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,

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.

Conclusion.

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.