. — Strnve, Etudes stell. p. 63. Sometimes the largest telescopes
reach a part of celestial space in which the existence of a remotely glimmering
sidereal stratum is only indicated "by an uniform dotting or stippling of
*he field of view." See in the Cape Observations, p. 390, the section " on
some indications of very remote telescopic branches of the Milky Way, or of
an independent sidereal System, or Systems, bearing a resemblance to such
branches."

O p. 131.— Cape Observations, § 314.

C264) p. 131.— Sir William Herschel in the Phil. Trans, for 1785, p. 21 ;
Sir John Herschel, Cape Observations, § 293. (Compare also Struve, Descr.
de TObservatoire de Poulkova, 1845, p. 267—271).

t265) p. 131.— "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 stratum,
but annular ; or, at least, that our system is placed within one of the poorer
or almost vacant parts of its general mass, and that eccentrically, so as to be
much nearer to the region about the Cross than to that diametrically opposite
to it" (Mary Somerville on the Connection of the Physical Sciences, 1846,
p. 419).

C266) p. 131.— Cape Observations, § 315.

(287) p. 136.— De admiranda Nova Stella anno 1572 exorta, in Tychonis
Brahe Astronomise instauratsc Progymnasmata 1603, p. 298 — 304 and 578.
I have followed in the text Tycho Brahe's own narrative. The unwarranted
assertion, repeated in many books on Astronomy, that Tycho's attention was
first called to the newly-appeared star by a concourse of country people has
not, therefore, been noticed.

(268) p. 136.— Cardanus, in his dispute with Tycho Brahe, went back to
the star of the Magi, which he was disposed to identify with the star of 1572.
.ideler, from his calculations of conjunctions of Saturn with Jupiter, and from

NOTES. Ixvii

suppositions similar to those enounced by Kepler on the appearance of the
new star in Ophiuchus in 1604, believed the star of the Wise Men, from the
frequent confusion between acrr?)p and aarpov, to have been not a single
great star, but a remarkable arrangement of stars, presented by the near' ap-
proximation of two bright planets within less than a diameter of the moon
from each other. (Compare Tychonis Progymnasmata, p. 324 — 330, with
Ideler, Handbuch der Mathematischen und Technischen Chronologic. Bd. ii.
(S. 399—407).

(269) p. 136.— Progymn. p. 324— 330. Tycho Brahe supports himself in his
theory of the formation of new stars from the cosmical vapour, or nebulous
matter of the Milky Way, on the remarkable passages of Aristotle, to which
I have aUuded in the 1st Vol. of Kosmos (Bd. i. S. 109 and 390, Note 18,
Engl. ed. p. 96 and xviii. Note 48,) respecting the supposed relations subsist-
ing between the tails of comets and the gaseous emanations from the nuclei
of comets, and the Milky Way.

(2?0) p. 140. — Other statements place the phenomenon in the year 388 or
398 ; Jacques Cassini, Elemens d'Astronomie, 1740 (Etoiles nouvelles),
p. 59.

(271) p. 148.— Arago Annuaire pour 1842, p. 332.

(272) p. 149.— Kepler de Stella nova in pede Serp. p. 3.

(273) p. 152. — On instances of stars which have not disappeared, see Arge-
lander in Schumacher's Astronom. Nachr. No. 624, S. 371. To cite an ex-
ample connected with antiquity, I will here recall how the carelessness of
Aratus, in drawing up his poetic Catalogue of stars, has led to the often-
renewed question, whether Vega (a Lyra), may be either a new star or one
which varies in long periods, since Aratus says that the constellation of the
Lyre has only small stars. It may, indeed, seem surprising that Hipparchus
does not notice this as an error in his Commentary ; whilst yet he blames
Aratus for his statements respecting the relative brightness of the stars in
Cassiopeia, and in Ophiuchus. However, all this is merely accidental, and
proves nothing ; for, Aratus having ascribed to the constellation of the Swan
only stars of middling brightness, Hipparchus (i. 14), in expressly contra-
dicting this error, adds, that the bright star in the tail (Deneb) is but little
inferior to "the star in the Lyre (Vega). Ptolemy places Vega among the
stars of the first order of magnitude ; and in the Catasterisms of Eratosthenes
(cap. 25), it is called XEUKOV icai XajuTrpov. Seeing the many inaccuracies of
a poet who was not himself an observer, would it be reasonable to found
upon his statement the belief that a Lyric (Pliny's Fidicula, xviii. 25) first

Ixviii NOTES.

shone forth as a star of the 1st magnitude between the years 272 and 127
B.C., or between the time of Aratus and that of Hipparchus ?

