Chapter XVII: Section III (11)

439. If now we suppose the body to revolve on its axis, all other things remaining as before, the surface bounding the sea will become different from what it was in the former case, and will be more swelled out toward the middle or equatorial regions. The land above the level of the sea will still, as before, be worn down and deposited in the bottom of the sea, so as to form strata nearly parallel to its surface: the tendency, therefore, is to render the real figure of the planet nearer to the statical. At the same time the _statical_ figure is changed, as explained above; so that the two figures mutually approach, and the limit, or ultimate figure to which they tend, is one over which the ocean might be diffused every where to the same depth, for then the causes of change would entirely cease. But this figure is no other than the spheroid of equilibrium, which, therefore, is the effect which the waste and reconsolidation of the land would necessarily produce, if the process were continued indefinitely, without interruption. In this, as in many other instances, when a body is subject to the action of causes by which its form is _gradually_ changed, the figure best adapted to resist those changes, is the figure which the changes themselves ultimately produce.

Also, whatever be the irregularities of density, the tendency to a change of figure will not cease till the body is moulded into that particular spheroid which admits of being covered with water every where to the same depth.[232] Thus it appears, that a solid of an irregular figure, and of irregular density, provided it be in part covered with water; and be at the same time subject to waste above the surface of the sea, and reconsolidation under it, has a tendency to acquire, in time, the same figure that it would have acquired had it been entirely fluid.

[Footnote 232: In the same manner as a transition is thus made from an irregular figure to a spheroid of equilibrium, so, if the actual figure were at first more simple than the spheroid, it would still be changed into this last by degrees.

Let us conceive, for instance, that the earth is at rest, and is a perfect sphere of solid matter, surrounded by an ocean every where of equal depth, for example, of one mile. Then, if a rotatory motion be communicated to it, so that it shall revolve on its axis in twenty-four hours, in consequence of the centrifugal force, the water circumfused about the sphere will immediately rise up under the equator, and will become part of a spheroidal surface, (not elliptical, but nearly so,) the equatorial diameter of which is greater than the polar axis, in the ratio of 588 to 577 By this means the water will be accumulated at the equator to the depth of nearly 2.5 miles, and form a zone surrounding the earth, and extending about 37° on each side of the equator. The remainder of the surface will be left dry, forming two vast circumpolar continents, that reach 53° on every side of the poles, and that are elevated in the middle more than four miles above the level of the sea.

Such would be the state of our globe, on the hypothesis above laid down; and, if there were no waste or destruction of the land, this order of things would be permanent, and neither the solid nor fluid part of the mass could ever acquire any other figure than that which has been described. But, if the same laws be supposed to regulate the action of the atmosphere in those circumstances, that do actually regulate it according to the present constitution of the globe, the vapours raised up from the surface of the sea, would be carried by the winds over the land, where they would be condensed and precipitated in rain. Thus, all the agents of destruction would be let loose on the two great circumpolar continents; rivers would be formed; the land would become deeply intersected by ravines; those ravines would gradually open into wide valleys; the masses of greatest resistance would be shaped into hills and mountains: and from a superficies originally smooth and uniform, the same inequalities would be produced which at present diversify the surface of the earth.

While the parts of the sphere without the spheroid are thus continually diminished, the loose earth and sand washed down from them, will be deposited at the bottom of the sea, and will form strata parallel to the surface of the superincumbent water. The actual and statical figure are thus brought nearer one another; and, at the same time the statical is changed, on the principle already explained, (the change in the direction of gravity,) and is made continually to approximate to a state, which when it has attained, no farther change can take place, viz. an oblate elliptic spheroid, of which the surface is perpendicular to the direction of gravity, having the equatorial diameter to the polar axis in the ratio of 230 to 229.]

