not have impressed, on the heavenly bodies, such movements as met his observation. He would not submit his judgment to the reigning systems of the day-for, though they had authority to recommend them, they had no proof: and thus it is, that he evinced the strength and the soundness of his philosophy, as much by his decisions upon those doctrines of science which he rejected, as by his demonstration of those doctrines of science which he was the first to propose, and which now stand out to the eye of posterity as the only monuments to the force and superiority of his understanding.

He wanted no other recommendation for any one article of science, than the recommendation of evidence-and, with this recommendation, he opened to it the chamber of his mind, though authority scowled upon it, and taste was disgusted by it, and fashion was ashamed of it, and all the beauteous speculation of former days was cruelly broken up by this new announcement of the better philosophy, and scattered like the fragments of an aerial vision, over which the past generations of the world had been slumbering their profound and their pleasing reverie. But, on the other hand, should the article of science want the recommendation of evidence, he shut against it all the avenues of his understanding-aye, and though all antiquity lent their suffrages to it, and all eloquence had thrown around it the most attractive brilliancy, and all habit had incorporated it with every system of every seminary in Europe, and all fancy had arrayed it in graces of the most tempting solicitation; yet was the steady and inflexible mind of Newton proof against this whole weight of authority and allurement, and, casting his cold and unwelcome look at the specious plausibility, he rebuked it from his presence. The strength of his philosophy lay as much in refusing admittance to that which wanted evidence, as in giving a place and an occupancy to that which

possessed it. In that march of intellect, which led him onwards through the rich and magnificent field of his discoveries, he pondered every step; and, while he advanced with a firm and assured movement, wherever the light of evidence carried him, he never suffered any glare of imagination or of prejudice to seduce him from his path.

Sure I am, that, in the prosecution of his wonderful career, he found himself on a way beset with temptation upon every side of him. It was not merely that he had the reigning taste and philosophy of the times to contend with; but, he expatiated on a lofty region, where, in all the giddiness of success, he might have met with much to solicit his fancy, and tempt him to some devious speculation. Had he been like the majority of other men, he would have broken free from the fetters of a sober and chastised understanding, and, giving wing to his imagination, had done what philosophers have done after himbeen carried away by some meteor of their own forming, or found their amusement in some of their own intellectual pictures, or palmed some loose and confident plausibilities of their own upon the world. But Newton stood true to his principle, that he would take up with nothing which wanted evidence, and he kept by his demonstrations, and his measurements, and his proofs; and, if it be true that he who ruleth his own spirit is greater than he who taketh a city, there was won, in the solitude of his chamber, many a repeated victory over himself, which should give a brighter lustre to his name than all the conquests he has made on the field of discovery, or than all the splendour of his positive achievements.

I trust you understand, how, though it be one of the maxims of the true philosophy, never to shrink from a doctrine which has evidence on its side, it is another maxim, equally essential to it, never to harbour any doctrine when this evidence is wanting. Take these two

maxims along with you, and you will be at no loss to explain the peculiarity, which, more than any other, goes both to characterise and to ennoble the philosophy of Newton. What I allude to is, the precious combination of its strength and of its modesty. On the one hand, what greater evidence of strength than the fulfilment of that mighty enterprise, by which the heavens have been made its own, and the mechanism of unnumbered worlds has been brought within the grasp of the human understanding? Now, it was by walking in the light of sound and competent evidence, that all this was accomplished. It was by the patient, the strenuous, the unfaultering application of the legitimate instruments of discovery. It was by touching that which was tangible, and looking to that which was visible, and computing that which was measurable, and in one word, by making a right and a reasonable use of all that proof which the field of nature around us has brought within the limit of sensible observation. This is the arena on which the modern philosophy has won all her victories, and fulfilled all her wondrous achievements, and reared all her proud and enduring monuments, and gathered all her magnificent trophies to that power of intellect with which the hand of a bounteous heaven has so richly gifted the constitution of our species.

But, on the other hand, go beyond the limits of sensible observation, and, from that moment, the genuine disciples of this enlightened school cast all their confidence and all their intrepidity away from them. Keep them on the firm ground of experiment, and none more bold and more decisive in their announcements of all that they have evidence for-but, off this ground, none more humble, or more cautious of any thing like positive announcements, than they. They choose neither to know, nor to believe, nor to assert, where evidence is wanting; and they will sit, with all the patience of a scholar to his task, till

they have found it. They are utter strangers to that haughty confidence with which some philosophers of the day sport the plausibilities of unauthorized speculation, and by which, unmindful of the limit that separates the region of sense from the region of conjecture, they make their blind and their impetuous inroads into a province which does not belong to them. There is no one object to which the exercised mind of a true Newtonian disciple is more familiarized than this limit, and it serves as a boundary by which he shapes, and bounds, and regulates, all the enterprises of his philosophy. All the space which lies within this limit, he cultivates to the uttermost, and it is by such successive labours, that every year which rolls over the world, is witnessing some new contribution to experimental science, and adding to the solidity and aggrandizement of this wonderful fabric. But, if true to their own principle, then, in reference to the forbidden ground which lies without this limit, those very men, who, on the field of warranted exertion, evinced all the hardihood and vigour of a full grown understanding, show, on every subject where the light of evidence is withheld from them, all the modesty of children. They give you positive opinion only when they have indisputable proof—but, when they have no such proof, then they have no such opinion. The single principle of their respect to truth, secures their homage for every one position, where the evidence of truth is present, and, at the same time, begets an entire diffidence about every one position, from which this evidence is disjoined. And thus you may understand, how the first man in the accomplishments of phi losophy, which the world ever saw, sat at the book of nature in the humble attitude of its interpreter and its pupil-how all the docility of conscious ignorance threw a sweet and softening lustre around the radiance even of his most splendid discoveries—and, while the flippancy

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of a few superficial acquirements is enough to place a philosopher of the day on the pedestal of his fancied elevation, and to vest him with an assumed lordship over the whole domain of natural and revealed knowledge; I cannot forbear to do honour to the unpretending greatness of Newton, than whom I know not if there ever lighted on the face of our world, one in the character of whose admirable genius so much force and so much humility were more attractively blended.

I now propose to carry you forward, by a few simple illustrations, to the argument of this day. All the sublime truths of the modern astronomy lie within the field of actual observation, and have the firm evidence to rest upon of all that information which is conveyed to us by the avenue of the senses. Sir Isaac Newton never went beyond this field, without a reverential impression upon his mind, of the precariousness of the ground on which he was standing. On this ground, he never ventured a positive affirmation-but, resigning the lofty tone of demonstration, and putting on the modesty of conscious ignorance, he brought forward all he had to say in the humble form of a doubt, or a conjecture, or a question. But, what he had not confidence to do, other philosophers have done after him-and they have winged their audacious way into forbidden regions-and they have crossed that circle by which the field of observation is enclosed-and there have they debated and dogmatized with all the pride of a most intolerant assurance.

Now, though the case be imaginary, let us conceive, for the sake of illustration, that one of these philosophers made so extravagant a departure from the sobriety of experimental science, as to pass from the astronomy of the different planets, and to attempt the natural history of their animal and vegetable kingdoms. He might get hold of some vague and general analogies, to throw an air of