Fig. 2. Figure showing the movement of a particle relative to a wave and to fixed axes respectively as
a wave of constant form advances in the direction of the large arrow from A to A{. The particle
(originally situated at position i near the leading edge of the wave) travels backwards relative to the
wave along the line . When the crest of the wave has reached An the particle is situated
(relative to the wave) at the posterior edge of the wave (position 9). The motion of the particle
relative to fixed axes is shown by the dotted line; the points marked on this line correspond with
those showing the movement of the particle relative to the wave. The dotted wave indicates the
position of the wave when the particle has reached position 5. The figures along the line A-An
indicate the position of the wave crest for each of the positions marked on the track of the particle