gests the necessity of receiving with caution, for the present, the generalisation that all the nebulous objects seen in the sky are remote star-firmaments. As, however, this forms the key of the essayist's position, so far as the nebulæ are concerned, it may be as well to let Sir John tell the result of his observations in his own words. The passage is extracted from the last edition of his "Outlines of Astronomy": "It must, therefore, be taken as a demonstrated fact that stars of the seventh or eighth magnitudes and irresolvable nebula may coexist within limits of distance not differing in proportion more than as nine to ten, a conclusion which must inspire some degree of caution in admitting as certain many of the consequences which have been rather strongly dwelt upon in the foregoing pages."

visible against the dark back-ground of the sky being the tracing of its course as it is thus brought up. The spiral nebulæ are not vortices of remote star-streams, bent into curves by orderly irregularities of movement; they are whiffs of infinitely thin curling smoke rolled up in a single twist. They are masses of luminous fog with very slight internal cohesion of parts, drifting through resistance, and, so dragged out into spiral lines:

"In the nebulæ we have loose matter of a thin and vaporous constitution, differing as more or less rare, more or less luminous, in a small degree; diffused over enormous spaces, in stragbrief curves, with no vestige of order or system, gling and irregular forms; moving in devious and or even of separation of different kinds of bodies. In the solar system we have the luminous separated from the non-luminous, the hot from the cold, the dense from the rare; and all luminous and non-luminous formed into globes, impressed with regular and orderly motions, which continue the same for innumerable revolutions and cycles. The spiral nebulæ, compared with the solar system, cannot be considered as other than a kind of chaos; and not even a chaos in the sense of a state preceding an orderly and stable system; for there is no indication in those objects of any tendency towards such a system. If we were to say that they appear mere shapeless masses, flung off perhaps, disturb those who are resolved to find in the work of creating solar systems, we might, every where worlds like ours, but it seems difficult to suggest any other reason for not saying so.

"So far, then, as the nebulæ are concerned, the improbability of their being inhabited appears to mount to the highest point that can be conceived. We may, by the indulgence of fancy, people the alis, with living beings of the same kind of substance as those bright appearances themselves; and in doing so we are not making any bolder assumption than we are when we stock the nebulæ with inhabitants, and call them in that sense distant worlds.'" (P. 232.)

summer clouds, or the beams of the aurora bore

The author of the Essay, however, does not find in these clouds inculcations of caution merely; they are in his eyes proof that all nebulæ are luminous fog. He holds them to be "lumps of light," in some cases resolvable by the telescope into sparkling dots. But these dots are not stars, they are merely brighter and denser parts of the curdled and granulated light. There are instances of like irresolvable luminosity furnished in the tails of comets. Such tails are manifestly vaporous masses through which stars are readily and distinctly seen. Nebula, therefore, are vaporous masses too; and this at once, in the essayist's eyes, accounts for the spiral arrangements of their parts, detected by Lord Rosse. Encke's comet is approaching the sun, because its rare filmy substance is moving through a medium that is capable of affording some resistance to its filminess. It may probably reach the sun after ten thousand revolutions round it, and its substance is probably one hundred thousand times denser than the re- Such are the conclusions of the essayist tarding medium through which it is re-in regard to these interesting objects that volving. But the spiral scrolls in many of the nebulæ only make one turn from their outer commencement to their inner termination. This is because their substance is only ten times denser than the retarding medium. Nebula are really the ten thousand times refined essence of comets' tails, and the exquisitely subtle substance of which they are composed, is whirling round, as the comet whirls about the sun, but it is so extremely light that the resisting ether through which it sweeps brings it up at one turn, the luminous spire

have excited so much attention, since the gigantic instrument of Lord Rosse has been added to the implements of astronomical research. It will be observed here that the gist of the matter is comprised in three distinct propositions. The nebula are not composed of stars: they are luminous vapor of a comet-like nature, and of extreme tenuity; and being only thin vapor, they are destitute of living inhab itants. The third of these propositions is made, in the reasonings of the essayist, to depend entirely upon the establishment

