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some other guiding authority than simply that of natural analogies, suggested and supported by the habitual recurrence to the sole test and standard of experimental evidence.
From the influence of the same cause, even in comparatively modern times, it required a long struggle to divest chemistry of that chimerical theory of combustion, whose advocates imagined "phlogiston," a sort of metaphysical something, they knew not what, which conferred on bodies the property of being combustible, and was abstracted during the process.
In this recurrence to principles alien from those of induction, we find the radical defect common to the ancient as well as the modern scholastic theories. This was the fundamental mistake which vitiated alike the system of the peripatetics and the Hutchinsonians; which upheld the crystalline spheres and the ætherial vortices-the starry influences and the diluvial cataclysms; the cosmogonists' chaos and the philosophers' stone.
It was to guard against such erroneous modes of speculation, that Bacon, in his Novum Organon, dwelt so earnestly on the principal sources of error which had arisen, or were likely to arise, in philosophical speculation, from the neglect of those just rules and principles. The several chief causes of mistake, which lead men into unsubstantial and delusive theories, classified under their respective heads, are what he designates in his somewhat
fanciful, but abundantly expressive, language, by the name of "Idola," the false divinities which the mind is apt to raise as the objects of its adoration, when it ought to be engaged in the sole worship of truth.
It is far from my design here to enter into any discussion of those sources of false philosophy. The excellence of Bacon's suggestions, as well as their importance, not merely for the guidance of the philosophical inquirers of his day, but as involving the correction of mistaken ideas, likely to be perpetually recurring, will be recognised by all who have examined his immortal work and it will be the less necessary for me to insist on them here, since I have elsewhere placed them in a light accessible to the general reader*.
I will merely remark here, that the class termed "Idola theatri," seems to include the chief source of error to which I am here more especially referring : the adoption of artificial systems, founded on an assumption either of fallacious physical principles, or of any whatsoever not physical: the former being essentially false, the latter, however good in their own way, utterly inapplicable to the purposes of physical inquiry.
* See "History of Physical Science," Cabinet Cyclopædia,
Objections to Physical Inquiries.
It is from such an erroneous assumption of first principles that most of the prejudices and misconceptions against sound physical conclusions take their origin. Hence originates the charge of presumption in scientific inquiries; hence the accusation of arrogance brought against the deductions of the physical inquirer, especially if they happen to stand in opposition to the preconceived notions and cherished prejudices of mankind, which are in reality far more presumptuous; hence the exclamations against the "pride of science," and the hostility felt against certain branches of inductive knowledge; while the objector is wholly blind to his own inconsistency in nevertheless accepting and adopting the conclusions of other departments, which are yet built on the very same kind of evidence.
This has been especially the case with geology. From ill-informed, or, too often, prejudiced persons, we hear frequent remarks disparaging the inquiries and conclusions of the geologist, while they allow and applaud the inferences of the astronomer and the chemist; they condemn as visionary and presumptuous the results of the one as to the antiquity of strata, and the successive æras of animal organization, the monuments of which are before their eyes, while they revere as unquestionable truths the most marvellous and paradoxical inferences of the other: which refer to subjects utterly beyond the scope of
the senses, to periods and distances which transcend our arithmetical powers to conceive, and to processes of nature which exceed our faculties to apprehend.
The mathematician in his study puts down a few characters and figures on paper, and then confidently announces that the matter of which Jupiter is composed, weighs somewhat more than one-fifth of the average weight of the materials of the earth: and that of the sun about one-fourth.
The chemist asserts that a bell glass, which appears empty, is, in fact, filled with a peculiar aërial compound; and invisible and impalpable as it may seem, yet is really formed of a vast collection of solid indestructible atoms; and these of more than one kind, aggregated together by the most perfectly regular laws and not only so, but he actually states the numerical ratio in which they are so combined, and what is more, assigns the weights of these ultimate molecules, which no microscope can ever detect, no balance verify: such conclusions, however, are universally accepted, and popularly held forth as among the most certain truths of science.
Yet when the geologist contends that the crust of the earth, with its organized productions, has been gradually brought into its present condition by a series of creative changes, going on through millions of ages, his conclusion is condemned as chimerical and dangerous.
There is a singular partiality shown to some sciences: the world are disposed to admit, without
hesitation, the most inconceivable assertions of the astronomer and optician: they allow the full claims of the powers of the human mind to assign spaces and periods which transcend the flights of the loftiest imagination; to Halley's comet an elliptic orbit whose long diameter is 3,420,000,000 miles, with a period of 75 years; and to a molecule of æther, in a polarized ray traversing a quartz crystal, an elliptic orbit whose long diameter may be about one-5000th of an inch, with a period of about one-500,000,000, 000,000,000th of a second; yet they talk of the arrogance of the geologist in pretending to maintain that millions of years ago the world was going on, governed by the same physical laws which prevail now, and replete with vegetable and animal life in all its varied forms of perfection and adaptation to a state of things, of which the existing order is only one of a series of gradual and regular changes.
The true answer to such objections is found in the question, What sort of reasoning will you adopt and allow in any such inquiries? Upon this the whole depends. Will you be satisfied with the same sort of evidence as that on which we ground any one of the best established laws of physical truth? Or will you contend that each branch of science is to be established on different arbitrary principles from the others? The very essence of all truly philosophic inquiry is to proceed throughout on one common principle of comparison and analogy, to advance from individual facts to classes of facts,