(a74) p. 155.— Compare Madler, Astr. S. 438, Note 12, with Struve, Stel-
larum compos. Mensurse microm. p. 97 and 98, star 2140. " I believe," says
Argelander, " that it is very difficult to estimate correctly in a telescope of
great power of light the brightness of such exceedingly different stars as are
the two components of a Herculis. My experience is decidedly against the
variability of the companion ; for, in my numerous day observations with the
telescopes of the Meridian circles at Abo, Helsingfors, and Bonn, I have
never seen a Herculis single, which yet would have been the case, if the com-
panion were only of the 7th magnitude when at its minimum. I believe it
to be constant 5m. or 5'6m.

C275) p. 155.— Madler's Table (Astron. S. 435) contains 18 stars, having
very different numerical elements. Sir John Herschel enumerates, including
those alluded to in a note, above 45 (Outlines, § 819—826).

C276) p. 156. — Argelander in Schumacher's Astr. Nachr. Bd. xxvi. (1848)
No. 624, S. 369.

t277) p. 158.— "If," says Argelander, " I take the least light of Algol, 1800
January 1, 18 h. 1 m., mean time at Paris, as my zero epoch, I obtain the
following table : —

Epoch. Duration of Period. Seconds.

- 1987 2 days, 20 hours, 48 min. 59.416 ± 0'316

- 1406 „ . „ „ 58-737 ± 0'094

- 825 „ „ „ 58-393 ± 0*175
+ 751 „ „ „ 58-454 ± 0-039
+ 2328 „ „ „ 58-193 ± 0'096
+ 3885 „ „ „ 57-971 ± 0-045
+ 5441 „ „ „ 55-182 ± 0'348

In this table the numbers signify as follows -.—The epoch of the minimum,
on the 1st of January 1800, being zero, the next preceding is — 1, the next
following is + 1, &c. ; the duration, or interval of time between the epochs
- 1987 and — 1986, is exactly 2 d. 20 h. 48 m. 59.416 s.; whilst that
between + 5441 and + 5442 is 2 d. 20 h. 48 m. 55.182 s. ; the first cor-
responding to the year 1784, the last to the year 1842. The final column,
with the ±; sign, contains the probable errors. That the decrease is becoming
more and more rapid is shewn by the last number, as well as by my observa-
tions since 1 847.

(278) p. 1 58.— Argelander's formula for representing all the observed maxima
of Mira Ceti, as communicated to me by himself, is the following : —

days d. / Q^n0 \

1751, Sept. 9, 76 + 331.8363 + 10.5 Sin. (^-E + 86° 23') .

+ 18.2 Sin. (g°E + 231° 42' ) + 33.9 Sin. 0^E + 170° 19')

Where E signifies the number of maxima which have occurred since Sept. 9,
1751, and the coefficients are given in days. Hence, for the year now in

progress, we have the maximum : —

d. d. d.

1751, Sept. 9, 76 + 36115-65 + 8'44 — 12-24

d. d.

+ 18.59 + 27.34 = 1850, Sept. 8.54.

The circumstance which appears most in favour of this formula is, that it
represents the observation of the maximum in 1596, (Kosmos, Bd. ii. S. 367;
Eng. ed. p. 326—327), which, on the supposition of a uniform period, would
deviate more than 100 days. Yet the law of the variations of light in this
star is apparently so complicated, that in single cases (ex. gr. for the very
exactly-observed maximum of the year 1840) the formula still deviates many
days (almost 25).