440. In the preceding reasonings, we have supposed the process of decay and subsequent stratification to be carried on without interruption, till the whole of the land is covered by the sea. This supposition is useful for explaining the nature of the forces which have determined the figure of the earth; but there is no reason to think that it has ever been realized in its full extent, the elevation of strata from the bottom of the sea interrupting the progress, and producing new land in one place, as the old decays in another. The very same land also, which is wasted at its surface, may perhaps be lifted up by the forces that are placed under it; or it may be let down, undergoing alterations of its level, from causes that we do not perceive, but of which the action is undoubted, (§ 388.) But notwithstanding these interruptions, the general tendency to produce in the earth a spheroidal figure may remain, and more may be done by every revolution, to bring about the attainment of that figure than to cause a deviation from it. This figure, therefore, though never likely to be perfectly acquired, will be the _limiting_ or _asymptotic_ figure, if it may be so called, to which the earth will continually approach.

441. If the preceding conclusions are just, and if the figure of equilibrium is only an asymptotic figure, to which that of the earth may approximate, but cannot perfectly attain, we are not to be surprised if considerable deviations from it are actually observed. This has accordingly happened, insomuch, that the results deduced from the most accurate measurement of degrees of the meridian, differ from one another, in the oblateness they give to the earth, by nearly one half of the quantity to be determined. When we compare the degrees measured in France, and in some other countries of Europe, with those measured in Peru, we obtain for the compression at the poles, less than 1/300 of the radius of the earth. But when we compare the degrees measured in France with one another, and with those lately measured in England, we find that they are best represented by a spheroid that has its compression 1/150 of its semi-axis.[233] There is reason to think, therefore, that the meridians are not elliptical; and other observations seem to show, that they are not even similar to one another; or that the earth is not, strictly speaking, a solid of revolution; so, also, the comparison of the degree measured at the Cape of Good Hope, with those measured on the opposite side of the equator, creates a suspicion, that the northern and southern hemispheres are not perfectly alike, and that the earth is not equally compressed at the Arctic and the Antarctic poles. These irregularities, though they do not affect the general fact of the earth's compression at the poles, show that the true statical figure is but imperfectly attained; and though this may be accounted for, without having recourse to the principles involved in our theory, it is in a manner very unsatisfactory, and, by help of suppositions, not at all consistent with the original fluidity ascribed to the whole mass, or to the exterior crust of the earth.

[Footnote 233: Exposition du Systéme du Monde, par La Place, p. 61, 2d edit.]

442. As the principles here laid down explain how a solid body may attain very nearly the figure which a fluid would acquire in order to preserve its parts in equilibrium; and since the oblate figure belongs to other of the planets as well as the earth, and the globular to all the great bodies of the universe, this suggests an analogy that goes deep into the economy of nature, and extends far beyond the limits within which the mineralogist is wont to confine his speculations.

443. That no very irregular figure is found among the planetary bodies, may therefore be considered as a proof of the universality of that system of waste and reconsolidation that we have been endeavouring to trace in the natural history of the earth. A farther proof of the same arises from considering, that for every given mass of matter, having a given period of rotation, there are two different spheroids that answer the conditions of establishing an equilibrium among its parts, the one near to the sphere, and the other very distant from it, and so oblate as to have a lenticular form. Thus the earth, supposing it homogeneous, might either be in equilibrium, by means of the figure which it actually has, or of one in which the polar was to the equatorial diameter as 1 to 768. The same is true of the other planets; and yet we no where find that this highly compressed spheroid is actually employed by nature. The reason, no doubt, is, that in so oblate a spheroid, the equilibrium between the gravitating and the centrifugal force is of the kind that does not re-establish itself when disturbed; so that the parts let loose, and not kept in their place by firm cohesion, would fly off altogether. In such a body, the waste at the surface would lead to an entire change of form, and therefore the constitution here supposed could not be permanent.

