instructive proof, how little the researches of inductive science are liable to be influenced by the wanderings of Imagination, in those regions which human reason is not permitted to explore, Whatever our opinion concerning the unknown physical or metaphysical cause of gravitation may be, our reasonings concerning the System of Nature will be equally just, provided only we admit the general fact, that bodies tend to approach each other with a force varying with their mutual distances, according to a certain law. The case is precisely similar with respect to those conclusions concerning the Mind, to which we are fairly led by the method of Induction, They rest upon a firm and indisputable basis of their own; and (as I have elsewhere remarked) are equally compatible with the metaphysical creeds of the Materialist and of the Berke, leian. *

The hypothesis which assumes the existence of a subtle fluid in the nerves, propagated by their means from the brain to the different parts of the body, is of great antiquity; and is certainly less repugnant to the general analogy of our frame, than that by which it has been supplanted. How very generally it once prevailed, may be inferred from the adoption into common speech of the phrase animal spirits, to denote that unknown cause which (according to Johnson's definition) "gives vigour " or cheerfulness to the mind ;"—a phrase for which our language does not, at this day, afford a convenient substitute. The late Dr Alexander Monro (one of the most cautious and judicious of medical inquirers) speaks of it as a fact which appeared to him to be almost indisputable. "The existence of a "liquid in the cavities of the nerves, is supported by little short "of demonstrative evidence."-See some observations of his, published by Cheselden in his Anatomy.

II. Intimately connected with the physiological hypothesis of the Hartleian school, is their metaphysical theory of Association, from which single principle they boast to have explained synthetically all the phenomena of the Mind. In Dr Priestley's Remarks on Reid's Inquiry, there is an attempt to turn into ridicule, by what the author calls a Table of Dr Reid's Instinctive Principles, the application of the Inductive Logic to these phenomena. How far this Table is faithfully extracted from Dr Reid's book, it is unnecessary to consider at present. Supposing, for the sake of argument, that the Twelve Principles enumerated by Priestley had been actually stated by his antagonist as instinctive principles, or as general laws of our nature, it is difficult to see for what reason the enumeration should be regarded as absurd, or even as unphilosophical, after the explanation given by Reid himself of the sense

The hypothesis of Vibrations first attracted public notice in the writings of Dr William Briggs. It was from him that Sir Isaac Newton derived his anatomical knowledge; along with which he appears plainly, from his Queries, to have imbibed also some of the physiological theories of his preceptor..

In the Monthly Review for 1808, I observe the following passage: "For the partiality which he (Dr Cogan) shews to "Dr Reid, we may easily account, as being a just tribute to the ❝ingenuity and industry of that writer, and to the numerous "valuable observations which enrich his works, unconnected "with his crude hypothesis on the subject of the Human Mind."

In what part of Dr Reid's writings is this crude hypothesis proposed ?

*The reader will be enabled to form a judgment on this point, by the Note (A) at the end of this Volume.

in which he wished his conclusions to be understood.

"The most general phenomena we can reach, are "what we call Laws of Nature. So that the laws "of nature are nothing else but the most general "facts relating to the operations of nature, which ❝ include a great many particular facts under them. "And if, in any case, we should give the name of a "law of nature to a general phenomenon, which "human industry shall afterwards trace to one more general, there is no great harm done. The most "general assumes the name of a law of nature when "it is discovered; and the less general is contain"ed and comprehended in it." *

In another part of his work, he has introduced the same remark. "The labyrinth may be too intricate, and the thread too fine, to be traced

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through all its windings; but if we stop where "we can trace it no farther, and secure the ground "we have gained, there is no harm done; a quicker eye may in time trace it farther.” †

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In reply to these passages, Priestley observes, that "the suspicion that we are got to ultimate princi

ples, necessarily checks all farther inquiry, and is "therefore of great disservice in philosophy. Let "Dr Reid," he continues, "lay his hand upon his “breast, and say, whether, after what he has writ"ten, he would not be exceedingly mortified to "find it clearly proved, to the satisfaction of all the

* Reid's Inquiry, p. 223, 3d ed.

+ Ibid. p. 9.

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"world, that all the instinctive principles in the "preceding Table were really acquired; and that "all of them were nothing more than so many dif"ferent cases of the old and well-known principle "of Association of Ideas."

With respect to the probability of this supposition, I have nothing to add to what I have stated on the same head, in the Philosophy of the Human Mind; "that, in all the other sciences, the progress of discovery has been gradual, from the less

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general to the more general laws of nature; and “that it would be singular indeed, if, in this science, "which but a few years ago was confessedly in its "infancy, and which certainly labours under many " disadvantages peculiar to itself, a step should all "at once be made to a single principle, compre"hending all the particular phenomena which we "know." *

As the order established in the intellectual world seems to be regulated by laws perfectly analogous to those which we trace among the phenomena of the material system; and as, in all our philosophical inquiries (to whatever subject they may relate), the progress of the mind is liable to be affected by the same tendency to a premature generalization, the following extract from an eminent chemical writer may contribute to illustrate the scope, and to confirm the justness of some of the foregoing reflections.

* Elements, &c. p. 398 (3d edition), where I have enlarged on this point at some length.

"Within the last fifteen or twenty years, several "new metals, and new earths, have been made "known to the world. The names that support "these discoveries are respectable, and the expe"riments decisive. If we do not give our assent to "them, no single proposition in chemistry can for a "moment stand. But whether all these are really

simple substances, or compounds not yet resolved "into their elements, is what the authors themselves "cannot possibly assert; nor would it, in the least, "diminish the merit of their observations, if future "experiments should prove them to have been mis"taken, as to the simplicity of these substances. "This remark should not be confined to later disco"veries; it may as justly be applied to those earths "and metals with which we have been long acquainted.". "In the dark ages of chemistry, the

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object was to rival nature; and the substance "which the adepts of those days were busied to "create, was universally allowed to be simple. In a more enlightened period, we have extended our inquiries, and multiplied the number of the ele"ments. The last task will be to simplify; and, by "a closer observation of nature, to learn from what a "small store of primitive materials, all that we be"hold and wonder at was created." *

This analogy between the history of Chemistry and that of the Philosophy of the Human Mind,

* Inquiries concerning the nature of a metallic substance, lately sold in London as a new Metal, under the title of Palladium. By Rich. Chenevix, Esq.