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from some characteristic apparent in one such class to seize upon an analogy with another; to argue from the known to the unknown; to trace the indications of uniformity; to perceive the points of parallelism even in the midst of circumstances the most dissimilar.
Reasonings, then, like those we have above referred to, as assigned for the explanation of existing and observed effects, are not only rational but unavoidable. Theories of this kind must be referred to, because they are the only kind cognisable in real physical inquiry. We have only the alternative of adopting these, or renouncing all inductive research.
THE results of science, however remote from ordinary apprehensions, however inconceivable some of the ideas they may involve, however at variance with received notions, are yet not only rational and logical, but absolutely unavoidable and undeniable, so long as we only consent to reason in all cases alike; so long as we only confine ourselves to arguing from the known to the unknown by rational induction; and pursue only the real analogies which are everywhere traceable in the operations of nature, and which we never fail to find continually amplifying and enlarging, confirming and corroborating, each other, at every step of our progress.
By this mutual confirmation of concurring trains of investigation, the evidence of each is enhanced in a continually increasing ratio. The connexion between whole classes of facts by such analogies, augments to an incalculable degree an assurance of their truth; and we advance with a confidence equal to that inspired by demonstration, to many of the most apparently remote conclusions of science: yet with a force of evidence which legitimately demands the abandonment of preconceived notions, and the surrender of long-cherished prejudices, if at variance with those conclusions. This advance and progression from one train of analogy to another is, in fact, the main characteristic which has distinguished the science of the moderns from that of the ancients. It is this increasing and accumulating evidence of uniformity throughout nature, which has been the main cause of the rapid and sure progress of modern science. It has been from following, under the guidance of such principles, the humble and unpretending path of induction, that all its most sublime inferences have been established.
I have dwelt more particularly on these topics, because they seem to be too much overlooked by those who take upon them to disparage the conclusions of some branches of physical philosophy; and it becomes peculiarly necessary to urge upon their consideration that the evidence is of one and the same kind in all branches: a whole science must not be objected to because it relies solely upon such inductive proofs as it has been our object to explain, and utterly discards and disowns all other authority. If the foundations of one science are to be so assailed, all the others must be involved: all the branches of physical inquiry must stand or fall together on the common ground of their inductive evidence. If the conclusions of the geologist are in principle and method fallacious, those of the astronomer and the chemist must be rejected on the same ground. If causes assigned in conformity to the entire series of natural analogies are to be rejected in one case, the whole principle, method, and system of reasoning on such analogies must be given up.
THE NATURE OF PHYSICAL TRUTH.
CAUSE AND EFFECT.
“ Certainly if the explaining a phenomenon be to assign its proper
efficient and final cause, it should seem the mechanical philosophers never explained any thing; their province being only to discover the laws of nature; that is, the general rules and method of motion; and to ACCOUNT FOR particular phenomena, by REDUCING THEM UNDER, or showing their conformity to such GENERAL RULES."
Bishop BERKELY, (Siris, p. 108.)
“ Si l'on considére avec attention la série des objets de même nature, on aperçoit entre eux et dans leurs changemens, des rapports et des lois, qui se manifestent de plus en plus à mesure que la série se prolonge, et qui, en s’etendant et se generalisant sans cesse, conduisent enfin AU PRINCIPE DONT ILS DEPENDENT.”-LAPLACE.
In the foregoing discussion, we have endeavoured to trace and analyse the nature of our conviction of the truth and regularity of the laws which prevail in the material world. We have noticed the natural tendency of our minds to generalize; the intuitive belief in the permanence and uniformity of physical laws; and the immense force of evidence with which analogy addresses itself to our conceptions. These intellectual phenomena harmonise most accurately with what we find by every experimental confirmation to be the actual state of things in the external order of nature. And the certainty with which we thus rely on the invariable truth of sound physical research arises from such a combination of concurrent testimony as to possess a force wholly irresistible even to the most sceptical, and full of the most sublime satisfaction to every well-ordered mind.
By the establishment of correct trains of analogy, the inductive philosopher connects the near and the remote, the minute and the immense, the present, the past, and the future. He argues from the laws of motion on the surface of the earth to those which prevail in the most distant regions of the heavens. He reasons from the forces which act between the minutest molecules, to those which connect sidereal systems. He extends his deductions from spaces subject to measurement under his hands to the most inconceivably remote distances; from æras of human date to the immensity of past duration. He advances from causes which he can put in operation, to those which affect the most immense masses; from action in sensible space and time, to that which belongs to molecules and periods of absolutely unimaginable minuteness; from changes now in progress, he infers those of past epochs; and from the work of actual alterations on the earth's surface computes the succession of those of which he traces the existing monuments. In the midst of the apparent irregularities of the