STATIONARY WAVES are the particular kind of vibration observed in stretched cords, the air in organ-pipes, etc. (See ACOUSTICS.) It is dent that, if waves are sent down a stretched rope toward the end which is fastened to some rigid support, they will be reflected when they reach the end. Consequently, if waves are con tinued to be produced, there will be in the rope at any instant two trains of waves of the same wave-length, velocity, and amplitude, but ad vancing in opposite directions. It must happen at certain points in the rope that one train of waves neutralizes the action of the other; and it is evident that these points must lie at a dis tance of half a wave-length apart. These posi tions of no motion are called 'nodes;' and the fixed end of the rope is one. In between two nodes the rope vibrates exactly like a short rope of a length equal to the distance from node to node and fastened at its two ends. A point mid way between two nodes is called a 'loop.' If a long rope is hanging vertically from a balcony, with its lower end free, waves sent down it will be reflected; and there will be nodes and loops as before, only in this case the free end is a loop.
Such a vibration is called a 'stationary wave,' an extremely poor name, because it is not a wave-motion at all. The vibrations of the air in an organ-pipe are of this kind; the nodes are points where there is the least motion but the greatest fluctuation in pressure, while the loops are the points of greatest motion but the least change in pressure. The open end of an organ pipe is a loop. The effect of opening a hole in a flute is to make that point a loop and thus alter the vibration of the column of air. Stationary waves may be produced by the ether-waves, as has been shown by Wiener and others. See LIGHT; for electrical waves, see ELECTRICITY, paragraphs on Adiernating Currents mud Eleetre cut Wares Along Conductors.