Astronomy and general physics considered with reference to natural theology

Front matter

ASTRONOMY

AND GENERAL PHYSICS CONSIDERED WITH REFERENCE TO NATURAL THEOLOGY

BY THE

Dedication

eminent talents and high character of your Lordship is one of its members; and I am persuaded that any effort in the cause of letters and religion coming from that quarter, will have for you an interest beyond what it would otherwise possess.

The subject proposed to me was limited ; my prescribed object is to lead the friends of religion to look with confidence and pleasure on the progress of the physical sciences, by showing how admirably every advance in our knowledge of the universe harmonizes with the belief of a most wise and good God. To do this effectually may be, I trust, a useful labour. Yet, I feel most deeply, what I would take this occasion to express, that this, and all that the speculator concerning Natural Theology can do, is utterly insufficient for the great ends of Religion ; namely, for the purpose of reforming men's lives, of purifying and elevating their characters, of preparing them for a more exalted state of being. It is the need of something fitted to do this, which gives to Religion its vast and incomparable importance ; and this can, I well know, be achieved only by that Revealed

DEDICATION.

Contents

[Within the last few years, several works have been published in this Country on subjects more or less closely approaching to that here treated. It may, therefore, be not superfluous to say that the Author of the following pages believes that he has not borrowed any of his views or illustrations from recent English writers on Natural Theology.]

Page

Chap. I. Object of the Present Treatise 1

BOOK I. Terrestrial Adaptations 11

Chap. I. The Length of the Year 21

II. The Length of the Day 33

III. The Mass of the Earth 42

IV. The Magnitude of the Ocean 52

V. The Magnitude of the Atmosphere 54

VI. The Constancy and Variety of Climates 55 VII. The Variety of Organization corresponding to the Variety of Climate 62

VIII. The Constituents of Climate 75

The Laws of Heat with respect to the

Earth 76

IX. The Laws of Heat with respect to Water 80

X. The Laws of Heat with respect to Air 96

XI. The Laws of Electricity 110

XII. The Laws of Magnetism 113

XIII. The Properties of Light with regard to

Vegetation 115

XIV. Sound 117

XV. The Atmosphere 125

XVI. Light 128

XVII. The Ether 138

XVIII. Recapitulation 141 xii

CONTENTS.

BOOK II. Cosmical Arrangements 148

Chap. I. The Structure of the Solar System 150

II. The Circular Orbits of the Planets'

round the Sun 154

III. The Stability of the Solar System 159

IV. The Sun in the Centre 169

V. The Satellites 173

VI. The Stability of the Ocean 177

VII. The Nebular Hypothesis 181

VIII. The Existence of a Resisting Medium

in the Solar System 191

IX. Mechanical Laws 210

X. The Law of Gravitation 214

XI. The Laws of Motion 231

XII. Friction 238

BOOK III. Religious Views 251

Chap. I. The Creator of the Physical World is

the Governor of the Moral World ... 254

II. On the Vastness of the Universe 268

III. On Man's Place in the Universe 279

IV. On the Impression produced by the

Contemplation of Laws of Nature ; or, on the Conviction that Law implies Mind 293

V. On Inductive Habits ; or, on the Impression produced on Men's Minds

by discovering Laws of Nature 303

VI. On Deductive Habits ; or, on the Impression produced on Men's Minds by tracing the Consequences of ascertained Laws 323

VII. On Final Causes 342

VIII. On the Physical Agency of the Deity 356 IX. On the Impression produced by considering the Nature and Prospects of Science ; or, on the Impossibility of the Progress of our Knowledge ever enabling us to comprehend the Nature of the Deity 366

ASTRONOMY

AND

GENERAL PHYSICS.

INTRODUCTION.

Chapter I. Object of the Present Treatise

HE examination of the material world brings before us a number of things and relations of things which suggest to most minds the belief of a creating and presiding Intelligence. And this impression, which arises with the most vague and superficial consideration of the objects by which we are surrounded, is, we conceive, confirmed and expanded by a more exact and profound study of external nature. Many works have been written at different times with the view of showing how our knowledge of the elements and their operation, of plants and animals and their construction, may serve to w. B

INTRODUCTION.

