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 philosophy, 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 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 affirmationbut, 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 intole

rant 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 on 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 plausibility around his

speculation. He might pass from the botany of the different regions of the globe that we inhabit, and make his loose and confident applications to each of the other planets, according to its distance from the sun, and the inclination of its axis to the plane of its annual revolution; and out of some such slender materials, he may work up an amusing philosophical romance, full of ingenuity, and having, withal, the colour of truth and of consistency spread over it.

I can conceive how a superficial public might be delighted by the eloquence of such a composition, and even be impressed by its arguments; but were I asked, which is, the man of all the ages and countries in the world, who would have the east respect for this treatise on the plants which grow on the surface of Jupiter, I should be at no loss to answer the question. I should say, that it would be he who had computed the motions of Jupiter-that it would be he who had measured the bulk and the density of Jupiter-that it would be he who had estimated the periods of Jupiter-that it would be