CAPTAIN SMYTH'S CYCLE OP CELESTIAL OBJECTS. THE leading purpose of
the author in the publication of these two ample volumes of his studies and observations, was to furnish to the somewhat advanced tyro, whether pursuing astronomy as a pri- vate occupation or combining it like the mariner with his pro- fession, the means of acquiring a general knowledge of the progress and present state of astronomical science, together with a detailed account of the most remarkable of the fixed stars, for the purpose of further carrying out their investigation or rather observation. With this object, he opens his work by a condensed historical sketch of the science ; tracing rapidly, but with fulness and pre- cision, the successive stages of astronomy, and noticing the phi- losophers by whom each step was made. Having brought down the narrative to the present time, Captain Sturm takes a survey of the Solar System ; commencing with the Sun, ending with Uranus, and giving a full description of these bodies as well as of the intermediate planets, in their popular fea- tures as well as their scientific points. A Glance at the Sidereal Heavens follows the Solar System; and consists of an account of the fixed stars, or at least of the more prominent ones, chiefly considered as regards their astronomical history, their distances, their colours, their relative positions, and their alleged motion ; after which, stars in clusters, the galaxy or milky way, and the nebular hypothesis, are passed in review, with an equal predominance of the scientific over what may be called the more popular characteristics. The fourth section is called "Details of the Observatory" ; and, partly under the form of a minute account of Captain SMYTH'S own observatory at Bedford, contains elaborate descriptions of astronomical instruments, with suggestions as to what are necessary for the private astronomer, and full instructions as to their use. These topics, with some miscellaneous matters in the appendix, and an elaborate index, complete the first volume ; which the author entitles "Prolegomena." The second volume contains the Bedford Catalogue ; an account of 850 stars or groups of stars ob- served by Captain SMYTH in his own observatory, each considered by itself, and exhibiting an account of its position, appearance, and the more scientific points, only interesting (and indeed only intel- ligible) to those who have made some advances in astronomy. To such, in fact, the Catalogue is addressed, to serve at once as a guide and a stimulus in directing them to follow out these observa- tions by additional observations of their own : but the more recon- dite matter is often relieved by anecdotes connected with the dis- covery of the star, its subsequent history, or the astronomers who have at any time particularly observed it.
The object of the author, and the nature of his work, as it may be gathered from this brief sketch, necessarily prevents it from being of a popular character. In all recondite subjects, a general interest can only be attained by a comprehensiveness which ap- proaches vagueness. A scientific knowledge even of the elements of a subject implies a power of drawing conclusions from scientific data, and to some extent imparts it. For a general reader these conclusions must be drawn, and drawn largely. The data frequently he cannot understand ; they speak a language of which he is igno- rant; and supposing they were interpreted for him, be would not be able to see those results, which the instructed deduce, and sometimes jump to. But this broad generality is injurious if not fatal to didactic purposes. An essay on the general character and peculiarities of a language will not do for him who wishes to master the language : he must submit to the drudgery ot grammar; and he who should attempt to popularize grammar into the attrac- tion of a " crack " article, would only display his ignorance or empiricism.
A Cycle of Celestial Objects is therefore for astronomers, not the people : yet it is popular enough where popularity is admissible. The leading features, especially of the Solar System, are capable of clear presentation : the vastness of the subject subdues the mind, whilst our apparent connexion with the Sun and planets attracts it. In many cases the zeal and unaffected straightforwardness of the author impress the reader ; and the sailor breaking out occasionally into nautical terms gives a zest to his style,—as when, speaking of the evidence of astronomy, he declares that every "link in the great chain has been ably overhauled." Anecdotes of the practical use of astronomy, especially in navigation, often vary and amuse ; whilst the sketch of the history of astronomy may be read with advantage for its succinct completeness. It is also suggestive, from its curious account of the just ideas which great geniuses, under all disad= vantages, jumped to respecting the true form of the Earth and the character of the solar system, whilst they even gained something like a gleam of the sidereal heavens. The fact is, the mass of philo- sophers are as prejudiced and obstinate as the mass of mankind in matters of novelty, or to which they have not been trained. Long before the dawn of authentic history, at least long before HERODO•
ANAXIMANDER, a disciple of TsuiLEs of Miletus, is "said to have had some idea of the Earth's axial movement ; and he dis- tinctly asserted its sphericity."
