  Let us select the following K(t). It is 0 for all time t except in 0 &lt; t &lt; 2. In that time interval, K(t) grows to a maximum value of K(t)=2 at t=1. Computing the field U′ = U+K(t) for t=1, where K=2, we find values for U′ as follows: U(6)=0, U(4)=−1, U(3)=−2 U(2)=−4.  Figure 8 illustrates this new field. The result of the transformation has been to shift regions of a particular value of U′ inwards. For example, at t=0 and t=2, U′=−2 at radial distance r=6. However at t=1, U′ has a different value at r=6; the points with U′=−2 have been shifted inward to radial distance r=3. As before, the vertical lines connect points with the same potential U′. They bend inward to reflect the shift in U′ in the time 0 &lt; t &lt; 2.