fore, are the premises that require to be examined. Touching the first, Professor Baden Powell writes thus, in his "Essay on the Unity of Worlds":

of the preceding two. Those two, there- | star-clusters should be arranged in a long column of space turned directly away from the earth, or, as the anonymous essayist puts the case:

as to fall in the same line of vision with, but con- | unlikely than the existence of a flat ring siderably behind, the loose cluster of small stars round the globe of Saturn, or of a group composing the rest of the cloud." (Jacob, p. 7.) of thirty-five minute planetoid bodies within the precincts of the solar system. Under these circumstances, it is clear that the beam inclines very considerably from the side of the essayist to that of the plurality of firmamental star schemes. But there is yet another consideration, so weighty in itself, that we think it entirely sets the question at rest, and decides it against the essayist, although it does not seem to have occurred to any of the controversialists who have answered the author of the Essay.

In this reasoning we fully concur. There can be no doubt whatever that if the ring of Saturn had never been seen, and if the thirty-four planetoids had never been detected between Mars and Jupiter, the assumption, that either such a ring or such a group of miniature planets could exist in the universe, would have been deemed so improbable as to be rash and fantastic in the highest degree. Yet there the ring and planetoids are, and each instance stands alone, so far as observation allows us to The light of the filmy transparent comet judge, in the vast realms of space. There is so faint, that as the cometic luminosity really could be nothing more extraordi- travels away from the earth, it is lost to nary in such a distribution of remote star-sight long before its dimensions have been clusters, as the appearance of the Magel- dwindled down to an unappreciable mealanic clouds indicates, than there is in these sure. It disappears as a perceptible body, unquestionable instances of unique and ex- or goes out" from the failure of its light, ceptional arrangement. We think, there- and not from the loss of its size. Yet the fore, that the difficulty sagaciously sug- greatest distance at which the cometic gested by Sir John Herschel is fairly met; wanderers are ever seen, as Sir David and that Captain Jacob has shown, in the Brewster strikingly puts it, "falls short first place, that the essayist has conside- of the distance of the nearest fixed star by rably exaggerated the points upon which nine million of millions of miles." The he mainly rests his cause in this particular nearest nebulæ, on the other hand, at the phase of his arguments; and, in the second lowest estimate are considerably further place, that the improbability, if admitted off than the nearest fixed star, and at that in its strongest form, is far from being distance not only retain their brightness, conclusive in regard to the point the es- but even become more brilliant in proporsayist contends for. In our apprehension, tion as larger telescopes are directed tothe matter stands thus: on the one side wards them, instead of getting paler and there is Sir John Herschel, holding the more diffuse, às cometic luminosity does doctrine that nebulæ are remote firma- under the same circumstances. Is it conments in a general sense, but suggesting ceivable, then, that a filmy luminosity that caution upon the exceptional evidence of vanishes from faintness within the realms the Magellanic clouds. On the other side, of the planetary scheme, remains visible there are the facts that more and more nine million of millions of times further off, nebulæ, before deemed irresolvable, are when "ten thousand times more thin and constantly being resolved into distinct star- rare?" Earnestly, but with all due regroups, with every fresh increase of opti- spect for the opinions and authority of cal power brought to bear in the examin- the essayist, we submit that nothing but tion; that this exceptional instance, which "a conviction that has gradually grown "gives" Sir John Herschel "pause," has from various trains of speculation" could never been subjected to the scrutiny of the maintain such a theory. There is quite great cloud-resolver, Lord Rosse's magni- enough in this peculiarity of nebulous ficent instrument; that Lord Rosse's own light, apart from the fact of its resolvabilexperience, he having really the best prac-ity into stars, incontrovertibly to establish tical right of any living man to be admit- its entire distinctness from the nature of ted as an authority in the case, induces comets. Whatever it may be, this at least him to believe that, with sufficient optical is clear, it is not cometic luminosity ten power, all the nebulæ of the sky would thousand times refined. be converted into stars; and that if the exceptional instance of the Magellanic clouds were proved, it still allows the possibility of an alternative which is not more

VOL. XXXVII.-NO. I.

