OBSERVATORIES IN THE SOUTHERN HEMISPHERE. was the first astronomer appointed by the Government. He was succeeded in 1831 by Mr. T. Henderson. The present astronomer in charge of the Royal Observatory at the Cape is Sir Thomas Maclear, who has occupied the office since the year 1834, on the appointment of Mr. Henderson to the chair of Practical Astronomy in the University of Edinburgh. Well equipped permanent observatories have also been established in various other places in the southern hemisphere. They are all in a condition to advance our knowledge of the southern skies. That at Melbourne, under the care of Mr. Ellery, is one of the first class. Australia contains two other public observatories, one at Sydney, the other at Adelaide, besides one or two private establishments. Of the latter, that under the direction of Mr. Tebbutt, of Windsor, New South Wales, deserves a special mention. The principal observatory in South America is that at Santiago, Chili, where a continuous series of astronomical observations has been carried on for several years past. After the publication of a valuable catalogue of nebulæ in 1833, Sir John Herschel considered that his labours would be incomplete without an examination of the sky of the southern hemisphere in the same systematic manner as that employed by him in his researches in England. He therefore determined at once to transport himself, family, and instruments to the Cape of Good Hope, where he could command that portion of the heavens not visible in Great Britain. On his arrival at the Cape on January 15th, 1834, he took up a temporary residence at Welterfreiden; but soon after, meeting with a suitable mansion at Feldhausen, about six miles from Cape Town, a spot charmingly situated on the last gentle slope at the base of Table Mountain, he selected it for his home during the four years he remained in South Africa. Here he erected, within an inclosure—a kind of orchard, surrounded on all sides by trees-a building for his equatorial, while his twenty-foot reflector was mounted in the open air, due precaution being taken for the protection of the speculum and other delicate parts of the instrument. The results of the labours of the illustrious astronomer have been published in a large quarto volume, full of original observations and research. As a remembrance of this scientific visit of Sir John Herschel to a distant part of the globe, for no other object than that of a pure love to a science for the advancement of which he has devoted the greater part of his life, a granite obelisk has been erected at Feldhausen, on the site of the twenty-foot reflector, with which most of his observations were made. This obelisk was completed, at an expense of £300, in February, 1842, in the presence of the subscribers, who attended on the occasion of placing the top stone. It stands eighteen feet high from the ground, the base being six feet square and six feet in height. There is an opening on the east face exhibiting the Herschel mark, which points out the site of the twenty-foot reflector. This opening is covered with a bronze plate, containing the inscription of the purpose for which the obelisk was erected. A proposition has lately been made, and there is every probability of its being carried out, for making a complete survey of the southern heavens, on the same plan as that pursued by M. Argelander, of Bonn, in his survey of the sky of the northern hemisphere. It is intended to observe the exact position of every star, at least, as low as the ninth magnitude, of which there are probably several hundred thousands. Many years must necessarily elapse before even a major portion of this undertaking can be completed; but by dividing the labour between the principal southern observatories, it is hoped that the work will be so far accelerated as to permit the completion of certain zones of the heavens within a reasonable time. The amount of patience and observing skill required to perform an astronomical work of such magnitude can scarcely be appreciated by any but those who have been more or less accustomed to this class of scientific labour. NEBULE AND CLUSTERS. To view the general appearance of a nebula, an observer is not required at first to call in the aid of a telescope; for there are several well-known clusters of stars which have for ages been distinguished solely as condensed and bright patches of light. The interesting group of the Pleiades is one of these; the principal stars in Coma Berenices form another woolly group. A somewhat similar cluster of stars called Præsepe, in the constellation Cancer, can be resolved into a number of stars with very slight optical assistance. Some NEBULE AND CLUSTERS. of the principal telescopic nebulæ may even be observed on very clear nights with the naked eye, as the great nebula of Orion and Argo Navis. An old chart containing the nebula in Andromeda has been found, by comparing the positions of the stars contained in it with modern determinations, to date as far back as the close of the tenth century. This nebula was thus recognised in the heavens, and its position in relation to the stars was known at least six hundred years before the invention of the telescope. More than five thousand nebulæ and clusters, including both hemispheres, have been observed and catalogued. Astronomy is indebted for the most part to the two Herschels for the complete analysis of the different varieties of these generally faint objects. Sir William Herschel, in his retired residence at Slough, assisted by his sister Caroline, took advantage of his splendid reflecting telescopes to scour the heavens for these almost invisible particles of star-dust. If anything special in their form was observed, the magnificent forty-foot telescope was directed to them, when many which in smaller instruments appeared as ill-defined matter, were resolved into hundreds or thousands of distinct stars. By a careful and systematic scrutiny, Sir William Herschel separated all objects which are classed under the head of nebulæ into six divisions as follows :— 1. Clusters of stars, in which all the objects are clearly separated, forming one close mass of stars, either in a globular or irregular form. 2. Resolvable nebulæ, or such as give the appearance of being stars, requiring only increased optical power to resolve the whole into distinct stars. 