Part 25

Observed November 30, 1874, at 5h. 50m. P. M.

Saturn is unique amongst the planets in that its globe is encircled by a series of concentric rings, which lie in the plane of its equator, and consist, according to present theories, of vast throngs of minute bodies revolving about the planet, like so many satellites, in closely parallel orbits. The globe of Saturn, like that of Jupiter, is surrounded by cloudy belts parallel to its equator. The broad equatorial belt, of a delicate pinkish tint, is both brighter and more mottled than the narrower yellowish white belts, which alternate with darker belts of ashy gray on both the north and south sides, but are seen here only on the northern side. The disk has an oval shape, owing to the extreme polar compression of the globe.

The outer, middle and inner rings, with their various subdivisions, are clearly shown in Plate X., and are best seen on the so-called ansæ, or handles, projecting on either side. The gray outer ring is separated by the dusky pencil line into two divisions, both of which appear slightly mottled on the ansæ, as if with clouds. The middle ring has three sub-divisions which are clearly distinguishable, although separated by no dark interval, viz., a brilliant white outer zone, distinctly mottled, as seen on the extremities of the ansæ, and two interior zones of gradually diminishing brightness. The gauze or dusky ring is seen at its full width on the ansæ, but on the background of the strongly illuminated globe only its outer and presumably denser border is visible. The shadow of the globe on the rings is seen on the lower portion of the eastern ansæ. The shadow on the dusky ring is with difficulty perceptible; the shadow on the middle ring is slightly concave toward the planet, which concavity is abruptly increased on the outer zone of this ring; while the shadow on the outer ring slants away from the globe. These appearances are fully accounted for by supposing a general increase of level from the inner edge of the dusky ring to the outer margin of the middle ring, and a uniform lower level on the outer ring. Other observers have regarded the deflection of the shadow as an effect of irradiation. The inner margin of the double outer ring presents on both ansæ a number of slight indentations, which, if not actual irregularities in the contour of this ring, may be explained as shadows caused by elevations on the outer border of the middle ring, or possibly by over-hanging clouds.

Approximate scale, 6,500 miles--1 inch.

PLATE XI.--THE GREAT COMET OF 1881.

Observed on the night of June 25-26, at 1h. 30m. A. M.

A view of the comet 1881, III., drawn as if seen with the naked eye, the minute details, however, being reproduced as seen with the telescope. The star-like nucleus is attended by four conical wings which cause it to appear diamond-shaped. The coma appears double, the brilliant inner coma, immediately enveloping the nucleus, being surrounded by a fainter exterior coma, which has a noticeable depression corresponding to that of the inner edge of the principal coma. The tail is divided lengthwise by a dark rift and is brightest on its convex or forward side. An inner portion of the tail, brighter than the rest, is more strongly curved, as if by solar repulsion. Stars are seen through the brighter parts of the tail, as they may be seen even through the coma and nucleus, with little diminution of their light.

PLATE XII.--THE NOVEMBER METEORS.

As observed on the night of November 13-14, 1868.

A partially ideal view of the November Meteors, combining forms observed at different times during the night of Nov. 13th, 1868. It is not, however, a fanciful view, since a much larger number of meteors were observed falling at once during the shower of November, 1833, and at other times. The locality of the observation is shown by the Polar Star seen near the centre of the Plate, and Cassiopeia's Chair at the left. The general direction of the paths of the meteors is from the north-east, the radiant point of the shower having been in the constellation Leo, beyond and above Ursa Major. While the orbits of the meteors are, in general, curved regularly and slightly, several are shown with very eccentric paths, among them one which changed its course at a sharp angle. In the upper left-hand corner appear two vanishing trails of the "ring-form," and several others still further transformed into faint luminous patches of cloud. Red, yellow, green, blue and purple tints were observed in the meteors and their trails, as represented in the Plate.

PLATE XIII.--PART OF THE MILKY WAY.

From a study made during the years 1874, 1875 and 1876.

The course of the portion of the Galaxy represented in Plate XIII. is as follows: From Cassiopeia's chair, three bright stars of which appear at the upper edge of the Plate, the Galaxy, forming two streams, descends south, passing partly through Lacerta on the left, and Cepheus on the right; at this last point it approaches nearest to the Polar Star, which is itself outside of the field of view. Then it enters Cygnus, where it becomes very complicated and bright, and where several large cloudy masses are seen terminating its left branch, which passes to the right, near the bright star Deneb, the leader of this constellation. Below Deneb, the Galaxy is apparently disconnected and separated from the northern part by a narrow, irregular dark gap. From this rupture, the Milky-way divides into two great streams, separated by an irregular dark rift. An immense branch extends to the right, which, after having formed an important luminous mass between the stars Gamma and Beta, continues its southward progress through parts of Lyra, Vulpecula, Hercules, Aquila and Ophiuchus, where it gradually terminates a few degrees south of the equator. The main stream on the left, after having formed a bright mass around Epsilon Cygni, passes through Vulpecula and then Aquila, where it crosses the equinoctial just below the star Eta, after having involved in its nebulosity the bright star Altair, the leader of Aquila. In the southern hemisphere the Galaxy becomes very complicated and forms a succession of very bright, irregular masses, the upper one being in Scutum Sobieskii, while the others are respectively situated in Sagittarius and in Scorpio; the last, just a little above our horizon, being always considerably dimmed by vapors. From Scutum Sobieskii, the Galaxy expands considerably on the right, and sends a branch into Scorpio, in which the fiery red star Antares is somewhat involved. In the upper left-hand corner of the Plate, at some distance from the Milky-way, is seen dimly the Nebula in Andromeda, which becomes so magnificent an object to telescopic view.

PLATE XIV.--STAR-CLUSTER IN HERCULES.

From a study made in June, 1877.

In the constellation Hercules, a small nebulous mass is faintly visible to the eye, a telescopic view of which is presented in Plate XIV. It is one of the most beautiful of the easily resolvable globular clusters. The brilliancy of the centre gives the cluster a distinctly globular appearance, while the several wings curving in various directions, have suggested to some observers an irregularly spiral structure. The large stars of the cluster are arranged in several groups which correspond, in a general way, with the faintly luminous wings.

PLATE XV.--THE GREAT NEBULA IN ORION.

From a study made in the years 1875-76.

This nebula, which is one of the most brilliant and wonderful of telescopic objects, readily visible to the naked eve as a patch of nebulous light immediately surrounding the middle star of the three which form the sword of Orion, and a little south of the three well-known stars forming the belt. The small stars in this, as in other Plates of the series, are somewhat exaggerated in size, as was unavoidable with any mode of reproduction that could be employed. The bright pentagonal centre of the nebula is traversed by less luminous rifts, the several subdivisions thus outlined being irregularly mottled as if by bright fleecy clouds. Toward the lower part of this bright pentagonal centre is a comparatively dark space containing four bright stars which form a trapezium and together constitute the quadruple star Theta Orionis, which, to the naked eye, appears as the single star in the centre of the sword. On three sides of the central mass extend long bright wisps, whose curves fail, however, to reveal the spiral structure often attributed to this nebula. On the east a broad wing, with wave-shaped inner border, stretches southward. East of the trapezium are two especially noticeable dark spaces. Close to the main nebula on the north-east, a small faint nebula surrounds a bright star, and a branch from another faint stream of nebulous matter forming a loop to the southward, encloses the nebulous star (Iota Orionis) shown at the top of the Plate.