at the same 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, whose nature must for ever remain unknown, serve to remind him of the infufficiency of his faculties to penetrate the fecrets of the universe. 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 juft 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 should be affured of the existence, in order to lay a foundation for the doctrines of natural theology, it hath not pleased the Author of the universe to reveal to us the wonders, in this infant ftate of our being. It was, in fact, chiefly by tracing out this line, that Lord Bacon did fo much service 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, many cases, to counteract the influence of habit, in weakening those emotions of wonder and of curiofity, 6

in

which

which the appearances of nature are so admirably fitted to excite. For this purpose, it is neceffary, either to lead the attention to facts which are calculated to strike 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 impulse, (as I already hinted,) is as unaccountable as any phenomenon we know; and yet, most men are difpofed 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 should ever be established on a fatisfactory 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 case 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

infuperable difficulties, they fo dazzle and bewilder the understanding, as, at once, to prevent us from ad, vancing, with steadiness, towards the limit of human knowledge; and from perceiving the existence of a region beyond it, into which philofophy is not permitted to enter, In fuch cafes, it is the business of genuine science to unmask the imposture, and to point out clearly, both to the learned and to the vulgar, what reafon can, and what fhe cannot, accomplish. This, I apprehend, has been done, with refpect to the history of our perceptions, in the most fatisfactory manner, by Dr. Reid.When a perfon little accuftomed to metaphyfical speculations is told, that, in the cafe of volition, there are certain invifible fluids, propagated from the mind to the organ which is moved; and that, in the cafe of perception, the existence and qualities of the external object are made known to us by means of species, or phantafms, or images, which are present to the mind in the fenforium; he is apt to conclude, that the intercourse between mind and matter is much less mysterious than he had supposed; and that, although thefe expreffions may not convey to him any very distinct meaning, their import is perfectly understood by philofophers. It is now, I think, pretty generally acknowledged by phyfiologifts, that the influence of the will over the body, is a mystery which has never yet been unfolded; but, fingular as it may appear, Dr. Reid was the first perfon who had courage to lay completely afide all the common hypothetical language concerning perception, and to exhibit the difficulty in all its magnitude, by a plain statement of the fact. To what then, it may be afked, does this statement

statement amount?-Merely to this; that the mind is fo formed, that certain impreffions produced on our organs of fenfe by external objects, are followed by correfpondent fenfations; and that these fenfations, (which have no more refemblance to the qualities of matter, than the words of a language have to the things they denote,) are followed by a perception of the existence and qualities of the bodies by which the impreffions are made; that all the steps of this process are equally incomprehenfiblé; and that, for any thing we can prove to the contrary, the connexion between the fenfation and the perception, as well as that between the impreffion and the fenfation, may be both arbitrary that it is therefore by no means impoffible, that our fenfations may be merely the occafions on which the correfpondent perceptions are excited; and that, at any rate, the confideration of these fenfations, which are attributes of mind, can throw no light on the manner in which we acquire our knowledge of the existence and qualities of body. From this view of the fubject, it follows, that it is external objects themfelves, and not any species or images of these objects, that the mind perceives; and that, although, by the conftitution of our nature, certain fenfations are rendered the conftant antecedents of our perceptions, yet it is juft as difficult to explain how our perceptions are obtained by their means, as it would be, upon the fuppofition, that the mind were all at once infpired with them, without any concomitant fenfations what

ever.

These remarks are general, and apply to all our various perceptions; and they evidently ftrike at the

root

root of all the common theories upon the fubject The laws, however, which regulate these perceptions, are different in the cafe of the different fenfes, and form a very curious object of philofophical inquiry.Thofe, in particular, which regulate the acquired per. ceptions of fight, lead to fome very interesting and important speculations; and, I think, have never yet been explained in a manner completely fatisfactory. To treat of them in detail, does not fall under the plan of this work; but I fhall have occafion to make a few remarks on them, in the chapter on Conception.

In oppofition to what I have here obferved on the importance of Dr. Reid's fpeculations concerning our perceptive powers, I am fenfible it may be urged, that they amount merely to a negative discovery; and it is poffible, that fome may even be forward to remark, that it was unneceffary to employ fo much labour and ingenuity as he has done, to overthrow an hypothesis of which a plain account would have been a fufficient refutation. To fuch perfons, I would beg leave to fuggeft, that, although, in confequence of the jufter views in pneumatology, which now begin to prevail, (chiefly, I believe, in confequence of Dr. Reid's writings,) the ideal fyftem may appear to many readers un. philofophical and puerile; yet the cafe was very different when this author entered upon his inquiries: and I may even venture to add, that few positive difcoveries, in the whole history of science, can be mentioned, which found a jufter claim to literary reputation, than to have detected, fo clearly and unanfwer ably, the fallacy of an hypothefis, which has de fcended