from an apprehension, that we understand the connexion between impulfe and motion, better than any other phyfical fact. From the detail which I have given, it appears how extenfive an influence this prejudice has had on the inquiries both of natural philo. fophers and of metaphysicians.

In the foregoing reafonings, I have taken for granted, that motion may be produced by impulse; and have contented myself with afferting, that this fact is not more explicable, than the motions which the Newtonians refer to gravitation; or than the intercourse which is carried on between the mind and external objects in the cafe of perception. The truth, however, is, that fome of the ableft philofophers in Europe are now fa. tisfied, not only that there is no evidence of motion being in any cafe produced by the actual contact of two bodies; but that very ftrong proofs may be given, of the abfolute impoffibility of such a fuppofi tion and hence they have been led to conclude, that all the effects which are commonly referred to impulfe, arife from a power of repulfion, extending to a fmall and imperceptible distance round every element of matter. If this doctrine fhall be confirmed by future fpeculations in phyfics, it must appear to be a curious circumftance in the hiftory of fcience, that philofophers have been fo long occupied in attempting to trace all the phenomena of matter, and even fome of the phe. nomena of mind, to a general fact, which, upon an accurate examination, is found to have no exiftence,

I do not make this obfervation with a view to depreciate the labours of these philofophers; for, although the system of Bofcovich were completely efta, blished,

blished, it would not diminish, in the smallest degree, the value of thofe phyfical inquiries, which have proceeded on the common hypothefis, with refpect to impulfe. The laws which regulate the communication of motion, in the cafe of apparent contact, are the moft general facts we obferve among the terreftrial phenomena; and they are, of all phyfical events, those which are the most familiar to us, from our earliest infancy. It was therefore not only natural but proper, that philofophers fhould begin their phyfical inquiries, with attempting to refer to thefe, (which are the most general laws of nature, expofed to the examination of our fenfes,) the particular appearances they wished to explain. And, if ever the theory of Bofcovich should be completely established, it will have no other effect, than to refolve thefe laws into fome principle ftill more general, without affecting the folidity of the common doctrine, fo far as it goes.

IT

SECTION III.

Of Dr. Reid's Speculations on the Subject of Perception.

was chiefly in confequence of the fceptical conclufions which Bifhop Berkeley and Mr. Hume had deduced from the ancient theories of perception, that Dr. Reid was led to call them in queftion; and he appears to me to have fhewn, in the moft fatisfactory manner, not only that they are perfectly hypothetical, but that the fuppofitions they involve, are abfurd and impoffible. His reafonings, on this part of our conftitution, undoubtedly form the

most important acceffion which the philofophy of the human mind has received fince the time of Mr. Locke.

But although Dr. Reid has been at much pains to overturn the old ideal system, he has not ventured to substitute any hypothesis of his own in its place. And, indeed, he was too well acquainted with the limits prescribed to our philofophical inquiries, to think of indulging his curiofity, in fuch unprofitable fpeculations. All, therefore, that he is to be understood as aiming at, in his inquiries concerning our perceptive powers, is to give a precise state of the fact, divested of all theoretical expreffions; in order to prevent phi lofophers from impofing on themselves any longer, by words without meaning; and to extort from them an acknowledgment, that, with refpect to the process of nature in perception, they are no lefs ignorant than the vulgar.

According to this view of Dr. Reid's reafonings, on the fubject of perception, the purpose to which they are fubfervient may appear to fome to be of no very confiderable importance; but the truth is, that one of the most valuable effects of genuine philofophy, is to remind us of the limited powers of the human understanding; and to revive those natural feelings of wonder and admiration, at the fpectacle of the universe, which are apt to languifh, in confequence of long familiarity. The most profound difcoveries which are placed within the reach of our researches lead to a confeffion of human ignorance; for, while they flatter the pride of man, and increase his power, by enabling him to trace the fimple and beautiful laws by which phyfical events are regulated, they call his attention,

at

at the fame time, to thofe general and ultimate facts which bound the narrow circle of his knowledge; and which, by evincing to him the operation of powers, whofe nature must for ever remain unknown, ferve to remind him of the infufficiency of his faculties to penetrate the fecrets of the univerfe. Wherever we direct our inquiries; whether to the anatomy and phyfiology of animals, to the growth of vegetables, to the chemical attractions and repulfions, or to the motions of the heavenly bodies; we perpetually perceive the effects of powers which cannot belong to matter. To a certain length we are able to proceed; but in every research, we meet with a line, which no induftry nor ingenuity can pafs. It is a line too, which is marked with fufficient diftinctnefs; and which no man now thinks of paffing, who has just views of the nature and object of philofophy. It forms the feparation between that field which falls under the furvey of the phyfical inquirer, and that unknown region, of which, though it was neceffary that we fhould be affured of the existence, in order to lay a foundation for the doctrines of natural theology, it hath not pleafed the Author of the universe to reveal to us the wonders, in this infant state of our being. It was, in fact, chiefly by tracing out this line, that Lord Bacon did fo much fervice to science.

Befide this effect, which is common to all our philofophical pursuits, of impreffing the mind with a fenfe of that mysterious agency, or efficiency, into which general laws must be refolved; they have a tendency, in many cafes, to counteract the influence of habit, in weakening those emotions of wonder and of curiofity, 6

which

which the

appearances of nature are so admirably fitted to excite. For this purpofe, it is neceffary, either to lead the attention to facts which are calculated to ftrike by their novelty, or to prefent familiar appearances in a new light and fuch are the obvious effects of philofophical inquiries; fometimes extending our views to objects which are removed from vulgar obfervation; and fometimes correcting our first apprehenfions with refpect to ordinary events.-The communication of motion by impulfe, (as I already hinted,) is as unaccountable as any phenomenon we know; and yet, moft men are disposed to confider it, as a fact which does not refult from will, but from neceffity. To fuch men, it may be useful to direct their attention to the univerfal law of gravitation; which, although not more wonderful in itself, than the common effects of impulfe, is more fitted, by its novelty, to awaken their attention, and to excite their curiofity. If the theory of Bofcovich fhould ever be established on a satisfactory foundation, it would have this tendency in a still more remarkable degree, by teaching us that the communication of motion by impulfe, (which we are apt to confider as a neceffary truth,) has no existence whatever; and that every cafe in which it appears to our fenfes to take place, is a phenomenon no lefs inexplicable, than that principle of attraction which binds together the most remote parts of the universe.

If fuch, however, be the effects of our philofophical pursuits when fuccefsfully conducted, it must be confeffed that the tendency of imperfect or erroneous theories is widely different. By a fpecious folution of

infuperable