from stars, or planets, or any other materials existing around us, which is diffused in immense masses throughout the spaces of the universe. The large nebula in Orion, described above, is considered as one of the most striking evidences that such a substance is distributed throughout the sidereal regions; for the whole light and power of Herschel's forty-feet telescope, though four feet in aperture, was insufficient to resolve it into stars, although from certain circumstances it appears to be one of the nearest, as it is one of the brightest, of those nebulous masses. It has therefore become a subject of interesting inquiry, "What are those huge masses of unformed matter we call the nebulæ ? and what purposes do they serve in the economy of creation?"

It is an opinion now very generally entertained, that the self-luminous matter to which we refer is the chaotic materials out of which new suns or worlds may be formed, and that it is gradually concentrating itself by the effect of its own gravity, and of the circular motions of which it may be susceptible, into denser masses, so as ultimately to effect the arrangement and establishment of sidereal systems. It is argued that this opinion is highly probable, from the consideration that we find the nebulæ in almost every stage of condensation. Such nebulæ as are represented in figures 59 and 62 are viewed as consisting of nebulous matter in its rudest and most chaotic state; and figures 63, 64, 65, and also figures 66, 67, 68, as similar matter in a state of progress towards condensation. The four figures marked 71 are considered as specimens of this gradual condensation, in which the progress may be traced from the left-hand figure to the right. It has even been maintained by some late writers on this subject, that this, in all probability, is the mode in which the different systems of the universe were gradually brought into the state in which we now behold them, and that the sun and planets of the system to which we belong derived their origin from a similar cause; and it has likewise been attempted to connect the geological changes in the structure of our globe with the operation of a principle or law by which such a thin, filmy substance as a nebula was condensed into such a heterogeneous mass of solidity as we find in the constitution of the terraqueous globe; and it has been insinuated that the zodiacal light is a portion of the original nebula of which the sun and planets were formed, and a presumptive evidence that the

nebular hypothesis is true. According to these theories, the sun is still to be considered as a nebulous star in a high state of condensation, and may exhibit such an appearance when viewed from a neighbouring system.

Such conclusions, to say the least, are obviously premature. We know too little, in the mean time, of the nature of that nebulous matter which is dispersed through the heavens, or of the motions with which its particles may be endued, to be able to determine its susceptibility of being condensed and arranged into suns and planets. We have never yet seen the same nebula progressing from one stage of condensation to another, from a chaotic to a state of organization; nor is it likely we ever shall, even supposing the hypothesis to be wellfounded, as an indefinite number of years, or even of ages, must be requisite before such a revolution can be accomplished. Yet the observations of future astronomers on this department of the sidereal heavens may tend to throw some additional light on this mysterious subject.

It forms no conclusive argument, however, against this hypothesis, that it is difficult to conceive how a fluid of a nature so apparently rare can ever be condensed to the hardness of a planet or a sun; for if we suppose a nebulosity in its most diffused state to be twenty minutes in diameter, and to be compressed by central attraction and rotary motion till it become only one minute in diameter, the ratio of its density in the latter state compared with that of the former would be as eight thousand to one, since spheres are to each other as the cubes of their diameters. Suppose its density in the first state were equal to that of atmospheric air; its density, when compressed in the proportion supposed, would be nine times heavier than water, which is nearly equal to the weight of silver, and twice the average density of our globe; but if such a process be going on in any of these bodies, numerous ages must elapse before such a consolidation can be effected, for no sensible change appears to have taken place during the period in which such bodies have come under our observation.

Nor do we conceive that this hypothesis is inconsistent with what we know of the attributes and operations of the Almighty; for all the movements and changes going on in our terrestrial system and throughout the universe, are the effects of certain laws impressed upon matter by the hand of the Creator, by the uniform operation of which his wise and beneficent

designs are accomplished. If, then, it forms a part of his designs that new suns and systems shall be formed to diversify the spaces of immensity, and if he has created huge masses of subtile luminous matter, and endued them with certain gravitating powers and rotary motions for this purpose, his almighty agency and infinite wisdom may be as clearly and magnificently displayed in this case as if a system of worlds, completely organized, were to start into existence in a moment. Perhaps the gradual evolution of his designs in such a case might afford matter of admiration and enjoyment to certain orders of superior beings who are privileged to take a near view of such stupendous operations. But, supposing such physical processes going forward, we must necessarily admit that a direct interference of the Deity is necessary before such worlds, after being organized, can be replenished with inhabitants; for matter and motion, by whatever laws they may be directed, cannot be supposed to produce the organization of a plant or an animal, much less of a rational being, whose intellectual principle and faculties must be communicated by the immediate inspiration of the Almighty." To suppose otherwise would be virtually to adopt a species of atheism.

