nestling, even one of the earliest, would be fit to provide for itself before its parent would be instinctively directed to seek a new residence, and be thus compelled to abandon its young one; for old cuckoos take their final leave of this country the first week in July.

Among the many peculiarities of the young cuckoo, there is one that shows itself very early. Long before it leaves the nest, it frequently, when irritated, assumes the manner of a bird of prey, looks ferocious, throws itself back, and pecks at any thing presented to it with great vehemence, often at the same time making a chuckling noise like a young hawk. Sometimes, when disturbed in a smaller degree, it makes a kind of hissing noise, accompanied with a heaving motion of the whole body. The growth of the young cuckoo is uncommonly rapid. The chirp is plaintive, like that of the hedgesparrow; but the sound is not acquired from the foster-parent, as it is the same whether it be reared by the hedge-sparrow or any other bird. It never acquires the adult note during its stay in this country.

There seems to be no precise time fixed for the departure of young cuckoos. I believe they go off in succession, probably as soon as they are capable of taking care of themselves; for though they stay here till they become nearly equal in size and growth of plumage to the old cuckoo, yet in this very state the fostering care of the hedge-sparrow is not withdrawn from them. I have frequently seen the young cuckoo of such a size that the hedge-sparrow has perched on its back, or half-expanded wing, in order to gain sufficient elevation to put the food into its mouth. At this advanced stage, I believe that young cuckoos procure some food for themselves; like the young rook, for instance, which in part feeds itself, and is partly fed by the old ones till the approach of the pairing season. If they did not go off in succession, it is probable we should see them in large numbers by the middle of August; for, as they are to be found in great plenty, when in a nestling state, they must now appear very nume rous, since all of them must have quitted the nest before this time. But this is not the case; for they are not more numerous at any season than the parent-birds are in the months of May and June.

The same instinctive impulse which directs the cuckoo to deposit her eggs in the nests of other birds directs her young one to throw out the eggs and young of the owner of the nest. The scheme of nature would be incomplete without it; for it would be extremely difficult, if not impossible,

for the little birds, destined to find succour for the cuckoo, to find it also for their own young ones, after a certain period; nor would there be room for the whole to inhabit the nest.

Catalogue of a Thousand of new Nebula and Clusters of Stars; with a few introductory Remarks on the Construction of the Heavens. By WM. HERSCHEL, LL.D. F.R. S.—[1789.] THE method I have taken of analysing the heavens, as it were, is perhaps the only one by which we can arrive at a knowledge of their construction. In the prosecution of so extensive an undertaking, it may well be supposed that many things must have been suggested, by the great variety in the order, the size, and the compression of the stars, as they presented themselves to my view.

To begin our investigation according to some order, let us depart from the objects immediately around us to the most remote that our telescopes, of the greatest power to penetrate into space, can reach. From the earth, considered as a planet, and the moon as its satellite, we pass through the region of the rest of the planets, and their satellites. The similarity between all these bodies is sufficiently striking to allow us to comprehend them under one general definition, of bodies not luminous in themselves, revolving round the sun. The great diminution of light, when reflected from such bodies, espe cially when they are also at a great distance from the light which illuminates them, precludes all possibility of following them a great way into space. This consideration brings us back to the sun, as a refulgent fountain of light, while it establishes, at the same time, beyond a doubt, that every star must likewise be a sun, shining by its own native brightness. Here, then, we come to the more capital parts of the great

construction.

These suns, every one of which is probably of as much consequence to a system of planets, satellites, and comets, as our own sun, are now to be considered, in their turn, as the minute parts of a PROPORTIONALLY GREATER WHOLE. By my analysis it appears, that the heavens consist of regions where suns are gathered into separate systems, and that the catalogues I have given comprehend a list of such systems; but may we not hope that our knowledge will not stop short at the bare enumeration of phenomena capable of giving us so much instruction? Why should we be less inquisitive than the natural philosopher, who sometimes, even from an inconsiderable number of specimens of a plant, or an animal, is enabled

to present us with the history of its rise, progress, and decay? Let us then compare together, and class some of these numerous sidereal groups, that we may trace the operations of natural causes as far as we can perceive their agency. The most simple form, in which we can view a sidereal system, is that of being globular. This also, very favourably to our design, is that which has presented itself most frequently, and of which I have given the greatest collection.

