centre being affected, and does not depend on the formation of an image on the retina, we have no alternative but to admit that the retinal affection is transformed by the Sensational Centre, and there the impression first becomes a sensation.

It may be added as confirmation of the foregoing doctrine respecting the centre as the seat of sensation, that Müller has cited examples of luminous spectra being excited by internal causes after the complete destruction of the retina; and "Luicke relates the case of a patient who, after the extirpation of the eye for fungoid disease, perceived all kinds of luminous appearances independently of external objects."*

When therefore it is asked, Why do we see objects erect, when they throw inverted images on the retina? the answer is, Because we do not see the retinal image at all; we see, or are affected by, the object; and our perception of the erectness of that object does not depend on vision, but on our conceptions of space and the relations of space-which are not given in the visual sensation, but are ideal conceptions: conceptions which are acquired in a complicated series of inferences, according to most philosophers; which are "forms of thought," according to Kant; but which are by no school held to be immediate elements of sensation.

We thus return to the position that in every act of consciousness the impression on the nerve becomes transformed into a sensation only in the Sensational Centre; and the old theories of “eidola,” “images," "impressions," are seen to be untenable. Just as the crystals of sugar have to be decomposed, and the sugar transformed into glucose, the glucose transformed into lactic acid, before sugar can be assimilable in the organism, so have the retinal images to be decomposed in the optic centre before a visual sensation can be produced. Attempt a more direct. process, and failure is inevitable: cane-sugar injected into the veins is expelled in the urine as a foreign substance, not assimila

* Müller, Physiology, Eng. Trans. i. 1072.

ble; and, in like manner, the most dexterous adjustment of rays of light falling immediately on the optic ganglion, not transmitted thereto by the optic nerve, would produce no visual sensation.

Does not this demonstrate the purely subjective nature of all our knowledge, and the necessary admixture of the ideal element in all perception? It also demonstrates the futility of the theory adopted by Hartley and Darwin, which attempts to explain mental phenomena by "vibrations" and "motions." Motion can only be motion, it cannot be the specific phenomena we name. sensation. To call sensations and ideas by the vague name of motions, is to violate the conditions of philosophic language, and to mislead those who accept it into the belief that an explanation has been given in the change of term. That Darwin was by it misled into absurdity will be apparent in the following attempt to explain perception:

"No one will deny," he says, "that the medulla of the brain and nerves has a certain figure; which, as it is diffused through nearly the whole of the body, must have nearly the figure of that body. Now it follows that the spirit of animation, or living principle, as it occupies this medulla and no other part, has also the same figure as the medulla . . . which is nearly the figure of the body. When the idea of solidity is excited, a part of the extensive organ of touch is compressed by some external body, and this part of the sensorium so compressed exactly resembles in figure the figure of the body that compressed it. Hence when we acquire the idea of solidity we acquire at the same time the idea of figure; and this idea of figure, or motion of a part of the organ of touch, exactly resembles in its figure the figure of the body that occasions it; and thus exactly acquaints us with this property of the external world."*

He is thus brought back to the old conception of the mind. being "impressed" by the exact forms of objects as wax is impressed by a seal. As he proceeds he gets more and more ab

* Zoonomia, pp. 111-2.

surd. Thus he says, although "there may exist beings in the universe that have not the property of solidity; that is, which can possess any part of space at the same time that it is occupied by other bodies; yet there may be other beings that can assume this property of solidity or disrobe themselves of it occasionally, as we are taught of spirits and of angels; and it would seem that the spirit of animation must be endued with this property, otherwise how could it occasionally give motion to the limbs of animals? or be itself stimulated into motion by the obtrusions of surrounding bodies, as of light or odor ?"* He is led to this by the Spinozistic axiom, that “no two things can influence or affect each other which have not some property common to both of them," which axiom destroys the possibility of spirit acting on body. Hartley, as we saw, tried to get over this difficulty by assuming the existence of a substance intermediate between body and spirit. Darwin finds it easy to assume that the spirit has the power of putting on or putting off the properties of matter just as it pleases. "Hence the spirit of animation at the time it communicates or receives motion from solid bodies must itself possess some property of solidity. And at the time it receives other kinds of motion from light, it must possess that property which light possesses to communicate that motion named Visibility. In like manner it possesses Saporosity, Odorosity, Tangibility, and Audibility."

This is enough to show how little Darwin understood the real value of his luminous idea respecting Psychology based on the laws of life; enough also to make every one understand how philosophers rebelled against such "materialism" as issued from the explanation of mental phenomena by "sensory motions." Before finally quitting the Zoonomia we must pause a moment over the explanation of our feeling for Beauty. He describes the sensations of the babe when "soon after it is born into this cold world it is applied to its mother's warm bosom," and the agree

Zoonomia, p. 114.

† Ibid., i. 115.

able influences which thus grow up in the mind associated with the form of the bosom "which the infant embraces with its hands, presses with its lips, and watches with its eyes; and thus acquires more accurate ideas of the form than of the odor, and flavor, or warmth, which it perceives by its other senses. And hence in our maturer years, when any object of vision is presented to us, which, by its waving or spiral lines, bears any similitude. to the form of the female bosom,-whether it be found in a landscape with soft gradations of rising and descending surface, or in the form of some antique vases, or in the works of the pencil or chisel,-we feel a general glow of delight which seems to influence all our senses; and if the object be not too large, we experience an attraction to embrace it with our arms, and to salute it with our lips, as we did in our early infancy the bosom of our mother.'

One of the happiest illustrations of ridicule being the test of truth, is the reply of Sheridan to this theory of Beauty. "I suppose," said he, "that the child brought up by hand, would feel all these emotions at the sight of a wooden spoon !"

Zoonomia, i. 145.

SEVENTH EPOCH.

SECOND CRISIS: IDEALISM, SKEPTICISM, AND SENSATIONALISM PRODUCING THE REACTION OF COMMON SENSE.

CHAPTER I.

REID.

DUGALD STEWART opens his Account of the Life and Writings of Thomas Reid with remarking that the life was "uncommonly barren of those incidents which furnish materials for biography;" and as our space is scanty, we will content ourselves with a bare enumeration of such facts as may be useful for reference. Thomas Reid was born in 1710, at Strachan in Kincardineshire. He was educated at Marischal College, Aberdeen. In 1752 he occupied the chair of Moral Philosophy in Aberdeen. In 1764 appeared his Inquiry into the Human Mind on the Principles of Common Sense. "In 1763* the Inquiry received a still more substantial testimony of approbation from the University of Glasgow," in the offer of the chair of Moral Philosophy, vacant by the resignation of Adam Smith. In 1780 Reid resigned his office, and passed the remaining years of his life in retirement and study. In 1785 appeared his Essays on the Intellectual Powers. He died in Glasgow in 1796, having survived four of his children.

* We follow Stewart; but there must be some error here. If the Inquiry was not published till 1764, Reid could not in 1763 have been offered the chair at Glasgow as a "testimony of approbation."