66

All that we require on this point is some more direct and decisive proofs of the validity of the hypothesis we are now considering; and, till such proofs be elicited, we are not warranted to enter into particular speculations, and to speak with so much confidence on the subject as certain theorists have lately done. Sir John Herschel, who has paid more attention to this subject, and made more accurate observations on the nebulae than almost any other individual, is far from being confident, and speaks with becoming hesitation and modesty in relation to this hypothesis. "If it be true," says he, "that a phosphorescent or self-luminous matter exists, disseminated through extensive regions of space in the manner of a cloud or fog-now assuming capricious shapes like actual clouds drifted by the wind, and now contracting itself like a cometic atmosphere around particular stars-what, we naturally ask, is the nature and destination of this nebulous matter? Is it absorbed by the stars in whose neighbourhood it is found to furnish, by its condensation, their supply of light and heat? or is it progressively concentrating itself by the effect of its own gravity into masses, and so laying the foundation of new sidereal systems or of insulated stars? It is easier to pro

pound such questions than to offer any probable reply to them. Meanwhile, appeal to fact, by the method of constant and diligent observation, is open to us; and as the double stars have yielded to this style of questioning, and disclosed a series of relations of the most intelligible and interesting description, we may reasonably hope that the assiduous study of the nebulæ will ere long lead to some clearer understanding of their intimate nature."

On the whole, the nebula, whether resolvable or irresolvable, open to view an inexhaustible field of contemplation and wonder. By far the greater part of the nebulæ are undoubtedly clusters of stars, some of them, perhaps, containing as many millions as our Milky Way, and occupying a space in the tracts of immensity which imagination can never fathom; but a considerable proportion of these bodies evidently appear to be masses of self-luminous substances, without any indication of being formed into organized systems; and how enormous must be the extent of most of those masses, and how vast the regions of space which they fill! If every one of those bodies be only one half the size of the great nebula in Orion, what a prodigious mass of matter must they contain, and what immense space must hundreds and thousands of them occupy! To limited minds such as ours, such spaces appear as approximating to infinity, and all our previous ideas of the amplitude of planetary systems sink into something approaching to inanity. Whatever purposes these immense masses of matter may serve under the administration of Infinite Wisdom, certain it is they exist not in vain. They accomplish designs worthy of the plans of Divine Intelligence, and have doubtless a relation, in one respect or another, to the enjoyments of intelligent beings; but the full development of the plans and agencies of the Deity in this and in many other parts of the economy of the universe, must be considered as reserved for another and a future scene of exist

ence.

SECTION VI.-List of some of the Larger Nebula.

For the sake of those who wish to inspect some of the nebulous bodies by means of telescopes, I have subjoined the following list from Messier's Catalogue, along with the more recent observations of Sir W. Herschel. The right ascensions and declinations are given in degrees and minutes, by

which the places of these bodies may be very nearly found on a celestial globe. If it be judged expedient to reduce the degrees and minutes of right ascension to time, it may be done by the following rules: Divide the number of degree by 15, the quotient is hours; and the remainder reduced to minutes, and divided by 15, gives the minutes, &c., of time: or, multiply the given number of degrees and minutes by 4, and divide the degrees in the product by 60, the quotient is hours, and the remainder minutes, &c. Thus, 320° 17′ is equal to 21 hours, 21 minutes, and 8 seconds of time.

In the following list, R.A. means right ascension; dec., declination; S., south; N., north; diam., diameter of the object, which is expressed in minutes of a degree.

1. R.A. 80° 0' 33"; dec. N. 21° 45′ 27′′; above the Bull's southern horn west of the star : this consists of a whitish light, elongated like the flame of a taper: it exhibited a mottled nebulosity to Sir W. Herschel.

2. R.A. 320° 17′; dec. S. 1° 47'; diam. 4'; in the head of Aquarius, near the 24th star: it appears like the nucleus of a comet, surrounded with a large round nebula: Sir W. Herschel resolved it into stars.

3. R.A. 202° 51' 19"; dec. N. 29° 32′ 57′′; diam. 3'; between Arcturus and Cor Caroli: it is round, bright in the centre, and fades away gradually: it exhibited a mottled nebulosity to Sir W. Herschel.

4. R.A. 242° 16' 26"; dec. S. 25° 55′ 40′′; diam. 24'; near Antares: a mass of stars.

5. R.A. 226° 39′; dec. N. 2° 57'; diam. 3'; near 6 Serpent: a round nebula, resolved into stars by Sir W. Herschel.

6. R.A. 261° 10′ 39"; dec. S. 32° 10' 34"; diam. 15; between the bow of Sagittarius and the tail of Scorpio: a mass of small stars.

7. R.A. 264° 30′ 24"; dec. S. 34° 40′ 34′′; diam. 30': a mass of small stars near the preceding.

8. R.A. 267° 29′ 30′′; dec. S. 24° 21'; diam. 30'; between the bow of Sagittarius and the right foot of Ophiuchus: an elongated mass of stars. Near this mass is the 9th of Sagittarius, which is encircled with a faint light. 9. R.A. 256° 20; dec. S. 18° 13′ 26′′; diam. 3′; in the right leg of Ophiuchus: round and faint, but resolved by Sir W. Herschel into stars.