"Pythagoras clearly demonstrated, from the varying 'altitudes of the stars by change of place, the spherical shape of the Earth, at which Anaximander Lad only guessed : and there are various evidences to show that about this time the notion of the Earth's being suspended in equilibria, and supported by the air, was widely prevalent ; or, as Socrates says in Plato's Phcedo, that it is wrapped about and pressed equally in every direction by the universe. It was Pythagoras who first gave substance to the floating idea of Apollonius Pergteus, that the Sun was fixed in the centre of the planetary orbits, and that the Earth moved round it with the other planets; who taught, in fact, the system which now immortalizes the name of Copernicus. But these were the conjectures of a sagacious mind, not possessed of the evidence requisite to give stability to its opinions. It was fortunate that Pythagoras escaped the persecution of ignorance and fanaticism which attended genius even in free and enlightened Greece ; for he was not only guilty of those heterodox no- tions, but also broached the doctrine of a plurality of worlds and the music of the spheres. It was he who first conceived the bold idea that the planets are inhabited, and that the myriads of stars which stud the immensity of space are so many suns,destined to afford light and heat around them. His sagacity detected that Venus was the morning and evening star ; and he divided the universe into twelve spheres. It is moreover asserted, that he saw in comets, which all the world then held to be mere atmospheric meteors, permanent stars revolving round the Sun under peculiar laws."
Whether these views have been correctly ascribed to PYTHA GORAS, or whether the merit may not properly be shared with some of his successors, is of no consequence as regards their being held : but the absence of recurring facts, and of instrumental help to acquire data, constantly checked the progress of genius when on the very verge of discovery, and drove the world upon theories based on "the evidence of their senses." Had not GALILEO'S invention of the telescope, and its subsequent improvements, enabled succeeding astronomers to establish the truth of the hypo- thesis of CorEamens, it would have ranked with the theories of PYTHAGORAS, and the Phcenician " tales " of the Southern hemi- sphere, till DE GAMA'S voyage established the veracity of those early navigators.
To some minds the sagacity of the ancient philosophers, groping along by the light of their own genius amid the almost total ob- scurity around them, and the dangers and persecutions they en- countered under the plea of impiety, will be the most interesting part of the volume. But for general readers, we will make some extracts of a more miscellaneous character.
ABSTRACT SCIENCE IN WAR.
The Newtonian theory of tides was put to practical test in the late war, which ought to have worked conviction in the minds of Naval officers. The blockade of the Texel was successfully managed on a system at once econo- mical in anxiety and labour. The ports of Holland admit of the ingress and ogress of large ships only during spring-tides ; two days before which, our squadron regularly took its station off the Texel, and remained there only as many days after the full and change of the moon ; so- that the Dutch lost all the advantages of high tides, and their heavy ships were effectually detained within their harbours.
LIGHT AND HEAT OF THE SUN.
The Sun has been usually considered as a planet ; but should rather he num- bered among the stars, because be agrees with them in the continual emission of light, and in apparently retaining his relative situation with very little va- riation. His radiant orb is in figure a spheroid, surrounded by an atmosphere of extreme tenuity and great extent. The Sun constantly emits streams of light, which, being reflected by the planets they fall upon, can be ascertained to extend with inconceivable swiftness into space nearly two thousand millions of miles : how far beyond the regions of Uranus is left to conjecture, as well as the further effects of their impingement upon planetary surfaces, and what eventually becomes of this wonderful traversing emanation. Must it not reach at least as far as the aphelia of comets ? The solar rays, thus transmitted through space in every direction, must affect the several heavenly bodies very differently, on account of the varieties in their atmospheres, and because the intensity of both light and heat dimi- nishes as the square of the distance increases. The appearance of the Sun is that of an intensely brilliant ball, far too dazzling for the unprotected eye. This light is so ardently strong, that the moat vivid flames which human art can produce, when held before the Sun, disappear ; and intensely ignited solids become dark spots on the solar disc when seen between it and the eye. "The ball of ignited quick-lime," says Sir John Herschel, "in Lieutenant Drum- mond's oxy-bydrogen lamp, gives the nearest imitation to the solar splendour which has yet been produced. The appearance of this against the sun was, however, as described, (viz, a dark spot,) in an imperfect trial at which I was present." The direct light of the Sun has been estimated to be equal to that of 5,570 wax-candles of moderate size, supposed to be placed at the distance of one foot from the object. That of the Moon is probably only equal to the light of one candle at the distance of twelve feet. Consequently the light of the Sun is more than 300,000 times greater than that of the Moon.
