The number of large telescopes having so greatly increased in recent years, and there being every prospect that the demand for such instruments will continue, it may be well to consider their advantages as compared with those of much inferior size. Object-glasses and specula will probably soon be made of a diameter not hitherto attained; for it is palpably one of the ambitions of the age to surpass all previous efforts in the way of telescopic construction. There are some who doubt that such enormous instruments are really necessary, and question whether the results obtained with them are sufficient return for the great expense involved in their erection. Large instruments require large observatories; and the latter must be at some distance from a town, and in a locality where the atmosphere is favourable. Nothing can be done with great aperture in the presence of smoke and other vapours, which, as they cross the field, become ruinous to definition. Moreover, a big instrument is not to be manipulated with the same facility as a small one: and when anything goes wrong with it, its rectification may be a serious matter, owing to the size. Such telescopes need constant attention if they would be kept in thorough working order. On the other hand, small instruments involve little outlay, they are very portable, and require little space. They may be employed in or out of doors, according to the inclination and convenience of the observer.

The instrument which has so vastly extended our knowledge of the Universe, which has enabled us to acquire observations of remarkable precision, and supplied the materials for many sublime speculations in Astronomy, was invented early in the seventeenth century. Apart from its special application as a means of exploring the heavens with a capacity that is truly marvellous, it is a construction which has also been utilized in certain other departments with signal success. It provided mankind with a medium through which to penetrate far beyond the reach of natural vision, and to grasp objects and phenomena which had either eluded detection altogether or had only been seen in dim and uncertain characters. It has also proved a very efficient instrument for various minor purposes of instruction and recreation. The invention of the telescope formed a new era in astronomy; and though, with a few exceptions, men were slow at first in availing themselves of its far-seeing resources, scepticism was soon swept aside and its value became widely acknowledged.

But though the telescope was destined to effect work of the utmost import, and to reach a very high degree of excellence in after times, the result was achieved gradually. Step by step its powers were enlarged and its qualities perfected, and thus the stream of astronomical discovery has been enabled to flow on, stimulated by every increase in its capacity.

Early in autumn, when the evenings are frequently clear, many persons are led with more force than usual to evince an interest in our satellite, and to desire information which may not be conveniently obtained at the time. The aspect of the Moon at her rising, near the time of the full, during the months of August, September, and October, is more conspicuously noticeable than at any other season of the year, on account of the position she then assumes on successive nights, enabling her to rise at closely identical times for several evenings together. The appearance of her large, ruddy globe at near the same hour, and her increasing brilliancy as her horizontal rays give way under a more vertical position, originated the title of “Harvest Moon,” to commemorate the facility afforded by her light for the ingathering of the corn preceding the time of the autumnal equinox.

It will be universally admitted that the Moon possesses special attractions for us, as being situated nearer than any other celestial body, and forming the inseparable companion or tributary world to the Earth. The many important influences she exercises have led to her becoming the object of close investigation; so that her motions and physical appearances have been ascertained with a remarkable degree of exactness and amplitude.

Appearance of the Planet.—Mars is the fourth planet in the order of distance from the Sun. He revolves in an orbit outside that of the Earth, and is the smallest of the superior planets. His brilliancy is sometimes considerable when be occupies a position near to the Earth, and he emits an intense red light, which renders his appearance all the more striking. Ordinarily his lustre does not equal that of Jupiter, though when favourably placed he becomes a worthy rival of that orb. In 1719 he shone so brightly and with such a fiery aspect as to cause a panic. The superstitious notions and belief in astrological influences prevailing at that time no doubt gave rise to the popular apprehension that the ruddy star was an omen of disaster, and thus it was regarded with feelings of terror. Fortunately the light of science has long since removed such ideas from amongst us, and celestial objects, in all their various forms, are contemplated without misgiving. They are rather welcomed as affording the means of advancing our knowledge of God's wonderful works as displayed in the heavens.

Period &c.—Mars revolves round the Sun in 686d 23h 30m 41a, and his mean distance from that luminary is 141,500,000 miles. The orbit is one of considerable eccentricity, the distance varying between 154,700,000 and 128,360,000 miles.

