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stance adducible in the ordinary course of experience; but the object will at least be kept in view; and, as I am very conscious of having, in making such attempts, gained for myself much clearer views of several of the more concealed effects of planetary perturbation than I had acquired by their mathematical investigation in detail, it may reasonably be hoped that the endeavour will not always be unattended with a similar success in others.

(10.) From what has been said, it will be evident that our aim is not to offer to the public a technical treatise, in which the student of practical or theoretical astronomy shall find consigned the minute description of methods of observation, or the formulæ he requires prepared to his hand, or their demonstrations drawn out in detail. In all these the present work will be found meagre, and quite inadequate to his wants. Its aim is entirely different; being to present to him in each case the mere ultimate rationale of facts, arguments, anil processes; and, in all cases of mathematical application, avoiding whatever would tend to encumber its pages with algebraic or geometrical symbols, to place under his inspection that central thread of common sense on which the pearls of analytical research are invariably strung; but which, by the attention the latter claim for themselves, is often concealed from the eye of the gazer, and not always disposed in the straightest and most convenient form to follow by those who string them. This is no fault of those who have conducted the inquiries to which we allude. The contention of mind for which they call is enormous ; and it may, perhaps, be owing to their experience of how little can be accomplished in carrying such processes on to their conclusion, by mere ordinary clearness of head ; and how necessary it often is to pay more attention to the purely mathematical conditions which ensure success, the hooks-and-eyes of their equations and series, than to those which enchain causes with their effects, and both with the human reason, that we must attribute something of that indistinctness of view which is often complained of as a grievance by the earnest student, and still more commonly ascribed ironically to the native cloudiness of an atmosphere too sublime for vulgar comprehension. We think we shall render good service to both classes of readers, by dissipating, so far as lies in our power, that accidental obscurity, and by showing ordinary untutored comprehension clearly what it can, and what it cannot, hope to attain.

(10 a.) To conclude: “Rome was not built in a day.” No grand practical result of human industry, genius, or meditation, has sprung forth entire and complete from the master hand or mind of an individual designer working straight to its object, and foreseeing and providing for all details. As in the building of a great city, so in every such product, its historian has to record rude beginnings, circuitous and inadequate plans; frequent demolition, renewal and rectification; the perpetual removal of much cumbrous and unsightly material and scaffolding, and constant opening out of wider and grander conceptions; till at length a unity and a nobility is attained, little dreamed of in the imagination of the first projector.

(10 b.) The same is equally true of every great body of knowledge, and would be found signally exemplified in the history of astronomy, did the object of this work allow us to devote a portion of it to its relation. What concerns us more is, that the same remark is no less applicable to the process by which knowledge is built up in the mind of each individual, and by which alone it can attain any extensive development or any grand proportions. No man can rise from ignorance to anything deserving to be called a complete grasp of any considerable branch of science without receiving and discarding in succession many crude and incomplete notions, which so far from injuring the truth in its ultimate reception, act as positive aids to its attainment by acquainting him with the symptoms of an insecure footing in bis progress. To reach from the plain the loftiest summits of an Alpine country, many inferior eminences have to be scaled and relinquished; but the labour is not lost. The region is unfolded in its closer recesses, and the grand panorama which opens from aloft is all the better understood and the more enjoyed for the very misconceptions in detail which it rectifies and explains.

(10 c.) Astronomy is very peculiarly in this predicament. Its study to each individual student is a continual process of rectification and correction-of abandoning one point of view for another higher and better- of temporary and occasional reception of even positive and admitted errors for the convenience they afford towards giving clear notions of important truths whose essence they do not affect, by sparing him that contention of mind which fatigues and distresses. We know, for example, that the earth's diurnal motion is real, and that of the heavens only apparent; yet there are many problems in astronomy which are not only easier conceived, but more simply resolved by adopting the idea of a diurnal rotation of the heavens, it being understood once for all that appearances are alike in both suppositions.

CHAPTER 1.

GENERAL NOTIONS. - APPARENT AND REAL MOTIONS. SIIAPE AND

SIZE OF THE EARTH. THE HORIZON AND ITS DIP. THE AT-
MOSPHERE. REFRACTION. TWILIGHT. APPEARANCES RE-
SULTING FROM DIURNAL MOTION FROM CHANGE OF STATION
IN GENERAL - PARALLACTIC MOTIONS. TERRESTRIAL PARAL-
LAX. THAT OF THE STARS INSENSIBLE. FIRST STEP TO-
WARDS FORMING AN IDEA OF THE DISTANCE OF THE STARS.
COPERNICAN VIEW OF THE EARTH'S MOTION. RELATIVE
MOTION. MOTIONS PARTLY REAL, PARTLY APPARENT. GEO-
CENTRIC ASTRONOMY, OR IDEAL REFERENCE OF PHÆNOMENA
TO THE
EARTH's

CENTRE AS A COMMON CONVENTIONAL STATION.

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(11.) The magnitudes, distances, arrangement, and motions of the great bodies which make up the visible universe, their constitution and physical condition, so far as they can be known to us, with their mutual influences and actions on each other, so far as they can be traced by the effects produced, and established by legitimate reasoning, form the assemblage of objects to which the attention of the astronomer is directed. The term astronomy* itself, which denotes the law or rule of the astra (by which the ancients understood not only the stars properly so called, but the sun, the moon, and all the visible constituents of the heavens), sufficiently indicates this; and, although the term astrology, which denotes the reason, theory, or interpretation of the starst, has become degraded in its application, and confined to superstitious and delusive attempts to divine future events by their dependence on pre

a

Aotnp, a star ; vouos, a luw; or veuely, to tend, as a shepherd his flock ; so that ast povouos means “shepherd of the stars.” The two etymologies are, bow. ever, coincident.

† Aogos, reason, or a word, the vehicle of reason; the interpreter of thought.

tended planetary influences, the same meaning originally attached itself to that epithet.

(12.) But, besides the stars and other celestial bodies, the earth itself, regarded as an individual body, is one principal object of the astronomer's consideration, and, indeed, the chief of all. It derives its importance, in a practical as well as theoretical sense, not only from its proximity, and its relation to us as animated beings, who draw from it the supply of all our wants, but as the station from which we see all the rest, and as the only one among them to which we can, in the first instance, refer for any determinate marks and measures by which to recognize their changes of situation, or with which to compare their distances.

(13.) To the reader who now for the first time takes up a book on astronomy, it will no doubt seem strange to class the earth with the heavenly bodies, and to assume any community of nature among things apparently so different. For what, in fact, can be more apparently different than the vast and seemingly immeasurable extent of the earth, and the stars, which appear but as points, and seem to have no size at all ? The earth is dark and opaque, while the celestial bodies are brilliant. We perceive in it no motion, while in them we observe a continual change of place, as we view them at different hours of the day or night, or at different seasons of the year. The ancients, accordingly, one or two of the more enlightened of them only excepted, admitted no such community of nature; and, by thus placing the heavenly bodies and their movements without the pale of analogy and experience, effectually intercepted the progress of all reasoning from what passes here below, to what is going on in the regions where they exist and move. Under such conventions, astronomy, as a science of cause and effect, could not exist, but must be limited to a mere registry of appearances, unconnected with any attempt to account for them on reasonable principles, however successful to a certain extent might be the attempt to follow out their order of sequence, and to establish empirical laws expressive of this order. To get rid of this prejudice, therefore, is the first step towards acquiring a knowledge of

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