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INTERFERENCE

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INTERNATIONAL DATE LINE

in governing and being governed; and not in a tyranny of uninteresting duty.

The influence of Rousseau, Herbart, Froe-bel and others has been powerfully felt in modern education. Teachers of ability have everywhere striven to make their schoolwork spring out of the interests of children, or, at least, fasten upon them. They have tried to make education interesting. The result has been what the surviving advocates of discipline and effort stigmatize as "soft pedagogy." Pupils, they say, are no longer trained to have the strength of will to do the hard and uninteresting work of life. They are left by the school weak and flabby, demanding continual entertainment and capable of doing only that which appeals to their inclinations. This criticism Professor Dewey declares to be justified, not as directed against the importance of interest, but as against an imperfect application of the idea to practice. He agrees with Kant and the disciplinarians that will and character consist in power to do difficult things. But he also agrees with Herbart that no one ever can or will do a difficult thing unless he be interested in it. Here, however, Professor Dewey makes his own contribution to the discussion. To be interested in a thing, he says, means not to find it easy, as " soft pedagogy" assumes. Nor does it mean simply to know something about it, as Herbart seems to think. Teaching means more than presenting material to the mind. It means rousing interest in that material by showing it to be worth while. Then and only then will effort be put forth and will be developed. Character means a trained sense of value as well as power of sustained effort. See APPERCEPTION, FEELING, CHILD-STUDY and SELF-ACTIVITY. Consult Mc-Murry's General Method and De Garmo's Interest in Education. E. N. HENDERSON.

In'terfer'ence, a term employed in physics, especially in the study of wave-motion, to denote the combination of two or more wave-motions at any point. If two waves of equal amplitude reach any point in opposite phases, that is, if the crest of one wave meets the trough of the other, they just counteract one another. Such a pair of waves are said to interfere. Since they completely annul one another, the interference is said to be destructive. In this manner two sound-waves may be added together and thereby produce silence; and two light-waves may be easily added together to produce darkness. For details of these experiments see any good text-book of physics. But two waves may meet in the same phase; and, if they have equal amplitudes, the resultant wave will have twice the amplitude of either of its components. This is also called interference. Indeed, when waves of any amplitude combine in any phase whatever, the process is called interference. A superb

illustration of interference is met with in the spring and neap tides. At any one port the tide due to the moon and that due to the sun are always combining to produce the actual tide; but when they meet in opposite phases, that is, when the solar high tide occurs at the same instant as the lunar low tide, we have the neap tide as the result of interference. But when the solar high tide coincides in time with the lunar high tide, we have the spring tide, as the result of interference. For a history of this subject, as employed in light, see Wave-Theory of Light in Harper's Scientific Memoirs.

Inter lake n fyn'ter-la'keri} (between the lakes) a village of Switzerland, in the beautiful valley of the Aar, between Lakes Thun and Brienz. It is a favorite resort for tourists, 24,000 to 35,000 in number yearly, and contains many inns and hotels. It is from here that the tour is made for reaching many of the most wonderful scenes of nature in the region. Near by are many of the celebrated glaciers of the Alps. The village was founded by Augustine monks in 1130. Its population is about 3,000.

In'terna'tional Date Line. Places on different longitudes have different times, if the time is counted from the arrival oi the sun at its zenith or highest point. Every nation, therefore, has a time of its own. usually taken from the moment when the sun is at its zenith over the capital citv. But it is necessary that there be one time which shall be accepted by all nations, especially for the use of sailors. This international time is taken from the time of Greenwich Observatory, near London, which is at o° longitude. On the opposite side of the earth, at 180° longitude, is the international date line. A person going east from Greenwich, round the world, moves towards the sun, and every day he sees the sun a little earlier than the day before. If he went round the earth, he would thus gain 24 hours, and, unless he corrected his date somewhere, he would be one day ahead of Greenwich. Now, it is arranged to correct such an error at the international date line in the same way as we correct our watches when we pass certain imaginary lines on the surface of the United States, so that they may agree with the time of the places to which we come. Thus, a person going west round the world would lose a day from the year, because his movement makes each day longer. Hence, if he gets to 180° at 3 P. M., Wednesday, according to the time of the places he has just left, he must now call it 3 P. M., Thursday, so as to agree with the places that he is just about to visit. In the north the date line is swerved a little to the west, to include the Aleutian Islands with the rest of the United States; while in the far south it swerves to the east, to include some British islands with the rest of Australasia.