VIBRATION, the limited reciprocal or oscillatory motion of the particle.s of an elastic body or medium, in alternately opposite direc tions from their positions of rest or equilib rium. A complete vibration comprises a motion to and fro, but some French physicists measure it as a motion to or fro; hence the latter is one-half of the former. When vibrations are comparatively slow they are lcnown as oscilla tions, the term vibration being reserved for all the rapid reciprocal motions beyond the ability of the eye to follow. In rods or strings vibra tions are distinguished as transverse, or longi tudinal. The rate of transverse vibrations in reds is inversely proportional to the square of the length of the rod. When fixed at both ends, a rod vibrates in the same manner as a stretched string. When fixed at one end only it vibrates either as a whole or in segments. When bent into a U-shape, as is the case in the tuning fork, the rod divides into three vibrat ing parts by two nodes near the base. The vibration of plates and discs has been exten sively investigated, as in the manufacture of diaphragms for telephones, phonographs, etc. For the laws governing these vibrations see textboolcs in physics (sound). A vibrating bell follows the same law as a disc. The rate of vibration is directly proportional to the thick ness and inversely proportional to the square of the diameter. Rods vibrate longitudinally, either as a whole or in proportion to the num bers, 2, 3, 4, etc. At the points of maximum vibration a rod suffers no change of density. Enclosed columns of air vibrate longitudinally, by alternate condensations and rarefactions. Free vibrations in air or gases proceed in straight lines from the point qf disturbance. Forced vibrations, or vibrations modified by one another, or some other influence, produce circular or elliptical revolutions of the par-.
ticles of the liquid or medium disturbed. The eye does not note vibrations more rapid than about 20 to 40 per second, and the moving picture photographers take advantage of this, showing usually about 20 pictures per second, which appear as one picture, with moving fig ures. In music, 16 per second is the lowe.st vibration the ear can note and 41,000 per second the highest. Our senses do not appreciate the vibrations above this until we come to a fre quency of 370 million million when we begin to see rays of ultra red light. Beyond 833 million million vibrations the highest light, the ultra violet, begins to disappear. Another class of vibrations we recognize as electricity, another class as X-rays, another as N-rays, another as the medium through which wireless tel egraphy takes place, and so on. Everything in nature vibrates; everything has its rate of vibration. Heat is a matter of vibra tion; where there is utter lack of vibra tion we attain the theoretical absolute zero, for with all absence of motion there can be no heat What limit there may be to higher vibrations is oot known, but it is claimed by oculists that the phenomena of Spiritualism, of telepathy and everything pertaining to a higher existence takes place within vibrations immensely higher than those we commonly experience and know about. The amplitude of a vibration is the maximum displacement of the vibrating partide. The phase of a vibration is any designated portion of this displacement The laws of vibration are the basis of modem theories regarding sound, heat, light and elec tricity,. See these subjects as well as WAVES