C279) p. 158.— Compare Argelander's Memoir at the secular festival of the
Konigsberg University, under the title of De Stella /3 Lyrse Variabili, 1844.

(28°) p. 159.— One of the first earnest endeavours to investigate the mean
duration of the period of variability of Mira Ceti, is that of Jacques Cassini,
Eleinens d'Astronomie, 1740, p. 66 — 69.

(281) p. 172.— Newton (Philos. Nat. Principia Mathem, ed. Le Sueur et
Jacquier, 1760, T. iii. p. 671) distinguishes only two kinds of these sidereal
phenomena : " Stellee fixse quse per vices apparent et evanescunt quseque paula-
tim crescunt, videntur revolvendo partem lucidam et partem obscuram per
vices ostendere." This explanation of the change of light had been previously
proposed by Kiccioli. Respecting the caution which should be exercised in
assuming the existence of periodicity, see the important considerations of Sir
John Herschel in the Cape Observations, § 261.

(282) p. 172.— Delambre, Hist, de 1'Astr. Ancienne, T. ii. p. 280 ; and Hist.
de 1'Astr. au ISeme siecle, p. 119.

(2S3> p. 174.— Compare Sir John Herschel in the Cape Observations,

x NOTES.

§ 71—78, and Outlines of Astronomy, § 830, (Kosmos, Bd. i. S. 160—416 ;
Eag. ed., p. 144— Note, 120).

(m) p. 174.— Letter from Lieut. Gilliss to Dr. Flugel, Consul of the United
States at Leipzic (MS.) The untroubled purity and serenity of the atmo-
sphere at Santiago de Chile, lasting for 8 months, is so great that, with the
first large telescope made in America, having an aperture of 6£ inches (con-
structed by Henry Fitz in New York and William Young in Philadelphia),
Lieutenant Gilliss distinctly recognised the 6th star in the trapezium of
Orion.

I285) p. 175.— Sir John Herschel, Cape Observations, p. 334—350, Note 1
and 440. (On older observations of Capella and a Lyrse, see "William Herschel
in the Phil. Trans, for 1797, p. 307, and for 1799, p. 121 ; and in Bode's
Jahrbuch for 1810, S. 148). Argelander, on the other hand, entertains great
doubts respecting the variability of Capella and of the stars in the Bear.

C*6) p. 176.— Herschel's Cape Observations, $ 259, No. 260.

t287) p. 176. — Heis, in manuscript notices in May 1850. Compare also
Cape Observations, p. 325, and P. Von Boguslawski ; " Uranus" for 1848,
p. 186. (The assumed variability of rj, a, and d, Ursse maj., is also supported
in Herschel's Outlines, p. 559.) See Madler Astr. S. 432, on the series of stars
which are successively to mark the North Pole by their vicinity, until, at the
end of 12,000 years, the place should be taken by the most brilliant of all
possible pole-stars, a Lyrse.

C288) p. 176.— Kosmos, Bd. iii. S. 134; English edition, note 165.

(289) p. 176. — "William Herschel, on the changes that happen to the fixed
stars, in the Phil. Trans, for 1796, p. 186 ; Sir John Herschel in the Cape
Observations, p. 350 — 352 ; and also in Mary Somerville's excellent work
entitled Connexion of the Physical Sciences, 1846, p. 407.

(29°) p. 178. — Encke, Betrachtungen iiber die Anordnung des Stern-
systems, 1844, S. 12 (Kosmos, Bd. iii. S. 36, Engl. ed. p. 27); Madler,
Astr. S. 445.

(»') p. 180.-Halley in the Phil. Trans, for 1717-1719, Vol. xxx.
p. 736. The consideration, however, referred only to variations in latitude;
Jacques Cassini first added variations in longitude (Arago in the Annuaire
pour 1842, p. 387).

C292) p. 180.— Delambre Hist, de 1'Astr. Moderne, T. ii. p. 658 ; the same
author in the Hist, de 1'Astr. au 18eme siecle, p. 448.

C293) p. 181.— Phil. Trans. Vol. lixiii. p. 138.