nourish and unfold our idea of a Creator and Governor of the world. But though this is the case, a new work on the same subject may still have its use. Our views of the Creator and Governor of the world, as collected from or combined with our views of the world itself, undergo modifications, as we are led by new discoveries, new generalizations, to regard nature in a new light. The conceptions concerning the Deity, his mode of effecting his purposes, the scheme of his government, which are suggested by one stage of our knowledge of natural objects and operations, may become manifestly imperfect or incongruous, if adhered to and applied at a later period, when our acquaintance with the immediate causes of natural events has been greatly extended. On this account it may be interesting, after such an advance, to show how the views of the creation, preservation, and government of the universe, which natural science opens to us, harmonize with our belief in a Creator, Governor, and Preserver of the world. To do this with respect to certain departments of Natural Philosophy is the object of the following pages ; and the author will deem himself fortunate, if he succeeds in removing any of the difficulties and obscurities which prevail in men's minds, from the want of a clear mutual understanding between the religious and the scientific speculator. It is needless here to remark the necessarily imperfect

OBJECT.

and scanty character of Natural Religion ; for most persons will allow that, however imperfect may be the knowledge of a Supreme Intelligence which we gather from the contemplation of the natural world, it is still of most essential use and value. And our purpose on this occasion is, not to show that Natural Theology is a perfect and satisfactory scheme, but to bring up our Natural Theology to the point of view in which it may be contemplated by the aid of our Natural Philosophy.

Now the peculiar point of view which at present belongs to Natural Philosophy, and especially to the departments of it which have been most successfully cultivated, is, that nature, so far as it is an object of scientific research, is a collection of facts governed by laws : our knowledge of nature is our knowledge of laws ; of laws of operation and connexion, of laws of succession and co-existence, among the various elements and appearances around us. And it must therefore here be our aim to show how this view of the universe falls in with our conception of the Divine Author, by whom we hold the universe to be made and governed.

Nature acts by general laws; that is, the occurrences of the world in which we find ourselves, result from causes which operate according to fixed and constant rules. The succession of days, and seasons, and years, is produced by the motions of the earth \ and these again are

INTRODUCTION.

governed by the attraction of the sun, a force which acts with undeviating steadiness and regularity. The changes of winds and skies, seemingly so capricious and casual, are produced by the operation of the sun's heat upon air and moisture, land and sea ; and though in this case we cannot trace the particular events to their general causes, as we can trace the motions of the sun and moon, no philosophical mind will doubt the generality and fixity of the rules by which these causes act. The variety of the effects takes place, because the circumstances in different cases vary ; and not because the action of material causes leaves anything to chance in the result. And again, though the vital movements which go on in the frame of vegetables and animals depend on agencies still less known, and probably still more complex, than those which rule the weather, each of the powers on which such movements depend has its peculiar laws of action, and these are as universal and as invariable as the law by which a stone falls to the earth when not supported.

The world then is governed by general laws; and in order to collect from the world itself a judgment concerning the nature and character of its government, we must consider the import and tendency of such laws, so far as they come under our knowledge. If there be, in the administration of the universe, intelligence and denevolence, superintendence and foresight,

OBJECT.

grounds for love and hope, such qualities may be expected to appear in the constitution and combination of those fundamental regulations by which the course of nature is brought about, and made to be what it is.

If a man were, by some extraordinary event, to find himself in a remote and unknown country, so entirely strange to him that he did not know whether there existed in it any law or government at all ; he might in no long time ascertain whether the inhabitants were controlled by any superintending authority ; and with a little attention he might determine also whether such authority were exercised with a prudent care for the happiness and well being of its subjects, or without any regard and fitness to such ends; whether the country were governed by laws at all, and whether the laws were good. And according to the laws which he thus found prevailing, he would judge of the sagacity, and the purposes of the legislative power.

By observing the laws of the material universe and their operation, we may hope, in a somewhat similar manner, to be able to direct our judgment concerning the government of the universe : concerning the mode in which the elements are regulated and controlled, their effects combined and balanced. And the general tendency of the results thus produced may discover to us something of the character of the

INTRODUCTION.

power which has legislated for the material world.

We are not to push too far the analogy thus suggested. There is undoubtedly a wide difference between the circumstances of man legislating for man, and God legislating for matter. Still we shall, it will appear, find abundant reason to admire the wisdom and the goodness which have established the Laws of Nature, however rigorously we may scrutinize the import of this expression.

Chapter II. On Laws of Nature

&||5^HEN we speak of material nature as Dem g governed by laws, it is sufficiently evident that we use the term in a manner somewhat metaphorical. The laws to which man's attention is primarily directed are moral laws : rules laid down for his actions ; rules for the conscious actions of a person ; rules which, as a matter of possibility, he may obey or may transgress ; the latter event being combined, not with an impossibility, but with a penalty. But the Laws of Nature are something different from this ; they are rules for that which things are to do and suffer ; and this by no consciousness or will of theirs. They are rules describing the

ON LAWS OF NATURE.

mode in which things do act ; they are invariably obeyed ; their transgression is not punished, it is excluded. The language of a moral law is, man shall not kill ; the language of a Law of Nature is, a stone ivill fall to the earth.