444. In the system of Saturn, we have a great deviation from the general order, which, nevertheless, has led to a very unexpected verification of some of the conclusions deduced above. A principle extremely like that which is the basis of all the foregoing reasonings, led one of the greatest philosophers of the present age to discover the revolution of Saturn's ring on its axis, and even to determine the velocity of that revolution, such as it has been since found by observation. LA PLACE, laying it down as a maxim, that nothing in nature can exist, where there are causes of change, not balanced or compensated by other causes,[234] concluded, that the-parts of the ring must be held from falling down to the body of the planet by some other force than their mere cohesion to one another. Were it otherwise, every particle detached from the ring, by any means, must descend in a straight line, almost perpendicular to the surface of Saturn; and the final destruction of the ring must be inevitable. The only force that could balance this effect of gravitation, seemed to be a centrifugal force, arising from the rotation of the ring on an axis passing through its centre, and perpendicular to its plane. La Place proceeded to inquire what celerity of rotation was adequate to this effect, and found that one of ten hours and a quarter would be required, which is almost precisely the time afterwards determined by Dr HERSCHEL from actual observation. If, with this rotation, the ring is a solid annulus generated by the rotation of a very flat ellipsis about a given point in its greater axis, coinciding with the centre of Saturn, it may be so constituted, that the attraction of Saturn, combined with the centrifugal force, may produce a force perpendicular to its surface, and may enable detached parts to remain at rest, animals, for instance, to walk on its surface, and fluids to be _in equilibrio_. The system of Saturn is thus fortified against the lapse of time, as effectually as that of the earth itself; and the means by which this is accomplished, seem to prove, that the weapons which time employs, are in both cases the same, viz. the slow wearing and decomposition of the solid parts. This slow wearing may have produced the figure by which its action is most effectually resisted.

[Footnote 234: La Place, _ubi supra_, p. 242.]

445. Thus Dr Hutton's theory of the earth comes at last to connect itself with the researches of physical astronomy. The conclusion to be drawn from this coincidence is to the credit of both sciences. When two travellers, who set out from points so distant as the mineralogist and the astronomer, and who follow routes so different, meet at the end of their journey, and agree in their report of the countries through which they have passed, it affords no slight presumption, that they have kept the right way, and that they relate what they have actually seen.

NOTE XXVI. § 133.

_Prejudices relating to
the Theory of the Earth._

446. Among the prejudices which a new theory of the earth has to overcome, is an opinion, held, or affected to be held, by many, that geological science is not yet ripe for such elevated and difficult speculations. They would, therefore, get rid of these speculations, _by moving the previous question_, and declaring that at present we ought to have no theory at all. We are not yet, they allege, sufficiently acquainted with the phenomena of geology; the subject is so various and extensive that our knowledge of it must for a long time, perhaps for ever, remain extremely imperfect. And hence it is, that the theories hitherto proposed have succeeded one another with so great rapidity, hardly any of them having been able to last longer than the discovery of a new fact, or a fact unknown when it was invented. It has proved insufficient to connect this fact with the phenomena already known, and has therefore been justly abandoned. In this manner, they say, have passed away the theories of Woodward, Burnet, Whiston, and even of Buffon; and so will pass, in their turn, those of Hutton and Werner.

447. This unfavourable view of geology, ought not, however, to be received without examination; in science, presumption is less hurtful than despair, and inactivity is more dangerous than error.

One reason of the rapid succession of geological theories, is the mistake that has been made as to their object, and the folly of attempting to explain by them the first origin of things. This mistake has led to fanciful speculations that had nothing but their novelty to recommend them, and which, when that charm had ceased, were rejected as mere suppositions, incapable of proof. But if it is once settled, that a theory of the earth ought to have no other aim but to discover the laws that regulate the changes on the surface, or in the interior of the globe, the subject is brought within the sphere either of observation or analogy; and there is no reason to suppose, that man, who has numbered the stars, and measured their forces, shall ultimately prove unequal to this investigation.

448. Again, theories that have a rational object, though they be false or imperfect in their principles, are for the most part approximations to the truth, suited to the information at the time when they were proposed. They are steps, therefore, in the advancement of knowledge, and are terms of a series that must end when the real laws of nature are discovered. It is, on this account, rash to conclude, that in the revolutions of science, what has happened must continue to happen, and because systems have changed rapidly in time past, that they must necessarily do so in time to come.