NOTES. x

(»«) p. 181.— Bessel in Schumacher's Jahrbuch for 1839, S. 38 ; Arago
Annuaire for 1842, p. 389.

(29S) p. 182. — See on a Centauri, Henderson and Maclear, in the Memoirs
of the Astron. Soc. Vol. xi. p. 61 ; and Piazzi Smyth, in the Edinb. Trans.
Vol. xvi. p. 447. The proper motion of Arcturus, 2"-25 (Baily, in t£e
Memoirs of the Astr. Soc. Vol. v. p. 165), as belonging to a very bright star,
may be called large in comparison with that of Aldebaran 0"'185 (Madler,
Central sonne S. 11), and that of a Lyrse 0"'400. Among stars of the 1st
magnitude a Centauri, with its very large proper motion of 3"'58, forms a
remarkable exception. The proper motion of the binary star-system in
Cygnus, amounts according to Bessel (Schum. Astr. Nachr. Bd. xvi. S. 93),
to 5"- 123.

(295) p. 182.— Schumacher's Astr. Nach. No. 455.

(S97) p. 182.— The same No. 618, S. 276. D' Arrest founds the result on
comparisons of Lacaille (1750) with Brisbane (1825), and of Brisbane with-
Taylor (1835). The star 2151 Puppis has a proper motion of 7"'871, and
is of the 6th magnitude (Maclear in Madler's Unters. iiber die Fixstern-Sys-
teme, Th. ii. S. 5).

(a8) p. 182.— Schum. Astr. Nachr. No. 661, S. 201.

(2") p. 183.— The same, No. 514—516.

(30°) p. 183.— Struve, Etudes d'Astr. Stellaire, Texte, p. 47, Notes,
p. 26, and 51—57 ; Sir John Herschel, Outl. § 859 and 860.

(301) p. 184.— Origenes in Gronov. Thesaur. T. x. p. 271.

(302) p. 184.— Laplace, Expos, du Systeme du Monde, 1824, p. 395.
Lambert, in his Cosmological Letters, shews a remarkable leaning to the as-
sumption of dark cosmical bodies of great size.

(303) p. 184.— Madler, Untersuch. iiber die Fixstern-Systeme, Th. ii.
(1848,) S. 3, and the same Author's Astronomic, S. 416.

(304) p. 185.— Compare Kosmos,Bd. iii. S. 96 and 130 (Engl.ed.p. 77—
78, Note 149) ; Laplace, in Zach's Allg. Geogr.Ephem.Bd. iv. S.i.; Madler,
Astr. S. 393.

(305) p. 186.— Opere di Galileo Galilei, Vol. xii. Milano, 1811, p. 206.
This remarkable passage, which expresses the possibility of a measurement,
and a project for its execution, was discovered by Arago ; see his Annuaire
pour 1842, p. 382.

(306) p. 187.— Bessel, in Schumacher's Jahrb. fur 1839, S. 5 and 11.

(307) p. 188.— Struve Astr. Stell. p. 104.

(s08) p. 188.— Arago, in the Connaissance des terns pour 1834, p. 281 :

Ixxii NOTES.

" Nous observames avec beaucoup de soin, M. Mathieu et moi, pendant le
mois d'aout 1812, et pendant le mois de novembre suivant, la hauteur angu-
laire de 1'etoile au-dessus de 1'horizon de Paris. Cette hauteur, a la seconde
epoque, ne surpasse la hauteur angulaire de 1'etoile au-dessus de 1'horizon de
Paris. Cette hauteur, a la seconde epoque, ne surpasse la hauteur angulaire a
la premiere que de 0"-66. Une parallaxe absolue d'une seule seconde aurait
necessairement amene entre ces deux hauteurs une difference de l"-2. Nos
observations n'indiquent done pas que le rayon de 1'orbite terrestre, que 39
millions de lieues soient vus de la 61e°»e <JU Cygne sous un angle de plus
d'une demi-seconde. Mais une base vue perpendiculairement soutend un
angle d'une demi-seconde quand on en est eloigne de 412 mille fois sa
longueur. Done la 61 e du Cygne est au mains a une distance de la Terre
egale a 412 mille fois 39 millions de lieues."

