spirits. These he imagined to be fine fluids pervading the nerves and brain, which, when an object affects any of our organs, are put in motion, and convey an impression of it up to the pineal gland in the brain, where he fancied the residence of the mind.

Leibnitz maintained that our body and mind had no influence at all on one another :-that the Creator had at first ordained a series of feelings to take place in the mind, in exact accordance with a series of impressions and motions, which he ordained to take place in the body: and that thus the mind and body went like two chronometers, maintaining exact correspondence in all their movements, without in the least degree affecting one another.

Hartley supposed that perception, and all our intellectual operations, took place by means of vibrations in the nerves, which were propagated along them to the brain; or rather he conceived that the nerves and brain were pervaded by a fine ether, which, by its elasticity, was adapted for receiving and transmitting the multiplied vibrations and vibratiuncles which formed the medium, or the elements of sensation and thought. This theory, which was originated by some slight suggestions of Sir Isaac Newton, is based upon the analogy of the laws of sound, as Aristotle's was upon the phenomena of vision. It is stated with much ingenuity by Dr. Hartley, in the first volume

of his work on Man; the principal merit of which consists in the attention he has bestowed upon the association of ideas, to the consideration of which he has contributed to turn the attention of later philosophers. His vibratory theory is utterly untenable.

Malebranche supposed that, when an object is presented to any of our senses, God opens to our minds his idea of the object; and that thus, external things are of no use in causing our sensations, farther than as they serve as memoranda to the Deity, when to give us the sensation or perception, and when not. The design of that worthy Father was to magnify the providential care of God over all his creatures, and to impress a deeper sense of our entire dependence upon him. But for these ends it was not necessary to have recourse to his hypothesis. Truths of such momentous import ought never to be rested on an infirm or uncertain foundation, and can derive no additional strength from such flimsy and precarious props.

Berkeley agreed with Malebranche that ideas are the only objects of perception, but denied that that there is any material world at all.

Hume agreed with Berkeley with regard to the non-existence of matter, but, advancing a step farther, affirmed the world of spirit to be equally unreal and illusory, leaving nothing remaining but trains of impressions and ideas.

Such are the principal theories which have been formed with regard to the mode of our perceptions. Several of them are ingenious, and supported with ability by their authors, but as their day is over, it is unnecessary to spend time at present in exposing their fallacies. Taught by past experience, philosophers now restrict themselves more to the statement of facts, endeavouring to explain these only by patient induction, and accurate analysis; and, although the subject still remains obscure, we have at least the comfort of treading on surer ground.

When an external object is presented to our organs of sense, we have an immediate sensation, which is followed by an instantaneous knowledge or perception of some quality in the object. The philosopher endeavours to explain the manner in which this knowledge is obtained. The first step in the investigation of the subject, must evidently be to examine the corporeal part of the process in sensation. And here the labours of the anatomist and physiologist have already explained the subject, as far, perhaps, as its nature will permit. It is quite unnecessary for me to enter on it. I may only observe, that in all our organs, the sense resides in the nerves. Colours affect the retina, which is an expansion of the optic nerve,-sounds affect the auditory nerve,-odours affect the olfactory nerves,-tastes affect the nervous papillæ of the tongue, and touch depends on the small

branches of nerves which are spread over the whole surface of the body. The proof of this is, that if the nerve, supplying any part of the body, be cut or destroyed, that part loses the power of sensation, and also, that any injury of a nerve is attended with violent pain. To prevent the confusion arising from unnecessary circumlocution, the general word impression is employed to denote any affection of the nerves of any organ, produced by the application of something external.

But this is conceived by writers on the subject to be but the first step in the investigation of a long process. In sensation, say they, there is an impression made on the nerves, and conveyed along them in some mysterious way to the brain, where it is felt by the mind there present. To me, I confess, this appears not only a mere hypothesis, but also an extremely useless, and I will venture to say an extremely pernicious one. No probable way has yet been discovered by which the impression could be conveyed to the brain: and the only assignable reason that I can find for the anxiety of philosophers to discover one, is that they have laid it down as an established principle, that the mind resides in the brain. This proposition requires proof. The spinal marrow and nerves are apparently of the same substance with the brain, and, therefore, if the latter be regarded as immediately in connection with the mind, the two former may have some claim to be considered as

also standing immediately in connection with the mind, as much so at least as any part of the brain.* Here I may state that I deem it better to say that the mind is immediately in connection with the brain, spinal marrow, or nerves, than to say that it resides in them. The latter is a mode of expression more popular than philosophical. Ideas of extension are apt to be associated with it, and these are certainly not much in unison with the best notions of spirit which we are capable of attaining.

If it be said that the necessity of the conveyance of the impression to the brain, appears from the fact before noticed, that, if the nerve supplying any part be cut, that part loses the power of sensation, which can only be accounted for by supposing that sensations are not communicated to the mind by the nerves, except through the medium of the brain, the fact is undeniable, but the deduction from it is purely hypothetical. The use of this fact is to prove that the medullary substance is the immediate seat or instrument of sensation, and not to prove the reverse of this, in reference to

* Dr. Brown (and I am happy in being able to call in the single authority of so great a name) considers the brain, spinal marrow, and nerves, as together constituting the sensorial organ, and very modestly states it as his conjecture, that the conveyance of the impression to the brain may be quite unnecessary. He has made some excellent observations upon the subject in his nineteenth Lect.