Electric fields (in red) at the origin of the coordinate axes for two different instants of time. First, for the same time as in Figure 2 and, second, for the time T/18 later (being T the time period). Thus, we see that both ${\vec{E}}_i\left(0\right),{\vec{E}}_r\left(0\right)$ get shorter, making ${\vec{E}}_i\left(0\right)+{\vec{E}}_r\left(0\right)$ to turn clockwise. Similarly, ${\vec{E}}_t\left(0\right)$ gets shorter and turns counterclockwise. The red dots show the tips of the electric fields for a full time period T.