(309) p. 188.— Bessel published in Schum. Jahrb. 1839, S. 39-49, and in
the Astr. Nachr. No. 366, the result 0"'3136, as a first approximation. His
subsequent final result was 0^3483 (Astr. Nachr. No. 402 in Bel. xvii.
S. 274). Peters found by his own observations, the almost identical result
of 0"-3490. (Struve, Astr. stell. p. 99.) The alterations which, after Bessel's
death, Professor Peters made in that astronomer's calculation of the angular
measurements obtained with the Konigsberg Heliometer, were founded on the
circumstance that Bessel himself (Astr. Nachr. Bd. xvii. S. 267) had promised
to subject the influence of temperature on the results with the heliometer to a
fresh examination, which intention he executed partially in the 1st Vol. of his
" Astronomischen Untersuchungen," but did not apply the temperature cor-
rection to the observations of parallax. This application was made by Peters
(Erganzungsheft zu den Astr. Nachr. 1849, S. 56), and in consequence this
distinguished astronomer found 0"'3744, instead of 0"-3483.

(31°) p. 188.— This result of 0"'3744 gives, according to Argelander, the
distance of the double star 61 Cygni from the Sun = 550900 mean distances
of the Earth from the Sun, or 11394000 German (45576000 English) geo-
graphical miles ; a distance which light traverses in 3177 mean days. By
the three successive assignments of parallax given by Bessel, 0"'3136,
0"'3483, and 0'3744, this star has come (apparently) gradually nearer to us ;
they correspond respectively to light-passages of 10, 9£, and 8T73 years.

(311) p. 188.— Sir John Herschel, Outlines, p. 545 and 551. Madler
(Astr. S. 425) gives for a Centauri, instead of 0"'9128, the parallax 0^9213.

(312) p. 189.— Struve, Stell. compos. Mens. microm. p. clxix. — clxxii.
Airy considers the parallax of a Lyrsc, which Peters has already diminished

NOTES. Ixxiii

to 0"'l, to be still less; i. <?. to be too small for measurement with our pre-
sent instruments (Mem. of the Royal Astr. Soc. Vol. x. p. 270).

(313) p. 189. — Strove on Micrometer- measurements in the large refractor
of the Dorpat Observatory (Oct. 1839) in Schum. Astr. Nachr. No. 396, S.
178.

(314) p. 189.— Peters in Struve's Astr. stell. p. 100.
(135) p. 189.— Idem, p. 101.

(316) p. 191. — On the relation of the amount of proper motion to the
proximity of the brightest stars, compare Struve, Stell. compos. Mensurae
microm. p. clxiv.

(317) p. 192.— Savary, in the Connaissance des Terns pour 1830, p. 56—
69, and p. 163 — 171 ; and Strnve, Stell. compos. Mensurse microm. p. clxiv.

(315) p. 193.— Kosmos, Bd. i. S. 150 and 414; English edition, p. 134,
and xxxvii. note 101.

(3I9) p. 193.— Madler, Astronomic, S. 414.

(32°) p. 193.— Arago (Annuaire pour 1842, p. 383) first called attention
to this remarkable passage of Bradley ; compare in the same Annuaire the sec-
tion on the movement of translation of the entire solar system, p. 389 — 399.

(321) p. 195. — According to a letter to myself, see Schum. Astr. Nachr.
No. 622, S. 348.

(32a) p. 195.— Galloway on the Motion of the Solar System, in the Phil.
Trans. 1847, p. 98.

(s23) p. 196. — The value or otherwise of such views is discussed by Arge-
lander in a memoir entitled Uber die eigene Bewegung des Sotinensystems,
hergeleitet aus der eigenen Bewegung der Sterne, 1837, S. 39, "on the proper
motion of the solar system, deduced from the proper motion of stars," p. 39.

C324) p. 197.— Compare Kosmos, Bd. i. S. 149 (Euglish edition, p. 134},
and Madler's Astr. S. 400.

(325) p. 197.— Argelander, work above quoted, S. 42 ; Madler Centralsonne,
S. 9, and Astr. S. 403.

