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women, she proposes also the secondary object of pointing out the Connexion of the Physical Sciences.


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The progress of modern science, especially within the last 'five years, has been remarkable for a tendency to simplify the 'laws of nature, and to unite detached branches by general principles. In some cases identity has been proved where there appeared to be nothing in common, as in the electric and mag'netic influences; in others, as that of light and heat, such ana'logies have been pointed out as to justify the expectation that 'they will ultimately be referred to the same agent; and in all, 'there exists such a bond of union, that proficiency cannot be ' attained in any without a knowledge of others.

Although well aware that a far more extensive illustration of these views might have been given, the author hopes that enough has been done to show the Connexion of the Physical 'Sciences.'-Preface.


Although the general view which Mrs Somerville has given of the Physical Sciences well illustrates their connexion and mutual dependence, yet it does not form any part of her plan to establish the identity of particular branches of knowledge, or to trace any bond of union by which they may be mutually enchained; or to point out the means by which the cultivation of any one science may lead to the extension of another. Such a discussion, however interesting in itself, and important to the progress of science, would have led her beyond the sphere of a popular treatise, and would have frustrated the principal object which she had in view.

This interesting volume, of which we shall proceed to convey some idea to our readers, cannot fail to be perused with a high degree of interest by all who have made the physical sciences the subject of their study. Without entering into minute details of facts, or diffuse explanations of phenomena, or tedious deductions of general laws, Mrs Somerville has given a condensed and perspicuous view of the general principles and leading facts of physical science, embracing almost all the modern discoveries which have not yet found their way into our elementary works. In this rapid sketch, to which the limits of a small volume have confined her, the author evinces a profound and accurate knowledge of her subject; and the great diversity of topics which pass under her review, are treated with much discrimination and sagacity. The style is simple, energetic, and perspicuous; and when the author has occasion to refer to some of the more striking phenomena of the material world, she rises into an eloquence at once striking and impressive.

But while we regard this volume as an excellent manual for those who have entered upon the study of natural philosophy, we

entertain some doubt whether it is sufficiently popular to initiate our fair country women into a knowledge of the laws of the material universe. Excepting in the Appendix, on the explanation of terms, there is not a single diagram in the work; and when we consider how difficult it has always been found to convey to general readers a tolerable knowledge of physics, even with the aid of numerous and minute diagrams, and with the still better accompaniments of apparatus and experiments, we have some misgivings respecting the success of this part of Mrs Somerville's plan.


When a scientific expositor is not allowed to appeal to the eye in explaining phenomena which are susceptible of a figurate representation, he is forced to substitute a diffuse and circuitous illustration, and thus to make a severe and unnecessary demand both upon the memory and the judgment. But this is not the only objection to the want of ocular delineation. Even when the desired knowledge, whether it be a process of reasoning or the account of a phenomenon, has been actually communicated, the hold which it takes of the mind is much more permanent when it has been received through the intermedium of the eye. diagram, indeed, and still more the exhibition of a phenomenon, not only associates with itself the ideas to which it relates, but forms the basis of a local memory, by which impressions, otherwise fleeting, may be rendered indelible. The mind is frequently unable either to apprehend or to fix ideas, of which the eye has not traced the symbols; and while there are many examples of the ear having parted with its acquisitions, there are few in which the eye has abandoned even its earliest phantasms. The memory of vision is certainly the trunk of the retentive faculty; and, when every branch has decayed, it remains the last and the firmest landmark of the mind.


Entertaining these views, we regret that, in imitation of La Place, in his celebrated Exposition of the System of the World,' Mrs Somerville should have declined the use of those auxiliaries which have been generally considered indispensable in the communication of scientific knowledge; and we would strongly urge her to reconsider this matter, before she publishes a second edition of her Treatise. A work on original science will not lose its value, even if it is conceived in mysticism, and written in hieroglyphics ; but the ablest digest of physical knowledge, which is intended for the instruction of those who are not the best fitted for abstract study, will lose half its value, if it fails in accomplishing, or accomplishes imperfectly, its primary object.david ani

From these general observations on Mrs Somerville's work, we shall now proceed to give our readers some idea of the man

ner in which it has been executed. The subject of Astronomy, which forms more than one-third of the volume, is introduced by the following admirable observations :—

'Science, regarded as the pursuit of truth, which can only be attained by patient and unprejudiced investigation, wherein nothing is too great to be attempted, nothing so minute as to be justly disregarded, must ever afford occupation of consummate interest, and subject of elevated meditation. The contemplation of the works of creation elevates the mind to the admiration of whatever is great and noble; accomplishing the object of all study,—which, in the elegant language of Sir James Mackintosh, "is to inspire the love of truth, of wisdom, of beauty, especially of goodness, the highest beauty, and of that supreme and eternal Mind, which contains all truth and wisdom, all beauty and goodness. By the love or delightful contemplation and pursuit of these transcendent aims, for their own sake only, the mind of man is raised from low and perishable objects, and prepared for those high destinies which are appointed for all those who are capable of them.'

The heavens afford the most sublime subject of study which can be derived from science. The magnitude and splendour of the objects, the inconceivable rapidity with which they move, and the enormous distances between them, impress the mind with some notion of the energy that maintains them in their motions with a durability to which we can see no limit. Equally conspicuous is the goodness of the great First Cause, in having endowed man with faculties by which he can not only appreciate the magnificence of His works, but trace, with precision, the operation of his laws; use the globe he inhabits as a base wherewith to measure the magnitude and distance of the sun and planets, and make the diameter of the earth's orbit the first step of a scale by which he may ascend to the starry firmament. Such pursuits, while they ennoble the mind, at the same time inculcate humility, by showing that there is a barrier which no energy, mental or physical, can ever enable us to pass that however profoundly we may penetrate the depths of space, there still remain innumerable systems, compared with which those apparently so vast must dwindle into insignificance, or even become invisible; and that not only man, but the globe he inhabits,―nay, the whole system of which it forms so small a part,―might be annihilated, and its extinction be unperceived in the immensity of creation.