Having thus carefully and fairly weighed the geological and nebular evidence adduced by the essayist, and found it wanting, we proceed to listen to what he has

3

in them and in their contemporaries. Nor are
we yet called upon to withdraw from them our
sympathy, or entitled to contradict their conjec-
times have given us, the extreme tenuity of much
ture. But all the knowledge that the succeeding
of the luminous matter in the skies, the existence
of gyratory motion among the stars, quite differ-
ent from planetary systems; the appearance of
changes in stars quite inconsistent with such per-
manent systems; the disclosures of the history of
our own planet, as one in which changes have con-
stantly been going on; the certainty that by far
it has been tenanted by creatures entirely differ-
the greater part of the duration of its existence

from those which give an interest, and thence
a persuasiveness, to the belief of inhabitants in
worlds appended to each star; the impossibility
which appears, on the gravest consideration, of
transferring to other worlds such interests as be-
long to our own race in this world; all these con-
siderations should, it would seem, have prevented
up, among a generation professing philosophical
that old and arbitrary conjecture from growing
caution and scientific discipline, into a settled be-
lief." (Plurality &c., p. 266.)

to urge in regard to the fixed stars. The
tenor of his remarks in this direction is
that amongst the sidereal host there are
individuals in which changes have occur-
red, or continue to recur periodically, in
the intrinsic brilliancy or in the color of
their light; this implies to him that those
stars are not in the permanent condition
in which the sun is, and which alone is
compatible with the necessities of a sys-
tem of worlds, but that they are in an un-
settled state and in the transition of pro-
gress.
The fixed stars are, it is true, self-ent
luminous, like the sun, but the nebulæ
and comets are also self-luminous, and it
is with them the true analogy lies. The
stars are simply nebulæ in forward stages
of maturation, advancing perhaps towards
the condition of planetary systems, of
which the solar one is the only perfected
specimen. Periodical variations of bril-
liancy, such as are illustrated in Algol, sug-
gest, not that there are large opaque bod-
ies of a planetary nature revolving round
the central source of light, but that the
light itself has not yet assumed the spheri-
cal form, and is an oblong revolving nebu-
lar mass, of which some parts are cooled
down, and have become opaque, and there-
fore intercept the rays emitted from the
rest when they pass before them. In the
case of Algol, it is known that the period
of the intermissions of brilliancy is grow-
ing gradually shorter. This is not a cos-
mical irregularity of elliptical movement,
as Herschel supposed, carrying its own
compensation with it, and promising, after
a time, a return to some original measure,
but it is a yet further indication that the
star is a crude nebular mass in process of
condensation. Even the facts that have
been ascertained in relation to the relative
distances and movements of the binary
stars point to the impossibility of their
having any connection with worlds. Some
of them confessedly have their constitu-
ents nearer together than the breadths of
space included in the dimensions of the so-
lar system, and if there were planetary
orbs circling round either constituent,
they would of necessity pass so near to the
attracting mass of the other as to render
it impossible to be sustained in any regular
and orderly course.

But again we submit that "succeeding
times have also given us" two or three par-
ticulars in the way of knowledge, which
are strictly relevant to the matter under
consideration, but which nevertheless the
essayist has altogether omitted from his
enumeration. We know that the sun
would appear to get smaller and smaller,
if we were further and further removed
from it, and that at last, on account of its
intensity of brilliancy, it would seem a
shining point of inappreciable dimensions.
Its size would of necessity escape from
the perceptive abilities of the organ of vis-
ion long before the light emitted from it
became too faint to excite sensation in its
nerves. We know that the stars are at
distances so remote, that if the sun were
there too, it would be sufficiently far to
have lost its size, and to have been con-
verted into a shining point, and conse-
quently we know that if the stars are like
the sun, they would present just the ap-
pearance they do, at the distance at which
they are placed. On the other hand, if
the stars be not like the sun, then we do
not know what they can be, for there is
nothing in this "train of speculation" of
the essayist that furnishes any positive in-
formation upon the matter which can in
the slightest degree pretend to take the
place of the notion he endeavors to sweep
away. For ourselves, we confess that
these common-sense considerations
every sense
appear
to us to possess immeasurably more weight
than all his remarks. The variable and

