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alimentary canal; in man and mammals divided into the smaller intestine, from the pylorus to the iliocaecal valve, and the larger, reaching from the caecum and colon to the end of the rectum. The word is frequently applied to the whole of the alimentary canal in invertebrates. (See ALIMENTARY- CANAL.)

INTOXICATION (Lat. toxicare, intoxicare, to smear with poison, toxicum, an adaptation of Gr. τοξικόν, sc. φάρμακον, a poison smeared on arrows; τόξον, bow), poisoning, or the action of poisons, whether of drugs, bacterial products, or other toxic substances, and hence the condition resulting from such poisoning, particularly the disorder of the nervous system produced by excessive drinking of alcohol (see Inebriety and Drunkenness).

INTRA, a town of Piedmont, Italy, in the province of Novara, on the W. shore of Lake Maggiore, 685 ft. above sea-level, 12 m. N. of Arona by steamer. Pop. (1901) 6924. It is situated between two torrents, which afford water-power for cotton and silk mills, hat factories, foundries, &c.; these chiefly belong to Swiss proprietors, who have fine villas with beautiful gardens. The church is a large edifice of 1708–1751.

INTRADOS (a French term, Lat. intra, within, Fr. dos, back), in architecture, the under-curved surface or soffit of an arch (q.v.).

INTRANSIGENT (adopted from the Fr. intransigent, taken, through the Spanish intransfigente, from the Lat. in, not, and transigere, to come to an understanding), one whose attitude is that of an irreconcilable. The term is used chiefly of politicians of an advanced type; those in complete antagonism to the existing form of government; but is especially applied on the continent of Europe to members of legislatures holding extreme Radical views. In this sense the word was first used in the political troubles which arose in Spain in the years 1873-1874. Intransigentism implies an attitude of uncompromising disagreement with political opponents. The word is also used non-politically, in the sense of intractability and intolerance.

INTRINSIC (through Fr. intrinsique, from Lat. intrinsecus, inwardly; inter, within, secus, following, from root of sequi, to follow), an adjective originally applied to something internal or inside another, but now ordinarily used to express a quality inherent in or inseparable from a person, thing or abstract conception. In anatomy the term is, however, still used of a muscle which has both its origin and insertion in the organ in which it is found.

INTROSPECTION (from Lat. intros pic ere, to look within), in psychology, the process of examining the operations of one's own mind with a view to discovering the laws which govern psychic processes. The introspective method has been adopted by psychologists from the earliest times, more especially by Hobbes, Locke, Berkeley, Hume, and English psychologists of the earlier school. It possesses the advantage that the individual has fuller knowledge of his own mind than that of any other person, and is able therefore to observe its action more accurately under systematic tests. On the other hand it has the obvious weakness that in the total content of the psychic state under examination there must be taken into account the consciousness that the test is in progress. This consciousness necessarily arouses the attention, and may divert it to such an extent that the test as such has little value. Such psychological problems as those connected with the emotions and their physical concomitants are especially defective in the introspective method; the fact that one is looking forward to a shock prepared in advance constitutes at once an abnormal psychic state, just as a nervous person's heart will beat faster when awaiting a doctor's diagnosis. The purely introspective method has of course always been supplemented by the comparison of similar psychic states in other persons, and in modern psycho-physiology it is of comparatively minor importance.

See Psvcnotocv, ATTENTION, &c.; a clear statement will be found in G. F. Stout's Manual of Psychology (1898), i. 14.

INTUITION (from Lat. intuéri, to look at), in philosophy, a term applied to immediate or direct apprehension. The truth of a theorem in geometry is demonstrated by a more or less elaborate series of arguments. This is not the case, according, to the intuitionalist school of philosophy, with the apprehension of universal principles, which present themselves as necessarily true in their own right, without any sort of proof. The fact that things which are equal to the same things are equal to one another is apprehended directly or immediately without demonstration. Similarly in ethics the intuitional school holds that the principles of right and wrong are immediately apprehended without reference to any other criterion and without any appeal to experience. Ethical intuitionalism sometimes goes even farther, and holds that the conscience when faced with any particular action at once assigns to it a definite moral value. Such a view presupposes that the moral quality of an action has, as it were, concrete reality which the special faculty of conscience immediately recognizes, much in the same way as a barometer records atmospheric pressure. The intuitionalist view is attacked mainly on the ground that it is false to the facts of experience, and it is maintained that many of the socalled immediate a priori judgments are in point of fact the result of forgotten processes of reasoning, and therefore a posteriori. Minor grounds of attack are found in the difficulty of discovering in certain primitive peoples any intuitive conception of right and wrong, and in the great differences which exist between moral systems in different countries and ages.

INULIN (C6H10O5)x in chemistry, a starch-like carbohydrate, known also as alantin, menyanthin, dahlin, synanthrin and sinistrin. It occurs in many plants of the large genus Compositae, to which the elicampane (Lat. inula) belongs; and forms a white tasteless powder, sparingly soluble in cold water, very soluble in hot water and insoluble in alcohol. It is not coloured blue by iodine; and it reduces ammoniacal silver and gold solutions, but not Fehling's solution. Heated with water or dilute acids, it is converted into laevulose.

INVAR, an alloy of nickel and steel, characterized by an extremely small coefficient of thermal expansion; it is specially useful in the construction of pendulums and of geodetic measuring apparatus, in fact, in all mechanical devices where it is an advantage to avoid temperature compensation. The name was chosen as expressing the invariability of its dimensions with heat. See Ctocx; Gaonasv.)

INVARIABLE PLANE, in celestial mechanics (see ASTRONOMY), that plane on which the sum of the moments of momentum of all the bodies which make up a system is a maximum. It derives its celebrity from the demonstration by Laplace that to whatever mutual actions all the bodies of a system may be subjected, the position of this plane remains invariable.

A conception of it may be reached in the following way. Suppose that from the centre of gravity of the solar system (instead of which we may, if we choose, take the centre of the sun), lines or radii vectores be drawn to every body of the solar system. As the planet revolves around the centre, each radius vector describes a surface of which the area swept over in a unit of time measures the areal velocity of the planet. The constancy of this velocity in the case of the sun and a single planet is formulated in Kepler's second law. Next pass any plane through the centre of motion and project the area just defined upon that plane. We shall thus have a projected areal velocity, the product of which by the mass of the planet is the moment of momentum of the latter. Form this product for every body or mass of matter in the system, and the sum of the moments is then invariable whatever be the direction of the plane of projection. In the case of a single body revolving around the sun this plane is that of its orbit. When all the bodies of the system are taken into account, the m variable plane is a certain mean among the planes of all the orbits.

In the case of the solar system the moment of Jupiter is so preponderant that the position of the invariable plane does not deviate much from that of the orbit of Jupiter. The influence of Saturii comes next in determining it, that of all the other planets is much smaller. The latest computation of the position of this plane is by T. J. I. See, whose result for the position of the invariable plane is inclination to ecliptic 1° 35' 7"-74, longitude of node on ecliptic 106° 8' 46”-7 (Eq. 1850).

INVENTORY (post-class. Lat. invenlarium, a list or repertory, from invenire to find), a detailed list, schedule or enumeration in writing, of goods and chattels, credits and debts, and sometimes also of lands and tenements.

(i) In law, perhaps its earliest, and certainly its most important