to find his way along streets and lanes, and to houses which he has never seen; to become familiar with the apartments of a house; to know a friend by his voice, or by his tread; to have a thorough understanding of complicated instruments, like pianos and organs, so that he can not only play them, but can tune and repair them, and many other such things. It is related of Laura Bridgman and Julia Brace, both of whom were deaf and blind, that they could distribute the clothes of other inmates of the asylum by the smell, and that one, and I presume both, could converse rapidly with the fingers, could read the books printed in raised letters for the blind, and write very intelligibly.

CHAPTER IV.

NATURE OF THE KNOWLEDGE ACQUIRED BY SENSEPERCEPTION.

als, not of

THE knowledge acquired by sense-perception is of Individuals and never of Classes. We see a tree, a house, an ox, a mountain. We hear a human voice, a Knowledge bird-song, the bray of a donkey, the roar of of individuthe wind, the report of a gun or a cannon. So classes. of the other senses. But let it be carefully noted that we do not think of these several objects as members of classes, though I have used class terms in referring to them. We perceive each of these by itself, and not in any relation whatever to any others as with them constituting groups. How groups or classes are formed will be considered hereafter when we come to the Elaborative Faculties. At present we are concerned about Perception and the nature of the knowledge it gives. This knowledge is only of one and another single object, and by itself would be of only moderate value.

But precisely what do we perceive? It must be remembered that we are now considering Perception, and not knowledge. We see an object before us; we Perception instantly know it to be a horse, or a bush, or a considered man, or a rock, as the case may be. We commonly use the term Perception for this act of the mind; but evidently if we analyze any such cognitions we shall find some other power or powers of the

by itself, and not as co-operating,

with other

powers.

Perception only one of the elements

Cognizes only qualities and not substances.

mind involved. The cognition, undoubtedly, is of the concrete, but this cognition, as I have intimated, is made up of several elements, of which Perception comprises only a part. Perception proper cognizes, of cognition. as it seems to me, only qualities or properties. The mind knows by one instantaneous act, of which Sensation and Perception are elements, the individual object as a whole. The eye is affected by the color of an object; there is at the same instant a perception of an external cause, and a knowledge of the object as colored. The acquired perceptions give, of course, other particulars concerning the body. But there is nothing appealing to the senses but certain qualities. I do not say that nothing else is perceived or known; because other powers of the mind, as we shall see later, co-operating with the senses in Perception, give us full cognition of the individual object.

The qualities which are thus directly cognized by SensePerception have been divided into primary and secondary. Primary and The primary are those which necessarily enter secondary into our notion of matter; we cannot conceive qualities of matter. of a body which does not possess them. Extension, divisibility, figure, and solidity are some of these. I have spoken of these as a class of the qualities affecting the senses. We are told by some writers that these do not in strict propriety affect the senses at all. They are, perhaps, all implied in the first, namely, extension; and extension is by some good authorities regarded as only the necessary quality attaching to all body, that it must occupy space. This, it is said, is not given by Perception, but by the Pure Reason, by the very constitution of the mind.

Others, however, take a different view of the

subject, and hold that extension and figure, etc., are given by sight.

The secondary qualities are those which are not necessary to our conception of matter, and yet by means of which we are variously affected. Such are smell, taste, sound, color, roughness, smoothness, etc. We can conceive of a body that is not red or yellow; of one that is wanting in a particular odor, or in any odor at all; that is not smooth; but we cannot conceive of a body that does not occupy space, or that does not have some kind of shape. It is true we speak of "shapeless masses," but that is a figurative expression, meaning probably that the shape has no

name.

Sir William

division of

Hamilton's

qualities.

Sir William Hamilton divides the qualities of matter into three classes: first, primary; second, secundo-primary; third, secondary. The primary are objective, not subjective, not sensations proper, but percepts. The secundo-primary are both objective and subjective, percepts proper, and sensations proper. The secondary are subjective, not objective, sensations proper. The primary qualities are all deduced from the two necessary ideas of occupying space, and being contained in space. Thus we have, first, qualities. extension, divisibility, size, density, and figure; secondly, incompressibility absolute, mobility, situation.

Primary

The secundo-primary are first, such as result from gravitation, as heavy and light; second, such as are implied in cohesion, as hard or soft, fluid or firm, tough Secundoor brittle, rough or smooth, etc.; third, from primary. repulsion result compressible and incompressible, resilient or irresilient; fourth, from inertia we have movable and immovable.

Secondary.

The secondary qualities are subjective affections rather than qualities, in the strict sense; that is, they are only qualities in the sense that they refer to certain characteristics in bodies which are capable of producing the affection of which we are conscious in ourselves. Such are color, sound, flavor, odor, smoothness, and all the various sensations of physical pleasure or pain which are caused by the peculiarity of bodies. Thus, as has before been noticed in the case of what we call hearing music, we are conscious of a certain state of mind. We learn by experience to refer this state of mind to some outward instrument, or some human voice, as its cause. It is not at all likely that the external object is itself, or that it has in it anything which is identical with, or at all resembles, this state of mind. Nevertheless we have come to believe unhesitatingly that there is something which corresponds to it, and we learn to locate it unerringly.