or brightness must be the result of central powers, we may venture to affirm that this theory is no longer an unfounded hypothesis, but is fully established on grounds which cannot be overturned.

Some of these round clusters consist of stars of a certain magnitude, and given degree of compression, while the whole cluster itself takes up a space of perhaps 10 minutes; others appear to be made up of stars that are much smaller, and much more compressed, when at the same time the cluster itself subtends a much smaller angle, such as 5 minutes. This diminution of the apparent size, and compression of stars, as well as diameter of the cluster to four, three, two minutes, may very consistently be ascribed to the different distances of these clusters from the place in which we observe them; in all which cases we may admit a general equality of the sizes, and compression of the stars that compose them, to take place. Other clusters there are that, when they come to be compared with some of the former, seem to contain stars of an equal magnitude, while their compression appears to be considerably different.

This method of viewing the heavens seems to throw them into a new kind of light. They now are seen to resemble a luxuriant garden, which contains the greatest variety of productions, in different flourishing beds; and one advantage we may at least reap from it is, that we can, as it were, extend the range of our experience to an immense duration. For, to continue the simile I have borrowed from the vegetable kingdom, is it not almost the same thing, whether we live successively to witness the germination, blooming, foliage, fecundity, fading, withering, and corruption of a plant, or whether a vast number of specimens, selected from every stage through which the plant passes in the course of its existence, be brought at once to our view?

Dr. H. then adds the catalogue of the 1000 new nebulæ and clusters of stars: the numbers, dates of observation, names, situations, and several other characteristic circumstances, are arranged in eight columns of a table, which is divided into eight classes or collections:-The first class is of such as are entitled, from their appearance in the heavens, bright nebula; the second class are the faint nebula; the third class, the very faint nebula; the fourth class, planetary nebulæ; the fifth class, very large nebula; the sixth class, very compressed, and clusters of stars; the seventh class, pretty much compressed clusters of large or small stars; and the eighth, or last class, coarsely scattered clusters of stars.

Discovery of a sixth and seventh Satellite of the Planet Saturn; with Remarks on the Construction of its Ring, its Atmosphere, its Rotation on an Axis, and its Spheroidical Figure. By WM. HERSCHEL, LL.D. F.R.S.-[1790]

He presents an account of two new satellites, which he dis covered by means of his large 40-foot telescope; and has called them the sixth and seventh, though their situation in the Saturnian system entitles them to the first and second place.

The planet Saturn is, perhaps, one of the most engaging objects that astronomy offers to our view. He observes, that the black disk, or belt, on the ring of Saturn, is not in the middle of its breadth; nor is the ring subdivided by many such lines, as has been represented in divers treatises of astronomy; but that there is one single, dark, considerably broad line, belt, or zone, on the ring, which he always permanently found in the same place. From his observations it appears, that the zone on the northern plane of the ring is not, like the belts of Jupiter or those of Saturn, subject to variations of colour and figure; but is most probably owing to some permanent construction of the surface of the ring itself. That, however, for instance, this black belt cannot be the shadow of a chain of mountains, may be gathered from its being visible all round on the ring; for at the ends of the ansæ there could be no shades visible, on account of the direction of the sun's illumination, which would be in the line of the chain; and the same argument will hold good against supposed caverns or concavities. It is also pretty evident, that this dark zone is contained between two concentric circles, as all the phenomena answer to the projection of such a zone. Thus, the zone is continued all round the ring, with a gradual decrease of breadth towards the middle answering to the appearance of a narrow circular plane, projected into an ellipsis.

With regard to the nature of the ring, we may certainly affirm, that it is no less solid and substantial than the planet itself. The same reasons which prove to us the solidity of the one will be full as valid when applied to the other. Thus we see the shadow of the body of Saturn on the ring. In the same manner we see the shadow of the ring cast on the planet. If we deduce the quantity of matter contained in the body, from the power by which the satellites are kept in their orbits, and the time of their revolution, it must be remembered, that the ring is included in the result. It is also in a very particular manner evident, that the ring exerts a considerable force on

these revolving bodies, since we find them strongly affected with many irregularities in their motions, which we cannot properly ascribe to any other cause than the quantity of matter contained in the ring; at least we ought to allow it a proper share in the effect, as we do not deny but that the considerable equatorial elevation of Saturn must also join in it.

The light of the ring of Saturn is generally brighter than that of the planet: for instance, the southern part of the ring, which passed before the body, was seen very plainly brighter than the disk of Saturn, on which it was projected.

Dr. H. comes now to one of the most remarkable properties in the construction of the ring, which is its extreme thinness. When nearly in the plane of the ring, he repeatedly saw the first, the second, and the third satellites, nay even the sixth and seventh, pass before and behind the ring in such a manner that they served as excellent micrometers to estimate its thickness by. July 18. 1789, the first satellite seemed to hang on the following arm, declining a little towards the north, and gradually advanced on it towards the body of Saturn; but the ring was not so thick as the lucid point.

