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ART. IV. Outlines of Astronomy. By SIR JOHN F. W. HER~ SCHEL, Bart. K.H. &c. Second Edition. London: Longman, Brown & Co.

ASTRONOMY claims the first place among sciences for many reasons. It is the most ancient, and also the most modern. It is the most clearly comprehended in its principles, yet affords the widest opening for all future investigations. It is the most perfect subject for the exact labours of the mathematician, and the most fruitful of interest to the student of physical philosophy. As a practical science none claims for its service so large a share of abstract thought and profound study, or none requires more toil, more diligence, more patience, more punctuality, more mechanical exactness from those who would minister at her shrine. Astronomy is the most comprehensive of all sciences, for most other sciences are either included within its ample range of subjects, and explained as lesser manifestations of the great principles divulged by it, or are employed as instruments to work out its extensive purposes. Mechanics, hydrostatics, or even pneumatics, and electrical phenomena, may for instance all be found closely allied to this parental science, while every branch of mathematics, the physical science of optics, and the wonderfully perfect art of instrument making, are all in the humble and honoured relation of tried and valued servants. Astromony is the most complicated of sciences as an exercise of the human intellect, yet the most sublimely simple as a subject for the imagination to dwell on. It is equally attractive to the lover of practical analysis and to the speculative theorist. Again, to those who search for instances of divine power and a reflection of divine attributes in the visible works of creation, no more wonderful examples are possible to be conceived than in the disclosures of Astronomy. Astronomy deals with subjects that, by a direct and legitimate analogy, are more associated with the religious idea and with religious contemplation than those of any other branch of physical knowledge. For instance, take the recent discoveries as to the motion of the remotest stars which instruments can reach. The uniformity of the principle by which their motions are governed with those that direct our own sphere, lays before us an astonishing example of the unity, the love of order, and the omnipresent power of that God, whom the Christian revelation describes as possessed of such attributes.

The ancient world never could fathom one astronomical principle, however observant of phenomena. Eastern astronomers laboured and toiled, they watched and meditated. The extreme accuracy of their observations even enabled them to foretell eclipses, for these events were discovered by them to come in a cycle. Yet all this was in the dark; they had no glimmer into the principles by which the heavenly bodies were guided. The Egyptians were not less devoted to astronomy, and consulted the heavens in all their mysterious and gigantic conceptions of philosophy, of symbolism, of sculpture and of architecture. Yet patience and thought were alike helpless in the heathen world to unravel any acting causes or principles of what they so accurately observed. For Christian times it was reserved to look beyond the surface of the earth, with some notion of the manner in which the attributes of divinity were there manifested. May we not conceive a secondary kind of revelation given to man, through the influence of wisdom,' on the subject of Christian art so wonderfully dominant for a certain period of the Church's history, unveiling in some slight degree nature's storehouse of beauty? May we not also apply this to science? True it is that science is a stronghold of scepticism and of temptation from the evil one, but surely this cannot be the result of so much of it as is true, for truth is intrinsically good and produces not evil. The danger of science rather shows how great pains the evil one takes to make it a source of misguidance, and therefore how great an opponent he considers it. Science, then, we contend, is a witness of the truth in the Christian world. We must of course understand such reflections in a general manner, for none can imagine that all attributes of wisdom are equally apportioned to individual Christians, so that he who excels in moral qualities should therefore have the knowledge of science in like proportion. It is very possible to conceive of a gift bestowed upon the Christian world, operating through individual members, quite independent of their personal merits on other grounds; nay, even if we supposed those very men peculiarly subject to the snares with which Satan encompasses the investigation of truth.

If then we take so high a view of the intellectual gifts manifested in the Christian world, it is important, as a practical question, to consider how far the science we are about to discuss can be made popular. It has been a prevalent idea that making knowledge popular is pulling it from its lofty pedestal, and depriving it of that dignity which commonly attaches to exclusive privileges. It is only, however, false knowledge which need fear to be despised, from being made general. Such exclusive appropriation of knowledge is the characteristic of

heathenism, as ancient and modern times alike testify, whether exemplified in the Eleusinian mysteries, or in the religion of Brahmah. But among ourselves there is also a method of popularizing knowledge, which from the shallowness of its intentions, so far partakes of the character of error, that it does lower science, and detract from its true dignity. In Astronomy, for instance, the sort of conception which people derive of that science from some popular treatises and lectures, illustrated by that very imperfect mechanical contrivance, an orrery, are not calculated to advance the science as suggesting subjects for the highest powers of imagination, which surely is its true province. To make Astronomy popular, and yet preserve its true dignity, we must not be content with detailing a few isolated facts, but the principle of heavenly motions must be understood in something of its sublime unity. It is too generally taken for granted, we think, that this branch of the science is confined, from its very nature, to the mathematician. It is the mathematician, indeed, who has to lead the way, and it is to him we are indebted for the labour of investigation, and for any definite knowledge we possess, and thus for the groundwork of the whole science. But surely there is a popular way of understanding the subject, without the means of solving all the details of its effects on the system of the universe. If the motions of heavenly bodies were on a principle for which we see no analogy on the earth, then we might grant it difficult to communicate such knowledge in a popular form, for we should only be acquainted with it as a mathematical science, and analogy is the chief means of bringing theories that are beyond the range of our senses, within their comprehension. The whole principle, however, of astronomical motions owed its discovery in the first instance to the simplest exhibition of a common terrestrial law of nature; and the remotest, and most laboured observations, up to the present advanced state of the science, only tend to identify the laws of every portion of the visible creation with the laws by which this world is constructed, and, which is more to the point as concerns analogy, by which every motion, and every position we see around us, and close to us, is absolutely governed. In one respect, indeed, it may appear that this very simplicity makes it all the more difficult to say much about it, and all that can be done after stating the law of gravitation is to work out its results by mathematics. But nevertheless there are very different degrees of realizing the simplest ideas, especially those which are gathered from observation. Two people may throw a stick into the air, and both may see it performing certain gyrations and evolutions, but to one these motions will present no idea but that of reckless chance; it will seem to him