Superstitious ideas with regard to comets as the harbingers of disaster have long since been discarded for more rational opinions. They are no longer looked upon as ill-omened presages of evil, or as

Many references are to be found among old writings to the supposed evil influence of these bodies, and to the dread which their appearance formerly incited in the popular mind. Shakespeare makes an allusion to the common belief :—

and in relation to the habit of connecting historical events with their apparition, he further says :—

But, happily, the notions prevalent in former times have been superseded by the more enlightened views naturally resulting from the acquirement and diffusion of knowledge; so that comets, though still surrounded by a good deal of mystery, are now regarded with considerable interest, and welcomed, not only as objects devoid of malevolent character, but as furnishing many useful materials for study. Mere superstition has been put aside as an impediment to real progress, and a more intelligent age has recognized the necessity of dealing only with facts and explaining them according to the laws of nature; for it is on facts, and their just interpretation, that all true searchers after knowledge must rely.

Choice of Telescopes.—The subject of the choice of telescopes has exercised every astronomer more or less, and the question as to the best form of instrument is one which has occasioned endless controversy. The decision is an important one to amateurs, who at the outset of their observing careers require the most efficient instruments obtainable at reasonable cost. It is useless applying to scientific friends who, influenced by different tastes, will give an amount of contradictory advice that will be very perplexing. Some invariably recommend a small refractor and unjustly disparage reflectors, as not only unfitted for very delicate work, but as constantly needing re-adjustment and resilvering.

Others will advise a moderate-sized reflector as affording wonderfully fine views of the Moon and planets. The question of cost is greatly in favour of the latter construction, and, all things considered, it may claim an unquestionable advantage. A man who has decided to spend a small sum for the purpose not merely of gratifying his curiosity but of doing really serviceable work, must adopt the reflector, because refractors of, say, 5 inches and upwards are far too costly, and become enormously expensive as the diameter increases. This is not the case with reflectors; they come within the reach of all, and may indeed be constructed by the observer himself with a little patience and ingenuity.

Refractors and Reflectors.—The relative merits of refractors and reflectors have been so frequently compared and discussed that we have no desire to re-open the question here.

The planetary observer has to accept such opportunities as are given him; he must use his telescope at the particular seasons when his objects are well presented. These are limited in number, and months may pass without one of them coming under favourable review. In stellar work no such irregularities can affect the progress of observations. The student of sidereal astronomy has a vast field to explore, and a diversity of objects of infinite extent. They are so various in their lustre, in their grouping, and in their colours, that the observer's interest is actively retained in his work, and we often find him pursuing it with unflagging diligence through many years. No doubt there would be many others employing their energies in this rich field of labour but for the uninteresting character of star-disks, which are mere points of light, and therefore incapable of displaying any detail. Those who study the Sun, Moon, or planets have a large amount of surface-configuration to examine and delineate, and this is ever undergoing real or apparent changes. But this is wholly wanting in the telescopic images of stars, which exhibit a sameness and lack of detail that is not satisfying to the tastes of every observer.

Number.—These bodies, also called minor planets, and, formerly, asteroids, comprise a very numerous class, and they are extremely small, being quite invisible to the naked eye except in one or two special cases. They all revolve in orbits situated between Mars and Jupiter. The total number discovered is about 300, of which Prof. J. Palisa of Vienna has found more than 70, and the late Dr. C. H. F. Peters of Clinton, N.Y., 49. I have not given exact numbers in the two former cases, because these discoveries are still rapidly progressing.

History of their Discovery.—The first known planetoid (Ceres) was sighted by Piazzi on Jan. 1, 1801. The following year, on March 28, Olbers found another (Pallas). In 1804, on Sept. 1, Harding discovered a third (Juno); and in 1807, March 29, Olbers was a second time successful (Vesta). Then for thirty-eight years no additions were made to the number. The host of planetoids circulating between Mars and Jupiter preserved their incognito without disturbance from the prying and wakeful eyes of astronomers.