LIGHT OF THE MOON.
As the Moon's axis is nearly perpendicular to the plane of the ecliptic, she can scarcely have any change of seasons. But what is still more remarkable, one half of the Moon has no darkness at all, while the other half has two weeks of light and two of darkness alternately : the inhabitants, if any, of the first half bask constantly in earth-shine without seeing the Sun, whilst those of the latter never see the Earth at all. For, as just stated, the Earth reflects the light of the Sun to the Moon, in the same manner as the Moon does to the Earth; therefore, at the time of conjunction or new moon, her further side must be enlightened by the Sun, and the nearer half by the Earth; and at the time of opposition or full moon, one half of her will be enlightened by the Sun, but the other half will be in total darkness. To the Lunarians the Earth seems the largest orb in the universe; for it appears to them more than three times the size of the Sun, and thirteen times greater than the Moon does to us,—exhibiting similar phases to herself, but in a reverse order : for when the Moon is full, the Earth is invisible to them ; and when the Moon is new, they will see the Earth full. The face of the Moon appears to us permanent, but to them the Earth presents very different appearances : the Pacific and Atlantic Oceans, in the course of each twenty-four hours, will successively rivet their attention; and the velocity of motion must excite both surprise and conjecture. Though, as aforesaid, certain of those gentlemen only behold the Earth for half a month at a time, those near the border see it only occasionally, and those on the side opposite the Earth never see it at all. The Moon being but the fiftieth part of the bulk of our globe, and within 238,000 miles of us, may be brought by a proper telescope, which magnifies 1,000 times, to appear as she would to the naked eye were she only 250 miles off. ODIt CELESTIAL KINSMAN.
The analogy between Mars and the Earth is greater than between the Earth and any other planet of the solar system. Their diurnal motion is nearly the same ; the inclinations of their equators to the planes of their orbits, on which the seasons depend, are not very 'different; nor is the length of his year very different from ours, when compared with the years of Jupiter, Saturn, and Uranus. The Earth, however, appears to be the more favoured of the two; since water would not remain fluid even at the equator of Mars, and alcohol woul& freeze in his temperate zones. The force of gravity on his surface is about one- tenth greater than at the surface of the Earth ; but his density is much lees than that of the Earth. A body which weighs one pound at our equator, would weigh only five ounces and sir drachms at that of Mars ; and were his course stopped, 121 days and 10 hours would elapse before he dropped upon the Sun. Should sentient beings exist there, they see the Sun's diameter less by one- third than we do ; and consequently the degree of light and heat they receive is less than that received by us in the proportion of 4 to 9, or rather less than I to 2; liable, however, to variations from the great excentricity of his orbit. If their atmosphere be as dense as is supposed, they probably scarcely ever discern Mercury and Venus, which will appear to borrow on the solar rays : the earth and Moon, however, will afford them a beautiful pair of planets alternately changing places with each other under horned or falcated phases, but never quite full, and not more than a quarter of a degree distant from each other. • •
There is not a planet within the reach of our telescopes which presents sa aspect so like that of the Earth as Mars; whose surface, independently of the changeable atmospheric influences, shows an appearance of well-defined seas and continent,; and this was very especially the case in August 1830, when the geographical lines of demarcation were so beautifully distinct that Sir John Herschel called my attention to them, saying that he was able to make a tolerable map of the surface. The predominant brightness of the polar regions leads to the supposition, that the poles of Mars, like those of the Earth, are covered with perpetual snow ; and Sir William Herschel concluded, that the observable changes in luminosity and magnitude are connected with the Sum- mer and Winter seasons in that planet. Sir John Herschel also remarks, that the brilliant polar spots are probably snow, as they disappear when they have been long exposed to the Sun, and are greatest when just emerging from the long night of their polar Winter. The latter astronomer, aided by the full power of the twenty-foot reflector, pronounced the seas to be of a greenish hue, re- sembling the colour of our own ; and the land of a red tint, perhaps owing to a quality in the prevailing soil, like that which our red sandstone districts would exhibit to an observer beholding the Earth from the surface of Mara.
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