Transverse and longitudinal waves. Illustration showing the propagation of transverse waves in a red string and longitudinal waves in a slinky spring. In transverse (or shear) waves the displacement is at right angles to the direction of propagation. In longitudinal (or compression) waves the displacement is along the axis of propagation. In transverse waves the wavelength is the distance between two peaks, and in longitudinal waves the it is the distance between two compressions.