But in 1845 Hencke, of Driessen, after years of watching, at length broke the spell of tranquillity by finding another small planet; and his example was emulated by many other observers in subsequent years. Hind, De Gasparis, and Goldschmidt were amongst the earliest and most successful of those who gathered new planets from amongst the stars of the zodiacal constellations.

A double star is one that divides into two with the help of a more or less powerful telescope. The effect is a strange, and might have appeared beforehand a most unlikely one. Yet it is of quite ordinary occurrence. Double stars are no freak of nature, but part of her settled plan; or rather, they enter systematically into the design of the Mind which is in and above nature.

The first recognised specimen of the class was ζ Ursæ Majoris, the middle ‘horse’ of the Plough, called by the Arabs ‘Mizar,’ which Riccioli found at Bologna, in 1650, to consist of a 2½ and a 4 magnitude star within fourteen seconds of arc of each other. Both are radiantly white, and they make a glorious object even in a very small telescope. The accident of a bright comet passing, on February 8, 1665, close to γ Arietis (‘Mesarthim’) led to the discovery of its duplex nature by Robert Hooke in the course of his observations on the comet. The components, each of the fourth magnitude, and eight seconds apart, are perfectly alike both in light and colour. Meanwhile Huygens had seen θ Orionis—perceived to be quadruple in 1684—as triple in 1656; a Crucis, in the southern hemisphere, was divided by some Jesuit missionaries sent by Louis XIV to Siam in 1685, and α Centauri by Richaud at Pondicherry in 1689; making in all five double stars detected during the seventeenth century.

Sidereal science has a great future before it. The prospects of its advance are incalculable; the possibilities of its development virtually infinite. No other branch of knowledge attracts efforts for its promotion, at once so wide-spread, so varied, and so enthusiastic; and in no other is anticipation so continually outrun by the brilliant significance of the results achieved.

For the due appreciation, however, of these results, some preliminary knowledge is required, and is possessed by few. To bring it within the reach of many is the object aimed at in the publication of the present volume. Astronomy is essentially a popular science. The general public has an indefeasible right of access to its lofty halls, which it is the more important to keep cleared of unnecessary technical impediments, since the natural tendency of all sciences is to become specialised as they advance. But literary treatment is the foe of specialisation, and helps to secure, accordingly, the topics it is applied to, against being secluded from the interest and understanding of ordinarily educated men and women. Now, in the whole astonishing history of the human intellect, there is no more astonishing chapter than that concerned with the sidereal researches of the last quarter of a century. Nor can the resources of thought be more effectually widened, or its principles be more surely ennobled through the vision of a Higher Wisdom, than by rendering it, so far as possible, intelligible to all.

The question whether nebulæ are external galaxies hardly any longer needs discussion. It has been answered by the progress of discovery. No competent thinker, with the whole of the available evidence before him, can now, it is safe to say, maintain any single nebula to be a star system of coordinate rank with the Milky Way. A practical certainty has been attained that the entire contents, stellar and nebular, of the sphere belong to one mighty aggregation, and stand in ordered mutual relations within the limits of one all-embracing scheme—all-embracing, that is to say, so far as our capacities of knowledge extend. With the infinite possibilities beyond, science has no concern.

The chief reasons justifying the assertion that the status of the nebulæ is intra-galactic, are of three kinds. They depend, first, upon the nature of the bodies themselves; secondly, upon the stellar associations of many of them; thirdly, upon their systematic arrangement as compared with the systematic arrangement of the stars.

The detection of gaseous nebulæ not only directly demonstrated the non-stellar nature of a large number of these objects, but afforded a rational presumption that the others, however composed, were on a commensurate scale of size, and situated at commensurable distances. It may indeed turn out that gaseous and non-gaseous nebulæ form an unbroken series, rather than two distinct classes separated by an impassable barrier.

