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to raise geological speculations must, on every ground, be utterly at variance with sound inductive principles.
Inductive Character of Geology.
In the illustrations above given, I have enlarged on those selected from geology in particular, with reference to objections often brought against that branch, as if it were of a less strictly inductive character than others. This, I conceive, is an idea which must totally vanish before the slightest real examination of the nature of the reasoning employed by any sound geologists; though it may be freely admitted that most extravagant speculations have occasionally been obtruded on the world under the name of geological theories. Yet these, the moment they are critically examined, are found to be defective, not merely in their details, but in the assumption of their first principles, and the very method by which the investigations are conducted. Among sound and rational geologists, whatever difference may exist as to certain theoretical views, none whatever can subsist as to the sole recognition of strict inductive reasoning, and the utter rejection of all other authority, on which to rest their conclusions.
Some persons have indeed been urgent in denying to geology the claim to be ranked among the exact sciences, and have appealed to the authority of great names in support of their assertion, having all
the while a very confused idea of the meaning of an “ exact” science; and imagining that when it has been refused this title, it was meant to withhold from it the character of substantial physical truth and inductive certainty. Whereas it is evident to those who are but moderately conversant with the current scientific language of the day, that the phrase “exact science” has been used solely as designating those branches of physical inquiry which could be brought under the dominion of mathematical laws, and whose results could be exhibited in a numerical form, and compared with theory by arithmetical computation. In this sense undoubtedly geology has not yet become one of the “ exact” sciences; though from the nature of some recent researches* on the effects of mechanical forces such as may be supposed to have acted in the elevations of the various parts of the earth's crust, it would seem to be fast approaching to the condition even of this class of investigations. But, at any rate, this is quite independent of its claim to be received as among the most incontrovertible of those systems of inductive truth which have not as yet been of a nature to receive the aid of mathematical demonstration.
* See the papers of Mr. Hopkins in the Cambridge Transactions.
Objections to Geology. I HAVE felt it desirable to dwell the more particularly on the strictly inductive character of geology, not only on general grounds, but more especially because much pains and some ingenuity have been employed to disparage and even deny the evidence of this science*. To some such objections we have already referred; and the rest are not more rational or more consistent. When refuted on other grounds, their upholders take refuge in the convenient maxim, that after all, geology is but in its infancy, and as many theories once adopted have now been rejected, so those now in vogue may be in their turn exploded : or again, they contend that the utmost extent of our researches has not penetrated beyond the mere crust of the earth, how then can we pretend to draw such general conclusions ?
If the science be in its infancy, we can only say that it has displayed such vigour as already to have grappled with and overcome the most formidable attacks. False theories have indeed been exploded; but the order of advance has been regular and systematic; the early cosmogonical speculations have indeed been discarded, for the simple reason that they were not founded on induction, but on some foreign principle or authority, and therefore had no substantial or enduring consistency. A remnant of the same spirit, however, continued
* See Note B.
to linger about the schools of geology, and displayed itself in later times in the diluvial hypothesis, and others of the same nature. These, in their various modifications, have since given way, and for the very same reason, because their foundation was defective; it was based on some other authority than that of simple induction. So the belief in vast and sudden revolutions in the state of the entire globe has been discarded; the inductive principle is extending its triumphs, and if all the phenomena presented by the observed state of the earth's surface have not been actually explained by the action of known causes, yet many have been which were before not perceived to be capable of such explanation; and it has become generally admitted that this is the only sound method to be pursued in the endeavour to throw any real light upon them.
In this way, and in this steady course of advance from the hypothetical to the matter-of-fact, may geological theories come to be successively modified, but in no other. Those who make this a topic of objection must, therefore, prepare themselves to expect, in the changes they may anticipate, nothing favourable to any preconceived hypotheses, but every thing tending still more and more to take a direction entirely opposed to those favourite schemes of cosmogony which have usually prompted these and the like objections.
And if, as the objectors urge, we have penetrated as yet only a thin film, as it were, of the mere outward crust of the earth, how completely does the obvious inference recoil on themselves! If by going only to this trifling extent, we have succeeded in obtaining such a mass of evidence, and substantiating such vast and overpowering conclusions, what may not result when our inquiries shall be able to penetrate still deeper ?
The introduction of imaginary systems of cosmogony into geology, is but an exemplification of the same fallacious principles of speculation, by which every branch of physical inquiry has, in its turn, been impeded and perverted. It was in the same spirit that Kepler believed the globe to be a living animal: that Tycho Brahe feigned the sun with his attendant planets to revolve round the earth: and that the equilibrium of the mercury in the barometer, was ascribed by Linus to a suspension by invisible threads.
False Philosophy from neglect of Analogy
THE same want of inductive principles, the same spirit of gratuitous theorizing, which prevailed in the disputations of the schoolmen, characterized in no less degree the speculations of Descartes and his followers, which in a later age took their place. The main error which pervaded the whole system of that eminent philosopher, was the adoption of a metaphysical basis, on which to rear the edifice of physical truth. Or, in a word, the introduction of