Figure 9. I create images A through D by looking down in the negative Y axis direction of a three-dimensional transversal wave source like the one in Figure 8. Hence, I am looking down on the X, Z plane. In image A, the wave is at time, t = 1. In this image, U (up) means that there is a wave crest at the center with a direction to the left, and D (down) means there is a wave trough with a direction to the right. Parallel to the Z axis the wave amplitudes are zero. I now stand at the center of image A facing the negative X axis direction and spin in a circle. I first see a pulse with up amplitude. As I continue to spin, this view would smoothly and continuously change to zero amplitude, then to down, and then back to zero amplitude. Finally, I would see the up amplitude where I started. While I spun in this complete circle, I would witness one complete wavelength. Therefore, the wave source presented in this figure has a one wavelength spin, or spin 1.

This wave source cycles through its phases. Image B is occurring at time, t = 2. At this time, the wave source has spun so that in the negative Z axis direction, the amplitude is up, and in the positive Z axis direction, it is down. Along both directions parallel to the X axis, there is zero amplitude. The wave continues to rotate through images C and D. Finally, it arrives back to image A.