He who would have reasoned so, and who had seen the ancient physical systems, at first all rivals to one another, and then swallowed up by the Aristotelian; the Aristotelian physics giving way to those of Des Cartes; and the physics of Des Cartes to those of Newton; would have predicted that these last were also, in their turn, to give place to the philosophy of some later period. This is, however, a conclusion that hardly any one will now be bold enough to maintain, after a hundred years of the most scrupulous examination have done nothing but add to the evidence of the NEWTONIAN SYSTEM. It seems certain, therefore, that the rise and fall of theories in times past, does not argue, that the same will happen in the time that is to come.

449. The multifarious and extremely diversified object of geological researches, does, no doubt, render the first steps difficult, and may very well account for the instability hitherto observed in such theories; but the very same thing gives reason for expecting a very high degree of certainty to be ultimately attained in these inquiries.

Where the phenomena are few and simple, there may be several different theories that will explain them in a manner equally satisfactory; and in such cases, the true and the false hypotheses are not easily distinguished from one another. When, on the other hand, the phenomena are greatly varied, the probability is, that among them, some of those _instantiæ crucis_ will be found, that exclude every hypothesis but one, and reduce the explanation given to the highest degree of certainty. It was thus, when the phenomena of the heavens were but imperfectly known, and were confined to a few general and simple facts, that the Philolaic could claim no preference to the Ptolemaic system: The former seemed a possible hypothesis; but as it performed nothing that the other did not perform, and was inconsistent with some of our most natural prejudices, it had but few adherents. The invention of the telescope, and the use of more accurate instruments, by multiplying and diversifying the facts, established its credit; and when not only the general laws, but also the inequalities, and disturbances of the planetary motions were understood, all physical hypotheses vanished, like phantoms, before the philosophy of NEWTON. Hence the number, the variety, and even the complication of facts, contribute ultimately to separate truth from falsehood; and the same causes which, in any case, render the first attempts toward a theory difficult, make the final success of such attempts just so much the more probable.

This maxim, however, though a general encouragement to the prosecution of geological inquiries, does not amount to a proof that we are yet arrived at the period when those inquiries may safely assume the form of a theory. But that we are arrived at such a period, appears clear from other circumstances.

450. It cannot be denied, that a great multitude of facts, respecting the mineral kingdom, are now known with considerable precision; and that the many diligent and skilful observers, who have arisen in the course of the last thirty years, have produced a great change in the state of geological knowledge. It is unnecessary to enumerate them all; FERBER, BERGMAN, DE LUC, SAUSSURE, DOLOMIEU, are those on whom Dr Hutton chiefly relied; and it is on their observations and his own that his system is founded. If it be said, that only a small part of the earth's surface has yet been surveyed, and described with such accuracy as is found in the writers just named, it may be answered, that the earth is constructed with such a degree of uniformity, that a tract of no very large extent may afford instances of all the leading facts that we can ever observe in the mineral kingdom. The variety of geological appearances which a traveller meets with, is not at all in proportion to the extent of country he traverses; and if he take in a portion of land sufficient to include primitive and secondary strata, together with mountains, rivers, and plains, and unstratified bodies in veins and in masses, though it be not a very large part of the earth's surface, he may find examples of all the most important facts in the history of fossils. Though the labours of mineralogists have embraced but a small part of the globe, they may therefore have comprehended a very large proportion of the phenomena which it exhibits; and hence a presumption arises, that the outlines, at least, of geology have now been traced with tolerable truth, and are not susceptible of great variation.

451. When the phenomena of any class are in general ambiguous, and admit of being explained by different or even opposite theories; if few of those exclusive facts are known, which admit but of one or a few solutions, then we have no right to expect much from our endeavours to generalise, except the knowledge of the points where our information is most deficient, and to which our observations ought chiefly to be directed. But that many of the exclusive and unambiguous instances are known, in the natural history of the globe, I think is evident from the reasoning in the foregoing pages, where so many examples have occurred of appearances that give the most direct negative to the Neptunian system, and exclude it from the number of possible hypotheses, by which the phenomena of geology can be explained. The abundance of such instances is an infallible sign, that the mass of knowledge is in that state of fermentation, from which the true theory may be expected to emerge.