These two kinds of laws direct the actions of persons and of things, by the sort of control of which persons and things are respectively susceptible ; so that the metaphor is very simple 5 but it is proper for us to recollect that it is a metaphor, in order that we may clearly apprehend what is implied in speaking of the Laws of Nature.

In this phrase are included all properties of the portions of the material world ; all modes of action and rules of causation, according to which they operate on each other. The whole course of the visible universe therefore is but the collective result of such laws ; its movements are only the aggregate of their working. All natural occurrences, in the skies and on the earth, in the organic and in the inorganic world, are determined by the relations of the elements and the actions of the forces of which the rules are thus prescribed.

The relations and rules by which these occurrences are thus determined necessarily depend on measures of time and space, motion and force ; on quantities which are subject to numerical measurement, and capable of being connected by mathematical properties. And thus

INTRODUCTION.

all things are ordered by number and weight and measure. " God," as^ was said by the ancients, " works by geometry:" the legislation of the material universe is necessarily delivered in the language of mathematics ; the stars in their courses are regulated by the properties of conic sections, and the winds depend on arithmetical and geometrical progressions of elasticity and pressure.

The constitution of the universe, so far as it can be clearly apprehended by our intellect, thus assumes a shape involving an assemblage of mathematical propositions : certain algebraical formulae, and the knowledge when and how to apply them, constitute the last step of the physical science to which we can attain. The labour and the endowments of ages have been employed in bringing such science into the condition in which it now exists : and an exact and extensive discipline in mathematics, followed by a practical and profound study of the researches of natural philosophers, can alone put any one in possession of all the knowledge concerning the course of the material world, which is at present open to man. The general impression, however, which arises from the view thus obtained of the universe, the results which we collect from the most careful scrutiny of its administration, may, we trust, be rendered intelligible without this technical and laborious study, and to do this is our present object.

ON LAWS OF NATURE.

It will be our business to show that the laws which really prevail in nature are, by their form, that is, by the nature of the connexion which they establish among the quantities and properties which they regulate, remarkably adapted to the office which is assigned them ; and thus offer evidence of selection, design, and goodness, in the power by which they were established. But these characters of the legislation of the universe may also be seen, in many instances, in a manner somewhat different from the selection of the law. The nature of the connexion remaining the same, the quantities which it regulates may also in their magnitude bear marks of selection and purpose. For the law may be the same while the quantities to which it applies are different. The law of the gravity which acts to the earth and to J upiter, is the same ; but the intensity of the force at the surfaces of the two planets is different. The law which regulates the density of the air at any point, with reference to the height from the earth's surface, would be the same, if the atmosphere were ten times as large, or only one tenth as large as it is ; if the barometer at the earth's surface stood at three inches only, or if it showed a pressure of thirty feet of mercury.

Now this being understood, the adaptation of a law to its purpose, or to other laws, may appear in two ways :— either in the form of the law, or in the amount of the magnitudes which it regu-

INTRODUCTION.

lates, which are sometimes called arbitrary magnitudes.

If the attraction of the sun upon the planets did not vary inversely as the square of the distance, the form of the law of gravitation would be changed; if this attraction were, at the earth's orbit, of a different value from its present one, the arbitrary magnitude would be changed ; and it will appear, in a subsequent part of this work, that either change would, so far as we can trace its consequences, be detrimental. The form of the law determines in what manner the facts shall take place ; the arbitrary magnitude determines how fast, how far, how soon ; the one gives a model, the other a measure of the phenomenon ; the one draws the plan, the other gives the scale on which it is to be executed ; the one gives the rule, the other the rate. If either were wrongly taken, the result would be wrong too.

Chapter III. Mutual Adaptation in the Laws of Nature

O ascertain such laws of nature as we have been describing, is the peculiar business of science. It is only with regard to a very small portion of the appearances of the universe, that science in any strict application of the term, exists. In very few departments of research have men been able to trace a multitude of known facts to causes which appear to be the ultimate material causes, or to discern the laws which seem to be the most general laws. Yet, in one or two instances, they have done this, or something approaching to this ; and most especially in the instance of that part of nature, which it is the object of this treatise more peculiarly to consider.

The apparent motions of the sun, moon, and stars have been more completely reduced to their causes and laws than any other class of phenomena. Astronomy, the science which treats of these, is already a wonderful example of the degree of such knowledge which man may attain. The forms of its most important laws may be conceived to be certainly known ; and hundreds of observers in all parts of the world are daily employed in determining, with

INTRODUCTION.

additional accuracy, the arbitrary magnitudes which these laws involve.

