A paper on “The Rings of Saturn” was read by Mr. T.L. Atkinson, B.A., LL.B., of which the following is an abstract.

Saturn’s planetary nature must have been known at an early period, but it was not until 1610 that his rings were first noticed as protuberances on either side of the planet, nor was it recognised till 1659 that these appearances were due to Saturn being surrounded by a thin, flat ring.

The planet revolves in its orbit once every 29 ½ years, the plane of the rings always moving parallel to itself and always inclined at an angle of 25° 10′ 21.95″ to its orbit. Consequently, in each complete revolution in the orbit there are two periods during which the plane of the ring cuts the earth’s orbit, each of these periods being rather more than a year’s duration. During each such period the rings will disappear at least once since the plane of the rings comes during some part of that period, between the earth and the sun, and only the unenlightened side of the rings is visible on earth.

About 100 years ago Herschell discovered that it was not one ring only which surrounded the planet, but two concentric rings with a considerable interval between them, and in 1850 it was found that there was within these another ring, not bright like the other two, but of a dusky tinge, and such that the planet’s disc could be seen through if without distortion. And now gaps have been discovered in these three rings, rendering it possible that the ring system consists of many rings. The total breadth of these rings has been estimated at about 37,000 miles, the mean diameter of the planet itself being over 70,000 miles.

It was formerly assumed that the ring (as we may call the ring system) was solid. Laplace showed that it must revolve, for if not it would at once fall down on the surface of the planet, and Herschel by observing certain spots on the ring found it did revolve in about 10 hours 32 minutes 15 seconds, this period referring to the outer ring. Laplace also showed that the ring system could not consist only of one ring, for such a ring would be unable to withstand the strain that would necessarily be put upon it, a fact which it is very easy to believe when we find that if we were to make a model of the ring 30 feet in diameter, it would have to be only about one-fifth of an inch thick. He also showed that the ring, if solid, could not be uniform, for if it were, the system would not be stable, and the slightest disturbance would precipitate the ring upon the planet. He suggested that the ring might be loaded at one point so that the centre of mass should not coincide with the centre of figure, and that this would be sufficient to preserve stability.

But in 1857 Maxwell in the Adam’s Prize Essay, showed that the distribution of mass would have to be so unsymmetrical that the rings could not have the appearance which they actually present. Hence he concluded that the ring is not solid, and therefore must either be fluid or consist of a number of disconnected particles. The former they cannot be for waves would be created and the ring broken up into satellites. The ring must therefore consist of a large number of small disconnected particles, most probably solid, and possibly arranged into rings, but at all events independent and revolving about the planet like satellites.

In the inner dark ring these particles must be sparsely distributed, and we thus have the explanation of the fact that Saturn is visible through the ring without distortion. It has been thought that the ring has grown in width, though it is not absolutely certain that such is the case, and if such growth has taken place it is probable that it has done so by the inner boundary of the ring approaching nearer to Saturn, and that the outer boundary has not receded furth from the planet to any appreciable extent.