why re.y upon it in the second, to prove that it is not re liable? If the senses do habitually deceive us, manifestly it can never be shown that they do. And, even if this could be shown, it would be impossible to find any thing better to rely upon in their stead. We have these guides or none. We have these instruments of observation provided for the voyage of life. We may pronounce them worthless nd throw them into the sea, but we cannot replace them.

Inconsistent and contradictory Testimony of Sense. But it may be replied that the testimony of sense is often inconsistent with itself, and contradictory of itself. What is sweet to one is sour and bitter to another. What seems a round tower in the distance becomes a square one as you approach; and the straight stick that you hold in your hand appears crooked when thrust into the water. There is in reality, however, no contradiction or inconsistency in the cases supposed. The change of circumstances accounts in every instance for the change of appearance. In the case of the stick, for example, the different density of the wat accounts for the refraction of the rays of light that pass through it, and this accounts for the crooked appearance of the stick that is only partially submerged. So in the other cases; it is no contradiction that an object which appears round at a distance of ten miles, should appear square at the distance of so many rods or that the taste of two persons should not agree as to the savor of a given object.

Deceptions of Sense. It may be further objected that in certain states of the physical organism, sensations are experienced which seem to be of external origin, but are really produced by internal changes; and that in such cases we have the same perceptions, see the same objects, hear the same things, that we should if there were a corresponding external reality, while nevertheless there is no such reality, and it can be proved that there is none. If this may happen in some cases, why not in others, or in all?

Reply.I reply, the simpl. fact, that in the case sup

posed the deception can be detected and proved, shows the difference between that and ordinary perception. If the senses were not habitually reliable, we could not detect the mistake in this particular instance. If all coin were counterfeit, how could we detect a counterfeit coin? We know, moreover, how to account for the mistake in the case before It occurs, by the supposition, only in a certain state of he organism, that is, only in a diseased, abnormal condition of the system. The exception proves the rule.

us.

Distinction of direct and indirect Testimony. — A dis tinction is to be made, in the discussion of this subject, between the direct and indirect testimony of the senses, be tween that which is strictly and properly perception, and that which is only conception, judgment, inference. What I really perceive, for example, in the case of the distant tower, or the stick partially under water, is only a given appearance; I infer from that appearance that the tower is round and the stick crooked, and in that inference I am mistaken. My judgment is at fault here, and not my senses. They testified truly and correctly. They gave the real appearance, and this was all they could give, all they ever give. This has been well stated by Dr. Reid, and, long before him, the same ground was taken, in reply to the same objection, by Aristotle and also by Epicurus.

Direct Perception gives what. In regard to direct and immediate perception, the case is different. Here the testimony is positive to the existence of the object. When something resists my voluntary movement, I am conscious of that resistance, conscious of something external and resisting. I cannot deny the fact of that consciousness. I may, however, deny the correctness, the truthfulness of what consciousness affirms. To do this, however, is to put an end to all reasoning on the subject, for, when we give up consciousness as no longer reliable, there is nothing left to fall back upon. If any one chooses to leap from this preci pice, we can only say finis.

t

§ VII-HISTORICAL SKETCH.

I. OF DIFFERENT DIVISIONS OF THE QUALITIES OF BODIES.

The Greek Philosophers. The distinction. of the quali ties of bodies into two classes, differing in important respects, is by no means a modern one. It was recognized by some of the earlier Greek philosophers, who held that the sweet, bitter, hot, cold, etc., are rather affections of our own senses than proper qualities of matter, having independent existence. Subsequently the view was adopted by Protagoras, and by the Cyrenean and Epicurean schools. Plato held it, and especially and very fully, Aristotle, who calls the qualities to which we have referred, and which are usually denominated secondary, affective qualities, because they have the power of affecting the senses, while the qualities now usually termed primary, as extension, figure, motion, number, etc., he regards as not properly objects of sense. former class he calls proper sensibles, the latter, common. The Schoolmen. The schoolmen made much of this distinction, and held, with Aristotle, that the qualities now called primary, require, for their cognition, other faculties than those of sense.

