united in such close systems as not to leave much room for the orbits of planets, or comets; and that consequently, on this ac count also, many stars, unless we would make them mere useless brilliant points, may themselves be lucid planets, perhaps unattended by satellites.

Postscript.-The following observations, which were made with an improved apparatus, and under the most favourable circumstances, should be added to those which have been given. They are decisive with regard to one of the conditions of the lucid matter of the sun.

Nov. 26, 1794, 8 spots in the sun, and several sub-divisions of them, were all equally depressed. The sun was every where mottled. The mottled appearance of the sun was owing to an inequality in the level of the surface. The sun was equally mottled at its poles and at its equator; but the mottled appearances may be seen better about the middle of the disc thau towards the circumference, on account of the sun's spherical form. The unevenness arising from the elevation and depression of the mottled appearance on the surface of the sun, seemed, in many places, to amount to as much, or to nearly as much, as the depression of the penumbræ of the spots below the upper part of the shining substance; without including faculæ, which were protuberant. The lucid substance of the sun was neither a liquid, nor an elastic fluid; as was evident from its not instantly filling up the cavities of the spots, and of the unevenness of the mottled parts. It exists therefore in the manner of lucid clouds swimming in the transparent atmosphere of the sun; or rather of luminous decompositions taking place within that atmosphere.

[Herschel, Phil, Trans. Abridged, 1795.]

CHAP. VII.

ON THE CONSTRUCTION OF THE HEAVENS, AND THE ORGANIZATION OF THE CELESTIAL BODIES.

A KNOWLEDGE of the construction of the heavens has always

been the ultimate object of my observations, and having been many years engaged in applying my forty, twenty, and large ten feet telescopes, on account of their great space-penetrating power to review the most interesting objects discovered in my sweeps, as well as those who had before been communicated to the public in the Connoissance des Temps, for 1784, I find that by arranging these objects in a certain successive regular order, they may be viewed in a new light, and, if I am not mistaken, an examination of them will lead to consequences which cannot be indifferent to an inquiring mind.

If it should be remarked that in this new arrangement I am not entirely consistent with what I have already in former papers said on the nature of some objects that have come under my observation, I must freely confess, that by continuing my sweeps of the heavens, my opinion of the arrangement of the stars and their magnitudes, and of some other particulars, has undergone a gradual change; and indeed when the novelty of the subject is considered, we cannot be surprised that many things formerly taken for granted, should, on examination, prove to be different from what they were generally, but incautiously, supposed to be.

For instance, an equal scattering of the stars may be admitted in certain calculations; but when we examine the milky way, or the closely compressed clusters of stars, of which my catalogues have recorded so many instances, this supposed equality of scattering must be given up. We may also have surmised nebulæ to be no other than clusters of stars disguised by their very great distance, but a longer experience and better acquaintance with the nature of nebulæ, will not allow a general admission of such a principle,

although undoubtedly a cluster of stars may assume a nebulous appearance when it is too remote for us to discern the stars of which it is composed.

Impressed with an idea that nebulæ properly speaking were clusters of stars, I used to call the nebulosity of which some were composed, when it was of a certain appearance, resolvable; but when I perceived that additional light, so far from resolving these nebulæ into stars, seemed to prove that their nebulosity was not different from what I had called milky, this conception was set aside as erroneous. In consequence of this, such nebulæ as afterwards were suspected to consist of stars, or in which a few might be seen, were called easily resolvable; but even this expression must be received with caution, because an object may not only contain stars, but also nebulosity not composed of them.

It will he necessary to explain the spirit of the method of arranging the observed astronomical objects under consideration in such a manner, that one shall assist us to undertstand the nature and construction of the other. This end I propose to obtain by assorting them into as many classes as will be required to produce the most gradual affinity between the individuals contained in any one class, with those contained in that which precedes and that which follows it and it will certainly contribute to the perfection of this method, if this connection between the various classes can be made to appear so clearly as not to admit of a doubt. This consideration will be a sufficient apology for the great number of assortments into which I have thrown the objects under consideration; and it will be found that those contained in one article, are so closely allied to those in the next, that there is perhaps not so much difference between them, if I may use the comparison, as there would be in an annual description of the human figure, were it given from the birth of a child till he comes to be a man in his prime.

The similarity of the objects contained in each class will seldom require the description of more than one of them, and for this purpose, out of the number referred to, the selected one will be that which has been most circumstantially observed; however, those who wish either to review any other of the objects, or to read a short description of them, will find their place in the heavens, or the account of their appearance either in the catalogues I have