lx + my + nz

Φ = ω(t - --------------------- )

c

Here (X₀, Y₀, Z₀) and (L₀, M₀, N₀) are the vectors which determine the amplitudes of the train of waves, (l, m, n) are the direction-cosines of the wave-normal.

Let us now ask ourselves about the composition of these waves, when they are investigated by an observer at rest in a moving medium k:—By applying the equations of transformation obtained in [§6] for the electric and magnetic forces, and the equations of transformation obtained in [§ 3] for the co-ordinates, and time, we obtain immediately:—

X′ = X₀ sin Φ′

v

Y′ = β(Y₀ - --- N₀) sin Φ′

c

v