The inquiries in which the mutual effects of heat, moisture, air, and the like elements are treated of, including, among other subjects, all that we know of the causes of the weather (meteorology) is a far more imperfect science than astronomy. Yet, with regard to these agents, a great number of laws of nature have been discovered, though, undoubtedly, a far greater number remain still unknown.

So far, therefore, as our knowledge goes, astronomy and meteorology are parts of natural philosophy in which we may study the order of nature with such views as we have suggested ; in which we may hope to make out the adaptations and aims which exist in the laws of nature ; and thus to obtain some light on the tendency of this part of the legislation of the universe, and on the character and disposition of the Legislator.

The number and variety of the laws which we find established in the universe is so great, that it would be idle to endeavour to enumerate them. In their operation they are combined and intermixed in incalculable and endless complexity, influencing and modifying each other's effects in every direction. If we attempt to comprehend at once the whole of this complex system, we find ourselves utterly baffled and overwhelmed by its extent and multiplicity.

ADAPTATION OF LAWS.

Yet, in so far as we consider the bearing of one part upon another, we receive an impression of adaptation, of mutual fitness, of conspiring means, of preparation and completion, of purpose and provision. This impression is suggested by the contemplation of every part of nature ; but the grounds of it, from the very circumstances of the case, cannot be conveyed in a few words. It can only be fully educed by leading the reader through several views and details, and must grow out of the combined influence of these on a sober and reflecting frame of mind. However strong and solemn be the conviction which may be derived from a contemplation of nature, concerning the existence, the power, the wisdom, the goodness of our Divine Governor, we cannot expect that this conviction, as resulting from the extremely complex spectacle of the material world, should be capable of being irresistibly conveyed by a few steps of reasoning, like the conclusion of a geometrical proposition, or the result of an arithmetical calculation.

We shall, therefore, endeavour to point out cases and circumstances in which the different parts of the universe exhibit this mutual adaptation, and thus to bring before the mind of the reader the evidence of wisdom and providence, which the external world affords. When we have illustrated the correspondencies which exist in every province of nature, between the

INTRODUCTION.

qualities of brute matter and the constitution of living things, between the tendency to derangement and the conservative influences by which such a tendency is counteracted, between the office of the minutest speck and of the most general laws : it will, we trust, be difficult or impossible to exclude from our conception of this wonderful system, the idea of a harmonizing, a preserving, a contriving, an intending mind ; of a Wisdom, Power, and Goodness far exceeding the limits of our thoughts.

Chapter IV. Division of the Subject

N making a survey of the universe, for the purpose of pointing out such correspondencies and adaptations as we have mentioned, we shall suppose the general leading facts of the course of nature to be known, and the explanations of their causes now generally established among astronomers and natural philosophers to be conceded. We shall assume therefore that the earth is a solid globe of ascertained magnitude, which travels round the sun, in an orbit nearly circular, in a period of about three hundred and sixty-five days and a quarter, and in the mean time revolves, in an inclined position, upon its own axis in about twenty-four hours,

DIVISION OF THE SUBJECT.

thus producing the succession jof appearances and effects which constitute seasons and climates, day and night ; — that this globe has its surface furrowed and ridged with various inequalities, the waters of the ocean occupying the depressed parts : — that it is surrounded by an atmosphere, or spherical covering of air ; and that various other physical agents, moisture, electricity, magnetism, light, operate at the surface of the earth, according to their peculiar laws. This surface is, as we know, clothed with a covering of plants, and inhabited by the various tribes of animals, with all their variety of sensations, wants, and enjoyments. The relations and connexions of the larger portions of the world, the sun, the planets, and the stars, the cosmical arrangements of the system, as they are sometimes called, determine the course of events among these bodies ; and the more remarkable features of these arrangements are therefore some of the subjects for our consideration. These cosmical arrangements, in their consequences, effect also the physical agencies which are at work at the surface of the earth, and hence come in contact with terrestrial occurrences. They thus influence the functions of plants and animals. The circumstances in the cosmical system of the universe, and in the organic system of the earth, which have thus a bearing on each other, form another of the subjects of which we shall treat. The former class of considerations attends

INTRODUCTION.

principally to the stability and other apparent perfections of the solar system ; the latter to the well-being of the system of organic life by which the earth is occupied. The two portions of the subject may be treated as Cosmical Arrange ments and Terrestrial Adaptations.

