science is founded. By analogy he argues that all flames will burn him, he argues from like to like, he generalizes and draws an inference; and I conceive it is by this analogical reasoning that all science is advanced. The inference which

he thus draws a priori, is merely an hypothesis, vπódeσiç, a supposition, probable indeed, but far from satisfactory. But when he brings it to the test of induction, and collects experiments, he either confutes or proves this hypothesis, or limits it to something not quite so general.

This analogical reasoning, when it is extended only from individual to individual of the same species, is commonly called experience, and not analogy; and from the perfect uniformity of nature, perhaps not improperly thus, we say, we know by experience that all stones gravitate to the earth. But when we extend it from species to species of the same genus, it is analogy, properly so called. If from the gravitation of all stones we reason to

that of earths, we reason by analogy, from like to like: we obtain a probable inference, not satisfactory till experiment be directed successively to individuals of the different species of earths, and thereby the inference converted into a conclusion. Having thus included earths as well as stones, we may proceed from one species to another by the same process of analogy and proof, till all bodies upon the surface of the earth be included under the general law of gravitation, whence we may rise to more general propositions. I am inclined to think that such has been the common process of discovery in all ages of the world.

When Sir Isaac Newton, from the fall of an apple, was led to the consideration of the moon's gravity, he is said to have made the discovery by Induction; which is true as far as the proof of it went. But, it is manifest, that, at first, he merely formed a probable hypothesis by Analogy, and then laboriously brought it to the

test of observation; and it is highly probable that the hypothesis he formed was, that the moon gravitated to the earth with a constant force, instead of a force varying inversely as the square of the distance; which was the result of another hypothesis, suggested by the elliptic orbits of the planets, and the force necessary to confine the motion of a projectile in such an orbit.

When Harvey observed the valves in the veins, he is commonly said to have made the discovery of the circulation of the blood by reasoning from final causes, or by asking of nature for what purpose such valves could be intended: but, perhaps he might have asked the question for ever, unless the resemblance between the valve of a vein and that of a pump had suggested a plausible hypothesis, in which he was confirmed by repeated experiments and observations directed to the point.

Analogy, so much slighted and over

looked, and to which such an inferior part in the advancement of science has been assigned, and that too with so much suspicious caution, appears to me to be the great instrument of generalization and invention, by which hypotheses are supplied, which are most commonly the subjects that call for the exercise of Induction. By Induction, as usually understood, we make it a rule to exclude all hypotheses: first of all, we collect the experiments, and, having obtained these, we are next to examine them and compare them; we then reject the irrelative and negative, and conclude upon the affirmatives that are left. By this means, says Lord Bacon, we question nature, and conclude upon her answers: yet I would venture to suggest, that, ninetynine times out of a hundred, the Analogy or comparison precedes the collection of the experiments: some resemblance is observed, some hypothesis is started, which is the subject that is brought to

the test of Induction. By this the hypothesis is either proved, or confuted, or more commonly limited to something less general.

I would not be understood to assert that the common inductive method is barren; for, no doubt, discoveries might be so made; but I really question whether a discovery was ever made according to its rules, which the discoverer had not, in his own mind, anticipated by Analogy as an hypothesis long before he had completed his investigation, and indeed guided his investigation by it. But, however that may be, it must be admitted, that thousands and thousands of discoveries are made and inventions brought into play, the result merely of analogy and a few experiments, or very commonly of a single experimentum crucis. By the common method proposed we take too wide a range, we embrace the whole subject at once, and require the completion of its natural history; but by