452. Another indication of the same kind, is the near approach that even the most opposite theories make, in some respects, to one another. There are so many points of contact between them, that they appear to approximate to an ultimate state, in which, however unwillingly, they must at last coincide. That ultimate form, too, which all these theories have a tendency to put on, if I am not deceived, is no other than that of the Huttonian theory.

453. The first example I shall take from the system of Saussure. It is to be regretted, that this excellent geologist has no where given us a complete account of his theory. Some of the leading principles of it are, however, unfolded in the course of his observations, and enable us to form a notion of its general outline. It was evidently far removed from the system of subterraneous heat, and seems, especially in the latter part of the author's life, to have been very much accommodated to the prevailing system of WERNER. Nevertheless, with so little affinity between their general views, Saussure and Hutton agree in that most important article which regards the elevation of the strata. Saussure plainly perceived the impossibility of the strata being formed in the vertical situations which so many of them now occupy; and he takes great pains to demonstrate this impossibility, from some facts that have been referred to above. He also believed that this elevation had been given to strata that were originally level, by a force directed upwards, or by the _refoulement_ of the beds, not by their falling in, as is the opinion of De Luc and some other of the Neptunists.

Now, whoever admits this principle, and reasons on it consistently, without being afraid to follow it through all its consequences, must unavoidably come very close to the Huttonian theory. He must see, that a power which, acting from below, produced this great effect can never have belonged to water, unless rarefied into steam by the application of heat. But if it be once admitted that heat resides in the mineral regions, the great objection to Dr Hutton's system is removed; and the theorist, who was furnished with so active and so powerful an agent, would be very unskilful in the management of his own resources, if he did not employ it in the work of consolidating as well as in that of raising up the strata. A little attention will show, that it is qualified for both purposes; though insuperable objections must, no doubt, offer themselves, where the effects of compression are not understood. We may safely conclude, then, that the accurate and ingenious Geologist of Geneva ought to have been a _Plutonist_, in order to give consistency to the principles which he had adopted, and to make them coalesce as parts of one and the same system. If he embraced an opposite opinion, it probably was from feeling the force of those objections that arise from our discovering nothing in the bowels of the earth like the remains left by combustion, or inflammation, at its surface. The secret by which these seeming contradictions are to be reconciled, was unknown to this mineralogist, and he has accordingly decided strongly against the action of fire, even in the case of those unstratified substances that have the greatest affinity to volcanic lava.

454. The theoretical conclusions of another accurate and skilful observer, Dolomieu, furnish a still more remarkable example of a tendency to union between systems professedly hostile to one another.

This ingenious mineralogist, observing the interposition of the basalt between stratified rocks, so that it had not only regular beds of sandstone for its base, but was also covered with beds of the same kind, saw plainly that these appearances were inconsistent with the supposition of common volcanic explosions at the surface. He therefore conceived, that the volcanic eruption had happened at the bottom of the sea, (the level of which, in former ages, had been much higher than at present,) and that the materials afterwards deposited on the lava, had been in length of time consolidated into beds of stone. It is evident, that this notion of submarine volcanoes, comes very near, in many respects, to Dr Hutton's explanation of the same appearances. If the only thing to be accounted for were the phenomenon in question, it cannot be denied that Dolomieu's hypothesis would be perfectly sufficient; but Dr Hutton, to whom this phenomenon was familiar, and who, like Dolomieu, conceived the basalt to have been in fusion, was convinced that the retreat of the sea was not a fact well attested by geological appearances, and if admitted, was inadequate to account for the facts usually explained by it. He conceived, therefore, that such lava as the preceding had flowed not only at the bottom of the sea, but in the bowels of the earth, and having been forced up through the fissures of rocks already formed, had heaved up some of these rocks, and interposed itself between them. This agrees with the other facts in the natural history both of the basaltes and the strata.