April 9. 1775, Dr. H. observed a northern belt on Saturn, which was a little inclined to the line of the ring. May 1. 1776, there was another belt, inclined about 15° to the same line, but it was more to the south, and on the following side came up to the place in which the ring crosses the body. July 13. the belt was again depressed towards the north, almost touching the line where the ring passed behind the body. April 8. 1777, there were two fine belts, both a little inclined to the ring.

We may draw two conclusions from what has been reported. The first, which relates to the changes in the appearance of the belts, is, that Saturn has probably a very considerable atmosphere, in which these changes take place; just as the alterations in the belts of Jupiter have been shown, with great probability, to be in his atmosphere. The next inference we may draw from the appearance of the belts on Saturn is, that this planet turns on an axis, which is perpendicular to the ring.

There is another argument, of equal validity with the former, which Dr. H. now mentions. It is founded on the following observations, and will show that Saturn, like Jupiter, Mars, and the Earth, is flattened at the poles, and therefore ought to be supposed to turn on its axis. It appears that Saturn is considerably flattened at the poles. And as the greatest measures were taken in the line of the ring and of

the belts, we are assured that the axis of the planet is perpendicular to the plane of the ring, and that the equatorial diameter is to the polar nearly as 11 to 10.

Observations on the Sugar-Ants. By JOHN CASTLES, Esq.

THE sugar-ants, so called from their ruinous effects on the sugar-cane, first made their appearance in Grenada about the year 1770. Thence they continued to extend themselves on all sides, for several years; destroying, in succession, every sugar-plantation between St. George's and St. John's, a space of about 12 miles.

All attempts of the planters to put a stop to the ravages of these insects having been found ineffectual, it well became the legislature to offer great public rewards for discovering a practicable method of destroying them, so as to permit the cultivation of the sugar-cane as formerly. Accordingly, an act was passed, by which such discoverer was entitled to 20,000l., to be paid from the public treasury of the island. In Grenada there had always been several species of ants, differing in size, colour, &c. which, however, were perfectly innocent with respect to the sugar-cane. The ants in question, on the contrary, were not only highly injurious to it, but to several sorts of trees, such as the lime, lemon, orange, &c.

Their numbers were incredible. The roads are seen coloured by them for miles together; and so crowded were they in many places, that the print of the horses' feet would appear for a moment or two, till filled up by the surrounding multitude. All the other species of ants, though numerous, were circumscribed and confined to a small spot, in propor`tion to the space occupied by the cane-ants, as a mole-hill to a mountain. The common black ants of that country had their nests about the foundation of houses or old walls; others in hollow trees; and a large species in the pastures, descending by a small aperture under ground. The sugarants universally constructed their nests among the roots of particular plants and trees, such as the sugar-cane, lime, lemon and orange trees, &c.

The use of fire afforded a great probability of success; for it was observed, that if wood, burnt to the state of charcoal, without flame, and immediately taken from the fire, was laid in their way, they crowded to it in such amazing numbers as soon to extinguish it, though with the destruction of thousands of them in effecting it. This part of their history

appears scarcely credible; but, on making the experiment himself, Mr. C. found it literally true. He laid fire, as above described, where there appeared but a very few ants, and in the course of a few minutes thousands were seen crowding to it and on it, till it was perfectly covered by their dead bodies. Holes were therefore dug at proper distances in a cane-piece, and fire made in each of them. Prodigious quantities perished in this way; for those fires, when extinguished, appeared in the shape of mole-hills, from the numbers of their dead bodies heaped on them. Yet they soon appeared

again as numerous as ever.

This calamity, which resisted so long the efforts of the planters, was at length removed by another, which, however ruinous to the other islands in the West Indies, and in other respects, was to Grenada a very great blessing, namely, the hurricane in 1780. These ants make their nests, or cells for the reception of their eggs, only under or among the roots of such trees or plants as are not only capable of protecting them from heavy rains, but are at the same time so firm in the ground as to afford a secure basis to support them against any injury occasioned by the agitation of the usual winds. This double qualification the sugar-cane possesses in a very great degree; for a stool of canes, which is the assemblage of its numerous roots where the stems begin to shoot out, is almost impenetrable to rain, and is also, from the amazing numbers and extension of the roots, firmly fixed to the ground.-At Duquesne, particularly at that time, they were pernicious in the highest degree, spreading themselves on all sides with great rapidity, when a sudden stop was put to their progress by the hurricane which happened near the middle of October that year.

When by the violence of the tempest heavy pieces of artillery were removed from their places, and houses and sugarworks levelled with the ground, there can be no doubt that trees and every thing growing above ground must have greatly suffered. This was the case. Great numbers of trees and plants, which resist commonly the ordinary winds, were torn out by the root. The canes were universally either lodged or twisted about as if by a whirlwind, or torn out of the ground altogether. In the latter case, the breeding ants, with their progeny, must have been exposed to inevitable destruction from the deluge of rain which fell at the same time. The number of canes, however, thus torn out of the ground, could not have been adequate to the sudden diminution of the sugar-ants; but it is easy to conceive that