(326) p. 197.-— Argelander, last cited work, S. 43, and in Schum. Astr.
Nachr. No. 566. Guided not by numerical investigations, but only by
fanciful conjectures, Kant had taken Sirius, and Lambert the Nebula in
Orion's belt, for the central body of our sidereal stratum. Struve Astr. stell.
p. 17, No. 19.

t327) p. 197— Madler, Astr. S. 380,400,407, and 414; his Centralsonne
1846, S. 44—47 ; his Untersuchungen iiber die Fixstern Systeme, Th. ii.
1848, S. 183—185 (Alcyone is in R. A. 54° 30', Decl. 23° 36', for the year
VOL. III. /

NOTES.

1840. If the parallax of Alcyone were really 0"'0065, then its distance
would amount to 31 £ million times the semi-diameter of the Earth's orbit ;
thus it would be fifty times more distant from us than the double star 61
Cygni, according to Bessel's earliest determination. Light which comes from
the Sun to the Earth in 8' 18*'2, would require 500 years to travel from
Alcyone to the Earth. The Imagination of the Greeks delighted in wild
estimations of space fallen through. In Hesiod's Theogony, v. 722 — 725,
it is said, speaking of the fall of the Titans to Tartarus, " When once an
iron anvil fell from heaven, nine days and nights it fell, and on the tenth it
reached the Earth." To this fall taking place in 777600 seconds of time,
the corresponding distance (taking into account, according to Galle's calcu-
lation, the great decrease of the Earth's attractive force at planetary dis-
tances) is 77356 German (309424 English) geographical miles, or once and
a half the distance from the Moon to the Earth. But according to Homer,
H. i. 952, Hephsestos fell down to Lemnos in only one day, and merely " still
breathed a little." The length of the chain hanging down from Olympus to
the Earth, by which all the gods were to essay to draw Zeus down (II. viii.
18), is left indefinite. It is an image intended to express, not the height of
heaven, but the strength and surpassing might of Jupiter.

(32S) p. 198. — Compare the doubts expressed by Peters in Schum. Astr.
Nachr. 1849, S. 661, and by Sir John Herschel in the Outlines of Astr.
p. 589. "In the present defective state of our knowledge respecting the
proper motion of the smaller Stars, we cannot 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."

(329) p. 199.— Compare Kosmos, Bd. i. S. 152—154 and 414 (Eng. ed.
p. 136 — 138, and xxxvii.) (Struve iiber Doppelsterne nach Dorpater
Micrometer-Messungen von 1824 bis 1837, S. 11).

C30) p. 200.— Kosmos, Bd. iii. S. 64—67, 110—113 and"l66— 168 (Eng.
ed. p. 47 — 50, and 108 — 110). As remarkable examples of visual power in
particular individuals, I may mention that Kepler's instructor, Mostlin, saw
with the naked eye 14, and some of the Ancients 9, stars in the group of
the Pleiades. (Miidler, Untersuch. iiber die Fixstern-Systeme, Th. ii. S. 36.)

(331) p. 200.— Kosmos, Bd. iii. S. 271 (Eng. ed. p. 185.) Dr. Gregory of
Edinburgh also recommended the same method in 1675 (33 years therefore
after Galileo's death) ; compare Thomas Birch, Hist, of the Royal Society,
Vol. iii. 1757, p. 225. Bradley (1748) alludes to this method at the end of
his celebrated treatise on Nutation.

NOTES.

(332) p. 201.— Madler, Astr. S. 44? .

(333) p. 201.— Arago in the Annuaire for 1842, p. 400.

(334^ p^ 201. — "An Inquiry into the probable Parallax and Magnitude. of
the fixed Stars, from the quantity of light which they afford us, and the par-
ticular circumstances of their situation, by the Rev. John Michell; in the
Phil. Trans. Vol. Ivii. p. 234—261.