It is plain, that, in this, there is a great approach of the two theories to one another: both maintain the igneous origin of basaltes, and its affinity to lava; both acknowledge that this lava cannot have flowed at the surface, and that the strata which cover it have been formed at the bottom of the sea. They only differ as to the mode in which the submarine or subterraneous volcano produced its effect, and that difference arises merely from the one geologist having generalized more than the other. Dolomieu sought to connect the basalt with the lavas that proceed from volcanic explosions at the surface; Dr Hutton sought not only to connect these two appearances with one another, but also with the other phenomena of mineralogy, particularly with the veins of basaltes, and the elevation of the strata.

455. In another point, the coincidence of Dolomieu's opinions and Dr Hutton's is still more striking. The former has remarked, that many of the extinguished volcanoes are in granite countries, and that, nevertheless, the lavas that they have erupted contain no granitic stones. There must be, therefore, says he, something under the granite, and this last is not, at least in all cases, to be considered as the basis of the mineral kingdom, or as the body on which all others rest. In this system, therefore, granite is not always a primordial rock, any more than in Dr Hutton's.

But Dolomieu makes a still nearer advance to the Huttonian theory; for he supposes, that under the solid and hard crust of the globe, there is a sphere of melted stone, from which this basaltic lava was thrown up. The system of subterraneous heat is here adopted in its utmost extent, and in that form which is considered as the most liable to objection, viz. the existence of it at the present moment, in such a degree as to melt rocks, and keep them in a state of fusion. In this conclusion, the two theories agree perfectly; and if they do so, it is only because the nature of things has forced them into union, notwithstanding the dissimilitude of their fundamental principles.

This ought to be considered as a strong proof, that the phenomena known to mineralogists are sufficient to justify the attempts to form a theory of the earth, and are such as lead to the same conclusions, where there was not only no previous concert, but even a very marked opposition. I have already observed, that there is a greater tendency to agree among geological theories, than among the authors of those theories.

456. Another circumstance worthy of consideration is, that in the search which the Neptunists have made, for facts most favourable to the aqueous formation of minerals, we find hardly any of a kind that was unknown to the author of the system here explained. The appearances on which WERNER grounds his opinion with respect to basaltes, and by which he would exclude the action of fire from any share in the formation of it, are all comprehended in the alternation of that rock with beds, or strata obviously of aqueous origin. Now these appearances were well known to Dr Hutton, and are easily explained by his theory, provided the effects of compression are admitted. From this, and the other circumstances just observed, I am disposed to think, that the great facts on which every geological system must depend, are now known, and that it is not too bold an anticipation to say, that a theory of the earth, which explains all the phenomena with which we are at present acquainted, will be found to explain all those that remain to be discovered.

457. The time indeed was, and we are not yet far removed from it, when one of the most important principles involved in Dr Hutton's theory was not only unknown, but could not be discovered. This was before the causticity produced in limestone by exposure to fire was understood, and when it was not known that it arose from the expulsion of a certain aerial fluid, which before was a component part of the stone. It could not then be perceived, that this aerial part might be retained by pressure, even in spite of the action of fire, and that in a region where great compression existed, the absence of causticity was no proof that great heat had not been applied. The discoveries of Dr BLACK, therefore, mark an era, before which men were not qualified to judge of the nature of the powers that had acted in the consolidation of mineral substances. Those discoveries were, indeed, destined to produce a memorable change in chemistry, and in all the branches of knowledge allied to it; and have been the foundation of that brilliant progress, by which a collection of practical rules, and of insulated facts, has in a few years risen to the rank of a very perfect science. But even before they had explained the nature of carbonic gas, and its affinity to calcareous earth, I am not sure but that Dr Hutton's theory was, at least, partly formed, though it must certainly have remained, even in his own opinion, exposed to great difficulties. His active and penetrating genius soon perceived, in the experiments of his friend, the solution of those difficulties, and formed that happy combination of principles, which has enabled him to explain the most enigmatical appearances in the natural history of the earth.