The study of the stars inevitably leads us to consider the advancing movement in the midst of them of the sun and its attendant train of planets. There can be no reasonable doubt—and the thought is an astounding one—that we are engaged on a voyage through space, without starting-point or goal that we can know of, but which may prove not wholly uneventful. Its progress may possibly bring about, as millenniums go by, changes powerfully influential upon human destinies; nay, an incident in its course may, at any time, by the inscrutable decree of Providence, terminate the terrestrial existence of our race, and consign the records of its civilisation, in dust and cinders, to the arid bosom of a dead planet. A curious sense of helplessness, tempered, however, by a higher trust, is produced as we thus vividly realise, perhaps for the first time, how completely we are at the mercy of unknown forces—how irresistibly our little ‘lodge in the vast wilderness’ of the universe is swept onward over an annual stretch of perhaps five hundred millions of miles, under the mysterious sway of bodies reduced by their almost infinite distances to evanescent dimensions.

But, as things are constituted, the translation of the sun's household is a necessity, albeit one of startling import to ourselves. The stellar system is maintained by the balance of forces, and motion is the correlative of force.

About two hundred and fifty stars have been formally registered as variable, and many more are open to the like suspicion. Gore's ‘Revised Catalogue’ includes 243 entries, besides 39 provisional additions; Chandler's nearly contemporaneous list enumerates 225 objects. Of these 160 are reckoned as ‘periodical,’ the rest as ‘irregular’ or ‘temporary.’ Periodical stars are further divided into those with ‘long,’ and those with ‘short’ periods. Nor is the distinction by any means arbitrary. The stars seem to separate of themselves into two principal groups, undergoing fluctuations in cycles of respectively less than fifty, and between two and four hundred days. The paucity of stars with periods of intermediate lengths is shown graphically in fig. 11, where the height of the curve represents the numbers of stars subject to changes proportionate in duration to the horizontal distance from left to right.

Variations requiring several months for their completion differ both in degree and kind from those run through in a few days. They are of much greater amplitude, ranging over five to eight instead of, at the most, two magnitudes; they are accomplished with less punctuality; and they are frequently attended by symptoms of atmospheric ignition entirely foreign to quicker vicissitudes. Most important of all, they affect bodies of peculiar constitution. Nearly all long-period variables are red stars with banded spectra; those of short period are white or yellowish in colour, and display Sirian or solar spectra.

The stars, speaking broadly, are suns. But what is a sun? We can only reply by taking function into consideration. A sun is a great radiating machine, and the obvious criterion for admission to the order is fitness for this office. Qualification to be a centre of light and heat is the dominant characteristic of each of its true members. Now the solar emissive activity is concentrated in a shining shell of clouds known as the ‘photosphere,’ which the entire energies of the organism (so to speak) seem directed to maintain and renew. And with reason, since its efficiency as a radiator depends upon the perpetuation of the condensing process by which this brilliant surface is produced.

The possession of a photosphere must then be regarded as an essential feature of the suns of space. But such a structure can only be formed in an incandescent atmosphere, the action of which modifies, more or less powerfully, the light emitted from it. The spectroscope can then alone decide whether a given sidereal object be, in the proper sense, a sun. For it is not so much the quantity as the quality of its radiations that determines the point. They must be such as can be supposed to emanate from condensed and vividly glowing matter bathed in cooler, though still ignited, vapours. That is to say, they must be primarily unbroken from end to end of the rainbow-tinted riband formed by prismatic dispersion, while showing the secondary effects of absorptive encroachments.

Are the stars subject to growth and decay? We might almost as well ask, Are they subject to the laws of nature? There can be in either case no doubt about the reply. We are perfectly assured, both from reason and revelation, that a time was when they were not, and that at some future date they will have ceased to be. And we may further confidently affirm, guided by the analogy of all other creative processes with which we are acquainted, that their present condition has been gradually attained and will gradually become modified.

Each has then a life-history. It is what it is, because it has been what it was. Nor is it conceivable that all should have arrived simultaneously at the same stage of development. A contemporaneous universal origin can by no means be assumed as a postulate; and even if it could, the rate of progress of individual stars must have been indefinitely varied. There is hence a strong probability that the present state of some represents the past of others, the future of many more. Among the hosts of heaven we may expect to find stars in embryo, stars half formed yet chaotic, full-grown stars in orderly and equable working order, stars still effective as radiators though of declining powers, and stars on the verge of decrepitude. Their comparative study ought then, under certain conditions, to enable us to compile, as it were, the typical biography of an average star.