Although it must be acknowledged that a complete acquaintance with physical astronomy can be attained by those only who are well versed in the higher branches of mathematical and mechanical science, and that they alone can appreciate the extreme beauty of the results, and of the means by which these results are obtained, it is nevertheless true that a sufficient skill in analysis to follow the general outline,— to see the mutual dependence of the different parts of the system, and to comprehend by what means some of the most extraordinary conclusions have been arrived at,-is within the reach of many who shrink from the task, appalled by difficulties, which, perhaps, are not more formidable than those incident to the study of the elements of every branch

of knowledge; and who possibly overrate them from disregarding the distinction between the degree of mathematical acquirement necessary for making discoveries, and that which is requisite for understanding what others have done. That the study of mathematics, and their application to astronomy, are full of interest, will be allowed by all who have devoted their time and attention to these pursuits; and they only can estimate the delight of arriving at the truths they disclose, whether it be in the discovery of a world or of a new property of numbers.'

After giving an account of the law of gravitation, and treating of the rules of Kepler, the figures of the heavenly bodies, and the inequalities in the motions of the planets, Mrs Somerville makes the following interesting observations on the stability of our system:

The stability of our system was established by La Grange: 66 a discovery," says Professor Playfair, "that must render the name for ever memorable in science, and revered by those who delight in the contemplation of whatever is excellent and sublime." After Newton's discovery of the mechanical laws of the elliptical orbits of the planets, La Grange's discovery of their periodical inequalities is, without doubt, the noblest truth in physical astronomy; and, in respect of the doctrine of final causes, it may be regarded as the greatest of all.

• Notwithstanding the permanency of our system, the secular variations in the planetary orbits would have been extremely embarrassing to astronomers when it became necessary to compare observations separated by long periods. The difficulty was in part obviated, and the principle for accomplishing it established, by La Place; but it has since been extended by M. Poinsot; it appears that there exists an invariable plane passing through the centre of gravity of the system, about which the whole oscillates within very narrow limits, and that this plane will always remain parallel to itself, whatever changes time may induce in the orbits of the planets, in the plane of the ecliptic, or even in the law of gravitation; provided only that our system remains unconnected with any other. The position of the plane is determined by this propertythat if each particle in the system be multiplied by the area described upon this plane in a given time, by the projection of its radius vector about the common centre of gravity of the whole, the sum of all these products will be a maximum. La Place found that the plane in question is inclined to the ecliptic at an angle of nearly 1° 35′ 31′′, and that, in passing through the sun, and about midway between the orbits of Jupiter and Saturn, it may be regarded as the equator of the solar system, dividing it into two parts, which balance one another in all their motions. This plane of greatest inertia, by no means peculiar to the solar system, but existing in every system of bodies submitted to their mutual attractions only, always maintains a fixed position, whence the oscillations of the system may be estimated through unlimited time. Future astronomers will know, from its immutability or variation, whether the sun and his attendants are connected or not with

the other systems of the universe. Should there be no link between them, it may be inferred, from the rotation of the sun, that the centre of gravity of the system situate within his mass describes a straight line in this invariable plane or great equator of the solar system, which, unaffected by the changes of time, will maintain its stability through endless ages. But if the fixed stars, comets, or any unknown and unseen bodies, affect our sun and planets, the nodes of this plane will slowly recede on the plane of that immense orbit which the sun may describe about some most distant centre, in a period which it transcends the powers of man to determine. There is every reason to believe that this is the case; for it is more than probable that, remote as the fixed stars are, they in some degree influence our system, and that even the invariability of this plane is relative, only appearing fixed to creatures incapable of estimating its minute and slow changes during the small extent of time and space granted to the human race. "The developement of such changes," as M. Poinsot justly observes, "is similar to an enormous curve, of which we see so small an arc that we imagine it to be a straight line." If we raise our views to the whole extent of the universe, and consider the stars, together with the sun, to be wandering bodies, revolving about the common centre of creation, we may then recognise in the equatorial plane, passing through the centre of gravity of the universe, the only instance of absolute and eternal repose.'

In the remaining section of Astronomy, Mrs Somerville treats, in succession, of the perturbations arising from the mutual actions of the primary and secondary planets-of the figure of the earth -of the phenomena of Precession, Nutation, and Libration-of the theory of the tides, and of the stability of the ocean; and the principles thus investigated are then applied to the determination of the figure of the earth, to the acquisition of standards of weights and measures, and to the rectification of chronological epochs. All these topics are treated with much sagacity and precision. The brief limits of the volume exclude all minute details, and the attention of the reader is arrested only by the leading doctrines and facts of astronomy. The condensation of thought and of language which is thus rendered necessary, may occasionally produce obscurity of expression, and ambiguity of meaning, in the mind of an ordinary reader; but when this does happen, it is never the fault of the author, but the inevitable consequence of the absence of diagrams, and the limitation of space.

The next branch of physical science which comes under Mrs Somerville's review, is Acoustics, which is introduced by an account of the chemical and physical constitution of the atmosphere. The theory and phenomena of sound are briefly and distinctly expounded; but the curious and almost enchanting subject of the vibration of solid bodies, is discussed in little more than two pages. This omission, which we cannot but consider as a defect,

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