XI

$$\begin{gathered} x^{\prime }\&=\frac{(c-v)t}{\sqrt{1-{\displaystyle \frac{v^2}{c^2}}}}, \\ {t}^{\prime }\&=\frac{(1-{\displaystyle \frac{v}{c}})t}{\sqrt{1-{\displaystyle \frac{v^2}{c^2}}}}, \end{gathered}$$

from which, by division, the expression $x^{\prime }=c{t}^{\prime }$ immediately follows. If referred to the system $K^{\prime }$, the propagation of light takes place according to this equation. We thus see that the velocity of transmission relative to the reference-body $K^{\prime }$ is also equal to $c$. The same result is obtained for rays of light advancing in any other direction whatsoever. Of course this is not surprising, since the equations of the Lorentz transformation were derived conformably to this point of view.