We shall begin with the latter class of adaptations, because in treating of these the facts are more familiar and tangible, and the reasonings less abstract and technical, than in the other division of the subject. Moreover, in this case men have no difficulty in recognising as desirable the end which is answered by such adaptations, and they therefore the more readily consider it as an end. The nourishment, the enjoyment, the diffusion of living things, are willingly acknowledged to be a suitable object for contrivance ; the simplicity, the permanence of an inert mechanical combination might not so readily be allowed to be a manifestly worthy aim of a Creating Wisdom. The former branch of our argument may therefore be best suited to introduce to us the Deity as the institutor of Laws of Nature, though the latter may afterwards give us a wider view and a clearer insight into one province of his legislation.

Book I. Terrestrial Adaptations

E proceed in this Book to point out relations which subsist between the laws of the inorganic world, that is, the general facts of astronomy and meteorology ; and the laws which prevail in the organic world, the properties of plants and animals.

With regard to the first kind of laws, they are in the highest degree various and unlike each other. The intensity and activity of natural influences follow in different cases the most different rules. In some instances they are periodical, increasing and diminishing alternately, in a perpetual succession of equal intervals of time. This is the case with the heat at the earth's surface, which has a period of a year ; with the light, which has a period of a day. Other qualities are constant, thus the force of gravity at the same place is always the same. In some cases, a very simple cause produces very complicated effects ; thus the globular form of the earth, and the inclination of its axis during its annual motion, give rise to all the variety of climates. In other cases a very complex and w. c

TERRESTRIAL ADAPTATIONS.

variable system of causes produces effects comparatively steady and uniform; thus solar and terrestrial heat, air, moisture, and probably many other apparently conflicting agents, join to produce our weather, which never deviates very far from a certain average standard.

Now a general fact, which we shall endeavour to exemplify in the following chapters, is this : — That those properties of plants and animals which have reference to agencies of a periodical character, have also by their nature a periodical mode of working ; while those properties which refer to agencies of constant intensity, are adjusted to this constant intensity : and again, there are peculiarities in the nature of organized beings which have reference to a variety in the conditions of the external world, as, for instance, the difference of the organized population of different regions : and there are other peculiarities which have a reference to the constancy of the average of such conditions, and the limited range of the deviations from that average; as, for example, that constitution by which each plant and animal is fitted to exist and prosper in its usual place in the world.

And not only is there this general agreement between the nature of the laws which govern the organic and inorganic world, but also there is a coincidence between the arbitrary magnitudes which such laws involve on the one hand and on the other. Plants and animals have, in their construction, certain periodical functions, which have a reference to alternations of heat and cold ; the length of the period which belongs to these functions by their construction, appears to be that of the period which belongs to the actual alternations of heat and cold, namely, a year. Plants and animals have again in their construction certain other periodical functions, which have a reference to alternations of light and darkness ; the length of the period of such functions appears to coincide with the natural day. In like manner the other arbitrary magnitudes which enter into the laws of gravity, of the effects of air and moisture, and of other causes of permanence, and of change, by which the influences of the elements operate, are the same arbitrary magnitudes to which the members of the organic world are adapted by the various peculiarities of their construction.

The illustration of this view will be pursued in the succeeding chapters ; and when the coincidence here spoken of is distinctly brought before the reader, it will, we trust, be found to convey the conviction of a wise and benevolent design, which has been exercised in producing such an agreement between the internal constitution and the external circumstances of org-anized beings. We shall adduce cases where there is an apparent relation between the course of operation of the elements and the course of vital functions ; between some fixed measure of

TERRESTRIAL ADAPTATIONS.

time or space, traced in the lifeless and in the living world; where creatures are constructed on a certain plan, or a certain scale, and this plan or this scale is exactly the single one which is suited to their place on the earth ; where it was necessary for the Creator (if we may use such a mode of speaking) to take account of the weight of the earth, or the density of the air, or the measure of the ocean, and where these quantities are rightly taken account of in the arrangements of creation. In such cases we conceive that we trace a Creator, who, in producing one part of his work, was not forgetful or careless of another part ; who did not cast his living creatures into the world to prosper or perish as they might find it suited to them or not ; but fitted together, with the nicest skill, the world and the constitution which he gave to its inhabitants ; so fashioning it and them, that light and darkness, sun and air, moist and dry, should become their ministers and benefactors, the unwearied and unfailing causes of their well being.

We have spoken of the mutual adaptation of the organic and the inorganic world. If we were to conceive the contrivance of the world as taking place in an order of time in the contriving mind, we might also have to conceive this adaptation as taking place in one of two ways ; we might either suppose the laws of inert nature to be accommodated to the foreseen wants