(335) p. 202.— John Michell, same work, p. 238. " If it should hereafter be
found, that any of the stars have others revolving about them (for no satellites
by a borrowed light could possibly be visible), we should then have the means
of discovering . . . ." He denies throughout the whole discussion, that
one of two revolving stars can be a dark planet, reflecting light not its own,
since both are visible to us notwithstanding the distance. He compares both
the stars, the larger of which he calls the " Central Star," with the density of
our sun, and applies the term " Satellite" only for the purpose of conveying
the idea of revolution, or reciprocal motion. He speaks of the " greatest
apparent elongation of those stars that revolved about the others as satellites."
Further on he says, " 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 highly 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 together, are under the
influence of some general law, such perhaps as gravity." (Compare also Arago
in the Ann. 1834, p. 308, and in the Ann. 1842, p. 400.) No great weight
can be ascribed to the numerical results of the calculus of probabilities, as
given by Michell, taken separately ; as the suppositions laid down, that there
are in the entire heavens 230 stars equal in intensity of light to (3 Capricorni,
and 1500 equal to the light of the six larger Pleiades, are not at all correct.
The ingenious cosmological memoir of John Michell terminates with the very
hazardous attempt to explain the scintillation of the fixed stars by a kind of
" pulsation in material effluxes of light," an attempt as little fortunate as that
put forth by Simon Marius, one of the discoverers of Jupiter's satellites (Kos-
mos, Bd. ii. S. 357 and 509, Eng. ed. p. 316, note 484) at the end of his
Mundus Jovialis (1614). Michell, however, has the merit of having called
attention (p. 263) to the circumstance that scintillation is always combined
with change of colour ; " besides their brightness, there is in the twinkling of
the fixed stars a change of colour." (See Kosmos, Bd. iii. S. 122, Eng. ed.
note 129.)

(336) p. 203. — Struve in the Recueil des Actes de la Seance publique da

Ixxvi NOTES.

1'Acad. Imp. des Sciences de St. Petersbourg, le 29 dec. 1832, p. 48 — 50;
Madler, Astr. S. 478.

C337) p. 203.— Phil. Trans, for the year 1782 p. 40—126; for 1783,
p. 112—124, for 1804, p. 87. On the observational basis of the 846 double
stars of Sir William Herschel, compare Madler in Schumacher's Jahrbuch fiir
1839, S. 59, and the same author's Untersuchungen iiber die Fisstern-Sys-
teme, Th. i. 1847, S. 7.

f338) p. 205.— Madler in the last-named work, Th. i. S. 255. We have for
Castor, two old observations of Bradley's, 1719 and 1759, the first taken con-
jointly with Pond's, the second with Maskelyne's, and two of William Her-
schel's, of 1799 and 1803. For the time of revolution of \ Virginis, see
Madler, Fixstern-Syst., Th. ii. 1848, S. 234—240.

(339) p. 205. — Strave, Mensurse microrn., p. xl. and p. 234—248. There
are, in all, 2641 + 146; therefore, 2787 observed multiple stars. (Madler,
i'\ Schom. Jahrb. 1839, S. 64).

C"0) p. 205.— Sir John Herschel, Astron. Observ. at the Cape of Good
Hope, p. 165—303.

(3U) p. 206.— Idem, p. 167 and 242.

(342) p. 206. — Argelander, in examining a large number of fixed stars for a
most careful investigation of their proper motion. See his memoirs, DLX
Stellarum fixaruni positiones mediae ineunte anno 1830, ex observ. Abose
habitis (Helsingforsise, 1825). Madler (Astr. S. 625), estimates at 600
the number of multiple stars discovered in the northern celestial hemisphere
at Pulkova since 1837.

(343) p. 247- — The number of fixed stars in which proper motion has been
perceived (while we may conjecture its existence in all), is a little greater than
*he number of multiple stars in which a difference of relative position has been
observed. Madler, Astr. S. 394, 490, and 520—540. Struve, in his Mens.
microm., p. xciv., gives the results of the application of the calculus of proba-
bilities to these relations, according as the distances apart of the double or
multiple stars are between 0' and 1', 2* and 8*, or 16* and 32.' Distances
less than C*'3 have been appreciated, and experiments with very closely placed
artificial double stars have confirmed the observer's hopes of such estimations
being for the most part secure, as far as 0*.l. Struve iiber Doppelsterne
nach Dorpater Beob. S. 29.