The

Doctrine of Galileo. Galileo points out the true ground. and philosophy of this distinction, and also gives the name primary to the class referred to, viz., those qualities which are necessary to our conception of body, as for example, figure, size, place, etc., while, on the contrary, colors, tastes, etc., are not inherent in bodies, but only in us, and we can conceive of body without them. The former are real qualities of bodies, while the latter are only conceptions which give us no real knowledge of any thing external, but only of the affections of our own minds.

The Moderns. Descartes and Locke merely adopted these distinctions as they found them, without essential modification. So also did Reid and Stewart, although both

included among the primary qualities some which are prop erly secondary, as roughness, smoothness, hardness, softness. Indeed Stewart restricted the primary qualities to those and such as those just named.

Hamilton. No writer has so fully elaborated this matter as Sir William Hamilton, to whom we are indebted mainly for the historical facts now stated, and whose dissertations are and must ever remain an invaluable thesaurus on the philosophy of perception. So complete and elaborate is his classification of the qualities of matter, that I shall be pardoned for giving a synopsis of its principal points in this connection.

Hamilton's Scheme

General Divisions. He divides the qualities of bodies into three classes, which he calls primary, secundo-primary, and secondary. The primary are thought as essential to the very notion of matter, and may be deduced à priori, the bare notion of matter being given; while the secundo-primary and the secondary, being accidental and contingent, must be deduced à posteriori, learned by experience. His deduction of the primary quali ties is as follows:

Primary Qualities. We can conceive of body only as, I. Occupying space; II. Contained in space. Space is a necessary form of thought, but we are not obliged to con ceive of space as occupied, that is, to conceive of matter. When conceived it must be under the conditions now named.

I. The property of occupying space is Simple Solidity, which implies, a. Trinal extension, or length, breadth, and thickness; b. Impenetrability, or the property of not be ing reduced to non-extension. Trinal extension involves, 1. Number, or Divisibility; 2. Size, including Density; 3. Shape.

II. The attribute of being contained in space, afford the notion, 1. Of Mobility; 2. Of Position.

The essential and necessary constituents then of our no

tion of matter are, 1. Extension (comprising under it, 2 Divisibility; 3. Size; 4. Density; 5. Figure); 6. Ultimate Incompressibility; 7. Mobility; 8. Situation. These are the primary qualities, products, in a sort, of the understanding, developing themselves with rigid necessity out of the given notion of substance occupying space.

Secundo-Primary Qualities.-The secundo-primary are contingent modifications of the primary, all have relation to space, and motion in space, all are contained under the cate gory of resistance, or pressure, all are learned or included as results of experience, all have both an objective and subjective phase, being at once qualities of matter, and also affections of our senses.

Considered as to the sources of resistance, there is, I. That of Co-attraction, under the forms of a, Gravity, b, Cohesion, II. That of Repulsion; III. Inertia; all which are capable of minute subdivision. Thus from cohesion follow the hard and soft, firm and fluid, tough and brittle, rigid and flexible, rough and smooth, etc., etc. From repulsion are derived compressible and incompressible, resilient and irresilient.

Secondary Qualities. — The secondary qualities are, as apprehended by us, not properly attributes of body at all, but only affections of our nervous organism. They belong to bodies only so far as these are furnished with the power of exciting our nervous organism to the specific action thus designated. To this class belong color, sound, flavor, savor tactile sensation, feeling of heat, electricity, etc. Such also are titillation, sneezing, shuddering, and the various sensa tions, pleasurable or painful, resulting from the action of ex ternal stimuli.

These Classes further distinguished. Of the qualities thus derived, the primary are known immediately in themselves, the secondary only mediately in their effects on us, the secundo-primary both immediately in themselves, and mediately in their effects on us. The primary are qualities. of body in relation to body simply, and to our organism