"That Copernicus, that Galileo, that Kepler,

should believe the stars to be suns in
of the term, was a natural result of the expansion
of thought which their great discoveries produced

unsettled condition of certain stars really
proves nothing more than that those few
exceptional luminaries are unlike to their
neighbors. It does not afford even a sha-
dow of a reason for the assumption that
fixed stars in general are unlike the sun.
Obviously the irregularities of a few indi-
viduals in any community cannot be laid
to the account of the greater number that
are of a staid and orderly character. The es-
sayist finds the comparatively close neigh-
borhood of the constituents of the binary
stars incompatible with the supposition
that there are planetary orbs revolving
about them in safety. Sir John Herschel,
however, holds a different opinion in this
matter; for while considering the proba-
bility of such a supposition being in ac-
cordance with fact, he writes, "unless
closely nestled under the protecting wing
of their immediate superior, the sweep of
their other sun, in its perihelion passage
round their own, might carry them off, or
whirl them into orbits utterly incom-
patible with the conditions necessary for
the existence of their inhabitants." Cap-
tain Jacob, too, points out how very pos-
sible it is that planetary spheres may re-
volve in orbits so large that they inclose
within them both the constituents of a bi-
nary star, whose common centre of gravi-
tation would thus become the general
gravitation-centre of the system. Under
such an arrangement there would be irre-
gularities of elliptical movement running
in cycles, and returning through com-
pensatory influences upon themselves, but
there would be no such dangerous inter-
ferences as those which are particular-
ised by the essayist as incidental to the
other case.
In fine, we are constrained to
decide against the essayist upon his side-
real argument.

ter, and therefore most probably is nothing but water. Its oblate form is just such a figure as a huge drop of water would assume if in very rapid rotation. The belts of cloud, which sweep transversely across its broad face, prove that it has water about it in abundance. So that taking into account the "bottomless waters" of this planet, the great force with which its vast mass must gravitatingly draw down whatever is placed near its surface, and the small amount of solar influence which, at its remote distance, it receives, it becomes clear that any inhabitants that belong to it, must possess only the very lowest forms of organization and life. As there are no solid substances, like bone, in the planet, they must be devoid of skeletons. As the temperature is very depressed, they must be very sluggish and inactive in all their functions and operations. Jupiter comes out, therefore, a mere spherical mass of water, with a few cinders in the midst, and a damp drapery of cloud and mist drawn around it; and with, at the best, a population of boneless, pulpy, glutinous monsters rolling about in its watery recesses; or, it is an oblately spherical lump of ice, with a few shallow pools of water here and there upon its surface, and entirely devoid even of pulpy monstrous life.

We now at length come to that portion of the Essay which really most closely concerns the question at issue, although its author does not seem to have viewed it in this light,-namely, the consideration of the condition of the planets which are associated with the Earth in its subordination to the solar mass. Here the essayist finds warranty no less strong for rejecting entirely the existence of other worlds. Neptune has not light enough to be of any available use in the service of organization. Its sun-derived light and heat are 900 times less than the Earth's. Jupiter has a density not greater than it would

Saturn, with its liquid and vaporous rings, with its cork-like lightness, and its illumination ninety times less than the Earth's, is in the same category with Jupiter, except only that it is in every respect worse off; so that its pulpy monsters, in its icy waters, are too sluggish to be even "deemed alive." The asteroids contained in the spaces between Jupiter and Mars, are avowedly too small to be peopled with living things. But they are nevertheless highly important to the argument in one sense. There are thirty-four of them, and therefore at least the " majority of the planets are uninhabited." Mars, a comparatively near neigbor to the Earth, certainly does approach in a degree to its state of physical existence. It is of nearly the same size, and is composed of substance of analogous density. It has, too, its clouds and snow, and possibly it may have inhabitants to boot. But it has longer years and a colder climate than the Earth. It has, too, really a smaller mass, and "perhaps no atmospheric investment;" therefore, after all, its inhabitants can only

have if it were entirely composed of wa-be of the rudimentary nature of corallines