As we are not yet far removed from the time when our chemical knowledge was too imperfect to admit of a satisfactory explanation of the phenomena of mineralogy, so it is not unlikely that we are approaching to other discoveries that are to throw new light on this science. It would, however, be to argue strangely to say, that we must wait till those discoveries are made before we begin any theoretical reasonings. If this rule were followed, we should not know where the imperfections of our science lay, nor when the remedies were found out, should we be in a condition to avail ourselves of them. Such conduct would not be caution, but timidity, and an excess of prudence fatal to all philosophical inquiry.

458. The truth, indeed, is, that in physical inquiries, the work of theory and observation must go hand in hand, and ought to be carried on at the same time, more especially if the matter is very complicated, for there the clue of theory is necessary to direct the observer. Though a man may begin to observe without any hypothesis, he cannot continue long without seeing some general conclusion arise; and to this nascent theory it is his business to attend, because, by seeking either to verify or to disprove it, he is led to new experiments, or new observations. He is led also to the very experiments and observations that are of the greatest importance, namely, to those _instantiæ crucis_, which are the _criteria_ that naturally present themselves for the trial of every hypothesis. He is conducted to the places where the transitions of nature are most perceptible, and where the absence of former, or the presence of new circumstances, excludes the action of imaginary causes. By this correction of his first opinion, a new approximation is made to the truth; and by the repetition of the same process, certainty is finally obtained. Thus theory and observation mutually assist one another; and the spirit of system, against which there are so many and such just complaints, appears, nevertheless, as the animating principle of inductive investigation. The business of sound philosophy is not to extinguish this spirit, but to restrain and direct its efforts.

459. It is therefore hurtful to the progress of physical science to represent observation and theory as standing opposed to one another. Bergman has said, "Observationes veras quàm ingeniosissimas fictiones sequi præstat; naturæ mysteria potius indagare quàm divinare."

If it is meant by this merely to say, that it is better to have facts without theory, than theory without facts, and that it is wiser to inquire into the secrets of nature, than to guess at them, the truth of the maxim will hardly be controverted. But if we are to understand by it, as some may perhaps have done, that all theory is mere fiction, and that the only alternative a philosopher has, is to devote himself to the study of facts unconnected by theory, or of theory unsupported by facts, the maxim is as far from the truth, as I am convinced it is from the real sense of Bergman. Such an opposition between the business of the theorist and the observer, can only occur when the speculations of the former are vague and indistinct, and cannot be so embodied as to become visible to the latter. But the philosopher who has ascended to his theory by a regular generalization of facts, and who descends from it again by drawing such palpable conclusions as may be compared with experience, furnishes the infallible means of distinguishing between _perfect science_ and _ingenious fiction_. Of a geological theory that has stood this double test of the analytic and synthetic methods, Dr Hutton has furnished us with an excellent instance, in his explanation of granite. The appearances which he observed in that stone led him to conclude, that it had been melted, and injected while fluid, among the stratified rocks already formed. He then considered, that if this is true, veins of granite must often run from the larger masses of that stone, and penetrate the strata in various directions; and this must be visible at those places where these different kinds of rock come into contact with one another. This led him to search in Arran and Glentilt for the phenomena in question; the result, as we have seen, afforded to his theory the fullest confirmation, and to himself the high satisfaction which must ever accompany the success of candid and judicious inquiry.

460. It cannot, however, be denied, that the impartiality of an observer may often be affected by system; but this is a misfortune against which the want of theory is not always a complete security. The partialities in favour of opinions are not more dangerous than the prejudices against them; for such is the spirit of system, and so naturally do all men's notions tend to reduce themselves into some regular form, that the very belief that there can be no theory, becomes a theory itself, and may have no inconsiderable sway over the mind of an observer. Besides, one man may have as much delight in pulling down, as another has in building up, and may choose to display his dexterity in the one occupation as well as in the other. The want of theory, then, does not secure the candour of an observer, and it may very much diminish his skill. The discipline that seems best calculated to promote both, is a thorough knowledge of the methods of inductive investigation; an acquaintance with the history of physical discovery; and the careful study of those sciences in which the rules of philosophising have been most successfully applied.

FINIS.

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Transcriber Note

Minor typos corrected. Some differences in application of accents and formatting were left as printed.