(344) p. 208.— John Herschel, Cape Observations, p. 166.

(345) p. 208. — Struve Mensurse microm., p. Ixxvii. to Ixxxiv.
(***) p. 208.— John Herschel, Outlines of Astr., p. 579.

NOTES. kxvii

(347) p. 208. — Two glasses, presenting complementary colours, being placed
over each other, give a white image of the Sun. During my long stay at the
Paris Observatory, my friend Arago employed this arrangement with great
advantage, in the place of the ordinary shade-glasses, for observations of solar
eclipses, and of the Sun's spots. The colours to be taken are — red and green,
yellow and blue, or green and violet. " Lorsqu'une lumiere forte se trouve
aupres d'une lumiere faible, la derniere prend la teinte complementaire de la
premiere. C'est la le contraste : mais comme le rouge n'est presque jamais
pur, on peut tout aussi bien dire que le rouge est complementaire du blen.
Les couleurs voisines du Spectre solaire ee substituent." (Arago, MS. of
1847).

(M8) p. 209. — Arago in the Connaissance des Terns pour 1'an 1828,
p. 299—300, and pour 1834, p. 246—250, and 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 dns la question
des etoiles doubles qu'avec la plus grande reserve. Le bleu est la cou-
leur reelle de certaines etoiles. II resulte des observations recueillies
jusqu'i9i que le firmament est non seulement parseme de soleils rouges et
jaunes, comme le savaient les Anciens, mais encore de soleils Ueus et verts.
C'est au terns et a des observations futures a nous apprendre si les etoiles
vertes et bleues ne sont pas des soleils deja en voie de decroissance ; si les dif-
ferentes nuances de ces astres n'indiquent pas que le combustion s'y opere a
differens degres ; si la teiute, avec exces de rayons les plus refrangibles, qae
presente souvent la petite etoile, ne tiendrait pas & la force absorbante d'une
atmosphere qut developperait 1'action de 1'etoile, ordinairement beaucoup pros
biUlante, qu'elle accompagne.— (Arago in the Annuaire for 1834, p. 295 —
301.

(3-9) p. 209. — Struve iiber Doppelsterne nach Dorpater Beobacht anger-,
1837, S. 33 — 36, and Mensurse microm. p. Ixxxiii., enumerates sixty-three
pairs of stars, in which both stars are blue or bluish, and in which, there-
fore, the colour cannot be the result of contrast. When it is necessary to
comnare together the colours of the same double stars, as given by differen
observers, it is particularly striking to remark how often the companion of a
red or yellowish red star is called blue by one observer, and green by another.

C350) p. 209.— Arago in the Annuaire for 1834, p. 302.

C351) p. 209.— Kosmos, Bd. iii. S. 168—172; Eng. ed. p. 110—114.

(352) p. 210.— "This superb double star (a Centauri) is beyond all com-
parison the most striking object of the kind in the heavens, and consists of

Ixxviii NOTES.

two individuals, both of a high ruddy or orange colour, though that of t
smaller is of a somewhat more sombre and brownish cast." Sir John Her-
schel, Cape Observations, p. 300. According to the valuable observations of
Captain Jacob, of the Bombay Engineers, in 1846 — 1848, the principal star
is estimated at the 1st magnitude, and the companion from the 2'5 to the
3rd magnitude.

(353) p. 210.— Kosmos, Bd. iii. S. 235, 249 and 259, Eng. ed. pp. 155,
249, and note 274.

(^ p. 211.— Struve iiber Doppelst. nach Dorpat. Beob. S. 33.

C355) p. 211.— Same work, S. 36.

(**) p. 211.— Madler, Astr. S. 517; John Herschel, Outlines, p. 568.

(K1) p. 211.— Compare Madler, Untersuch. iiber die Fixstern-Systeme, Th.
i. S. 225—275, Th. ii. S. 235— 240 • the same Author, in hi Astr. S. 541 ;
and John Herschel, Outlines, p. 573.

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