But first of all it will be necessary to explain what is our idea of a cluster of stars, and by what means we have obtained it. For an instance, I shall take the phenomenon which presents itself in many clusters: it is that of a number of lucid spots, of equal lustre, scattered over a circular space, in such a manner as to appear gradually more compresed towards the middle; and which compression, in the clusters to which I allude, is generally carried so far as, by imperceptible degrees, to end in a luminous centre, of a resolvable blaze of light. To solve this appearance, it may be conjectured that stars of any given, very unequal magnitudes, may easily be so arranged, in scattered, much extended, irregular rows, as to produce the above-described picture; or, that stars, scattered about almost promicuously within the frustrum of a given cone, may be assigned of such properly diversified magnitudes as also to form the same picture. But who, that is acquainted with the doctrine of chances, can seriously maintain such improbable conjectures? To consider this only in a very coarse way, let us suppose a cluster to consist of 5000 stars, and that each of them may be put into one of 5000 given places, and have one of 5000 assigned magnitudes. Then, without extending our calculation any further, we have 25,000,000 of chances, out of which only one will answer the above improbable conjecture, while all the rest are against it. When we now remark that this relates only to the given places within the frustrum of a supposed cone, whereas these stars might have been scattered all over the visible space of the heavens; that they might have been scattered, even within the supposed cone, in a million of places different from the assumed ones, the chance of this apparent cluster not being a real one will be rendered so highly improbable that it ought to be entirely rejected.

Mr. Michell computes, with respect to the six brightest stars of the Pleiades only, that the odds are near 500,000 to 1, that no six stars, aut of the number of those which are equal in splendour to the faintest of them, scattered at random in the whole heavens, would be within so small a distance from

each other as the Pleiades are. Taking it, then, for granted, that the stars which appear to be gathered together in a group are in reality thus accumulated, I proceed to prove also that they are nearly of an equal magnitude.

The cluster itself, on account of the small angle it subtends to the eye, we must suppose to be very far removed from us. For, were the stars which compose it at the same distance from one another as Sirius is from the sun, and supposing the cluster to be seen under an angle of 10 minutes, and to contain 50 stars in one of its diameters, we should have the mean distance of such stars 12 seconds; and therefore the distance of the cluster from us about 17,000 times greater than the distance of Sirius.

Now, since the apparent magnitude of these stars is equal, and their distance from us is also equal, because we may safely neglect the diameter of the cluster, which, if the centre be 17,000 times the distance of Sirius from us, will give us 17,025 for the farthest, and 17,000 wanting 25 for the nearest star of the cluster; it follows, that we must either give up the idea of a cluster, and recur to the above refuted supposition, or admit the equality of the stars that compose these clusters. It is to be remarked, that we do not mean entirely to exclude all variety of size; for the very great distance, and the consequent smallness of the component clustering stars, will not permit us to be extremely precise in the estimation of their magnitudes; though we have certainly seen enough of them to know that they are contained within pretty narrow limits and do not perhaps exceed each other in magnitude, more than in some such proportion as one full-grown plant of a certain species may exceed another full-grown plant of the same species.

If we have drawn proper conclusions relating to the size of stars, we may with still greater safety speak of their relative situations, and affirm, that in the same distances from the cen tre an equal scattering takes place. If this were not the case, the appearance of a cluster could not be uniformly increasing in brightness towards the middle, but would appear nebulous in those parts which were more crowded with stars; but, as far as we can distinguish, in the clusters of which we speak, every concentric circle maintains an equal degree of compression, as long as the stars are visible; and when they become too crowded to be distinguished, an equal brightness takes place, at equal distances from the centre, which is the most luminous part.

The next step in my argument will be to show that these

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clusters are of a globular form. This again we rest on the sound doctrine of chances. Here, by way of strength to our argument, we may be allowed to take in all round nebulæ, though the reasons we have for believing that they consist of stars have not as yet been entered into. For what I have to say concerning their spherical figure will equally hold good, whether they be groups of stars or not. In my catalogues we have, I suppose, not less than 1000 of these round objects. Now, whatever may be the shape of a group of stars, or of a nebula, which we would introduce instead of the spherical one, such as a cone, an ellipsis, a spheroid, a circle or a cylinder, it will be evident that out of 1000 situations, which the axes of such forms may have, there is but one that can answer the phenomenon for which we want to account; and that is, when those axes are exactly in a line drawn from the object to the place of the observer. Here, again, we have 1,000,000 of chances, of which all but one are against any other hypothesis than that which we maintain, and which, for this reason, ought to be admitted.

The last thing to be inferred from the above-related appearances is, that these clusters of stars are more condensed towards the centre than at the surface. If there should be a group of stars in a spherical form, consisting of such as were equally scattered over all the assigned space, it would not appear to be very gradually more compressed and brighter in the middle, much less would it seem to have a bright nucleus in the centre. A spherical cluster of an equal compression within, for that such there are will be seen hereafter, may be distinguished by the degrees of brightness which take place in going from the centre to the circumference. Now as a gradual increase of brightness does not agree with the degrees calculated from a supposition of an equal scattering, and as the cluster has been proved to be spherical, it must needs. be admitted that there is indeed a greater accumulation towards the centre. And thus, from the above-mentioned appearances, we come to know that there are globular clusters. of stars nearly equal in size, which are scattered evenly at equal distances from the middle, but with an increasing accumulation towards the centre. The formation of round clusters of stars and nebulæ is either owing to central powers, or at least to one such force as refers to a centre. Since, then, almost all the nebulæ and clusters of stars I have seen, the number of which is not less than 2300, are more condensed and brighter in the middle; and since, from every form, it is now equally apparent that the central accumulation