'With obligation charged, with service tax'd,
No more than the loose pendent to the wind,
Upon the tall mast streaming;'

while to the other will be perceived the ever present law of exact balance, governing with despotic power every movement before him. Not an autumn-leaf floats in the wind but is guided on absolutely exact mathematical principles; attraction, even here, being one steady cause of motion, subject to certain perturbations from atmospheric influence.

The book before us treats of every branch of Astronomy, as fully, perhaps, as most amateurs in the science would desire, though the author trusts there are few who will terminate their studies with such an introductory treatise. To a Herschel, however, astronomy is more than an accomplishment, or a subject for entertainment and enlargement of the mind. It is the business of life pursued with unremitting assiduity, and the full powers of body, mind, and estate; as Sir John's expedition to the Cape of Good Hope will bear witness to, among other labours connected with his honoured name. But it is as a subject capable of being studied by an amateur that we would wish to see Astronomy brought before the public, without too great discouragement from the knowledge of mathematics required. The scientific knowledge requisite for this work is stated in the author's introduction:

The preliminary knowledge which it is desirable that the student should possess, in order for the more advantageous perusal of the following pages, consists in the familiar practice of decimal and sexagesimal arithmetic; some moderate acquaintance with geometry and trigonometry, both plane and spherical; the elementary principles of mechanics; and enough of optics to understand the construction and use of the telescope, and some other of the simpler instruments. Of course, the more of such knowledge he brings to the perusal, the easier will be his progress, and the more complete the information gained; but we shall endeavour in every case, as far as it can be done without a sacrifice of clearness, and of that useful brevity which consists in the absence of prolixity and episode, to render what we have to say as independent of other books as possible.'-Pp. 4, 5.

This may alarm some who wish to know a little of astronomy, but still have forgotten, or never had much acquaintance with this list of accomplishments. With the exception, however, of the part on planetary perturbations, this work will convey a very intelligible notion of the science, with but little power of solving the mathematical problems introduced.

The arcana of the science are strictly guarded from profane handling by the following authoritative exclusion of any vain imaginations which the amateur may dare to suggest.

'Admission to its sanctuary, and to the privileges and feelings of a votary, is only to be gained by one means,-sound and sufficient knowledge

of mathematics, the great instrument of all exact inquiry, without which no man can ever make such advances in this or any other of the higher departments of science as can entitle him to form an independent opinion on any subject of discussion within their range. It is not without an effort that those who possess this knowledge can communicate on such subjects with those who do not, and adapt their language and their illustrations to the necessities of such an intercourse.'-P. 5.

This is a useful axiom to lay down, and no doubt saves the initiated much trouble; but we rather question the correctness of it, as too universal a statement. The power of working out astronomical problems we have seen connected with very little conception of the science itself; and the reverse of this we also believe to exist. A man to have any real weight attached to his opinion must unquestionably be up to the machinery of his science, as any workman must know the use of his tools; but mathematics alone do not constitute the mind of an astronomer, and may often be found with scarcely any power of its practical application to the physical science.

It is time, however, now, that we should come to the facts themselves of astronomy as described by Sir John Herschel. The most popular and attractive parts of astronomy are more suitable to the purposes of a reviewer; we shall therefore eschew the idea of writing a treatise on astronomy, and consider ourselves at liberty to dart from one point of space to another with absolute freedom, unchecked by any obligation to mathematical proof or continuity of subject. In so doing, a tribute is due to the literary merits of Sir John, apart from his scientific knowledge, which shall stand on its own merits, and to review which would be great presumption on our part, though this very undertaking is mentioned in the history of Pendennis as a task which that bold young reviewer would have felt himself able to encounter unassisted as he was by any close application to the science during his college career. Sir John's style is clear and easy, with great flow of language and considerable power of illustration, and a most happy art of relaxing from the severer parts of his subject to the more discursive regions of speculation.

The work before us is divided into four parts. The first is elementary, and occupies more than half the volume, being an extension of the treatise on astronomy, by Sir John Herschel, in the Cabinet Cyclopædia, published in 1833. The second part is on planetary perturbations, a subject of great interest in modern science, but, as a study, requiring more mathematical knowledge than many would possess who can read the other parts of the work with perfect ease. It is not elementary, for it concerns the minutest details in the working of gravitation; still the knowledge from such powers of investigation, and a general notion of the physical laws that are open to such calcu