3. Nebula where there is no indication of stars, or probability that no telescopic power could alter their appearance. This division has been subdivided into subordinate classes, depending on their magnitude and comparative lustre. 4. Planetary nebula. These objects owe their name to an apparent resemblance to a planetary disk. Generally they are either circular, or slightly oval. Some of the planetary nebula present some remarkable illustrations of colour. One in the Southern Cross Sir John Herschel noticed to be "a fine and full blue colour, verging somewhat upon green." 5. Stellar nebulæ. the centre of the nebula. This class of objects has generally a condensation of light in 6. Nebulous stars. Here we have a nebulosity with one or more distinct stars shining through it. Nebulous stars are sometimes circular, sometimes oval, sometimes annular, but always of regular form. When the nebula is circular, the star is generally in the centre; when elliptical, two stars are often seen in the foci of the ellipse. Among the most remarkable of the nebula which have attracted the attention of astronomers, the following may be mentioned:-The great nebula in Orion, near Theta Orionis; the great nebula in Argo Navis; the cluster-nebula in Perseus; the nebula in Andromeda; the dumb-bell nebula; spiral nebulæ, etc. The nebulæ in Orion and Argo Navis, and the star-cluster in Perseus, are already briefly described in the notes on these constellations. The first detailed observations of the nebula in Andromeda were made by Simon Marius in 1612. It appeared to him "to be composed of rays of light, increasing in brightness as they approached the centre, which was marked by a dull, pale light, resembling the light of a candle seen at some distance shining through horn." According to Sir William Herschel, it is one of the nearest of all the great nebulæ, about one and a half degree in length, and in one of its narrowest places about a NEBULE AND CLUSTERS. quarter of a degree in breadth. The most luminous portion of it approaches the resolvable nebulosity, and exhibits slight indications of a faint red colour. Sir John Herschel, writing in 1826, gives the following detailed description of the great nebula in Andromeda, which he had frequently observed with the great reflecting telescope at Slough. "At present it has not, indeed, a star, or any well-defined disk in its centre; but the brightness, which increases by a regular gradation from the circumference, suddenly acquires a great accession, so as to offer the appearance of a nipple as it were in the middle, of very small diameter, but totally devoid of any distinct outline, so that it is impossible to say precisely where the nucleus ends and the nebula begins. Its nebulosity is of the most perfectly milky absolutely irresolvable kind, without the slightest tendency to that separation into flocculi described in the nebula of Orion, nor is there any sort of appearance of the smallest star in the centre of the nipple. This nebula is oval, very bright, and of great magnitude, and altogether a most magnificent object." Since the date of these remarks, which give the appearance of the nebula as viewed in Herschel's forty-foot reflecting telescope, it has been observed through some of the largest refracting telescopes, especially the fifteen-inch object-glass equatorial of Harvard College, United States, by Mr. G. P. Bond. No signs of resolvability have, however, been detected. The nebula is one of those which give a continuous spectrum like the stars; it is therefore probably only nebulous in an optical sense, owing to the extreme minuteness of its constituent stars. Mr. Huggins remarks, however, that "it may be possible that nebulæ, which have little indication of resolvability, and yet give a continuous spectrum, such as the great nebula in Andromeda, are not clusters of suns, but gaseous nebulæ, which, by the gradual loss of heat, or the influence of other forces, have become crowded with more condensed and opaque portions. far as my observations extend at present, they suggest the opinion that the nebula which give a gaseous spectrum are systems possessing a structure, and a relation to the universe, altogether distinct from the great group of cosmical bodies to which our Sun and the fixed stars belong." So The nebula shaped like a dumb-bell or hour-glass is in the constellation Vulpecula. This is another of the irresolvable nebulæ, but it differs so far from that in Andromeda, as to give a spectrum of one bright line only. It is thus evidently composed of gaseous matter. The dumb-bell nebula consists of two luminous symmetrical patches, joined together by a narrow isthmus, the whole of which is surrounded by a faint nebulosity of an oval form. As the appearance of this and most of the other nebulæ changes considerably according to the magnifying power used, it may be remarked that when viewed through a good telescope a low power is always to be preferred when examining these faint objects. The variety of figure of the nebula is very great. They are of every conceivable shape, circular, elliptical, spiral, double, triple, quadruple, and indeed of the most extraordinary irregularity. In many the form changes completely when viewed in telescopes of different magnitudes. A nebula in Taurus, observed by Sir John Herschel, of an oval form of some regularity, when seen in the great reflector of the Earl of Rosse is changed into the |